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would a wide angle lens such as the 72mm xl schneider with more coverage than necessary for 4x5 have an advantage over using a standard 75mm or even the 80mm xl lens. Specifically would there be less fall-off and therfore less of a need for a centerfilter ?
Going to the 72xl over a 75 has no advantage re: light fall-off, so a center filter will still be necessary. In fact, the edges of the larger image circle produce more light fall-off. Also, the shorter the focal length for a given format, the more light fall-off unless special consideration is given in the design of the lens to counter this. Such design considerations lead to compromises in other areas, so the use of a center filter is usually considered the best solution.
A key difference (and I own both the 75mm and 72mm Schneiders) is that with the 72mm, you have much more movement potential and will utilize the best part of the optics viz. central area more. I use CFs with both lenses - a Schneider 3B on the 75mm (which in fact is not the recommended CF, but the same one I use on my 58mm and 110mm) and a Heliopan on the 72mm. Both work very well (I'm yet to notice any ill effects...). I like the 75mm, but bought the 72mm because I shoot quite a bit of 6X17 and found the image circle of the 75mm very limiting on movement on 6X17. For shooting architecture on 4X5, you will find the image circle of the 72mm much more useful.
I echo the comments about light falloff. In theory, light fall off is proportional to the fourth power of the cosine of the angular displacement from the center. For a shorter focal length lens, this angle is greater, so there is more fall off. Some lenses by design can reduce this to the third power of the cosine, which would be less, but there isn't much that can be done beyond that. If you do a search on this topic of this and other related websites, you will find a list of wide angle lenses which manage the cube instead of the fourth power. I know that Rodenstock wide angle lenses are included in that list.
As Donald said....the larger image circle of the 72mm XL often comes in handy when shooting architecture.
I shoot architecture for a living and also for pleasure.....and when you are at the point where you are pulling out the sub 90mm lenses....you are usually pushing the limits of your equipment. I have many photographs where the limits of the 72mm XL were pushed...and the 75mm lens would have just left me a nice black nothing at the top of the frame.....
My other reason for choosing the 72mm XL....is that if you shoot 5x7....you now have an extreme wide angle. Where the 75mm wins over the 72mm is filtering....the huge front element of the 72mm XL makes it very diffcult to use gels (I have the older sinar 4x4 filter holder....and if you are not careful...it vignettes).
The same point goes for the various 90mm lenses on the market....I have a 4.5 Grandagon...which has a huge image circle.....I have used the 90mm XL which has tremendous image circle and I have yet to run out of movement with either. However....I did own and use a Schneider 90mm 5.6 SA and that lens has run out of image circle quite a bit.
The bottom line is it falls down to what you shoot. In my business I always end up shooting buildings in urban settings....and have almost no control over the situation. In a perfect world we can stand anywhere we want with no cars,people, or other distractions on the way. But since we don't....I do depend a LOT on the problem solving abilities of my equipment as do all architecture photographers. There is not a lot of times when you can "just move back 30 feet" or move your tripod....usually your standing on a ladder between two parked cars on third avenue....
If your thing is landscapes with the occasional building or interior thrown in....by all means use the 75mm lens. The added cost and bulk is not a good trade off. But if you find yourself having to shoot a three story building from 15 feet away.....
A very similar question was asked a week ago: Light fall-off at http://largeformatphotography.info/l...ic/498056.html. You might find the answers and links there useful.
The fact that the 72 SA-XL has lots of coverage isn't directly the reason that it has improved light falloff. As Leonard mentions, some LF lenses have designs that improve the light falloff to the third power of cosine. The 72 SA-XL falls into this category, as does the plain 75 mm Super-Angulon. This means that within the circle of coverage common to both lenses, the light falloff is the same (neglecting the slight difference in focal lengths). As Henning says, the relative illumination of the 72 SA-XL is further reduced past the circle of coverage of the 75 SA, but the greater coverage is better than vignetting, or not having a usably sharp image.
Lenses that use the tilting pupils approach to improve the relative illumination off-axis to the third power of cosine include the various Super-Angulons, Grandagons, Nikkor-SWs, and Fuji-SW types. This class does NOT include the older Angulons, nor the modern Super-Symmar-XL series. So if there existed a 72 mm Angulon and a 72 mm Super-Symmar-XL, they would have greater illumination falloff off-axis than the 72 mm Super-Angulon-XL. This might be a reason to buy a 75 mm SA or an 72 mm SA-XL instead of an 80 mm SS-XL. As James says, the choice between the 75 mm SA and the 72 mm SA-XL is cost, filter size, size and weight against the 72 mm versus its larger coverage as a reason to buy it.
Both Schneider and Rodenstock publish graphs of the relative illumination of their lenses, which can be compared to my statements.
Hey, there, Michael, don't neglect the Super Angulon's ancestors, which include Russar, Aviogon, Super Aviogon, and, oh, yes, Biogon. All have tilting pupils, all but the Biogon have large coverage.
Cheers,
Dan