American Association of Variable Star Observers (AAVSO)
Wed, 12/28/2022 - 17:28

I am ready to purchase Chroma filters for photometry but do not have the experience to decide between a set of Bessell or Classic Bessell. I read that both sets are considered Johnson-Cousins. An advice on this topic would be greatly appreciated. Of note, the two models have very different light curves.



American Association of Variable Star Observers (AAVSO)
Which Chroma Filters?


If I wanted to buy Chroma filters today I would get the version with passbands which closely followed the classic UBVRI prescription.   As far as I have seen, there has  been no information or guidance in the AAVSO forums about how well the Chroma flat top, i.e. non-standard, UBVRI filters perform.  You don't need to buy a full set, and you certainly don't need a U.  I'd suggest just a V for a starter.  If you eventually decide to transform your magnitude measurements you will also want at least a B in addition.

The Chromas are high quality filters but expensive. You may also want to consider the Optolong filters.   Arne Henden's review of the Optolong UBVRI filters is here: .


American Association of Variable Star Observers (AAVSO)
Interesting, I didn't…

Interesting, I didn't realize Chroma starting making a "Classic' line, these are new. I still have some of their original filters with the JC shapes, but these new ones look to be much higher transmission. I had some issues with the coatings failing so have replaced with Optolongs.



photometric filters

I have standard-cluster images now with most of the possible filter choices:

- Schuler colored glass

- Astrodon interference

- Optolong interference

- Baader interference

- Chroma flat-topped

- Chroma classic

I'm on vacation now, but about mid-January, I'll give the transformation results from all of these.


photometric filters

Hi Arne,

have you been able to analyze your standard-cluster images through the various filter sets you mentioned in your post? 

I am about to put a new photometry rig together and would appreciate any information on how well each of the currently available options perform. Cheers,