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-   Canon XL and GL Series DV Camcorders (https://www.dvinfo.net/forum/canon-xl-gl-series-dv-camcorders/)
-   -   Depth of Field and Zoom (https://www.dvinfo.net/forum/canon-xl-gl-series-dv-camcorders/28869-depth-field-zoom.html)

Jean-Philippe Archibald July 13th, 2004 07:49 PM

Ho, that's new to me Don. Can you explain this a little bit more? Is the reduction in DOF if significant?

Jeff Donald July 13th, 2004 07:53 PM

Aaron, no, if everything is equal, the lens with the longest focal length (highest mm) produces the highest magnification. Smaller chips do not inherently have higher magnification or greater DOF. But if you choose to have the image on the smaller chip match identically the image on the larger chip, then the focal length must be changed or the distance from subject to chip plane must be changed. Changing distance to subject or the focal length changes DOF.

Nick Hiltgen July 13th, 2004 07:54 PM

I follow you barry, I don't follow you don, can you explain further, is anyone else impressed by hwo quickly the xl2 forum took off... a lot of talk for a camera 99% haven't even SEEN in person!

Jeff Donald July 13th, 2004 07:56 PM

The number of blades will not change the DOF, but will effect the Bokeh, or how out of focus highlights will appear.

Rob Lohman July 14th, 2004 03:09 AM

Nick: that's because a lot of questions are asked and a lot can
be answered as well due to careful inspection of the specs and
other information (like the XL2 watchdog) that IS available. And
a lot of this still depends a great deal on knowledge and experience.

Like the topic we are discussing now. It is a well known fact
that video zoom factors are not the same as microscopes for
example. It is also well known that the properties of DOF will
change if you change the chip size (or the READOUT size)
without changing the lens. This also "changes" the focal length
of your lens etc.

Nick Hiltgen July 14th, 2004 08:39 AM

ROb totally understand, I just think it's great that we can do all this now before most of us even touch the darn thing, quite a resource.

Jeff Donald July 14th, 2004 12:15 PM

Quote:

This also "changes" the focal length of your lens etc.
No, changing chip size does not change the focal length of a lens. A millimeter is still a millimeter, nothing has changed.

Rob Lohman August 1st, 2004 07:17 AM

Indeed, I worded this wrong. Thanks for catching this. Nothing
will change on your lens, ofcourse. What would be a better way
to describe this Jeff? Apparent focal length or something?

Jeff Donald August 1st, 2004 08:48 AM

In most digital still photography communities the term "crop factor" has been adopted, to indicate a change in image size. The reason being is that the image isn't magnified, it's just a smaller portion of the image. Video communities don't really think in those terms and generally refer to it as a magnification factor. For example the magnification factor of EOS EF lenses on the XL1 is 7.2X.

Barry Green August 1st, 2004 04:48 PM

<<<-- Originally posted by Rob Lohman : Apparent focal length or something? -->>>
The Field of View is what changes when you change the imaging size. A smaller chip will have a narrower field of view.

Jeff Donald August 1st, 2004 06:20 PM

This is where the debate, or perhaps confusion is a better word, starts. Barry is 100% correct in his thinking, except chips (CCD, CMOS etc.) don't have Fields of View. Lenses have FOV, for example, zoom a lens and the FOV changes, not the chip. The FOV is related to the diagonal of the chip, but FOV changes with change of change of focal length. It basically boils down to FOV being a characteristic of the lens and the chip is the device which displays the FOV.

Field of View is measured from the rear nodal point to the two opposite sides of the chip, when the lens is focused at infinity and the rear nodal point is one focal length from the chip.

Barry Green August 1st, 2004 09:39 PM

Yeah, it's overwhelmingly difficult to say it all and cover all bases.

What I meant was: given the same lens and all other things being the same, if you substitute in a smaller chip, you will have a narrower field of view as your resulting image. The reason being, the lens projects the same image at the same focal plane, but the smaller chip can (obviously) only record a smaller subsection of that same image. DOF and other such characteristics do not change, as those are all factors determined by the lens and are all set in stone by the time the image gets projected on to the chip. So Chip size determines how much of the lens' frame is seen. Larger chips = more of the image displayed, which means for an equivalent lens, you would see a wider field of view when using a bigger chip.

Jeff Donald August 1st, 2004 09:47 PM

Quote:

which means for an equivalent lens, you would see a wider field of view when using a bigger chip.
Correct, which is why 50mm is "normal" on 35mm film, 80mm to 105mm is normal on medium format and 210mm is normal on 4x5 format. A 50mm lens would be extremely wide on a 4x5 camera.

Aaron Koolen August 1st, 2004 09:49 PM

I think we're getting nit picky here, and talking mainly semantics.

Your "perceived" FOV changes with chip size but Jeff is probably being technically correct saying the chip doesn't change the "real" FOV, the focal length does.


Aaron

Jay Gladwell August 2nd, 2004 05:10 AM

<<<-- Originally posted by Aaron Koolen : Your "perceived" FOV changes with chip size but Jeff is probably being technically correct saying the chip doesn't change the "real" FOV, the focal length does. -->>>

Aaron, with all due respect, Jeff isn't being nit picky, he's being 100% factual. Would a 4x5 negative have a greater FOV than a 35mm negative? No! Why? Because the FOV of the light sensitive medium--negative, transparency, CCD--regardless of its size, is determined by the focal length of the lens. That's not being nit picky, it's being accurate.

Jay


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