pinhole sharpness

[baronvonaaron]

so i've been doing a series of very long exposures of theatrical set builds and rehearsals. i'm using a laser pinhole with a stack of ND gels in front, to get exposures times ranging from 2 hours to 6 days.

now the exposures all look great, but i've reached a threshold of optimal sharpness that i'm unsatisfied with. i'm thinking of incorporating a lens, but i'm not sure if i should just get a glass lens with a shutter and stack even more NDs in front, or somehow make a frankensteined pinhole/lens chimera? i don't even know where to start doing research on that.

I know I'm not the first photographer to be doing long exposures like this, so I'm hoping somebody here has some experience.

here's some photographic evidence (dust included for scale):

[Graham Patterson]

Without knowing the pinhole to film distance and the size of the pinhole, it is going to be hard to judge if you are hitting practical limits. A 'stack' of ND gels would be better replaced by fewer, denser ones - the fewer surfaces the better. There is a practical limit on sharpness - the optics industry developed for a reason, after all 8-)

[Jac@stafford.net]

Pinhole photography has no sharpness. It is what it is.
You might consider using a lens.
.

[Jim Noel]

You are taking an already not tack sharp pinhole and multiplying it's softness with a stack of filter gels.

[xkaes]

If your goal is just long exposures, just get a VERY dense ND filter and put it on the lens. If, for some reason you want to use a pinhole, you need to handle the pinhole in certains ways. Here are two websites to help you calculate the f-stop of your pin-hole(s) and the focal length(s) that will produce the optimal (i.e., sharpest) results:

http://www.mrpinhole.com/index.php

http://pinhole.stanford.edu/pinholemath.htm

Sharpness will depend on the diameter of the pinhole, as well as getting it focused correctly, which depends on its focal length.

[loonatic45414]

Just to add my 2 cents. Finding a really slow film helps cut down on all the filters. Think copy film or inter-negative film, maybe even microfilm (but use a low contrast developer with the latter).

6 days?? I'd look at lengthening the pinhole to film distance which lowers the amount of light reaching a given spot on the film.

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[baronvonaaron]

the sample image is without any NDs at all. and i've used the mr pinhole calculator to construct my camera. the focal length is 90mm with a .3mm hole i believe.

i'm not necessarily married to pinhole, it's just the path of least resistance when i started to project. i've tried out copy film, but the box i have is quite fogged and has some fungus, so i'm reluctant to purchase more. are new batches being manufacture still?

[baronvonaaron]

i guess it's time to break out the view cam for this project. one of the reasons for going pinhole is how inconspicuous my camera was.

[stawastawa]

two things,

* one not mentioned is that (I believe) Sharp edged and thinner pin holes make sharper images. so if you can use a good loop or place the pin hole in an enlarger and check that the shadow is even and not jagged that would be a place to start. If you can use thinner material, try it and see what that changes.

* The other is roundness. It looks like you have a nice and round pin hole, which is also helpful (oval shaped and the fuzzy edges on the light-sources shown would not be equal.)

* ( I also second the motion to replace stacks of ND with a single ND if possible, but your example shows that the issue is there without the ND's to begin with)


And if you do have to go view camera, a view camera can be very inconspicuous too. Think kodak brownie type box with a compact 65 or 90mm lens. maybe paint the chrome bits black. Good luck!

[Ted R]

six days! ? vibration? thermal expansion and contraction?