Mamiya 7 - Field Coverage at Infinity

[Jesse Taylor]

I'm reading online that the field coverage at infinity is 83%.

My question, will I get less photo on the film or more than what is framed in the viewfinder?

Say if I have a mountain framed perfectly to the edges, would I have to move closer or further away?

Probably a silly question, but I just want to be sure.

 

[TimmyMac]

Coverage is normally the percentage of the frame (film area) that is covered by the viewfinder frame lines.

 

[Jesse Taylor]

So if a mountain was framed perfectly to the edges of the frame lines at infinity, would it cut off some of the mountain or would the film show more than the mountain?

 

[Matus Kalisky]

The film would show more than the frame-lines suggest. To account for this effect you would have to move a bit closer. The reason for this non 100% viewfinder "coverage" is that while the size of the frame-lines is fixed, the true angle of view (or the effective focal length) of the lens changes as you focus closer - namely it gets a bit longer. Most frame-lines are calibrated for some middle distances of a few meters so that in the infinity they show less than what ends up on the film and for the closest focus (about 1 - 1.5 m for Mamiya 7 lenses) they show a bit more.

This problem (of changing fraction of the image shown in the viewfinder with different focus distance) does not exist with SLR cameras - their viewfinders show always the same fraction of the image (usually between 90 - 100%) as you are looking through the lens.

I hope this makes sense.

 

[Jesse Taylor]

Thanks! Your first sentence was enough for me to understand.