Angle of view not matching specs?

[a6k]

I compared the angle of view of my SONY HX-50 to my a6000 using my Nikon 300 legacy with Metabones adapter plus Nikon 1.4x extender. I expected the HX-50 (129 mm with advertised "35 mm equivalent" of 720 mm) to give a "longer" lens. 300 x 1.4 x 1.5 = 630.  In other words I expected that my pocket SONY would reach out a little better than my legacy "stack" of glass. 630 is much less than 720.

 

To my surprise, the results were clearly the opposite of what I expected. The image on the a6000 was bigger (relative to the frame) and it did not take fine measurements to see it. This is not a trivial difference. Something is not as it looks OR I'm simply not using the numbers correctly.

 

For those who wish to double check my specs, I'm using 6.17 mm x 4.55 mm for the sensor size of the HX-50 and the 129 mm = 720 mm is what SONY says. 

 

When I use an online calculator of field of view, I get 3.8 degrees for the a6000 and 3.1 degrees for the HX-50. That agrees with what I was expecting.

 

Are there any experts out there who can clear this up?

 

I can supply test shots later, but for now, assume I am accurately describing my results.

 

Thanks.

http://www.sony.com/electronics/cyber-shot-compact-cameras/dsc-hx50-hx50v/specifications

HX-50 picture: 5184 x 3888  vs a6000: 6000 x 4000. 

[Username]

My math says that with a 7.82mm sensor a 129mm optic has

a 35mm equivalent [42.3mm sensor] of 697mm. So there's a

23mm difference from your math. 

   

Next we encounter your "stack". You have based your math 

on believing that Nikon's 1.4X TC is truly 1.4X, and also that 

Nikon's 300mm is truly 300mm. These are unfounded beliefs.   

     

###############################################  

     

 All in all, i don't find your surprises very surprising. Also I'd 

suggest ignoring ANGLE of view stated in degrees. A more 

realistic spec is magnification. Acoarst magnification must be 

relative to some starting point. My comfort zone in this regard 

is that I use 1.0 X magnification to mean that the width of the 

subject field equals the subject distance. I like the idea that

with my default 35mm lens, the distance to the subject is also 

the width of the scene encompassed in my view. Thus for me

a 35mm lens has a magnification of 1.0 X. You can acoarst

use any basis you choose. 

[a6k]

"My math says that with a 7.82mm sensor a 129mm optic has

a 35mm equivalent [42.3mm sensor] of 697mm. So there's a

23mm difference from your math. "

-------------------------------------------------

We don't agree on the sizes. The dimensions of the standard full frame sensor are 35.8 x 23.9 = 43.04 diagonal. The reference to 35 mm comes from the original width of the film which was half of the 70 mm standard film. The image size on the film was approximately 24 mm across the film and 36 mm along the film. The aspect ratio of 36 x 24 is 1.5. The aspect ratio of the Sony HX-50 is, however, 1.33 vs the 1.5 on the a6000, matching full frame aspect ratio.

 

• The dimensions of the a6000 sensor are 23.5 x 15.6 = 28.21 diagonal.
• The dimensions of the 1/2.3" sensor in the HX-50 are 6.17 x 4.5 = 7.67 diagonal. (The reference to inches in this case is based on an historical but irrelevant thing and not actual size.)
• The horizontal crop factor of the HX-50 is 5.8 vs the a6000 horizontal crop factor of 1.523. 
• The vertical crop factor will vary because the aspect ratio varies. For the HX-50, it's 5.253 vs 1.5 for the a6000 or a difference of 3.5x vertical but 3.87x horizontal. This complicates the visual comparison for me because I was looking at the verticals.

 

I agree with you that we cannot assume that the specs given by Sony and/or Nikon are perfectly accurate and yet that's a pretty big "error".  I did not base my observation on calculated angle of view; I only threw that in for reference. My pictures were my criterion. When I get home from this vacation I can re-do the pictures with more obvious subjects for comparison (such as a rule). If this thread is still getting views, I'll post them then.

 

Sony appears to be using the diagonal crop factor for the HX-50 which would be 5.61. That CF times 129 mm gives 723.7 equivalent. 

If I use the diagonal CF for my a6000 it is 1.526 x 1.4 x 300 = 640.9 equivalent.

 

But if I use the vertical CF's it's 5.253 x 129 = 677.6 compared to the a6000 at the same 640.9. In this version the HX-50 is only slightly "longer".

 

But my pictures still show a marked size difference between the cameras with the a6000 giving the bigger image of the same object at the same distance. I don't have to measure it because it's so visually obvious. It's still a marked difference in the wrong direction. When the observation contradicts the theory then the theory is likely wrong.

 

So the question boils down to:

1. Is there something wrong with the method of calculating equivalents that I am using?

2. Is there something wrong with how we understand lens focal length when using a legacy full frame lens (and/or extender) on a mirrorless camera with a smaller sensor?

3. Some other error?

4. Some combination of the above?

 

 

   

"Next we encounter your "stack". You have based your math 

on believing that Nikon's 1.4X TC is truly 1.4X, and also that 

Nikon's 300mm is truly 300mm. These are unfounded beliefs.   

     

###############################################  

     

 All in all, i don't find your surprises very surprising. Also I'd 

suggest ignoring ANGLE of view stated in degrees. A more 

realistic spec is magnification. Acoarst magnification must be 

relative to some starting point. My comfort zone in this regard 

is that I use 1.0 X magnification to mean that the width of the 

subject field equals the subject distance. I like the idea that

with my default 35mm lens, the distance to the subject is also 

the width of the scene encompassed in my view. Thus for me

a 35mm lens has a magnification of 1.0 X. You can acoarst

use any basis you choose. "