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Nikon Bob
03-12-2005, 12:58
Has anyone compared DOF of the same lens on an RD1 to a M Leica? Curious to see if the smaller sensor size really has an affect on DOF similar to going MF/LF where aperature for aperature I have been told there is less DOF when compared to 35mm format. I am not talking the amount of light let in, just any change in DOF. I am guessing that there would be more DOF with the smaller sensor.

Bob

driggett
03-12-2005, 13:14
Bob,
Why would this be? DOF should be consistent across the whole film plane(ccd plane). The smaller sensor should just have the effect of cutting the 35mm neg. If you put a mask around a 35mm negative so that only the sensor area of aps was showing you should get the same DOF(Depth of Field). Did aps camera have different DOF then 35mm cameras?
Thanks,
Chris

jlw
03-12-2005, 13:16
In principle, DOF at a given numerical aperture should always be the same for the same final image magnification (object size on the actual print.) But this would be a tricky comparison to make, since the R-D1 image would be a cropped version of the full-frame 35mm image.

-- Would you compare by shooting a photo with the R-D1, then moving closer with the 35mm camera until the lens covered the same subject area?

-- Or would you shoot both photos from the same distance, then crop the center part of the 35mm image and enlarge the cropped section to the same size as the R-D1 image?

-- Or would you shoot both photos from the same distance and print the full image area, disregarding the fact that objects in the 35mm image will be smaller?

Just to make things more complicated, there really is no such thing as depth of field -- it's an optical illusion caused by the eye's limited ability to resolve fine detail. Since there's no way to view an R-D1 image except on some type of computer output -- monitor, inkjet print, whatever -- your apparent DOF is going to be based on the eye's ability to resolve detail on that particular type of output. So it could be that the apparent DOF of an R-D1 photo would vary according to the way you're viewing it!

This isn't a new problem. Newspapers reproduce photos via a fairly coarse halftone screen (typically 65 lines per inch) that divides the photo into dots that are visible on careful viewing. A side effect of this is that a photo reproduced in a newspaper has somewhat greater apparent DOF than the same photo viewed as a print: the halftone dots break up the image so that slightly out-of-focus areas look just as sharp as in-focus areas, creating the impression that subjective DOF is larger.

driggett
03-12-2005, 13:25
jlw,
To make the comparison the same you need to shoot with the same lens at the same f/stop and the same distance. Then crop the 35mm negative to the size of an aps and then measure the DOF. If you change the distance of the cameras so that the image size is the same size relative to the film/sensor size then you will have different DOF as this relates to f/stop and subject to lens distance not sensor size.
Cheers,
Chris

Nikon Bob
03-12-2005, 13:57
Ok, seems like there is no simple answer. I was just wondering as I said I had been told that you you have less DOF with MF/LF at same aperatures as 35mm and that was related, somehow, to format size. I was guessing that by going down in size then the reverse was true. I am also guessing that the DOF in LF is smaller otherwise tilts and swings would not be as popular as they are. I was just wondering if anyone had done an actual test to see if an F1.4 lens in front a smaller sensor was really a F2 lens DOF wise.

Chris

The question about APS vs 35mm re DOF was right in line and I wish I knew the answer. That is why I am asking. As APS died so rapidly nobody cared but when you spent big $$$ on fast lenses in part to isolate parts of the image it might be worth giving it some thought.

Bob

driggett
03-12-2005, 14:29
Bob,
Try this link. I just read the page and I think it will give you the answers you seek.
http://www.photo.net/learn/optics/dofdigital/
Cheers,
Chris

David Kieltyka
03-12-2005, 15:25
With the R-D1 you gain about a half stop of DOF compared to using the same lens at the same aperture, with the same framing, on a 35mm RF. This means with the R-D1 you must move back a bit because its smaller format gives you a narrower field-of-view with any given focal length. If you shoot the same subject with the R-D1 and, say, a Leica M7 with the same lens & aperture from the same vantage point, then crop the M7 photo to the same FOV as the R-D1 photo, the DOF will be identical. This is all in line with the photo.net article Chris has linked to.

jlw is also right that DOF is sort of an illusion. It describes a zone of acceptable unsharpness agreed upon by consensus. But only the point of focus is truly in focus. :)

-Dave-

Nikon Bob
03-12-2005, 16:10
Chris

Thanks

Dave

Circles of Confusion? I thought that it was generally agreed DOF was an zone of acceptable unsharpness in which the point focus (sharpness) exists. Thank you for the answer which is yes more or less if I read you correctly.

Bob

Bob

David Kieltyka
03-13-2005, 14:41
Bob, yeah, the zone of acceptable unsharpness exists around the point of focus. The circle of confusion is another way of expressing (and calculating) the same thing.

-Dave-

J. Borger
03-13-2005, 22:13
When i went from a Canon D30 to a 1D and after that to the full frame 1Ds the differences in dof in day to day use were very evident .... never did side to side tests, nor do i have the technival knowledge to interfere with the discussion above about coc etc. ..... all i can say is that with a full frame camera it is far more difficult to get a macro shot or a landscape with tele-lens completely in focus .... so yes dof is more limited with full frame or film camera's.

Han

Nikon Bob
03-14-2005, 03:17
Han

Your answer was more along the lines of what I was originally asking. I had similar experiences when using my Olympus C5050 and wondered if anyone could substantiate what I felt I was seeing. How it got to what DOF is I don't know. At least I am not alone in seeing it, thanks.

Bob

J. Borger
03-14-2005, 03:45
BoB,

In comparisson with a P&S digital like the Olympus the R-D1 has limited dof!
In general expect the following:

- with a R-D1 it will be more difficult to have enough dof in a landscape than with a P&S
- with a R-D1 it will be easier to throw the background partly out of focus than with a P&S but it will be a bit more difficult with a R-d1 than with a full frame or film camera

With respect to dof the difference between the R-D1 and a full frame or film camera is small in comparison to the difference between a P&S and a digital SLr or the R-d1 with a 1,5 crop factor!


Han

Jim Watts
03-14-2005, 03:46
My subjective impression from a number 10 x 7 inch (on A4 paper) inkjet prints (as distinct from a proper scientific analysis) is that my 35mm f/2 Summicron in most cases gives less "Depth of Field", note the quotation marks, on my R-D1 than on my Leica M4. Closer to my 50mm f/2 Summicron printed using full frame from the M4, but this is roughly what you would expect from the 1.53 magnification (53mm) without going too far into "Circles of Confusion" :confused: :confused:

Nikon Bob
03-14-2005, 04:53
I guess that sometimes simple questions are not really simple. By test I had thought of the old ruler laid flat and focussed on a certain point and comparing the apparent DOF on an M body to the same lense on an RD1. The difference in DOF to me using a P&S digital seemed really huge considering that it has an even smaller sensor than the RD1. Seems everyone can agree that there is a difference towards more apparent DOF when using a sub fullframe (35mm) sensor.

Bob

Doug
03-14-2005, 10:22
True, Bob, that it's not quite so simple. A smaller sensor/film area will be accompanied by a shorter focal length lens for a normal angle of view, and that shorter lens at the same subject distance, same f/stop and same print size will give more apparent DoF. Have to add in all these qualifications to make it true!