Diffraction Grating question

[Mattronium]

I don't know if this is a silly question or not, so I'll ask it anyway.

I am confused by the 13,500 line/inch diffraction gratings.
They should be 13,500 line/inch or 532 lines/mm, but from observation they appear to be 5,182 lines/inch or 204 lines/mm.
I do have 500 lines/mm and 1000 lines/mm gratings that I compared them to.

Hopefully someone can shed some light on this. (pun intended)

Mattronium

 

[Cyparagon]

from observation they appear to be 5,182 lines/inch

Please be more specific about your observation.

 

[Mattronium]

My observations were:
First, from when I was trying to measure different wavelengths and used the HeNe 632.8nm as a reference.
Second, the general observation of the order spacing compared to 500 lines/mm and 1000lines/mm.

My measurements were quite precise, but the lines/inch calculation I made might still be +/- a few percents.

 

[Cyparagon]

Oh, you're talking about these, yes?

I just checked with the three I have, and the 13500/in does have the most narrow spacing, but that's the only one that has dual axis, so I suspect they're counting the lines in each axis? It's still a bit off from your measurement, but that would account for some of the error.

 

[Mattronium]

Yes, those are the types.

Hmm, I guess they might be counting both axes.