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Old June 30th, 2005, 10:36 AM   #1
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Does a condenser affect the focal length?

Just wondering if adding a condenser at the back of the lens and one in front of the GG is going to affect the FL of the lens I am using. Any ideas?

Also, a bigger diameter condenser is better, right?
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Old June 30th, 2005, 10:39 AM   #2
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Yes, it will.
It will affect the image quality as well.
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Old June 30th, 2005, 10:49 AM   #3
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I thought a condenser was to spread the light out more evenly - are you saying that it will cause an adverse effect on the image - or are you stating that more glass in the mix equal less quality?
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Old June 30th, 2005, 10:53 AM   #4
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Put the condenser lens between the lens and GG will affect image plane. It won't focus to the same plane that it designed to.
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Old June 30th, 2005, 02:42 PM   #5
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From what I've read you want nothing between the lens and the GG...though I did accidently put a DCX between them once (due to making my adaptor backwards from what James's guide actually said)...it didn't seem to affect the image much at all...but it definately didn't have any positive effect to speak of.
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Old June 30th, 2005, 06:18 PM   #6
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When I put an 80mm FL PCX condenser between the GG and lens it caused blurring of the image edges, even with another 80mm FL PCX on the other side of the GG. I think I've solved my hotspot, I have GG PCX PCX cam |)( and moved the camera back another 20mm and the vignette seems to have completely gone, and I get a full 36 x 24mm image area. That is with 80mm FL, only problem being there's still a bit of barrel distortion and chromatic aberration, I'm waiting on two 120mm FL PCX's and hoping they will fix it.
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Old June 30th, 2005, 07:55 PM   #7
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For the record: I have a (thin) condenser between the lens and the GG. Another one between the GG and the camcorder. The image quality only increases due to better spread of light. I didn't notice any effect on the focal length, maybe a fraction. SLR cameras often have a small condenser between the mirror and the GG/Fresnel.
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Old June 30th, 2005, 09:10 PM   #8
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So long as the condensor is pressed up against the GG there shouldn't be anything hardly at all.

The softening of the edges is due to the nature of the optics used. An achromat would alleviate this problem.
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Old July 1st, 2005, 12:11 PM   #9
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I'm confused, are you saying an achromat between the SLR and the GG?

I have had some interesting results today.
I have a bunch of loose lenses lying around from 8mm camera, slide proj. etc, so I took a set of double lens that were cased together (i don't know why they were) and used one of them inbetween the SLR and the GG (I am not sure if it is a condenser or not - but looking through it at my hand makes my hand smaller, not bigger, so I figured it is not a macro or an achromat). The interesting thing is when viewed on my GG, the image is bigger! Weird?! Looking through it at my hand, the image of my hand is smaller, but the image on the GG when the lens is between the GG and the SLR, the image on the GG is alot bigger- so I am still not sure what I am dealing with but - the hotspot seems to be reduced somewhat, which is a good thing. It is still there, although I am not as much vignetting - BUT the image quality is reduced due to the addition of more glass (I am guessing). Anyone know, from this description, if I am dealing with a condenser (micro's images when looking through it, like my hand - but gives a larger image when projecting on the GG)?

Last edited by Leo Mandy; July 1st, 2005 at 12:38 PM.
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