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04-12-2012, 10:36 PM   #16
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Speaking of change in perspective - this is a great illustration of the difference between "zooming with one's feet" and a change in focal length. For different focal lengths, the field of view can be made to match only for a single distance.


Last edited by Ikarus; 04-12-2012 at 11:05 PM.
04-12-2012, 11:06 PM   #17
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You will never get the same FOV with a different focal length.

/thread
04-12-2012, 11:10 PM   #18
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QuoteOriginally posted by paperbag846 Quote
You will never get the same FOV with a different focal length.

/thread
Yes, you can, but only for a flat surface like a wall or a newspaper.
04-12-2012, 11:49 PM   #19
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QuoteOriginally posted by Ikarus Quote
Yes, you can, but only for a flat surface like a wall or a newspaper.
Or you can crop and get the same FOV and perspective as if using a longer lens. Or you can mount the lens on another camera body and get a different FOV without changing the perspective again. The possibilities!

04-13-2012, 02:54 AM   #20
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I think some are confusing FOV with AOV. For any specific frame (film or sensor) size, a specific focal length has a specific AOV, *angle* of view. But we can change FOV, *field* of view, ie the apparent width of a subject image, by changing distance (while shooting) or crop (in PP).

So even though 30mm and 45mm lenses will always have distinct AOVs on a given frame, we can get a 45mm lens' FOV with a 30mm lens by moving forward 50%. But changing the camera-subject distance will change perspective and DOF. All equivalences are approximate.
04-13-2012, 03:18 AM   #21
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I can't remember how many steps I walk backward when using the Tamron 500/8 mirror to frame a portrait
04-13-2012, 08:45 AM   #22
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QuoteOriginally posted by RioRico Quote
So even though 30mm and 45mm lenses will always have distinct AOVs on a given frame, we can get a 45mm lens' FOV with a 30mm lens by moving forward 50%.
By specifying the distance change in percent rather than absolute numbers, you're saying the same thing - the field of view can be made to match only in a single plane parallel to the sensor at a time, that is, the plane, where the cones of sight are made to intersect. In other words, there is no answer to the OPs original question about the number of steps to take without tying it to a specific subject distance, and even then - that subject better be flat as a pancake, or it won't look the same.

Last edited by Ikarus; 04-13-2012 at 09:26 AM.
04-13-2012, 08:51 AM   #23
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QuoteOriginally posted by Jeff Charles Quote
No. There are both DOF and FOV calculators on the page I linked to, but I used the Dimensional FOV calculator. The calculator can be misleading in that it does not account for the change in perspective as you move back.
OK, that's a difference in terminology, then. "Most" people, in my experience, do not make this distinction between "dimensional" FOV - measuring the size of an object at one particular distance that will fit in the frame - versus "angular" FOV, which takes into account objects at *all* distances. Stepping back may allow more of a given subject to fit in the frame, but it won't change the angle of view, and that means the background will not be as affected as the foreground. As I said, stepping back may allow you to capture more of a person standing in front of some scenery, but it won't appreciably change the amount of scenery you fit - what you are terming "change in perspective". So, you are of course correct, assuming we use the terms in this way.

There's a decent chance your answer is the one the OP wanted - maybe he/she only cares about the foreground subject.

04-13-2012, 09:24 AM   #24
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You can crop a 31mm shot to get a 43mm shot, but with worse resolution.
You can patch 43mm shots to get a 31mm shot, with better resolution,
but only for static subjects.
No foot movement required.
04-13-2012, 11:06 AM   #25
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QuoteOriginally posted by hoanpham Quote
I can't remember how many steps I walk backward when using the Tamron 500/8 mirror to frame a portrait
Falling down a cliff can do things to your memory, eh? Wait, you don't remember the fall, do you?
04-13-2012, 11:27 AM   #26
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QuoteOriginally posted by hoanpham Quote
I can't remember how many steps I walk backward when using the Tamron 500/8 mirror to frame a portrait
As I lay in the hospital bed, I bore myself to sleep by mentally counting those steps...

QuoteOriginally posted by Ikarus Quote
By specifying the distance change in percent rather than absolute numbers, you're saying the same thing - the field of view can be made to match only in a single plane parallel to the sensor at a time, that is, the plane, where the cones of sight are made to intersect. In other words, there is no answer to the OPs original question about the number of steps to take without tying it to a specific subject distance, and even then - that subject better be flat as a pancake, or it won't look the same.
That's right, it's all relative. Like asking a relative to walk backwards towards the cliff edge...

Anyway, different FLs at different distances can capture images with the same FOV (apparent width). Whether or not the subject plane is steeply angled, the images will differ due to perspective changes. I don't know if|how that angle affects the relationship between focal length ratios and distance to move for the same FOV. Time for a test, eh?
04-13-2012, 01:55 PM   #27
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I was shooting with the Tamron 500/8 in a castle:
https://picasaweb.google.com/117325951715314372265/Gamlebyen

As MFD of 1.5m, the Tamron 500/8 55BB is more like a macro lens.
That close focus ability tricked my mind for a while.
The edges are 30 feet down, but I got home safely that day. Thanks for your concern
04-13-2012, 02:36 PM   #28
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Use a protractor to draw separate angles on a piece of paper, one angle for each lens, using the horizontal angle of coverage of the lenses. So, now you have a wide angle and a narrower angle. Now, make the base of the triangle on each angle 3 inches (or whatever is convenient).

Cut out the triangles. Put the small one on top the larger one, aligning the bases. The proportionate differences in height is what you have to replicate in the field. You can do it for more than 2 lenses.

You can also do it a bit differently by using the same apex and hypotenuse, just drawing the different angles of view, which I did when I first got the DA Ltds.

I like graphic thingies, without the math :-)
04-13-2012, 08:52 PM   #29
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QuoteOriginally posted by Ikarus Quote
Yes, you can, but only for a flat surface like a wall or a newspaper.
Also works for a polar bear in a snow storm.
04-13-2012, 08:54 PM - 1 Like   #30
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QuoteOriginally posted by SpecialK Quote
Use a protractor to draw separate angles on a piece of paper, one angle for each lens, using the horizontal angle of coverage of the lenses. So, now you have a wide angle and a narrower angle. Now, make the base of the triangle on each angle 3 inches (or whatever is convenient).

Cut out the triangles. Put the small one on top the larger one, aligning the bases. The proportionate differences in height is what you have to replicate in the field. You can do it for more than 2 lenses.

You can also do it a bit differently by using the same apex and hypotenuse, just drawing the different angles of view, which I did when I first got the DA Ltds.

I like graphic thingies, without the math :-)
I guess using a zoom lens to actually see the difference between the two focal lengths would be too complicated and time-consuming.
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