Field stop ID for Vixen LV 30mm?

[RikM]

Does anyone know what the field stop diameter is for the big black and red Vixen LV 30mm 60° aFOV 2" eyepiece?

To measure it do I just turn it upside down and stick a vernier calliper in there or is it a bit more 'delicate' than that?

[John]

It depends on the eyepiece design Rik. Some have their field stops and focal points below the lowest field lens (and accessible for mearurement) but increasingly these days manufacturers are using a 2nd lens group in the eyepiece barrel with the field stop within the main body of the eyepiece and harder of course to get at without disassembly.

I seem to recall a figure of 34mm as the field stop diameter for a 30mm Vixen NLV - is that the same eyepiece as the LV ?.

[RikM]

Thanks John. It is a very different eyepiece to the NLV and looks a lot more like the LVW.

The fieldstop ring is nicely placed, just too far up inside the barrel to measure easily. I resorted to cutting a strip of paper and poking it (carefully) up inside the barrel and comparing to the FS ring, then trimming it until it matched. I measured 32mm, which is close enough for me.