Clipped corners . . . What do I see?

[Steve Feldman]

Hi y'all,

I have a new (to me) 5x7 B & J wood view with a gg that has clipped corners. I understand that one reason for the clip is to relieve air pressure inside the bellows. The other reason is to see if your lens, when stopped down, is vignetting. My question: what does vignetting look like when looking through the back?

Thanks.

[Joseph O'Neil]

Monday morning cynical answer for you. This answer implies an obvious coffee/caffine shortage.

First, IMO, the real reason for clipped corners on ground glass is so the people assembling the camera do not cut themselves on sharp corners of the glass. It's also entirely possible, since making a nice, square corner is actually something that takes a few, living, functioning brian cells (not many mind you, just some), that any ground glass with clipped corners will allow for looser tollerances when assembling the camera.

A bit more seriously, on squares/sheets of glass, it's real easy to crack a corner. Also, I suppose once you use a micrometer to get the depth of the ground glass just perfect, it does help to have a bit of loose tollerance on other parts. Easier to manouver the glass overall during assembly.

The bit about air pressure (yes, heard that one myself too) is probally from some smart marketing type possibly too embarressed to tell the truth . :)

Vignetting - how do you mean - when you have reached the limit of your image circle? You can usually see that as a darkness on the corners of your ground glass. Ah, but wait a minute - if you don't have corners, how do you see the dark corners. A new conspiracy theory then - the purpose of clipped corners is to hide your vignetting, not let you see it. :)

joe

(of in search of another mug of coffee.....)

[John_4185]

Geeze, Joe, you were wrong on every count. You don't drive when you are decaffinated, do you?

[Eric Biggerstaff]

I don't think the clipped corners are there for air pressure.

To use them to check for vignetting, stop the lens down to your taking apreture. Once this is done, look through the clipped corners to the lens. If you can see out the of the lens, then you are not vignetting. Do this through each of the clips to make sure.

[David A. Goldfarb]

If you can see the entire aperture as a circle through the corners of the groundglass, then you shouldn't have any vignetting or falloff of illumination in the image. If the aperture of the lens is cut off by the lens barrel or shade or sagging bellows, or if it appears as an oval or (American) football shape, then you'll have vignetting or dark corners due to falloff of illumination.

[Paddy Quinn]

Wrong time of the month Joe?

"Vignetting - how do you mean - when you have reached the limit of your image circle? You can usually see that as a darkness on the corners of your ground glass."

point being it frequently doesn't show up as obviously darkened corners - so looking through the cut of corners is more helpful.

"The bit about air pressure (yes, heard that one myself too) is probally from some smart marketing type possibly too embarressed to tell the truth"

My camera came without cut-off corners on the GG, but is so nicely air tight when the back is closed and a lensboard in place that if I move the front standard in even moderately rapidly from say 450mm to 250mm or 210mm the bellows ballon out and the creases start to pop outwards. So that means I eather have to make sure I do that with the lenses off or let the new GG with it's cut-off corners do its thing

[Alan Davenport]

Clipped corners on the groundglass are NOT NECESSARY to check for vignetting, as this can be done by looking through the lens. Since cutting the corners requires an additional manufacturing step, there is no reason why it would have been done unless there were another reason, such as letting air move in and out. Ansel Adams said the corners were clipped to allow air to escape. I accept his statement as correct, and subsequent claims as revisionist.

When looking through the clipped corner, you are looking for the actual aperture of the lens. If you can see the entire aperture, and nothing in front of it but the desired scene, you'll have no problem. If you can see part of the lens shade in front, or if part of the aperture is blocked by the rear element structure inside the camera, you will have vignetting. The alternative is to look through the aperture from in front of the camera; if you can see the corners of the GG without them being blocked, you're OK.

[Jim Noel]

David Goldfarb gave you the correct answer.
If the opening appears like a cats eye, or american football, the corner is vignetted. If all of the diaphragm is visible and essentially round, you are in the clear.

[Steve Feldman]

Thank you all for your insitefull responses. Even Joe's.

Ok. Especially Joe's. Gotta lighten up - it's only exposed silver.

Now all I gotta do is get my head, a loop, an eyeball and my readers under the cloth, while the camera is only a foot of the ground and angled up. Make movements by feel. Upside down and backwards. Legs and feet cramping up all the while.

Easy - nothing to it.

I love is stuff.

~:o)

[Mark Sawyer]

Remember when checking the corners for illumination, on many lenses you could still be outside the "useful coverage" of the lens. The image can get fuzzy well before the light falls off. I usually only check one or two corners, as it's obvious where the vignetting might be.

"If the opening appears like a cats eye, or american football, the corner is vignetted."

I think this would qualify more as fall-off than actual vignetting. It might also contribute to the much-beloved "swirly bokeh" of some older lenses, but being a near-complete idiot, I'm unsure about this.

" Ansel Adams said the corners were clipped to allow air to escape."

It's a little known fact that Ansel Adams' crooked nose was broken when he folded up an 8x10 without clipped corners too quickly, and the sudden increase in air pressure caused the camera to explode in his face...

[Steve Feldman]

Mark,

A likely excuse for his appearance. I had a '52 MGTD. While re-connecting the battery, I momentarily forgot that this British beastie had a positive ground system. Double grounded the battery. Blew up in my face. That's the excuse for my appearance.

True or not - they're good stories.

[Bill_1856]

What you see is an aerial image, so when the projected image on the ground glass is too dim to visualize you can determine the exact field of coverage by viewing through the corners with a loupe.

[Brian Ellis]

"I understand that one reason for the clip is to relieve air pressure inside the bellows. "

This is one of those rare things about which Ansel Adams was dead wrong. That isn't the purpose of the clipped corners. A view camera isn't an air-tight object, there are plenty of places from which air can escape without needing cut corners in the ground glass. If clips were needed in order for air to escape then no one would use an unclipped ground glass but plenty of people do.

The corners are there for the second reason you gave. As to what you look for, with the lens wide open when you look through one of the corners you'll likely see something shaped kind of like a football, i.e. oblong. If you keep looking as you stop down you'll see the football shape gradually get wider until eventually it ceases to look like a football at all and instead is either circular or shaped like an aperture. At that point you should have sufficient coverage to prevent vignetting. If there is mechanical vignetting (e.g. from a lens shade or filter ring) you'll see that too by looking through the corners.

[John_4185]

How many times does a person use a specific lens before he just plain knows whether he's getting vignetting? For me a few uses tells all.

[William Mortensen]

Yes, jj, but with so many variables (swing and tilt front and back, plus some shift,add some rise, add a red filter, plus a polarizer, maybe a lenshood...) and keeping track in your mind of half-a-dozen lenses... I admit I've been unpleasantly surprised a couple of times.

"True or not - they're good stories."

Here's a true one: when I was a kid, someone stuffed straw in the gas tank spout of my mom's station wagon. She decided to get it out with the vacuum cleaner. No human injuries involved, but the old Hoover was never the same after jumping six feet in the air with flames shooting out the sides...

[giancatarina]

if you can't see the entire shape of the iris, this means that you are outside from the coverage of your lens... what we call image circle !!!
fall off is progressive, as is sharpness... this is an other history !
For example, if you are using a 58 xl with 6x7 without mvts, looking at the slide, you can't see any fall off, if you use it with 4x5, then the fall off is obvious while you still in the image center and you still can see the iris (looking in the clip corner). In this case you can use a center filter in order to correct the fall off, but the image circle remains the same !
Considering sharpness, the center of the image circle is allways sharper than the border, so you can use a lens with movements, and be able to see the entire iris (looking in the clip corner), but the corners of the image won't be necessery sharp !

Off center sharpness, image fall off, Image circle... it all depends on the lens design !
I've test an apo ronar that was sharp till the end of the IC, but the Image circle was quite small,
Some lens have a big image circle, but the quality in the extreme of the image circle is poor... compromise...
the 110 xl is my favorite lens because it have a big image circle, without compromising on image quality, the best of both worlds !

I don't know if my explanation is clear enought, soory english is just my second language !

[Brian Ellis]

"Clipped corners on the groundglass are NOT NECESSARY to check for vignetting, as this can be done by looking through the lens"

I don't think anyone suggested that clipped corners were the only way to check for vignetting. You can do it by looking through the lens as you say. But for me the clipped corners are more convenient because I don't have to get out from under the dark cloth, walk around to the front of the camera, peer through the lens, then get back under the dark cloth as is done when checking hrough the lens.

[Alan Davenport]

This is one of those rare things about which Ansel Adams was dead wrong. That isn't the purpose of the clipped corners.

With due respect, what you're saying is the revisionist perspective. Adams said, "...the corners of the groundglass may be cut off to permit the movement of air when the bellows is expanded or collapsed." Implicit in this, I think, is the situation where one is making gross movements of the bellows, such as open and closing a folding camera, or a large movement on a monorail when changing lenses or such. Yes, there are lots of ways for air to move in and out of the camera slowly when focusing and adjusting, but not when you work the bellows like an accordion.

Occam's Razor tells us that the logical reason to add a feature, is to accomplish a purpose that could not be accomplished with what was already there. Cut corners were not put there (originally) to check for vignetting, because there were other ways to do that. They were not put there to allow air to move in and out when focussing, because it wasn't needed. The corners were originally clipped so a photographer could change from a long lens to a very short lens, and then unlock the camera and squish the front and back together -- and not damage the bellows in the process.



If I may mention smaller formats: another camera feature that has fallen victim to revisionist history is the mirror lockup feature on some 35mm cameras. The accepted belief is that MLU is there so we can reduce vibration when taking photos with very long lenses, high magnifications, etc. But the truth is that MLU was invented as a way to mount extremely short (i.e., "wide angle") lenses, in the era before the availability of retrofocus designs. A non-retrofocus lens, if too short, will be so far back into the camera body that the mirror would hit the rear of the lens. So they came up with MLU to get around the problem; you lock the mirror out of the way, then mount your WA lens. Framing was accomplished either by guess and by golly, or by using an accessory viewfinder that mounted on top of the camera. It wasn't long, however, until retrofocus designs became the standard for short focal lengths, making the original purpose for MLU a moot issue. Sometime in the interim, a few people had noticed that they could get much sharper images with their long lenses if they locked the mirror up first. Now almost everyone believes mirror lockup was always there for the reason they use it. Thus was history revised.



...don't think anyone suggested that clipped corners were the only way to check for vignetting. ...the clipped corners are more convenient...

And I never said, that anyone suggested that. I merely pointed out that the addition of clipped corners did not add the functionality of checking for vignetting, since that was already there, and that from a manufacturer's perspective there had to be another reason. Yes, using the clipped corners is MUCH more convenient in practically every case.



The point made (I hope) is that devices and ideas often end up being used for purposes entirely different than what was originally envisioned. History is written by the victors. I guess this is the case in every arena of human activity, not just wars. And so it goes.

[J.Koger]

Hi y'all,

I have a new (to me) 5x7 B & J wood view with a gg that has clipped corners. I understand that one reason for the clip is to relieve air pressure inside the bellows. The other reason is to see if your lens, when stopped down, is vignetting. My question: what does vignetting look like when looking through the back?

Thanks.

[J.Koger]

I imagine you're long since gone from this forum and I've just begun, (again). After you've focused, composed, you'll stop down then return to the ground glass and look thru the clipped corners. If the lens opening is dark it's totally outside the image circle and vignetted. If you observe the other observations, football etc., I suppose you can evaluate those comments.

[Tracy Storer]

Another reason for clipped corners not yet mentioned, from a manufacturers perspective, is the way the ground glass rebate is cut in the ground glass frame. This rebate is usually cut with some sort of round tool, resulting in corners which are either rounded, or "ramped". It was easier in some manufacturers eyes to clip a glass corner than square the corners of the rebate in a wooden frame.

[John Kasaian]

This is one of those rare things about which Ansel Adams was dead wrong. That isn't the purpose of the clipped corners.

With due respect, what you're saying is the revisionist perspective. Adams said, "...the corners of the groundglass may be cut off to permit the movement of air when the bellows is expanded or collapsed." Implicit in this, I think, is the situation where one is making gross movements of the bellows, such as open and closing a folding camera, or a large movement on a monorail when changing lenses or such. Yes, there are lots of ways for air to move in and out of the camera slowly when focusing and adjusting, but not when you work the bellows like an accordion.

Occam's Razor tells us that the logical reason to add a feature, is to accomplish a purpose that could not be accomplished with what was already there. Cut corners were not put there (originally) to check for vignetting, because there were other ways to do that. They were not put there to allow air to move in and out when focussing, because it wasn't needed. The corners were originally clipped so a photographer could change from a long lens to a very short lens, and then unlock the camera and squish the front and back together -- and not damage the bellows in the process.



If I may mention smaller formats: another camera feature that has fallen victim to revisionist history is the mirror lockup feature on some 35mm cameras. The accepted belief is that MLU is there so we can reduce vibration when taking photos with very long lenses, high magnifications, etc. But the truth is that MLU was invented as a way to mount extremely short (i.e., "wide angle") lenses, in the era before the availability of retrofocus designs. A non-retrofocus lens, if too short, will be so far back into the camera body that the mirror would hit the rear of the lens. So they came up with MLU to get around the problem; you lock the mirror out of the way, then mount your WA lens. Framing was accomplished either by guess and by golly, or by using an accessory viewfinder that mounted on top of the camera. It wasn't long, however, until retrofocus designs became the standard for short focal lengths, making the original purpose for MLU a moot issue. Sometime in the interim, a few people had noticed that they could get much sharper images with their long lenses if they locked the mirror up first. Now almost everyone believes mirror lockup was always there for the reason they use it. Thus was history revised.



...don't think anyone suggested that clipped corners were the only way to check for vignetting. ...the clipped corners are more convenient...

And I never said, that anyone suggested that. I merely pointed out that the addition of clipped corners did not add the functionality of checking for vignetting, since that was already there, and that from a manufacturer's perspective there had to be another reason. Yes, using the clipped corners is MUCH more convenient in practically every case.



The point made (I hope) is that devices and ideas often end up being used for purposes entirely different than what was originally envisioned. History is written by the victors. I guess this is the case in every arena of human activity, not just wars. And so it goes.

Why exactly does Occam say clips prevent damaging the bellows when changing from long to short lenses?:confused: And why doesn't Occam just grow a beard?:rolleyes:

[Jim Andrada]

As someone who does a lot of woodwork I can vouch for it being difficult to get really square recessed/rabbeted corners without clever use of a paring or perhaps a corner chisel which can make messy looking corners if you aren't really experienced at doing it - and even if you are experienced it's still easy to cosmetically muck up an otherwise well done camera back. I vote for this as the real reason because it would cost a lot more money for the maker.

Of course, being a revisionista at heart I'd like to suggest that the corners are clipped so we can have endless speculation as to why the corners are clipped.

[Tin Can]

I made up my own rationalization. Clipped corners do release internal air pressure and aid in preventing dust being forced inside a lens.

Since I started making my own GG, I have found I prefer clipped corners for the 3 most mentioned reasons. I tried square, not as good, and I like peering through the open corners.

And cutting nice corners on small GG is not a doodle. Big ones are easier.