Pinhole body cap help please

BADGER.BRAD

BADGER.BRAD

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Hello all,

Ready for pinhole photography day I have made a M42 body cap pinhole using a body cap a drinks can and a 0.32mm diabetic lancet I thought I would give it a go on my DSLR for test purposes. It works but seems to show up black marks like dust or dirt on the sensor but these marks are not there with a lens connected ? Is this just the fact the pinhole is not very clean cut ? I would have thought they would have shown on the edge of the photo.The first photo is taken with 50mm of extension tube and is a lot more focused but narrow and probably hard to point at the subject (using film) the second just with a body cap has wider field of view but is not so focused (check out the number plate.
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basically, it's just the pinhole "lens" aperture is absolutely tiny... the smaller the aperture of a lens, the sharper the shadow that the dust/crap on the sensor casts.

if the pinhole was ragged, you'd get light level inconsistencies around the edge of the frame, rather than dust bunnies in the middle of the screen.

Treat it as a heads up that you were (over)due for cleaning your sensor.


eta: a 0.32mm aperture on a 50mm lens equivalent would be something like f/156 - 6 stops down from a typical lens max of f22
 
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Cheers much appreciated any idea how much a professional lens clean would cost ?
 
As Mark says, tiny aperture + dirty sensor = dust bunnies with sharp edges!

0.32mm is quite big for a pinhole at such short focal lengths, I have a Thingify (Kickstarter) pinhole "lens" which has an assortment of hole sizes from 0.1 up to 0.8 in 0.05mm increments up to 0.35 then 0.5 and 0.8. Not done much experimentation yet (not enough light!) but there is apparently a sweet spot for every focal length, where relative sharpness and diffraction create a (relatively...) sharp image.
 
It's the sensor that's dirty not the lens. A sensor clean is around £50 or so - about the same as 3 or 4 sets of swabs and fluids to do the (fairly simple) job yourself.
 
yep - optimum pinhole size varies with the distance between sensor and the pinhole plate. So for a canon EOS, with a "registration distance" (that's the fancy term for the distance between the sensor (or film) and the front of the lens mount plate) of 44mm the optimal size would be 0.23mm for a Nikon at 46.5mm the optimal size is 0.24mm and for a micro 4/3 camera at 20mm registration distance, the optimal pinhole size is 0.16mm.

to calculate the diameter of the pinhole (d) from the registration distance (D) use the following formula - d = 0.0353 sqrt(D) (I can't remember where I got this formula from, but it was basically a simplification of a much more complex one - a/D = 1.22λ/d, where a is the radius of the diffuse spot, D is the distance from the pinhole to the “screen”, λ is the wavelength of light and d is the pinhole diameter)

if you don't know your registration distance, have a look here - http://www.graphics.cornell.edu/~westin/misc/mounts-by-register.html
 
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That explains why it seem better with the extension tubes on ,giving longer focal length (plus 50mm ) I only brought the extension tubes initially ( they were only £2.09 from ebay) to allow for a more measurable exposure time when using the manual film camera that I could measure by my own judgment (seconds instead of fractions of a second) The extension tubes separate into three separate lengths so it looks like it may be worth trying each length out. The 0.32 mm was the smallest measured size I could find other wise I would have gone smaller.

Again thanks everyone for the info.
 
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I found that I had some needles at 0.23mm but unfortunately I cannot get them through the material used for the pinhole ! On using MrPinholes calculator I have found that using just the 10mm extension gets me very near to the optimal pinhole diameter of 0.32mm so I will have a go at that later. Unfortunately there is a slight difference in focal length between the film camera I intend to use and the DSLR I'm using for the tests but I'm hoping it will be near enough to get some reasonable results.

http://www.mrpinhole.com/calcpinh.php
 
I remember to get the needle through the drinks can I was using, I ended up taking the square of material I was going to use, and placing a sheet of very fine wet and dry paper on some plate glass (to get a completely flat base to work on) then basically sanding the can until I was almost through the metal. That and using aluminium sheet from a tin of Irn Bru pretty much left me with something that I could get even a really fine needle-tip through...
 
I've used aluminium kitchen foil sandwiched between 2 pieces of cardboard (OK, it was a christmas card!) with a fine pin as the piercer. I kept pushing the pin through in tiny increments until I had actually made a tiny hole. Can't remember what the diameter was - it was 40 years ago, although I did measure it with a travelling microscope (it was part of a physics project).
 
another option is aluminium foil adhesive tape - the link is to ebay, where you can purchase a sample length of it (1 metre of 48mm tape) for 99p - that should keep you in pinholes for the conceivable future...

one way of checking the pinhole, if you have a scanner, is to scan the pinhole plate at the highest res that the scanner will do (usually 4800/9600 dpi) and count the pixels of the hole diameter... it also lets you see if the hole is ragged edged or ovalised, so you can scrap it and try again.
 
Thanks Mark I'll try the Ali Foil tape sounds like an ideal way to use the fine needle.I'll post up the results.
 
If you use the "battle damage repair" tape, clean the glue off the area where the pinhole is going - even a tiny bit of fluff will block the hole!
 
Nod said:
If you use the "battle damage repair" tape, clean the glue off the area where the pinhole is going - even a tiny bit of fluff will block the hole!
Click to expand...

yeah, I forgot to mention that...
 
I take it you found that out the same way I did... :whistle:
 
Indeed! (But would you have pushed her?)
 
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