Standard sizes are 1.25″, 31mm, 50mm round, and 50mm square. The 1.25″ is 27.5 mm of filter glass mounted in a 1.25″ filter cell. The 31mm is 27.5mm of filter glass mounted in a 31mm ring. More information here:
Unlike other Astrodon filters, the Photometric filters (Johnson-Cousins and Sloan) do not come as 36mm of unmounted glass. For those who want 36mm round for use in a 36mm filter wheel, 27.5 mm of filter glass can be mounted in our 36mm adapter. More information on 36mm mount here:
We also have a limited quantity of 12mm and 25mm (call for pricing and availability). All Astrodon Photometric filters are 100%-Coated for long-term durability and consistency of research with the highest throughput.
NOTE: In Astrodon part numbers we pronounce the ‘ character (apostrophe) as “prime” and the _ character (underscore) we pronounce as “sub”). So u’2_27R should be read as “u prime 2 sub 27 R”.
However, our dinosaur website software software chokes on ‘ (apostrophes) if they are in a SKU field part number. So we have replaced ‘ with ! in these places. So the above part number (when used in a SKU field) on our website will appear as u!_27R. But it is really u’_27R. Again, this is due to our dinosaur software, but if you Google Astrodon you will find that Astrodon was a dinosaur with star shapes in the fossils…so appropriate, eh? In any event, forgive our software, move on, and be happy.