Center neutral density filter

[Sean Galbraith]

New to large format...

I've never used a central ND filter before in photography (medium format and DSLR), but in the few large format shots I've taken with a 90mm lens before, I can see how one would be needed. Is there a rule or thumb or something that says how wide a lens is likely to be before you need to use one?

[Ron Marshall]

New to large format...

I've never used a central ND filter before in photography (medium format and DSLR), but in the few large format shots I've taken with a 90mm lens before, I can see how one would be needed. Is there a rule or thumb or something that says how wide a lens is likely to be before you need to use one?

For myself, and many others who have posted, the focal length at which a CF is required depends on what type of film is being used. Positive films have more inherent contrast than neg films and so a CF might be required at a longer focal length with a pos than with a neg film.

I shoot only neg and find I only need a CF on my 55mm. I somtimes use one on my 75, or even the 90 when using large movements.

[anchored]

Just to expand a little on Ron's answer:

In addition to length of lens and film type used, subject matter also comes into play. For many if not most landscape, portraiture, and general genre photography the vignetting you get from not using a center filter is not objectionable, and in many cases can be beneficial to the image. But for instance, in architectural photography the vignetting is usually unwanted.

I shoot mainly color transparency landscapes (most often Velvia and Provia) and always use a center filter using a 75mm lens, and rarely on 90 or above.

[Mark Stahlke]

Another factor is the optical design of the lens. I never felt the need for a center filter with my Caltar II-N 75/4.5 (same as a Grandagon N), even shooting chromes. With the 80mm SSXL I find the light fall off objectionable so I always use a center filter with that lens. Just in case it matters, I mostly shoot landscapes.

Cheers,
Mark

[Sean Galbraith]

Thanks for the info. Here is an example



This was shot on Kodak 160VC with a Sinar F1 and a Grandagon N 90mm/4.5.

Perhaps it was operator error, or the high contrast lighting conditions? I see a similar light falloff/colour shift in the corners of a few of the shots.

[Drew Wiley]

True wide angle lenses can have a considerable amount of light falloff. You can download lens-specific charts from the major manufacturers. Roughly, the wider the
angle of view, the worse the falloff. But again, it depends on the particular lens design.
With most 90's you need about a stop and a half correction. With Schneider, for
example, there are several choices of CF depending on the exact lens. Sometimes
falloff can be used artistically, to created a center glow in the image. This is a trick
often employed in black-and-white photography. With commercial color work, however,
I always use a CF. A tranny just does not have enough latitude to sacrifice a stop or two.