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Andrew Prokos
15-Feb-2005, 15:02
Hi there, I was wondering if anyone has any recommendations for a center filter that will work well with a Nikkor 90mm f4.5? Are they designed to suit the amount of falloff per lens, or will any CF work? I called Nikon and they had no clue...told me that a CF wasn't necessary at all. Thanks

Armin Seeholzer
15-Feb-2005, 15:25
Hi Andrew

I find it almost not needed if you have not very critical applications and you do not shift to the limits it is not needed in my opinion!

Frank Petronio
15-Feb-2005, 15:32
A good justification for the faster, more expensive wide angle lenses is that their wider coverage also means more even illumination even when you don't use a lot of movements.

Andrew Prokos
15-Feb-2005, 15:58
Sorry, just want to clarify. this is not being used on a 4x5, but a 617 panoramic camera. Since the equivalent is a 5x7 I have read that falloff will be a problem.

Michael S. Briggs
15-Feb-2005, 17:13
Probably no LF optical subject causes more confusion that illumination fall off. The issue isn't helped by the failure of the Japanese manufacturers to publish illumination data on their lenses.





Most LF lenses, when stopped down sufficiently to eliminate mechanical vignetting, have illumination that goes as cosine theta to the fourth power, where theta is the angle from the exit pupil to a spot on the film. This group includes plasmats and some wide-coverage designs such as the Super-Symmar-XL series. Most very wide-coverage LF lenses use an optical trick to improve the illumination falloff to cosine to the third power. This group includes the Biogen, Super-Angulons (but not plain Angulons), Grandagons, Nikkor-SW, etc. The graphs published by Rodenstock and Schneider follow this theory fairly well. Based on the similarity of the designs, I expect the Nikkor-SW and Fuji-SW lenses to also follow the cosine to the third dependence.





Once you are in a given lens type, switching to a faster version will NOT improve the evenness of the illumination. For example, I expect the 90 mm f4.5 Nikkor-SW to be no better for even illumination than the 90 mm f8 Nikkor-SW, within their common circles of coverage. The published graphs of Rodenstock and Schneider show this. So wanting more even illumination is not a reason for buying a faster lens of the same type.





You might want to wait and take photos to see if you feel that you need a center filter. For the 6x17 format I will assume a diagonal of 177 mm, as for the Fotoman camera. If no shifts or front tilts are used, the radius of coverage used is 88 mm.
The angle theta for a 90 mm lens will be 44.5 degrees and so the illumination falloff, center to corner, will be about cosine to the third of 44.5 degrees, which is 0.36. This is a reduction of 1.5 stops. Many photographers will find this acceptable, particuarly if they use a negative film.





Andrew, your same question was recently asked here: Center Filter Recomendations for Nikon SW Lenses? at http://www.largeformatphotography.info/lfforum/topic/499775.html (http://www.largeformatphotography.info/lfforum/topic/499775.html). You could try asking Mike which filter he choose and whether he liked the results. Other than this, since Nikon provides no recommendations, just guessing and buying some other manufacturer's center filter of the correct diameter is about all you can do.





Previous discussions of these issues: hoya neutral density center filter at http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=00AJZW (http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=00AJZW), Light fall-off at http://www.largeformatphotography.info/lfforum/topic/498056.html (http://www.largeformatphotography.info/lfforum/topic/498056.html), Wide Angle lenses, Image Circles and Light Falloff at http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=004fzV (http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=004fzV) and Image circle and fall-off at http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=005gK2 (http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=005gK2).

Andrew Prokos
16-Feb-2005, 13:05
Thanks for the info guys...I called Nikon on this and they didn't have a clue. The tech support person told me that this lens wouldn't need any CF because of it's unique design.... "That's the reason people buy this lens!". I found a used Heliopan .45 CF and I'll try it out. and repot back here. Thanks again

harshan thomson
16-Feb-2005, 19:27
I have been using a schneider 90/5.6 SA on the art-panorama 617 . There is a considerable difference in lightfall off without a CF. i got myself a heliopan CF and now i am getting evenly exposed pictures even with some amount of movements!.