Meade LRGB

allan gould · #1 23-03-2010, 10:03 AM

A really dumb question that I can't seem to get a straight answer to. After trolling the internet I'm still confused and I hope someone here who actually uses the Meade LRGB filters can answer these questions.
1) are the filters parfocal?
2) are the filters uv/ir blocking or do you have to use the L filter to block uv/ir ie when shooting a red frame do you use L+R to stop star bloating; B+L and G+L and then L alone for luminance?
Thanks for looking

TheDecepticon · #2 23-03-2010, 02:59 PM

The RGB filters are "weak" uv/ir. You will need another uv/ir filter. I put another uv/ir filter on the snout and the LRGB filters in the slide, this way providing uv/ir across the range and attempting to keep them parfocal. I think green was always just a touch off, but that could've been me and my very poor technique back then.

I used to have a graph somewhere of the light curves for each filter, however, I am unable to find it, sorry.

allan gould · #3 24-03-2010, 10:36 AM

Quote:

Originally Posted by TheDecepticon

The RGB filters are "weak" uv/ir. You will need another uv/ir filter. I put another uv/ir filter on the snout and the LRGB filters in the slide, this way providing uv/ir across the range and attempting to keep them parfocal. I think green was always just a touch off, but that could've been me and my very poor technique back then.

I used to have a graph somewhere of the light curves for each filter, however, I am unable to find it, sorry.

Thanks for the information, Deception. I think Ill give them a try and if not suitable upgrade to something else.

CoolhandJo (Paul) · #4 24-03-2010, 11:31 PM

Yes they need additional IR/UV filtering. Yes they are parfocal. Attached the spectral response. (this graph has an IDAS LPS2 overlay on it in dark black)

CoolhandJo (Paul) · #5 25-03-2010, 08:01 AM

I should explain the graph in my last post a bit more. The Coloured lines correspond to the RGB filter set of Meade. Closley on the RGB line there is a thin black line which representes the L of the Meade filter set. Above the thin black line there is another black line which representes a Baader UV/IR filter, and the dark black lines over the entire. The graph represents a Hutech IDAS LPS 2.
This is a good representation of the various efficiencies of filters and you will notice that the Baader is more efficient.
Having said that, when comparing the Meade filters to other filters, the Meade actually isnt too bad in terms of spectral response, but where they suffer a bit is in the "quality" and "sharpness" of the resultant image. But for the price...not too bad.

allan gould · #6 25-03-2010, 04:24 PM

Paul thanks for your input. As I said I think Ill try them but probably get something better.