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View Full Version : Large circles of illumination (not IC) choices



genotypewriter
28-Nov-2012, 22:08
A lot of the lens literature mention only the image circle of good definition (for enlarging) and lenses that produce ICs around and above 1000mm are process-type lenses with typical angles of coverage in the 45 degrees mark.

My question is, if we're not enlarging, which lenses/designs are good for much larger image circles at infinity, if we're not enlarging (i.e. can go down to ~6 lpmm)?

I don't have any process lenses but I have experienced some Tessar lenses that are rated at ~60 degrees but when heavily stopped down (but before diffraction upsets direct viewing) they can go close to ~80 degrees.

Would be interesting to hear what everyone has experienced.

Thanks!

Guy

ic-racer
29-Nov-2012, 06:58
Any focal length in particular or what size film are you trying to cover?

E. von Hoegh
29-Nov-2012, 07:41
A lot of the lens literature mention only the image circle of good definition (for enlarging) and lenses that produce ICs around and above 1000mm are process-type lenses with typical angles of coverage in the 45 degrees mark.

My question is, if we're not enlarging, which lenses/designs are good for much larger image circles at infinity, if we're not enlarging (i.e. can go down to ~6 lpmm)?

I don't have any process lenses but I have experienced some Tessar lenses that are rated at ~60 degrees but when heavily stopped down (but before diffraction upsets direct viewing) they can go close to ~80 degrees.

Would be interesting to hear what everyone has experienced.

Thanks!

Guy

Dagors. They're a 65 to 70 degree lens, but illuminate a considerably larger field. Some think this means they have huge coverage, they don't unless you're contact printing and don't mind soft corners.

jp
29-Nov-2012, 20:29
meniscus lenses have very wide coverage, but will be soft of course unless you stop them down to a hard-to-focus brightness.

genotypewriter
30-Nov-2012, 00:09
Any focal length in particular or what size film are you trying to cover?

As I noted in my original post, any lens that produces a 1000mm or larger IC is of interest to me and especially if their coverage (that is good enough for contact prints) is much larger than the rated ~40 degrees.



Dagors. They're a 65 to 70 degree lens, but illuminate a considerably larger field. Some think this means they have huge coverage, they don't unless you're contact printing and don't mind soft corners.

Speaking about Dagors, the Schneider 550 XXL supposedly does 78-degrees (900mm IC). Wonder if it can be pushed much further, especially since Schneider's known to be very conservative with their numbers. Are there any other Dagors that'll cover more than the 550 XXL?



meniscus lenses have very wide coverage, but will be soft of course unless you stop them down to a hard-to-focus brightness.

I wanted to (http://www.largeformatphotography.info/forum/showthread.php?97108-Achromatic-doublets-coverage-and-resolution) go down this path but it's difficult to find good achromats (coated, large diameter, etc.) in focal lengths longer than 1000mm to have usable image circles of around and over 1000mm before running in to diffraction issues (~f/125) even for direct viewing.

E. von Hoegh
30-Nov-2012, 10:22
Speaking about Dagors, the Schneider 550 XXL supposedly does 78-degrees (900mm IC). Wonder if it can be pushed much further, especially since Schneider's known to be very conservative with their numbers. Are there any other Dagors that'll cover more than the 550 XXL ?

Dagors were made in focal lengths up to 30"; good luck finding one, 19" are scarce and expensive, 24" are rare and very expensive.

I don't know, but I have a feeling the 550 XXL cuts off pretty steeply beyond it's stated coverage. It is a WA Dagor design, slightly different from the classic Dagor.

genotypewriter
21-Dec-2012, 20:44
Dagors were made in focal lengths up to 30"; good luck finding one, 19" are scarce and expensive, 24" are rare and very expensive.

I don't know, but I have a feeling the 550 XXL cuts off pretty steeply beyond it's stated coverage. It is a WA Dagor design, slightly different from the classic Dagor.

Also I find it interesting how both types of XXL lenses have the same sort of coverage. I can understand the 550 not being able to do much more because the 900mm is the stopped down diameter. The 1100 version doesn't seem to change at all when stopped down.