Pentax 67 pinhole size

[markbau]

I have a spare body cap for my 67 and would like to play around with making some pinhole images. What size hole would I have to drill into a metal plate embedded into the body cap to get a workable aperture?

Thanks for any help.

Mark

 

[Jim Jones]

For best results it depends on the distance between the pinhole and the film. A good free program for determining the pinhole diameter is www.pinhole.cz/en/pinholedesigner/www.pinhole.cz/en/pinholedesigner/. Much information on pinhole photography and camera improvising is at http://www.f295.org/main/forum/ and Dead Link RemovedDead Link Removed. Drills small enough for this application are scarce and fragile. Pinholes are often made by slightly penetrating very thin material (usually brass or aluminum) with a needle, sanding off the burr that this produces, and repeating the process until the desired size is reached. It isn't difficult.

 

[Jeff Searust]

Use several formulas for determining pinhole size. They will all be slightly different--- See Eric Renner's book also.

I had a drill bit for doing pinholes at one pint, and I dropped it on a linoleum floor from about 3 feet and the bit broke into 3 pieces.... that's how tiny and fragile they are. Go for the needle method and measure with a scanner.

 

[Loris Medici]

A nice formula is: SQRT(2.44 x .00053 x focal length in mm)

For instance, the optimum pinhole size for (say ...) 60mm focal length would be:
SQRT(2.44 x .00053 x 60) ~= .2786mm ~= 280um

Note: .00053 is the median wavelength (in mm) of green light.

Hope this helps,
Loris.

 

[TheToadMen]

For best results it depends on the distance between the pinhole and the film. A good free program for determining the pinhole diameter is www.pinhole.cz/en/pinholedesigner/www.pinhole.cz/en/pinholedesigner/.

+1

 

[markbau]

Thanks for the replies. Unfortunately I am 100% Mac so the program wont run on my computer. I should have no problem drilling small holes as I've been doing it since I was 15 building scale models out of brass, the smallest hole I regularly drill in 30 thou brass for my model work is 0.34mm (.0135") As best I can measure the pinhole to film distance on my 67 is 55mm (approx 2 1/4 inches)

 

[SMBooth]

if the film to hole distance is about 55mm then a pinhole diameter of .3mm is fine, your .34 will work fine to just adjust the f stop. That's f183 for the .3mm and f161 for your .34mm

 

[Poisson Du Jour]

if the film to hole distance is about 55mm then a pinhole diameter of .3mm is fine, your .34 will work fine to just adjust the f stop. That's f183 for the .3mm and f161 for your .34mm

The film plane to inner flange distance would be 55mm, yes. But a body cap adds about 8mm (the Pentax one I have), placing the pinhole further away? I noticed this when I put the body cap on the 67 earlier. Just a thought. I have been mulling a pinhole for the 67 for a few weeks now. Most interesting.

 

[markbau]

I was allowing for the lens cap. My measurement wasn't exact as I couldn't get the mirror up as I have a roll of film in it. I never have figured out how to fire the shutter without film in the camera even though I've owned it for 20 years, just never needed to!

The film plane to inner flange distance would be 55mm, yes. But a body cap adds about 8mm (the Pentax one I have), placing the pinhole further away? I noticed this when I put the body cap on the 67 earlier. Just a thought. I have been mulling a pinhole for the 67 for a few weeks now. Most interesting.

 

[markbau]

Is there any reason not to make a bigger hole so that the exposures are shorter or am I missing something? f161, according to the sunny 16 rule, would be approx 2 second exposure meaning I'm in reciprocity land even on a sunny day!

 

[SMBooth]

That's pinhole! If you make the hole bigger it will soften the image. But try it,you may like it.

 

[Loris Medici]

Is there any reason not to make a bigger hole so that the exposures are shorter or am I missing something? f161, according to the sunny 16 rule, would be approx 2 second exposure meaning I'm in reciprocity land even on a sunny day!

Hi Mark,

What film is that? ISO 100 film will need 1 sec. exposure. There's not much point in using high resolution ISO 25/ 50 or 100 film; just use ISO 400 film when shooting pinhole. With 400 film, your exposures will be around 1/4 sec. (@ F161) in bright / sunny days. Since your format is (relatively) small (I do 4x5 pinholes), you'd better opt for the sharpest possible result. Pinhole doesn't look that nice to me for smaller formats, but that's highly subjective...

Regards,
Loris.

 

[ChuckP]

I've noticed that the person selling one on Ebay indicates a 75mm focal length.

 

[Poisson Du Jour]

Is there any reason not to make a bigger hole so that the exposures are shorter or am I missing something? f161, according to the sunny 16 rule, would be approx 2 second exposure meaning I'm in reciprocity land even on a sunny day!

Exposures can go from 2 seconds to XXX minutes on a pinhole camera. Don't sweat over "long" exposures. Who cares about reciprocity. A pinhole photograph will not be perfect, but it will be a very nice artistic variation on the bog standard photography of SLRs, digital, and anything else you can think of. Be it noted that the nature of pinhole cameras is to record the image in time — often a lot of it. DaVinci took 5 weeks to record the Sun's movement in the Tower of Winds using the first known pinhole!

 

[Poisson Du Jour]

I was allowing for the lens cap. My measurement wasn't exact as I couldn't get the mirror up as I have a roll of film in it. I never have figured out how to fire the shutter without film in the camera even though I've owned it for 20 years, just never needed to!

The best and safest way is to load a dud roll into the 67, or try two empty spools loaded. A slender penny-sized tool is used to tweak the winding mechanism to allow 'dry firing', however, Pentax has never been too keen on dry firing: the camera was not designed for it; that is to say, it will only cock the shutter and initiate the winding mechanism when film is loaded. It is also too easy to damage the shutter curtain or mar the mirror. And old roll of film in it will be a much safer way to examine things.

 

[SMBooth]

To dry fire open the back and then use your finger to roll the film counter past 1 or 2 hold it there and close the back, wind and fire all you like. A dud roll will not stop you being a klutz a breaking sometime though. If you just want to check the film flange distance open the back and measure the distance between the pressure plate and camera back then measure the flange to back and subtract that measurement, won't need to stick thing into the camera unless its for pleasure

 

[Dr Croubie]

Hi,
Just on the difference between drilling a cap and poking a piece of aluminium foil, the generally-accepted theory is that foil is best, because thickness matters a lot. Including the sanding, that's designed to make it as thin as possible. Here is a bit of an explanation of how it affects angle-of-coverage. I thought there was another effect on other things but my google is failing me, or maybe that's the only problem.

I'm thinking of my lens caps, they're generally 1-2mm thick, way too much for a real hole. If you weren't already going to, I'd drill a 10mm or so hole in the lenscap and attach a piece of foil or otherwise to that...

(Or take the lazy way out and buy a Skink Pinhole kit like I did)

 

[markbau]

I will be drilling into very thin brass (not sure what thickness yet) and then drilling a wide flat bottom impression into the body cap (that has a small hole drilled through it) that the drilled brass will slip into, this way I can have several different size pinholes to experiment with. Still working on how to hold the brass plate into the body cap

Hi,
Just on the difference between drilling a cap and poking a piece of aluminium foil, the generally-accepted theory is that foil is best, because thickness matters a lot. Including the sanding, that's designed to make it as thin as possible. Here is a bit of an explanation of how it affects angle-of-coverage. I thought there was another effect on other things but my google is failing me, or maybe that's the only problem.

I'm thinking of my lens caps, they're generally 1-2mm thick, way too much for a real hole. If you weren't already going to, I'd drill a 10mm or so hole in the lenscap and attach a piece of foil or otherwise to that...

(Or take the lazy way out and buy a Skink Pinhole kit like I did)

 

[Jim Jones]

One way to have interchangeable pinholes and zone plates in a body cap or in a home-made camera is to mount a filter with the glass removed in the cap or camera. Another filter ring can retain a disc with the pinhole or zone plate. A third filter with opaque material substituted for the glass works as a shutter for longer exposures. A handful of old filters all the same size can be cheap online or in some camera stores.

I usually use .002" brass shim stock for pinholes. Thinner shim stock is more difficult to work with. Thicker shim stock is unnecessarily thick. For critical results, the pinhole diameter is important. I'd use about .010" for a 55mm focal length, based on testing for optimum central sharpness. A slight increase in diameter will favor off-axis sharpness. Making the pinhole large enough to significantly reduce exposure will yield awfully unsharp images.

 

[edp]

Fuji Acros has excellent reciprocity characteristics, making it great for pinholes.