PDA

View Full Version : Bellows extension rule of thumb



ndwgolf
11-Mar-2019, 06:53
I’m trying to get my head around bellows extension compared to focal length of a lens (8x10)
What I mean is when I have tried in the past to take close up pictures with my 360mm lens on my Chamonix 8x10 it’s been very hit and miss trying to get focus..,,,., I keep hearing people on here quoting things like 1:1 and 1:3 followed but a certain length of bellows, can someone please try and explain this to me or point me in the right direction to learn about this?
Thanks in advance
Neil

Louis Pacilla
11-Mar-2019, 07:14
I suggest you read & study with the threads already posted on this forum regarding 8x10 close up photography. Read & study thoroughly and then ask any question your unclear on.

https://www.google.com/search?biw=1600&bih=786&ei=nmuGXKHRFe7L5gK6z5f4DQ&q=close+up+photography+with+8x10++large+format+camera+site%3Awww.largeformatphotography.info&oq=close+up+photography+with+8x10++large+format+camera+site%3Awww.largeformatphotography.info&gs_l=psy-ab.12...13945.17588..20607...0.0..0.76.405.6......0....1..gws-wiz.......0i71.Et7E-v8n3Hw

Dan Fromm
11-Mar-2019, 07:15
I think of it in terms of magnification. The magic formulas are:

rear node-to-film plane distance = focal length * (magnification + 1)

front node-to-subject distance = focal length * (magnification + 1)/magnification

For most lenses used for LF the nodes are near the diaphragm and the internodal distance is a small fraction of focal length.

If you think a little about the magic formulas, you'll see that for m = 1 the two distances are equal. For all other magnifications there's a pair of front node-to-subject and rear node-to-film plane distances for which film plane-to-subject distance is the same. Because of this, the best way to focus for close up work is to set extension to get the magnification desired and then move the subject or the camera-lens assembly to focus.

I use a tape measure to set the magnification. When the magnification or framing aren't exactly what I want I move the front standard (not much. If it has to move a lot, start over.) to fine tune.

The list has a list of books on closeup work that I recommend, with short reviews. Buy a copy of Lester Lefkowitz' book The Manual of Closeup Photography. Available at reasonable prices from vendors on abebooks.com, alibris.com, amazon.com, bn.com, ...

G Benaim
11-Mar-2019, 07:46
Keep it simple: for every extra length of bellows the size of the focal length at infinity add one stop. For instance, say you're using a 12" lens and because it's a close up you're racked out to 24". Compensate by adding one stop of exposure. I.e. If you would normally shoot at f64 and 1/10, you would now shoot at f64 and 1/5. Half stops for half the focal length, etc.

Alan9940
11-Mar-2019, 12:17
Keep it simple: for every extra length of bellows the size of the focal length at infinity add one stop. For instance, say you're using a 12" lens and because it's a close up you're racked out to 24". Compensate by adding one stop of exposure. I.e. If you would normally shoot at f64 and 1/10, you would now shoot at f64 and 1/5. Half stops for half the focal length, etc.

Not correct. A 12" lens extended to 24" would require 2 stops compensation.

Jerry Bodine
11-Mar-2019, 20:41
+1
Alan is correct. The general formula for LF bellows compensation is: Exposure Factor (EF) = [bellows extension / focal length]^2 . Bellows extension is the distance from film to lens. So, in the example presented, the factor would be 24/12 squared (2 squared = 4). A factor of 4 means two stops of correction. Of course, always keep the extension and focal length in the same units, either inches or millimeters. This general formula is valid for symmetrical lenses; it doesn't apply to lenses such as telephotos or significantly unsymmetrical lenses.

FWIW, my Leica Manual explains that, since many lenses for 35mm are UNsymmetrical designs, the formula is a bit more complex:
EF = (1 + m/mp)^2
where m is the ratio of image size to object size, and mp is the ratio of exit pupil diameter to entrance pupil diameter (mp = 1 for a symmetrical lens). Since mp is a number less than 1, the EF will be greater than that for a symmetrical lens. Fortunately, the built-in meters of many 35mm cameras provide the needed correction automatically.

ndwgolf
11-Mar-2019, 23:38
I think of it in terms of magnification. The magic formulas are:

rear node-to-film plane distance = focal length * (magnification + 1)

front node-to-subject distance = focal length * (magnification + 1)/magnification

For most lenses used for LF the nodes are near the diaphragm and the internodal distance is a small fraction of focal length.

If you think a little about the magic formulas, you'll see that for m = 1 the two distances are equal. For all other magnifications there's a pair of front node-to-subject and rear node-to-film plane distances for which film plane-to-subject distance is the same. Because of this, the best way to focus for close up work is to set extension to get the magnification desired and then move the subject or the camera-lens assembly to focus.

I use a tape measure to set the magnification. When the magnification or framing aren't exactly what I want I move the front standard (not much. If it has to move a lot, start over.) to fine tune.

The list has a list of books on closeup work that I recommend, with short reviews. Buy a copy of Lester Lefkowitz' book The Manual of Closeup Photography. Available at reasonable prices from vendors on abebooks.com, alibris.com, amazon.com, bn.com, ...

Hi Dan
So for my new lens that is a 210mm I would need to set my bellows to 420mm from the rear of the camera where the film holder sits to the front standard ~ middle of the lens and this will give me 2 times magnification. Then place the object getting photographed 210mm from the middle of the lens........is that correct?
Thanks
Neil

Dan Fromm
12-Mar-2019, 04:52
Try again, Neil.

If magnification = 2, magnification + 1 = 3. 3 * 210 = 630. To get 2:1 with a 210 mm lens, the diaphragm (your "bellows" is impossibly vague) should be approximately 630 mm from the film plane.

If magnification = 2, (magnification + 1)/magnification = 3/2 = 1.5. At 2:1 with a 210, the subject will be approximately 315 mm from the diaphragm.

Your arithmetic is also wrong for 1:1, where the distances are 420 mm film to diaphragm and 420 mm diaphragm to subject. What were you thinking?

ic-racer
12-Mar-2019, 05:52
Hi Dan
So for my new lens that is a 210mm I would need to set my bellows to 420mm from the rear of the camera where the film holder sits to the front standard ~ middle of the lens and this will give me 2 times magnification. Then place the object getting photographed 210mm from the middle of the lens........is that correct?
Thanks
Neil

Almost correct. That is the setting for 1x magnification, or 1:1. Try it. A flower 3cm tall should be 3cm on the ground glass. Add 2 stops to your exposure.

David Schaller
13-Mar-2019, 05:58
I use the formula and make a list of corrections for each focal length. Then round to the nearest third of a stop when taking the picture. When in doubt, on B&W negative film, give a little bit more exposure.

Willie
13-Mar-2019, 08:33
Your 210 is about an 8 inch lens. So - figure f/8. Extend the bellows to 16 inches and figure f/16. Two stops compensation. Not perfect, but close enough for "zone" system type of figuring on exposure compensation. Easy to figure with a 6 inch lens(150) or a 12 inch lens(300). Again - not perfect, but close enough to work for most of us. You figure "inch" to f/stops and keep it simple.

Use the "inch conversion" method for figuring exposure compensation for bellows extension and it is pretty easy. A lot easier for those of us who are mathmatically challenged. Some of us hear "formula" and think of race cars rather than X and Y and computations.

Jim Galli
13-Mar-2019, 08:51
Here's the hillbilly method I use in Tonopah Nevada. I get the image I want on the ground glass. i could give a flying rip about magnification etc. I measure the hole up front with a ruler. I measure the distance from where my guess about the node, ie. aperture blades, to the ground glass. Plus or minus a half inch is no big deal for hillbillies. Then I divide the size of the hole into the length. That gives me an aperture number. Measure available light and come up with a viable exposure.

I don't care what the numbers on the lens say. Hell, some of my lenses don't even have any numbers and never did. For example, I get an image I like on the glass. I measure the hole up front. 36mm. I measure the length from aperture to ground glass. 820mm. 820/36=22.777777777777777 I measure and expose for f22 2/3. Simple simon. You'd be amazed at how many good pictures I've taken this way.

But I fully understand that other peoples minds do not function at the simplicity of mine and all the mathematics is important. Even fun! I therefore return you to your previous discussion.

ndwgolf
20-Mar-2019, 17:47
Okay so my new Rodenstock Macro 210 arrived and yesterday I picked this flower to try my hand an a close up. I must admit I really struggled in getting the focus, what I did in the end was set the bellows extension on my Chamonix 8x10 to 420mm and then pretty much had the lens nearly touching the flower, from there I just moved the camera back slowly while looking at the ground glass and bobs your uncle the flower came into focus.............i fine tuned it but to be honest I would move the bellows out 1 inch and back 2 inches and nothing really changed so took the picture and here it is.
I also did the same process with a really nice lily with the bellows set at 630mm but screwed up the exposure as I was trying to get an Incident light reading on my Seconic 758 but it was set to spot metering...............I will try that again tomorrow

https://www.dropbox.com/s/3ostkh3kolkipxu/Neil%27s-Photography042.jpg?raw=1

Neil

Jim Galli
20-Mar-2019, 18:30
Okay so my new Rodenstock Macro 210 arrived and yesterday I picked this flower to try my hand an a close up. I must admit I really struggled in getting the focus, what I did in the end was set the bellows extension on my Chamonix 8x10 to 420mm and then pretty much had the lens nearly touching the flower, from there I just moved the camera back slowly while looking at the ground glass and bobs your uncle the flower came into focus.............i fine tuned it but to be honest I would move the bellows out 1 inch and back 2 inches and nothing really changed so took the picture and here it is.
I also did the same process with a really nice lily with the bellows set at 630mm but screwed up the exposure as I was trying to get an Incident light reading on my Seconic 758 but it was set to spot metering...............I will try that again tomorrow

Neil

Neil, not to confuse you further, but did you know you can take the back off the camera after it's focused, grab an old film Nikon, take the lens off and hold it (the camera body) so that part of your image lands on the Nikon mirror and gg, and that old Nikon will tell you what it would shoot it at.

Nice shot, well done.

Dave Wooten
20-Mar-2019, 18:51
Neil, not to confuse you further, but did you know you can take the back off the camera after it's focused, grab an old film Nikon, take the lens off and hold it (the camera body) so that part of your image lands on the Nikon mirror and gg, and that old Nikon will tell you what it would shoot it at.

Nice shot, well done.

Wow! Didn't know that!

ndwgolf
20-Mar-2019, 19:29
Neil, not to confuse you further, but did you know you can take the back off the camera after it's focused, grab an old film Nikon, take the lens off and hold it (the camera body) so that part of your image lands on the Nikon mirror and gg, and that old Nikon will tell you what it would shoot it at.

Nice shot, well done.

Thanks for that.
It’s the second time I’ve done this screw up with the meter. I will make a sticker for it to remind me in the future.
Neil

Jim Noel
21-Mar-2019, 09:44
Your 210 is about an 8 inch lens. So - figure f/8. Extend the bellows to 16 inches and figure f/16. Two stops compensation. Not perfect, but close enough for "zone" system type of figuring on exposure compensation. Easy to figure with a 6 inch lens(150) or a 12 inch lens(300). Again - not perfect, but close enough to work for most of us. You figure "inch" to f/stops and keep it simple.

Use the "inch conversion" method for figuring exposure compensation for bellows extension and it is pretty easy. A lot easier for those of us who are mathmatically challenged. Some of us hear "formula" and think of race cars rather than X and Y and computations.

I'm with Willie. ALthough I know and can calculate various formulae mentally, it is faster, and close enough to relate bellows extension to f-stops.

Jim Noel
21-Mar-2019, 09:51
If I know I want 1:1 or close to it, i set the bellows at 2x focal length of lens, and the object the same distance in front of the lens. Make minor adjustments, and Increase exposure 2 stops.

Larry Gebhardt
21-Mar-2019, 11:37
i fine tuned it but to be honest I would move the bellows out 1 inch and back 2 inches and nothing really changed so took the picture and here it is.

Neil,

If your camera focuses by moving the front standard you are changing the magnification while you change the focus. You might get into a situation where you can't achieve focus. So what you need to do is either focus by moving the rear standard only, or move the whole camera in and out without changing the focus (length of the bellows). On the Chamonix 4x5 you can coarsely slide the rear and this can work in a pinch. I'm guessing your 8x10 is the same. Or get a heavy duty macro rail to move the camera.

The rear focus for macro is one of my favorite features of the Canham MQC and most/all monorail type cameras.

Jim Galli
21-Mar-2019, 11:48
http://tonopahpictures.0catch.com/14NoNamwRR14BLTessar1C/CenturyRig_2.jpg

http://tonopahpictures.0catch.com/AnEquipmentTourDeForce.jpg

Here's what you need. The whole monster rolls back and forward on the stand's wheels while you look at the glass. The old timers sort of knew what they were doing. I'm an old timer.

Larry Gebhardt
21-Mar-2019, 12:06
Jim, that's a cute little baby chair and table you have there.

ndwgolf
21-Mar-2019, 16:51
Neil,

If your camera focuses by moving the front standard you are changing the magnification while you change the focus. You might get into a situation where you can't achieve focus. So what you need to do is either focus by moving the rear standard only, or move the whole camera in and out without changing the focus (length of the bellows). On the Chamonix 4x5 you can coarsely slide the rear and this can work in a pinch. I'm guessing your 8x10 is the same. Or get a heavy duty macro rail to move the camera.

The rear focus for macro is one of my favorite features of the Canham MQC and most/all monorail type cameras.

Thanks a lot for this. I didn’t realize that you can move the rear part of the camera in and out........ I will try that next time.
Just to confirm
With my 210 lens set the bellows to 420mm
Then position the camera in front of say the flower.
Pull the camera back until you get a clear picture on the ground glass.
Now fine tune the focus by adjusting the rear part of the camera.
Is that correct

Neil

Larry Gebhardt
21-Mar-2019, 17:55
Thanks a lot for this. I didn’t realize that you can move the rear part of the camera in and out........ I will try that next time.
Just to confirm
With my 210 lens set the bellows to 420mm
Then position the camera in front of say the flower.
Pull the camera back until you get a clear picture on the ground glass.
Now fine tune the focus by adjusting the rear part of the camera.
Is that correct

Neil

If you care about the exact magnification set the extension and move the whole camera to get focus. If the magnification isn't important you can focus with what ever method is easier. If I was using my Chamonix for macro I'd use a macro rail and move the whole camera since it would be the most precise. I think the really right stuff rail would probably work fine for your 8x10, but I haven't tried it.

ndwgolf
22-Mar-2019, 19:04
Thai Lilly

Starting to get the hang of it...............Chamonix 8x10 HP5+ Developed in LC29 shot at f7 1/60
https://www.dropbox.com/s/zdg20wdskl4yn40/Neil%27s-Photography044.jpg?raw=1