testing for image circle

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I have a 260 mm Nikkor process lens which has a strange bulbuous design to it (big hemispherical lens elements that protrude way out the barrel front and rear) and whose image circle exceeds anything I can subject it to on my 8x10. Is there any way to test image circle without building a camera around the thing? I am curious to know if it will cover 8x20 but do not want to construct an 8x20 camera to answer this question if there is an easier way. Thanks.

-- Erik Ryberg (ryberg@seanet.com), February 01, 1999


hi Erik,

i read somewhere something like this: put a piece of photographic paper in one of your big holders (i can't get over just how big an 810 holder is) to do this test; then put on the max amount of rise and or shift that you can, and then expose it to see if there is fall off. i don't know if this will answer your 820 question, but it might give you an idea just how far you can go off axis and still get coverage. meanwhile, do you know: is there a difference between a process lens and an enlarger lens? and what would be the effects of using an enlarger lens as both a taking lens and a enlarging lens on the same image?

-- david clark (doc@ellensburg.com), February 02, 1999.

How about a cardboard box about 24" square and 260mm deep. Cut a hole in the front for the lens. Mount the lens (mounted on a board) on the front with strong tape. Cut a big hole in the back. Attach drafting vellum or mylar, or some other transluscent paper to the back. Draw an 8x20 rectangle on the screen. Throw a focusing cloth over the whole thing and look through it. Sounds like a camera doesn't it --- but it will only take about 20 minutes to do this and then you will have your answer.

-- Wayne Firth (wfirth@aoc.gov), February 02, 1999.

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