Is the Fstops on Digicams similar to conventional SLRs?


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Revo

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#1
AS topic suggests....

I came across the f stops on digicams differ to SlRs by a few stops...

May i know where can i find out the F stop of a digicam (eg F2.8) equates to which f stop in a SLR??

:)
 

denizenx

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#2
I think u mean depth of field?
the f-stop shd be relative to the frame I think, i.e. "how much light".
the dof between medium format, 35mm and digicam lenses all diff...
 

Revo

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#3
Originally posted by denizenx
I think u mean depth of field?
the f-stop shd be relative to the frame I think, i.e. "how much light".
the dof between medium format, 35mm and digicam lenses all diff...
i cc....

I was just wondering f2.8 on digicams would be ard which f stop in an slr....35mm ones...in particular....=)
 

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#4
f-stops in a digicam are identical to the f-stops in a conventional camera as far as the light metering is concerned. Meaning if you shoot 1/125s at f/8 on iso 100 film in a conventional camera to get a properly exposed shot, the same setting would give the right exposure for a digicam as well...

But as denizenx pointed out, the depth of field at a particular f-stop would be different between a digicam and a film camera... The digicams have much larger depth of fields because the "film" size and hence the absolute focal lengths are so small...
 

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Midnight

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#5
What Radix Lecti wrote is completely correct and summarises the entire situation very well. :thumbsup: As noted, digicam aperture f-numbers still work the way you would expect in terms of exposure control. However, with the exception of full-frame digital SLR bodies whose physical sensor sizes correspond to the 36x24mm format of 35mm film, since the f-stop refers to the ratio of the aperture diameter to the physical lens focal length and most digicam lens focal lengths are shorter than a 35mm lens with the same field of view, the physical aperture size at the same f-number and same 35mm-equivalent focal length will be smaller for a digicam than for a 35mm camera (just as the aperture size for a 35mm camera will be smaller than that for a medium format camera).

The following web page is considered to be an authoritative source on this subject: http://www.wrotniak.net/photo/dof/index.html . Basically, if the focal length multiplier of a digicam is N with respect to the equivalent 35mm focal length (eg. if a physical 10mm focal length on the digicam corresponds to a 35mm-equivalent of 40mm, then N=40/10=4), then the depth of field obtained by the digicam set to an aperture of f-number 1/q, is the same as that of a 35mm camera set to an f-number of 1/(N x q). In the case of N=4, then a digicam at f/4 has the same depth of field as a 35mm camera at f/16.

As you can imagine, this typically means that most (non-SLR) digital cameras tend to have plenty of DOF to spare, even at their widest aperture settings. This is generally a good thing, but it can be irritating when one is trying to employ selective focus in one's composition.
 

StreetShooter

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#6
Originally posted by Midnight

As you can imagine, this typically means that most (non-SLR) digital cameras tend to have plenty of DOF to spare, even at their widest aperture settings. This is generally a good thing, but it can be irritating when one is trying to employ selective focus in one's composition.
And, I might add, if you have a P&S digicam and still want to enjoy the ability to blur the background, the best way is to use a telephoto attachment.
 

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