Does a 90mm lens need a center filter?greenspun.com : LUSENET : Large format photography : One Thread
Hi, I'm considering a purchase of a 90mm lens for my 4x5. I understand that with some wide angle lens there is sufficient light fall off at the edges that a special filter is used to correct for this. Does a 90 mm need such a thing or does it depend on the image circle such that a SW 90 mm would need one and a regular 90mm would not. Thanks for you input.
-- (firstname.lastname@example.org), June 20, 2000
There are a few factors to consider.
Image circle is an impt. consideration (this is related to lens design) certainly. The older 90mm Schneider Angulons and other double gauss designs which just cover 4x5 will exhibit a lot more light fall off than lenses with much bigger coverage like the Biogon types - e.g. Super Angulons and those of similar ilk.
However, if you push a Biogon type towards the edge (e.g., when you using a lot of front rise), you will also notice the light falling off. So your mode of use matters as well. If you shoot with a 90mm Super Angulon straight on with no movements, it will be hard to see the falloff.
The effect is also a lot more noticeable with colour chromes than with print film. If you do your own black and white printing, a bit of dodging helps in reducing the falloff areas.
Also, the scene itself matters. If the scene is rather dark, it probably won't matter towards the final aesthetics. The effect is of course a lot more pronounced in bright evenly lit scenes.
Finally, I find the acceptability of light fall off is very much an aesthetic issue. Surely there'll be occasions where it will be undesirable/unwanted, but in many cases, it doesn't quite detract.
-- K H Tan (email@example.com), June 20, 2000.
The corners will be darker then the center.
Does this bother you?
then the center filter will help correct the problem.
If it doesn't bother you or if you dodge and burn or if you can over light the edges then you don't need the filter.
-- Bob Salomon (firstname.lastname@example.org), June 20, 2000.
I have a 65mm, 75mm, and 120mm lens and I do not use center filters. Here are my reasons:
1. They are very expensive.
2. They add time, errors, and complexity to calculating exposures. Ease of use, speed, and simplicity are very important to me when shooting at twilight.
3. I can correct for the fall off in the darkroom.
4. In most cases I like the effect the fall off adds to the composition. In generally, it is only noticable in skys and tends to pull the eye toward the center. It is very rare that I dodge the corners to correct for light fall off.
Hope this helps.
-- Stephen Willard (email@example.com), June 20, 2000.
The very slight fall-off with my 90mm Grandagon-N never used to bother me much. As stated above, on a lot of subjects it can actually be an improvement, or you can incorporate it into the composition. Lately, however, I've been scanning a lot of film, and it seems that the scanning process makes any wide-angle vignetting much more obvious, and obtrusive. Something to consider if you plan on joining in the so-called "digital revolution".
-- Pete Andrews (firstname.lastname@example.org), June 20, 2000.
Two quick comments. It mainly depends on subject matter... if you are documenting white walls, yes!
Second, scanning can seem to exacerbate the situation as Pete suggests, but it can also be fixed digitally. We do falloff correction with airphoto data as a standard part of the processing. Its a bit tougher when tilts and shifts were involved since you have to change the circular correction to ellipsoidal (for tilt) and move the centroid location (for shift). It can still be done with great success if necessary.
-- Glenn C. Kroeger (email@example.com), June 20, 2000.
I second Glenn in his advice. I always carry one with me. But in landscape photography, unless I use lots of movements, I usually won't screw it. But when it comes to interior photography, images are considerably better with it. I am not sure an XL has more fall off than a regular 90mm. It's rather a matter of film format. If you shoot 6x9, don't bother. In 4x5", use it sometimes and in 5x7", use it always.
-- Paul Schilliger (firstname.lastname@example.org), June 20, 2000.
All the 90mm lenses have falloff. I think there's way to design to a lens so that the falloff isn't as severe, but the design is likely to be sub-optimal (i.e., not as sharp?). I have a 90XL and use the filter all the time in daylight (I shoot velvia most of the time, so darkening would otherwise be emphasized), and sometimes at night (if the sky is dark, you won't notice; this is where the filter kills you in speed).
-- James Chow (email@example.com), June 20, 2000.