The Good, the Bad and the ..

[ZeroID]

Bit gutted after what was supposed to be a brilliant night last night. Cool southerly blowing all day so air was clear and the CBD LP dome was minimal. Moon wasn't going to show till a lot later so setup with SONY on the LUNT and decided NGC253 was a starter despite being in the NNE. Added the Astronomik CLS filter just for good measure and took 25 mins at ISO 1600 and 30 mins at ISO 3200. Images looked excellent on the camera screen.
Guiding wouldn't work, couldn't find a star bright enough up there to lock onto but alignment is as perfect as I've ever had so it stayed put for over 100 mins just tracking.
Felt so good I stayed up till midnight and processed 110 x 30 sec frames with darks and flats. DSS looked good
Ok, there is an image but the TIF histogram is plastered up against the left side so tight that there is almost nothing left when I try to expand it.
I suspect the CLS as the culprit but for 55 mins I would have expected a lot more luminance, especially at ISO 3200. I can even get better results processing a single lo-res sample frame jpeg.
Unfortunately I don't think tonight is going to be as good otherwsie I'd be pulling the CLS filter out and just fighting the LP in processing.

Does a CLS (non CCD version) have that much effect on exposure times ?

On the good side I've got the Lunt and the 80 f11 all aligned so I can do visual checks and the seeing was good enough that once I was dark adapted I could just make out NGC253 in the 80mm. And it wasa nice night after all, 3 satellites, 2 meteors and some scan time with the binocs.

[PRejto]

I did a comparison of the CLS and Hutech IDAS filters some time ago (ccd versions) and found the CLS extracted something like a 30-40% penalty in sub exposure time. For modest LP I think the Hutech is a better choice and gives good colour balance.

Peter

[ZeroID]

Cheers Peter. been doing some more processing experiments with the image and it does look like there is a lot of photons missing. I used it very successfully on Trifid and Lagoon a while back but they are obviously a lot brighter and more colourful than an exceedingly dim galaxy.
Back to the drawing board..

[LewisM]

I discarded my CLS some time ago. It was not working for me. I obtained an IDAS LP from Paul Haese, and could not be happier. Strong blue cast to the stacked image, but EASY to process that out (in CCDStack, just desaturate bakground!).

I thoroughly recommend the IDAS filter. I have a LOT of orange street lights around me, and it handles them easily.

[cometcatcher]

If you use the CLS on galaxies, be prepared to take a big exposure hit. They only let through about 33% of total light. The CLS works better for nebula.

[LightningNZ]

I agree with everything that been said here. I agonized over which to buy and have been extremely pleased with my IDAS filter.

[ZeroID]

Figures .... !! I probably could have gotten away without it last night too, wasted one of the few 'good' nights I've seen recently.

Thanks

(33% !! mumble, mumble, mutter, *%#!! )

:P