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Old February 23rd, 2004, 03:26 PM   #301
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Roman: I am using After Effects' native transform options to rotate the image 180 degrees. I'm sure you can do this in Premiere or Vegas.

I'm not sure about what kind of condenser. I was assuming they were all pretty much the same. I do not know for sure, though.
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Old February 23rd, 2004, 03:37 PM   #302
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I just did a test, I put the fresnel on the camera side of the gg and it did smooth out the hotspot by making it about 20% larger, so it moved the light outward.

This is good for theory just proving that we need a good acromat. A fresnel has rings which are visible, not good but did well for experimenting.

I will have some acromats in a few days, to solidify the theory.
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Old February 23rd, 2004, 03:47 PM   #303
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Thanks, Frank! John, just for the fun of it, could you try to put the Fresnel on the SLR lens side of the GG? I wonder what the results would be...
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Old February 23rd, 2004, 04:19 PM   #304
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<<<-- Originally posted by Roman Shafro : So, my order would be:
SLR lens -> spacer -> GG -> Condenser -> spacer -> Macro (if needed) -> DV -->>>

But the probleme remains ... what's the best deal for the condenser part...

a field lens is a good choice but it gives a lot of distortion....2 identical field lenses is much better...but it's bigger...this is the reason why the first field lens is replaced by a fresnel just after the GG in all the SLR viewing system...

we have a lot of options
1- single field lens
2- 2 field lenses
3- 1 Fresnel (but a lot of ghosting effetcs)
4- 1 fresnel and a field lens
4- an achromatic

think that now, experimentation will be the key...
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Old February 23rd, 2004, 04:32 PM   #305
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heres some pics of my fresnel placement test, as you can see the fresnel does its job best on the camera side of the gg, however the rings are visible, thus I will replace the fresnel with an acromat later this week.

http://aequantum.com/fresnel.jpg
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Old February 23rd, 2004, 05:32 PM   #306
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cool john, that's great! can't wait to see what it looks like when you get your achromats.
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Old February 23rd, 2004, 06:25 PM   #307
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Thanks, John! I guess the question of which side the condenser should be on is over... Olivier, I'd say a thin achromat field lens is your best choice, and the focal distance shouldn't matter...
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Old February 23rd, 2004, 08:06 PM   #308
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ground glass and corrective lens(es)

The reason why I thought you needed two corrective lens (one on each side of the ground glass) is because I was under the understanding that in a traditional SLR viewfinder system the order was as follows:

35mm lens>mirror>FRESNEL>GROUND GLASS (sometimes the fresnel and ground glass was one piece with the fresnel on the 35mm lens side and the ground glass on the other)>followed by a condenser>and then the prism and eyepiece optics of coarse.

I'm going to call a local guy that repairs used cameras tomorrow so find out and finally put this issue to rest. In the mean time if someone wants to open their old SLR I would be very interested in what they find.

-B
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Old February 23rd, 2004, 08:19 PM   #309
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Brett

I have done this, and the one I have is a glass whith fresnel on each side then the pantaprisme and eyepiece optics .

The mark on the fresnel, normaly a circle ,is a small circle on one side and a biger one on the oher side, so it look like when you are perfectly in focus the image that correspond to the film plane are in between the two fresnel .

Alain
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Old February 23rd, 2004, 10:49 PM   #310
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Alain let me make sure I understand what your saying. The SLR you opened up had a piece of glass that had one fresnel pattern on one side and another on the other side and seperate from that was the ground glass?
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Old February 24th, 2004, 12:17 AM   #311
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Brett

No ,It's only one piece whit a fresnel on each side,apparently no ground glass.But it's realy hard to see.I have take a look at it whit my microscope and it look that they make a( ground fresnel )or maybe it's just the quality of the fresnel that look grainy.This is made from plastic also. Probably a cheap way to make this thing.

Alain
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Old February 24th, 2004, 12:38 AM   #312
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brilliant Giroud!

totally forgot about holographic diffusers in laptop LCD screens! that's VERY similiar or even the real a real holographic diffuser, this could very well be another key to improving high quality low-light transmition. possibly (yet another and possibly better?) alternative to ground glass (!). just a hunch, but great idea Giroud!
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Old February 24th, 2004, 01:03 AM   #313
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My old dusty Canon AE-1 which had previously been just sitting on a shelf collecting dust (since the purchase of my digital camera) contained ( in this order from behind the lens):
  • nice mirror: 35mm film size
  • real condenser - not fresnel right up against: 35mm size
  • ground glass/focusing screen (reticle on glass): 35mm size
  • very nice pentaprism 35mm entry - smaller exit
  • viewfinder had small real lens to magnify - size of small exit
And of course, the real question - was the condenser on the lens or viewfinder side of the ground glass... answer:

"I DON'T KNOW!!" (it popped out as I removed the last screw and I didn't see which way it was. C'est la vie).

I didn't have any fresnels in there.
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Old February 24th, 2004, 01:35 AM   #314
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Thats alright Johnathon. I just wanted to know if it had both. Besides the condenser goes between the gg and the prism. Take a real close look at the profile of that condenser's glass. Is it two lenses cemented right on top of each other or a simple single lens. It will be hard to tell so look closely. If its two they are using a two element achromat condenser if not its a simple single element condenser.
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Old February 24th, 2004, 03:10 AM   #315
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Hmmmm... upon closer inspection - my ground glass/focusing screen must be a fresnel... because it magnifies as I move it closer and farther away from a subject... but its just very very very fine. I can't see the rings at all, even under magnification. It appears (can hardly tell - even under magnification) that the back of the fresnel has a sort of 'ground glass' finish. (plastic)

And as I look at the shapes of these things, I'm almost positive the condenser was on the lens side. with the 'ground glass' pressed against it, leaving the fresnel side of the focus screen pressed right up against the entrace plate of the prism. (It all seems to 'fit' together this way)... When I hold it all together and put my 35mm slr lens in front of it at the right distance... even with no light baffling, it completely and evenly fills the viewfinder with no obvious vignetting.

The condenser to the best of my magnified attempts appears to be a single element. Must not be an achromat.

(heh, Brett, I see you're awake on the CML threads too...)
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