Will it vignette?

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JH
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Will it vignette?

Post by JH »

Will it Vignette?

I have tried my 400mm 5,6 Canon tele objective on my microscope - it does not vignette at f 5.6 with a microscope objective - I have tested with some Nikons and Mitutoyos. Stopping down the rear lens causes vignetting, easily noticeable at f10.

OFN on Nikons are 25mm so I guess that I can use a 360 mm lens and still get a god picture all the way to the corners on a FF sensor.

I am considering to buy a 360mm f9 enlarger lens (Ronar or Gerogon) and use it as a tube lens, but before I do I would like to know if any one knows if they will Vignette on a FF sensor.

Regards Jörgen

rjlittlefield
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Post by rjlittlefield »

It is very unlikely that the enlarger lenses will vignette. At 360 mm focal length and f/9, their entrance pupil diameter will be 40 mm diameter. The entrance pupil will probably be located near the center of the lens, only a few cm back from the front surface. This combination of a large entrance pupil, close to the objective, means that the tube lens is very unlikely to block any light that gets through the objective.

--Rik

ray_parkhurst
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Post by ray_parkhurst »

Those long focal length process lenses were designed for mag ratios around 1:1, so are probably not going to work well as a tube lens for infinity-corrected objectives.

Edited to add: the extension required even for infinity focus is also fairly prohibitive.

JH
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Post by JH »

Thanks Rik and Ray

So if I understand this right, probably no vignetting but might not be the quality I am after due to the fact that these lenses was optimized for 1:1.

Guess the only way to be sure is to buy one and do some testing. :D


Regards Jörgen

rjlittlefield
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Post by rjlittlefield »

JH wrote:Guess the only way to be sure is to buy one and do some testing. :D
True enough.

Personally, I'm not very worried about aberrations in the tube lens, considering that sticking a Mitutoyo objective in front of a 360 mm tube lens will stop it down to about f/32 (or narrower, for objectives at 20X and above).

--Rik

JH
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Post by JH »

Thanks again for the advice!

I have tested with an APO Ronar 360 mm and a Nikon TU plan 10x 0,3. There is no vissible vignetting, the picture quality seems to be OK all the way to the corners on a Canon 5D mark II (FF sensor).

Regards Jörgen

Image

JH
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Post by JH »

Two test pictures with a 40x lens at
http://www.photomacrography.net/forum/v ... hp?t=31211

No problems with corners or colors.

I also did some testing with other lenses. To my surprise the Canon macro photo lens 35mm works quite well with this tube lens. But it does not have the same resolution as a 10x Na 0.3.

Regards

Jörgen

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