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05-08-2020, 07:25 PM   #16
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DoF is a range around the focus point As perceived on the sensor , But physically measured at the subject

I am not sure where and whether there is any relevance to a physical place in a lens. But it would likely be around the lens theoretical location on lenses with retro focus elements or lenses that focus by changing focal length as opposed to simply moving the entire optical group

05-08-2020, 08:35 PM   #17
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QuoteOriginally posted by swanlefitte Quote
I am curious if dof is measured from the sensor, the lens center, or front of the lens. With macro that matters alot.
Focal plane

Edit: I made a major boo boo here in that DOF exists on the "object" side of the lens and is relative to the plane of focus. While the near and far extent are often stated as distance from the focal plane, the DOF is never relative to the focal plane per se except that the distance determines the magnification.


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Last edited by stevebrot; 05-09-2020 at 09:10 PM.
05-08-2020, 08:51 PM   #18
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QuoteOriginally posted by stevebrot Quote
Focal plane


Steve
Focal plane would be sensor then.
05-09-2020, 08:49 PM   #19
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QuoteOriginally posted by swanlefitte Quote
Focal plane would be sensor then.
For cameras that have digital sensors, yes. Note: I added an edit to my comment above clarifying the reference points for DOF.


Steve


Last edited by stevebrot; 05-09-2020 at 09:08 PM.
05-09-2020, 08:58 PM - 2 Likes   #20
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While on the subject of DOF, there is a series of short articles/tutorials on the Coin Imaging Web site on the subject, with an emphasis on macro photography. The author is a favorite of mine and I have found his explanations useful...

Optics Articles

(DOF articles are towards the bottom of the list of links. The articles are intended to be consumed in order.)


Steve
05-09-2020, 10:52 PM   #21
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QuoteOriginally posted by stevebrot Quote

(DOF articles are towards the bottom of the list of links. The articles are intended to be consumed in order.)


Steve
Good links. I find it funny how he uses both metric and imperial in the same sentence. 8x10 viewed at 25cm. Why not viewed at 10?
05-10-2020, 07:58 AM   #22
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QuoteOriginally posted by swanlefitte Quote
Good links. I find it funny how he uses both metric and imperial in the same sentence. 8x10 viewed at 25cm. Why not viewed at 10?
What's weirder to me is how popular 8x10 still is as a format. I usually have to go to a crop I don't particularly like to put an image in an 8x10 frame. Even in film my preference was 8x12. But these things no longer refer to the actual measurements, they refer to ratios as well.

The lack of other than 4x5, 8x10, 16x20 frames (4:5 ratio) got me into custom mats back when I was printing. I just couldn't find what I wanted off the shelf.

The 25mm close focusing distance is not a ratio, so CM makes more sense (or at least if does if you're from a metric country.)

That's my take.

05-10-2020, 11:43 AM - 1 Like   #23
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QuoteOriginally posted by normhead Quote
What's weirder to me is how popular 8x10 still is as a format.

The 25mm close focusing distance is not a ratio, so CM makes more sense (or at least if does if you're from a metric country.)

That's my take.
I agree. 4x5 is my least used crop. 2x3 my most of course and it is difficult to find large printing let alone frames.

As far as cms why not use 20x25 at viewing of 25? I am thinking it just came natural to say. I hate sensors be 1" etc be consistent. I am not against us imperial either. It is like fstops. 16 cups=8pints=4quarts=1gallon.
Sometimes grouped by doubling is better.
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