Measuring focus distance

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Howdy,

 

I would like to know where the focus plane is measured from? When a lens says it will focus at closest a distance of 28 inches, where does that start? My power of deduction, which is sometimes faulty, tells me that it is on the rear element, but I do not know if that is correct.

 

Thank you,

 

Justin

[FrozenInTime]

Measure from the film / sensor plane

 

On film M series cameras, there is a Φ mark corresponding to this under the film advance

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Thank you Frozen, I genuinely appreciate that. I hope it isn't cold where you are!

 

Thank you,

 

Justin

 

My next question is: Is the rated minimum focus distance accurate? I only have Leica lenses and I assume that the information that they tell me is perfectly accurate, but maybe I'm not in the know.

[lars_bergquist]

(a) Digital M cameras do not have the focal plane mark. But the distance from the front surface of the camera bayonet to the focal plane is 27.8mm, so you can put it there yourself if you wish.

 

( Most M lenses can focus to a hair closer then the official 0.7m/28". Some non-Leica M lenses go closer, but then the rangefinder follower (that little roll inside the bayonet) cannot folllow the cam surface on its way out, so you have to focus by scale. I have for instace a ZM 18mm Distagon and a ZM 25mm Biogon which both focus to 0.5m (20"). When you pass 0.7m the rangefinder images do no longer move (and the parallax compensation ceases to operate) as the rangefinder disengages.

 

The old man from the Age of the Focusing Cloth

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Thank you for your responses,

 

I still use an M6 because I don't like the look of digital. When I bought my M6 new in 1998 I was a young man just graduating college and it was a great deal of money for me. In my mind I made the justification that it was a camera for a lifetime. Today I make my entire living with it and I believe that my customers actually respect me more because I still use film, especially when they see the beautiful pictures that I can produce.

 

I've never used my camera to do anything macro and a customer recently asked me to do some close up work. I ask about the focus plane because I'd rather calculate my depth of field with a tape measure in this instance because the pace of this project will be very fast and I want it to be perfect.

 

Thank you,

 

Justin

[Michael Geschlecht]

Hello Justin,

 

Welcome to the Forum.

 

The distance being measured is from the the film/sensor plane to the object to be photographed. W/ my M3 the measuring point I use for the the focal plane is the back of the accessory shoe. I measure from there to the object in question. Works for me & the back of the accessory shoe is a convenient place to put the hook @ the end of a measuring tape or a measuring rule.

 

My 35mm Summicron w/ goggles set @ 0.7 meters has the images coincide @ the edge of a dark object placed 0.7 meters in front of that point. This test requires a light background behind the object being measured. The measurement is done by moving the object to be measured back & forth over the measuring tape & putting it down where the images coincide.

 

Best Regards,

 

Michael.