# Thread: Lenses for circular pictures on 8x10

1. ## Re: Lenses for circular pictures on 8x10

8" is about 200mm so look for lenses with image circle around 200mm. There is a chart here with most info you will need: http://www.largeformatphotography.info/lenseslist.html

2. ## Re: Lenses for circular pictures on 8x10

Originally Posted by ic-racer
8" is about 200mm so look for lenses with image circle around 200mm. There is a chart here with most info you will need: http://www.largeformatphotography.info/lenseslist.html
That chart is an usefoul resource, but not for what OP would like. Those data are for objective focused at infinity. On the other hand with a bit of trigonometry, one can calculate image circle at any distance.
Marko

3. ## Re: Lenses for circular pictures on 8x10

Originally Posted by Marko Trebusak
That chart is an usefoul resource, but not for what OP would like. Those data are for objective focused at infinity. On the other hand with a bit of trigonometry, one can calculate image circle at any distance.
Marko
Yes, or if he has his camera and a lens handy he can use simple math and divide his (bellows draw) by (focal length) and multiply that by (image circle at infinity) to find his effective image circle.

4. ## Re: Lenses for circular pictures on 8x10

It's a linear relationship.

The IC diameter at 1:1 (life-size image) is twice that at infinity focus.

It also varies with aperture, getting smaller as the aperture gets larger (smaller f/number).
The IC you find on lens datasheets is usually three stops down from wide open, i.e. f/16 for an f/5.6 lens.

- Leigh

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