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Author Topic: DOF and Multipliers (sorry - one more time)  (Read 1869 times)

samirkharusi

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DOF and Multipliers (sorry - one more time)
« on: November 22, 2002, 08:05:51 am »

[font color=\'#000000\']The D30, crop factor or not, is fairly easy, IMHO. There are not enough pixels for huge prints, so presumably the question should not be addressed from the size-of-print you are looking for (normal approach), but what is the smallest circle of confusion that the pixels can resolve. The pixels in a D30 are 9.5x9.5 microns, so, IMHO, it would be quite pointless to use a circle of confusion with a diameter smaller than 9.5 microns = 0.0095mm. The usual approach starts from the print size (usually taken as 8x10" or 8x12" = 8x magnification of an uncropped 35mm full format frame). Normal vision resolves around 5 line-pairs/mm or 0.1mm COC in the print = 0.0125mm on film. With the 1.6 crop factor this would translate to 12.8x magnification (instead of 8x) or 0.008mm in a D30 or a D60. As per earlier statement it would be useless to go below 0.0095 in a D30, but OK to use 0.008 in a D60 (which has 7.5 micron pixels = 0.0075mm). Hope this helps.[/font]
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Tim Gray

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DOF and Multipliers (sorry - one more time)
« Reply #1 on: November 19, 2002, 11:00:16 am »

[font color=\'#000000\']I know that this topic has been addressed, but I can't find the thread searching either for DOF and 1.6 or DOF and multiplier.

My recollection was that the calculation simply related to the FL of the lens, the aperture, distance to subject, and the COF (which was based on the lens only).... Ie. you didn't adjust the focal length by the multiplier and something between .03 and .025 was appropriate for the COF - the same COF you'd use in a 35mm film camera.  Am I remembering correctly?  

There's a thread at http://www.robgalbraith.com/cgi-bin....=001807  that's getting me confused all over again suggesting that I should probably be using a COF of .019 (.019 x 1.6 = .03) rather than .03.  Actually you could get the same effect by using a FL multiplier of the square root of 1.6 = 1.265.  I have a program in my Palm that I actually do use to calculate HF distance and near/far in-focus points so it's more than academic.[/font]
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