Focusing distance is the length from the focal plane (film or sensor) to the subject.

Working distance is the length from the front of the lens to the subject.

The difference is the length of the tube plus the length of the lens which changes with focus (unless it's an internal focus lens). In your example this value is 93mm at min. focus and 85mm at infinity.

Trouble with Maths
 

The image I have attached was taken with a D70 – PB-5 Bellows at 80mm with an M2ext ,105mm 2.8D lens, f32 at 1/60, the working distance, lens to subject was 4” and lit by a lateral undiffused 60watt tungsten light. WB set to tungsten ISO100.

The subject is a balance wheel in a small wrist watch, which measures 8mmDia – how do I determine the magnification?

I tried to find it by measurement – converted the Raw file to jpeg in PS and the rulers showed the Image size as 24.7 x 16.5, which is roughly the size of the CCD – would the Mag be the ratio of the Dia of the wheel to the overall width of the image?.

Thanks for any help.

I don't know about the maths, but thought I would say that it is a pretty impressive macro shot. :)

Don

Thanks Don

All my stuff is trial and error at the moment, I like photographing small things that dont hop about too much.

Thanks be to Digital, makes the learning curve so much easier being able to adjust, lighting, focus etc. etc., and see the results instantly throgh the display or PC.

PS. I would still like to be able to work out the Mag Ratio though. lol

I will have a search when my brain is a bit fresher. Been doing other things today and its a bit fried.

Quick look though and found this .. don't know if it will give the necessary info. http://www.jeffree.co.uk/Pages/macro-lens-calcs.html

Keep going with the pics, agree things are easier if they don't move of their own accord.

Don

Well after half an hour of searching I found this site that may be interesting http://www.macrophotography.org/index.php

Don

Thanks Don
Off to a family wedding have to travel - have packed lens, spare batteries etc. ( nice venue Highclere Castle)
Will give your link a visit tomorrow.

Regards