"Rack and Pinion" focus on LF lens?

[Vaughan]

That's a video camera looking at a ground glass. Two cameras, two lenses. On which lens do you think having a helicoid will make it compact? Say you use a 300mm lens on the 8x10 (which the other person did in the link) and you want it to do head-and-shoulder portraits, the bellows extension at infinity will need to be about 300mm and the helicoid (or rack and pinion, or whatever) will need to allow another 120mm extension to get focus close enough. There is no way to make this more compact, other than use a shorter focal length lens.

Once the video camera is focussed on the ground glass it should never need to be changed.

[Dan Fromm]

Thanks for the reply, much appreciated! Apologies, I was not clear enough...

I want to try something like what has been done here....

https://www.newsshooter.com/2018/01/...-video-camera/

Am thinking having a lens with Helicoid will make it a bit easier and compact.

Thanks!

Oh! Not that dishonest gimmick again.

If you must do it, consider a sliding box camera.

[wallpaperviking]

That's a video camera looking at a ground glass. Two cameras, two lenses. On which lens do you think having a helicoid will make it compact? Say you use a 300mm lens on the 8x10 (which the other person did in the link) and you want it to do head-and-shoulder portraits, the bellows extension at infinity will need to be about 300mm and the helicoid (or rack and pinion, or whatever) will need to allow another 120mm extension to get focus close enough. There is no way to make this more compact, other than use a shorter focal length lens.

Once the video camera is focussed on the ground glass it should never need to be changed.

Thanks for the response, much appreciated! Yes, am aware of all that.. Am just trying to negate the need for a bellows. So like what he has done here but in a box I guess.

What lenses came in a helicoid? Any idea?

Thanks!

[wallpaperviking]

Oh! Not that dishonest gimmick again.

If you must do it, consider a sliding box camera.

Dishonest? That is pretty good..

A sliding box camera would not work as it would require you to focus twice. It can be done, just another extra step in the process. Also, cannot be used for video.

[Dan Fromm]

Dishonest? That is pretty good..

A sliding box camera would not work as it would require you to focus twice. It can be done, just another extra step in the process. Also, cannot be used for video.

Well, the guy said he was shooting digital 8x10. He was using a tiny digicam to shot an image on an 8x10 ground glass. My monitor is larger than 8x10. Following that logic, if I used a tiny digicam to photograph an image it displayed I'd be shooting ULF. Wow! Not very portable, but still ...

Seriously, I don't understand why using a sliding box camera to do this would require focusing twice. Please explain.

Re video, there are video-capable DSLRs and mirrorless digital cameras. I understand there are adapters for hanging these devices behind an LF camera. If what you want is to shoot video with a long lens, why won't this approach work for you? If you want to shoot video with the lens that started this discussion, why not cobble up or commission an adapter to hang it in front of a video-capable interchangeable camera?

[wallpaperviking]

Well, the guy said he was shooting digital 8x10. He was using a tiny digicam to shot an image on an 8x10 ground glass. My monitor is larger than 8x10. Following that logic, if I used a tiny digicam to photograph an image it displayed I'd be shooting ULF. Wow! Not very portable, but still ...

Seriously, I don't understand why using a sliding box camera to do this would require focusing twice. Please explain.

Re video, there are video-capable DSLRs and mirrorless digital cameras. I understand there are adapters for hanging these devices behind an LF camera. If what you want is to shoot video with a long lens, why won't this approach work for you? If you want to shoot video with the lens that started this discussion, why not cobble up or commission an adapter to hang it in front of a video-capable interchangeable camera?

Zev Hoover did not write the article, so terms like that are not on him.. If you read the article, it points out very clearly what the process is, so not exactly that deceiving.

A sliding box camera changes the distance of the rear board from the digital taking lens (in this case one that has been shifted), so as you move the L.F lens further away (for a C/U) the rear board moves further away from the digital camera/lens and does not fill the frame anymore. You could use a "zoom" lens on the digital camera but this would require recomposition and refocusing each time the L.F lens was moved. It would also need to be "off centred" and would not be in the sharp, central part of the L.F lens' image circle.

Using an Industar 300mm lens hung in front of a video camera just gives you the F.O.V of a 300mm lens on a full frame/apsc sensor. The whole point is to get the F.O.V of a 300mm lens on an 8x10 image area.

[Dan Fromm]

A sliding box camera changes the distance of the rear board from the digital taking lens (in this case one that has been shifted), so as you move the L.F lens further away (for a C/U) the rear board moves further away from the digital camera/lens and does not fill the frame anymore

Hmm. Perhaps I don't understand how sliding box cameras work. As I understand them, the rear standard on the larger box is fixed. The front standard with lens, on the smaller inner box, moves to focus.

Using an Industar 300mm lens hung in front of a video camera just gives you the F.O.V of a 300mm lens on a full frame/apsc sensor. The whole point is to get the F.O.V of a 300mm lens on an 8x10 image area.

Complete agreement, except that there's another way to get the F.O.V. of, say, a 300 mm lens on 8x10 with any camera of any format. Use the equivalent lens on the any camera. 8x10's aspect ratio is 4:5 or so and, say, full frame's is 2x3 or so, so with the any full frame camera cropping will be needed to replicate only what's in the 8x10 frame. 300 mm is normal on 8x10. 43 mm is normal on 24x36. Where's the problem?

To be clear, I'm not trying to discourage you from tinkering. I suffer from the joy of tinkering m'self, and I tend to go to extremes. With respect to going to extremes, you're proposing to go farther than I've been comfortable with.

[LabRat]

Another thing to note is if you expect to use a lens with focusing mount on a camera with full T/S, moving the lens away from the rear nodal point (mostly at just behind iris with most lenses), it will throw off T/S planes you set previously...

But would work well on portrait cameras with rough rack focus, and trying to fine focus on a point on a face in C/U shots (without movements)...

Steve K