Lens focusing scale

Chan Tran · Jun 16, 2012

I am wondering that the distance marking on the focusing ring on most SLR lenses are supposed to measure from film plane to subject or from front nodal plane to subject or what? None seems to really agree (they are close but not right on so can't say they are marked for one o another). Any information on this?

E. von Hoegh · Jun 16, 2012

Chan Tran said:
I am wondering that the distance marking on the focusing ring on most SLR lenses are supposed to measure from film plane to subject or from front nodal plane to subject or what? None seems to really agree (they are close but not right on so can't say they are marked for one o another). Any information on this?

Film plane. On most older cameras, there was a marking to show the location of the film plane, it looks like a zero with a line through it.

RalphLambrecht · Jun 16, 2012

i thought, this was true for all camerasand filmbacks. it's true for allof mine, but all of mine are old!

E. von Hoegh · Jun 16, 2012

RalphLambrecht said:
i thought, this was true for all camerasand filmbacks. it's true for allof mine, but all of mine are old!

Yeah, I don't recall seeing the marks on the few newer cameras I've handled.

tkamiya · Jun 16, 2012

I have the said mark on Nikon F100 and all of my digis (D200 and D60)

I guess it's time for me to upgrade!

Chan Tran · Jun 16, 2012

Thanks all! All my cameras have film plane mark and I knew about it. Just that my measured distance and what's on the focusing ring don't agree.

semi-ambivalent · Jun 16, 2012

E. von Hoegh said:
Film plane. On most older cameras, there was a marking to show the location of the film plane, it looks like a zero with a line through it.

On the Nikon F bodies the film plane was denoted by the "top" of the serial number on the rewind-side top cover. (Factoid, fer sure.)

E. von Hoegh · Jun 18, 2012

semi-ambivalent said:
On the Nikon F bodies the film plane was denoted by the "top" of the serial number on the rewind-side top cover. (Factoid, fer sure.)

I'd have to look, but I don't recall a mark on my F. I'll look in the instruction manual. The Nikkormat Ftn sitting here on the desk has the filmplane mark, though.

Peltigera · Jun 18, 2012

Chan Tran said:
Thanks all! All my cameras have film plane mark and I knew about it. Just that my measured distance and what's on the focusing ring don't agree.

Suggests that someone has had the lens apart at sometime and failed to set infinity focus when reassembling. Or poorly manufactured.

E. von Hoegh · Jun 18, 2012

Chan Tran said:
Thanks all! All my cameras have film plane mark and I knew about it. Just that my measured distance and what's on the focusing ring don't agree.

Don't agree by how much? More than a few inches could be a problem at close distances.

Chan Tran · Jun 18, 2012

E. von Hoegh said:
Don't agree by how much? More than a few inches could be a problem at close distances.

Not by much! Setting the focusing ring at 2 m the actual distance to have the subject in focus is 1.9 so it's 5%. At close distance the scale is set at 0.5 m and actual distance is 0.48 it's 4%. That's for the Nikkor 50mm f/1.4 AI.

Peltigera · Jun 19, 2012

Seeing as the whole point of a SLR is that you focus through the lens, why does it matter? And unless you are shooting at f2 or bigger, won't the depth of field cover any inaccuracy if you are relying on measuring the focus for some reason?

E. von Hoegh · Jun 19, 2012

Peltigera said:
Seeing as the whole point of a SLR is that you focus through the lens, why does it matter? And unless you are shooting at f2 or bigger, won't the depth of field cover any inaccuracy if you are relying on measuring the focus for some reason?

That's true. I cannot think of many circumstances when you'd need to focus with a tapemeasure.
The OP didn't say what camera it was, on an autofocus camera they're likely just ballpark figures.

Chan Tran · Jun 19, 2012

what's the difference if I use an autofocus camera? The lens is a manual focus lens. For the measurement I used a Nikon FM because it has the split image. The reason I asked to question because out of curiousity a long time ago I made the measurement and remember that it's not accurate. Recently upon a D forum and some people used manual focus lenses on their mirrorless and can't focus with the D.. LCD so they resorted to the scale and found they are not accurate. I actually never used the scale on the SLR.

Lens focusing scale

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