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Digital vs Film DOF?
Old 10-21-2005, 10:59 AM   #1 (permalink)
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Can somebody put into simple terms for my pea-brain why we gain depth of field on digital? It hasn't been a major problem for me so far but have notice a little difference. I've seen the formulas and heard all the moaning about it but have not EVEN had the inclination to dig into it to understand why it happens. I've always thought that if you know why something happens you can find a way around it. Anybody up to it? [img]/ubbthreads/images/graemlins/crazy.gif[/img]

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Re: Digital vs Film DOF?
Old 10-21-2005, 01:14 PM   #2 (permalink)
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This link may help with your answer.

http://www.photo.net/learn/optics/dofdigital/


/James J.
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Re: Digital vs Film DOF?
Old 10-21-2005, 01:53 PM   #3 (permalink)
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Thanks for that James
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one thing to note
Old 10-21-2005, 05:28 PM   #4 (permalink)
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James' link below is a good, though somewhat over technical explanation. However, remember it has nothing to do with film vs digital, its about the size of the image recording area - i.e., the chip (or sensor) in digital, or film in a film camera. While the 10D and most digital SLRs have 1.5x or 1.6x magnification factors because of their smaller-than-full-size chips, cameras like the Canon 1DsM2, the 5D, and the Kodak 14n/14c, which have full-size chips, have exactly the same DOF as 35mm film cameras, using the same lenses, distance, f-stop, etc.

Here's another explanation, maybe simpler. We all know DOF is dependent on focal lenght of the lens, f-stop, and focusing distance. If you use a 300mm lens on a 35mm camera (full size chip) you get the same field of view (the framing of the subject in the viewfinder) as someone using a 200mm lens on a APS (1.5 or 1.6) chip camera, like the 10D, 20D, any Nikon or Fuji, etc. BUT..... because you're using a 200mm lens instead of the 300mm lens, you have more DOF, partly because you have to be 50% farther from the subject in order to get the same framing. You can extrapolate that to any lens/distance/format/f-stop combination. And by the way, this is why larger format cameras - 6x7, 4x5, 8x10 - have even shallower DOF and require more light (hence a smaller f-stop) to achieve the same working DOF. Hope that makes sense.

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Andy Pearlman
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Re: Digital vs Film DOF?
Old 10-22-2005, 03:37 PM   #5 (permalink)
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[ QUOTE ]
Can somebody put into simple terms for my pea-brain why we gain depth of field on digital? It hasn't been a major problem for me so far but have notice a little difference. I've seen the formulas and heard all the moaning about it but have not EVEN had the inclination to dig into it to understand why it happens. I've always thought that if you know why something happens you can find a way around it. Anybody up to it? [img]/ubbthreads/images/graemlins/crazy.gif[/img]

DP Ellis

[/ QUOTE ]


Hmmmmm........well,.......you really don't..

A film plane is a film plane regardless if it is a digital sensor, or a flat strip of film against a preassure plate..and the lenses don't change either... a 50mm lens on a film body, gives you the same exact depth of field on a digital body, regardless what size the sensor is..1.0, 1.3, 1.5, 1.6, or 2.0....it's all the exact same.

I've read that placing a lens on a digital body that is not a full frame camera,...like the 20D,...which has a "cropping factor" of 1.6x,.....that, that will somehow "equal" putting a 1.6 telephoto extender on your lens...when in reality,... (I have the 1.4 & 2.0 telephoto extenders)......they don't provide any more magnification whatsoever. All that happens is that the frame of the film/sensor format changes to a much smaller area of coverage. Much like my 6x8cm reduction back on my 4x5" format camera..it just didn't make the same lenses any longer... it just cropped in tighter into the coverage area.....and the depth of field remained the same too.

I hope that helps.. [img]/ubbthreads/images/graemlins/smile.gif[/img]

JP
 
 
Re: one thing to note
Old 10-22-2005, 04:22 PM   #6 (permalink)
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EUREKA! I think I've got it. That second explanation makes tons of sense. Since it's really a 200mm (shorter focal length hence more DOF) and not really a 300mm then we have "more" DOF on the digital. I get it. It's more about distance than something inherent in the digital process. I love it when the lightbulb goes on.

Many thanks Andy. Sometimes all it takes is putting it in different words from a different angle.

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Re: Digital vs Film DOF?
Old 10-22-2005, 04:36 PM   #7 (permalink)
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Gotcha JP. The lens is the lens. Just that with the 1.6 factor for digital it would be like comparing two 80mm lenses if apples are apples. And since the 80mm is really a 50mm on the digital then the digital has more DOF than the film's actual 80mm focal length. It's more about distance really since using the same lens on both cameras means the film plane to subject distance has to be greater with the digital to get the same crop.

Thanks,

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