Compensating for light fall off [110 XL]greenspun.com : LUSENET : Large format photography : One Thread
To the franternity of LF shooters:
Being a tryo to the incredibly discouraging world of LF photography I have a question dealing with light fall off on wide angle lenses. Mr. Bill G. was correct about my schneider 110XL losing a bit around the edges despite its so-called state-of-the-art design and vast coverage; horizontal shots of a clear blue north sky confirm this. My concern with using a center filter, aside from the $$$, is if you put an 81B on top of the CF, this makes for two extra pieces of glass, which surely must degrade image quality and negate the reason for buying this superior lense (didnt know this B4 I bought it; ignorance makes for expensive bliss).
If I shoot as is and make Ilfachrome prints using B&W contrast masking, will the masking rectify the fall off on the print? What about scanning and electronic manipulation, can this solve the problem when making the final print?
THX in advance
-- todd tiffan (email@example.com), January 24, 2000
Todd: Sorry you find LF discouraging. There is a learning curve, but it will all fall into place for you and give you a lot of pleasure if you stick it out. If you feel the center filter is necessary, you can use it in front of the lens and the 81B filter behind the lens for better results. Ilfochrome is an enlargment process and a good lab should be able to correct the edge falloff during the printing process. You should certainly be able to correct falloff by scanning and electronic manipulation. Good luck with it and hang in there. Doug.
-- Doug Paramore (firstname.lastname@example.org), January 25, 2000.
Not an answer, but a question... are you seeing this falloff on 4x5 or 5x7 film with the 110XL?
-- Glenn C. Kroeger (email@example.com), January 25, 2000.
are you experiencing fall-off, or vignetting? my 110mm XL doesn't tolerate much of an extension on a filter (I now use 3mm filters), and in my aviation work I have noticed this effect. it is not fall- off as much as the angular displacement of where the sun reflects from off of clouds. most noticeable when the sun is directly behind the camera, the reflected light from water vapours is diminished at oblique perspectives.
one of the advantages of scanning, is that you can easily build a graduated centre filter mask and overlay it across the scan. by the way, you have a lens that I know many professionals lust for, or have mortgaged their house to purchase. I am so impressed, I am giving thought to picking up the 150mm XL for the 4x10.
-- Daniel Taylor (firstname.lastname@example.org), January 25, 2000.
to avoid confusion, the mask is built in Photoshop, not overlayed physically across the film. just think of the frustration as part of a hazing process. you pay your dues, you enter the club, and reap the rewards. I can echo your sentiments in learning to play the cello, fly an airplane, or learn Large Format techniques. it makes the fruits of your labours taste all the more sweet.
-- Daniel Taylor (email@example.com), January 25, 2000.
A few more details would help us advise you. You say your test exposure was of the North sky. Was this on 4x5? Was the lens centered? What f-stop did you use?
Mostly I would expect light falloff to be acceptable when this lens is used on 4x5 film. Moderate falloff is normal and can be corrected in the darkroom or digitally. Wide-open, the lens will vignete because the glass elements aren't big enough. If they were made larger, the lens would be more expensive and heavier. Mostly wide-open is intended for viewing and not taking. Stopping down a few stops will eliminate this effect and the laws of optics will determine the light falloff. For most lenses, the illumination will go as cos theta to the power of four, where theta is the angle between the center of the lens (not correct optical terminology, but good enough) and the image point on the film.
You can confirm that the cos^4 theta law applies to this lens by looking at the data that Schneider has posted on their web page: http://www.schneideroptics.com/large/super_symmar/110xl/daten.html The figure "Relative Illumination" shows 6 lines in two groups. One group is for some wide f-stop (not specified) and the upper-group for a stopped down lens (not specified, probably f16 or f22). The applicable curve is the upper, solid line for focused at infinity at f16 or f22. If you use the lens without movements on 4x5 film, the corner of the negative is 75 mm from the center, so the image height is 75 mm. This is 52% of the maximum image height for this lens. It is also theta = 34 degrees. This gives a relative illumination of 47%, which agrees with the graph. This means that the corners get 1 stop less light.
If this is an unacceptable light loss than you can either use a true wide angle design, like a Super Angulon, Grandagon, Nikkor-SW (these have somewhat less falloff) or a center filter. I doubt that many people use center filters on this lens. Using two high quality glass filters shouldn't cause significant degradation of the image quality. The second one would need to be larger in diameter to avoid vignetting, if you are using movements.
My advice: try taking some photographs with the lens at f11 or further stopped down and see whether the illumination is acceptable in practice. It you like the photographs, don't worry about a center filter.
The lens really is state of the art via its use of a non-spherical surface. It has impressive coverage for its small size.
-- Michael Briggs (MichaelBriggs@earthlink.net), January 25, 2000.
This is not an answer to the original question, but it has to do with using one size of ND center graduated filters for lenses of different focal lengths with the same filter thread size.
I am thinking of purchasing a Heliopan 67mm center filter for use on a 47mm, 58mm and a 90mm all of the same filter thread size. (47mm SA XL, 58mm SA XL, 90mm Fujinon f8)
Should I be buying a 'matched' center filter for each lens (that'll totally break the bank), or will one filter do for all three lenses?
Also, what on earth is the difference between B+W, Heliopan and the Rodenstocks in terms of quality? Do they all graduate to the same degree?
Sorry if this is slightly off thread but I'd really appreciate some advice.
-- K H Tan (firstname.lastname@example.org), January 26, 2000.
I agree with Michael's math... the 110 XL seems to operate at the limits imposed by geometry, cos^4. Another caveat here is that clear north skys are not a constant brightness across the field of a lens as wide as a 110. Sky brightness varies as a function of angle above the horizon, and angle subtended from sun to observer due to changes in scattering angles.
-- Glenn C. Kroeger (email@example.com), January 26, 2000.
I don't think you will find many people, if any, who have actually used all 3 on the same lens with the same film at the same time who could answer your question.
We are in a unique position. We are the Heliopan and the Rodenstock importer and also the Linhof importer. As such we import the Heliopan and Rodenstock ceter filters as well as Schneider ones for the 58 through 90mm XL lenses we sell.
WE HAD THE SAME QUESTION.
The editor of Shutterbug prior to Bob Shell was an extremely knowlgeable photographer named Lief Erickson (tragically died too early) and he too had this question.
So he took the Linhof Technorama 617 and the old Fuji 617 with a Schneider, Rodenstock and heliopan center filter for a test.
He found no difference on film between them.
However that was before Rodenstock redesigned their center filters.
No center filter is totally neutral. They tend to shift torwards green under cetain conditions. The latest version of the Rodenstock ones are the most neutral of all center filters.
Rodenstock does publish an interesting 2 page sheet on center filters and there use which we would gladly MAIL to anyone in the U.S. who would like it. Simply send a request in firstname.lastname@example.org and request it. If you ask Rodenstock for it they will forward the request to the same address so your direct request would be the fastest.
-- Bob Salomon (email@example.com), January 27, 2000.