View Full Version : creative technique obviates expensive center-filter purchase

Daniel Taylor
14-May-2001, 15:53
I have been using my Schneider 72mm XL Super Angulon on my Linhof Technikardan w ith great success. I do not use the center-filter as the slight fall-off is not objectionable and is actually a welcomed characteristic in some of my work. my p rofessional colleagues however have been critical of my judgement, and within th eir own work require it. I had loaned my architectural photographer friend the 7 2mm XL which promoted lengthy discussions and his insistence that this lens need ed the expensive center-filter without question. it was not the expense, but the added workload of removing/attaching the filter and the associated losses that compelled me to look at this problem deeper. I scan all my 4x5 negatives, and si mply made an image of a evenly lit white/featureless backdrop. scanning this neg ative allows me to characterize the lens response and create a Photoshop gradien t mask used to normalize the response of the overlayed subject scan.

nothing new here, other than allowing solutions to surface from keeping an open and playful mind. in my case, a good cabernet sauvignon contributed profoundly.

14-May-2001, 15:58
On a different tangent, do many people feel the need for a center filter on the Super Angulon XL 90mm? Or just the 'regular' 90mm?

Paul Chaplo
14-May-2001, 16:04
I strongly recommend the center filter for the 90mm SA XL. (Unless you have the Cabernet Sauvignon and Photoshop :)) With enough of the proper vintage, you don't even need film...

Armin Seeholzer
14-May-2001, 18:03
Cheers Daniel

I`m working with a Nikon f4,5 75mm and a Schneider SA f8 90mm without any center-filter and I make some scans and some Ilfochromes and I`m happy and also my customer. If I have to shift to the limits of the lens than I use not the full frame from neg. or I work with hold back under the enlarger or what ever is needed it depends on neg. or pos. but I never take a center- filter!

David A. Goldfarb
14-May-2001, 18:12
Yes, it is easy to remove falloff with the center gradient tool in Photoshop if you're scanning, or by dodging the corners if you are in the darkroom, but be sure to compensate when exposing to make sure that you don't lose detail in the corners.

Daniel Taylor
14-May-2001, 18:41
the thrust behind my solution is to offer refinement and accuracy to normalizing the response. obviously, you can create a generic radial gradient layer that approximates the response that might suffice.

as for Dan Smith's response, his commentary is interesting though I believe flawed. his belief is that the 'right' way is the existing way and apparently the only way:

"If you have to go to the trouble to make corrections in Photoshop, why not do it right from the start? How much trouble is it to screw on a Center Filter?"

how much trouble is it to avoid the expense of the center-filter, leverage the light that is not lost to filter attenuation, take advantage of the decreased setup times allowed by not requiring the filter? screwing a filter on/off is not necessarily a burden, but then, neither are two mouse clicks to add the compensation layer. once again, I am arguing from the Photoshop realm, where we are scanning directly into our process environment.

I also want to point out that advances in our pursuits can certainly come from an open and playful mind. we can lock ourselves into existing ways of thought and convince ourselves that any deviation must be surely detrimental to our clients cause. this of course is not true at all.

the point of my comments on having a glass of wine, was only to represent thinking outside of our self-imposed limitations. Dan, and others can surely understand that you don't have to add another layer of glass with its associated problems, to compensate correctly. understanding math and physics can allow a better and more accurate solution, cabernet sauvignon influenced or not.

14-May-2001, 19:46
Folks, I have a 47mm F5.6 XL and I wouldn't bother taking photographs without the filter on, even with B & W! The fall-off is very profound to say the least. Also, I'm having enough trouble trying to minimise its distortions.

Daniel Taylor
14-May-2001, 20:02
> "What may be OK for you might be trashcan material for another photographer."

and though this might be true, I can easily transpose this and say "what may be OK for you, based on your old-world and Luddite- centric view, would be totally unacceptable and below the standards practiced and demanded by those imploying the refinements and increased accuracy afforded by the latest technological advancements."

the point is, that we think ... clearly and freely without prejudice and bias. we express our ideas without self-imposed boundaries or bullshit ideas of what is 'right' and immutable.

Cesar Barreto
15-May-2001, 01:28
Maybe it isn't too late to add some comments on center filters. First, they really become a pain if one needs some other filters, like usually happens in B&W. But, if contrast control acts in development, N+1 or above, the fall-of problem certainly gets worse. And it can be impossible to solve if the subject already shows some kind of middle hot-spot. Exposure doesn't change while using such filters, as the borders would be under-exposed anyway. So, as a conclusion, I'd would never say never about center filters. They can be quite handy sometimes. Thanks to all,

Cesar Barreto

Daniel Taylor
15-May-2001, 02:41
no one is arguing against center filters. they do introduce the potential contributions of distortion and flare. they also are expensive, which is hard to justify when the kids want a new 27" Sony Trinitron and you blow the family savings on a two-inch piece of glass for the same price. maybe you need the $400 to replace those old Firestone tires that tend to explode on your Ford Explorer.

or maybe .. you just keep forgetting to put the darn filter on, or found that you, once again, have left it in your other camera bag. it happens.

enjoy the moment ...

Erik Ryberg
15-May-2001, 12:40
Daniel, I tried the cabernet but got a huge loss of film speed, at least with Tri-x. Maybe I need to play around more with the dilutions.

Philip Y Graham
16-May-2001, 19:19

I agree with you that centre filters are a pain. Not only their expense but something else for me to carry, to get lost or to get broken. I have also ended up having to buy a separate centre filter for each of my wide-angle lenses.

Although I can see that it is possible to improve light fall-off by dodging in the darkroom or using Photoshop on the computer, my query is whether this is as effective as using a centre filter?

With a wide-angle lens, the light fall-off can be up to 3 stops at the edge of the image circle which means that if a centre filter is not used then the edges of the negative or transparency may be significantly under-exposed assuming the centre is correctly exposed. As has been mentioned above, this under-exposure will lead to some loss of detail and clarity and am I not correct in thinking that although Photoshop can correct the difference in brightness between the centre and the edge, it cannot restore this lost detail?

It seems to me that if you scanned and manipulated a negative or transparency that was 2-3 stops under-exposed you might be able to get a reasonable print but I?m not sure it would be as good as the print that you would get from a correctly exposed negative or transparency. In effect isn?t this what you are doing to the edges of your negative or transparency by not using a centre filter. I suppose that increasing the initial exposure would help to reduce the under- exposure at the edges but at the cost of producing some degree of over-exposure at the centre.

Since I shoot mostly transparency film (as the end product) then darkroom or computer manipulation has not been of any particular relevance to me but, time permitting, I have recently decided to delve into the digital world and so I would be grateful to hear what you feel of my beginner?s comments.

I like the elegant way you have created a gradient mask individualised to your 72mm SA XL but I wonder how well this works when you are using camera movements where the light fall-off problem on the negative or transparency may become asymmetric.

As to the question above about the 90mm SA XL, I consider that if no camera movements are being used then the light fall-off is not a big problem and a centre filter is not always essential. However, with significant movements I would personally always use a centre filter.

Daniel Taylor
16-May-2001, 21:36
thank you for your input Philip. the posting was more philosophical in nature than practical. as you mentioned, there are many instances where the level of ingenuity does not warrant implementation, as in asymmetric corrections. as many have noted, center filters are needed in many critical applications. my point, was rather than craft a radial gradient scale that only approximates the lens loss in Photoshop (essentially corner dodging), there were creative (or lame dependent on your views) and more accurate methods available.

Bob Salomon
16-May-2001, 22:40
Cosine failure in wide angles can be controlled without a center filter

1: have images with naturally darker corners (avoid open sky) etc. 2: Control the light by overlighting the edges. 3: Dodge and burn the print.

Or to be consistent, since none of the above can be over multiple prints, use a center filter.

Daniel Taylor
17-May-2001, 02:08
if I sold center-filters I would surely agree. as a consumer, I bristle from the fact that my expensive lens purchase requires an additional expense to use properly. much like buying a car, and finding out a steering wheel is an expensive option.

Bob Salomon
17-May-2001, 09:22
Your lens requires no additiona filter.

The only reason one buys a center filter is because some photographers do not like the effect of the fall off and don't want or can't use other means to correct it.

there are many photographers who do not use the filter and, as you can see by the answers, see no need for the filter.

The only one that determines if the filter is beneficial is you and your work.

Have you ever called us to discuss the purchase of a wide angle lens or a camera like a Technorama you would find that we always reconmmend not buying the filter with the lens and shoot and see if your your type of work the filter will help.

And yes it would be spiffy neat if we all included the filter when you buy the lens. But you are right. The fillter isn't inexpensive. It would make the lenses more expensive.

imagine what people who don't want the filter would say if they were forced into always buying one.

It's your choice Dan. The physics of the lens dictates the falloff.

THhe photographer has some choices.

1: Buy longer lenses and don't shoot wide angle 2: Live with the fall off 3: Overcome the fall off by control of composition 4: Overcome the fall off by careful lighting 5 Overcome the fall off with corrective burning and dodging and, if necessary making a copy neg from the corrected print. 6: Buy a filter.

That's the life of a photographer.

You also can to some extent control how much you have to pay for the fitter

You can use Schneider, Rodenstock or heliopan center filetrs (except for some extreme wide lenses from 35 to 47 where the manufacturers filter works best to avoid mechanical vignetting).

Daniel Taylor
17-May-2001, 11:50
Bob, you have turned my posting on its head. I do not use the filter, and as my post states, I do not desire a filter as I use the fall off to underscore the true distribution of light from my lens. I also recognize that not everyone has this same relationship and may want to add corrections. post-exposure, my idea works well, though not necessarily offering grand improvements over simple dodging.

you do not have to remind us that we have choices as a photographer. I embrace that with a passion, which is the essence of this post. my choice? to think smart, explore ideas, keep an open mind, and have a wonderful time along the journey.

sid crandall
17-May-2001, 13:32
You have to also consider the cost factor of the 4x5" size (or other) digital film scanner to achieve a file for your computer. I have never sceen a large format scanner for the cost of a center gradient filter. The additonal cost for digital bureau scanning could quickly add up to the cost of the center filter. The inconvienince of dealing with these digital bureau persons and the time it take to get to them also has to be a factor. After being forced into digital by the market, my heart is begging for the good old days of doing it right the first time! My two cents worth!

Daniel Taylor
17-May-2001, 13:53
good point sid. of course, if you own several lenses and require center filter for all of them, it quickly adds up. I work almost exclusively with B&W and use a $400 Epson 1640 to scan my 6x6 and 4x5 negatives. the correction layer is a mouse click away, so the time investment is essentially zero. this assumes you are already including scanning into Photoshop as part of your workflow.

I guess the bottom line, is that if the technology you embrace does not help you meet your goals, does not stretch you closer to your true vision, save you money and energies, or whatever your objectives are, then you should reconsider this choice of direction.

the center-filter idea is to throw away light in the best part of the lens, to better equalize the response from center to edge. why is this the 'right way', when in many instances it is simply an unnecessary waste of precious light?

we've beaten this up pretty good. I suspect we could all use a fine glass of cabernet and let the ideas flow.