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A really off-the-wall question...

 
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vic valis



Joined: 21 Nov 2001
Posts: 247
Location: San Francisco

PostPosted: Tue Aug 24, 2004 9:49 pm    Post subject: Reply with quote

...and a really crazy idea I've just had, but you never know. I have a load of old parts I will someday auction off on you-know-what auction site. I think among them I have a functioning focal plane shutter in a body otherwise damaged. Okay so far. Now it gets interesting... what I need is a camera I can use my 9 inch Verito lens with. I currently shoot with my Speed graphic, but for portrait purposes I have the front standard racked all the way out. For some time I've wanted to make a field camera (I always either have a photography or carpentry project going, here's my chance to combine the two). Now I shoot 4x5, and I think my body is one of the smaller formats. I have in mind one of those flat bed cameras where the front and back standards pull out from the center. My question is, if I were to figure out a way to build a new camera body of the sort I have in mind, and I were to set the smaller focal plane shutter in the center, what are the potential problems? I assume it's called a FOCAL PLANE shutter because it is supposed to be as close to the focal plane as possible without scratching the film. Anyhow, this is a crazy idea that just popped into my head I'm only semi-seriously considering it, so I'll understand if everyone out there tells me it's a seriously nutso idea. I can see that being located midway in the bellows, there's going to be some bleeding of light. Would this alter the exposure? Sound off everyone.

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Dan Fromm



Joined: 14 May 2001
Posts: 2148
Location: New Jersey

PostPosted: Tue Aug 24, 2004 10:35 pm    Post subject: Reply with quote

Quote:

On 2004-08-24 14:49, vic valis wrote:
...and a really crazy idea I've just had, but you never know. I have a load of old parts I will someday auction off on you-know-what auction site. I think among them I have a functioning focal plane shutter in a body otherwise damaged. Okay so far. Now it gets interesting... what I need is a camera I can use my 9 inch Verito lens with. I currently shoot with my Speed graphic, but for portrait purposes I have the front standard racked all the way out. For some time I've wanted to make a field camera (I always either have a photography or carpentry project going, here's my chance to combine the two). Now I shoot 4x5, and I think my body is one of the smaller formats. I have in mind one of those flat bed cameras where the front and back standards pull out from the center. My question is, if I were to figure out a way to build a new camera body of the sort I have in mind, and I were to set the smaller focal plane shutter in the center, what are the potential problems? I assume it's called a FOCAL PLANE shutter because it is supposed to be as close to the focal plane as possible without scratching the film. Anyhow, this is a crazy idea that just popped into my head I'm only semi-seriously considering it, so I'll understand if everyone out there tells me it's a seriously nutso idea. I can see that being located midway in the bellows, there's going to be some bleeding of light. Would this alter the exposure? Sound off everyone.

Well, the big risk is vignetting. To reduce it, put the FPS as close to the lens as possible. In the middle may work, but can limit movements.

The lens sends a cone of light backwards. If the ray from the lens' exit pupil to the corner of the film isn't intercepted by the shutter, you're golden. If it is, then you'll lose the corners. Think about the geometry, draw the triangles, and you should be able to design something that will work.

Cheers,

Dan
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vic valis



Joined: 21 Nov 2001
Posts: 247
Location: San Francisco

PostPosted: Wed Aug 25, 2004 3:24 am    Post subject: Reply with quote

Vignetting hadn'd occurred to me... see how little thought I had given the idea. Since then I thought of placing the FP shuter close to the lens as suggested; a fixed shutter up front and moving rear standard, but that's ass-backwards and unstable. The camera would be dedicated to portraiture so I wouldn't need much rise or fall, but could use some tilt and so forth. So my current idea is a front standard connected to shutter by a short bellows to allow some movement, and having the shutter/front standard move as a whole unit for focusing so that the rear standard can stay fixed. It would be easier to just have the lens mounted to s normal shutter, but I like going about things the hard way... and besides, I need a smaller scale woodworking project then my current cabinet project. So long as nobody knows of any problems with the shutter a short distance from either the film or the lens, I may just keep woring on the idea.

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t.r.sanford



Joined: 10 Nov 2003
Posts: 812
Location: East Coast (Long Island)

PostPosted: Wed Aug 25, 2004 3:35 am    Post subject: Reply with quote

Why not adopt a "tailboard" design, mount the shutter right behind the lensboard, and build a swing back? Several classic portrait cameras used this configuration, which allows you to take three-quarter views and swing the back to bring the catchlights in both eyes into sharp focus. And limiting the movements to the back prevents worrying about the rather small image circle produced by the old fast portrait lenses.

Better yet, mount the shutter on a hinged or sliding extension so it will lie snugly against the lens when ready for use, but can easily be pivoted out of the way for focusing.
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RichS



Joined: 18 Oct 2001
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Location: South of Rochester, NY

PostPosted: Wed Aug 25, 2004 3:37 am    Post subject: Reply with quote

I could be wrong, but I don't think your idea is original? I sort of remember hearing about an old shutter that was a sliding curtain design behind the lens (or maybe in froont of it?)...

Anyway, there's another problem you'll face. Shutter speed. With the FP shutter right behind the lens, the effective speed of the moving slit will be much faster than when it was right in front of the film. You could calculate the new speed or test it, but it will be faster...
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jsiladi



Joined: 20 Aug 2004
Posts: 34
Location: midwest

PostPosted: Wed Aug 25, 2004 4:47 am    Post subject: Reply with quote

What difference does it make if the shutter is directly behind the lens or directly in front of the film?? I'm not suggesting you are wrong but trying to understand.. I do know there's a difference comparing between lens leaf type shutters such as the supermatic, and focal plane shutters. However, I don't quite understand why it matters where the shutter is placed when between lens and film (aside from physical construction and size of the box holding all of it)..

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RichS



Joined: 18 Oct 2001
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Location: South of Rochester, NY

PostPosted: Wed Aug 25, 2004 5:23 am    Post subject: Reply with quote

Quote:

On 2004-08-24 21:47, jsiladi wrote:
What difference does it make if the shutter is directly behind the lens or directly in front of the film?? I'm not suggesting you are wrong but trying to understand.. I do know there's a difference comparing between lens leaf type shutters such as the supermatic, and focal plane shutters. However, I don't quite understand why it matters where the shutter is placed when between lens and film (aside from physical construction and size of the box holding all of it)..



I doubt I'd be able to explain this right, but what the heck...

Think of the size of the image.

At the film plane, it's 4x5. The shutter slit is timed for the slit to tavel 4 inches with a certain width slit to give a set effective shutter speed. While the slit is travelling, a section of film is exposed to the light.

Now move the shutter to right behind the lens. What's the image size??? Half inch? Quarter inch? But the slit size and speed remain the same. Combine that with the angle of the light and you're moving the exposed part of the film faster.

In other words (maybe)... It takes the slit in the shutter 1 second to travel 4 inches (not a real number). That gives you the proper shutter spead and exposure. Move the shutter to behind the lens. Now you're still moving at 1 second for 4 inches but your light area is only 1/4 inch high. So the effective exposure would be 1/16 of what it would be if the shutter was at the film plane...

If that doesn't make sense, I can try again at a decent hour of the day
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vic valis



Joined: 21 Nov 2001
Posts: 247
Location: San Francisco

PostPosted: Wed Aug 25, 2004 6:00 am    Post subject: Reply with quote

RichS is correct, I've seen little wind-ups up for auction the work like wind-up packard shutters. Almost bought one, but never thought at the time that 1) I'd ever get it working and 2) still hadn't come up with this idea. yeah, the shutter speeds would be different with the shutter up close; I'd have to recalculate the speeds and come up with a new table. More I think of it, more I'm thinking I should go with a 4x5 body, if I can find one in such bad cosmetic condition that I don't mind giving it a new front standard, ellows, etc. In fact. I'm liking that idea more and more.

jeff

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jsiladi



Joined: 20 Aug 2004
Posts: 34
Location: midwest

PostPosted: Wed Aug 25, 2004 6:32 am    Post subject: Reply with quote

RichS first paragraph answered the question.. I hadn't put together that the traveling light is conical in shape from the lens to the film plane (for some reason, yes, it's late).. It also explains the difference in between the lens types and focal plane types.. Yes, I knew they were different but never thought of why.. I now see the light. Jeff.
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Nick



Joined: 16 Oct 2002
Posts: 494

PostPosted: Wed Aug 25, 2004 11:49 am    Post subject: Reply with quote

Take a look at most of the old portrait cameras on Ebay you won't see much or any movements. That means you don't really need bellows. A simple two box camera will work. If all you want is rear swing then just put a pivot on the rear. Building movements only get complicated when you want multiple movements. Right now some one is selling a 5x7 Ansco portrait camera. Looks like no front movements but rear tilt. Putting axis tilt would be no different then adding swing. Just put the pivots in a different spot-)

So if you can build two boxes that slide together in a smooth way then it doesn't take much more.
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t.r.sanford



Joined: 10 Nov 2003
Posts: 812
Location: East Coast (Long Island)

PostPosted: Wed Aug 25, 2004 2:59 pm    Post subject: Reply with quote

Shutters using fabric blinds and designed to fit in front of the lens were around for a long time. The English seem to have been especially fond of them; my father remembered Thornton-Pickard "roller blind" shutters being marketed right up to the outbreak of World War II, and I've seen descriptions of earlier ones by Kershaw and Newman & Guardia.

BTW, a shutter really needs to be as close to the film or as close to the lens as you can manage; putting one somewhere in between reduces its efficiency dramatically.
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glennfromwy



Joined: 29 Nov 2001
Posts: 903
Location: S.W. Wyoming

PostPosted: Wed Aug 25, 2004 6:16 pm    Post subject: Reply with quote

Thanks to the help of one of our fellow members, I have just completed a focal plane shutter box camera. It is the back section of an Anny w/shutter and a homemade box extension with a 165mm Tessar in focus mount. It looks kind of like a Combat Graphic. Sort of. I had some parts, he had some parts, now we both have new outfits. Great!

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Dan Fromm



Joined: 14 May 2001
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Location: New Jersey

PostPosted: Thu Aug 26, 2004 1:39 pm    Post subject: Reply with quote

Quote:

On 2004-08-24 20:37, RichS wrote:
I could be wrong, but I don't think your idea is original? I sort of remember hearing about an old shutter that was a sliding curtain design behind the lens (or maybe in froont of it?)...

Anyway, there's another problem you'll face. Shutter speed. With the FP shutter right behind the lens, the effective speed of the moving slit will be much faster than when it was right in front of the film. You could calculate the new speed or test it, but it will be faster...

Rich, I'm not sure about that second point. You're right that the shutter's moving slit will cut the cone of light the lens projects in less time, other things equal, when it is closer to the lens. But I drew a sketch that makes me think the length of time the narrow strip of film the slit uncovers will be uncovered is the same regardless of where the slit is located. I could, as often happens, be wrong.

Cheers,

Dan
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