Variable star observing - filters

Hi,

So the AAVSO CCD handbook still recommends starting out with a Johnson V filter. However that makes no reference to the Sloan filterset which appear to be used quite widely (from what I see in forums/email lists). So I was wondering if Johnson V is still recommended or if a Sloan g' filter would be more suitable?

I'm also thinking of what would make most sense over time - would it be better to build up a Sloan or UVBRI set?

Another consideration is whether the filters will degrade in the wet Irish climate. Perhaps that's not an issue with modern filters though.

Filters in both sets seem to be comparable in price - though finding a dealer for some is tricky!

Cheers,
~Al

I use the Bessel UBVRI photometric filter set which is the same as Johnson. The Johnson V is fine for photometric observations if your target object is bright enough. The Sloan g’ will get down slightly fainter because of the higher transmission.

I would go for the Sloan set because that has become more common standard usage and is particularly suitable for small telescopes (8 to 10in).

I’ve used my Bessel set for the past 13 years and I have had no degradation. I normally take the filter wheel out and store it in a dry dessecant box in a warm room beside the telescope.

I understand that filters now are significantly more rebust for harsh environmental conditions.

Eamonn

Hi Al,

At the moment most CCD photometrists use Johnson-Cousins filters, although a few are using the Sloan filters. So if you want to compare you observations to others the Johnson-Cousins can be more useful. I use BVIc Johnson-Cousins for my CCD photometry.

The best place to get views on your question is the AAVSO Forum (Photometry sub-section). Please see
Link .

John

Hi,

So I asked the AAVSO and their advice was to go with the V filter. The discussion is at www.aavso.org/choosing-first-ccd-filter

There are advantages to the Sloan filters as Eamon suggested, but for a first filter for photometry, given the current usage and amount of historic data it's the best choice at the moment.

Cheers,
~Al