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Thread started 02 Feb 2008 (Saturday) 06:35
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Viewfinder perspective and crop format observations

 
djeuch
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Feb 02, 2008 06:35 |  #1

Here's an interesting experiment for those of you with a 40D (could be others, but the 40D has a different viewfinder than previous xxD versions) and a 50mm lens (or zoom that covers 50mm). If you're using a zoom, set it to something like approximately 45-48mm.

I try and keep both eyes open so I can see if I'm going to run into something when shooting. What I noticed is somewhere in the 45-50mm range, the "view" through the viewfinder is the exact same perspective as my non-viewfinder eye. Just like it is with my 35mm film camera and a 50mm lens.

50mm is every so slightly zoomed in, but not 1.6 times zoomed in... it's a much smaller percentage.

Someone else can do the math, but the crop format along with viewfinder sizing and some viewfinder cropping yields almost the same perspective.

I just found this surprising. I know that compared to a FF view (again, using an old film camera) the image is 1.6x smaller, but I guess I was just surprised that viewfinder perspective didn't have the same factor!

Anyway, enough random rambling. Just very interesting results to me at least!


Canon 40D w/BG-E2N Battery Grip | Canon 5D w/BG-E4 Battery Grip | EF 70-200mm f/2.8L IS USM | EF 24-105mm f/4L IS USM | EF 85mm f/1.8 w/ET-65III | EF 50mm f/1.4 w/ES-71II | Canon 1.4x TC | Lowepro SlingShot 200 AW | B+W 77mm MRC (010) filter x2 | Speedlite 580EX II

  
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xarqi
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Feb 02, 2008 06:38 |  #2

Did you take into account the viewfinder magnification factor? It's 0.9 on a 30D, don't know about the 40D but it'll be in your manual.




  
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runninmann
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Feb 02, 2008 06:42 |  #3

djeuch wrote in post #4835452 (external link)
Here's an interesting experiment for those of you with a 40D (could be others, but the 40D has a different viewfinder than previous xxD versions) and a 50mm lens (or zoom that covers 50mm). If you're using a zoom, set it to something like approximately 45-48mm.

I try and keep both eyes open so I can see if I'm going to run into something when shooting. What I noticed is somewhere in the 45-50mm range, the "view" through the viewfinder is the exact same perspective as my non-viewfinder eye. Just like it is with my 35mm film camera and a 50mm lens.

50mm is every so slightly zoomed in, but not 1.6 times zoomed in... it's a much smaller percentage.

Someone else can do the math, but the crop format along with viewfinder sizing and some viewfinder cropping yields almost the same perspective.

I just found this surprising. I know that compared to a FF view (again, using an old film camera) the image is 1.6x smaller, but I guess I was just surprised that viewfinder perspective didn't have the same factor!

Anyway, enough random rambling. Just very interesting results to me at least!

I wouldn't expect the crop factor to affect the magnification of what you see through the viewfinder, just how much of the scene you can see. Am I wrong?


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Madweasel
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Feb 02, 2008 08:07 |  #4

runninmann wrote in post #4835469 (external link)
I wouldn't expect the crop factor to affect the magnification of what you see through the viewfinder, just how much of the scene you can see. Am I wrong?

That's true in principle, but the missing variable is the optics of the viewfinder itself. You're looking at a magnified image of the focusing screen, and the camera manufacturer could make that magnification anything he likes, the only trade off being that a bigger image would be proportionally dimmer.


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xarqi
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Feb 02, 2008 08:18 |  #5

Madweasel wrote in post #4835679 (external link)
That's true in principle, but the missing variable is the optics of the viewfinder itself. You're looking at a magnified image of the focusing screen, and the camera manufacturer could make that magnification anything he likes, the only trade off being that a bigger image would be proportionally dimmer.

Or brighter! The factor is less than unity in the 30D - maybe that's why.




  
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runninmann
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Feb 02, 2008 09:33 |  #6

Madweasel wrote in post #4835679 (external link)
That's true in principle, but the missing variable is the optics of the viewfinder itself. You're looking at a magnified image of the focusing screen, and the camera manufacturer could make that magnification anything he likes, the only trade off being that a bigger image would be proportionally dimmer.

Oh yes. I understand that. I was specifically referring to the OP statement from which I inferred that he attached some significance to the fact that the image was not 1.6X life size.


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SolidxSnake
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Feb 02, 2008 11:33 |  #7

Yes, that is going to happen. It makes sense too. The focal length of the lens does not change. Grab a zoom, set it to whatever find is the same as your non-viewfinder eye in perspective on a 1.6x camera, then keep the zoom at that setting and move the lens to a FF camera. You'll find it is the same thing (provided VF magnification is the same) because the focal length is not changing. The only difference is the area being captured.


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ggw2000
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Feb 02, 2008 13:39 |  #8

SolidxSnake wrote in post #4836526 (external link)
Yes, that is going to happen. It makes sense too. The focal length of the lens does not change. Grab a zoom, set it to whatever find is the same as your non-viewfinder eye in perspective on a 1.6x camera, then keep the zoom at that setting and move the lens to a FF camera. You'll find it is the same thing (provided VF magnification is the same) because the focal length is not changing. The only difference is the area being captured.

You get the prize;). A crop camera does NOT magnify anything. I gives you the illusion of it my giving you a smaller FOV than a FF sensor. You'll find that most people use the term "reach" but it is not a politically correct term. I use to have a link to a great picture that shows you how it works but have somehow lost it:o.
Gerry




  
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jra
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Feb 02, 2008 17:27 |  #9

djeuch wrote in post #4835452 (external link)
I just found this surprising. I know that compared to a FF view (again, using an old film camera) the image is 1.6x smaller, but I guess I was just surprised that viewfinder perspective didn't have the same factor!

I'm guessing that you're noticing the different viewfinder magnification between the two cameras. The crop camera viewfinder does reflect the 1.6 crop factor otherwise it would be pretty worthless.




  
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number ­ six
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Feb 02, 2008 17:46 |  #10

I never noticed that, since I always close my left eye when focusing. But I tried it just now on my 30D looking at a horizontal bar (window frame) where I could adjust the lens until the right eye and left eye images were the same height. Yep, it's about midway between the 35 and 55 markings, I'll guess at 44.

The Snake has the explanation - crop sensor or no crop sensor, I'm still looking at the center of the image from a 44 mm lens.

-js


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jra
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Feb 02, 2008 18:09 |  #11

SolidxSnake wrote in post #4836526 (external link)
Yes, that is going to happen. It makes sense too. The focal length of the lens does not change. Grab a zoom, set it to whatever find is the same as your non-viewfinder eye in perspective on a 1.6x camera, then keep the zoom at that setting and move the lens to a FF camera. You'll find it is the same thing (provided VF magnification is the same) because the focal length is not changing. The only difference is the area being captured.

I would think that you are incorrect. If the vf magnification was the same on both cameras, the viewfinder would show the larger FOV of the ff camera in the same area, therefore making the scene seem "further away" and not consistant with what your "free eye" was viewing. Hope that makes sense :) I haven't tested this....I'm just making a guess :)




  
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number ­ six
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Feb 02, 2008 19:25 |  #12

jra wrote in post #4838568 (external link)
I would think that you are incorrect. If the vf magnification was the same on both cameras, the viewfinder would show the larger FOV of the ff camera in the same area, therefore making the scene seem "further away" and not consistant with what your "free eye" was viewing. Hope that makes sense :) I haven't tested this....I'm just making a guess :)

Try it. I did. The Snake speaks truth. :cool:

-js


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jra
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Feb 02, 2008 20:34 |  #13

number six wrote in post #4838916 (external link)
Try it. I did. The Snake speaks truth. :cool:

-js

What two cameras did you use? Was the VF magnification the same on both cameras?




  
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djeuch
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Feb 02, 2008 21:36 |  #14

The viewfinder size and magnification must make up for some of the difference - otherwise either the viewfinder would be 1.6x smaller to make up for the same "crop" sensor size.

40D:
Viewfinder
Type
Eye-level SLR with solid glass pentaprism

Coverage
Approx. 95% horizontally and vertically

Magnification
0.95x (-1 dpt with 50mm lens at infinity)

Eyepoint
Approx. 22mm

5D:
Viewfinder
Type
Eye-level SLR with fixed pentaprism

Coverage
Approx. 96% horizontally and vertically (coverage against JPEG Large)

Magnification
0.71x (-1 dpt with 50mm lens at infinity)

Eyepoint
20mm


Canon 40D w/BG-E2N Battery Grip | Canon 5D w/BG-E4 Battery Grip | EF 70-200mm f/2.8L IS USM | EF 24-105mm f/4L IS USM | EF 85mm f/1.8 w/ET-65III | EF 50mm f/1.4 w/ES-71II | Canon 1.4x TC | Lowepro SlingShot 200 AW | B+W 77mm MRC (010) filter x2 | Speedlite 580EX II

  
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jra
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Feb 02, 2008 22:09 |  #15

djeuch wrote in post #4839561 (external link)
The viewfinder size and magnification must make up for some of the difference - otherwise either the viewfinder would be 1.6x smaller to make up for the same "crop" sensor size.

40D:
Viewfinder
Type
Eye-level SLR with solid glass pentaprism

Coverage
Approx. 95% horizontally and vertically

Magnification
0.95x (-1 dpt with 50mm lens at infinity)

Eyepoint
Approx. 22mm

5D:
Viewfinder
Type
Eye-level SLR with fixed pentaprism

Coverage
Approx. 96% horizontally and vertically (coverage against JPEG Large)

Magnification
0.71x (-1 dpt with 50mm lens at infinity)

Eyepoint
20mm

That was pretty much the point I was trying to make I think :) The VF magnification is what is making up the difference...if the magnification factor were the same, it wouldn't work out as you have noticed.




  
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Viewfinder perspective and crop format observations
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