Which CLS filter

[pmrid]

I’m looking at using a CLS-type filter in conjunction with my NB filters. But I hesitate because I can’t convince myself that they would achieve anything much. My NB filters are Astrodon 5nm but despite that my images seem to have a slight haze that I put down to stray urban light fogging things up.

And so I wonder whether a CLS would help. The various manufacturers seem to offer a basically similar specification with the main bands being in the 400-550 nm and 600-700nm more or less taking in OIII(500.7), Ha (656.3) and SII (671.6). In theory though, my NB filters ought to be enough without a CLS which would only duplicate (at best) what they already do. But the fog persists.

Happy to be put straight.

[RyanJones]

Hi Peter,

I have the same haze in my images which I’ve been chasing with varied success for a while so I’ll be watching this thread so see if any other tips come in from the wiser folk. What type of scope are you using ? I found on my Newtonian that I was leaking a lot of light around my mirror and down the draw tube of my focuser. Reducing that really helped, but didn’t get rid of, some of the haze. On the topic of CLS filters, I’ve tried a couple. I recently bought an optolong L-pro to use to take subs to ad back star colour. I’m really impressed with it. I’ve had Baader and Astronomik CLS filters and in my humble opinion the L-pro works significantly better than either.

Cheers

Ryan

[pmrid]

Hi Ryan. I’m using a newt. With that light-leak around the mirror possibility, I have made a sort of shower cap thing I can tie over the end of the OTA but have yet to try it out. I’m concerned not to create a heat trap around the mirror though.

I had a look at the Optolong L Pro specs. It covers the big 3 in 2 bands but has 3 other bands as well which it describes as being for “ultimate color balance”. Seems to me to be making the point that these are for use with OSC and DSLR cameras - not mono.

[Startrek]

I’ve tried Astronomik CLS filters and don’t see any additional benefit from that of NB filters
I too use newts and found you can’t image anywhere near the moon ( within 50 to 60 degrees) using my L Extreme filter without ending up with some faint circular reflective artifacts in your images. Also stray lights like xmas led house lights play havoc as well
I’ve tried putting up tarps to stop the direct glare but it still finds its way in

The joys of being an Astrophotographer living in a big City

Cheers
Martin

[ChrisV]

I don't understand why would you use a cls-type filter on top of the NB filter. The NB filter is determining the pass band.

To me, all the CLS filter will do is reduce transmission across its narrow band?

[pmrid]

Which is precisely what I said in my first post - but I was really looking to identify the source of the light fog I mentioned.
rocesses of elimination!

[RyanJones]

Very keen to see what other potential causes come up.

I think the shower cap idea is a good one if your cooling fan isn’t covered by it too. I’m with you with your thoughts. You could fix a haze issue and end up introducing a thermal one.

[alpal]

Hi Chris,
You're right but I leave my Astronomic 2" CLS-CCD filter
in front of all other filters as I'm too lazy to remove it
and it prevents dust getting into my imaging train -
and all over the other filters.
My setup is here:

https://www.flickr.com/photos/24719437@N03/8029429824/in/photostream


cheers
Allan

[Camelopardalis]

Something with the reputation of an Astrodon should absolutely be free of stray reflections, but that doesn’t mean it’s getting introduced by some rogue element elsewhere in the optical train.

Can you point the scope in another direction and reproduce the issue?

And what exactly do you mean by the fogging? Lacking contrast?