Canon 7D Mark II - DXOMark Review

[Loswr]

I speak from lots of personal experience digging the faintest details possible out of the read noise from image stacks produced from high end CCD cameras, Nikon cameras and Canon cameras. I speak from a lot of experience, it isn't just me being anti-Canon or spouting bullshit. How much this matters ultimately depends on what you do and how you process...but whether it matters to you or not does not change the actual facts.

Right, but you don't get to choose the facts that matter to everyone. Notably, the facts about how many dSLR buyers feel the issues which are problematic for you are problems for them. Those are the facts that Canon cares about...and it's that, not any amount of complaining on the Internet, that will effect change at Canon.

The usual response (not universal, just usual) to the issues of Canon's read noise and/or lower DR at low ISO compared to other manufacturers isn't that those facts aren't correct. It's not 'spouting bullshit', but it's information that's not novel and hasn't been for years, and that's not relevant to a majority of Canon's market.

I understand that for many people, being told things that are critically important to them aren't really that relevant to most others can seem like a personal attack...but that does not change the actual facts.

 

[rrcphoto]

this picture is breathtaking. is your 5D full spectrum modded?

how do you find the clip filters?

 

[jrista]

this picture is breathtaking. is your 5D full spectrum modded?

how do you find the clip filters?

Thank you very much. I am pretty happy with the framing and overall composition myself. That is actually a very preliminary image...it's one single hour of integration time (total exposure, across all subs). My goal is 10 hours...so, as you can imagine, I have a very long way to go. Hopefully tonight will pan out clear (and moonless) by the time Orion gets high enough in the sky, and I'll get a couple more hours.



As far as the camera, It is unmodded. It's my only 5D III...I still use it for everything else (just got back from trying to photograph some birds...tough, the light was poor, and I had to use my TCs to get them large in the frame, so I was shooting at high ISO.) I have the benefit of using a very fast "telescope"...my f/4 600mm lens. A lot of astrophotographers who are in my position, their first year, are usually stuck using f/6-f/10 scopes. They are also usually smaller in terms of aperture (entrance pupil, for clarity)...my aperture is 150mm, while most beginners are stuck with as little as 80mm, and rarely more than 120mm.


The large aperture fast lens gives me a leg up, in that in a five or eight minute exposure, I can get much deeper exposures than you can with an 80mm f/6 or slower scope. Coupled with the light pollution filter, and I am able to get some exposure on that outer dust, dimmer reflection nebula, etc. The DSLR is really holding me back though. The bayer array is a huge limiting factor, reduces light/increases noise, requires significantly longer integration time to get half-way decent results. I can't wait till I can get a proper astro CCD camera...the readout noise is exceptionally clean, and about as low as a DSLR at ISO 400...and with the -45°C dT cooling, dark current (and all the consequences of it) nearly disappears.

 

[jrista]

here Clark basically states that "Nikons truncating of the raw data, which artificially improves dynamic range by about a stop" which is basically consistent with what you're stating. But he doesn't stop there, he also states that Nikons RAW is not actually RAW data but has been tinkered with: "Also Nikon filters the raw data, improving noise and dynamic range further. I believe, based on some experiments, that if the canon data were treated similarly, it would result it numbers at least as good. … But Nikon's raw files look "wormy" in the shadow areas from the in camera filtering of the raw data. The Canon 7D2 raw data looks much more random, as it should be." You completely ignored that fact.

I'd be curious to see an example of this "wormy" look. The D800 shots I've seen blown up look like random noise with a Gaussian distribution, much like my 6D's shots do.

The issue is discussed here: https://nikonhacker.com/viewtopic.php?t=85 I wonder that jrista is not aware of that "star eating quality" of the Nikon bodies given that he always claims to be such a great astro-photographer.

I am very aware of that problem. I am also aware that NikonHacker figured out how to control the black point clipping. By disabling it, they restored the bias offset (which was very, very low...a mere 5-6e- tops). I have used data from both hacked and non-hacked Nikon cameras. The non-hacked do eat stars...but only the smallest/dimmest, stars that are often obliterated by standard processing anyway (especially when using scopes with smaller apertures.) The quality of data from Nikon cameras using Exmors and even the Toshiba sensor (D5200, and I think the D7100?) is excellent. Very clean, random noise.


The black point does not need to be offset very much in Nikon cameras...either those using an Exmor or Toshiba sensor. It's nothing compared to Canon's MASSIVE bias offset. Restoration of the bias offset preserves tiny stars, and makes the signal more linear (it removes the "foot" at the bottom end of the tone curve), which is better for astro.

You can see the wormy look here (and understand why he called it "wormy"): http://www.astrosurf.com/buil/nikon_test/test.htm the site is in french but I assume you know how to use google translate.

Those are old Nikon designed and manufactured sensors. They are not Exmor sensors. The Nikon cameras I am impressed with are the new ones that use Exmor and Toshiba sensors. In particular, the D5100/5200/5300 and D800/810. These cameras (and I think maybe some of the D7000 series) have had their black point clipping disabled by nikonhacker. Coupled with the superior sensor technology, which natively has lower read noise and dark current, they make for much better astro DSLRs.


Most Canon users, modded and others, start at ISO 400 and beginners are frequently using ISO 800 and 1600, for astro. I myself use ISO 400. At these ISO settings, clipping stars is a major concern. I have to deal with that all the time, every bright star tends to get clipped, which kills off the color, and it's a PITA to correct that (or, you end up having to make the color up, and artificially messing with stars never looks as good as natural stars.)


I know beginner Nikon users who are shooting at ISO 100 and 200!! With less RN than I have at ISO 400 on the 5D III! That is nearly unheard of when using Canon cameras for astro due to the extremely high read noise. Limited dynamic range is a big issue for astro, as stars can be many orders of magnitude brighter than nebula and dust. When trying to get a "deep" exposure, the amount of read noise, even a difference of 1-2e-, the amount of dark current, and the dynamic range are very, very significant factors. Read noise in particular is the key limiting factor in astro...you have to expose long enough to get the dimmest parts of nebula above the RN floor. A couple of electrons higher RN and you might have to expose up to twice as long to get the dimmest details above that read noise.


Canon cameras used to be preferred because they did not clip to black...they used a bias offset, and were more linear (although not entirely linear...Craig Stark of Stark Labs did an analysis years ago, and found that Canon cameras do indeed cook the RAW (and in some odd ways), so it's not as linear as it could be). Today, with the black point hack, Nikon cameras (well, all Exmor cameras really) offer much better linearity as well as lower dark current, read noise and more dynamic range.


I think the D5100 will soon become the beginners favorite, and I think Nikon cameras in the long run (or maybe Nikon and Sony...people are starting to hack and use the A7s as well; I recently saw some real-time night sky videos done with the A7s...rather incredible, that camera is so insanely sensitive it can pick up satellites and the milky way at VIDEO frame rates! ) will topple Canon's dominance in the astrophotography world. And for good reason, too.

 

[Synkka]

So does this mean the 7dii won't be a choice camera for astronomy photography? I would have thought the 7dii strengths were for wildlife and sports?

 

[jrista]

So does this mean the 7dii won't be a choice camera for astronomy photography? I would have thought the 7dii strengths were for wildlife and sports?

These days, I don't generally recommend Canon cameras for astrophotography. They used to be ideal because of their better linearity, however Nikon cameras offer even better linearity with the black point hack. If I were to recommend a DSLR for astrophotography, to a beginner, it would be a used D5100. For those who have experience and are more serious, the D810. Both with the black point hack. The D810 has been described as having "CCD-like linearity and noise quality, with very low dark current" by those who currently employ it for astrophotography.


The D810 is a rather expensive full-frame camera. The only time I do recommend a Canon camera for astrophotography is the 6D. While it still has high noise and a huge bias offset, it is currently Canon's best camera from a noise characteristic standpoint. It's also a hell of a lot cheaper than the D810 on the street...so if you want full frame, it's really the best deal, and offers good performance.


I would not recommend the 7D II for astro. It's a high speed action camera, and it seems to serve that purpose well. I don't think it has anything particularly unique or great to offer an astrophotographer...nothing better than any Nikon offering at least, and it has a smaller field than the 6D.

 

[Synkka]

Yeah that's what I would have thought, and definitely would imagine if using a dslr a larger sensor will be better for noise.

Going slightly off topic, when I look at a lot of Nikon and sony cameras if recent I often feel they are too specialised to be big successes in the market. While they have technological advantages I think unless you are chasing one particular feature they won't be the best across the board. I think it is no secret that the 5d3 is popular due to it being a well rounded camera, I expect the d750 would also sell as well but I think some of the d600 d800 users may not swap to it, but those who had held out would.

Coming back to the 7dii I think it will be very successful despite where it ranks in apc sensor scores because it's well rounded. And most importantly coming from a 7d I think the noise is now at a point it can be used at low light indoor events without as much trouble.

 

[jrista]

Yeah that's what I would have thought, and definitely would imagine if using a dslr a larger sensor will be better for noise.

Well, not really. Everything is at the same distance with astrophotography. So, unlike with terrestrial subjects, where you can get closer to fill the frame, for a given focal length, you simply get a bigger field of view. That doesn't help with noise. You are also primarily read-noise limited, it takes very long exposures to swamp read noise and make photon shot noise the dominant factor.


The 6D is better simply because it has lower/cleaner read noise than most other Canon cameras, and moderately large pixels which help improve light gathering capacity.


Astro is very different from regular photography.

Going slightly off topic, when I look at a lot of Nikon and sony cameras if recent I often feel they are too specialised to be big successes in the market. While they have technological advantages I think unless you are chasing one particular feature they won't be the best across the board. I think it is no secret that the 5d3 is popular due to it being a well rounded camera, I expect the d750 would also sell as well but I think some of the d600 d800 users may not swap to it, but those who had held out would.

Probably true, for sure. Sony cameras definitely lack in certain areas. Nikon doesn't have anything to really compete with the 7D line, and it seems clear Nikon users want something (i.e. a D300 successor.) That said, I think the D810 and D750 are both extremely nice well-rounded, general purpose cameras. I mean, the D810 could do with that extra 1fps when using full frame, but they have the crop mode, which allows faster frame rates...and the small pixels. That makes for a pretty good general purpose camera, and it's IQ trounces anything from pretty much anyone else, Sony included.


I think the D810 is what the D800 should have been from the start...but Nikon seems to prefer iterating rather than thinking hard. Still, they just keep iterating, and the issue count just keeps dropping. As much as I think Nikon has a schizophrenic camera model naming scheme, they are closing in on what consumers want, and they have the IQ on top of everything else. Remember also, Canon had to catch up to Nikon in regards to AF system, metering, and linking the two together...Nikon was leading in that area for a while (much like they are leading in the IQ area now.)

Coming back to the 7dii I think it will be very successful despite where it ranks in apc sensor scores because it's well rounded. And most importantly coming from a 7d I think the noise is now at a point it can be used at low light indoor events without as much trouble.

I think it will succeed because it is specialized. It's a fairly unique part...an ultra high frame rate APS-C action camera (with some additional highly specialized features, like the 120Hz light oscillation feature). I wouldn't say the 7D II is as general purpose as either the 5D III or D810...it has it's niche, a popular niche, and it serves it very, very well. I think the NX1 is the first REAL competition to the 7D line, and I think it is just as specialized of a camera...and it tops the 7D II on a number of features (and yet still lags behind in a couple others...rear-button AF and decoupling AF from the shutter button for one, a big one.)

 

[rrcphoto]

this picture is breathtaking. is your 5D full spectrum modded?

how do you find the clip filters?

Thank you very much. I am pretty happy with the framing and overall composition myself. That is actually a very preliminary image...it's one single hour of integration time (total exposure, across all subs). My goal is 10 hours...so, as you can imagine, I have a very long way to go. Hopefully tonight will pan out clear (and moonless) by the time Orion gets high enough in the sky, and I'll get a couple more hours.



As far as the camera, It is unmodded. It's my only 5D III...I still use it for everything else (just got back from trying to photograph some birds...tough, the light was poor, and I had to use my TCs to get them large in the frame, so I was shooting at high ISO.) I have the benefit of using a very fast "telescope"...my f/4 600mm lens. A lot of astrophotographers who are in my position, their first year, are usually stuck using f/6-f/10 scopes. They are also usually smaller in terms of aperture (entrance pupil, for clarity)...my aperture is 150mm, while most beginners are stuck with as little as 80mm, and rarely more than 120mm.


The large aperture fast lens gives me a leg up, in that in a five or eight minute exposure, I can get much deeper exposures than you can with an 80mm f/6 or slower scope. Coupled with the light pollution filter, and I am able to get some exposure on that outer dust, dimmer reflection nebula, etc. The DSLR is really holding me back though. The bayer array is a huge limiting factor, reduces light/increases noise, requires significantly longer integration time to get half-way decent results. I can't wait till I can get a proper astro CCD camera...the readout noise is exceptionally clean, and about as low as a DSLR at ISO 400...and with the -45°C dT cooling, dark current (and all the consequences of it) nearly disappears.

yeah there's some APS-C astro imagers that caught my eye the last little while. and they are cheap running less than 2K.

however how much do you think having the stock IR filter still in the camera is holding you back. I could be wrong but aren't you getting around 2-3 stop attenuation there? especially in nebulosity? I know canon's pretty extreme now (if you've ever tried taking IR photos with a R72,etc) I believe it's around an 70 to 80% attenuation around hAlpha - which is why canon did the 20/60Da

IMO - you may be an idea getting a cheap assed APS-C junking off the IR filter and giving it a go.

you have quite the setup - and that's some great patience and your autoguiding setup is impeccable - but you are losing some of your nebulosity because of the cut filter.

your final image will be amazing I'm sure.

 

[jrista]

however how much do you think having the stock IR filter still in the camera is holding you back. I could be wrong but aren't you getting around 2-3 stop attenuation there? especially in nebulosity? I know canon's pretty extreme now (if you've ever tried taking IR photos with a R72,etc)

Oh absolutely, the IR cut filter in DSLRs kills off a ton of the Hydrogen-alpha light. My red channel lags my green and blue channels by at least a couple stops, and as such it is always noisier. There are mods out there, from Baader and from Astrodon, where you can pull out the LPF filters in Canon cameras and replace them with astro-geared IR/UV cutoff filters that have a square cutoff, rather than a gradual rolloff into the reds. That can improve Ha and SII transmission from around 20% to around 90% (Baader) or 99% (Astrodon). The problem with these mods is they make regular photography more difficult. You can use custom WB settings, but there is always a strong red hue, and it is very difficult to get rid of.


My 5D III is my main regular photography camera...so I have no plans to mod it. I have thought about modding my 7D, though. I'd go with the Astrodon mod, their filters are superior to everything else at the moment. In the end, I don't think modding a DSLR is really what I want to do...I really do want to just move to a proper astro CCD camera. There are lots of benefits. Even modded, the DSLR will still be Canon, and it will still have Canon's high noise levels. It will also still be a bayer color sensor, which while "easy" is actually really not that easy. You have to get a LOT of integration time just to get noise under control, and so much integration time as to be impractical to even approach mono CCD quality.



With a mono CCD that is thermally regulated, you effectively kill dark current (and thus dark current noise, hot pixels, etc.), and you have the ability to use filters. You get a 100% fill factor for every color, you gain the ability to do narrow band imaging (at the very least, Ha, which is frequently used as a luminance boost layer to improve detail of lower resolution color). You also get the benefits of CCD, which currently, for astro and other scientific applications, still produce better linearity and noise characteristics than CMOS. The top two CCD manufacturers as far as astro goes are QSI and FLI. FLI, or Finger Lakes Instrumentation, are currently considered the top manufacturer, however their equipment is large and expensive, and not as well integrated as QSI's. QSI, or Quantum Scientific Imaging, produces integrated cameras that include an off-axis guider port with a very short backfocus requirement.


I personally like the QSI design better, and it's about five grand for their full package (8 position filter wheel and integrated guider port, along with some 31mm LRGB filters). That's a very good deal, and I can pick up the camera with either a Kodak KAF-8300 sensor (older, but larger with larger pixels) or a newer Sony ICX sensor (newer, smaller pixels...but very tiny sensor areas.) The Sony CCD sensors are phenomenal...an order of magnitude lower dark current noise (eliminates the need to take and use darks during calibration), and lower read noise...about 5e- vs. 8-10e- of the KAF sensors.


I haven't decided which to get yet...I really love wide field work, and the ultra tiny size of the Sony sensors means I would have to mosaic to get the kind of field I want, even if I dropped to a 300mm focal length. The KAF sensor is much larger, at least three times the area of a Sony sensor (depending on which Sony your comparing.) I would still have to mosaic to get the field of view that a FF sensor offers, but it's a lot less work. (There are also full-frame and even large format KAF sensors...but all of those cameras cost more than ten grand, and I cannot justify that yet....not to mention a lot of telescopes only have an image circle large enough for a 26mm FoV, meaning APS-C sized tops.)


Anyway...mono CCDs actually require less total integration time for most of the DSLR-accessible targets than DSLRs themselves require. Being monochrome, with a 100% fill factor for each and every color, you don't have to deal with the consequences of a bayer array (which are actually many...much, much higher dark current, higher read noise in many cases, patterned read noise (which cannot be averaged out), more hot pixels, problems with things like correlated noise, requiring dithering each sub frame to offset pixels and support better hot pixel rejection, etc.) That means it is actually easier to get all the necessary sub frames with a CCD than with a DSLR...because you need less in total to get the same amount of noise levels in the end. So, sure...I could mod my DSLRs and everything...but since I am very serious about astrophotography...it isn't just a second hand hobby, I think the far better investment is to just go with a proper CCD camera.

 

[Marsu42]

I haven't decided which to get yet...I really love wide field work, and the ultra tiny size of the Sony sensors means I would have to mosaic to get the kind of field I want, even if I dropped to a 300mm focal length. The KAF sensor is much larger, at least three times the area of a Sony sensor (depending on which Sony your comparing.) I would still have to mosaic to get the field of view that a FF sensor offers

You've lost me here - could you please explain that to simple /me :-o ?

As far as I understand this relation, you can get an equivalent fov by raising the focal length for a smaller sensor size? But you're writing for a smaller sensor you need to "drop" to 300mm? And what's the need for more or less mosiaic about depending on sensor size, when you can adjust the fov with the focal length?

Thanks for any elaboration, probably it's an astro thing, but then maybe it's not.

 

[jrista]

I haven't decided which to get yet...I really love wide field work, and the ultra tiny size of the Sony sensors means I would have to mosaic to get the kind of field I want, even if I dropped to a 300mm focal length. The KAF sensor is much larger, at least three times the area of a Sony sensor (depending on which Sony your comparing.) I would still have to mosaic to get the field of view that a FF sensor offers

You've lost me here - could you please explain that to simple /me :-o ?

As far as I understand this relation, you can get an equivalent fov by raising the focal length for a smaller sensor size? But you're writing for a smaller sensor you need to "drop" to 300mm? And what's the need for more or less mosiaic about depending on sensor size, when you can adjust the fov with the focal length?

Thanks for any elaboration, probably it's an astro thing, but then maybe it's not.

Cropped sensors effectively magnify. So, if I am using a 600mm lens, the FoV is LARGER with a FF DSLR than it is with a 1/3" Sony CCD. To make the field as large with a smaller sensor, I need a shorter lens/telescope.


For best results, camera lenses are not the best options for astro. You have extremely limited backfocus. With Canon lenses, it's 56mm. That's enough for the camera, that's it. Most telescopes offer at least 110mm of backfocus, many over 210mm. With that backfocus, you can get robotic focusers, filter wheels, off-axis guiders, etc. A good scope is VERY expensive. A minimum of five grand, many are over ten grand, plus extra for things like field flatteners, focusers, etc. So, you don't really change your focal length much.


Hence...smaller sensor == smaller FoV, and the need to mosaic to get a larger field of view. Keep in mind, when using a mono sensor, mosaicing requires getting all the necessary subs for all the necessary color channels. If your doing LRGB, that is a minimum of 10 subs per channel, four channels (L = luminance), so a minimum of 40 subs for each panel of a mosaic. I think I'd need six panels with a Sony ICX 694 to equal the area of a KAF sensor, accounting for cropping out integration artifacts and overlap. So I'd need 6x40 subs, or 240, just to equal the FoV of the larger sensor. The minimum is often not enough to reduce noise to an acceptable level...just to the minimum required level to be able to process. Me, I prefer very low noise, and deeper exposures. So, were now talking at least 20 subs per channel, and subs that are probably 50% longer at a minimum. That's 480 longer subs.


I get a handful of clear nights a month, between clouds and the moon. I've had months where I got no clear nights at all. On a given night, I can image for about four hours on a single target tops.


Mosaicing is a b*tch.

 

[rrcphoto]

however how much do you think having the stock IR filter still in the camera is holding you back. I could be wrong but aren't you getting around 2-3 stop attenuation there? especially in nebulosity? I know canon's pretty extreme now (if you've ever tried taking IR photos with a R72,etc)

Oh absolutely, the IR cut filter in DSLRs kills off a ton of the Hydrogen-alpha light. My red channel lags my green and blue channels by at least a couple stops, and as such it is always noisier. There are mods out there, from Baader and from Astrodon, where you can pull out the LPF filters in Canon cameras and replace them with astro-geared IR/UV cutoff filters that have a square cutoff, rather than a gradual rolloff into the reds. That can improve Ha and SII transmission from around 20% to around 90% (Baader) or 99% (Astrodon). The problem with these mods is they make regular photography more difficult. You can use custom WB settings, but there is always a strong red hue, and it is very difficult to get rid of.

yes, I do infrared photography, so what I tend to do is get a full or dual spectrum converted camera (a UV block only) and then use filters in front.

thus the camera still works as a terrestrial camera and also as an astro imager.

but you are right - nothing will beat a dedicated CCD imager and the inclusion of the consistent cooling if you are serious about the craft.

looks like where you are, you are in a pretty good area for it to as well - I look at your images and my fingers start twitch to get back into it seriously - however living in a downtown city core isn't' exactly a good location for serious work.

have you looked at the QHYCCD?

 

[jrista]

however how much do you think having the stock IR filter still in the camera is holding you back. I could be wrong but aren't you getting around 2-3 stop attenuation there? especially in nebulosity? I know canon's pretty extreme now (if you've ever tried taking IR photos with a R72,etc)

Oh absolutely, the IR cut filter in DSLRs kills off a ton of the Hydrogen-alpha light. My red channel lags my green and blue channels by at least a couple stops, and as such it is always noisier. There are mods out there, from Baader and from Astrodon, where you can pull out the LPF filters in Canon cameras and replace them with astro-geared IR/UV cutoff filters that have a square cutoff, rather than a gradual rolloff into the reds. That can improve Ha and SII transmission from around 20% to around 90% (Baader) or 99% (Astrodon). The problem with these mods is they make regular photography more difficult. You can use custom WB settings, but there is always a strong red hue, and it is very difficult to get rid of.

yes, I do infrared photography, so what I tend to do is get a full or dual spectrum converted camera (a UV block only) and then use filters in front.

thus the camera still works as a terrestrial camera and also as an astro imager.

but you are right - nothing will beat a dedicated CCD imager and the inclusion of the consistent cooling if you are serious about the craft.

looks like where you are, you are in a pretty good area for it to as well - I look at your images and my fingers start twitch to get back into it seriously - however living in a downtown city core isn't' exactly a good location for serious work.

I live in a red/orange zone (depends on the night)...the LP is pretty bad here. Far from a great area for AP though. I do some unfiltered imaging, on brighter targets. I filter all the rest, as it is pretty essential. I am actually looking to sell the Astronomik CLS-XL and get a 52mm screw-in for my drop-in filter on my 600mm lens. I'm going to be getting the IDAS, probably the LPS-D1, although I may pick up the LPS-P2 instead (if I can find it.) The IDAS filters are a little more tuned, and block narrower bands while passing the rest, so color balance is a bit easier (and they don't cut out as much light, so you don't necessarily have to expose for as long.)

have you looked at the QHYCCD?

I have. I've also looked at Atik. I own the QHY5L-II guide and planetary camera, which uses an Aptina sensor. I checked out the larger QHY cameras. Their full-frame 11002 camera is actually probably one of the best priced out there...however I've heard a number of times about fogging/frosting problems with the QHY design, and I have never really heard much about their noise quality. QHY and FLI both put a lot of effort into ensuring non-patterned read noise, which is essential for AP as we average many frames together. Any pattern, instead of getting averaged out, ends up getting strengthened like any other signal.

 

[rrcphoto]

I live in a red/orange zone (depends on the night)...the LP is pretty bad here. Far from a great area for AP though. I do some unfiltered imaging, on brighter targets. I filter all the rest, as it is pretty essential. I am actually looking to sell the Astronomik CLS-XL and get a 52mm screw-in for my drop-in filter on my 600mm lens. I'm going to be getting the IDAS, probably the LPS-D1, although I may pick up the LPS-P2 instead (if I can find it.) The IDAS filters are a little more tuned, and block narrower bands while passing the rest, so color balance is a bit easier (and they don't cut out as much light, so you don't necessarily have to expose for as long.)

damn you .. I didnt' need you telling me you live in orange / red

When I go south for the winter, that's approximately where I end up - it's around 1 hour outside of Houston.

I've been itching and debating setting up a semi permanent arrangement down there for at least the 3-4 months Jan through March when I'm there.

was debating getting a CGEM package with a 8" HD and getting the hyperstar conversion.

 

[jrista]

I live in a red/orange zone (depends on the night)...the LP is pretty bad here. Far from a great area for AP though. I do some unfiltered imaging, on brighter targets. I filter all the rest, as it is pretty essential. I am actually looking to sell the Astronomik CLS-XL and get a 52mm screw-in for my drop-in filter on my 600mm lens. I'm going to be getting the IDAS, probably the LPS-D1, although I may pick up the LPS-P2 instead (if I can find it.) The IDAS filters are a little more tuned, and block narrower bands while passing the rest, so color balance is a bit easier (and they don't cut out as much light, so you don't necessarily have to expose for as long.)

damn you .. I didnt' need you telling me you live in orange / red

When I go south for the winter, that's approximately where I end up - it's around 1 hour outside of Houston.

I've been itching and debating setting up a semi permanent arrangement down there for at least the 3-4 months Jan through March when I'm there.

was debating getting a CGEMDX package with a 8" HD and getting the hypestar conversion.

As far as mounts go, your better off with a non-Celestron mount. The CGEM and CGEM DX both have a gearbox problem that creates a wicked non-periodic error that is apparently quite difficult to guide out. It can be "mild", or severe. For those who have it severe, it can add (on top of the base 30-40" PE) another 20" or more PE.


If your looking for a lower end mount, I highly recommend the Orion Atlas EQ-G. It uses a better set of gears, and if those prove to be problematic, you can belt mod them (I just installed the Rowan belt mod in mine, which helped with tracking by eliminating a lot of the higher frequency errors from the transfer and spur gears.) The Atlas is also compatible with EQMOD, which is beyond awesome for AP work.


Also, for an ideal imaging scope, SCTs are not at the top of the list. They suffer from mirror flop, and have the correcting miniscus (and an Edge has the corrector at the back as well.) The added glass can cost IQ. Personally I'm looking at picking up the $895 Astro-Tech 8" RC steel tube, which is a Ritchey-Chretien astrograph. Better 8" scope IMO than the Celestrons. (And cheaper, too!)

 

[rrcphoto]

I live in a red/orange zone (depends on the night)...the LP is pretty bad here. Far from a great area for AP though. I do some unfiltered imaging, on brighter targets. I filter all the rest, as it is pretty essential. I am actually looking to sell the Astronomik CLS-XL and get a 52mm screw-in for my drop-in filter on my 600mm lens. I'm going to be getting the IDAS, probably the LPS-D1, although I may pick up the LPS-P2 instead (if I can find it.) The IDAS filters are a little more tuned, and block narrower bands while passing the rest, so color balance is a bit easier (and they don't cut out as much light, so you don't necessarily have to expose for as long.)

damn you .. I didnt' need you telling me you live in orange / red

When I go south for the winter, that's approximately where I end up - it's around 1 hour outside of Houston.

I've been itching and debating setting up a semi permanent arrangement down there for at least the 3-4 months Jan through March when I'm there.

was debating getting a CGEMDX package with a 8" HD and getting the hypestar conversion.

As far as mounts go, your better off with a non-Celestron mount. The CGEM and CGEM DX both have a gearbox problem that creates a wicked non-periodic error that is apparently quite difficult to guide out. It can be "mild", or severe. For those who have it severe, it can add (on top of the base 30-40" PE) another 20" or more PE.


If your looking for a lower end mount, I highly recommend the Orion Atlas EQ-G. It uses a better set of gears, and if those prove to be problematic, you can belt mod them (I just installed the Rowan belt mod in mine, which helped with tracking by eliminating a lot of the higher frequency errors from the transfer and spur gears.) The Atlas is also compatible with EQMOD, which is beyond awesome for AP work.


Also, for an ideal imaging scope, SCTs are not at the top of the list. They suffer from mirror flop, and have the correcting miniscus (and an Edge has the corrector at the back as well.) The added glass can cost IQ. Personally I'm looking at picking up the $895 Astro-Tech 8" RC steel tube, which is a Ritchey-Chretien astrograph. Better 8" scope IMO than the Celestrons. (And cheaper, too!)

one reason I was going to go with the Celestron is that you can polar align it in the daytime with Alt/Az goto - the only other one I know that you can do that with is Vixen I think.

the atlas is amazing - especially when they sold it without GoTo but still EQMOD capable.

Not sure about the RC 8" though, since I'm thinking I may want the faster glass since my window of opportunity will be less (only having 3 months a year with it)

was looking at this guy's work .. and it looks good enough for me - mind you this is the 11" with CGEMDX - which may be a worthwhile upgrade.

 

[Lee Jay]

I have an Atlas Pro and an Edge HD 11. Here's why I prefer that to an RC - I just hate diffraction spikes. It also gives the option to go Hyperstar and thus shoot at 560mm and f/2. I'm in a white zone which means read noise isn't half the problem that sky glow is.

That said, I haven't tried shooting DSOs yet, just planetary and satellites.

 

[jrista]

I have an Atlas Pro and an Edge HD 11. Here's why I prefer that to an RC - I just hate diffraction spikes. It also gives the option to go Hyperstar and thus shoot at 560mm and f/2. I'm in a white zone which means read noise isn't half the problem that sky glow is.

That said, I haven't tried shooting DSOs yet, just planetary and satellites.

For planetary, there is little that beats a C or an Edge. Further, there is little that beats raw focal length, which the C11 Edge has in spades (especially with a barlow.) For imaging, the C11 is fine, but you do have to deal with mirror flop (something which is immaterial to planetary imaging, where you are using high speed video instead of slow, long exposures.)


The RC does have diffraction spikes...but that's a matter of taste. I like em myself, others don't. You still have the central obstruction with an edge, which can create it's own issues, as it's still an obstruction, and still causes diffraction. That issue is magnified when doing hyperstar...it's one of the key issues that I notice with most hyperstar images, the giant central obstruction artifacts around stars.


Regarding read noise, it's still a problem, since you can extract the skyfog now. With PixInsight, either DynamicBackgroundExtraction or AutomaticBackgroundExtraction can be used to identify and remove the gradients caused by light pollution. GradientXterminator can be used with photoshop. In either case, those tools subtract the skyfog, leaving behind just the image...and all the read noise.

 

[jrista]

I live in a red/orange zone (depends on the night)...the LP is pretty bad here. Far from a great area for AP though. I do some unfiltered imaging, on brighter targets. I filter all the rest, as it is pretty essential. I am actually looking to sell the Astronomik CLS-XL and get a 52mm screw-in for my drop-in filter on my 600mm lens. I'm going to be getting the IDAS, probably the LPS-D1, although I may pick up the LPS-P2 instead (if I can find it.) The IDAS filters are a little more tuned, and block narrower bands while passing the rest, so color balance is a bit easier (and they don't cut out as much light, so you don't necessarily have to expose for as long.)

damn you .. I didnt' need you telling me you live in orange / red

When I go south for the winter, that's approximately where I end up - it's around 1 hour outside of Houston.

I've been itching and debating setting up a semi permanent arrangement down there for at least the 3-4 months Jan through March when I'm there.

was debating getting a CGEMDX package with a 8" HD and getting the hypestar conversion.

As far as mounts go, your better off with a non-Celestron mount. The CGEM and CGEM DX both have a gearbox problem that creates a wicked non-periodic error that is apparently quite difficult to guide out. It can be "mild", or severe. For those who have it severe, it can add (on top of the base 30-40" PE) another 20" or more PE.


If your looking for a lower end mount, I highly recommend the Orion Atlas EQ-G. It uses a better set of gears, and if those prove to be problematic, you can belt mod them (I just installed the Rowan belt mod in mine, which helped with tracking by eliminating a lot of the higher frequency errors from the transfer and spur gears.) The Atlas is also compatible with EQMOD, which is beyond awesome for AP work.


Also, for an ideal imaging scope, SCTs are not at the top of the list. They suffer from mirror flop, and have the correcting miniscus (and an Edge has the corrector at the back as well.) The added glass can cost IQ. Personally I'm looking at picking up the $895 Astro-Tech 8" RC steel tube, which is a Ritchey-Chretien astrograph. Better 8" scope IMO than the Celestrons. (And cheaper, too!)

one reason I was going to go with the Celestron is that you can polar align it in the daytime with Alt/Az goto - the only other one I know that you can do that with is Vixen I think.

the atlas is amazing - especially when they sold it without GoTo but still EQMOD capable.

Not sure about the RC 8" though, since I'm thinking I may want the faster glass since my window of opportunity will be less (only having 3 months a year with it)

was looking at this guy's work .. and it looks good enough for me - mind you this is the 11" with CGEMDX - which may be a worthwhile upgrade.

With the RC, you usually use a focal reducer. The popular one is the Astro Physics CCDT67, a .67x reducer. When spaced right for the AT8RC, that usually gets you f/5.8 (to get a flat field, you usually cannot get down to the max f/5.3 due to the necessary spacing required.) An f/5.8 scope is faster than anything Celestron produces, by a long shot.


One thing to keep in mind...imaging with an 11" scope is difficult. You need all the right conditions, and excellent, excellent tracking. Celestron is somewhat misleading in the way they package their product deals. The CGEM DX's capacity is a VISUAL OBSERVING capacity. So, while it's enough to hold an 11" SCT, it is not stable enough to image with most of the time.


The general rule of thumb is to use at most half the capacity of a mount, unless it is explicitly specified as an imaging capacity. There are only a few mounts that advertise as imaging capacities...Astro-Physics, 10Micron, ASA, Software Bisque, Avalon. Maybe one or two more European manufacturers. Any other mount is NOT going to be an imaging capacity. So, with a DX, instead of 50lb of capacity, you really only have 25lb. That precludes the use of the C11 for imaging on that particular mount. You would have to get something with a higher capacity.


In Celestron's world, the next highest option is the CGE Pro. It's a capable mount, but if you are going to spend that kind of money, the Orion HDX110 is superior. It's a newer design, and it has a lower PE. The Losmandy G11 or Titan would work as well. In all of these cases, the price doubles or more.


Speaking from experience, mounts like the CGEM, CGEM DX, Atlas, Atlas Pro, Skywatcher EQ6, etc. are going to barely get you there with very good guiding. In the case of my Atlas, I have to fight to maintain a 0.6" RMS guiding rate, which is still around 2" P2P. And that is with my relatively lightweight setup using the 600mm lens. The AT8RC is the largest scope I'd put on any one of those mounts. Anything higher, and I am looking at an Avalon belt driven mount for portability and accuracy, and probably a 10Micron or maybe ASA for an observatory-installed large scope (16" or larger). The Avalon itself, and I'm thinking M-Uno, is over $7000 (of course, it's rated for 44lb imaging capacity, and designed to give you pinpoint stars with up to 3000mm focal length, so it's actually a damn good price considering other mounts that offer the same cost $15,000 and beyond.)


Anyway...I've seen a LOT of imagers over the last 10 months start with long scopes, just because they had them, then give up because they couldn't get things working well enough to image on the puny little mounts they had. In the astrophotography world, you will hear people say that the mount is the most important thing. It really is. I figure I'll have a half dozen scopes of differing focal lengths for different purposes in a couple of years time...they are kind of like camera bodies. They come and go, new ones are always being designed, some are better for some things and terrible at others (SCTs are usually the planetary imagers scope of choice, but not the go-to design for DSO imaging; refractors and RCs dominate the DSOs.)


If you want a mirror only telescope, something that would actually be easier to use on a CGEM DX, I still highly recommend the AT8RC. Another option would be to get an 80-120mm refractor, of which there are too many to go into...research 'em, get whatever tickles your fancy. Either way, your overall load on the mount is going to be smaller than with the Edge, and with reducers/flatteners/coma correctors, you can get a flat, sharp field edge to edge. Celestron sells very pretty products, and they have some great package deals...but their mounts are far from the best (even in the low end range), and their SCT designs are ideal for planetary but not for DSOs. The edge does have locks for the mirror...however if you lock the mirror down to prevent flop, you cannot refocus, and refocusing is essential to maintain star quality and detail throughout the night.


To be complete, there are guys who do image with Celestron scopes. Some even do it with low end mounts. The caveat is they either invest a hell of a lot of time doing it and they have many years of skill and know how to do handle everything...the image scale, the tracking/guiding, etc. or they are using a very high end mount. I see the AP Mach 1 GTO being used fairly often with Edge's, both the 11" and 14". The Mach1 is an $8000 mount.