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Messages - jrista

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1021
Photography Technique / Re: How To Remove Weird Colours
« on: February 01, 2014, 08:32:19 AM »
I don't know about the numbers exactly, I'm not a scientist! I did buy my 5dii slightly used (shutter count under 5000), so it's always possible the filter has been changed without my knowledge! However I highly doubt that! My test was simply to point a 940nm IR led at it, which it clearly recorded as pinkish white light with red in the middle! Many cameras can actually see IR in the 900 range. I agree with your explanation about the violet in the OP's photo, that's what it seems to be. I'm surprised OP didn't see it, that's exactly how I've seen yellow (tungsten) and blacklight violet/UV mix, I instantly recognized it! The yellow shadows in the deep purple (the object blocking the blacklight but not the tungsten) is a dead giveaway! The only difference to viewing it with your bare eyes is that the tonality is poorer :)

It would depend on how long you exposed for. Pointing an IR led directly at the sensor, I assume from a relatively short distance, is quite a bit different than picking up IR and UV along with whatever other light is reaching your sensor during any normal exposures. Most modern digital camera sensors use a standard silicon substrate, and silicon is naturally sensitive to a spectrum ranging from ultraviolet (maybe ~250nm) through deep infrared (up to 5000nm). The peak sensitivity range is from maybe 300nm through maybe 2000nm, beyond that the natural sensitivity levels for both deep UV and deep IR are relatively low.

It also depends on the exact characteristics of the IR cutoff filter. As I mentioned before, most DSLRs don't use high quality UV/IR filters that have high transparency to desired wavelengths and a strong and total cutoff to undesired wavelengths. They have a more gradual curve to them...filtration usually starts in the deep reds of visible light, and tapers off into near infrared. It's possible the 5D II has a rather long falloff period that allows more IR through.

It was from a close distance yes, but after reading this I did another test: I asked someone to hold the IR source (a remote controller with a 940nm led, the wavelength of the led was verified) a little further away at a distance of 3.5 meters. The light seemed a little weaker but was still perfectly visible and had both the white and the pinkish component. Checked in LV at 10x magnification using sigma 35/1.4 at f/1.4, 1/50s shutter speed. Inside lighting illuminating the remote controller was very yellow CFL (around 2800K), WB was adjusted to neutralize the color temperature.

I'd offer that 3.5 meters isn't all that far for a concentrated IR emitter like a TV remote. Those things emit a pretty powerful signal, even though we can't see it. They have to combat the ambient temperatures in peoples homes, the energy emitted by direct sunlight hitting the receivers (well, in some cases...one of my IR remotes still works when the receiver is bathed in direct sunlight, the others tend to be sketchy), etc. In terms of infrared light, those remote controls send out a pretty "bright" beam...kind of like a bright visible light of a handheld search light vs. the dimmer beam of a flashlight.

You also have to wonder if your little remote control is just emitting IR, or whether it is emitting some visible light as well. I know that I can see a faint yellow light emitted from the IR LED in one of my TV remotes if I look at it while it's emitting. I think I once had a remote that emitted bright red light as well as IR, as it doubled as the indicator light telling the user that the remote was actually indeed sending a signal.

1022
EOS Bodies / Re: Will Canon Answer the D4s? [CR2]
« on: February 01, 2014, 08:22:52 AM »
Wifi is such a cheap feature to implement and it does not compromise wheathersealing or structural stability of a camera at all. those, who dont need it, can switch it off.
And it is not for the facebook / instagram crowd, since they will not bother lugging around a big old mirrorslapper. It is for those photogra├╝hers who have to shell out 300 bucks for cam ranger - simply because canon refuses to put a 5 dollar wifi chip + antenna into a 2012 camera for 3 grand.

Luckily its getting cheaper to make up for canons marketing differentiation ploys ...
http://www.canonrumors.com/forum/index.php?topic=19342.msg363433;topicseen#new


I think you are gravely underestimating the cost of adding WiFi. It isn't simply some chip you just buy and stuff into the camera. It has to be integrated into the camera! It requires changes to the body design to ensure the signal can get through without requiring that the user point a specific part of the body directly at a wifi access point and without encountering interference issues (all while still complying with FCC regulations regarding RF and all that!), it requires specific design changes to integrate it into the main boards along with all the other far more critical electronics, it requires updates to firmware to ensure it can be controlled and configured appropriately, etc. Adding WiFi to a camera isn't just a "simple" $5 cost...there is the part cost, as well as the increase in manufacturing cost of the whole camera, as well as increases to firmware development and testing costs, as well as increases to testing costs (testing WiFi would be somewhat time consuming...having to enter in access point information, let it connect (and twiddle your thumbs while it does), make sure information can be transferred reliably, rinse & repeat for verification, then finally ship it. All that stuff, all those various stages of a lengthy design, manufacture, assembly and testing pipeline, add cost! Adding WiFi costs more than $5.

This is a common mistake with people asking for new features in software & web development: "Oh, but it's 'just' an extra menu item!" or "Oh, but it's 'just' an extra button!" No! It's NEVER just an extra menu item or an extra button! You have to plan for the new menu item, make sure it fits into the design of the application or web site, you have to add the additional UI code and styling, then you have to add code to make it function, then you have to TEST that code, then you have to redeploy the application. Nothing is ever "just" as simple as a clever individual can whittle things down and make them seem. (As a software developer of over 15 years, I swear that every company I've ever worked for carefully hired people who had special training in the art of VASTLY OVERSIMPLIFYING to decide what features were necessary for the ridiculously overcomplicated products they wanted to develop...  ::))

NOTHING is as simple as it "sounds". EVERYTHING is more complex when you factor in the reality of its design, development, and integration into a complete product.

You also seem to forget that TODAY, wifi and gps are becoming more common in most portable consumer devices...but that research and design on the 5D III probably started not long after the 5D II was released! That was a long time ago. It takes a long time to design new technology, and design it as well as Canon designed the 5D III and 1D X. As subtle as some of it may seem (and really, that's to Canon's credit!), there was quite a lot of new technology in those two cameras. It was probably in prototype stage a good year or so before it was released, and it was released a couple of years ago now. The 5D III is older than the 6D, which really did not need all that much R&D in the first place, as it is basically a glorified 5D II with a newer sensor, and GPS & WiFi.

It's naive to bash on the 5D III, which required some significant redesign, much of which was probably done alongside design for the 1D X (as it inherited much of the 1D X's functionality), as some radically inferior product just because it doesn't have WiFi. In all the years I've done photography and moderated photo.stackexchange.com, or for that matter all the years I've been reading CR...WiFi NEVER even came up as the most important thing that Canon just HAD to add to the 5D III. I don't even think it was on anyone's radar to even request in the first place...certainly not before the 6D anyway. The things people were asking for with the 5D III were less noise, and better AF. Well, we got a hell of a lot less noise at high ISO with the 5D III, and the AF is mindblowingly good when compared to the 5D II AF system. Given that, Canon delivered exactly what their customers asked them to deliver...

1023
Photography Technique / Re: How To Remove Weird Colours
« on: February 01, 2014, 07:06:50 AM »
I don't know about the numbers exactly, I'm not a scientist! I did buy my 5dii slightly used (shutter count under 5000), so it's always possible the filter has been changed without my knowledge! However I highly doubt that! My test was simply to point a 940nm IR led at it, which it clearly recorded as pinkish white light with red in the middle! Many cameras can actually see IR in the 900 range. I agree with your explanation about the violet in the OP's photo, that's what it seems to be. I'm surprised OP didn't see it, that's exactly how I've seen yellow (tungsten) and blacklight violet/UV mix, I instantly recognized it! The yellow shadows in the deep purple (the object blocking the blacklight but not the tungsten) is a dead giveaway! The only difference to viewing it with your bare eyes is that the tonality is poorer :)

It would depend on how long you exposed for. Pointing an IR led directly at the sensor, I assume from a relatively short distance, is quite a bit different than picking up IR and UV along with whatever other light is reaching your sensor during any normal exposures. Most modern digital camera sensors use a standard silicon substrate, and silicon is naturally sensitive to a spectrum ranging from ultraviolet (maybe ~250nm) through deep infrared (up to 5000nm). The peak sensitivity range is from maybe 300nm through maybe 2000nm, beyond that the natural sensitivity levels for both deep UV and deep IR are relatively low.

It also depends on the exact characteristics of the IR cutoff filter. As I mentioned before, most DSLRs don't use high quality UV/IR filters that have high transparency to desired wavelengths and a strong and total cutoff to undesired wavelengths. They have a more gradual curve to them...filtration usually starts in the deep reds of visible light, and tapers off into near infrared. It's possible the 5D II has a rather long falloff period that allows more IR through.

1024
Photography Technique / Re: How To Remove Weird Colours
« on: February 01, 2014, 03:36:01 AM »
Guys, modern cameras have a UV filter built into them, part of the low pass filter stack (along with an IR Cut filter.) You don't need to filter UV. The light was probably your standard fluorescent blacklight. Cheap blacklights include a considerable amount of deep violet visible light. There isn't a UV cutoff issue here...the camera just picked up the deep violet visible light, which human eyes are naturally rather insensitive to. Thats all!
You're giving bad advice. First of all, many humans can see deeper than "visible violet", but that's a whole different point. What's relevant here is that certain cameras also seem to pick up a little bit of near-UV, between 350 and 400. Light in that region is considered UV because it's soft focusing and causes fluorescing. Some modern cameras have really bad UV filters or really bad low-pass filters that don't include a separate UV filter. Canon mk ii and iii see IR quite well up to at least 940 nm. I haven't tested higher.

I never said humans couldn't see deeper than visible violet...simply that our eyes are not very sensitive to those wavelengths.

As for the visible light range, visible light (if you account for all people of all different ranges of vision) spans from 380nm through around 750nm. "Officially", the range spans from 390nm to 700nm. As an astrophotographer who has been in the market for some kind of imager for deep sky narrow band imaging for a while now, and who has done a MASSIVE amount of research on the subject recently, both UV and IR sensitivity in modern DSLR cameras is really low. The range of sensitivity fits pretty closely to the 380nm through 750nm, with a strong signal only really found from about 400nm through 690nm due to UV and IR filtration.

The UV/IR cut filters are not perfect, however they block out some 90% or more of the near bands, and nearly 100% of the far bands, and the silicon itself takes care of the rest. The IR filter in Canon cameras is actually a bit aggresive...it attenuates the deep red signal, which is part of the reason why the red channel in Canon sensors tends to be rather noisy. The natural response curve for silicon is much less sensitive to UV light either, sensitivity up to 390nm remains relatively strong (although still about half that or less than for visible visible wavelengths of light), and falls off very rapidly from there till it finally tapers out completely at 250nm. It is the near IR spectrum that silicon is more sensitive to, and that can extend well past 1100nm, with strong sensitivity up to 900nm or so without any IR cutoff filter.

In astrophotography, some of that near infrared signal is useful, however you have to modify modern DSLR cameras to enhance that sensitivity. Canon actually makes the 60Da, specially designed with a weaker IR cutoff filter that allows a much stronger hydrogen-alpha (656nm) and sulfur-II (672nm) signal to get through, (and even that still isn't as strong as green sensitivity. In all other Canon CMOS sensors with the IR cut filter, these wavelengths are less than half as strong, and falloff for wavelengths longer than that is rapid. Even if some 900nm IR does get through, the signal is so weak that it isn't going to have a significant effect...it's all probably lost to Canon's read noise anyway.

Manufacturing IR cutoff filters that allow full spectrum transparency up to 750nm, with a sharp cutoff, are much more expensive. They would technically be much better, but DSLR camera manufacturers generally don't use them. To find cameras with IR and UV filtration that is "square", with >90% signal transparency through the entirety of the desired band and <0.1% transparency outside of the band, you usually have to look to the scientific grade devices. An SBIG CCD camera for astrophotography, for example, will usually have high quality IR and UV cutoff like that, but those cameras tend to cost anywhere from $3000 bare, to over $10,000 with some  additional features.

The kind of bright purple in the photos of the OP were most likely caused by that very near-UV (380nm) + deep violet light (390nm up through 400nm), a rather broad-ish band that is emitted by those cheap fluorescent tubes.

1025
Pricewatch Deals / Re: Canon EOS 5D Mark III Body $2549
« on: January 31, 2014, 08:19:27 PM »
I think the fact that they feel there are only 48 states in the USA should make their approval rating 0%!

They used the term "lower 48 states"...that's a pretty common and well used term, and they certainly don't think that there are "only" 48 states. They only ship to the lower 48, and not to Alaska or Hawaii, because they always cover shipping, it's free for every purchase.

1026
Pricewatch Deals / Re: Canon EOS 5D Mark III Body $2549
« on: January 31, 2014, 08:14:51 PM »
Does anyone know the Canon warranty status on these items? Gray market? I couldn't find anything other than 6aves' own 1-year parts and 90-day labor warranty. I know how good Canon service is...I don't really know what 6aves service is...do they farm it back out to Canon?

1027
Photography Technique / Re: How To Remove Weird Colours
« on: January 31, 2014, 07:02:41 PM »
Guys, modern cameras have a UV filter built into them, part of the low pass filter stack (along with an IR Cut filter.) You don't need to filter UV. The light was probably your standard fluorescent blacklight. Cheap blacklights include a considerable amount of deep violet visible light. There isn't a UV cutoff issue here...the camera just picked up the deep violet visible light, which human eyes are naturally rather insensitive to. Thats all!

1028
EOS Bodies / Re: Will Canon Answer the D4s? [CR2]
« on: January 31, 2014, 06:59:10 PM »
The 5D 3 really is nothing more than a 5D 2 with - at long last - a decent af-system in it. Hardly any improvement in IQ and resolution. Blatant lack of connectivity (not even wifi which canon manages to put into any 200 dollar powershot). It should really have been called 5D 2N.

The 5D 3 is really dated in every respect.

You REALLY don't know what the 5D III is, man. The 5D III was a complete and total overhaul of the 5D II. New body, better sealing, RADICALLY improved AF, improved metering, significantly bumped frame rate, improved ergonomics, etc. etc.

Use of wireless options like WiFi and GPS requires punching holes in the magnesium body...something that compromises ruggedness and sealing. So it isn't a cut and dry point there, and I would suspect that currently, more pros prefer to have the rugged body and sealing rather than the WiFi (otherwise, Canon would have stuffed a WiFi chip in it already.)

The 5D III is current and advanced in EVERY respect EXCEPT the image sensor. Get your facts strait, bub!

1029
Third Party Manufacturers / Re: Is Sony junk....
« on: January 31, 2014, 12:05:23 AM »
In the past, didn't Moodys also rate General Motors as junk?
And Ford?

Aye, they did. And, both companies deserved the rating at the time! Both companies worked their ASSES off, GM even wrote down some 46 BILLION in deferred taxes, to get their ratings back up. Ford still doesn't make the greatest cars, for that matter neither does GM, however I did gain a lot of respect for Ford for not taking a government bailout. If a junk rating is deserved, it should be given. If Sony turns themselves around, restructures themselves into a better, more reliable, and most importantly profitable corporation, then their credit rating should improve. If they do not, however, their credit rating will continue to degrade.

What might happen in the future doesn't play a role in what their rating should be right now, though. And what happened to other companies that have been rated junk in the past has absolutely no bearing on what Sony should be rated right now.

1030
The discussion on mirrorless is a great example of why the term slr is increasingly inappropriate. If you stuck a mirrorless mechanism in the 1dx, would it not be an slr? And, on the other hand, if you took the existing 1dx shutter mechanism and installed it into a rifle-shaped mount that had balancing weights to adjust for different lenses, would it not be an slr?

Um...the answer to both questions is: No!

The 1D X is ONLY an SLR so long as it is an SLR: Single-Lens Reflex. That implies a very specific design with rather specific construction to support the notion that the camera is a single-lens reflex camera...a camera that reflects light from a single lens to the viewfinder, allowing the operator "through the lens" framing. Take away the mirror box, and no matter what you end up with, it will never be an SLR. It'll be something else. A mirrorless is called a mirrorless, or an ilc, because it quite simply is NOT an SLR, and never will be because it can't be.

Great discussion. My personal opinion is that the slr market is severely hindered by our pre-conceived notion that a camera should look like an slr. In the future, I'd anticipate this model to be broken. Right now, some people think of it as a shutter mechanism, as the name implies. Most people think of it as the big "camera-shaped" hunk of metal and plastic that makes it look professional-ish. I don't think the shape is at all optimized, however, for taking pictures, except for the use of very small lenses. 

As others have pointed out earlier in this thread, when digital SLRs first hit the market, they took on a variety of different forms and shapes. All of those shapes failed, and the DSLR took over.

Timeless designs don't become timeless for no reason. The basic SLR design has persisted for decades. Many, just as you are now, probably proclaimed just the same things when the film SLR was first phasing into the DSLR. Obviously some companies even tried to mix things up a bit. The the SLR design is timeless. The earliest forms of SLR came onto the scene, what, in the 1920's? That is about NINETY YEARS. That's a really long time for the same basic camera design to persist.

Why does it persist, though? I mean, as early as the late 30's/early 40's SLRs had taken on the form they still have today. The general concept of an interchangeable lens camera that allowed through the lens composition was solidified by the 40's at the latest. It persists today because it is the most convenient design. Your comment above, that "the model is broken", is either entirely naive, or simply baiting. Well, sorry for taking the bait, but the SLR design is the farthest thing from being broken. It persists because it is the best form people have found to assist them in serious photography.

Modern DSLR's, particularly from Canon, are highly ergonomic. Their shape fits the hand ideally. Their weight nicely balances against the average size of DSLR lenses. Their button placement allows for optimal efficiency when changing settings during operation, allowing for procedural memory to support operation without the operator ever taking their eye away from the viewfinder! The modern DSLR body is really the pinnacle of camera body design. It persists because it's the best. Not because it is broken.

"Most people" aren't photographers. Most people don't really care about photography...they care about snapshots and visual chit-chat and instagram. The DSLR wasn't designed for most people. It was designed for photographers. So long as photographers persist, the DSLR will persist. It best solves the problem of critical photography for critical photographers. Perhaps someday someone will simply remove the mirror from the DSLR, and replace the pentaprism with an EVF...but will leave the general DSLR body design alone. I predict that the first company to do that will be the hero of the critical photographer (for a while). I predict Canon will do it best, and maintain their dominance in the market of providing critical equipment for critical photographers.

Everyone else? The snapshotters (and also the critical photographers who want something in addition to their DSLR...so basically everyone), will go with whatever is most convenient...damn the quality, damn the capabilities...they just want something that will snap photos and do instagram. Having 36mp and extensive DR doesn't mean squat to the snapshotter...they are going to obliterate all that such fancy technology has to offer anyway when they pass it through one of those (sorry, gotta say it) hideous filters for exhibition on instagram.

Sony, as the original article that the OP quoted says, makes "cool technology", but has rather bland packages that they put that cool technology into. For a critical photographer, the technology is important, but the package is more important. The A7/r is an intriguing technological advancement...sensor wise and due to the fact that it's mirrorless...but it's package kinda sucks. Everyone, even Fred Miranda, has mentioned how it doesn't really handle AF all that well (even with Zeiss lenses), and that functionally it isn't on the same playing field as Canon and Nikon. And it's small. That might be nice if the most important thing for you is portability...but it would still be better if that amazing sensor was packaged in a better body. I'd take a Canon 5D III style DSLR body with a Sony Exmor in it every time over the A7/r. (Hell, I'll still take the 5D III with it's 22.3mp Canon sensor over the A7/r!) The bigger body is one of the things that makes the 5D III so appealing...it is an ergonomic masterpiece packed full of exceptional technology in addition to the sensor, built on nearly 90 years of refinement of the best camera body known to man.

1031
Third Party Manufacturers / Re: Is Sony junk....
« on: January 30, 2014, 09:23:22 PM »
Yes, "Junk" is just a colloquial term which does make for good press, however it is also used in unofficial investment nomenclature. Junk refers to non-investment grade ratings. Because Sony is now Ba1, they are no longer a "prime" investment. There are three classes of prime investments and prime credit: Triple As, the As, and the triple Bs (or, in the case of Moodys odd nomenclature, Baa{n}.) Sony is now a Ba1/BB+ rating, which takes it out of the prime investment category, and classifies it as NON-investment. In other words...STEER THE HELL CLEAR, VERY HIGH RISK! The rewards can be very great, but the chances are also very great that instead of being rewarded, you'll lose whatever you invest in non-prime (i.e. junk) rated investments.

Junk is a very appropriate term. That's why it's been used to describe this class of non-investment worthy funds for decades.

Agreed....it was a one step decrease in the rating that when from investment to "speculative."  It certainly isn't a good thing....but I bet most investors see it not as black and white...AAA or Junk....but as something that was already risky to something that has even more risk....

Sure, it isn't like it went from AAA to Junk in one move. However, dropping from Baa2 to Baa3 is less hazardous to a fund than dropping from Baa3 to Ba1. There is that additional line that is being crossed...simultaneously Sony went from being prime to being non-prime. That makes the one-step move from Baa3 to Ba1 more meaningful than the move from Baa2 to Baa3. Hence the reason it's made a rather obvious ripple in the media...it's a move that has more significance than any other prior move, even more significant than when it went from A class to B class.

1032
Animal Kingdom / Re: Show your Bird Portraits
« on: January 30, 2014, 09:06:15 PM »
Not much of a shot but here's the twist.  It was shot using the 6D wifi from my computer in warmth while it's -20 C on the deck! ;)

However, I'm not too thrilled as I've been having problems keeping the connection and can't get it back.  Anyone have experience with this 6D wifi and know the typical pitfalls?  The EOS utility and live view shooting seems very clunky and I was getting pretty frustrated with the slowness of focus and the time transfering files to the computer etc.  Seems a mixed bag.

Jack

It's entirely possible the -20┬░C temps are the problem. When it's that cold, the batteries used in DSLRs don't function well. They often can't consistently deliver enough juice to keep the camera operating properly...the shutter will slow, mirror slap may not function properly, and radio connections become intermittent.

1033
Third Party Manufacturers / Re: Is Sony junk....
« on: January 30, 2014, 07:45:37 PM »
The power of labels is funny.  Moody's didn't rate Sony as "junk."  They down graded their rating of Sony BONDS by one step, out of 23 steps.  The step just happened to drop Sony's rating from the lowest "investment" grade to the highest "speculative" grade.  There are still 10 steps below Sony's current "Ba1" grade. 

The primary functions of these ratings are to given investors looking to buy bonds a sense of the risk that the investor may be taking on that the company (Sony) won't be able to pay back that bond and to help set the rate of return/yield/interest that will attract investors.  This is as much about comparisons as absolutes so that investors know that Sony bonds are about the same risk as bonds from company XX or more risky than company YY. 

And speculate about Moody's all you want...but, given Sony's debt and recent financial losses, would you buy Sony debt for a very low interest rate?  Or is the chance that they may default/go into bankruptcy enough that you may want more of a return on your investment to justify the risk.  That is all this is. 

"Junk" is just a label that makes for good press.

Yes, "Junk" is just a colloquial term which does make for good press, however it is also used in unofficial investment nomenclature. Junk refers to non-investment grade ratings. Because Sony is now Ba1, they are no longer a "prime" investment. There are three classes of prime investments and prime credit: Triple As, the As, and the triple Bs (or, in the case of Moodys odd nomenclature, Baa{n}.) Sony is now a Ba1/BB+ rating, which takes it out of the prime investment category, and classifies it as NON-investment. In other words...STEER THE HELL CLEAR, VERY HIGH RISK! The rewards can be very great, but the chances are also very great that instead of being rewarded, you'll lose whatever you invest in non-prime (i.e. junk) rated investments.

Junk is a very appropriate term. That's why it's been used to describe this class of non-investment worthy funds for decades.

1034
Animal Kingdom / Re: Show your Bird Portraits
« on: January 30, 2014, 04:37:29 AM »
Snow day today in NC, so I sat in my blind to shoot some birdies near my suet feeder. 5DMKIII, 600 II + 1.4X III, better beamer flash fill (-1 & 2/3 stops), AV at f8, ISO 1250, shutter speeds 1/800-1/2000, rear focus.

Beautiful shots, Vern! You have a wonderful diversity of birds where you live, especially with the Cardinals. (They only live in about the eastern half of the country.)

1035
Landscape / Re: Deep Sky Astrophotography
« on: January 30, 2014, 04:32:02 AM »

Hmm, interesting about the N2 band. And 5nm filters are about $300 cheaper than 3nm filters are (~$600 vs. $900), so a decent savings in money.

I would recommend getting the H-alpha in 5nm, S2 in 3nm, and O3 in 3nm.  The only drawback to 3nm is if you have a fast system (i.e. f/3 or faster).  They become less efficient and your almost better off getting all 5nm.

Wade

Yeah, I read a bit about the f/3 issue on Astrodon's site. I am actually planning to use my 600mm f/4 lens as a fast APO refractor. Probably with an SBIG STF-8300m in the long run, with the filter ring accessory. Is f/4 fast enough to cause problems?

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