160mm distance

[mark_h]

I have read many times about the 160 or 200mm distance but I don't know from what point to what point is the measurement measured?

[Craig Gerard]

Mark,

The measurement is from the camera sensor or film plane to the objective shoulder (where the objective thread meets the objective barrel).

I believe the general concensus is to aim for a distance of 150mm for a /160 objective and 200mm for a 210/ objective.

Some cameras have a small symbol on the outside of the camera to indicate sensor location. The symbol looks like a circle with a line through it. As an example, the sensor on my Canon 50D is internally located 15mm from the rear external LCD screen. If I'm not mistaken, the sensor symbol on the Olympus E-1 is clearly visible just to the right of the hotshoe.

Other members will go into much more detail than I can; but the above info should get you in the ballpark.

I'm now looking at your setup. You have some interesting components.

Craig

[Pau]

Mark, Craig is right. The ideal tube lengh for a 160 objective is 150mm between the objective shoulder and the intermediate image in the eyepiece (or with Nikon CF objectives the camera sensor).
Some low power objectives are fairly tolerant to changes in this distance. Changing it you change the magnification. In your pictured setup you are likely obtaining lower magnification than the specified 10X. The limits are different in different models and sensor sizes and you can find them when the borders of the image are unsarp or when vignette begins.
There are lots of posts about this topic in this fora, in particular Rik did performed a lot of tests whith different objectives.

[DaveW]

Usually it will tell you in your camera manual how the film plane or sensor position is indicated. In some of the old Nikon film cameras I believe it was indicated by the line of either top or bottom of the camera serial number stamped on the top plate.

DaveW

[Charles Krebs]

Mark,

You've gotten the correct answers above.

Here's the value for your particular camera body:

Your camera body (Olympus E-1) has a 38.6mm body depth ("register" distance, "flange-focal" distance).

So you need to provide an additional 111.4mm extension from the front of the body mount to the shoulder of the objective threads.
(But as has been mentioned, some variation is usually OK with objectives that have a NA below 0.40).

Nice looking set-up!

[mark_h]

thank you everyone for the information, this is a good learning experience I am really enjoying, just a couple of more parts to arrive and I am all set for the winter.