Homemade "drop slit" shutter, for Jdef and everyone else too

[Foto Ludens]

I was trying to attach these images in a PM to Jay, but since I can't the rest of you will have to see them as well (goodbye, future patent and fortune ).

This is the "drop-slit" shutter I made for my barrel lens. The bracket that hugs the lens is made out of foam core and shoe goo, and it tested very well in the field. It holds well, and it allows for easy turning (this lens twists the whole barrel as you change the aperture).

The shutter board (made out of mat board) hasn't seen any field use, but a it tested out at 1/5 of a second with my homemade speed tester (someone posted a plan here, a while back, at that's what I followed). I plan to make boards for speeds up to 1/100, but higher than that might be tricky. Anything less than 1/5 can be done by manually covering the lens, so no worried there.

The only problem I can think of is wind affecting the descent of the mat board. Other than that, provided I hold the board right, the shutter has tested out very consistently.

I'll try to build faster speeds and test this set up on the field soon. But seeing as my film has an e.i. of 3, I'll have to get a different film for this. I'm in the process of testing some JandC and Foma films, and I should have a faster film in a couple of weeks or so.

Anyway, hope this helps out other shutter-less APUGers.

André

 

[PhotoPete]

I know this post is not directed at me, but this is the coolest thing I've seen all day. A little weight on the board may help cancel out some wind effects and overcome most of the friction between the board and its holder. I bet you could get some adjustments to the speed with a longer board with the opening higher up on it. That way, the board is in freefall longer and going faster when the opening passes before the lens. Do you make the faster speeds by using a smaller opening, the way a curtain shutter does?

 

[Foto Ludens]

Pete,

No worries about the post not being directed towards you, I just put "for Jdef" so Jay would find this easily. I agree that a little weight might help with friction and wind, and I might make the next speed that way, just in case. I don't know if adding weight would change the speed on this one, though. I keep thinking about that "all objects fall at the same speed" deal. I can always put that to the test .

As for making different speeds, you got it. Smaller openings should give me smaller speeds. In fact, an opening half as big should give me a speed one stop faster... That'll be my starting point for the next one, anyway. I believe that I can get to 1/100s without much trouble, but faster than that might require too small of slits to be practical.

Thanks for the comments,

André

 

[big_ben_blue]

I keep thinking about that "all objects fall at the same speed" deal.

You listened too much to your old highschool physics teacher, LOL.
Remember, the "same Speed" thingy only works in an ideal environment without any resistance from air and friction from foamboards.

Cool shutter - have to try it one day myself.

Chris

 

[Michel Hardy-Vallée]

Very cool idea. It's like a focal plane shutter but not on the focal plane (perhaps you still stand a chance for the patent!) I would easily see a production version of this made of something a bit stiffer like plastic: you push some lever down and it moves an interchangeable obturating board in the grooves.

 

[David A. Goldfarb]

You should be able to get pretty good speeds like this. The focal plane shutter on my 5x7" Press Graflex can do 1/1500 sec. with the 1/8" slit at maximum tension.

 

[Lee L]

People have also done higher speed shutters with the same basic layout, and achieved higher speeds by loading the shutter gate with springs or rubber bands.

Lee

 

[rbarker]

Nice job, Andre. I'll have to try making one of those for my 600mm APO Nikkor monster.

 

[phfitz]

Hi there,

Andre, you could try a few of the small squeeze-on fishing weights for more weight on the matboard for more speed without rubberbands.

Just a thought.

 

[argus]

Cool!
Must try that.

G

 

[markbb]

Remember, the "same Speed" thingy only works in an ideal environment without any resistance from air and friction from foamboards.

Chris

Taking aside friction, wind, etc. the speed is not a function of mass. However, it is a function of 'g', which varies with location, ie at sea-level it is 9.780 m/s² at the equator and 9.832 m/s² at the poles. Obviously height above sea-level will also affect the speed.

 

[Murray@uptowngallery]

Someone tried to dissuade me from doing non-FP slit shutters behind a lens, claiming there would be some visual (refractive?) artifact introduced.

I assumed something similar would occur in front, so I began considering 'full opening' panels...more along the lines of the 'shooting plane' type discussed in ...oh, gotta run,, fire alarm at work...

 

[Murray@uptowngallery]

OK, the cafeteria keps burning toast in the morning, and there was freezing rain outside!

I would prefer a slit over a full opening, as I'm looking at doing this to an Aero-Ektar 309/2.5 which is over 6" diameter. For a full aperture and before and after space, that's a pretty long board!

How do you like the results?

 

[noseoil]

Andre, wonderful design and great idea. I have a similar lens in 480 (Nikkor f9) for my 8x10 I want to try this on, as the lens cap shutter seems to lend itself to camera shake. This looks so simple it must work. For a good slow film combo you might want to try Efke 25 at asa 6 with pyrocat and azo. Seems to be a great combination and prints very nicely. Might be better for "speed" with this rig of yours. A couple of questions come to mind.

Is the moving shutter able to keep enough light out before it is dropped to be effective against fogging, or must it be dropped as soon as the darkslide is pulled? I may try one with a couple of layers of foam core to prevent light leaks (like a packard) so there is a sandwich effect to make a light trap.

Would it be better if the lens side were black?

Thanks for posting this one, can't wait to try it! tim

 

[Ole]

I've been thinking along similar lines...

I have several shutterless lenses which I'd like to use wide open, but my hat just isn't quick enough even for an f:7.7 Aplanat at full opening outdoors. Or maybe "modern" film is just far too sensitive?

I have a packard shutter I could mount inside the camera, but I don't like having to make another hole in the camera(s). I could make a front mount for it, but that would only fit with some lenses, which isn't what I want either.

So I thought about a slit shutter inside, where the shutter "blade" is kept up by means of a magnet on the outside. Set up, focus, remove GG (which I have to do anyway, since I'm using a plate camera for this), then put the shutter plate in place. Hold it up while fitting magnet on top of front standard. Then insert plate holder, pull dark slide, pull magnet. Shutter plate drops, exposing film.

Sound sensible?

 

[Struan Gray]

What happens when you tilt the camera?

 

[knutb]

I have been thinking about a falling/sliding slit plate shutter as well... Seems like a simple starting point for a home made device.

What happens when you tilt the camera?

That has been one of my concerns too. When the camera is tilted, only a component of the gravity force will act on the slit plate. Tilted an angle X the acceleration should be: a = g*cos(X), not taking friction losses into account. So I think the relevant question is how much you will tilt the camera (or more accurately, the front standard). Assume a 20 degree tilt: a = g*cos(20) = 0.94g, ie. a reduction of 6%; not much in this context.

As mentioned somewhere above in this thread, a slit plate driven by a eg. a spring could be an alternative. If oriented so that the plate's motion is not affected by gravity, the shutter time should not be influenced by tilt. When doing the simple math above however, it seems the gravity version should work just fine in the majority of situations, at least for me. In any case the principle is so simple and reliable that it's worth a try.

Thanks for the inspiration!

 

[127]

Someone tried to dissuade me from doing non-FP slit shutters behind a lens, claiming there would be some visual (refractive?) artifact introduced.

There will be artifacts but any shutter introduces artifacts...

The FP shutter is probably the worst, as different parts of the image are exposed at different times, producing stretching, compression or skewing effects depending on the movement of the object relative to the camera.

Moving the slit closer to the lens will expose more of the film at the same time, and the effect will be reduced. There may be some DEfractive effect if the slit is very small, but it's likly to be negligable for a large slit.

Then the shutter reaches the focal node (as in a leaf shutter) then the whole image is exposed simulataneously, but the level of exposure varies over time. In fact this is a GOOD thing - low efficiency shutters actually produce nicer images!

A shutter between the lens and the FP will behave somewhere between the two designs...

The degree of effect dependant on the speed of the objects - if nothings moving then there's no problem.

Ian

 

[argus]

So I thought about a slit shutter inside, where the shutter "blade" is kept up by means of a magnet on the outside.

Sound sensible?

Sure. Add this: magnets can be controlled by electricity.

Since I am a total loser at electrical wiring etc. - I have to taste 220V each and every year - I won't give you any tips on how to do it.
Maybe add a timer to activate and deactivate magnets. Tilting the camera won't be a problem any longer.

I should get a patent on this

G

 

[Ole]

Sure. Add this: magnets can be controlled by electricity.

Since I don't like the taste of 230V, nor the smell of dead batteries, I take great comfort in the fact that magnets can be used without electricity too

 

[Struan Gray]

Sliding friction will go as the cosine of the tilt angle too, although the coefficient will vary with the materials you use. A strip of low-friction plastic conduit on the edges of the shutter might help. Something like the plastic mouldings used to hang up posters would be cheap and workable.

I have heard of rubber-band driven versions that are surprisingly repeatable, but the rubber band will age unpredictably. A 'pusher' of flexible plastic or spring steel might be useful to get the shutter started, even if gravity does the rest.

 

[Wilbur Wong]

You have a very nifty workable shutter there. If one were to be nit picky about it, it probably acts slightly like a graduated neutral density filter with more exposure toward the sky which might not be desireable.

The dropping of the board must follow the laws of gravity with an acceleration of 9.8 meters per second per second. In other words it keeps going faster after it is released. Perhaps if it had more free fall before the slit goes by, it would be more consistent in exposure.

A refinement you might make would be to incorporate a variable size slit within one single board.

 

[Wilbur Wong]

Placing the slit behind the lens, or near the film would cause more exposure to the foreground, and less for the sky!

 

[phfitz]

Hi there,

Ole:"I have a packard shutter I could mount inside the camera, but I don't like having to make another hole in the camera(s). I could make a front mount for it, but that would only fit with some lenses, which isn't what I want either."

The 'Rembrant' portrait cameras have a rebate between the front standard and bellows for an air tube for the packard shutter, virtually invisible.

For Agfa/ Ansco or Korona type front tilt cameras, an air fitting in the camera back, lower left corner in landscrape, lower right for portrait and a rubber hose that stays inside the bellows.

Both work well, have fun with it.

 

[Ole]

... But it would interfere with the folding of this one:

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And even worse with this one, I fear:

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