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Old December 28th, 2005, 02:33 PM   #1
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Letus35a Vignetting & concerns

I am still having problems resolving my vignetting with the Letus35a. The overscan doesn't help either because of what I can see doesn't necessarily show up the same when I capture.
Today I was outside with a 24mm (Kitstar, not great) and my Tamron 80-200mm. I have also experienced this with my Canon FD 1.4 lens at well. Just at the edges I can see the vignetting and this is before the overscan comes in. I am not sure whether I need to use the Century optics achromat to come in closer or it is something else (maybe even my PV852 panasonic?).
I also noticed that my letus35a starts to make louder noises at difference angles. When looking up at the sky, it is quit loud and noticeably vibrates. I am guessing this has more to do with the weight being put on the front with a larger lens, but I can't be sure.
Also the more I use it, the less quiet my Letus35a has become. Not sure why.
Anybody else experience this problems?
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Old December 28th, 2005, 02:54 PM   #2
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Leo,
The Panasonic PV-DV852 has a 43mm thread size like my Panny, and i have found that the smaller lens cams need to be further away from the GG in order to eliminate vignetting. With the same lenses as the letus, i have found that its not untill the distance is increased from 40mm to 70mm away from GG that all vignetting is eliminated. Only other option other then increasing distance is to replace the PCX with a shorter FL one, but this will give more barrel distortion and chroma seperation
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Old December 28th, 2005, 02:57 PM   #3
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EDIT: Man, I had this great explination but Wayne totally blew it away. Never mind.
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Old December 28th, 2005, 03:00 PM   #4
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I did notice that too, since I built my own 35mm adapter a while back, but switched to the Letus35 because of the portability. I have also tried to bring the camera back from the GG and I see cannot get close enough that way...just tried it again and same problem.

I might have to put in some spacers between the step-up ring and the letus, if they make such a thing.

Also,
1) I took apart the Letus35a today and found the GG had slipped out of its pocket. Part of it was sticking up - not sure if it is from use or the vibrating.
2) The FL is off. It was fine when I first got it, but now it is off on infinity.

I might just be unlucky, but I am not getting the results I was hoping for...
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Old December 28th, 2005, 03:14 PM   #5
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Leo,
If you do attempt to space it out, its best to keep the achromat lens as close to the cams lens as possible. Just something to keep in mind.
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Old December 28th, 2005, 03:19 PM   #6
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Hmm, ok. I have two step up rings right now - 43-46, 46-58. Not much room at all which you are saying is a good thing? I don't really want to try and move the achromat from the LEtus35a anywhere. It is just really frustrating...

Also a note for Letus35(a) users - if you already didn't know, having a set of rails is going to be a good thing. My plastic seems to have warped slightly and not see-saws in the aluminum casing from heavy lenses. It is ok because I ran an elastic around the edge to combat it - but something to definitely keep in mind.
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Old December 28th, 2005, 03:50 PM   #7
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Leo,
Im only saying that the achromat being close to the cam is the best setup, but it may not be needed.
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Old December 30th, 2005, 03:16 PM   #8
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Leo, did you say you put a 70-200mm zoom on your letus35a?

I have an 80-200mm tokina. I just can't bring myself to put it on there. It just seems like too much weight. Am I paranoid or missing something? Anyone else using a big zoom?
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Old December 30th, 2005, 03:23 PM   #9
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As I said, you really should get a set of rails for it. I was holding it the entire time, so I can't really say that I 'let it hang' naturally (no pun intended). I find my letus35a see-saws now, from all the different lenses I have tried and have put a rubber band around the plastic mount inbetween it and the aluminum casing to try and stop the problem. Seems to work for now. I think an extra screwhole is probably necessary at some point.
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Old December 31st, 2005, 09:12 AM   #10
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A new development. I have added a condenser (convex) lens right in front of my DV lens just to see what difference it would make to vignetting and barreling - and wow, I am grateful I did. The brightness has increased dramatically during my brief test and vignetting is nowhere to be seen even with a couple 60 watt bulbs in the basement. I am not sure the effects of adding more glass is going to be, but I am definitely going to be trying this new method out for darker situations. Also I can zoom in alot farther which is a plus.
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Old December 31st, 2005, 11:50 AM   #11
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Leo,
Check for chroma seperation (abberation), im guessing this will introduce some.
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Old December 31st, 2005, 12:25 PM   #12
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I already had separation with it, so that is nothing new - but something else I did notice, my pana 852 is focusing on the lens right in front, so I am seeing unwanted static particles (when I turn the Letus35A on, the particles do not move, therefore they are not from the GG but from one of the lens between the GG and the DV) from the new condencer lens or the macro or the achromat. Just can't win I guess. I am going to try some different things with it and see what happens.

Note : I also found out a few things about the GG - it does indeed streak for me. The up and down movement of the vibrations are causing some unwanted artifacts. Quyen, any suggestions?

Last edited by Leo Mandy; December 31st, 2005 at 06:10 PM.
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