11x14 focal length question

[Motdarnoc]

I just recently acquired an old 11x14 film back. I’d like to build a pinhole using it. That part is pretty simple. However, because of the size and expense of that format I’d like to know what I’m going to get before I shoot. I have a ground glass with the film holder, but, the pinhole would be too small to see anything. I’m thinking I will build the front to accept my 8x10 lens boards, put the pinhole in one board and use my 270mm lens (on a different board) to compose the shot, switch to the pinhole board, and shoot. My question is, how long do I make the pinhole to film plane depth? I won’t be able to focus, so I need to build it to a predetermined focus. Any advice?
Tom

[Mark Sawyer]

I just recently acquired an old 11x14 film back. I’d like to build a pinhole using it. That part is pretty simple. However, because of the size and expense of that format I’d like to know what I’m going to get before I shoot. I have a ground glass with the film holder, but, the pinhole would be too small to see anything. I’m thinking I will build the front to accept my 8x10 lens boards, put the pinhole in one board and use my 270mm lens (on a different board) to compose the shot, switch to the pinhole board, and shoot. My question is, how long do I make the pinhole to film plane depth? I won’t be able to focus, so I need to build it to a predetermined focus. Any advice?
Tom

With a pinhole, everything is always in focus, so no worries. Just extend the bellows to your desired focal length. But be aware that different focal lengths have different optimal sizes for pinholes.

[xkaes]

Check out:

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

[Tin Can]

U may also tape smaller film ON inside your DDS

for testing

I do it all the time

[LabRat]

You can use a much larger pinhole for composition with a very large format, but it won't be very sharp, but enough to compose rough forms on the GG...

Or you can add a matching angle of view finder from a 35mm camera that is close to FL to check about what the film would see...

Steve K

[jnantz]

if you want laser cut holes or zone plates pinhole billy is fantastic
http://www.pinholeedun.com

[Greg]

Finder on top of the camera to compose the shot.

[Motdarnoc]

Thank you all for your ideas! Mostly, I’d like to be able see what the composition will be before I shoot. The larger pinhole just for viewing I’ve tried before with no luck- although not with this big of a format. Steve, any idea what size might work for viewing through 11x14?

Mark, you're right about the pinhole size, but building a box with bellows is way above my pay grade. Whatever the distance is I would have to size the pinhole to that length. I have a bunch of them so no problem there.

Put another way, my question is, if I built the box 270mm deep and attached my 270mm lens, would the ground glass be in focus or close enough? Or would I have to build it to some other length? Like maybe 270mm plus the mm to infinity? This makes my brain hurt…��*��

[Kiwi7475]

All lenses are not exactly true to their quoted focal length down to the first decimal place. A variation of several mm is possible, sometimes even more, which may make you miss focus wide open if you just assume a nominal 270mm. Unless you have another camera with which to make very accurate measurements of the real distance to the film plane, which it’s tricky but doable, it wouldn’t be a bad idea to build in a helicoid into the lens to allows for movement of at least +/-6mm or so. This is what all 3D printed cameras tend to do, to ensure the ability to focus.

[xkaes]

Thank you all for your ideas! Mostly, I’d like to be able see what the composition will be before I shoot. The larger pinhole just for viewing I’ve tried before with no luck- although not with this big of a format. Steve, any idea what size might work for viewing through 11x14?

Mark, you're right about the pinhole size, but building a box with bellows is way above my pay grade. Whatever the distance is I would have to size the pinhole to that length. I have a bunch of them so no problem there.

Put another way, my question is, if I built the box 270mm deep and attached my 270mm lens, would the ground glass be in focus or close enough? Or would I have to build it to some other length? Like maybe 270mm plus the mm to infinity? This makes my brain hurt…��*��

There are lots of tiny "director viewer" / previewers -- zooming scopes. Some of these fit on flash shoes so you can preview what the lens sees. There are many designed for large format cameras -- usually 4x5 -- but you can use any, if you convert the format to the 11x14 " format. So a viewer for 35mm film would work if you convert the 28mm mark on the viewer to 300mm (?) for 11x14", for example.

Another option -- used by many -- is to carry along a small digital camera with a zoom lens covering the angles of view you are interested in. Choose the perspective you like -- or focal length / perspective you want to use -- and adjust it for 11x14".