Testing a camera's actual 35mm equivalent zoom

[Fardringle]

I read recently that if you look into the viewfinder of a camera with your right eye and keep your left eye open at the same time, objects should appear to be the same size with both eyes when the zoom length is set to about 50mm equivalent. I tried it out with my Fuji S6000fd and I actually have to move the zoom to the 100mm marking before objects are the same apparent size to me.

If what I read is correct, this seems to show that my camera is actually giving me a much wider field of view/lower magnification than would be expected from the listed "28-300mm" equivalent lens.

I don't have another camera I can use to test other than my old P&S Olympus and it doesn't even list 35mm equivalent numbers.

I was wondering if any of you would be willing to take a picture of a 12-inch ruler from 6 feet away and see what 35mm equivalent zoom length you need to use in order for the ends of the ruler to "touch" both sides of the field of view. On my camera, this is about 220mm.

For reference, if you want to measure it this way instead, the field of view for my camera is 7 1/2 feet across (horizontally) at 6 feet away at 28mm, about 4 feet across at 50mm, roughly 27 inches at 100mm, 13 inches at 200mm, and 8 inches at 300mm. At 10 feet away using 28mm I get a field of view 14 feet across.

It's not a really big deal but I'm curious and I'd like to know if the 4.7x crop factor that Fuji used to get the 35mm numbers is accurate for my camera.


Edit: Added the 10 foot measurement and fixed a typo I didn't notice earlier. Evil typos.

 

[Zenmervolt]

Originally posted by: Fardringle
I read recently that if you look into the viewfinder of a camera with your right eye and keep your left eye open at the same time, objects should appear to be the same size with both eyes when the zoom length is set to about 50mm equivalent.

They lied. That's simply not at all true.

http://www.mhohner.de/essays/myths.php#50mm

ZV

 

[ElFenix]

not to mention that due to different magnifications used by different cameras, then even if the myths about 50 mm lenses were true, it'd still be different from camera to camera.

 

[Fardringle]

That link says that the field of view isn't the same which is true. A fisheye lens with nearly a 180 degree field of view (counting peripheral vision) would be awesome, but impractical if it's even possible.

What I'm curious about is the actual "magnification". Simply, what focal length do you need to use on a full frame camera in order for objects in the viewfinder to appear the same size as they do to the naked eye at the same distance away?

 

[fuzzybabybunny]

This depends a lot on eye to viewfinder distance and the design of the viewfinder itself.

On my 30D, if I slap on my 50mm, put one eye flush with the viewfinder and have the other eye open, it's an almost exact 1:1 match in terms of magnification.

 

[Fardringle]

That is part of what I was looking for, and it agrees with the article I read. Thanks.

Would you mind testing with that same 50mm lens, or using a lens at one of the other lengths I listed, to see what your field of view is (how much horizontal distance can you see across the wall) when standing 6 feet away from a flat wall? I don't need an exact number, just a close approximation would be great.

 

[soydios]

magnification is a function of the viewfinder. a 50mm lens on a 135 camera (full-frame 35mm film) yields the same perspective as the human eye. by perspective, I mean the ratio of the sizes of objects at different distances.

 

[Fardringle]

That's why I'd like to know the visible size/magnification of objects at 50mm compared to the naked eye, which fuzzybabybunny already answered, as well as the actual field of view from a set distance (6 or 10 feet) away from a flat wall.

 

[Zenmervolt]

Originally posted by: Fardringle
That's why I'd like to know the visible size/magnification of objects at 50mm compared to the naked eye, which fuzzybabybunny already answered,

He answered it for one camera only. It will change depending on which camera and how the viewfinder is set up. It is dependent ENTIRELY on camera type and viewfinder design. You CANNOT use this to determine if the crop factor is accurate on your Fuji.

ZV

 

[Zenmervolt]

Originally posted by: soydios
magnification is a function of the viewfinder. a 50mm lens on a 135 camera (full-frame 35mm film) yields the same perspective as the human eye. by perspective, I mean the ratio of the sizes of objects at different distances.

Nope, it doesn't. That's a myth that's been propagated for years. It just is a simple lens that is easy to cheaply make high quality.

ZV

 

[Fardringle]

Originally posted by: Zenmervolt

Originally posted by: Fardringle
That's why I'd like to know the visible size/magnification of objects at 50mm compared to the naked eye, which fuzzybabybunny already answered,

He answered it for one camera only. It will change depending on which camera and how the viewfinder is set up. It is dependent ENTIRELY on camera type and viewfinder design. You CANNOT use this to determine if the crop factor is accurate on your Fuji.

ZV

I understand that. The appearance of objects in the viewfinder was just what led me to wonder if the actual focal length measurements are correct for my camera. I don't have anything to compare it against which is why I asked for the field of view at specific focal lengths as well. If you don't think that is a way to approximate the actual focal length of the lens either, I'd appreciate suggestions of how I can compare my results to the 35mm film standards.


Edit: Maybe I'm not explaining things properly? What I want to know is: If I stand in the same spot and take a picture with a full frame SLR using a lens at 28mm (assuming all other settings the same) will I get approximately the same field of view as I do standing in the same spot with my Fuji set to 28mm?

For a specific example of what I want to know, the Canon FD 14mm f/2.8L has a field of view of 114 degrees. That's about 18.5 feet horizontal field of view at 6 feet from a flat wall. Surprisingly, I can't find the field of view numbers for a 28mm lens.

I don't want to make anyone do the math (unless you really want to ) to calculate your own field of view in degrees, so I suggested standing at 6 feet (or 10) from a flat wall and measure the horizontal field of view of the lens at any of the focal lengths I listed earlier (i.e. 7 1/2 feet wide at 6 feet from the wall for me) so that I can compare it to my results.


As I mentioned before, it doesn't REALLY matter since I'll keep using and enjoying my camera just as it is, I just want to know to satisfy my own curiosity.

 

[ElFenix]

zoom lenses are only rated that focal length at infinity. they will vary when a closer focal point is selected.


http://forums.dpreview.com/for...=1029&message=26793545

 

[corkyg]

As Fuzzy indicated, I see the same thing with the 5D FF camera with a 50mm lens. I must use my left eye on the viewfinder - the right eye has never been much good after surgery for a detached retina. But, with the 5D and a 50mm prime lens, objects in the viewfinder are visually the same as naked eye view.

And, yes, - this is not necessarily true for all cameras.