Center Filter Requirements

[Kerry L. Thalmann]

Jorge,

Apology accepted (but not really necessary - you'd have to try a lot harder than that to REALLY offend me).

Not sure what you mean by "defocused" in this context. Just keep in mind that t he fall-off will be worst with the lens focused at infinity. The size of the im age circle increases as you focus closer (increase extension). At 1:1 (extensio n = 2x focal length), the image circle will be twice as large as it will be when focused at infinity. So, if the wall was closer than infinity (or, more accura tely, your extension was greater than required for infinity focus), you will not see the worst case fall-off. This is one possible explanation for your test re sults.

When I shoot landscapes (approaching infinity) on color transparency film with t he 75mm Nikkor SW, there is definite fall-off in the corners. It is especially obvious when there is a bright blue, even toned sky. The fall-off from center t o edge is on the order of 1.5 - 2 stops. That is why I find a center filter nec essary with this lens.

FWIW, I have yet to find any lens under 90mm (on 4x5) that did not require a cen ter filter for MY needs. That includes the 75mm f4.5 Nikkor SW, 75mm f6.8 Grand agon-N, 65mm f5.6 Super Angulon and 80mm f4.5 Super Symmar XL.

Again, there is no "correct" answer to this question. The answer will depend on the user and the application. FWIW, I truly do wish I didn't require a center filter on my wide angle lenses. They are a pain - expensive, you lose 1 1/2 sto ps, and it makes it a pain to use other filters. If you find them unnecessary, count your blessings.

Kerry

[Micah Marty]

"I have several Nikon super wide angle lenses (120 and 150SW) and have not noticed fall off problems, although I only shoot B&W."

Michael, I don't know which formats you're shooting, but with color you'd probably notice more light falloff. I think it's quite noticeable--if not objectionable--in Provia shot with the 120SW on 8x10 and also with some RTP I shot with the 150SW on 11x14. These two lenses just barely cover these two formats, so even if I wanted to use a center filter (and even if I could afford the 95mm CF for the 150!) I probably wouldn't choose to use it because it would definitely vignette, no matter how thin the filter.

[Walter Glover]

Michael, Kerry, Jorge, at al.,

I have referred back to the earlier post on this topic and feel that I may also have been in the running for the erudite donkey epithet, along with Kerry.

I would point out, however, that in their literature Rodenstock state " ... largely compensates light fall-off towards the edges by an optical trick (making use of pupillary distortion) ... " with regard to the Grandagon-N range.

In other words, the apparent size of the aperture is optically distorted towards the periphery of the image circle to lessen fall-off. No claim is made that it eradicates fall-off completely and, in fact, it is suggested that a centre-grad be used for optimal rendition.

Clearly Nikkor lenses display this same property, even if it is not stated in their literature, and as noted by Jorge this results in a less eliptical aperture when viewed obliquely.

That said, and in agreement with the earlier posts, it is down to personal perception and interpretation of a motif as to whether or not application of a CF is desirable. The Centre-Grad is another tool in our vast asenal along with polarisers, contrast filters, expanded or contracted development and every other manipulation known to us to assist in making a visual statement. If you want to use it, use it ... if you don't, then don't. But please, let's be concilliatory and avoid the temptation to transform it into a catalyst for paroxysm.

Cheers ... WG

[Jorge Gasteazoro]

Kerry, exactly....I thought if the fall off is worst at infinity...in this case focusing distance of 65mm, then if I focus at infinity and place the wall 6 feet from the camera then there would not be any sharp image and all I get would be light transmission. Am I mistaken thinking this way? This method has worked very good for me to test development since all I get is an uniform negative....this way I can see development problems, uniformity in development and yes...light fall off....

[Ellis Vener]

Uh, guys, if you look atthe specs Nikon uses a different lens formula from the one Rodenstock uses for the Grandagon series and Schneider uses for the Super Angulon lenses. if you do test and find you need a center weighted filter, might I be so bold as to suggest the Heliopan 0.45ND CWF filters?

[Ellis Vener]

Uh, guys, if you look at the specs Nikon uses a different lens formula from the one Rodenstock uses for the Grandagon series and Schneider uses for the Super Angulon lenses. if you do test and find you need a center weighted filter, might I be so bold as to suggest the Heliopan 0.45ND CWF filters?

[Michael Kadillak]

Thanks for the great contributions to all. I use the Nikon 120 SW for 5x7 and the Nikon 150 SW for 8x10 so I have plenty of coverage. As a result, I have not had to deal with the expense of a center filter (these must be very difficult to produce because they are big $$)for B&W and the extra exposure requirements.

I was contemplating a 75mm or 65mm for 4x5, but may just stay with my Nikon 90mm f8.

[Kerry L. Thalmann]

Ellis,

It doesn't matter if the Nikkor design is different than the Schnedier, Rodensto ck, Fuji or Zeiss Biogon type from which they are all derived. It still must ob ey the laws of physics. The fall-off characteristics cannot be better that the theoretical limit for an ideal lens. This is simple geometry at work here. Of course, having said that, I admit my memory is a tad fuzzy (it's been decades si nce I had a physics class that dealt with optics) and I have no text handy. So, from memory (not that I need to encourage it, but everyone please feel free to correct me if I'm wrong)...

The theoretic, best case fall-off for a lens with an entrance pupil that appears elliptical off-axis is a function of cos^4. For a design that uses a so-called tilting entrance pupil, the theoretic limit becomes a function of cos^3. I bel ieve all modern Biogon derived large format wide angles are of tilting entrance pupil design. Other than a center filter (or similar trick), I know of no way t o improve upon this theoretic minimum for light fall-off in lenses designed to b e relatively free of distortion. Of course, a fish-eye lens will not have this c os^3 fall-off, but suffers from severe distortion (no free lunch). Based on rea l life use, and looking at the MTF curves (for Schneider and Rodenstock), it wou ld appear that modern large format wide angles from all four major manufacturers come close to, but do not beat this cos^3 best case limit (for subjects at infi nity).

Now we're arguing physics and not photography. I still say the best way to find out if you need a center filter is to run some tests without one. If you don't find the fall-off obectionable for your materials, subjects and application - s crew the theory and skip the center filter. Some people will absolutely claim t hey NEED a center filter on a 90mm for 4x5, others will say they shoot with a 55 mm (also on 4x5) and say they've never felt the need for one. To each his own. My personal "limit" seems to be anything less than 90mm on 4x5. But, again, th at is based on what and how I shoot and what my eyes see in the results. YMMV!

Kerry

[Kerry L. Thalmann]

Michael,

Given the fact that you don't find a center filter necessary for your 150mm SW o n 8x10, you would probably not find one necessary using the 75mm SW on 4x5 (assu ming the same materials). After all, theta stays the same in these two cases. You've just cut the two sides (focal length and distance to the corner of the fi lm) of the triangle in half. Similar triangles with identical angles.

Kerry

[William Marderness]

I have used a Nikkor 90SW and a 120SW for 4x5. With color print film, the fall off with the 90SW was objectionable. Even the fall off of the 120SW with rise bothered me.