Greetings,
I am currently building my filter collection with an eye to populate a 8 position filter wheel. I currently have V and R filters, B is back ordered. Currently I'm doing primarily V photometry. I initially focus with a open filter spot then have offsets to my filters. I believe adding a clear filter would perhaps minimize the amount of offset I'm needing to use to bring my photometric filters into focus. I've read about clear blue blocking filters and Astrodon has them but are fairly pricey for a focusing aid. Would a Luminance filter suffice as well as help out with exoplanet observations in the future? It claims to block UV and IR and looks to be more affordable. I do hope to do some exoplanet measurements in the future so if a CBB filter is called for then I'll spring for it, just checking my options!
Thanks!!
Wayne Hilliard
Astrodon makes (made?) a "clear" focusing filter that matches the focus of the J-C filters. It blocks UV but not IR. With that I don't notice any offset with the Astrodon J-C filters. It was significantly cheaper than the J-C filters.
I think an Astrodon Luminance filter would also work fine for this if you don't care about losing the IR signal. if you use compact clusters for focusing the faint stars will be a bit fainter with a luminance filter compared to a UV blocking "clear" filter. If you're going to use an Astrodon luminance filter, I would check with Astrodon just to be sure the thickness of the luminance filter is the same as the J-C filters.
Phil