Any design tips on constructing a darkslide light baffle for a plate holder?

[smieglitz]

Anyone have a good idea for construction of a light baffle in the darkslide slot of a plate holder? I'm making a full-plate wetplate holder and have limited woodworking skills. I'm trying to fit an acrylic insert, flush hinged door with spring and the darkslide slot and light baffle into a holder about 1.25" thick or less.

I'm thinking of using some satin fabric surrounding a small channel on the side nearest the plate. The opposite side would have a bent piece of metal covered with felt or flannel that would spring across the gap hopefully into the opposite channel. I thought I might also pair these from oppposing surfaces if I can fit them in. That way they would overlap in sort of an offset "V" shape. What would be the best metal strip to use for this application?

I've also thought of using a wooden dowel that would rotate across the gap and into the opposite channel. Wonder how I might reinsert the darkslide with this arrangement though?

Another thought is a hinged flat pushed upward and across the gap by a small spring. The flat would be just wide enough to enter the opposite channel.

I'm trying to design this so I can disassemble the holder to change the baffle material in case it wears.

Any other ideas?

Thanks,

Joe

 

[Neil Miller]

Hi Joe,

This diagram might help...

wetplate back diagram

It looks like a half bullnose slat of timber is used, set against something springy, that locates into a partial groove made on the far side of the darkslide. It seems like some of the downward slope of the bullnose is left in the channel so that the darkslide can push it aside when reinserted.

I was thinking of building a back using this method or with a circular dowel locating in a partial groove, but haven't got round to it yet. I was also thinking of attaching something to the bottom of the darkslide once it is in the channel to stop it from being withdrawn completely and which would also help block extraneous light.

All the best,
Neil

 

[David A. Goldfarb]

The light trap in a film holder is usually a kind of springy brass comb covered with black felt. I'm not sure where you can get this brass comb material, but I'm fairly sure it's out there, perhaps for some other application. Maybe Sandy can offer some suggestions.

You could also cannibalize an old 8x10" wooden holder for the light trap. I think Graflex holders are usually made with screws, so they're not too hard to take apart. You could reuse the comb, cut it down to size, and replace the felt.

 

[smieglitz]

...
You could also cannibalize an old 8x10" wooden holder for the light trap...

Forgot to mention the plate holder will be designed as a square with a cross-like arrangement to hold plates either vertically or horizontally so I need to have the baffle width exceed the 8.5" dimension by about an inch total. That rules out grabbing a spring from an 8x10 holder (I think) and I don't really want to cannabalize one of my 11x14 holders for this.

I do have a old 11x14 Graflex film holder that I've taken apart at the darkslide light baffle and it looks like a very thin piece of spring steel (0.025"?) is in there covered by felt. I found some spring steel at McMaster-Carr so maybe I'll buy a piece of that and see how it works.

Joe

 

[Donald Miller]

One of the common metals used for the "comb" on a darkslide is beryllium copper. As a metal it wouldn't be subject to the same considerations of corrosion that steel would experience.

Small Parts sells it.

It pays to protect oneself for possible inhalation of any dust from the material if you work with it (perhaps if grinding).

 

[smieglitz]

Hi Joe,

This diagram might help...

wetplate back diagram

It looks like a half bullnose slat of timber is used, set against something springy, that locates into a partial groove made on the far side of the darkslide. It seems like some of the downward slope of the bullnose is left in the channel so that the darkslide can push it aside when reinserted.
...
Neil

Neil,

Thanks for the link to that diagram. It looks like it would be simple to construct and it should work. A weak compression spring or maybe something like compressible foam rubber in the rear of the thing might be sufficient to allow the movement in both directions.

Thanks again for the tip.

Joe

 

[Jim Chinn]

The material in question is commonly called "fingerstock". I measured some out of an 8x10 holder once and IIRC it was .010" steel. Don't get stainless, way to brittle to bend. fingerstock comes in strips with the bottom half solid and the top half cut so there are gaps leaving "fingers". I suppose this is to account for discrepencies in surfaces allowing the fingers and covering material, in our case felt) to better fit against various materials.

I think its primary use is in the electronics industry.

As someone else pointed out you can buy the steel from various suppliers (MSC, McMaster-Carr, Reid Tool and Supply) and make your own.

If you want to get real serious (especially if one considers the cost of ULF film or the time involved in coating a plate) you can use two baffles, one mounted to the septum and the other in a channel above the darkslide slot. Mount one ahead of the other so the end of the darkslide completely clears the first one and allows it to close.

You may read about some people using a neoprene similar to what is used for windshield wipers. Not a good choice. All neoprene will eventually deteriorate, even without exposure to UV. The surface turns to dust and will end up on either the wet plate or the negative.

Oh another good source for all kinds of thin steel of this type is Brownells. they sell gun and gunsmithing accesories and tools.

 

[c.d.ewen]

http://www.surplussales.com/RF/RFFingerstk-1.html

 

[smieglitz]

I wonder if the spring material used with weather stripping on aluminum screen doors is similar?

Thanks everyone for the tips and pointers.

I worked on the holder for a couple hours today and I think it will eventually work. This project has been challenging. If I were to start again, I think I would design the holder first, build it, and then start designing the rest of the camera around the holder. I think it will turn out to be the most difficult and critical part to make.

Joe