Brightness of 8x10" GG image with 210mm G-Claron

[Tim V]

Hi all,

Just trying to ascertain if my ground glass is useless–it's a a very thick chunk of plastic made by Gibellini for it's early cameras–or if my 210mm G-Claron lens is simply very dark on the edges wide open due to smaller image circle wide open at f9. I can accept the latter, but I'm looking for an excuse to upgrade the ground glass with something with finer grain and the possibility of better brightness anyway. I'm used to high end focusing screens on my Linhof Techno, so not sure if my expectations are out of whack for this format or not...

For others using the 210mm G-Claron, how do you find the image on the ground glass? With my camera, the only way I can see anything outside the central portion of the image is to position my eye very close to the ground glass, right at a corner, and even then I can only see that corner as the rest of the images goes very dark. If I stand back and try to take in the entire image on the ground glass, I estimate I can only really see about 50% of the image relatively clearly, being only in the centre part, as the corners and edges are too dark to assess.

Anyway, just looking to hear other peoples experiences. The g-claron is a great little lens especially as I only use it stopped down to f45 where the image circle is more than ample, but perhaps the pay off for it's tiny size and price tag is simply a very dim ground glass image? Maybe this is compounded by a really crappy focusing screen?

Thanks,

Tim

[ic-racer]

If the specs show 226mm circle at f9 then I suspect it will look dark 150mm out from center at f9.

The 210mm I use has a documented image circle around 300mm at f5.6 and with those specs and a fresnel, I can report my view under the cloth is pretty bright all around. In fact I do my initial composition without the cloth, and only use that for the final checks and fine-tuning before exposure.

[Tim V]

Thanks for your reply.

I guess I ask mainly because it's widely reported that the IC specs for the g-claron range of lenses is drastically underrated, as it was marketed (if not designed) for the reproduction market. For such a purpose, very conservative IC specs were given due to the higher demands or expectations of the application, i.e. the need to stay within the area of coverage of the lens where resolution is at its best. Now, I have no idea what the 'real world' specs are for the lens used in the field, but I do expect there to be a large falloff wide open. I suppose I am not sure if at such an aperture–as opposed to a typical working aperture of f22-45–if there would be a drastic amount of both light and resolution. In other words, I wondered if the area of good illumination might be okay for the purposes of image composition, but just the outer edges would lose definition.

In any event, it's not impossible to use the lens for for field work, I'm probably looking for an excuse to replace my crap ground glass...

[G Benaim]

I've used it on my 810 and though the corners are darker than the middle I didn't experience the extreme vignetting you're describing, and it certainly covers the negative without vignetting. So I would look for a brighter gg if I were you.

[Tim V]

My feeling is you're right, and the ground glass (actually thick plastic) does seem really bad... That'll be my next job, I think, right after calibrating the position of the GG as I'm also experiencing a bit of back focus...

[cdavis324]

You might want to try a Fresnel first... I cut down a full sheet magnifier(from an office supply store) to fit. Not sure a different ground glass will be much brighter - saying this as a gibellini owner. A Fresnel is really essential with wide lenses on 8x10.

Sent from my LM-V350 using Tapatalk

[Dan Fromm]

Tim, about y'r vignetting. I just did the calculation, also took a quick look at my 210 G-Claron. With a 210 focused to infinity and assuming no mechanical vignetting, 8x10's corners should be ~ 1.2 stops down from the center. I saw a little mechanical vignetting with the lens wide open, perhaps enough to cause the effect you saw. To check, mount and focus the lens wide open, remove the GG, and look at the lens from the corner of the frame. If the exit pupil is invisible or even much occluded, bingo!

About coverage increasing on stopping down. Stopping down can reduce mechanical vignetting -- whether it does depends on the lens' mechanical design -- and expand the circle illuminated. Stopping down reduces the effects of some off-axis aberrations, improving image quality towards the edge of the field. This has nothing to do with illumination.

[Drew Wiley]

I never use fresnels. The secret is a properly ground glass. I have a Satin Snow glass on my 8x10. My shortest G-Claron is the 240, which is no problem in use except for the mechanical vignetting wide open at strong front tilts. Best to use rear tilts as much as possible. But I have played around with my Fuji A 180 just for fun on the 8x10. It is a very similar optical design to the G-Claron. The 180 isn't sufficient for good corner sharpness on full 8x10 film, but the circle of illumination covers, and I have no problem focusing with it, at least in the usable part of the image. All my 8x10 lenses are f/9 or even dimmer. So a 210 G should present no serious problems. There will be some illumination falloff, but not like that of true wide-angles lenses. If you need movements, you'll most likely be working in the f/45 to f/64 neighborhood. I generally compose the image and set movements with the lens wide open, then fine tune things viewing thru a loupe with the aperture set halfway down, then finally close the aperture clear down to the working stop.

[Leigh]

The GG brightness should be the same with ANY lens set for the SAME aperture.

That's the only reason photographic exposures work.

If using a fresnel, there may be a slight difference in observed brightness with angle of incidence, so a wide-angle and a telephoto may produce slightly different views.
But this is only slight, and does not affect exposure since the fresnel is on the GG.

- Leigh

[Dan Fromm]

The GG brightness should be the same with ANY lens set for the SAME aperture.

t/stops, anyone?

[Drew Wiley]

No Leigh. What you're saying applies only to the on-axis center of the field. With longer focal length lenses relative to film or matching groundglass size, illumination tends to be rather even, but as angles get wider, most lenses have significant illumination falloff from the center. That's why things like center filters and fresnel brightening screens exist. You know that. And the difference might be not slight at all. Some center filters must accommodate two full stops of falloff. In color film work, lack of such correction can potentially spoil the whole shot. Composition and focus is easier on my 4x5 through an f/12 450 Fujinon C lens than an f/4 Nikon 90mm superwide. It's not just the center of the image I'm interested in! I don't own any true wide-angle lenses for 8X10, but instead use either a 250 G-Claron or 240 Fuji A for such purposes. They're wide enough for everything except architectural interiors and tight caves. I imagine a 210 would be just a little harder to manage.

[Mark Sawyer]

If the ground glass/plastic is sub-par, I'd replace it. It will make all your lenses easier to focus and compose with. And a poor ground glass will make a dark lens even worse. BTW, have you checked for the beginnings of vignetting at the corners? And do your negatives taken with this lens thin out at the corners?

[Leszek Vogt]

t/stops, anyone?

Dan, I appreciate the ideology or even sarcasm. Don't think we can see this type of accuracy (across the board) in our lifetime. Perhaps in my next one ?:rolleyes: The only thing I could suggest to the OP is to obtain a better GG or lower F-stop lenses, in other words anything below F9....and that could get more expensive.

Les

[Tim V]

Thanks all,

I think a new GG is indeed in order and will be my first port of call before spending up large on a new lens. 210mm is my favourite focal length and in time I will acquire a Kowa Graphic, but obviously for the extra IC rather than brightness.

My experience with 4x5" is with cameras with excellent gg screens and very good fresnel lenses, so the very basic and thick plastic Gibellini screen is somewhat of a shock to the system. I have no idea why they chose to go that way for the screen, except for the fact that it's harder to break. It's the achilles heel of an otherwise fine camera, as it affects the fundamental pleasure of focusing and composing on such a big screen. Anyway, rant off and thanks for the advise and feedback.

Thanks again,

Tim

[Dan Fromm]

Dan, I appreciate the ideology or even sarcasm. Don't think we can see this type of accuracy (across the board) in our lifetime. Perhaps in my next one ?:rolleyes: The only thing I could suggest to the OP is to obtain a better GG or lower F-stop lenses, in other words anything below F9....and that could get more expensive.

Les

Les, no sarcasm intended. I was just pointing out that Leigh was mistaken when he assumed that all lenses have the same transmission. Low transmission isn't much of a problem with relatively ancient but still usable LF lenses, e.g., tessar and dagor types, would be a problem, but for coating, with some modern types.

Hollywood, where highly precise exposure is important, finds t/stops very useful. And older zoom lenses can have low transmission. For example, the 8x8B Angenieux on my 4008ZM was f/1.9, t/3.3. The difference matters considerably for reversal film. I know, tiny format, but still ... I encountered the same problem with the Nikon R10 (7-70/1.4, t/stopped significantly slower) I tried out and rejected. Funny thing is that the Schneider zooms on my 5008S-MS and 4008ZM2 t/stopped at their rated f/stops. This determined by film tests using a known good light meter. The cameras' speeds were good, shutter angles were known.

[Leigh]

I was just pointing out that Leigh was mistaken when he assumed that all lenses have the same transmission.Sorry, Dan.

I normally agree with you, but not in this case.

If your assertion is correct, why do exposure meters have no method of entering lens information ? ? ?

Do you agree or disagree with the following statement:
Any lens at f/8 will produce the same exposure on film as any other lens at f/8.
This is assuming accurate f/8, disregarding tolerances and such errors.

- Leigh

[Dan Fromm]

Leigh, the 8x8B 8-64/1.9 Angenieux that came on my 4008ZM disagrees strongly with you. It t-stopped a stop and a half slower than it f/stopped.

An uncoated air-glass interface transmits around 95% of the light striking it. An uncoated six surface lens such as a dagor type or tessar type or triplet transmits 0.95^6 (73.5%) of the light that strikes the lens' front element. An uncoated eight surface lens such as a dialyte or plasmat transmits 0.95^8 (66%). An uncoated twelve surface lens such as some Fujinons transmits 0.95^12 (54%). Coating is a blessing.

Hand-held exposure meters have no way of knowing the construction of the lens used. When the lens transmits less than the geometric aperture indicates they'll give bad advice. TTL meters also don't know, but can measure what the lens actually transmits. That's why I was in deep trouble when my 4008ZM's on-board meter failed while I was on a shoot in Costa Rica. I hadn't calibrated a hand-held meter or even my Nikon's TTL meter for that infernal Angenieux lens.

I use some uncoated CZJ Tessars, get good exposures with a hand-held meter. This doesn't mean that the lenses transmit as much light as their geometrical apertures would lead one to believe, it means that the films I use have enough latitude to hide the exposure error.

[Leigh]

Dan,

Do you agree or disagree with the following statement:
Any lens at f/8 will produce the same exposure on film as any other lens at f/8.
This is assuming accurate f/8, disregarding tolerances and such errors.

I'm not talking about t/stops, nor about film speed tolerance, nor shutter tolerance.

I'm talking about f/stops as implemented on lenses that we all use routinely.

- Leigh

[Dan Fromm]

Dan,

Do you agree or disagree with the following statement:
Any lens at f/8 will produce the same exposure on film as any other lens at f/8.
This is assuming accurate f/8, disregarding tolerances and such errors.

I'm not talking about t/stops, nor about film speed tolerance, nor shutter tolerance.

I'm talking about f/stops as implemented on lenses that we all use routinely.

- Leigh

Absolutely not. f/stops are geometric, not photometric.

Absolutely not. Given format, not all lenses see the same angle. A lens that sees a larger angle on a format will have lower illumination off-axis on that format. For an explanation of that and its implications with examples, see my article on the Horseman Optical Exposure Computer. There's a link to it in the list.

[Leszek Vogt]

Oooops, Dan and I were writing about the same time.

Don't know about Dan (not answering for him), but I don't think F8 equals F8. The problem is that the 'tolerances and errors' turns to something other than the F8....which essentially answers the question. Indeed, some of these can vary small amounts and as much as 2 and even more F-stops, and these variances can be resolved in adjusting the film development or aligning ISO'sn with exp meter.

Here is a portion from wiki: Cinema camera lenses are typically calibrated in T-stops instead of f-numbers.[10] In still photography, without the need for rigorous consistency of all lenses and cameras used, slight differences in exposure are less important.....

I've worked with Angenieux, Zeiss, Cook and some other obscure cinema lenses and the T-stops are required to intercut the footage accurately, I mean even if it was shot with two or even 3 lenses simultaneously. Coloration of the lens can be tweaked in post, but most self respecting cinematographers are fanatics about exposure of a lens (+DOF).....and that has to match. Granted, 35mm (or 16mm) may be a small format, but it's highly enlarged in presentation. OK, for some, this may be beating a dead horse.

Les

[Leigh]

Absolutely not. f/stops are geometric, not photometric.
Then you claim that 100 years of successful photographic technology is rubbish ? ? ?

You'll find your opinion contradicts that of many accomplished photographers.

- Leigh

[Dan Fromm]

The problem is that the 'tolerances and errors' turns to something other than the F8....which essentially answers the question.

Les, I must not have been clear. What matters for uncoated lenses' transmission is the number of air-glass interfaces. This isn't 'tolerances and errors,' its the lens design.

You young folks won't recall this, but while Eugene Lacour, Claude Berthiot's nephew and successor, was Berthiot's chief designer all of the anastigmats they sold were cemented triplets or pairs of cemented triplets, with two and four air-glass interfaces respectively. Towards the end of Lacour's working life, other makers supplemented these type with tessar and celor types, with six and eight air-glass interfaces. Berthiot's 1908 catalog contained a defense of their practice on, among other grounds, higher transmission.

[Leigh]

Berthiot's 1908 catalog contained a defense of their practice on, among other grounds, higher transmission.
I thought we were talking about modern lenses, not 100 year old lenses.

Certainly there is more light loss for each surface pair, but the amount is trivially small. And the aperture scales for a given lens should be corrected for that minor error. They're not "purely" geometric.

You vacillate from one extreme (t/stops) to the other (century-old glass). How about addressing lenses that we currently buy and use.

- Leigh

[Leszek Vogt]

Granted, Dan, I should have included lens design in addition to Leigh's 'tolerances and errors'. OK, throw me under the bus for short-sided lumping.

Ha, the differences between the lenses continue.....for most of us. If you want matching lenses (highly precise), one has to drop anything from 30 to over 100K for a set of primes (Mot pic Schneider, Zeiss, Leica, Cook).

Les

[Dan Fromm]

Granted, Dan, I should have included lens design in addition to Leigh's 'tolerances and errors'. OK, throw me under the bus for short-sided lumping.

Did you mean short sighted? No reason to throw you under a bus for a typo that may have been due to autocorrect. You understand arithmetic, which is what this shining example of thread drift is about.

We're lucky that most of the time our photographs' success is quite resistant to, um, approximations and doesn't require us to understand most of what we do.

[Tim V]

I received a new borosilicate screen from Steve Hopf last week. After installation, I must say that it's a real revelation. Back to what I'm used to with the Linhof screens I've used; very sharp and easy to focus, and much brighter–especially in the corners. Money well spent, in my book. The stock Gibellini screen should go in the bin, but I'll keep it in case of emergency.

[Bob Salomon]

Granted, Dan, I should have included lens design in addition to Leigh's 'tolerances and errors'. OK, throw me under the bus for short-sided lumping.

Ha, the differences between the lenses continue.....for most of us. If you want matching lenses (highly precise), one has to drop anything from 30 to over 100K for a set of primes (Mot pic Schneider, Zeiss, Leica, Cook).

Les

We had supplied matching spec lenses for a small fraction of that from Rodenstock. Usually about a $300.00 surcharge.

[Leszek Vogt]

Bob, I had no idea that Rodenstock was able to do this. However, that would still be a small portion of all those lenses that are out there, as they would continue with F-stop variations.

Recently made T-stop lenses have become v. expensive....well, maybe not Rokinon (cine). Yet, the light transmission of Angenieux 18.5mm T2.5, that was made in the early 1950's will have the same output qualities as recently made Canon 11.5-138mm T2.5, Panatar (Panavision) T 2.5 ....or slew of other optics at this opening. Granted, the image from Ivotar or Panchro Cook (or other glass) may have several other qualities that's desired (sharpness, contrast, coloration, etc), but the light transmission (@T2.5) will remain the same....and that is the beauty of being able to match and intercut scenes in the motion picture. Without going on other tangents, that was all I was trying to say.

Les

[Bob Salomon]

Bob, I had no idea that Rodenstock was able to do this. However, that would still be a small portion of all those lenses that are out there, as they would continue with F-stop variations.

Recently made T-stop lenses have become v. expensive....well, maybe not Rokinon (cine). Yet, the light transmission of Angenieux 18.5mm T2.5, that was made in the early 1950's will have the same output qualities as recently made Canon 11.5-138mm T2.5, Panatar (Panavision) T 2.5 ....or slew of other optics at this opening. Granted, the image from Ivotar or Panchro Cook (or other glass) may have several other qualities that's desired (sharpness, contrast, coloration, etc), but the light transmission (@T2.5) will remain the same....and that is the beauty of being able to match and intercut scenes in the motion picture. Without going on other tangents, that was all I was trying to say.

Les

They, for a charge, will test, match and calibrate lenses.