Shutter mechanisms for pinhole

[MattKing]

Pinhole on 6x9 T-Max 100:

Yes - the larger the film, the "sharper" the pinhole image - once you optimize the pinhole size for the pinhole to film distance.

Part of it, of course, is due to the fact that the larger negative needs less enlargement at the printing stage.

One observation though - using a grain focuser under the enlarger with a 6x9 T-Max 100 negative from a pinhole camera has to be about as challenging an example of using a grain focuser that I've ever encountered - although I admit 120 roll film is as large as I go.

 

[MattKing]

Circling back to the subject of the thread - the reason I preferred using T-Max 100 for pinhole is that it permitted long enough exposure times - faster film makes the manually operated swinging flap shutter hard to be sufficiently precise with.

 

[xkaes]

Umm -- your numbers sound like inches -- Chuck1 was talking 0.05 mm; that might suggest a sub-centimeter hole-to-film distance.

You're right -- I was using inches. Here's a table -- in mm -- that might help everyone:

http://www.subclub.org/fujinon/pinmath2.htm

.05mm would be a very short focal length -- 1.8mm!!!

 

[xkaes]

Circling back to the subject of the thread - the reason I preferred using T-Max 100 for pinhole is that it permitted long enough exposure times - faster film makes the manually operated swinging flap shutter hard to be sufficiently precise with.

Good point, but pinholes can be made in low light as well -- where higher ISO can help (unless you have a folding chair handy).

 

[xkaes]

Why do "larger format" pinholes look sharper?

As the size of the negative gets bigger, so does the size of the ideal pinhole for the same angle of view.-- meaning less diffraction.

Here are the total lines of resolution for each format, from 35 mm to 8x10 -- for a sample/example "wide-angle" pinhole (adjusted for each format).

Lines of resolution is the size of the pinhole x five for daylight.

 

[cliveh]

I think pinhole favors large format. I tried pin hole with the 35mm and the result isn't good.

This can't be true, as the optimum same geometry of height, breath, width must be the same for all sizes.

 

[xkaes]

This can't be true, as the optimum same geometry of height, breath, width must be the same for all sizes.

Read my response above -- larger format = larger pinhole = less diffraction.

Most 4x5 images (with lenses) are taken at f22, while most 35mm camera lenses don't even have f22. Why? Diffraction is greater on the smaller format.

 

[cliveh]

Read my response above -- larger format = larger pinhole = less diffraction.

Most 4x5 images (with lenses) are taken at f22, while most 35mm camera lenses don't even have f22. Why? Diffraction is greater on the smaller format.

But why can't a smaller format use a larger pinhole?

 

[xkaes]

A smaller format can use a larger pinhole, of course, but that increases the focal length. If you read the responses above, the focal length of the pinhole is determined by the diameter of the pinhole. The larger the diameter, the longer the focal length.

You can use any size hole you want on any size format, but your ability to actually form an image depends on the combination of the size of the hole and the distance from the film. The table about shows examples for the best resolution/clarity -- to create an image AND avoid diffraction. If your pinhole gets wider, you lose image formation. If your pinhole gets smaller, you get more diffraction..

 

[cliveh]

A smaller format can use a larger pinhole, of course, but that increases the focal length. If you read the responses above, the focal length of the pinhole is determined by the diameter of the pinhole. The larger the diameter, the longer the focal length.

Don't you mean the focal length of the camera, rather than the pinhole? And are you referring to sharpness re small/large camera in relation to relative pinhole diameter?

 

[xkaes]

I have yet to meet a camera that has a focal length or a "sharpness".

 

[MattKing]

A smaller format can use a larger pinhole, of course, but that increases the focal length.

More accurately, a larger pinhole only gives you something close to an optimum result if the pinhole to film distance is longer.
All the pinhole calculations are designed to balance two factors - diffraction that comes from using a too small hole, and blur resulting from using a too large hole.
The blur that results from using too large a hole is a function of the pinhole to film distance - the longer the distance, the less the effect.
A hole that is too large for the pinhole to film distance used means that there is relatively less diffraction resulting from the hole itself, but too many light rays cross over each other and blur the image.
A hole that is too small for the pinhole to film distance used means that far fewer light rays cross over each other and blur the image, but at the same time the small hole means that there is relatively more diffraction affecting the result.

 

[John Koehrer]

ZERO IMAGE sold a simple shutter for their cameras and may have a picture for an example. IF THEY'RE STILL IN BUSINESS

Don't they have markets in Spain? The English call the "boot" sales, here in the U.S. flea markets. A decent source for old & broken stuff.