Is there such thing as a 1 3/4" (44mm) focal length lens?

Lasers
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1

Is there such thing as a 1 3/4" (44mm) focal length lens?

Let’s just make sure I’m thinking about this right, a ramp test:
-Put a piece of wood in on a slope
-Laze a line across it
-You get wide scorches at each end, and a cut in the middle
-The middle of the cut section is the focal length, measured from center of lens to center of wood

I’ve done this twice, got 44mm once and 43mm once. Which would be “1 3/4”, which doesn’t exist?

Are the Chinese screwing with me, or am I up too late at night?

2

Is the lens in place with the crown up (toward the laser tube)?

3

Bump goes up

4

Repeat with lens other way up

5

Some people use a q-tip to make sure they are getting the correct distance.

6

Thanks everyone.

Conclusion: I need to learn when to give up and go to bed. Just tried again, and got 50.5mm

So either I put the lens in backwards on two separate occasions, or my brain can’t deal with numbers at all at night.

I’m embarrassed.

7

I have forgotten how many hours wasted fault finding electronic devices to find out the next day it was not plugged in