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Old Sep 23, 2002, 5:48 PM   #11
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Sparhawk, I understand what kind of a device you mean but I'm not aware that anyone makes one or has even tried. It's also looking like there may be no needed as Kodak just announcd a full frame, 14mp camera with a CMOS sensor that doesn't have the falloff problems anticipated in other full frame SLRs. It's $4,000 but I expect it will trickle down to the $2k cameras within a year or so.
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Old Sep 23, 2002, 11:05 PM   #12
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Sparhawk ..

Again, if you realize that all the dSLR chips do is crop, then yuo will be on track.

A converter of the sort you describe would essentially be the same as using a wider angle lens ... that is making a 35 mm equiv lens act like a 28. From an optics sense this makes little sense .. it makes more sense to use a wider lens in the first place.

Morever, if we are talking about a 28 mm (real focal length lens) the elns you are talkng about would turn it into the equiv of a 19mm or so. That might work because yuo would only be using part of the 19 mm projection filed BUT the cnverting lens would have to preserve the focval plane and the eveness of illumnation .. not likley.
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Old Sep 24, 2002, 6:39 PM   #13
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Default Not quite right....

Again, if you realize that all the dSLR chips do is crop, then you will be on track
This is only partly correct. The "crop factor" results in an enlargement to the "effective focal length." It work like this:

The full resolution of the sensor is vested in a smaller footprint than the 35mm frame which, in essence, means that the electronic signal which represents a value to be made into a pixel describes its "area" X number of times within this parameter. This results in a horizontal by vertical matrix of values which correspond to the sensor's photo site count on the horizontal by vertical axis.

When this information is relayed to a display or print device, a fixed size pixel is used for the display or print. For example, if the display resolution is set for 72 dots per inch (a common setting) then each pixel worth of information from the sensor will result in a display portion relative to this fixed dot pitch.

This means that when comparing a full sized (from 35mm equivalent or 1:1 sensor) un-cropped image from a capture to one made from a sensor with a "crop factor of equal electronic resolution," the images will both be of equal horizontal and vertical size, but the image from the sensor with the crop factor will display less geography and the subjects will be larger by the extent of the crop factor. That is to say that there will be a magnification in accordance with the "effective" focal length of the lens or combination being used compared to a 1:1 capture.

For example, if I shoot an image with my 100-400 lens at 400mm with my D30, the image size in print or display at a given appearance will be as if a 35mm slide or negative were shot of the same subject with a 640mm focal length lens.

The image from the 1.6x crop factor sensor will have the depth of field and other characteristics associated with the 400mm true focal length, but it will have the size (magnification factor) of the 640mm capture with a 35mm film or 1:1 digital sensor.

I do this on a daily basis when comparing my DCS-760 (crop factor 1.3x) with my associates D60 (crop factor 1.6x). For all practical purposes, the resolution is identical (approximate pixel count) but the image display magnification is not.

The essence is as if one were to crop a 35mm contact print, enlarge the result back to the original 35mm frame size, then do what ever with the result.

Though the "magnification" comes electronically, the result is as if there were a longer lens.

Now - you can't get something for nothing. The "trade-off" is light loss. The light loss from the crop factor with a 1.6x factor is as if one were shooting with a 1.6x telephoto attached to a 35mm film camera.

If you stop and consider this from a consumer camera perspective, it will make more sense to you. When you have a small zoom lens with a true focal length of around 7mm to 24mm, how do you get the equivalent of 38 to 132mm in 35mm equivalency? It's by the same process. The MUCH shorter true focal length lens is "acting" like much longer glass because of the "crop factor" You have a very small field of view which is captured with "X" (substitute pixel count here) number of photo sites. This is then displayed and printed with devices which have fixed pixel sizes - thus the "magnification" to 35mm equivalencies.

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