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Old Jan 11, 2004, 7:04 AM   #11
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There are a couple of things to remember in this discussion. First of all, yes, the frame is smaller with a 1.6 crop factor. But most of us would then blow that image up MORE than we would a 35mm frame.

For example: suppose I shoot a bird to fill most of the frame on a 35 mm frame, and it takes a 640mm lens (not a standard size Now, we will use the full frame to make an 8x12 print. Since the short side of the frame is 24mm, about 1 inch, we enlarged it by about 8X. So far so good?

Now, on my D60, I can get the same bird at the same distance to fill the same portion of my frame with a 400mm lens.. The short side of my frame is only 15mm, or 6/10 of an inch, roughly. If I enlarge that the same 8X, I get a print that is somewhat less than 5x7.5". Let's assume that there are enough pixels in both images so that resolution does not enter as an additional problem.

If both images were equally well-focused, the smallest point of light will come out to the same size dot on the image (the so-called circle of confusion) and will appear equally sharp on both prints.

But I use my D60 to make an 8x12 print of the bird. Now, I am blowing up the shorter side of the frame (15mm) by about 13X (roughly.) That same smallest point of light in the image now can be seen with a loupe as being a larger circle on the print. The result? less apparent sharpness, less apparent detail, less apparent resolution. It would also follow that the area in apparent good focus would also be smaller, giving an impression of less depth of field.

But understand, too, that on this 8x12 print, which is blown up more for the D60 than for, say, the 1Ds, that any camera movement also is blown up more. This means that the rule of thumb for handholding the lens (the reciprocal of the focal length, 1/400, as the minimum shutter speed) would hold true, possibly, for the 5x7.5" print. But if I blow the frame up to the 8x12" size, I should probably use a shutter speed of the reciprocal of the focal length of the 640mm lens to avoid blur from camera movement.

I hope I haven't caused anybody's (circle of) confusion to get bigger with this post- :roll:
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Old Jan 13, 2004, 1:09 PM   #12
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Thanks Walter! Very nice explanation.

A smaller sensor means a bigger enlargement factor to get to a certain size print, and therefore the image taken with the smaller sensor needs to be sharper than one taken with a bigger sensor.

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