April 19, 2014, 07:49:45 PM

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Messages - jrista

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61
Animal Kingdom / Re: Show your Bird Portraits
« on: April 15, 2014, 04:40:17 AM »
Thanks, guys! :)

62
Third Party Manufacturers / Re: Zeiss Otus Initial Impressions
« on: April 15, 2014, 03:51:53 AM »
Based on the design of the DC light, it does look like it is a diffuse bulb of some kind. It also has a reflecting shroud, I guess? Dunno, that's a pretty complex system. I think it would be difficult for someone far more versed in the concepts of wavefronts and diffraction and the mathematics behind it all to figure out how the light from those DC lamps would diffract.

Anyway, regardless of the specific causes, I truly do not believe it is your lens that's the problem. The fact that you got different results from different light sources should alone be enough to tell you it can't be the lens. ;)

63
Third Party Manufacturers / Re: Zeiss Otus Initial Impressions
« on: April 15, 2014, 03:29:03 AM »
Actually, I did see just a slight bit of faint rings in one of the DC lamp images. At  first I thought it was compression artifacts, but I'm pretty sure it is some slight warping of the blur circle.

I would have to see the DC lights photographed sharply to tell you any more. It all depends on the materials and quality of materials between the actual light source and the lens. I know that your average christmas light uses pretty cheap glass for the bulb. They pretty much always produce lots of little diffraction spots and funky warped and rainbowed blur circles.

Other lights use better glass, and bulbs with diffuse inner coatings tend to exhibit less diffraction patterning due to the diffusion, which again changes the nature of the wavefront. Noble gases aren't going to be creating diffraction, however noble gases can emit light themselves. A neon bulb of some kind would effectively BE the light source, in which case once again, you end up with just air between the light source and the lens.

You aren't guaranteed to get "onion rings", nor any diffraction pattern for that matter, from every light bulb or other artificial light source. It depends on what things between the actual light emitting source and the lens may be causing diffraction. There aren't really any hard and fast rules here.

64
Third Party Manufacturers / Re: Zeiss Otus Initial Impressions
« on: April 15, 2014, 02:27:03 AM »
Thanks jrista, that was clarifying. So that means that it has nothing to do with the design of the specific lens, since the diffracted wavefront already exists when hitting the lens. Criticizing a lens for onion-ring bokeh is therefore incorrect. Right?


I would indeed say "right"! There is no way the Otus, touted as such a high quality lens, and clearly seeming to be such a lens, would produce such "onion ringing." Zeiss should be sued if they allowed that...that would mean they used glass of poor quality with impurities, which simply couldn't be the case given how sharp the lens is corner to corner.

For comparison, here is a photo of some christmas lights on a christmas tree that I took years ago. I tweaked the focus of this shot to purposely bring out the effects of diffraction. You can clearly see the primary diffraction pattern, the large circular pattern that dominates the shape of each blur circle, caused by the lens aperture. (NOTE: The blur circles here also exhibit spherical aberration, hence the reason the outer edge is brighter than the center, which is counter to your standard airy pattern, where the center is much brighter than the outer rings).

You can also see the diffraction patterns caused by the obstructions presented by impurities within the glass of each christmas light. They look like rocks in a pond, causing additional waves in response to an incoming mechanical water wavefront.



This is definitely not the lens, it was the EF 100mm f/2.8 macro lens, an otherwise high quality lens (certainly not as good as the Otus, but very good otherwise)...notice that each light exhibits a different pattern of obstructive diffraction, where as the primary circular diffraction wave caused by the aperture exhibits the same in each light. Two causes of diffraction converging in a single image. The "warping" and inconsistent gradient/rainbowing and larger but softer internal rings of each blur circle is also due to the glass of each Christmas light, not the lens. You can tell because those aspects of each blur circle change per light.

If the nature of the wavefront and it's diffraction pattern changes with each light source, then the issue is most likely rooted within  the light source, itself. If the nature of the wavefront and it's diffraction pattern remains consistent across light sources, then it is likely due to either an obstruction within the light path between the source and the lens, or the lens itself. Obstructions within the light path will remain consistent themselves, but may change position within the blur circle of each light source. Diffraction effects caused by the lens itself will always be exactly the same for each blur circle in the image...usually, if you have focused right, that will present as a circular waveform that should be pretty uniform and otherwise clean in nature.

65
Third Party Manufacturers / Re: Zeiss Otus Initial Impressions
« on: April 15, 2014, 02:13:19 AM »
There are only two things I don't like about the Otus 1.4/55:
1) The price... because I would have to sacrifice too much other stuff to buy it  :'(
2) The onion bokeh... but this is only really noticeable with specular highlights that are OOF. In normal shots its not really noticeable.

Price is price and I agree that you should really want it to buy it. I also agree on the bokeh issue. But there is something I don´t really understand about boked. Because it varies, depending on light source.

I have attached two examples. The first is of five candle lights and the second is a chandelier with electric light. The bokeh from the electric light has a clear onion bokeh, whereas the candle lights are clean. If someone could explain why this happens, it would be most appreciated.


This is due to the nature of light wavefronts and diffraction. Diffraction is an INTRINSIC property of light. It exists within the wavefront itself, to be 100% accurate...it is not actually due to light bending around obstructions or anything like that. Light diffracts around obstacles and through openings intrinsically, the effect of which appears to be the "bending" of light (hence the colloquial descriptive terms most often used). The difference between the two sample photos you took is that one is a "naked" light source...the flames of candles; the other is an enclosed light source...either light emitting diodes or tungsten filaments, encased within a class or plastic bulb.

Because of imperfections and impurities in the bulb of your lights, the light coming from them is not a pure, uninterrupted wavefront. Therefor, the effects of diffraction, which occurs when the wavefront from the enclosed light source encounters imperfections and impurities (i.e. a microscopic opaque granule in the glass or plastic of the bulb), show up in your boke blur circles.

There is nothing wrong with your lens. The difference in the two images is due to the difference in the nature of the wavefronts coming from them. Flame is THE actual light source, and so long as there is no other obstruction between you and the flame, a pure, unadulterated wavefront enters your lens. The electric lights are a light source enclosed within a bulb, and an already diffracted wavefront is what enters your lens.

An excellent (although rather technical) explanation of the true nature of light can be found here:

http://www.telescope-optics.net/wave.htm

In quote:

Quote
Diffraction

According to Huygens' principle, every wavefront point is a source of secondary wavelets, through which spreads in the direction of propagation. This constitutes a micro-structure of energy field propagation, with the energy advancing in the direction of the wavefront, but also spreading out in other directions. Principal waves, or wavefronts, form in the direction determined by extending straight lines from the point source. Waves moving in other directions generate phase difference, preventing them from forming another effective wavefront (FIG. 1, top right). However, these diffracted waves do interfere with both, principal waves and among themselves.

As a consequence of the existence of diffracted wave energy, placing obstruction of some form in the light path will result in the "emergence" of this energy in the space behind obstruction. But the obstruction did not change anything in the way the light propagates - it merely took out energy of the blocked out principal waves, with the remaining diffracted field creating some form of intensity distribution in the space behind obstruction - the diffraction pattern.

Similarly, by limiting energy field to an aperture, the portion passing through it is separated from the rest of the field, and its energy - this time consisting from both, aperture-shaped principal waves and diffracted waves within - will create a pattern of energy distribution behind the aperture. Again, there is no actual change in propagation for the light passing the aperture, including those close to the edge of obstruction (light does not "bend around the edge"); whatever the form of energy distribution behind the aperture, it is caused by the interference of primary and diffracted waves inherent to the energy field (FIG. 1, middle and bottom).

66
Photography Technique / Re: Tomorrow's eclipse
« on: April 15, 2014, 02:00:47 AM »
I started my imaging sequence with BackyardEOS about 10 minutes ago. I couldn't see it, but my camera picked up the first bit of the eclipse before I could see it with my naked eyes.

I'm using a tracking mount, so my settings once we get to totality will probably be much different than most. I started out at ISO 100, 1/250th, f/8 w/ 600/4 II. That pushes the histogram to the right with my 7D, but not too far that the highlights blow out. The current part of my imaging sequence has dropped to 1/125th second now, and it'll drop to 1/60th about the time the moon is half-eclipsed...not yet sure exactly what settings I'll be using once the moon is fully within the umbra...

67
Landscape / Re: Total Lunar Eclipse - #1 of 4 - April 2014
« on: April 15, 2014, 12:55:16 AM »
Ah, looks like they come in cycles. There was a 300 year gap up through 1908. Looks like the total cycle time is 565 years, so we'll have a bunch for a couple centuries, then another lull. I don't know what I read before, but I'm not even sure it actually projected future cycles...I guess I just assumed that it was a rarer event based on the history of Tetrads.

Anyway, here is one of my shots, taken as the moon was entering the umbra:


68
Third Party Manufacturers / Re: Zeiss Otus Initial Impressions
« on: April 15, 2014, 12:02:10 AM »
Someone needs to go out and take some pictures of mossy stumps and cattails. We need to determine if he who shall not be named had talent, or if it really IS the lens! :P

(Sorry, just trying to spice up this thread again with some beautiful nature photography.)

69
Landscape / Total Lunar Eclipse - #1 of 4 - April 2014
« on: April 14, 2014, 11:54:29 PM »
There are FOUR total lunar eclipses occurring over the next two years. Tonight is the first of the four. It starts at 1:58pm ET, 11:58 MT, and 10:58 PT. If you are planning on photographing the first lunar eclipse this year, share your photos here!

I'm aiming to get a full sequence of the entire eclipse, from the first penumbral dimming through totality and ending at the point the moon moves out of the penumbra (for me, that's from 11:58pm through 3:30am.)

For more details, see here: http://www.mreclipse.com/LEdata/TLE2014Apr15/TLE2014Apr15.html
For exposure tips, see here: http://www.mreclipse.com/LEphoto/LEphoto.html

70
Animal Kingdom / Re: Show your Bird Portraits
« on: April 14, 2014, 04:44:31 PM »
One of my dove photos just hit the first page of popular on 500px. First time any of my photos have gotten quite that far. Given that it was a from-the-hip shot without ANY planning or artistic goals whatsoever, I'm pretty stunned:

http://500px.com/photo/66945531?from=popular

UPDATE: Now it's the first image in the second row of the popular page! :D Pulse is 99.7. I wonder if it will hit the top row before it's pulse is knocked back at 24hrs...

71
Photography Technique / Re: Tomorrow's eclipse
« on: April 13, 2014, 10:35:09 PM »
You probably want around 50-100mm of focal length to get a shot like that. You will also likely need to take separate shots of the foreground and moon (after setting up your camera on  your tripod, without reframing) in order to get both the tree and the moon sharp. You'll need to composite the two in post. You will also probably need to shoot the tree around late civil twilight (blue hour) to get it silhouetted properly.

To avoid failure, make sure you are set up for the moon WELL ahead of time, so you have some time to focus sharply on the moon, plan your exposure times, and be ready to take each image at exactly the right time. As the eclipse progresses, you MUST change your shutter speed and ISO to compensate for the darkening that occurs. You cannot simply set your intervolometer and let it go...otherwise you'll end up with an extremely deep, dark brown moon that is barely brighter than the black background of the sky, instead of a nice, bright, richly colored red moon. You have to think ahead, do some research, figure out what the EV of a full uneclipsed moon is and the EV of a fully eclipsed moon is, and extrapolate how bright it will be at each interval you want to image at, and write down what shutter speed and ISO setting you will be using.

From full through half eclipsed, you will probably just want to increase your exposure time, however as you get into the crescent eclipsed phases and into the fully eclipsed phases, you will want to start increasing ISO and keep shutter the same (otherwise, you have to expose so long that the transit of the moon blurs all the detail away).

So long as you know roughly what exposure settings you need for each phase of the eclipse, and what the longest shutter speed you can expose at without the movement of the moon itself causing blur, then you should be fine. Small changes in total exposure (i.e. between the first fill uneclipsed frame and the next frame where the earths shadow is just beginning to eclipse the moon) shouldn't matter...you can normalize the small differences in post. It's the bigger differences that matter, i.e. full to gibbous eclipsed, gibbous to half eclipsed, half to fully eclipsed, etc.

From an artistic standpoint, a lot of these composites only show the fully eclipsed moon in the reddish color. If your careful and clever, you can actually push your exposure really far to the right and make some of the crescent images just before total eclipse show off some of that same reddish color. That way you get more of a gradual transition from full uneclipsed moon, to fully eclipsed moon, rather than that sudden, harsh transition from white partially eclipsed to blood red fully eclipsed.

72
Lenses / Re: Focal lengths
« on: April 13, 2014, 10:03:42 PM »
Excluding telescopes, I've used the EF 600/4 L II with both 2x and 1.4x TCs (a Kenko in this case, as they stack directly without the need for an extension tube...IQ suffers a little bit). That gets you to 1680mm.

With telescopes, I've poked around with focal lengths up to around 8000mm to 10,000mm using SCT and RC type OTAs with barlow lenses. The only real reason you would use such focal lengths is for planetary (to get any real kind of sharp detail on planets, you need at least 8000mm), solar (sunspot closeups) and lunar (individual craters and finer surface detail).

I haven't purchased my own OTA yet, once I do, I really can't wait to do planetary imaging at over 8000mm. :P

How do telescope focal lengths relate to sensor size? Like, is 8000mm an equivalent in full frame lens terms?

Well, it depends on the scope. When it comes to the popular SCTs (like Celestron EdgeHD and the Meade Aplantics) and RCs, they are usually designed to cover at least the 42mm diagonal of a 35mm sensor frame. But when it comes to telescopes in general, they have a pretty wide range of image circle sizes. If you attach focal reducers, that affects the amount of backfocus, which in turn usually has an impact on image circle size. It seems to be a general standard that your average refractors (which often need at least a field flattener, if not a full focal reducer, to get a flat field) support a 22mm image circle. That is for fairly small sensors, which are more common in astrophotography CCD imagers. APS-C sized sensors are usually supported "natively" without focal reducers usually (~27mm diagonal.)

Larger scopes, as well as the new Rowe-Ackermann Schmidt Astrograph from Celestron, support image circles from 50mm up to 70mm. The larger scopes are ultimately designed to be used with both full-frame (36x24mm) and square full frame (37x37mm or larger, usually 4096x4096 pixels) CCD sensors. The 37x37mm sensors have a 52mm diagonal. There are some newer, larger sensors coming on the market soon that will have around a 65mm diagonal, and the ultimate top of the line is expected to be around 70mm in the future. Kodak is primarily the manufacturer supplying either FF or large square sensors, with 9µm, 11µm, and 24µm pixels. Sony has entered the market as well, and is supplying some of the highest sensitivity (highest Q.E.) small sensors (up to 22mm) that are often used in autoguiding cameras (ultra high sensitivity, configurable frame rate video cameras that are very similar to webcams, basically.) Some Sony sensors have found their way into entry-level Atik CCD cameras. Aptina also supplies 22mm and APS-C sized sensors.

There really isn't a standard sensor size that is supported by telescopes. Most support the 22mm and APS-C sensor diagonals. Larger OTAs usually support 35mm full frame. Outside of Celestrons new RASC Astrograph (which produces a 70mm image circle and costs a mere $3400), you usually have to buy either an RC Optical Systems or PlaneWave truss to get a 65mm (RCOS) or 70mm (PlaneWave) image circle...and those puppies cost tens of thousands of dollars.

73
Lenses / Re: Teleconverter advice
« on: April 13, 2014, 05:54:14 PM »
I also have the Teleplus Pro 300 DGX. Trust me, the quality is not as good as the Canon 1.4x TC III.

74
It isn't just these sites. OpenSSL is used in about 70% of web servers running open-source operating systems and web server software. It's also used for the majority of email servers, and OpenSSL is used ALL OVER the place for all kinds of other things.

This bug is really a disaster...you can no longer simply rely on the notion that if you are in SSL, your safe. It will take weeks at least for really critical sites to upgrade to the patched SSL version, and it could take months or years for the majority of affected servers to be patched.

That basically means you can no longer trust that when your browser says your secure (i.e. it's using SSL over HTTPS), that you actually are secure.

Trust nothing anymore, ppls! :P Web site security is now a highly nebulous thing. Unless you directly verify that the server is using OpenSSL 1.0.1g (or something else entirely, like Windows Server which is not affected), I wouldn't trust ANY web site under SSL for a while.

75
Lenses / Re: Teleconverter advice
« on: April 13, 2014, 02:20:19 PM »
I have the kenko pro 1.4x and the canon 1.4xiii. They both have about the same IQ. The kenko is about half the price and works on just about everything, the canon has weather sealing.

Thanks!

As I own the EF 600/4 II, and have used both the 1.4x III and Kenko 1.4x, I can attest to the fact that they do NOT have the same IQ. You wouldn't notice the difference that easily with the 100-400, largely because that lens just doesn't offer the initial IQ to see it without looking for it. The key difference with the Kenko is how it messes with your boke quality. Without the Kenko, my 600/4 II produces the creamiest, cleanest, richest background boke you'll ever see. WITH the Kenko, however, my boke gets muddy and loses the clean, smooth, creamy look that it has without any TC. With the 1.4x TC III, my backgrounds are largely the same, albeit more blurred, as with the bare 600.

The area where the lower IQ of the Kenko comes out most is in point highlights. If you are shooting birds on a beach, for example, you'll have specular highlights in the background water. With the 600 and TC III, those specular highlights result in nice, clean, normal boke blur circles. With the Kenko, those highlights become these warped, spotted, deformed, and generally UUUUGLYYYY blur circles. I mean, think about the worst blur circle you can imagine...and that's what you get with the Kenko.

These are not generally IQ factors you look for when your shooting, but once you start processing, the lower background quality (and even some of the slightly smudged midframe and corner detail) show up. The ugly blur circles in particular are a MAJOR turnoff with the Kenko TC. The blur circles are going to be visible on all lenses, regardless of quality.

So it's unfair to say the Kenko and Canon TCs offer the same quality. They do not offer the same IQ, and while the drawbacks of the Kenko on lower end lenses are certainly harder to discern, it's something to think about. You may not have the option, as the design of the Kenko allows it to be used with pretty much any and all Canon lenses except EF-S mount. It also allows AF with lenses that would normally not AF with the TC attached (note that this is due to misrepresentation of the aperture to the camera by the Kenko...this results in missmetering, so if you do not use manual mode, you MUST be aware of this, and you must underexpose your images by 1/3rd to 2/3rds of a stop to compensate. You must also still be aware of it when using manual, as it will throw off the metering scale by the same amount, which can lead you to adjust your exposure by the wrong amount if you don't keep the Kenko's misrepresentation of aperture in your mind at all times).

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