Ground Glass Dark Around The Edges

[drgoose]

Hello, I am new to LF photography. I am using a calumet cadet 4x5 camera with a Schneider Angulon 90mm f/6.1. I am having trouble viewing my ground glass. Even on sunny days with the lens wide open, the center of the ground glass appears bright and it is easy to focus with. As distance increases from the center of the ground glass towards the periphery, the image becomes progressively darker, and in order to focus I kind of have to look at it at an angle. I am assuming that this is because of some light fall off at the edges of the Image Circle of the lens and because the lens has a small image circle the problem is worse than if I was using a lens with a larger image circle.

Is this reasoning correct?

Thanks in advace.
Joaquin

[Bob Salomon]

You should have a Fresnel lens on the camera to even the light spread out. A newer ground glass would probably also help. But wide angle lenses do have fall off. Actually all lenses do, wide angles just have more. And you have a 90mm 6.8 not a 6.1, correct?

[Michael S]

I suggest that you refer to the home page of this web site, and click on "Large format lenses: specific wide angle and normal lenses". There you will find a description of the 90mm Angulon lens. I, myself own and use the 90mm Angulon for landscape photography purposes. Light fall-off is endemic in the lens, so critical applications, such as architectural photography, would be better served by the more modern Super Angulon lenses. That having been said, the 90mm Angulon is one of my most used lenses in the field, and it is far lighter than the Super Angulon which I used to lug around with me. By the way, the Super Angulon has a bit of fall-off as well.

[drgoose]

Sorry , you are correct it is a 6.8.

This is the back of the camera, I assume that the fresnel lens would go on top of the current ground glass so that it would not change the distance from the focusing plane to the film plane in the film holder. Is there a manufacturer of fresnel lenses, are they camera specific or do they have to be cut to seize for a particular back?

Again thank you.
Joaquin

[ROL]

But wide angle lenses do have fall off. Actually all lenses do, wide angles just have more. And you have a 90mm 6.8 not a 6.1, correct?

Hey Bob, I have a followup question conversely related to the OP's. Is it usual for long lenses with great image circles per format film area to scatter enough light internally from a presumably good light absorbing bellows to cause overexposed margins (halo) on the film?

[Bob Salomon]

Hey Bob, I have a followup question conversely related to the OP's. Is it usual for long lenses with great image circles per format film area to scatter enough light internally from a presumably good light absorbing bellows to cause overexposed margins (halo) on the film?

Not that I have experienced.

[Bob Salomon]

Sorry , you are correct it is a 6.8.

This is the back of the camera, I assume that the fresnel lens would go on top of the current ground glass so that it would not change the distance from the focusing plane to the film plane in the film holder. Is there a manufacturer of fresnel lenses, are they camera specific or do they have to be cut to seize for a particular back?

Again thank you.
Joaquin

Most better camera manufacturers, if not all of them, offer a Fresnel for their cameras. I am not aware if Calumet had one for the Cadet but since Calumet is in the process of a Chapter 11 Bankruptcy you can't ask them. However, the size of the gg on your camera should be the same as or close enough to other cameras that there should be lots that will fit your camera. The question is how does it get held onto the camera?

[ROL]

Thanks. I'm in the middle of trying to fix a very vexing problem.

[Chauncey Walden]

Joaquin, try something like a $7 page magnifier from WalMart or a book shop cut to your size and see what you think. That's what I used on a 4x5 with an Angulon.

[Tin Can]

I agree! I tried this on my 11x14 and I was astounded to see the many times brighter image and corners. I found 7x10" for 2 for $7 online. I can't give a link as I bought these 2 years ago and only tried it yesterday.

These are so thin, I am sure they could be easily cut down with good scissors.


Joaquin, try something like a $7 page magnifier from WalMart or a book shop cut to your size and see what you think. That's what I used on a 4x5 with an Angulon.

[John Kasaian]

Most better camera manufacturers, if not all of them, offer a Fresnel for their cameras. I am not aware if Calumet had one for the Cadet but since Calumet is in the process of a Chapter 11 Bankruptcy you can't ask them. However, the size of the gg on your camera should be the same as or close enough to other cameras that there should be lots that will fit your camera. The question is how does it get held onto the camera?
Wow! Calumet in Chapter11?:(

[Tin Can]

Where have you been?

Yes!


Wow! Calumet in Chapter11?:(

[Doremus Scudder]

Thanks. I'm in the middle of trying to fix a very vexing problem.

=== Hijack Warning! ===

Okay Ben, I'm intrigued. Why not start a new thread about your vexing halo?

In the meantime, and without knowing the details, I could speculate on some possible causes: internal reflections could cause a halo, but I'd rather think that would be more overall and not just the film edges. In my experience, dense negative edges are usually a development issue, but you've been doing this for a while without such problems, so we can probably rule that out.

So, how about a new thread with some images?

Best,

Doremus