Some screw hooks and rubber bands is all I ever use to keep film holders in place with my LF pinhole cameras. Send me your holder dimensions and I'll cut some pieces for you(though I dont forsee it getting completed by Sunday). I come down to the McKeesport/White Oak/Monroeville area every couple of weeks and will be there the first weekend of May(I was just there last weekend).
Just under the wire for WPPD -- my 8x10 design appears in my PBase galleries.
(Hope I'm not too tired to get out there with it!)
A scanned and inverted copy of the second test shot.
15 minutes on AristaEDU RC #2 graded paper, 4 minutes in Dektol 1+7. The exposure was dragged out, as by the time this sucker was ready to try, day was dying in the west!
Hopefully more will appear elsewhere after daylight ends tomorrow. :D
Originally Posted by DWThomas
The larger the camera the more you'll get light fall-off (vignetting) at the borders. Especially at a scene like in your 2nd shot.
Did you ever try to dodge & burn inside the camera? The principles are the same as in a darkroom.
Here is an example; how to & demonstration:
Bert from Holland
Compensating is an interesting idea (but complicated!) I disagree that it's the camera size, it's the angle of view. As you move off-axis, the round pinhole becomes an ellipse and ultimately narrows to zero minor axis dimension at points 90º off the optical axis. (In real life it happens well before that from mounting hardware, thickness of the pinhole plate etc.)
Originally Posted by TheToadMen
In my shot above, I think the fall-off is only minor. I'm on a wooded property and the sun was about 30 minutes from dipping below the western horizon. So all the trees and shrubs at the sides and foreground were in shadow while the wooded slope in the background was getting direct light.
I'll post some of today's effort later. So far I see one design shortcoming -- I need to add a handle. With no filmholder, the back is open, so carrying it around the workshop was no problem. Alas, in the field, with the filmholder making it a closed box, it's a bit awkward to handle. The weight is not too bad, 2.23 Kg with filmholder (less than five pounds), but switching cameras, even with quick releases, was a pain because it's difficult to handle and control with one hand.
And it just hit me, in addition to the pinhole appearing elliptical (smaller effective aperture) off-axis, the distance from the pinhole to film is also increasing, shrinking the effective size even more. So those two effects compound things. I could probably figure out an equation, but since I retired I don't do trigonometry. :p
Fall-off with pinholes in thin material is equal to the cosine of the angle raised to the 4th power. This means a pinhole camera with a corner to corner coverage of 90 degrees will lose two stops of illumination in the corner, or a bit more if the pinhole edges aren't perfectly sharp.
Originally Posted by DWThomas
(from lazy Dave) :cool: