Yeah, I know. That's the reaction I always get when people find out it was me - disappointment.

Anyway...I'm older than you (not hard on this forum) but I'm also a student.

You've got a K-7 - I don't...

What I meant is that it's just not right to own expensive equipment and then involving cheap aids in the process. If people saw it...

Must have been a pretty big praying mantis, then.

Still have to find an acceptable way to gain more magnification. MOAR!

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newarts, what I meant to say is that it's not really possible to determine the lenses extension and the distance to the stacked lens since you would need to know the optical center of the lens (or don't you?).

But I just know the distance the stacked lens has to the priamry lens' front element.

So this is highly guesswork. You said in another thread the thin lens formulas still aplly to actual lens systems but then how to use the variables?

If I use this formula, I'd get:

(f' -d) /f" = m.stack.infinity

(105mm-30mm)/50mm =1.5

But by measuring magnifaction I got 2.3:1

I must have done something wrong with the second formula because I got m=-0,986...

Not that great.

Reusing the sum from the second formula I get

m = (m.primary.extension+1)(m.stack.infinity+1) -1 =

(1+1)*(1.5+1)-1=4

I guess I'll just leave the maths to people who know their way around them and I'll keep it practical and simply measure my results.

Hmmpf...