16"x12" camera, cant get a sharp negative

[Roseanne]

I have a 16"x12" camera, ebay from Russia, that whilst sharp on the ground glass (which broke in transport so I had to replace) when I expose a sheet of film in the old wooden dark slide, it come out out of focus. Im using a orthocromatic film, El Camera by Kodak, that is intended for graphic work I think. I tape it into the dark slide that I think was intended to take a glass negative.
Can anyone advise me as to why my negs are out of focus please? It seems that focus is further away than what appears sharp on the ground glass.
I would appreciate any help on this. Thank you.


www.roseannelynch.com

[ic-racer]

Do you know how to measure the T-distance?

I guess even if you could measure it, who knows what it is supposed to be. The correct T-distance for 16x12 is not listed in the chart on this page, though I suspect it should be 0.354" : http://www.filmholders.com/filmho1.html

[Robert Perrin]

From your description, the film and the ground glass are not in the same plane (distance from the lens). My first thought was if the film holder is made for glass plates, the film being thinner may not be the correct distance back from the face of the holder, but if sitting too far back it would focus closer rather than further. I'd suggest that you remove the focusing back and accurately measure from the front where it fits against the camera to the ground glass (be sure it's the frosted side) then tape a negative into your film holder and measure the distance from the holder face. If they are not the same one or the other should be modified to match. Alternately, at least to test, you could try moving your lensboard or back the exact difference between focusing and taking the picture.

[Michael E]

I tape it into the dark slide that I think was intended to take a glass negative.

You should start here. The plane of focus is on the front of the glass. If you tape the film to the back of the holder, your focus must be off at least by a couple of mm. I don't know if this is enough to throw the focus off (you probably stopped down the lens), but this is definately wrong. Also, how do you tape the film? If it can curl away from its position, this might be worse than the aforementioned.

Michael

Edit: Too slow...

[Jay DeFehr]

Try taping your film to a sheet of glass cut to fit your holder. And you don't have to use a full sheet of film; you can tape any size piece you like to the glass. You can even use paper instead of film, which might speed up your testing iterations. Good luck!

[Robert Perrin]

Focus on the film further than the ground glass? To clarify what I just touched on in my earlier comment, be sure that the replacement ground glass is installed with the frosted side toward the camera lens and also if a fresnel is installed that it is on the plain side of the ground glass, not the lens side.

[Daniel Stone]

just wondering,

IF the OP was to install the g/g BACKWARDS(so frosted side to him), would it give him a better reference T-distance wise than creating some "spacer" for him to tape the film to? This way he could continue the way he's been going up until now, its just that the g/g would be flipped.

just wondering

Dan

[Roseanne]

Thank you all, I will do more tests. Im just presuming the film back is designed to take a glass plate due to the age of camera, but the space for the glass is very thin so Im wondering if that is correct. Also I do stop down to f32 and the focus is really quite far out still. It has to be down to physics so I will do more tests and post the results.
Thank you for your time.
Roseanne

[Justin Cormack]

Thank you all, I will do more tests. Im just presuming the film back is designed to take a glass plate due to the age of camera, but the space for the glass is very thin so Im wondering if that is correct. Also I do stop down to f32 and the focus is really quite far out still. It has to be down to physics so I will do more tests and post the results.
Thank you for your time.
Roseanne

The glass plate thickness is usually about 2mm.

How close are you focussing and how long is the lens? You could try taking a picture of something receding, and mark on it where you focussed and see how far out it is.

[Roseanne]

I did that and thats how I worked out it is focusing beyond what I focused on. I will take all the above on board and be more mathematical about it, (not my natural habitat!) The lens is a 310mm, and Im focusing on the far side of a room, 17 feet ish away. There is also fall off/ vignetting as lens not covering the back.
I am loving how the image looks on the ground glass and how the world looks through the camera. But sometime I do want to get the neg I want, the quality of a contact will be beautiful.
Thank you again,
Roseanne