Box camera experiment

[seany65]

Hello all,

I've just recently started on my much delayed Box Camera Experiment Number One.

Basically, I've got a Gevaert Gevabox type 1 (but the one with the two flash sync knobs on top, not the one with the two flash sync sockets on the bottom-as in the Manual), so I don't know if it's a "1A" or a "1B" or what. Anyway, the lens has three red dots marked focusing positions but the lens can turn freely and be left amywhere between the first between "5ft and 10ft" (so I thiink the dot is atabout 7.5ft), and "23ft and Inf" and Tunalegs said He reckoned that it would be at about 50ft. I wanted to several things:

1) Find out st what distance those dots actually indicate.

2) Add two or three more dots for better focus.

To these ends I bought a knackered, unusable example of the same camera and hacksawed the back "plate" off so that the side with the film insert could be put replaced with a focusing screen taped to the film rails.

Earlier today I finally got around to starting the experiment. I put the camera on a tripod and measured the distance to the far wall. It was 20ft from where the camera was. I got an old plastic slide viewer (having removed the opaque plastic in which the slide rests while being viewed) and went through the focusing range.

I was a little surprised to find that the image seemed rather out of focus when the lens was set to the middle red dot of between "13ft and 20ft", and completely out of focus at the between "23ft and inf" third red dot, but as far as I could tell (which is more of a "guess" than anything, due to how dark and rough the image on the plain focusing screen is), it seemed to be marginally more in "focus" than anywhere else about halfway between the first red dot and the second red dot, putting it where I'd think "12 1/2ft" would be.

Now, I know the camera no longer has either aperture mechanism nor the apertures in place, meaning the lens is no longer an f8 lens, I presume this means it could be the equivalent of an f5.6 lens, but could the fact that the apertures are missing affect the focused image in any way?

Any help would be much appreciated.

 

[joe bosak]

A smaller aperture will increase the depth of field, so things further away from the plane of focus will be more in focus.

Not sure whether aperture makes much difference if you are at the plane of focus. I guess that be more to do with aberrations and different light frequencies focusing slightly differently.

 

[seany65]

Joe, Thanks for the reply.

I do understand about smaller and larger apertures, I was just wondering if a lens that was designed to work with an aperture would be affected by having no aperture of any description other than the thing that's holding the lens in place.

I also need to find a brighter, finer focusing screen to make it easier to see if the image is actually in or out of focus.

 

[joe bosak]

A sort of related question has crossed my mind lately, as to how much difference the position of an aperture might make. For example when putting together a set of extension tubes and/or a helical, plus a diaphragm, between an aperture-less lens and the sensor... is there any way to determine the "best" place for the diaphragm? Also relevant to adapting certain lenses where there is only electronic aperture adjustment so you'd need to add a diaphragm when adapting the mount).

 

[seany65]

Hmm, interesting questions you've come up with.

Unfortunately the only answer I can come up with is "Hit it with a Hammer", any more sensible answer is far beyond my two braincells.

 

[rfaspen]

Dark cloth "hood" and a loupe might help with determining focus on your screen? Much like a typical LF photographer does.

 

[seany65]

Thanks for the suggestion rfaspan. The camera was on a tripod in my bathroom aimed towards the far end wall of a bedroom. The bathroom window is small, frosted and on the West side of the house, and the bedroom has a window on the east side, the "experiment" was done in the late morning and the bedroom light was on. I also used one of those plastic single slide viewers with the opaqu plastic bit taken off, so there wasn't much light getting onn the cheap focusing screen from the back. I'll probably have to wait a while to save enough to buy a better focusing screen (around the £30-£40 range). I'll see if the shop I bought my Yashica 635 has one of theirs in at the time. Thy say they are sort of Bright screen type but I presume not quite as good a Olsen screens.