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Old February 13th, 2007, 11:20 PM   #1
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Really, What am I doing wrong?

Here are a couple of grabs from an adapter I'm working on for my Sanyo HD1.
http://www.imagehosting.com/out.php/...3_SANY0138.JPG

http://www.imagehosting.com/out.php/...1_SANY0139.JPG

Yes the grain is crud, whatever, my focus screen cost a dollar. I'm not using expensive parts until I put away the hot glue gun. The issue that I am having is that you can see in the farther shot there is a relatively wide fov with little vignetting. However, when I attach the adapter and place it 2cm from the screen there is a huge amount of vignetting in a much smaller FOV. It seems to be opposite of what should be happening. In a related trial I discovered that if I moved the camera away from the GG and zoomed into it I could get a pretty decent image but this process added too much overall length.

Why is there so much vignetting when up close with a wide angle? Any help would be appreciated. Thanks, Chuck.

Sorry about the mess. I don't know how it happened.
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Old February 13th, 2007, 11:34 PM   #2
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Originally Posted by Charles Hurley
Sorry about the mess. I don't know how it happened.
If you hit submit on a post or thread and the system times out...DO NOT keep hitting submit. This will result in multiple postings.

When this happens, simply press the back button on your browser and then refresh the page using your browser's refresh button. You will see that your post has actually been added.

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Old February 14th, 2007, 01:05 AM   #3
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Quote:
Originally Posted by Charles Hurley
Here are a couple of grabs from an adapter I'm working on for my Sanyo HD1.
http://www.imagehosting.com/out.php/...3_SANY0138.JPG

http://www.imagehosting.com/out.php/...1_SANY0139.JPG

Yes the grain is crud, whatever, my focus screen cost a dollar. I'm not using expensive parts until I put away the hot glue gun. The issue that I am having is that you can see in the farther shot there is a relatively wide fov with little vignetting. However, when I attach the adapter and place it 2cm from the screen there is a huge amount of vignetting in a much smaller FOV. It seems to be opposite of what should be happening. In a related trial I discovered that if I moved the camera away from the GG and zoomed into it I could get a pretty decent image but this process added too much overall length.

Why is there so much vignetting when up close with a wide angle? Any help would be appreciated. Thanks, Chuck.

Sorry about the mess. I don't know how it happened.
In summary, you must either move your camera back or use a plano-convex lens. You're asking too much of the incident angle of the GG when you have the camcorder close. The image can only come off of the GG at greater than or equal to a certain angle, and when you have the camcorder close, you lose the edge of the image (this vignetting) because the light simply can't bounce off the GG at that small of an angle. However a PCXL compensates for you...at some expense. Here, maybe this drawing of mine will help...

Also keep in mind that wide angle lenses will always exhibit some vignetting in adapter usage.
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Old February 14th, 2007, 02:31 AM   #4
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Quote:
Originally Posted by Ben Winter
In summary, you must either move your camera back or use a plano-convex lens. You're asking too much of the incident angle of the GG when you have the camcorder close. The image can only come off of the GG at greater than or equal to a certain angle, and when you have the camcorder close, you lose the edge of the image (this vignetting) because the light simply can't bounce off the GG at that small of an angle. However a PCXL compensates for you...at some expense. Here, maybe this drawing of mine will help...

Also keep in mind that wide angle lenses will always exhibit some vignetting in adapter usage.
Ben,

Nice Cartoon. A picture is worth a thousand words.
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Old February 14th, 2007, 02:59 AM   #5
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Aha so it's the angle, that makes perfect sense, thanks.
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Old February 14th, 2007, 04:38 AM   #6
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Charles,
2 questions,
Is this a static adapter or Vibrating/rotating?
Are you using a close up or macro lens in front of your camera?
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Old February 14th, 2007, 10:35 AM   #7
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Static for now. At wide angles the HD1 will focus to within 10mm of the imager which pretty much means on the front glass. So to answer the second question, no. However it may become necessary once I relocate the camera and have to zoom into the gg. Thanks.
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Old February 14th, 2007, 01:58 PM   #8
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It finally makes sense. I always thought that people were zooming into a smaller area on the gg when in fact it is the longer focal lengths that reduce vignetting. I've been doing it all wrong. With an achromat I can get down to about 12mm without vignetting. Without it about 24mm but at that focal length close focus is impossible. My GG is 50x50mm and I'm probably using about 45mm of it without vignetting. The next step is to find a larger screen and try to get the full 70mm(Pentax 67 lenses), then I can worry about oscillation. Here's a grab. Thanks again Ben, I'm making progress at last.
www.imagehosting.com/out.php/i219061_gotsit.jpg
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Old February 14th, 2007, 02:39 PM   #9
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Two is better than one

I'm sure it's been covered in other threads in this forum, but can't you basically eliminate barrel distortion and chroma by sticking your scattering screen directly between two PCX lenses?

If the two PCX lenses are of equal strength, the barrel distortion of the front should be balanced by the barrel distortion of the back.

And if you keep the aperture of the front lens (actually the exit pupil) the same distance from the scattering plate as the aperture of the back lens (entrance pupil), the chromatic aberration should mostly take care of itself. You will add other aberrations, though (I believe astigmatism is the main culprit in wide-field blurring).

The strength of the two PCX lenses should be equal to the plate-to-pupil distance. You can actually get away with a weaker lens if you don't use PCX, but instead use biconvex lenses the proper distance from the scattering plate... but I haven't tried that yet, so good luck if you do (it's actually a trade-off - if you scatter only a little, the PCXs should be better). It's worth noting, though, that ideal shape for minimal aberrations would be a lot closer to a biconvex than a PCX - a PCX sandwiching the focal plane is actually near the *worst* shape possible (check out any optics web page about lens bending and spherical aberration). Basically, the goal is to bend the ray bundles so they're pointing directly from the back aperture of the taking lens towards the front aperture of the back lens, but by doing it with the least extreme angles on glass as possible.

I must post the caveat that I've been working with large format lenses and a 70mm image plane, so the physical distances involved are easier to work with (the taking lens is frequently four inches or more away from my scattering plate (which is fiber optic). At medium f/#s, my setup is lossless (but only because I fully bend the ray bundles; the PCX lenses are rather strong).

I'm also abandoning my rig in favor of a RED in a few months.
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Old February 14th, 2007, 10:05 PM   #10
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Large format, right on. I'm curently working with the pentax 67 system which when everything is working properly should give me roughly 40X70mm. I'm not currently experiencing problems with barrel distortion or CA but right now the resolution is so low it's the last of my worries. I have used a couple of biconvex lenses with some success. In fact I thought I had a dual biconvex system worked out months ago but when I tried to recreate it, it failed. Turns out you need to give the gg some room to breath. I think the dual biconvex system is more effective than the achromat in shortening overall length and avoiding vignetting.
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Old February 15th, 2007, 12:27 AM   #11
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Some Interesting Finds

The dual biconvex setup is definitely working better for me. Even though I'm using medium format lenses the overall length of the adapter is 5 1/4". I could probably shorten it further by using stronger lenses and fine tuning the placement, but for now I'm happy. On to the interesting finds part. Does anyone know why this happens?
www.imagehosting.com/out.php/i220660_Wierdo.jpg
At full wide, beyond the edges of the GG the aerial image is black.
Here it is zoomed in a little further.
http://www.imagehosting.com/out.php/i220658_Aerial.jpg
This grab answers the questions that pop up every so often about aerial image. You can see how background elements are still relatively sharp if you focus on an aerial image as opposed to a gg. It's interesting to think that you can use an adapter as a teleconverter or wide angle adapter. This lens has a 45 degree fov but it's 105mm.
http://www.imagehosting.com/out.php/i220659_grainy.jpg
Well it's still nice and grainy but getting better all the time. Given the earlier grabs I can now easily push out to a full 70mm with no vignetting once I get a larger screen. The vignetting from the first 2 pics of this series is actually from some step rings. I had to go all the way down to 58mm(limited stock on hand) at one point, but it keeps everything aligned. My plans for the immediate future are bigger screen, shortening, then oscillation. Thanks for the help dvinfoers.
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Old February 15th, 2007, 12:33 AM   #12
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Oh yeah. This last bit was all done on the HVX. The HD1 was still vignetting under about 8-10mm. On the HVX I could take it all the way out to 4.2mm and in to about 30mm and still maintain focus with no vignetting but there is still the weird aerial image thing under about 6mm.
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Old February 15th, 2007, 12:47 PM   #13
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Aerial images = "purely optical solution"

Hey Charles,

There's a discussion that directly relates to aerial images at this thread:

http://www.dvinfo.net/conf/showthread.php?t=83854

(Most of the technical stuff is on later pages.)

Basically, we're discussing the situation where there's no scattering plate, which is analogous to what you're doing. JVC has introduced an adapter which does exactly that, converting 16mm lenses to the 1/3" chip HD200, and Angenieux apparently has one that goes from 35mm to 2/3" without scattering. The limitations are discussed in the above thread, but basically the back aperture becomes the limiting aperture, and you need a super-fast rear lens to get the use of the full aperture of the front lens.

When you say 'full wide', I assume you're talking about the taking lens? If you're using the taking (front) lens to zoom, the likely reason the image vignettes completely is that the ray angles get steeper the wider the lens goes - so the aerial image ray bundles actually miss the rear lens completely (despite the bending introduced by the intermediate field lenses, biconvex or otherwise).

(If you're talking about zooming the rear lens, and consequently repositioning the camera, the same holds - if you're not repositioning the camera, it's probably something odd like the entrance pupil shifting due to the floating elements in the zoom lens... but it's difficult to hazard a guess without more info.)

As for the 'super sharp' aerial image without scattering, that's related to the above discussion: basically, by magnifying the effective image plane without scattering ray bundles (like the JVC/Angenieux adapters, and your adapter without the scatter plate), you actually optically reduce the effective f-number of your rear lens by the magnification factor. (I have a couple of posts on the above thread that explain it in more detail.)

Because the ray bundles remain unscattered, the effective aperture is strictly the rear aperture - basically, the front lens passes large ray bundles on, which are clipped by the aperture in your HVX. The effect on the image is you get the DOF of either A) the back lens/f-number/chip size, or B) the front lens/f-number of back lens divided by magnification factor/large image plane... my gut feeling says they're optically equivalent.

So it turns out that if you could get a sufficiently fast lens on the HVX, you could focus on the aerial image of a 35mm (or larger) lens and - again, if the relay lens were fast enough - capture the entire ray bundle without scattering. Unfortunately, it turns out that relay lens would have to be unrealistically fast to work. But it's a nice idea, no?
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Old February 16th, 2007, 12:21 AM   #14
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I hear what you're saying about alignment. Anyone else ever notice how the HVX lens isn't centered on the CCDs, or is it just mine? A purely optical adapter is interesting as an exercise but really what is the point? At best you'll probably get .5x wide or 2x tele. Screw the Century adapter on the front and call it a day.

http://www.imagehosting.com/out.php/...6_Picture2.png

http://www.imagehosting.com/out.php/...5_Picture1.png

These are my latest grabs. They are both from the HVX@1080p. One is native and the other is from the adapter. The native shot is zoomed out to 7.5mm to match the adapter shot(105mm Pentax67). You can see how even with medium format a wide 45mm lens would give the equivalent of maybe 3mm on a 1/3rd ccd. You'd have to go to about 800mm to match the tele of the stock lens, 400 with 35mm lenses.

I'm at about 60mm wide on the gg right now. The barrel isn't large enough to allow a 70mm rectangle so the whole project has to go back to formula. I think that I've accomplished what I set out to do. My GG for this latest round is anti-glare picture frame plexiglass. I stole it from one of my GF's pictures since she's out of town, it'll be interesting to see if she notices. 1 layer didn't offer enough diffusion so I glued 2 pieces together. It's hard to believe but my GG is actually going down in price. I could cut about 20 screens from a 6 dollar piece so about 35 cents per.

I could use the 35 cent gg with a vibrator or a high quality gg without and still get really good results. Now that I've established POC I think I can have it built for real and put away the PVC and hot glue. If you can afford the light loss medium format is going to come out on top every time.

I included both shots so you can judge the diffference between the adapter footage and native. Other than focal length nothing was changed between the two shots.
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Old February 20th, 2007, 02:38 PM   #15
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MF looks nice

Charles,


Great job on the adapter. That frame pull looks superb. I did notice a color shift - that might be from the plastic screen, but a simple white balance would take care of that (it looks slightly yellowish compared to the non-adapter footage).

You mentioned POC - are you planning on getting a diffractive scatterer made, or are you buying one stock? (I presume POC refers to that company that produces beam-shaping diffusers.)

Again, nicely done.


Cheers,


Ryan
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