Rangefinder check

[Guest V64]

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Is it possible to check the accuracy of the rangefinder at close distances (circa 1 m,) by using a tape measure?

 

If so where on the M8 do you put one end of the tape?

 

I just set my M8 at 1m from a 'pin', I set the lens focus at the '1m focus mark', and moved the camera until the RF images of the pin aligned.

 

Tape Measurement from the Pin to where I thought the sensor plane would be measured at 102 cm. (or thereabouts).

 

What conclusions can I draw?

 

Incidentally, a normal focus check using the pin and ruler (at 45 deg.) suggested that the image plane was in front of the pin by 2.0cm.

 

Comments please! Lens or camera?

 

Thank-you

 

PS I only have one lens - so I cant do any of the obvious checks!

[Guest mc_k]

the scale is only a rough focusing system compared to the rangefinder. I think with only one lens and one body you will not be able to make any guess about which item(s) are off.

[Guest mc_k]

...on the other hand, assuming your scale is exact and you corrected for the angle of the ruler, your two methods did agree on a 2 cm front focus for the body + lens combination.

[el.nino]

try this:

 

For closer distances, put a lipstick mark on a mirror ([or] black tape) set your camera to one meter and focus by moving the camera in and out. Once you have focused on one meter, move to the side a bit and refocus on the camera body. The scale should say two meters - if it doesn't then it's off.

Leica FAQ - Easy way to test rangefinder accuracy?

[DOUG66]

Is it possible to check the accuracy of the rangefinder at close distances (circa 1 m,) by using a tape measure?

 

If so where on the M8 do you put one end of the tape?

 

I just set my M8 at 1m from a 'pin', I set the lens focus at the '1m focus mark', and moved the camera until the RF images of the pin aligned.

 

Tape Measurement from the Pin to where I thought the sensor plane would be measured at 102 cm. (or thereabouts).

 

What conclusions can I draw?

 

Incidentally, a normal focus check using the pin and ruler (at 45 deg.) suggested that the image plane was in front of the pin by 2.0cm.

 

Comments please! Lens or camera?

 

Thank-you

 

PS I only have one lens - so I cant do any of the obvious checks!

 

The focal plane of the M8 (according to Leica) is 27.95mm +/- 0.02mm from the lens flange. Remember that the sensor is behind a cover glass which has a finite thickness and a refractive index. This means that the surface of the sensor is closer to the lens flange than the above figure, but use the above figure in any testing set up.

Firstly check your focusing mount for play, my 50mm Summicron had 0.04mm and it did not affect the performance in my M6. Film because of its thickness and its tendency to bulge in the camera is much more forgiving than a digital sensor. I got Malcolm Taylor to tighten up my mount and do a CLA on the lens, he also coded it for me. I have nothing but praise for his work. His number is +44(0)1568 770542.

I have made a test chart for testing front and back focus at the distances you are interested in. E-mail me at reidcrabtree@eircom.net with your postal address and I will send you a copy. It will not email, it looses to much definition.

Doug Reid

[Guest mc_k]

the "mirror test" above is equivalent to the OP's first test; it compares the rangefinder to the scale. But the scale may not be zeroed, or the engravings may not be accurate, etc.

[Guest V64]

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Thank-you all for your comments - I guess the rotational tolerances in the mount preclude any accurate focus checks using a 'tape measure'. The 'mirror' test at 1m to the surface and 2m to the camera's reflection measured correctly using the camera range finder.

 

DOF for a 28mm f2 using http://www.dofmaster.com/dofjs.html online calculator, is -5 to +6 cm at 1m, but I still think I will get it checked out. I have, in the past, used other lenses, and there was no suggestion then that I had a focus problem.

 

Thank again for your help

[Islandmike]

On the basis that what matters most is that the rangefinder/lens combination is focusing accurately, I use the chart that can be downloaded and printed at the URL below. Whether or not you shot strictly at the angle suggested in the instructions, it gives a good indication of the amount of back- or front- focus of any lens.

 

I also find that my Mac computer LCD screen makes a good target for focus check, as the 'grain' of the screen is really only visible if the focus is spot on. I use a weather page off the internet, with lots of numbers and colour squares - set the page to largest possible under the view menu.

 

http://focustestchart.com/focus21.pdf

[archi4]

Put the tape measure at a 45 degree angle to the camera and focus on one of the marks (for example 1 meter or 3 ft.) and then see whether the focus is on the mark, in front of it or in back.

You can do this at any diatance from the camera.

Sorry if I misunderstood what you want!

MMaurice

[jaapv]

On the basis that what matters most is that the rangefinder/lens combination is focusing accurately, I use the chart that can be downloaded and printed at the URL below. Whether or not you shot strictly at the angle suggested in the instructions, it gives a good indication of the amount of back- or front- focus of any lens.

 

I also find that my Mac computer LCD screen makes a good target for focus check, as the 'grain' of the screen is really only visible if the focus is spot on. I use a weather page off the internet, with lots of numbers and colour squares - set the page to largest possible under the view menu.

 

http://focustestchart.com/focus21.pdf

Well, from where you live I suppose that page only gives a whiteout just now.

[Islandmike]

A little off topic, but funnily enough, from where I live, this was the view this afternoon. We have very little white on the island, but the mountains 50 kms over the sea are covered.

 

Back on topic, I simply set the lens to infinity and shot with the M8 on auto.