How much corner clipping of the GG is needed?

[Stephen Willard]

I have had a few photographs vignetted by my lens hood this summer and have decided to clip the corners of my ground glass. Hopefully this will allow me to better inspect for vignetting. What I need to know is how much clipping of the corners is needed not including the frame edge that holds the GG in place?

Any help would be greatly appreciated.

[Jim Jones]

You can also check for lens hood vignetting after setting the camera up by looking in the lens to see if the corners of the ground glass are unobstructed.

[Dave Parker]

In actuallity, there is NO required clipping of the corners, I make a ton of screens with no clip at all..that said, the theory behind clipping is if you can see the full aperture of the lens by looking through the clip then you will not be vignetting, of course there is variations that do happen depending on the lens.....

What size camera are we dealing with...here is what I consider standard clips for various screens we make:

4x5 = 3/8"
5x7 = 1/2"
8x10 = 5/8"
11x14 = 3/4"
16x20 = 1"
20x24 = 1.5"

Now oddball sizes

14x17 = 3/4"
7x17 = 3/4"
8x20 = 3/4
12x20 = 1"

Now these are what I consider "normal" but as I said, there are many variations on what others consider normal and we clip screens as small as 1/8" as as big as 2" it just depends..

The way I measure a screen for a clip is from the corner back to the measurement required and then clip across the two measurements IE" if someone wants a 3/8" clip, I will measure back 3/8" from the corner on each side of the glass and then clip across the measurements.

Dave Parker
Satin Snow Ground Glass

[Frank Petronio]

The clip also serves as an exit path for air when compressing the camera's bellows.

[Michael Kadillak]

Clipping your ground glass is really not necessary. Stop down and the vignetting will jump out at on the edge of the ground glass. You need to stop down and check your critical focus anyway. That is the same principal I use for using my compendium. In fact that is exactly why I want to see to each corner on the ground glass as it is independent of the optical rays reaching the ground glass. Besides, you do not want to be operating anywhere near the edge of the image circle anyway because of inherent light fall off and potential image degredation.

Case in point. I dearly love my 14" Ektar on 8x10. Experience has taught me that when I have a decent rise that I need to put on combined with a front tilt out comes the 355 G Claron. This lens covers 12x20 with 2" to spare so the concerns about vignetting vaporize. All I need to do is check the edges of the wide angle compendium on the ground glass. Every photograph I make now has some form of compendium of lens shade protection.

Take off the lens and the air has plenty of opportunity to escape from the camera.

At the end of the day do whatever works fpr you.

Cheers!

[C. D. Keth]

How exactly do clipped GG corners help to detect vignetting? If anything, I would think it would hinder since you can't check the picture right up into the corners, where it's most likely to occur. Please tell me I'm not nuts.

[Dave Parker]

Christopher, if you read my message you would see, but again, the theory is if you can see the full aperture of the lens when you look through the clipped corner, then your not vignetting, also, you look back through the lens and can see the corners of the glass, the same applies. As far as air escaping, in the many cameras I have owned, I have never found this to be a problems, but as Michael said, taking the lens board loose performs the same function.

Dave

[Stephen Willard]

Dave, would clipping measurements be the same for 4x10 and 4x5?:)

Micheal, all of my vignetting has come from my adjustable Lee lens hood when shooting into the sun. What I did in the two cases it occurred was simply extend the hood until the glass was completely shaded. My thinking was if vignetting occurred, then I was either going to have vignetting or glare, and neither was acceptable nor was there anything I coud do about it. In both cases I was in a mad dash for fast changing light, and I missed the vignetting. With clipped corners I can make a very quick inspection after adjusting the lens hood and then abort and save the film if vignetting/glare occurs.;)

[Dave Parker]

Stephen,

Yes the few 4x10's we have done, we have clipped the same as the 4x5 screens, unless you have a big mounting lip on your camera that should be fine to do a quick inspection once your ready to shoot. if your going to do the clip yourself, a couple of suggestions, fir, get a good straight edge, not a ruler you want an edge that is about 1/4 inch think and flat, then dip your glass cutter in a light machine oil and hold the straight edge on the line, and adjust until the roller wheel is exactly on the line that you mark, don't try to clip from the edge to the edge of the glass, but start your cut with medium pressure about 1/16 inch from the edge of the glass to about 1/16 inch from the other edge, if you allow the roller wheel to snap off the edge of the glass, you will chip it, but if you start real close and run it to real close, then you can take a pair of pliers with a flat surface and snap the clip off, then take a piece of 100 grit sandpaper with a small block behind it, to finish the glass, be careful, I have cut the heck out of my fingers on corner clips..

Let me know if you need any more help.

Dave

[N Dhananjay]

I dislike clipped GGs because you cannot check the image in the corners. I think it is easy enough to take the GG off and check from the corners of the rear standard frame to see if you can see the whole aperture and check to see if filter rings or bellows shades are intruding.
As regards the fact that clipped frames help with air escaping out of or into the bellows when the bellows extension is changed rapidly, some cameras have elaborate baffles to provide the same benefit. If the camera does not have this, it is easy enough to just open the GG frame a small amount (as though you were starting to insert a film holder) to provide a passage for the air, or be a little more measured and slow in making changes in bellows extension. All this may sound a little awkward but like any habit, it becomes second nature fairly quickly.
Cheers, DJ

[GPS]

...What I did in the two cases it occurred was simply extend the hood until the glass was completely shaded. My thinking was if vignetting occurred, then I was either going to have vignetting or glare, and neither was acceptable nor was there anything I coud do about it. In both cases I was in a mad dash for fast changing light, and I missed the vignetting. ...)

Your mistake was to think that you can extend the hood so that it shades completely the lens. In doing so, you will often put the shade in the lens field of view, especially if the offending light source is near the lens axis. In such a case the glare is always there in some amount. Much better for you would be to have a note of the maximal extension you can have with the given lens and the hood. Then you can always put the maximal allowed extension and you know that everything else is too much. Of course, if you use movements then it changes the situation. Still you have the starting point, at least.

[Vaughn]

I have used GG clipped and unclipped. I prefer clipped, but survive with my unclipped 8x10 fine. If I break the GG I'll order a Snow with clipped corners...especially since I am occasionally using wider lenses than I use to.

I find it easier to see what is in my corners with clipped GG. I can easily see the "arial image" in the corner -- easier than if it is thrown onto a GG. But then I am very near-sighted and, without my glasses, can focus very close to my eyes (I stopped using a loupe a long time ago).

Vaughn

[David A. Goldfarb]

Much better for you would be to have a note of the maximal extension you can have with the given lens and the hood. Then you can always put the maximal allowed extension and you know that everything else is too much. Of course, if you use movements then it changes the situation. Still you have the starting point, at least.

It also changes the situation if you focus closer than infinity.

[GPS]

Maybe yes, maybe not. Can you elaborate?

[Doug Kerr]

Does anyone know the original motive for the clipped corner design? The following conjectures are afoot:

1. Allow air bleed from bellows pumping.

2. Provide peepholes for checking for obstruction vignetting.

3. Easier then a rounded corner for use in a recess with rounded corners (that is, the whole recess cut with a cutter whose axis is perpendicular to the glass plane).

4. Only practical solution for a recess in which each side "ledge" ends in a "turned-up" curve (that is, cut with a cutter whose axis is parallel to the glass plane). [I have an old back made that way.]

5. One corner got broken, the guy broke the rest for symmetry, other people thought there was some reason for it and kept replicating it.

[David A. Goldfarb]

Unless you put a distance scale indexed to the focal length on the lens shade (which would require knowing the subject distance), then normally one would only mark the maximal hood extension for infinity. If you focus closer than infinity, you can and ideally should increase the hood extension just short of vignetting to prevent bellows flare. It's just easier to look through the clipped corners if you have them or remove the back or sight the corners through the lens to check for this.

[GPS]

That's correct. On the other hand for close-ups the danger of flare is usually much diminished so the given hood length is for all practical purpose just question of the lens focal length and the film format.

[Dave Parker]

Does anyone know the original motive for the clipped corner design?

My guess would be the construction of the backs in the past and difficulty in rounding the corners to fit this configuration, hence just clip the corner off to remove the obstruction, many of the old backs I have seen have been very rounded in the corners making a square cornered glass impossible to fit.

That would be my guess, I have no information to back that up. Just based on my own observations over the years.

Dave

[Alan Davenport]

Does anyone know the original motive for the clipped corner design?

=======================

St. Ansel mentioned cut corners somewhere, I think it's in The Camera. He stated without equivocation, that the reason for cutting the corners is (1): to allow air to escape when you make large bellows movements. He did not offer any alternative purpose for the feature. I won't participate in any discussion positing that Adams did not have an adequate knowledge of his equipment, an allegation which I've heard before in discussions of this topic.

While I can't prove it, I believe #2 is a new use that was invented later on by some enterprising photographer(s) who was/were too lazy to go around to the front of the camera and check by looking back through the lens. (Nor, I'll warrant, can anyone still living disprove my conjecture.) :) The assumption that cut corners were originally for checking vignetting, is similar to the belief that some 35mm cameras have mirror lockup to enable photographers to reduce vibration from the mirror slap. Wrong.)

#3 and #4 are probably backward in terms of cause and effect. Since true craftsmen (oops, I mean "craftspersons") have never had any difficulty in producing square corners, it can only mean that some camera manufacturers chose a slambamthankyoumaam method of production in order to save a penny here or there.

As for #5, I've been lucky so far....

[David A. Goldfarb]

That's correct. On the other hand for close-ups the danger of flare is usually much diminished so the given hood length is for all practical purpose just question of the lens focal length and the film format.

The danger of some kinds of flare is diminished, but in some ways (mainly bellows flare, but also in the studio if you have light sources just outside the scene) it is increased. I use a compendium shade even for macro with a 35mm or medium format camera for this reason.

[GPS]

I thought he too spoke about a compendium shade..?

[Doug Kerr]

Hi, Alan,


...The assumption that cut corners were originally for checking vignetting, is similar to the belief that some 35mm cameras have mirror lockup to enable photographers to reduce vibration from the mirror slap. Wrong.

So what do you believe is the reason some 35mm cameras have mirror lockup?

[Alan Davenport]

Hi, Alan,
So what do you believe is the reason some 35mm cameras have mirror lockup?

The original reason for MLU, was so people with SLR cameras would be able to mount and use wide angle lenses. Before wides were available as retrofocus designs, the rear of the lens stuck so far into the camera body that the mirror would hit the lens. So, the manufacturers gave us mirror lockup. You'd first lock the mirror out of the way, then mount your short focal length lens. Usually there was also an accessory viewfinder for the lens, which mounted into the camera's flash shoe.

Getting rid of vibrations may be the current reason for MLU, and it might even be the best reason, but it wasn't the original.

[Doug Kerr]

Hi, Alan,


The original reason for MLU, was so people with SLR cameras would be able to mount and use wide angle lenses. Before wides were available as retrofocus designs, the rear of the lens stuck so far into the camera body that the mirror would hit the lens. So, the manufacturers gave us mirror lockup. You'd first lock the mirror out of the way, then mount your short focal length lens. Usually there was also an accessory viewfinder for the lens, which mounted into the camera's flash shoe.

Getting rid of vibrations may be the current reason for MLU, and it might even be the best reason, but it wasn't the original.

All makes sense to me. Thanks for the info.

But I didn't agree with your original observation the way it was stated - no reference to "original reason".

[Alan Davenport]

But I didn't agree with your original observation the way it was stated - no reference to "original reason".

I tend toward bluntness, so it never occurred to me to reference that. sorry.

Hey, I don't make up the news, I just report it...

[Michael Kadillak]

There is a post under "Style" by Robert Zeicher where he make reference to an article he has authored concerning the proper use of a lens shade or compendium in LF and ULF. I have not seen the article but believe that this should address any concerns about actually needing to clip ground glass corners.

Cheers!

[Stephen Willard]

There is a post under "Style" by Robert Zeicher where he make reference to an article he has authored concerning the proper use of a lens shade or compendium in LF and ULF. I have not seen the article but believe that this should address any concerns about actually needing to clip ground glass corners.

Cheers!

I just read his article very carefully for possible considerations for my application along with the responses I am getting for this posting. I am not sure what the difference is between using barn doors and the Lee adjustable shade. Can any one comment on that?