More DOF Calculator b*llsh#t

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Archive 2009 · More DOF Calculator b*llsh#t

David Clapp
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p.1 #1 · More DOF Calculator b*llsh#t

http://cpn.canon-europe.com/content/technical/depth_of_field_calculator.do

DOF calculators in the digital world are total nonsense. After ruining a good few digital images with them in the early digital days, the only way to get accurate 'digital' DOF charts was to start all over again, ignore the distance scales on the lenses, make my own scales and test the lenses myself and examine the results at 100% in RAW.

Quote Canon's new DOF calculator - "To create a constant certain assumptions are made. These assumptions are that the eyesight of the viewer is able to determine resolution of around five line pairs per millimetre, it is viewed from around 25cm and the viewing size is approximately a 10x8inch print."

Yet again we are left by pioneers of digital technology with this age old bunkum.... how about a total revision of the whole entire situation, somebody PLEASE!!!! The time has come (seeing as 99% of the camera world is shooting digitally) to revise and recreate hyperfocal distance / DOF ledgers on all new lenses so we can just stop all this garbage

Stick on Scales - All my lenses are tested inside out hyperfocally. I have to make all my own stick on 'scales' , increments that ignore all the totally inaccurate metres and feet values values these scales spit out. How on earth can I set my 17-40 lens to 2.36m anyway?! The scale is so bad I can't even set it without guessing....

Nikon are you listening too?!- Nikon are just as bad. The 14-24 has such a deeply recessed focus scale that you can actually get parallax errors between the plastic window's zero point and the scale beneath! Come on. Even if the scales were 100% accurate I would get it wrong if my line of sight was slightly to the left or right.

High Resolution - A high resolution 21mp image losing focus at infinity can be so utterly fine it can't even be seen that clearly with 10x LIVE VIEW on wide angle lenses with the DOF preview pressed.(far easier on telephotos mind you) It has to be examined in RAW by looking at the centre and corners of the lens.

Field Curvature Issues - As some lenses have a curved image plane the centre of the image will be in focus and the edges will be slightly out of focus. Again the calculators do not allow for this phonomena either.

But well we dont care do we, as long as its there abouts.

I dont care as long as my failing eyes can see a print from 25cm in focus. Tell that to a picture editor. It drives me around the bend that all camera manufacturers still wont address this situation. But then where is my mirror lock up button?! haha

Edited on Jul 31, 2009 at 11:41 AM · View previous versions

Jul 31, 2009 at 09:14 AM

Jman13
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p.1 #2 · More DOF Calculator b*llsh#t

So, you're complaining because you're looking at images the equivalent size of a 50" print and seeing different depth of field? Depth of field has ALWAYS been an estimate based on a roughly 8x10 print. Even with today's lenses and such, make an 8x10 print and the scales will be pretty accurate. You blow up larger, apparent blur becomes bigger, so you need more DOF. This has always been the case. DOF is an appearance thing....no matter how far you stop down, the focus point is still the only thing that is really truly in focus...everything else is making the blur as small as possible.

Jul 31, 2009 at 10:04 AM

Makten
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p.1 #3 · More DOF Calculator b*llsh#t

I've never understood why anyone would try to calculate DOF. It depends on so many variables that it's totally pointless to even try.

"How heavy is a rock?" Ummm, it depends.

Jul 31, 2009 at 10:11 AM

David Clapp
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p.1 #4 · More DOF Calculator b*llsh#t

Jman13 wrote:
So, you're complaining because you're looking at images the equivalent size of a 50" print and seeing different depth of field? Depth of field has ALWAYS been an estimate based on a roughly 8x10 print. Even with today's lenses and such, make an 8x10 print and the scales will be pretty accurate. You blow up larger, apparent blur becomes bigger, so you need more DOF. This has always been the case. DOF is an appearance thing....no matter how far you stop down, the focus point is still the only thing that is really truly in focus...everything else is making the blur as small as possible.

To a landscape photographer its extremely important not to lose infinity focus whilst maximising depth of field. Why on earth would I be interested in sharpness of an 8x10 print? Ok, I know this isnt calculating hyperfocal distances, but the problem is the accuracy of the scales that these lenses are manufactured with are very poor. The variables that occur with focus mean they can never be set accurately. Thats what my gripe is, we live in a digital world of precision, but this seems so unprecise.

We spend all our time on this forum criricising image detail and lens sharpness at 100% to the n'th degree, but its ok to just use some stupid calulator thats based on some archaic principle to maximise focusing accuracy? If I told agencies I work for "oh ok, its out of focus on your screen but the client wont notice it unless is a 50" print" I would have my contracts terminated.

Edited on Jul 31, 2009 at 11:27 AM · View previous versions

Jul 31, 2009 at 11:19 AM

David Clapp
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p.1 #5 · More DOF Calculator b*llsh#t

Makten wrote:
I've never understood why anyone would try to calculate DOF. It depends on so many variables that it's totally pointless to even try.

"How heavy is a rock?" Ummm, it depends.

Do you shoot landscapes? If you dont then fair enough...

Jul 31, 2009 at 11:20 AM

Jman13
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p.1 #6 · More DOF Calculator b*llsh#t

I guess I just don't understand why this is a new phenomenon...DOF scales have always been useless for large landscape prints. You start your rant by stating how they are useless in the digital world....the exact same DOF occurs digitally for a same print (on a full frame sensor) as it does on film.

Jul 31, 2009 at 11:27 AM

Makten
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p.1 #7 · More DOF Calculator b*llsh#t

David Clapp wrote:
Do you shoot landscapes? If you dont then fair enough...

I occasionally do, but I don't print 'em.

I see what you mean, but the calculations are still not enough. It depends on viewing distance, eyesight, image size, and so on. Everyone isn't gonna look at your picture from the exact same distance.
For a landscape where great DOF is needed, I'd stop down as much as possible without getting into diffraction limitation. Now THAT is something worth calculating, since it goes for any lens on a particular camera.

Jul 31, 2009 at 11:32 AM

jpeter
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p.1 #8 · More DOF Calculator b*llsh#t

To get beyond the 8x10 issue, why not just calculate dof using the circle of confusion that matches your digital sensor ?

Jul 31, 2009 at 11:52 AM

Spyro P.
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p.1 #9 · More DOF Calculator b*llsh#t

David I'm with you but we are a tiny minority, nobody else cares. Olympus recently launched a camera that is supposed to be a half serious photographic tool, and it doesnt even have a focus distance scale, at all. Not even on the LCD. Forget hyperfocal markings, that's science fiction. And guess what, you go to dpreview's and countless other reviews and its not even mentioned, not as a problem, I'm talking not even mentioned at all. But hey, you get a menu option to select between the lens spinning clockwise or counter-clockwise, doesnt that make you feel special?

As for the focus scale on your 17-40, they could make it bigger but that would probably involve making the focus throw longer, which would probably make autofocus a fraction of a second slower. God forbid, a lethal sin. No photos were ever taken without superfast autofocus. Its a matter of priorities, ask your average DSLR user today what is hyperfocal distance, I bet you 90% of the time the answer will be "Huh?"

Also, since you seem to know the subject I'd appreciate it if you could help me with some theory. Its my understanding that with digital one must use much tighter CoC values in the dof calculation?

Jul 31, 2009 at 11:54 AM

edwardkaraa
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p.1 #10 · More DOF Calculator b*llsh#t

Jman13 wrote:
I guess I just don't understand why this is a new phenomenon...DOF scales have always been useless for large landscape prints. You start your rant by stating how they are useless in the digital world....the exact same DOF occurs digitally for a same print (on a full frame sensor) as it does on film.

Having shot and scanned film until recently I can assure you that DOF is not the same with film as with digital. My understanding is that film has more DOF than digital because it has a physical dimension, a certain thickness, and slide film is thicker than negative film, which makes it not as sharp but allows for more DOF. This allows the image to form on different layers and I always wondered why my DSLR, even older 6mp models have less DOF even compared to 22mp film scans.

Jul 31, 2009 at 12:20 PM

jcolwell
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p.1 #11 · More DOF Calculator b*llsh#t

Spyro P. wrote:
Its my understanding that with digital one must use much tighter CoC values in the dof calculation?

If you base the DOF calculations on the same viewing parameters (i.e. print size & viewer distance), then it's a linear function of sensor widths (for 3:2 sensor aspect ratios). So, if you use CC = 0.030mm for full frame DSLR or 35mm film format, then for a 1.6x CF EOS DSLR, with 22.2mm wide sensor, it's 0.030 * 22.2/36 = 0.019mm. Similarly, the CC gets bigger for MF and LF DOF calculations, unless you change the print size (they're often larger), or viewing distance.

Jul 31, 2009 at 12:27 PM

edwardkaraa
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p.1 #12 · More DOF Calculator b*llsh#t

I think the name of the problem is USM, SSM whatever the manufacturers call it. My Sony screw drive lenses, based on old Minolta designs, as well as the 2 Zeiss primes have an absolutely accurate focusing scale that stops exactly at infinity. The focusing ring has a long throw and the ring resistance is very similar to MF lenses, though not as smooth. The DOF scale is probably based on film but I never use it since I rely on previous experience for determining the best aperture + a very important feature that we enjoy nowadays called chimping

USM lenses need a very short focusing throw and the focusing scale is next to useless since the distance varies with temperature and focus goes beyond infinity.

Spyro P. wrote:
David I'm with you but we are a tiny minority, nobody else cares. Olympus recently launched a camera that is supposed to be a half serious photographic tool, and it doesnt even have a focus distance scale, at all. Not even on the LCD. Forget hyperfocal markings, that's science fiction. And guess what, you go to dpreview's and countless other reviews and its not even mentioned, not as a problem, I'm talking not even mentioned at all. But hey, you get a menu option to select between the lens spinning clockwise or counter-clockwise, doesnt that make you feel special?

Jul 31, 2009 at 12:28 PM

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p.1 #13 · More DOF Calculator b*llsh#t

Great rant - I agree that dof calculators are pointless. In the digital age it's easy though: focus bracket from infinity backwards. That way you can pick the optimal shot, and even stack focus if appropriate.

My understanding is that film has more DOF than digital because it has a physical dimension, a certain thickness, and slide film is thicker than negative film, which makes it not as sharp but allows for more DOF. This allows the image to form on different layers and I always wondered why my DSLR, even older 6mp models have less DOF even compared to 22mp film scans.

I'd like to see a more scientific explanation than that...

Jul 31, 2009 at 12:30 PM

edwardkaraa
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p.1 #14 · More DOF Calculator b*llsh#t

brainiac wrote:

I'd like to see a more scientific explanation than that...

Me too

It's based on my own observations, having shot the same Zeiss lenses with Contax film bodies and 16.7 mp Canon 1Ds2. Unfortunately I have never done direct comparisons but this is the impression I've always had.

Jul 31, 2009 at 12:34 PM

Grenache
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p.1 #15 · More DOF Calculator b*llsh#t

David Clapp wrote:
Makten wrote:
I've never understood why anyone would try to calculate DOF. It depends on so many variables that it's totally pointless to even try.

"How heavy is a rock?" Ummm, it depends.

Do you shoot landscapes? If you don't then fair enough...

I do shoot landscapes, and one of the most important items in a landscape shooter's kit if they want to get away with as close to the minimum hyperfocal distance is a tape measure. Generally, people's eyes are also pretty good at estimating 5 feet or 10 feet as well.

Camera manufacturers makes lenses. They help get shots, but it is the photogs responsibility to ensure the shot is properly executed. Your taping on of scales sounds a bit more laborious than necessary, but if it works for you, great.

Are you sure that your real problem in making the large prints is not simply undersharpening? In the digital age, assuring sufficient information content in a large print is as much about that as anything else.
Jim

Jul 31, 2009 at 12:36 PM

David Clapp
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p.1 #16 · More DOF Calculator b*llsh#t

My main problem is the lens designs, the lens distance scales are totally useless. I can't argue the physics angle because so many people here are far more clued up than I am.

What anoys me more than ever is that precision with DOF / hyperfocal distance cannot even be set correctly with modern AF lenses. Brainiac explains quick a DIY solution, but for precision there has never been a modern lens that helps even in the slightest.

Going back to hyperfocal distance, why can there be new ledgers on lenses showing hyperfocal distance points at given focal lengths based on raw file examination? Or why cant they just include a series of marked increments so you can at least make your own?! I have to have all manner of stick on scales, even a smaller arrow stuck to the focus wheel and a reset point on the 14-24 just so I can guarantee correct hyperfocal focus for a given focal length and aperture. The 14-24 isnt even parfocal, so infinity at 14mm isnt in the same place as 24mm.

I need to be this precise without thinking when the waves are crashing or the light is shifting fast, I can't be guessing. It's all built on past disasters, feeling gutted that I had messed up, that infinity focus was out. Hyperfocal and DOF calculators are pointless in this digital age, but you can test your kit out and make it work. Remember that great statement "oh I just focus a third into the scene", well if your happy with that then great, but if you earn a living from imagery thats a lacklustre approach.

The camera manufacturers are doing nothing to help. They'll give us every other bell and whistle we all disable but the ones we really need they ignore more often than not. Are they still making cameras with DOF mode like the old EOS 5 I used to own? I don't know...Far too many variables is bound to confuse us.... perhaps this is why?

Jul 31, 2009 at 12:48 PM

jcolwell
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p.1 #17 · More DOF Calculator b*llsh#t

It's easy to mark DOF scales on a push-pull zoom, like the old Sigma 70-150/3.5 shown below, but it's not common practice now.

2012 © jcolwell

Jul 31, 2009 at 01:22 PM

jcolwell
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p.1 #18 · More DOF Calculator b*llsh#t

David Clapp wrote:
...Remember that great statement "oh I just focus a third into the scene", well if your happy with that then great, but if you earn a living from imagery thats a lacklustre approach.

It's also incorrect with most lenses, see Harold Merklinger's "The INs and OUTs of Focus", at http://www.trenholm.org/hmmerk/#TIAOOF. Apparently, some lenses optimized for wide aperture portraiture do have critical focus in the forward part of the DOF, to give better background separation and blur. This is not the case for most lenses, where cricital focus is in the middle of the DOF.

Jul 31, 2009 at 01:42 PM

David Clapp
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p.1 #19 · More DOF Calculator b*llsh#t

Totally agree Mr Cowell. I would literally be 100% convinced that if they marked hyperfocal distance on modern lenses based on a new digital approach, (what with copy to copy variation problems we are all aware about on this forum), they would have wave after wave of returned lenses that 'do not focus hyperfocally with the scale'. It would probably be a very stupid move for them the more I think about it....

Jul 31, 2009 at 01:54 PM

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p.1 #20 · More DOF Calculator b*llsh#t

David Clapp wrote:
Totally agree Mr Cowell. I would literally be 100% convinced that if they marked hyperfocal distance on modern lenses based on a new digital approach, (what with copy to copy variation problems we are all aware about on this forum), they would have wave after wave of returned lenses that 'do not focus hyperfocally with the scale'. It would probably be a very stupid move for them the more I think about it....

And each time they stuffed a few million more pixels into the sensor you'd need to upgrade all your hyperfocal scales. I think they are dead and gone. Liveview is quite a generous consolation.

Jul 31, 2009 at 02:41 PM

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