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Mark Sawyer
29-Dec-2013, 12:43
Disclaimer: I never use those tables or calculators myself, preferring inspection with a loupe after closing down the aperture instead. (As if those dof calculations could take into account the contortions of my focal plane anyways...) But I was curious...

When using a dof calculator, should one use the factory-indicated f/stop at infinity, or the actual f/stop being used?

Example: If doing a 1:1 close-up on 8x10 with a 300mm lens set at f/22 on the aperture scale, would you use f/22 in your calculation, or f/44 (okay, f/45, close enough...), which is the actual f/stop in that situation?

Bob Salomon
29-Dec-2013, 12:51
On the rodenstock calculator an indicator tells you howw much exposure correction is necessary. So you can keep f22 and just increase your exposure time as it indicates (1 second at 1:1 becomes 4 seconds) or you open the aperture as indicated so f22 becomes f11 or a combination of both.
The Rodenstock calculator has a scale to read off your mognification ratio being used and the very first step is to tell it what format is being used and the next step is to set the angle of the camera to the subject. Then you focus on the near and far points, tell the calculator how far apart the are in mm on the camera and the camera back is then set to the indicated point on the calculator.

So it will also do your DOF and Scheimpflug calculations. Regardless of your contortions.

Dan Fromm
29-Dec-2013, 13:38
Mark, you have to use effective aperture, that is, aperture adjusted for magnification. I have no idea whether any DoF calculator does this. I also don't know, and this is a fine point that isn't always relevant for LF work, whether any DoF calculator takes proper account of the lens' orientation (facing normally or reversed) and pupillary magnification.

Bob, it isn't a question of exposure correction, but of using the right aperture when calculating DoF.

Bob Salomon
29-Dec-2013, 14:25
107327107328
Mark, you have to use effective aperture, that is, aperture adjusted for magnification. I have no idea whether any DoF calculator does this. I also don't know, and this is a fine point that isn't always relevant for LF work, whether any DoF calculator takes proper account of the lens' orientation (facing normally or reversed) and pupillary magnification.

Bob, it isn't a question of exposure correction, but of using the right aperture when calculating DoF.
I know, the Rodenstock calculator tells you what aperture is required for any given displacement between the near and far point and how much exposure correction is required for the magnification desired for that magnification ratio. Your choice is do you do it strictly by adding time, or not.

Here are the instruction sheets for the DOF side and the Scheimpflug sides of the calculator.

Dan Fromm
29-Dec-2013, 15:03
Thanks, Bob, for adding considerable clarity. What a cute device.

Mark Sawyer
29-Dec-2013, 15:22
Mark, you have to use effective aperture, that is, aperture adjusted for magnification. I have no idea whether any DoF calculator does this...

Thank you, Dan! I thought that would be the case, but wasn't sure so I had to ask. I wonder how many users of such calculations are aware of this? I suspect quite a few photographs have had unexpectedly out-of-focus areas because the photographers used the infinity-based scale rather than figuring out what f/stop they were really at.

Bob, that's a nifty little field guide, but I noticed it didn't inform the photographer about determining the effective ("real") f/stop when using the scale. (I'd guess this is true for all Depth of Field and Scheimpflug tables and calculators.) In the example illustrations on the guide, I'd say the calculations will be off by about an f/stop given the camera-to-subject distance. Something to correct if Rodenstock ever reprints these?

As I mentioned in my first post, I prefer making decisions visually with a loupe. Kinda like cooking to taste rather than following a recipe. Besides, as much of my work is either soft-focus or wet plate, it's seldom simply "how do I get everything in focus", but rather "what degree of focus do I choose?"

Dan Fromm
29-Dec-2013, 15:54
Mark, one of the really cute things about Rodenstock's calculator is that magnification is an input. I take that to mean that it automatically uses effective aperture internally, shows aperture to set. Bob, is that right?

Mark, most of my closeup work is with flash illumination at magnifications where DoF is too small to be worth thinking about. I use my wonder-working macro flash rig that gives correct exposure over a wide range of magnification with constant flash output and a fixed aperture set or I use GN arithmetic with an adjustment for magnification. All mental arithmetic, its not that hard.

Bob Salomon
29-Dec-2013, 15:56
Mark, one of the really cute things about Rodenstock's calculator is that magnification is an input. I take that to mean that it automatically uses effective aperture internally, shows aperture to set. Bob, is that right?

Mark, most of my closeup work is with flash illumination at magnifications where DoF is too small to be worth thinking about. I use my wonder-working macro flash rig that gives correct exposure over a wide range of magnification with constant flash output and a fixed aperture set or I use GN arithmetic with an adjustment for magnification. All mental arithmetic, its not that hard.

correct

Steven Tribe
29-Dec-2013, 16:46
I can't turn the dial on Bob's figures!

Hint for an animated version on a website?

Dan Fromm
29-Dec-2013, 17:07
Only 44.95 at B&H, Steven, and requires no batteries.

Mark Sawyer
29-Dec-2013, 17:26
Mark, one of the really cute things about Rodenstock's calculator is that magnification is an input. I take that to mean that it automatically uses effective aperture internally, shows aperture to set. Bob, is that right?


correct

I stand corrected. And thank you, gentlemen!

Nathan Potter
29-Dec-2013, 23:11
Was not aware of the Rodenstock DOF calculator. Looks like a neat little device. I think I need one. Thanks Bob.

Nate Potter, Austin TX.

Jeff Conrad
30-Dec-2013, 03:30
Most calculators of which Iím aware (e.g., www.dofmaster.com) use the marked aperture. For this to be the case, either focused distance or magnification must be an inputóbut a calculator missing one of these inputs would seem pretty lame. That said, I hardly ever use such calculators.

Tim Meisburger
8-Aug-2014, 00:07
I just got one of these and read the instructions, but am still pretty confused. How do you determine magnification? (Maybe I just need to read the instruction again when not sleepy!)

David A. Goldfarb
8-Aug-2014, 00:40
You can estimate it by comparing the width of the field of view at the subject plane to the width of the format, or if necessary, put a ruler in front of the subject (like a still life) and measure it on the groundglass. If a 12" ruler appears to be 6" on the groundglass, the magnification is 1:2. If you take a tight headshot with an 8x10" camera and the subject's shoulders touch the edges of the frame, say it's 18" shoulder to shoulder. The magnification is 8:18 or 4:9. The same portrait made with a 4x5" camera would have a magnification of 4:18 or 2:9. You can also express magnification as a decimal value.

Toyon
8-Aug-2014, 07:43
I have been using the "DOF Calculator" app. It is very nicely laid out. Unfortunately in practice it proves way to optimistic. I have learned to dial in the figures for a given stop then use the data for the next larger stop as my guide.

Tim Meisburger
8-Aug-2014, 08:31
Thank David. That makes sense. I guess its not really relevant at landscape distances.

Jim Andrada
8-Aug-2014, 08:34
I'm with Mark - looking at the GG works for me.

But I do like these little analog calculators. I think it would be easy enough to scan the calculator, place a circular selection over the dial, and rotate in Photoshop.