Exposure compensation for ULF ?

I have recently taken up the 12X20 format. I have noticed that when I

use the same meter, same film (FP4+), and same lens (450 Nikkor M)

that I have consistantly underexposed negatives on the 12X20 film as

compared to 8X10 negatives (using all of the same componants). Am I

missing something here, does the larger film surface require a

compensation since the light is being projected over a larger circle?

If I were to guess, I would guess the underexposure to be on the

order of 2-3 stops. Any input would be appreciated. Thanks.

When focussed at infinity, the exposure should be the same. The center 8x10 area of the 12x20 film gets the same exposure as the 8x10 film, because the focal length is the same. There has to be some other factor.

 

If you were filling the frame with the same object, then you would need to compensate.

 

PJW

I would cut a piece of the 12X20 "fp-4" to 8X10 and make exposures on that film and my factory film of same subject same time same everything and see if I got something different. You may have to rate your 12X20 film at a very different asa even though it's supposed to be the same.

The image circle of light projected out the back of the lens is obviously larger than the film, to allow for lens shifts without vignetting.

 

In a 4x5 Ebony (for example) this "extra" light will be partially absorbed by the bellows, but some will bounce back onto the film, causing increased density and fog. The larger bellows on an 8x10 Ebony with a 4x5 reducing back will tend to absorb more of this extra image and reflect less, giving you more contrast and less negative density.

 

But definitely not to the tune of two or three stops.

 

In your case, the problem is that a Nikkor M Series lens is a process lens (meant for printers, not photographers) with extremely small film covering power. Nikon's specifications state that a 450mm lens at f22 covers an area of only 10"x12" and even less at f9.

 

It seems you are vignetting almost half your negative. The solution is a lens with a larger image circle.

John, where did you get your info about the Nikkor M lenses being process lenses? They are a tessar formula(as I understand it) and the 450 M is supposed to have a huge image circle(odd for a tessar, but none the less what I have learned from other posts!) I am interested because I'm about to start messing about with a 12x20 with a 450 M out front, using what I believe to be FP-4(not "+")---cheers!

There should not be any exposure correction for the larger format. The Nikkor M cover perfectly the area, I have many 12x20 to prove it. I think the problems is with bellows factor, you are probably racking out the bellows more and getting underexposure. Next time you shoot bring a tape measure and measure the bellows extension from film plane to the lens board. I use the 450 both on 8x10 and 12x20 and I am getting correct exposures.

Another thing, have you checked your reciprocity? FP4 (well most likely the photowarehouse film) has terrible recipocity, if you are using the 450 at 90 or 64, then most likely you are running into recipocity failure.

As you go up in format, you'll be in bellows factor territory more often than you think. If you're photographing anything remotely close to the camera (portraits, still lifes, etc.), you might want to check how wide the field of view is, and if it's less than 120x200" (or greater than magnification of 1:10), then you need to compensate. I have a magnification/exposure factor table taped to the backs of all my cameras as a reminder.

 

The other alternative is that you're doing something different with your development process.

Hi John'

 

A few years ago I telephoned Nikon in Melville, NY, because there is virtually no large format information on their web site. The numbers were: (516) 547-4200 and (516) 547-4321.

 

They were EXTREMELY patient and helpful and sent me excellent literature, including a "slim-jim" pamphlet called "Nikkor Lenses for Large-Format Cameras" number 8908/B copyright 1989.

 

On page 36 is the information I quoted earlier. You can, of course, get better coverage in the macro-mode, rather than at infinity. But you will need ten feet of bellows.

 

For whatever it's worth, The data for other M lenses state image circle for the 200mm f8 at 210mm 0r 5"x7" and the 300mm f9 at 325mm or 8"x10", both at f22 at infinity. Wide open is also smaller.

John, it is a well known phenomena that lens manufacturers publish conservative

image circle numbers for their lenses, probably anticipating enlargement of the

resulting

negatives. When it comes to ULF, the data can be wildly wrong. For instance, the 355

G-claron should not cover 12x20, if you believe Schneider's numbers. In fact, it does,

and quite well, and I have the negatives to prove it. Since ULF users generally contact

print and shoot at small apertures because of depth of field issues, the sharpness is

more diffraction limited than anything else. I know many people who use the 450

Nikkor on 12x20 with no problem whatsoever. I personally use the 450C Fuji, which

also, in theory, does not cover. But of course it does, in spades.

 

As to your problem in exposure, I think most likely it is a reciprocity effect, (What

exposure times WERE you using?). The 450 is not terribly wide angle on a 12x20, so I

don't think you are seeing the natural light falloff at the edges due to geometry. I pick

this effect up on 12x20 only when I get in the 220-300mm range of lenses. Given the

same film and the same lens, there really should be no appreciable difference

between and 8x10 and a 12x20 in terms of exposure. One other angle: How are you

developing the negatives? Are you using the same technique for both 8x10 and

12x20? Because tray development can be quite different than a Jobo Expert drum, for

instance.

Nikon's descriptions of the Nikkor-M series seems to cause much confusion.

 

The 1989 brochure doesn't say much about the series; it has the specs that John cites.

 

The 1982 brochure has the longest description of the Nikkor-M series: "...... are designed around the the renowned Apo-Nikkors and meet the same stringent requirements for the most demanding reproduction and photoengraving work." This might make one think that these lenses are optimized for near work, but the description goes on to say "The Nikkor-M series, unlike photomechanical lenses which are corrected for 1:1, are corrected for infinity." That statement is very clear that the Nikkor-M lenses are designed for distant subjects.

 

The comparison to the Apo-Nikkor process lenses has caused much confusion. The Nikkor-Ms were not designed for printers, they are intended for "normal working distances" (to quote the brochure again).

At the minimum the similarity between the two series of Nikkors that Nikon is asserting is that both are Tessar designs. (This applies to the early Apo-Nikkors, the later ones are symmetrical dialyte types.)

 

Nikon is also asserting similarities in the chromatic correction:

"Now for the first time photographers can achieve "Apo" performance at normal working distances." As far as I know Nikon has never published quantitative data to support calling the Nikkor-Ms apochromats, so I am inclined to consider it unknown whether the Nikkor-Ms are apochromats according to the classical definition of the term.

I'm willing to bet that Jorge is right on this one! In the ultra large formats, you

do get into bellows correction much further away than you would think. It is a

function of the object size to image size ratio: the image on the film is so

much larger at 12X20 that you are a lot closer to 1:1 than you think! Are you

shooting subjects that are at all close up?

 

As for the lens being to blame, whatever Nikon materials, web sites and

helpful theoreticians will tell you, I can assure you that the Nikkor 450 M

covers 12X20 with gobs to spare. I'm typing this right now with my hands still

wet from processing a series of 10 shots done yesterday with this lens on

12X20. It's my standard, along with the Fuji 600 C, and it covers sharply to the

corners at infinity, and has done for dozens of shots for me. Good luck, and

enjoy 12X20. It's a blast!

 

Regards,

Nathan