[monochrome]

It is all about understanding your format, not playing with little calculators

Just for fun, someone from 'Dunlieth-on-Feith' should register with the User Name 'PlayingWithCalculators' and limit his posts to the FF Forum.

[stevebrot]

They are a bit deceiving because they adjust the distance required to maintain the same crop as you change from one sensor size to another.

Huh? I've never seen an online DOF calculator that automatically adjusts distance to subject

What Jay said. I have used many DOF calculators and the calculations on the better ones (including the one on my phone) are correct. Nothing is done under the covers. What they do NOT (significantly) do is provide a correction for equivalent subject magnification at the sensor. For that reason, they suck for comparison between formats and should not be used for such.

What has been noted in several comments on this thread is worth repeating:

• Don't waste your time and energy trying to calculate equivalent DOF based on the scales (see below comparisons)
• Know your gear
• DOF is a perceptual, not a physical concept
• For equivalent framing and perspective (same camera position relative to subject), a larger format will provide less DOF at a given aperture than a smaller format

I own multiple normal 35mm film lenses from multiple manufacturers and the DOF scales are often, and sometimes comically, inconsistent between makers or even lens lines. For example, the near point for the hyperfocal at f/16 for several 55mm lenses on my shelf:

• Pentax-K 55/1.8: 10'
• Auto-Rikenon 55/1.4: 9'
• Auto Mamiya/Sekor 55/1.8: 7'

For 58mm:

• KMZ Helios 44M 58/2: 7'
• MC Rokkor-PF 58/1.4: 12'

For a selection of 50mm:

• Pentax-M 50/1.7: 8'
• XR Rikenon 50/2.0: 9'
• Auto-Rikenon 50/1.7: 9'
• MC Rokkor-PG 50/1.4: 9'
• KMZ Jupiter-8 LTM 50/2: 6.5'
• Arsenal Jupiter-8M Contax/Kiev 50/2: 6'

The Soviets (the Jupiter and Helios lenses) apparently had a fairly liberal interpretation of DOF (Zeiss rather than the more common Leitz convention for CoC). Was Mamiya using a similar factor? Notice that Ricoh (via Tomioka) used the same scales for both the 55/1.4 and 50/1.7 lenses from the same era.

Steve

[FrankC]

s

Huh? I've never seen an online DOF calculator that automatically adjusts distance to subject, it's always presented as a user-set variable or as an unchanging constant, as it has to be for the calculator to be of any worth. It doesn;t automatically change in any one I've seen.

jsherman999 - It appears that you posted a screen shot from dofmaster.com. On their home page they clearly state the following:
"Use the actual focal length of the lens for depth of field calculations. The calculator will automatically adjust for any "focal length multiplier" or "field of view crop" for the selected camera."

Making this adjustment in "field of view crop" is being done behind the scenes as part of the algorithm to calculate the DOF. The user doesn't see the change so, again, it's confusing a lot of people. Like I had written earlier, DOF is affected by three and only three things: Focus distance, f/stop and focal length. It's literally impossible for the same lens to produce two different amounts of DOF as you claim is being accomplished solely by switching from a FF to an APS-C camera.

[stevebrot]

The calculator will automatically adjust for any "focal length multiplier" or "field of view crop" for the selected camera."

You are (honestly enough) misreading the instructions. Crop factor or focal length multiplier is not part of the calculation. The appropriate CoC for the media size (determined by camera model) is part of the calculation and is accounted for on the online form. I would suggest that you consult the Wikipedia article on Depth of Field as a reference. For an equivalent and less technical discussion, I can recommend the excellent article at the "Cambridge In Color" Web site.

http://www.cambridgeincolour.com/tutorials/dof-calculator.htm

Click the "Advanced" link on the calculator to see how final image size and viewing distance factor in.


Steve

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Last edited by stevebrot; 04-25-2014 at 01:00 PM.

[Lowell Goudge]

Just for fun, someone from 'Dunlieth-on-Feith' should register with the User Name 'PlayingWithCalculators' and limit his posts to the FF Forum.

it is not a knock against calculators. I often tell people to do just a teeny bit of math, from time to time, to address what lens to use. specifically

Image height = focal length * subject height / distance

but for depth of field, because it all comes back to a print size that very few actually use any more, printing the full image frame to an 8x10 inch print, that you need to really look at DoF differently. i view my images on a 22 inch monitor which is just about equal to a 13 x 19 print, and many times i crop. so regardless of what ever format i use, the DOF calculator is worthless to me, because i never look at the print in 8 x 10 format.

so arguing about equivalent DOF across different formats is useless when we never look at the images the same any way

[BrianR]

but for depth of field, because it all comes back to a print size that very few actually use any more, printing the full image frame to an 8x10 inch print, that you need to really look at DoF differently. i view my images on a 22 inch monitor which is just about equal to a 13 x 19 print, and many times i crop. so regardless of what ever format i use, the DOF calculator is worthless to me, because i never look at the print in 8 x 10 format.

There also calculators that include print size, visual acuity, and viewing distance as options: A Flexible Depth of Field Calculator (click 'show advanced'). (edit- whoops, same link as Steve's a couple posts back)

While I almost never go to a calculator to figure out what settings I need to get the DoF I need for a given shot, understanding the variables and the equations involved goes a long way towards understanding what effect changes in the variables will have on the end result. Some people can get a basic understanding of this by mucking about with calculators, some by diving into the equations, some by testing out multiple settings for the same picture, some won't care one way or the other. The calculator can have a terrific role as a quick test bed when trying to understand how it all fits together.

so arguing about equivalent DOF across different formats is useless when we never look at the images the same any way

Knowing what happens when you change format can help you understand what happens if you heavily crop an image. That alone should make it worthwhile to look at for some people.

[stevebrot]

The calculator can have a terrific role as a quick test bed when trying to understand how it all fits together.

They can also be sort of fun. What I typically do when people get too hot about DOF calculations is to point them to my avatar photo. I then refer them to a larger version of the photo from which it was made...


K10D, LZOS MC Jupiter-9 85/2 @ f/5.6

There is even less DOF on the full resolution version.

So, does the DOF follow the scales on the lens if I use my Q? Should I multiply by 1.5? Why is there more DOF in the viewfinder than I see on the screen/print? I set the lens to the hyperfocal, but the mountains are still soft...what went wrong? And so on and so on and so on...


Steve

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Last edited by stevebrot; 04-25-2014 at 03:26 PM.

[severalsnakes]

Digital Camera Sensor Sizes: How it Influences Your Photography

Very interesting! Thanks for sharing!