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ImageMaker
04-23-2005, 10:22 PM
Watch this thread -- this morning, before my wife was up, I made a pinhole "lens" to fit one of the two interchangeable shutters I have for my 1927 Zeiss-Ikon 250/7 Ideal (9x12 cm plate camera). The hole was my first from .001" brass shim stock, using a #10 embroidery needle, and it was easy to get within about .001" of the desired .018" hole diameter. It was also easy to construct the "lens" housing from black posterboard -- it fits into the front of the shutter in place of the front lens group, and the rear group is removed; this allows me to use the shutter's timed speeds (though I won't need them unless I'm using TXP and Diafine to get EI 1000), as well as the B and T settings for longer exposures.

The first test exposure is drying now -- f/300, 88 minutes in my dining room/kitchen, and it's a little underexposed (not enough reciprocity compensation -- only 3x, should have been about 6x, but I couldn't leave the camera up for 3 hours).

I also took a number of digital pictures while I was working, and will upload those on this thread when I have time to resize them. Meantime, I'm ready for WPPD and the f295 challenge -- I can develop and scan single exposures easily, instead of having to shoot a whole roll of 36 and find the time to develop and scan a whole roll. And the resulting image *ought* to look a lot sharper, with the much larger negative, than the .014" hole on a 24x36 mm frame...

ImageMaker
04-26-2005, 08:52 AM
Okay, now that I have my computer working again, I've been able to process the digital images I took while making the pinhole lens replacement to fit my 1927 plate camera.

This first image shows the shutter I used, which is from a slightly older version of the camera (1926 or older), and is a spare. The glass was removed and carefully put away against future need (no breaking out the glass here, not when it unscrews easily and is excellent quality glass in excellent condition). Please pardon the focus -- the camera has auto-focus, and the LCD screen is so small it's impossible to see the defocus on the display. Attached files http://f295.f295.org/uploads/shutter1_6856.jpg (http://f295.f295.org/uploads/shutter1_6856.jpg)

ImageMaker
04-26-2005, 08:56 AM
The first order of business was to cut a piece of black poster board to fit past the internal threads and sit on the steeply tapered area just ahead of the original shutter. I had originally planned to put the pinhole behind the shutter, but there isn't enough clearance over the diaphragm, and I didn't want to risk damaging the shutter (almost 80 years and it only needed a little cleaning -- I won't be in such good condition when I'm 79!).

Attached files http://f295.f295.org/uploads/insert1_1731.jpg (http://f295.f295.org/uploads/insert1_1731.jpg)

ImageMaker
04-26-2005, 08:59 AM
Now I needed to make a hole in the insert through which the pinhole (routine fabrication for this group, I didn't see any need to document that process) would peep. If I'd had one handy, a heavy 1/4" plier type hole punch would have worked nicely, but since I didn't, and have a set of these hollow punches, I used this -- took the stuff outside, set the wood block on a brick wall, centered the punch as well as possible, and whacked it sharply with a 250 g machinist's hammer, which (if the punch had been sharp) should have produced a nice clean hole. As it was, the punch was dull (teach me to trust the workmanship of cheap Chinese tools) and left a rather ragged, but serviceable hole.

Attached files http://f295.f295.org/uploads/punch1_3799.jpg (http://f295.f295.org/uploads/punch1_3799.jpg)

ImageMaker
04-26-2005, 09:04 AM
Now the insert goes back into the shutter, and a strip of the same poster board is cut to exact length to fit around the edge; inserted in the shutter threads, it holds itself by tension, and is secured with a small piece of black masking tape, then with fit verified and the curve evened out over the circumference, is glued in place with a very light bead of white all-purpose glue (polyvinyl acetate, aka craft glue) -- though pretty nearly any glue would work for this. This is not a light-tight joint, it merely serves to keep the flat piece located and snugly bedded against the inside of the shutter; light that goes through this joint still has to reflect two or three times from the dull black interior surfaces of the shutter housing and/or the black poster board insert to find its way through the shutter's aperture and appear as fog (and if this is noticed as a problem, closing the shutter's aperture to f/32 gives only a 2.5 mm hole for the light to go through and should eliminate the stray exposure).

Attached files http://f295.f295.org/uploads/collar1_7463.jpg (http://f295.f295.org/uploads/collar1_7463.jpg)

ImageMaker
04-26-2005, 09:07 AM
Finally, the pinhole itself (blackened with a Sharpie permanent marker on the film side, left bright on the subject side so it's obvious this isn't a common glass lens) is attached to the back side of the insert with black masking tape. Here, two strips are in place, but two more will be added to completely secure the .001" brass shim stock pinhole.

Attached files http://f295.f295.org/uploads/complete_744.jpg (http://f295.f295.org/uploads/complete_744.jpg)

ImageMaker
04-26-2005, 09:17 AM
With this completed, the above assembly is reinserted in the front of the shutter, and the shutter mounted to the plate camera (this camera is nice for this because it has a bayonet mount on the front standard and matching bayonet on the shutter -- I can change from one to the other in seconds). The collar does protrude slightly from the front of the shutter's threads, but I have to open the aperture and shutter and reach from behind to push the insert out, rather than being able to pull it with the collar. However, the collar does act as a "lens" shade to keep direct sun off the pinhole aperture, at least if the sun isn't too close to the image axis.

This setup allows me to use a familiar camera body, large format sheet film in holders (I have ten holders that fit this camera, each holding a single sheet of 9x12 cm film), and even take advantage of the movements the camera has (for instance, to control perspective so that a shot of a building doesn't have converging verticals), but also has the capability to be used as a "zoom" pinhole -- the camera's focus mechanism can give useful focal lengths from about 90 mm to well over 200 mm, and though the hole isn't optimum at those other lengths, it isn't far enough from optimum to cause a large degradation of image quality. Care must be taken, of course, to ensure the correct effective aperture is used when focal length other than the "infinity stop" position (which gives approximately 138 mm, due to the pinhole's position ahead of the shutter's diaphragm) is used.

In the test exposure, the original scan (5.5 megapixels even at only 600 ppi) shows considerable fine detail that isn't visible in the image "Breakfast Ghosts" as resized for web viewing -- this lens setup is capable of producing very good images on a steady tripod. I look forward to using it, starting with WPPD (film in the tubes waiting to be developed) and the f295 Challenge (yesterday's images still in the plate holders, waiting their turn).