Newbie question re Centre filters

I am planning to make the great leap forward into large format and am trying to find out as much info in advance as possible before I buy anything.

How important are centre filters for large format photography? I notice for example that Schneider publish tables of which centre filters they recommend for their lenses and presumably this is to prevent vignetting problems - I'm familiar with this principle because I also use a Hasselblad Xpan which uses CFs to prevent vignetting in panoramic mode.

Anyhow my question is do I have to really worry about this for landscape photography? I am planning to buy an LF outfit exclusively for landscapes (using mostly transparency film) and I imagine since landscape photography generally requires stopping down a lot for depth of field, vignetting will be less of a problem at small apertures (as with the Xpan when centre filters aren't really needed below f11). Do I need to worry about expensive centre filters since I will probably never use the lenses at wider apertures anyhow?

When shooting transparency film with 4x5, my experience is that I need a center filter when shooting any lens wider than 90mm, regardless of aperture setting. I rarely use a center filter when shooting color neg or B&W film.

The use of center filters has nothing to do with vignetting but rather evenness of exposure. The physics of light and lenses produces fall-off toward the edges of the frame, more so with wide angle lenses, simply because the light rays must travel further.

A center filter is more dense toward the center, less toward the edges to counteract the light fall-off. I've never used one. My shortest lens is a 90 and I use black and white exclusively. If you're scanning color transparencies, it should be relatively easy to fix in Photoshop.

There's a great article by Kerry Thalmann in View Camera this month. Usually light fall-off becomes noticable on slide films when you get below the 90mm focal length, except with the Super Symmar XL series which has noticable light fall-off below the 110mm focal length. <bk>
You will notice that some of great landscape photographers don't use center filters and the vignetting is noticable but not objectionable. David Muench and Jack Dykinga shoot mostly without CND's on 75mm lenses. One reason not to use a CND is that you loose over a stop of film speed due to the ND effect.
However, now that Velvia is available in ISO 100 speed, I routinely use a CND with my SSXL80, and since I was previously shooting the old Velvia at 40, it's a wash.
Hope this helps.

It also depends on your shooting style. While a center hotspot in a photograph may be tolerable, use of camera movements that shift the hotspot towards the edge of the shot can make things look mighty strange (think graduated sky running from one side to other). I've got a 180 that I use on 5x7 which I wish I had a center filter for.

How important are they? As much important as you want them to be! If you mind the visible effect you can correct it, if not, you don't care. It's more a question of your taste rather that a real necessity.

I agree with gps. I'd get the lens(es) first and if you find objectionable vignetting, you can always get the CF later if you feel you need it. I use a CF fairly often on my 72mm SA-XL, but others who use the same lens don't find it necessary. Also see www.vanwalree.com/optics/vignetting.html for a decent article on various kinds of vignetting.

I use a 90 mm lens regularly and a 75 mm less often. I find I rarely need a center filter in landscapes with either. But for architectural photography, particularly if I use rises, I find that the difference in intensity (and color balance for color film) makes adjustment necessary. I tried doing this digitally, and it worked to some degree, but it is much more satisfactory with the center filter I finally decided to purchase.

For longer docal length lenses, I don't find any need for a center filter.

Since this supposed to be a beginner's question, I'd like suggest to Matthew J. that the question of light fall-off in extreme wide-angle lenses should not prevent him to get into large format photography.

While small format cameras users dreamed of large numerical apertures in faster and faster lenses in the sixties, and then dreamed about wider and wider amplitude zooms ranges, large format lens manufacturers have tremendously improved their lenses and wide-angle photography is a field where the large format camera, IMHO, definitely rules.
So, Matthew, get a large format camera and a wide angle view camera lens, and follow the good advice by "gps" and Tom W.., eventually the question of purchasing or not an additional centre filter (or is is a center filtre ? ;-);-) will be easily solved afterwards.
Centre filters are not built-in. They are an (expensive) optional add-on. I do not know if some readers of this forum have any experience about correcting light fall off by digital processing but this is, at least in theory, easy to do, finding where the optical axis is located in the final image and using the manufacturers' light fall-off data.

Some early extreme wide angle view camera lenses used a correcting mechanical "counter-vignetting" system based of a kind of fan rotating in front of the lens during part of exposure !!
The light fall-off effect in any lenses is not only related to the additional distance that light has to travel to reach the corners of the image, this accounts only for "half" of the effect. The second effect is due to the fact that seen from the corners the exit pupil can look smaller, and than the slanted area in the corners of the film receives less light per square area (like the Earth's poles). This globally makes 4 cosines multiplied together, and the pinhole camera suffers from light fall-off exactly like any ordinary glass lens.
As explained in the excellent paper by Kerry T. the engineers have succeded in counter-balancing the shrinking exit pupil effect by introducing an "expanding" effect of pupillar distorsion ; so, modern wide-angle lenses do their best to avoid the use of a centre filter... but there are still 3 cosines instead of 4 ;-)

Quote:

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Emmanuel Bigler: engineers have succeded in counter-balancing the shrinking exit pupil effect by introducing an "expanding" effect of pupillar distorsion

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Is that the design that some Biogons have to help lessen falloff? Here's a closeup of the rear of a Biogon close to where it would be at Infinity. (It would actually be closer to the glass.)
elearning.winona.edu/jjs/nl/close1.jpg

Is that the design that some Biogons have to help lessen falloff?

Yes, the Biogon® design uses this phenomenon as well as most modern wide-angle lenses covering 90° and above. The invention is to be credited to a Russian engineer, M.M. Roosinov just after the end of World War II.
The Zeiss Biogon® derives from the Wild Aviogon®... for the simple reason that both were designed by the same engineer, Dr. Ludwig Bertele. Both designs were patented in the early fifties.
Read more info by Marc James Small here : www.jborden.org/photo/Aviogon.html



The ideas cannot be better described than by reading Roosinov's US patent application.



US Patent 2,516,724

Patented July 25,1950
"Wide angle orthoscopic anastigmatic photographic objective"
Michael Michaelovitch Roosinov, Leningrad, Union of the Soviet Socialist Republics
Application August 23, 1946, Serial No. 692,477

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Page one of the patent mentions this text which explains everything.


The diminution in the illumination of the image from the center
towards the edges of the field of view in conventional objectives is
in accord with Lambert's law cos^4 beta (the decrease is proportional to the fourth power of the cosine of one-half of the angle of
view), but in reality it is even greater due to the phenomenon of
'vignetting" -i.e. due to the sharp decrease of the area of the
entrance aperture of the objective towards the edge of the image, this
is an essential drawback of the existing objectives.



Thus, in all modern objectives the decrease in illumination according
to Lambert's law causes the illumination on the edge of the field of
view to be but 15-20 per cent of the illumination in the center, and
the decreasing the illumination attributed to vignetting causes the
illumination on the edge of the field to be but 30-35 per cent of the
illumination in the center; this reduces the total illumination on the
edge of the field, as was stated previously, to about only 5 per cent
of the illumination in the center of the field.



The urgent necessity for increasing the illumination at the edge of
the field of view brought about the use of the following arrangements;
(1) A star shaped rotating diaphragm built into the objective, serving
the purpose of increasing the exposure on the edge of the field of
view, and (2) the use of the Miethe compensator, however these devices
are not sufficiently satisfactory.



In a wide-angle objective embodying the present invention the
decrease in the illumination follows the law of cos^3 beta and this
makes possible the widening of the angle of view up to 120° and more.



The outstanding feature of the present invention is an arrangement
of a super-wide-angle objective in which the phenomenon of
aberrational vignetting is utilized is such a manner that it increases the area of the entrance aperture towards the edge of the
field approximately by a factor of two; thus making possible a
broadening of the angle of view up to 120° or more, with the resulting illumination on the edge of the field approximately equaling
10-12% of the illumination in the center of the field; thus, the
illumination of the edge of the field is twice that obtained with
conventional wide-angle objectives the angle of view of which covers
about 100°.

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As you can seen, the fan-shaped mechanical compensator device is a pre-WW-II system. Early wide-angle lenses like the Goerz Hypergon were very difficult to use due to the cos^4 fall-off effect. Moreover the achievable image sharpness in the edges was extremely poor if judged by our modern standards. I have no idea of what a Miethe compensator is, but thin film deposition was not well mastered in the forties and fifties. Centre filters require a very precise control of the deposition of a thin absorbing film with decreasing thikness from the centre to the edges, following a precise law... something that has to comepensate for the cos^3 fall-of of our modern lenses.