Fri, 06/07/2024 - 23:44
I'm getting started in photometry and am looking to purchase J-C V and B filters. I saw a post [1] where Richard Berry mentioned a survey was done to determine suitability and availability of these filters from various manufacturers and another post [2] where Arne Henden mentioned he has standard cluster data for many of these filters.
Does anyone know if the results of this survey or the analysis of the standard cluster data are available?
In short, I'd like to know if there's any reason to prefer, say, the Chroma classic vs the Baader filters.
Thanks!
[1] https://www.aavso.org/survey-who-needsreceived-johnsoncousin-or-sloan-photometric-filters
No reason to prefer either, and especially so if you transform your data. You could also consider Optolong which is what I have, definitely most cost effective.
Keith
There was discussion of a red leak in the Optolong U filter a couple of years ago. Does anyone know if they have resolved that issue?
https://www.aavso.org/optolong-ubvri-filters
Thanks,
Walt
Arne posted a favorable forum comment on the Optolong BVRI filters about a year or two ago. It's worth looking up.
As I remember his main concern was that the U filter should not be used for photometry of very red stars. Since glass and the atmosphere absorb UV, and most cameras used by amateurs are relatively insensitive in UV, this is the least useful filter for most of us.
For people buying a full filter set I think the best use of the U filter is to sell it on Astromart or Cloudy nights to people who want to take pictures of Venus. I'm told U filters are in demand for that purpose.
Phil SPP
Phil,
Do you mean the comment that I link above? Was there another thread?
-Walt
Walt,
Oops! I missed that. Yes, that's Arne's comment I was referring to.
More on Optolongs and transforms:
A few years ago I compared the B,V,I transforms produced by my Astrodons with those produced by Chromas (square shoulder, flat top) and Optolongs. The images were all done with the same camera and telescope. I used an SBIG CFW-10. All the filters fit in the wheel at the same time. The camera is an SBIG ST-10me. I used Landolt field SA32 for the standard stars. This study was limited by the fact that the reddest star in the field was only B-V= 1.159. If I did this again I'd use a larger selection of standard stars from NGC 7790 or M67 to get some redder stars.
The Astrodons were were clearly the best filters, giving the best (closest to ideal) results for every transform. The Chromas and Optolongs were close to each other. Both gave decent, usable transforms.
I decided to keep the Optolongs, and they are still in use.
I didn't test the Baaders. At that time Baader had discontinued making UBVRI filters and was planing to introduce new UBVRI filters of a different design. I think Arne made some comments about the newer Baaders in another form post.
Phil SPP