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bvy
12-Jul-2018, 14:46
I recently acquired a Calumet/Xenophone behind-the-filter holder for my 8x10. It fits a 3" square gel filter. I have a 14.75" Caltar lens in an Ilex #5 shutter. Not a lot of documentation about mounting these filter holders. I've read everything from Velcro to double side tape to clipping it on. And I notice the three clips have screws but I have no idea what they're for. I was able to just use the tension of the three clips and fit it around the rear barrel of the lens inside the camera. It stays in there but doesn't feel quite right.

Also, having a filter inside the camera isn't really conducive to quick changes or adjustments. I do studio portrait work, and if I'm doing a lot of black and white, it can stay in there... I guess. Do people using these typically frame and focus through the filter? Mine is a Wratten #58 gel filter. Everything is green and not as bright in the ground glass.

Thank you.

Bob Salomon
12-Jul-2018, 14:54
You must focus through the filter since, besides other adverse effects on the image, it will also create a focus shift. Filters belong in front of the lens unless they are part of the lens design.

Randy Moe
12-Jul-2018, 16:05
https://www.bhphotovideo.com/c/product/22617-REG/Horseman_27556_Behind_The_Lens_Adapter_Ring.html

https://www.keh.com/shop/large-format-horseman-behind-the-lens-filter-holder-27551.html

Rare

I once bought a lens on a Sinar board with a DIY setup, which I removed,

Liquid Artist
12-Jul-2018, 16:29
I have the filter behind my lens quite often, and have never had an issue while focusing through the filter

Mark Sampson
12-Jul-2018, 20:11
The Xenophon BTL filter holder sold by Calumet was designed for the Schneider 121/8 (or 120/8) Super-Angulon lens. Gaffer tape has held mine in place for over 20 years. Not, perhaps, the most elegant solution, but few people have ever seen inside any of my cameras.
When using that lens I choose the filter first (Kodak Wratten gels), install it, and then focus. Never a resolution issue yet.

bvy
13-Jul-2018, 07:15
Thanks everyone. For now, I just have it sort of clipped to the rear of the lens as shown. It's snug, but I don't know if it's the intended way to mount it.
180413

neil poulsen
13-Jul-2018, 07:37
You must focus through the filter since, besides other adverse effects on the image, it will also create a focus shift. Filters belong in front of the lens unless they are part of the lens design.

Gell filters are so thin; would the focus shift involved really be that much of a problem?

consummate_fritterer
13-Jul-2018, 08:47
Gell filters are so thin; would the focus shift involved really be that much of a problem?

I very much doubt it.

Alan9940
13-Jul-2018, 10:11
Gell filters are so thin; would the focus shift involved really be that much of a problem?

I've used gel filters behind the lens on my 8x10 for 30+ years and I've never noticed any issue with focus shift. Can't say I've tested with/without side-by-side, but I would have had I noticed anything unexpected with my negs.

Pere Casals
13-Jul-2018, 10:27
I've used gel filters behind the lens on my 8x10 for 30+ years and I've never noticed any issue with focus shift. Can't say I've tested with/without side-by-side, but I would have had I noticed anything unexpected with my negs.

With a thin gel you won't notice a focus shift, because the shift it is said to be 1/3 of the filter thickness. But if you place a thicker filter (like a Pol) behind the lens then you should be able notice the shift, like bob stated.

Drew Wiley
13-Jul-2018, 10:36
You'll have some image degredation regardless. Behind-the-lens should always be a last-resort option. It always has a penalty. That might not be a nuisance
in a contact print or deliberately soft image, but it is there and will compromise any image intended to be truly crisp.

Pere Casals
13-Jul-2018, 10:45
You'll have some image degredation regardless. Behind-the-lens should always be a last-resort option. It always has a penalty. That might not be a nuisance
in a contact print or deliberately soft image, but it is there and will compromise any image intended to be truly crisp.

It would be interesting to make a side by side comparison...

Bruce Barlow
13-Jul-2018, 12:00
"It would be interesting to make a side by side comparison..."

Why? Instead we can just endlessly speculate from our armchairs about things we don't know or understand.

Besides, if we DON'T do a side-by-side comparison, we'll avoid learning anything useful. Not to mention all the other things I seem to learn when I actually do real work.

Drew Wiley
13-Jul-2018, 12:55
Side by side real comparisons have been done for in labs for decades. I've done em myself, lab and field. This is ancient history for optical designers, and should be for photographers too. The era of any speculation about it was over long before the web was invented, and how the web created a tsunami of uninformed opinion about everything, which seems to assume that nothing was either known or in print before the web. But since various factors can cumulatively contribute to problems on the focal plane, you need to isolate them one by one even to attain an objective test. The one I keep harping on is the lack of film retention flatness in conventional sheet film holders. Your comparison test itself could be potentially bunk because you're seeing the consequence of more than one problem at a time. In the meantime, why not just believe the people who make lenses to begin with? Their own literature will point out those rare exceptions where a lens was in fact designed for an intermediate or rear filter application.

Greg
13-Jul-2018, 16:29
With a thin gel you won't notice a focus shift, because the shift it is said to be 1/3 of the filter thickness. But if you place a thicker filter (like a Pol) behind the lens then you should be able notice the shift, like bob stated.

I remember reading one time in a in a Kodak publication that their gel filters caused a shift of 1/2 of the thickness of the gel... Heck, if their gels caused a shift of the full thickness of their gel filters, I seriously any of us would notice it.

Mark Sampson
13-Jul-2018, 16:50
The question was far more important back in the days of thick glass-mounted filters; see somewhere in Ansel Adams' writing.
I've not found any degradation of image quality from using gel filters behind the lens, but then I'm an ignorant picture-maker not really concerned with theoretical perfection. I'm a long way from that in many ways, despite my best efforts toward it.
A good photograph (I have made a few of those in my life) is my goal; if that means putting a gel behind the lens, so be it.
None of my corporate supervisors, professional clients, buyers from galleries, or viewers of my prints have ever suggested that they weren't sharp enough, or wondered how I could possibly destroy the picture's resolution by putting a filter behind the lens.
I will admit that I started using gels BTL because I didn't want to spend out on a whole set of 82mm filters for the front of the 121/8 SA, but that answer has worked for me.
YMMV.

Drew Wiley
13-Jul-2018, 17:30
Going around saying you've never seen the far side of the moon doesn't mean it doesn't exist!

consummate_fritterer
13-Jul-2018, 20:43
Precisely how much does a BTL gel filter in new condition affect image quality? Any measurements? Any direct comparisons of front-mounted gel vs. BTL gel?

Bob Salomon
13-Jul-2018, 22:02
Precisely how much does a BTL gel filter in new condition affect image quality? Any measurements? Any direct comparisons of front-mounted gel vs. BTL gel?

Focus shift of about the thickness.
Loss in resolution from less then flat gel or filter
Loss in resolution from any defects like dust, grease, fingerprints, scratches.

Christopher Barrett
14-Jul-2018, 05:47
For the first dozen years of my career I shot architecture on 4x5 film at the studio of Hedrich Blessing. All of our photographers, up to a dozen shooting in the heyday, had custom filter holders 'permanently' mounted behind our lenses. We used 1 or 2 filters on every shot. Behind the lens mounting removed the possibility of filter flares. The studio produced tens of thousands of photos this way and were renown for the quality of our images. What does focus shift matter if you're focusing through the filter?

As with anything, you should do your own testing and weigh the benefits of convenience versus any loss in quality.

CB

Pere Casals
14-Jul-2018, 05:54
Focus shift of about the thickness.
Loss in resolution from less then flat gel or filter
Loss in resolution from any defects like dust, grease, fingerprints, scratches.

Bob, perhaps we can also add that gels lack anti-reflective coatings, and that has an impact in certain situations.

Randy Moe
14-Jul-2018, 06:16
I wrote I removed a DIY rear filter mount. I did that years ago under the influence of some on this forum.
.
CB I respect highly for his actual images and will now reconsider rear filters in certain situations.

The Chicago way is still an influence on me, despite my escape to rural life.

Thanks, Chris!



For the first dozen years of my career I shot architecture on 4x5 film at the studio of Hedrich Blessing. All of our photographers, up to a dozen shooting in the heyday, had custom filter holders 'permanently' mounted behind our lenses. We used 1 or 2 filters on every shot. Behind the lens mounting removed the possibility of filter flares. The studio produced tens of thousands of photos this way and were renown for the quality of our images. What does focus shift matter if you're focusing through the filter?

As with anything, you should do your own testing and weigh the benefits of convenience versus any loss in quality.

CB

Pere Casals
14-Jul-2018, 06:26
What does focus shift matter if you're focusing through the filter?

It does not matter.

The problem may happen if we want to focus without the (behind the lens) filter because we have a dim image in the GG, and with a deep red we have an even harder image to focus.

A front filter does not have focus shift, if we are not doing macro.

Also if filter is a gel focus shift shuld be irrelevant. But if stacking 2 glass filters behind the lens... this is another thing !

bvy
14-Jul-2018, 09:35
All very interesting, but more than the potential effects to image quality (or lack thereof) I was just concerned if I had the damn thing mounted acceptably!

brucetaylor
14-Jul-2018, 10:09
If you focus your ground glass through a filter mounted behind the lens focus shift is obviously accounted for. On the subject of focus shift using (single) gel filters behind the lens it is inconsequential. Many motion picture cameras (including Panavision and the workhorse Bolex) had behind the lens filter slots for gel filters both for ease of use and getting the filter out of the reflex viewfinder path. This on formats (35mm and 16mm) with depth of focus tolerances are small fraction of any of the formats discussed here. Additionally there were MoPic lenses made that required the use of a rear glass filter to maintain depth of focus.
Not that this in any way helps answer your question, bvy (sorry!), but I wanted to add to the behind the lens filter discussion.

Pere Casals
14-Jul-2018, 10:14
Many motion picture cameras (including Panavision and the workhorse Bolex) had behind the lens filter slots for gel filters both for ease of use and getting the filter out of the reflex viewfinder path.

Very interesting, an smart solution...

consummate_fritterer
14-Jul-2018, 10:40
Assuming one gel filter.


Precisely how much does a BTL gel filter in new condition affect image quality? Any measurements? Any direct comparisons of front-mounted gel vs. BTL gel?


Focus shift of about the thickness.
Loss in resolution from less then flat gel or filter
Loss in resolution from any defects like dust, grease, fingerprints, scratches.

Thanks, Bob, but filters in new condition don't have dust, grease, fingerprints or scratches. I think gels in new condition should be flat enough. A very gradual wave affects nothing measurable. A new filter won't have sharp waves or wrinkles. What's the average half-thickness of a gel filter? I think it's far less than most focus errors.


Bob, perhaps we can also add that gels lack anti-reflective coatings, and that has an impact in certain situations.

This 'might' have some tiny effect but I suspect very little considering it's only one uncoated surface that matters.

Pere Casals
14-Jul-2018, 10:53
This 'might' have some tiny effect but I suspect very little considering it's only one uncoated surface that matters.

Two uncoated surfaces, a gel has two sides... I guess it would have an effect if another uncoated filter is stacked, of it the lens is single coated, reflecting back to the film the reflections in the gel.

consummate_fritterer
14-Jul-2018, 12:10
Two uncoated surfaces, a gel has two sides... I guess it would have an effect if another uncoated filter is stacked, of it the lens is single coated, reflecting back to the film the reflections in the gel.

Right, if two or more filters were stacked then yes, rear-mounted filters toward the front would have two reflective surfaces that matter. The rear uncoated surface of one filter is so far away from the film that it has no effect. I'd not use stacked rear filters though. I can't imagine ever needing more than two filters in 99 percent of any images. I might use a color (8, 11, 25, 29, 58, etc.) filter plus a ND (or CF) plus a polarizer but that would be a very rare event. A polarizer and/or CF I'd front-mount. If I ever did stack rear-mounted filters (I won't), the one with the most filter factor would go in front. I'd also never rear-mount an IR filter or very deep ND filter due to light bouncing from the front surface of the filter.

cdavis324
14-Jul-2018, 14:23
For the first dozen years of my career I shot architecture on 4x5 film at the studio of Hedrich Blessing. All of our photographers, up to a dozen shooting in the heyday, had custom filter holders 'permanently' mounted behind our lenses. We used 1 or 2 filters on every shot. Behind the lens mounting removed the possibility of filter flares. The studio produced tens of thousands of photos this way and were renown for the quality of our images. What does focus shift matter if you're focusing through the filter?

As with anything, you should do your own testing and weigh the benefits of convenience versus any loss in quality.

CBIt was standard practice in ny as well... We'd also put a ring of tape around the lens and stick the gel to the tape either in front of or behind the lens. Fingerprints, dings or other issues with the filters had no effect on the image unless the filter was in really, really bad shape.

Sent from my LM-V350 using Tapatalk

Drew Wiley
14-Jul-2018, 21:02
Gosh, why on earth use fragile gels now that they're often more expensive than top quality coated glass filters?? Of course, I'm referring to real Wratten
gels and not polyester filters which degrade the image even more. But I get a kick out of all these references to old ways of doing things that were once allegedly produced perfect results, but now would look iffy side-by-side with prints taking advantage of decades of learning curve. Go back far enough and
Alley Oop was perfectly healthy and happy not even cooking his meat. My eyes can immediately tell when there are fingerprints or other smudges on my sunglasses. Don't tell me there is no effect.

cdavis324
15-Jul-2018, 04:55
Gosh, why on earth use fragile gels now that they're often more expensive than top quality coated glass filters?? Of course, I'm referring to real Wratten
gels and not polyester filters which degrade the image even more. But I get a kick out of all these references to old ways of doing things that were once allegedly produced perfect results, but now would look iffy side-by-side with prints taking advantage of decades of learning curve. Go back far enough and
Alley Oop was perfectly healthy and happy not even cooking his meat. My eyes can immediately tell when there are fingerprints or other smudges on my sunglasses. Don't tell me there is no effect.If it's that obvious, you must have examples to show!

Sent from my LM-V350 using Tapatalk

Drew Wiley
15-Jul-2018, 13:50
Well, that kind of thing does make a difference. It's one of the first things I learned when making prints. Then I found it highly ironic that photographers would go to considerable expense and into nitpicky arguments about the very best lenses, then defeat the whole point by putting a junky or dirty filter over the lens (admittedly, not as bad as doing the same behind the lens). This is really just common sense. Is your view driving down the road as equally clear with smeared bugs and grime over the windshield as when it is clean?

consummate_fritterer
15-Jul-2018, 22:25
I agree that damaged filters affect image quality. I have serious doubts that a single gel filter in new condition placed behind the lens noticeably adversely affects image quality without using lab grade measurement devices.

Pere Casals
16-Jul-2018, 05:49
I agree that damaged filters affect image quality. I have serious doubts that a single gel filter in new condition placed behind the lens noticeably adversely affects image quality without using lab grade measurement devices.

In theory, if the lens is single coated it would generate some flare, of around 5% of the total incoming light. If it is a multicoated lens that flare would not be noticed, because the light that the gel reflects to the front it won't be much reflected back again by the multicoated surfaces.

Regarding Image Quality, possibly a wide angular lens would notice more the gel, because the rays are more angled. This is in theory, it would be good to check it in practice...

Drew Wiley
16-Jul-2018, 10:07
There's no substitute for a lens hood or other effective shade. Flare can occur even with multicoated optics, or conversely be brought to a minimum using lesser optics which are effectively shaded from unwanted light. But oh my, Pere and Mr. Fritterer, you both abound in untested theory. Kinda like the annual running of the bulls in Spain. I'm certainly not smarter; but one does remember a thing or two after being gored and trampled by the bulls over the years. And in my case, having lugged very heavy packs for days on end into remote places I probably will never see again, losing a special image or having it compromised was indeed disappointing. Back then I tended to print big highly-detailed Cibachromes; and some things which seem to be matters of mere opinion on these web forums were plain as day under those kind of stringent darkroom expectations. I have nothing against breaking the "rules" on purpose, or softening images for esthetic reasons; but
misinformation has the potential of producing unwanted effects.

consummate_fritterer
16-Jul-2018, 12:47
It's true it's been awhile for me, Drew, but I'm not entirely unpracticed in the field. ;)

Pere Casals
16-Jul-2018, 16:22
There's no substitute for a lens hood or other effective shades.....

Drew, of course

Anyway it is interesting to guess when a gel behind the lens produces some flare

Drew Wiley
16-Jul-2018, 16:33
Well, sometimes it doesn't matter. I remember running into a stock photographer with a beat-up 4x5 Tachi, seven lenses, and a stack of at least twenty Wratten gels, all of them roughed up and with masking tape markings. It was nearing sunset below Fremont Peak in Wyoming. I got my shot and packed up and left while he was still fiddling around with too many gear choices, and it went dark before he could get a shot. But back then large format color images still yielded decent stock fees, yet many of them were printed even smaller than the original 4x5 film image. Even a cover shot would only equate to 2X or so enlargement. And just this month the Postal Service is going to release a whole sheet of stamps based on the work of a local color landscape photographer. Forgot his name - it's awfully "scenic" stuff; but he uses pro equipment. So in those kinds of cases, potentially paying ones bills for the duration of a career, minor discrepancies in sharpness aren't even going to show, much less in the case of some portrait studio which routinely employs Softar filters or the equivalent. But most of my game involves very crisp images - not "sharpness for sharpness' sake", but as a contributory tool within a certain kind of look
I'm known for. It's not the only kind of image I make, but one I've gotten good at.

consummate_fritterer
16-Jul-2018, 17:02
Drew, do you have any comparisons of using any kind of single filter in front vs. a like-new gel of the same type, behind the lens?

Drew Wiley
16-Jul-2018, 17:30
Well, I don't think the web is very good at illustrating such distinctions, and if I ever did save behind-filter examples, it would be somewhere on the bottom of a reject pile of negatives. The tests were done with top-notch G-Claron and Fuji A lenses. The difference wouldn't be objectionable on an 11X14 print from 4x5, but would be obvious in a bigger print or certainly under a loupe. I take very good care of my Wratten gels as well as glass filters.

consummate_fritterer
16-Jul-2018, 17:41
Drew, all I'm trying to convey is I've used like-new single gels behind the lens and in front. I couldn't tell the difference. However, like you, I've no existing examples to prove my point.

Drew Wiley
16-Jul-2018, 17:58
Other than such testing, I have no use for gels except for specialized lab applications where there are no other options. In the field, multicoated glass is not only far more durable, but much more resistant to moisture. I'm in the weather quite a bit. I also keep a large set of Lee polyester filters for testing purposes, but would never use them for high-quality purposes. A nice thing about Wratten gels is that there are published spectrograms and other pertinent data for each one of them, quite helpful for scientific or technical applications. But there are all kinds of sources for glass filters for general shooting. Some of the common Wrattens for black and white work can now be obtained cheap; but most of them are so old I'd ask questions about storage conditions first. I gave up on them almost instantly for outdoor work due to wind issues. But recently I did take one of my sandwich-style gel holders and put some diffusion sheets along with a warming gel in it, in order to make a flashing attachment for Ektar color film. I don't use it very often - but that's just about the only way to handle mixed lighting where the highlights are warm, but shadows in deep shade bluish, a circumstance Ektar does not handle elegantly at all. And no, this can't be post-corrected without a penalty to hue accuracy because it's due to underexposure in one particular dye peak. Other specialized Wrattens are employed in my lab to generate very precise exposure light for making color contact internegs, internegs, and separation negatives.

consummate_fritterer
16-Jul-2018, 18:06
Only three times have I shot in conditions which could harm a gel filter. Each time, it was a mistake to have my equipment exposed to those conditions at all. One time was during a dust storm... sand got into the lens. A second time was in very light rain... the bellows was never quite the same. A third time, was in high wind and the camera blew over... only a ding and a scratch but didn't get the image. So I think most conditions which would damage a gel filter wouldn't be good for the other equipment either.

Drew Wiley
16-Jul-2018, 18:40
Guess you wouldn't like Death Valley in March. Neither do I. It takes only seconds to get salty clay dust into everything. But I've routinely been in extreme conditions with view camera gear. More than once even my 8x10 along with its heavy Ries wooden tripod got picked up just like a kite and tossed over twenty feet - luckily landing on soft foliage. But once a Sinar 4x5 was not so lucky during a mountain storm. I'm just grateful it wasn't me. The only time I've been busted up was indeed ironic - I was 16 and had just finished free-climbing 22 running waterfalls in a single day, about 2000 vertical feet overall. But that evening I met my friends at the rural high school gym to play basketball. During the game I tripped over one of them and went headlong into an old style fire hose box with a projecting handle, broke my wrist and needed stitches above my eye. Guess the Fates caught up with me that day!

consummate_fritterer
16-Jul-2018, 19:47
Hey Drew, remind me never to buy your used gear. Kidding!! :D

Drew Wiley
16-Jul-2018, 20:07
Most of my gear is immaculate. Certain lenses have never been used except for testing; I retain them as eventual replacements for the ones that do get tortured. But when it comes to buying used gear, I myself gravitate to single owner-operator indoor studio sources. Got a lovely Sinar Norma that way. The original tapered bellows looks brand new - over forty years old! How often do those turn up? (Well, I did bag a "spare" original Norma bellows that was totally unused a short time later!) But big studio assistants can be brutal on gear. Japanese dealers can also be excellent for selling cameras and lenses that had been essentially hoarded rather than actually used much. But buying used filters is riskier because they're not generally inspected well, and one doesn't save much anyway.