mmcgavin

Calculating the Ratio of Reproduction by measuring the dimension of one side of the frame.
I have use this method for many years with a full-size 35mm Nikon and the length of the ruler in inches, visible across the height of the frame, gives the RR. However I am a little confused about the reliability of doing this in the viewfinder because viewfinders do vary in how much of the image they cover and also in magnification. Some of the last single lens reflex film cameras I owned, had viewfinder magnification factors as low as 0.7 5X as the designers attempted to cram all of that information onto the screen. I think the viewfinder of the Nikon SLR I used had about 95% magnification.
At present I am using a Nikon D-80 for personal photography, and the accuracy of the area included in the viewfinder is very poor, particularly with views and photographs of groups of people. Far more is included in the image than is seen in the viewfinder-almost like using a 28 mm instead of a 35mm wide-angle lens on a full-size 35mm camera. I tried the ruler across the frame on the D-80 and surprisingly it was quite accurate. In other words, if I put 4 inches of a vertical ruler across the height of the viewfinder the same length was visible in the digital image. Frankly I don’t understand that.
Could you refer me to a source that would explain the effect of sensor size and viewfinder magnification on this method of measuring RR or any of your personal experiences?
Most of my close up photography is of pathological specimens i.e. autopsy room photography.
Any insight you could give me would be appreciated.

BebuLamar

The viewfinder magnification has no effect on what you did. The finder accuracy would if it doesn't show 100% of the captured image.

mwsilvers Loc: Central New Jersey

I think you may be confusing magnification with coverage. Magnification like .75 is rated usually dependent on use of a 50 mm lenses as a standard. In other words, when looking through the viewfinder with a 50mm lens attached, how big does the field of view appear to your eye when compared to looking at the same subject directly. Additionally, as I believe you know, sensor size will affect that as well, but let's presume we're talking about a full frame 35 millimeter sensor. Coverage has to do with how much of the image in the final photograph you were able to see through the viewfinder. This varies from camera to camera, but generally appears to be somewhere between 95% and 100% for most of the better cameras today, with full frame or APS-C sensors. Below I've attached a link which may explain some of this to you better than I did.

https://luminous-landscape.com/understanding-viewfinders/

The Nikon D80 has, I believe, .94x coverage or 94%. Many newer Nikons, especially full frame models, have 100% coverage viewfinders. My Canon 7D Mark II has a crop sensor and has a 100% viewfinder, so what I see in the viewfinder is what I get. If I am misunderstanding your point, I apologize, but it seemed that you are more interested in viewfinder coverage rather than magnification.