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

[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 ? 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 ? 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