While not true for all filters Heliopan makes filters of different densities by grinding the glass to reach the required density. So Mark’s solution would not work.Originally Posted by r.e.
While not true for all filters Heliopan makes filters of different densities by grinding the glass to reach the required density. So Mark’s solution would not work.
Just one more reason to run a simple test.
In post #3, you wrote:
Just about any question on this -- or any other forum -- is asking for trouble.
My advise? Just run a couple of simple tests -- with X vs without X, with X vs Y, etc.
I'd also advise that you are free to experiment with CND [center neutral density] filters. That is, what the manufacturer recommends may not be what fits your needs, lens(es), situation, etc. best. Just use them as a starting point -- much like ISO.
This is now the second post in which you've recommended "simple tests".
Re the centre filter... If you're just talking about whether or not to use it, I imagine that anybody who uses a centre filter knows that that's a judgment call. That said, based on discussions about this particular lens when used for 8x10, I expect to use the centre filter most of the time.
I'm now considering options for solid neutral density. I've asked for, and received, some very useful comments on one option, which is ND on the rear element. Given the cost of 8x10 sheets of film, this discussion is likely to save me quite a lot of money, not to mention time, compared to testing the various ways of doing this, one of which would require the purchase of gelatin filters that I don't have. If I do test, this discussion will narrow what's tested and how it is tested. Posts #18 and #21 have also prompted me to send a message to B+W asking about the thickness of the glass on its XS-Pro filters. Due to the design objective of the XS-Pro line, it's possible that the glass thickness is uniform, or close to it. The discussion is also helping me to evaluate this option against two options for placing ND in front of the lens. Those options are in post #10 and are quite expensive. To give you an idea, a single high quality 112mm screw-in ND filter costs US$200 and up, and a glass rectangular ND filter made by Schneider, Tokina or Lee/Panavision, large enough to cover 112mm, costs about $500.
Last edited by r.e.; 24-Dec-2021 at 08:51.
So problem #1 could be addressed by focusing with a UV filter in place, so long as the glass is the same type and thickness.
As for problem #2, spherical aberration from the rays of light travelling through thicker glass the more oblique the angle, the problem is the same whether the glass is in front of or behind the lens. And if the lens is designed to take that into account in front of the lens, he is already using a center filter and I very much doubt the lens is designed to compensate for 2 stacked filters.
Mark Sawyer, in post #18, suggested focusing with a UV filter as a stand-in and replacing it after focusing with an ND filter. Two forum posts from 2006 also suggest this. They are in a thread called filter for Schneider 210mm SS XL. On that lens, the rear element thread is 72mm and the front thread is 135mm:
Ron Marshall:
"I use rear mounted filters on one of my lenses, because some of my filters would contact the front element. I focus with a UV filter in place, then replace it with a colored filter."
Michael S. Briggs:
"Assuming an index of refraction of 1.5 (which is reasonable), a glass filter on the rear shifts the focus by 1/3 the thickness of the filter. Obviously this is much less than a centimeter. In some cases the shift won't be important compared to the depth of focus. It's best to refocus with the filter in place. If the filter is too dense, you can substitute a lighter filter of the same material and thickness, as suggested by Ron.
"The rear mounted filter (in the converging beam) will also introduce some spherical aberration (as mentioned by Eric [Leppanen]), but I suspect that the effect will be unimportant at typical taking apertures.
"If you use a gel or thin polyester filter, both effects will be negligible."
In post #21, Bob Salomon notes that the glass for Heliopan ND filters varies in thickness. I have a set of B+W XS-Pro ND filters that I could use. I've asked B+W about glass thickness for the XS-Pro series, and will provide the response, if I receive one, here.
Last edited by r.e.; 24-Dec-2021 at 15:01.
As far as I know, placing the filter in front of the lens, where the light rays are random and not yet collimated by the lens does not introduce a focus shift nor any aberrations as long as the filter glass is plano-parallel and of good quality. It's the proportional refraction of the collimated (directional) rays from the rear of the lens passing through glass at different angles of incidence, which causes it to pass through different thicknesses, that causes the distortion.
Two stacked filters of good quality will also not add distortions. The problem with stacking filters is that there are more air-to-glass surfaces for reflections (from interfaces of different refractive indexes) and that can degrade the image somewhat through flare (although I stack filters all the time and find this effect negligible to non-existent).
Best,
Doremus
Picking up on Michael Briggs's comment, quoted in post #25, about gelatin...
Steve K (LabRat) suggested Kodak gelatin filters earlier in this thread, and Doremus Scudder, in post #20, says:
"As suggested, a gel filter will minimize the focus shift. You can get holders for them and you get to focus without the ND in place. I think that would be my preference. Just be aware that gel filters are fragile and need careful handling."
A search of old threads reveals that some very experienced photographers share Doremus's view.
In Kodak's Wratten system, gelatin ND filters, regardless of density, are #96 Wratten filters. As I note in post #14, B&H prices for new Kodak filters are fairly high. However, new old stock, in a variety of sizes, appears to be readily available on eBay. Assuming that the vendors are legitimate, and that the filters haven't deteriorated due to age, the prices strike me as quite good.
Kodak gelatin could be used either behind or in front of the lens. Behind, I think that 3"x3" would work well with the rear element of the Schneider XL 150mm. In front, 6"x6" would not only cover a diameter of 112mm, but could be used handheld or taped to the lens, or in a holder that fits to the lens. The author of one older post on the forum says that S.K. Grimes made a holder for this purpose.
In my case, one option is to use my Arca-Swiss compendium lens shade and rig a filter holder (the Arca-Swiss holder takes 4"x4" filters). I could use either gelatin or resin square/rectangular filters. This would also make it possible to use resin graduated ND filters. I exclude glass for cost reasons. Large, rectangular, high quality glass ND filters run US$500+ apiece. I'll have to check my Schneider 150mm lens+compendium pairing for vignetting.
Note: I've determined that Lee's SW150 holder can't be fitted to this lens's centre filter. The largest lens adapter is 105mm. Assuming that it didn't cause a vignetting problem, I suppose that S.K. Grimes could make a 112mm adapter. In any event, it's possible to use Lee's SW150 filters without its holder.
Last edited by r.e.; 24-Dec-2021 at 16:34.
I'd like to thank everyone who contributed comments.
I've made a decision, at least for the time being, about filters for Schneider's Super-Symmar XL f/5.6 150mm when used with its IVa centre filter.
Note that the centre filter requires the lens to be used at f/11 or smaller, and comes with a loss of about 1.5 stops of light.
Polariser, 112mm screw-in
I made a decision about a polariser before starting this thread. I would much rather add a 112mm polariser to the centre filter than spend time trying to get the rotation right on a 62mm polariser screwed onto the lens's rear element. Indeed, I see a 112mm diameter as a benefit. I can use my hand to hold up a filter that large in front of my eyes and easily see how rotation is affecting the image. Normally, I use B+W and Heliopan screw-in filters, but neither makes a 112mm polariser. As noted in post #10, I chose NiSi's Natural Polariser, which appears to be well-regarded.
Neutral Density, 112mm screw-in
Very few companies currently make 112mm ND filters. With one exception, those that do offer very limited selection in terms of strength. Japan's Tokina makes a line of prime and zoom cinema lenses that have 112mm filter threads. It makes its Cinema Pro IRND filters in 112mm, eight strengths, for these lenses*. IRND means that the filters cut infrared as well as visible light, which has become more or less standard in digital filmmaking. Yesterday, I acquired two of the Tokina filters, which will serve my needs for the time being.
Rationale
I'm satisfied that adding filters to the front of the lens is preferable, from both ease of use and optical perspectives, to adding them to the rear element. My decision was made easier by the fact that I've been able to acquire the three filters at prices that make them affordable, which means that I should be able to sell them eventually without losing a meaningful amount of money. I was just lucky in coming across the two Tokinas yesterday.
I have a Nikkor W f/6.5 360mm lens that also made the decision easier. This lens has a 95mm filter thread. I think that a step-up ring to the 112mm filters may be more convenient in some cases than using my Lee100 system.
Follow-up
I plan to speak with S.K. Grimes after the holidays about how I might be able to use Lee's SW150 System graduated neutral density filters. I also plan to ask Lee whether it sees a problem if I have S.K. Grimes make a 112mm adapter for its SW150 holder. Lee's own largest adapter is 105mm.
If B+W responds to my query about the thickness of the glass on its XS-Pro line of filters (see post #25), I'll post what it says.
I think that the ideas in this thread are of on-going interest because they offer ways to address vignetting from stacking filters.
* Tokina also makes its Cinema Pro IRND filters in five other other diameters, as well as in 4"x5.65" and 6.6"x6.6" for matte boxes. Tokina owns Formatt-Hitech, but my understanding is that the Cinema Pro filters are made in Japan rather than in the U.K.
Last edited by r.e.; 25-Dec-2021 at 21:22.
Mat Marrash, a member of this forum who has a large format YouTube channel, frequently uses Schneider's Super-Symmar XL f/5.6 150mm for 8x10. In this video, which I came across yesterday, he uses the lens with a screw-in R72 filter and Efke infrared film. His filter is 77mm, not large enough for the lens's 95mm front thread. At 18:10, he uses a 62mm to 77mm step-up ring to screw the filter onto the lens's rear element. This is one of the options that I was considering (post #1), except in my case with a 62mm to 82mm step-up ring*:
Shooting Infrared 8x10" B&W Film - Large Format Friday
* Marrash doesn't use a centre filter with the Schneider lens, at least in his videos. I don't know whether he addresses fall-off in processing, although he appears to be content with a certain amount of fall-off in his images. Marrash also uses a 100mm Benro Filter Holder for square/rectangular filters, including graduated neutral density filters. That holder won't fit Schneider's IVa centre filter, and in any event doesn't accept filters that are large enough to cover 112mm.
Last edited by r.e.; 28-Dec-2021 at 21:37.
I sent an e-mail to Lee support this morning and received a reply two hours later. Lee doesn't make adapter rings to order, but the support person thinks that a custom 112mm adapter ring should work. He's asked me for some info, now sent, about the Schneider lens and centre filter. This info will be looked at by one of their engineers in the U.K. after the holiday break.
I've had three other occasions to contact Lee support since purchasing one of its Lee100 holders about two years ago. Every time, I've had a quick, helpful response. Panavision owns Lee, and in North America I suspect that the support comes from its office in Burbank. In any event, I have nothing but good things to say about my dealings with Lee support staff.
In addition to S.K. Grimes, @Kiwi7475 has pointed out to me that 3D printing might be an option for a custom adapter ring.
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