Why does a subject look the same size to my eye and in the viewfinder at about 55mm?
Asked 3/13/2011
3 views
2 answers
0
Using a Canon 18-135mm zoom on a DSLR, I look through the optical viewfinder with one eye and keep the other eye open. As I zoom, there’s a point around 55mm where a subject appears about the same size in the viewfinder as it does to my unaided eye. Is there a name for this, and does that focal length mean anything special about the subject or lens?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
15y ago
2 Answers
17
There's a specification on (d)SLR bodies called viewfinder magnification; this refers to how large an object appears in the viewfinder when a 50mm lens is mounted and focused at infinity.
On mid-range DSLRs, which typically have around 0.95x magnification, an object will appear to be life-sized at 52.6mm. With entry-level DSLRs, you might have around 0.8x magnification, so you'd have to zoom in to 62.5mm to get a 1:1 magnification. I'm betting your camera has somewhere around 0.9 to 0.95x magnification.
This has very little to do with the object, except that the front of the camera is slightly closer to the object. With far-away subjects (landscapes, etc), the distance between your eyes and the front of your camera won't matter much, but close subjects will appear larger to the camera than to your eye even with a 1:1 magnification.
Originally by user378. Source · Licensed CC BY-SA 4.0
user378
15y ago
0
Generated from our catalog & community — verify before relying on it.
What you’re noticing is mainly the camera’s viewfinder magnification, not a special property of the subject. DSLR optical viewfinders are designed so that, with a roughly “normal” focal length, the viewfinder image looks close to life-size when compared with your other eye.
The exact focal length where this happens depends on the camera body’s viewfinder magnification and sensor format, not just the lens. On many APS-C DSLRs, it often ends up somewhere a little above 50mm, so about 55mm is plausible.
So, that focal length does not mean anything special about the object you’re looking at. With a different camera body, the same object could match at a different focal length. Distance can also affect the comparison slightly for close subjects, because your eye and the camera are not in exactly the same position.
In short: it’s basically a 1:1 apparent-size match caused by the viewfinder design, not a unique property of 55mm or of the subject.
Recommended products
UniqueBot
AI15y ago
Your Answer
Related Questions
Why does 50mm look life-size through my APS-C DSLR viewfinder?
What changes when you zoom and move to keep the subject the same size?
Why doesn’t 25mm on Micro Four Thirds look “normal” through the viewfinder?
How does optical zoom relate to subject size in the image?
Why does my Canon SL1 focus accurately in Live View but miss focus through the viewfinder?