Bellows extension

[ndwgolf]

Question regarding optimum bellows extension for 8x10 large format camera.
I have recently started taking still pictures of anything and everything. I tend to take ages to try and nail focus and I am wondering if there is a rule of thumb whereby you set the bellows to X and then position the camera until you get a sharp image on the ground glass. My only two lenses are Rodenstock 210mm Macro, and 360mm graphic.
Thanks in advance
Neil.

 

[RalphLambrecht]

Question regarding optimum bellows extension for 8x10 large format camera.
I have recently started taking still pictures of anything and everything. I tend to take ages to try and nail focus and I am wondering if there is a rule of thumb whereby you set the bellows to X and then position the camera until you get a sharp image on the ground glass. My only two lenses are Rodenstock 210mm Macro, and 360mm graphic.
Thanks in advance
Neil.

Yes;bellows extension, subject distance and focal length are in a mathematical defined relationship but, I can see executing thesse calculations to be (more cumbersome and vague) then just adjusting andfinding sharp focus on the ground glass. Nevertheless,the attached file may help.

 

[Ian Grant]

A lot depends on the camera itself and how it focusses, It's a lot easier when a camera has a sliding block as well as front and rear focussing. That's the case with my 10x8 Agfa Ansco Commercial View, it;s harder with the Agfa Ansco Universal View which has no sliding block and only rear focussing.

So it's finicky with a fixed front standard, easier if the tripod is on a dolly (wheels) but that's only practical in a studio. I set the Commercial View up roughly for close up work then fine tune with front and rear focus perhaps slight adjustment with the sliding block.

Recently I've been shooting close up testing a Kodak Specialist 2 half plate (7x5) camera these were sold for general use as well as industrial, scientific and medical, it's designed for up to 1:1 and has metric scales on the focus rail and extension rail, plus a table on the side for the bellows extension factor. What's great about this camera is front and rear focussing is geared as is the sliding tripod block so it's easy to use for macro work. I don't think the Kodak 10x8 cameras had the same features (these are Kodak Ltd cameras made in the UK).

I would make yourself an extension table for each of your lenses and carry a small tape measure, with my Wista 45DX I just marked the brass rail with a indelible marker (I think they call them Sharpies in the US).

Ian

 

[Dan Fromm]

Neil, I think I've answered this question for you on LFPF. Here it is again. Pay attention this time.

Extension given magnification is f*(m + 1) where f is the lens' focal length and m is magnification. For your two lenses, measure from the diaphragm. Not exact, but close enough.

Front node to subject distance given magnification is f*(m + 1)/M. For your two lenses, measure from the diaphragm. Not exact, but close enough.

Optimum bellows extension? Ain't no such thing. Right for the lens' focal length and desired magnification, yes, best in general, no.

 

[ndwgolf]

Neil, I think I've answered this question for you on LFPF. Here it is again. Pay attention this time.

Extension given magnification is f*(m + 1) where f is the lens' focal length and m is magnification. For your two lenses, measure from the diaphragm. Not exact, but close enough.

Front node to subject distance given magnification is f*(m + 1)/M. For your two lenses, measure from the diaphragm. Not exact, but close enough.

Optimum bellows extension? Ain't no such thing. Right for the lens' focal length and desired magnification, yes, best in general, no.

Dan I’m trying really hard to pay attention and appreciate your patience, but I’m still struggling to get my head around it. I’m an old roughneck so need it in simple terms.
I’ve just bought myself a macro rail so hopefully that will help me.
Today I took a picture of a flower in a vase with my 210mm lens. I set the bellows to 420mm 2x focal length. I then put the lens close to the flower and pulled the camera a tripod back until it was sharp on the ground glass. But when I tried to fine tune the focus by adjusting the front standard in and out I just couldn’t get it tac sharp. I ended up just getting it in the ball park and took the picture. It’s hanging in the drying cabinet just now so I don’t know how sharp it is but what I’m trying to do is be able to get it tac sharp without hoping it’s sharp
Neil

 

[Ian Grant]

When you use front focussing you're also adjusting the distance between the lens and object which makes fine focussing much harder than when you use rear focussing, you've also got extremely shallow DOF so you need a good dark-cloth and look what happens as you stop the lens down.

Ian

 

[Dan Fromm]

Dan I’m trying really hard to pay attention and appreciate your patience, but I’m still struggling to get my head around it. I’m an old roughneck so need it in simple terms.
I’ve just bought myself a macro rail so hopefully that will help me.
Today I took a picture of a flower in a vase with my 210mm lens. I set the bellows to 420mm 2x focal length. I then put the lens close to the flower and pulled the camera a tripod back until it was sharp on the ground glass. But when I tried to fine tune the focus by adjusting the front standard in and out I just couldn’t get it tac sharp. I ended up just getting it in the ball park and took the picture. It’s hanging in the drying cabinet just now so I don’t know how sharp it is but what I’m trying to do is be able to get it tac sharp without hoping it’s sharp
Neil

Neil, I told you how to calculate lens-to-subject distance (measured from the diaphragm, not from the front of the lens).

If you do the calculation for 1:1 (that's what extending the lens 2 focal lengths from the film plane gets) you'll find that the lens-to-subject distance is also 2 focal lengths.

If you do the arithmetic for other magnifications, you'll find that for any magnification but 1:1 there are two magnifications for a film plane-to-subject distance. Try, for example, 1:2 and 2:1. They'll give the same film plane-to-subject distance, different lens-to-subject distances. This is why focusing closeup by moving the front standard is dangerous.

Changing extension -- moving either standard does this -- changes magnification and the focused distance. The advantage of focusing with the rear, not the front, standard is that it doesn't change lens-to-subject distance.

 

[jim10219]

Here's the quick and dirty way I do it if I'm not wanting to do the math to get everything precise.

Roughly measure the distance of the bellows at infinity focus. That's your baseline. If you extend the bellows 50% of that distance further, add a stop. If you double the length of the bellows, add two stops. Adding half and third stops aren't usually necessary as the latitude of the film will usually cover it.

If I'm doing macro work in the studio, I'll usually sit down and do the math, since I have the time and a convenient place to work it out anyway.

Keep in mind with telephoto (and retrofocal) lenses, you don't actually measure the length of the bellows but what the bellows would be if the lens were a normal lens. In other words, you use the printed focal length of the lens as your baseline, which without a measuring tape, can be a bit hard to guess.

 

[John Koehrer]

So if ndwgolf gets the focus close as he says, could he then make minute adjustments using the sliding bed to
change the magnification & get sharp focus?

Awkward/inconvenient but doable?

 

[Dan Fromm]

So if ndwgolf gets the focus close as he says, could he then make minute adjustments using the sliding bed to
change the magnification & get sharp focus?

Awkward/inconvenient but doable?

That's how its usually done. When the magnification has to be exact, then we measure, set up and use a focusing rail, not changes in extension, to fine tune.

Getting the magnification exactly as needed is rarely needed. For one of my projects I'm x-raying a lot of small fish. I put a 1 cm piece of radio-dense material next to the subject. Instant scale bar.