Light Fall-off Vs Center Filter for SA75/5.6 & 110XL

At a point in the image circle corresponding to the corner of the

4X5 frame, the Super Angulon 75mm f-5.6 shows a 1.5 stop light fall-

off. At about the same point, the Super Symmar 100XL shows a light

fall off of about 1 stops therefore the difference is 1/2 stop more

light fall off for the 75mm SA. Using the #3b center filter intended

for the Super Symmar 110 XL, on the SA 75mm f/5.6 would then result

in a 1/2 stop darker at the corner of the image than if the #3

filter which is the one recommended for the 75mm, which would

provide completely even illumination. As I have both these lenses I

want to avoid buying two center filters and therefore am considering

buying the #3B filter for use on both lenses, realizing the 1/2 stop

less illumination in the 75mm SA which will result. (This is at the

corners with no movements. -Movements will of course increase the

loss in illumination.

 

Bob Salomon will be quick to point out that this is not recommended

but what I need to know is if my calculations are right in which

case I will have to live with the 1/2 stop loss of illumination at

the corner when using the 75mm SA f/5.6 with the #3B center filter,

and a saving of about $300. Has any one tried this? Your opinions?

Thanks.

Well, I think that your assumptions and calculations are correct. If you would use the #3 CF on both lenses then you might get a bright halo with the 110XL, as the dark spot would be too small. And as you are aware of, using the #3b CF on the 75 SA will make the corners too dark.

 

There is another factor that might be relevant depending on your intended use: Schneider CFs with the same thread size are not necessarily mechanically identical, so there might be a vignetting problem. For example, the #3c CF for my 47XL is thinner than the #3 CF for my 65 SA. In your case, as the 110XL has wider coverage than the 75SA, using the #3b filter on the 75SA is probably OK.

 

I'd say get (or borrow!) the CF that you feel that you need the most, and try it on both lenses.

<p>Julio, your figures about the falloff in illumination for these lenses without center filter are correct. The 75 mm Super-Angulon is demonstrating the approximately cosine to the third power falloff of the better wide-angle lenses, and the 110 mm Super-Symmar-XL the cosine to the fourth falloff of most lenses. This difference in illumination behavior explains why the falloff at the corner of a 4x5 film is so similar despite the factor of 1.5 difference in the focal lengths of the lenses.</p>

 

<p>I think your reasoning goes off-track with the idea that the #3 filter intended for the 75 mm SA results in completely even illumination. The brochure <a href="http://www.schneiderkreuznach.com/pdf/foto/CENTERFILTER.pdf">CENTERFILE.pdf</a> available at <a href="http://www.schneiderkreuznach.com/pdf_downloads.htm">Schneider's German website</a>, has the statement "To avoid too long exposure times and with consideration of the exposure latitude of the film emulsions, the vignetting of the lenses has not been fully compensated." So Schneider (and probably the other manufacturers of center filters) has reasoned that a small amount of illumination falloff is acceptable and preferable to the longer exposure times that would be needed to obtain perfectly even illumination.</p>

 

<p>The next step of your reasoning is that the #3b filter changes the center-to-4x5-corner illumination difference of the 110 mm SS-XL by 1 stop, therefore it will change the center-to-4x5-corner illumination difference of the the 75 mm SA by 1 stop. First, from the previous paragraph, the improvement with the #3b and the 110 mm SS-XL is less than 1 stop. Second, I think the reasoning that "since on lens A the improvement from a center filter is X stops, therefore on lens B the improvement is also X stops" probably isn't valid. The effect of the center filter should depend on how far it is positioned from the enterance pupil of the lens. Imagine using the center filter on the 75 mm SA, then taking another photo with the center filter 1 cm further forward of the front of the lens -- obviously the effect on the illumination would be different. That said, using the #3b center filter on the 75 mm SA might work very well, it just isn't simple to calculate what the illumination falloff of that combination. The positioning of the center filter probably isn't too critical, because several manufacturers make generic center filters that can't be designed for a specific lens.</p>

 

<p>Are you sure that you need a center filter for the 110 mm SS-XL? If you haven't been used the lens, I suggest using it for a while to see if you notice unacceptable illumination falloff. From postings here, it seems that very few photographers find a center filter use a center filter for this lens and 4x5 film. In my use of this lens with 4x5 negative films, I have only one photo that I wished I had used a center filter, one in which I used an extreme amount of front rise.</p>

 

<p>There are two ways to go with the idea of trying to use one Schneider center filter for both lenses. The first approach would be to get the #3b filter because it has the weaker effect. The second approach would be to get the #3 filter because it is the intended filter for the 75 mm SA and the 75 mm SA has less even illumination and thus greater "need" for a center filter. Whichever your decide to buy (first), you could experiment with on the other lens to see if you like the result.</p>

Let me add to Michael's caution that you should use the lens or lenses for awhile

before deciding that you need a center filter. I used to use one with my 65 mm SA

but have never, repeat never used one with eitehr my 110 SS XL or my 75 mm f5.6

SA. I have been using both lenses for 2-3 years and have no 'real life; noticable fall

off. I use the 110 far more than the 75 but still have shot enough with the 75 to have

reasonable experience. Of course, your shotting style and subject matter will dictate

your needs. Generally I use both these lenses for landscape work. I also use the 75

mm for interior architectural work and sometimes interior shots of restaurant table

settings, in the indoor instances I am working with lots and lots of cvontrolled light.

Many thanks for the three replies from Ake, Michael and Ted. I am glad I asked for every time I do, the awsome depth of knowdlege in this forum comes to my rescue. Thanks again.