CLS Filter - Experiments

[MarkS]

I've got myself a CLS filter - here are some experiments.  In each case I've combined 2 images of the same exposure length in Photoshop to show the "before and after" side by side. 

Tree at bottom of my garden:



Spectrum from sodium streetlight (in a CD) - the gap down the middle shows effect of CLS filter



Spectrum from incandescent bulb (in a CD) - the gap down the middle shows effect of CLS filter

[JohnP]

Good work Mark - it's pretty good eh... did you go for 1 1/4 or 2-inch...? You can already see a star in your image from the bottom of the garden.....

Cheers,  John

[Ian]

nope, still don't recognise the tree. can you post another pic?

Interesting work with the CD, the cls seems to block quite a chunk of spectrum. I might have a go with my uhc, see how that looks...

[Rick]

That's quite a chunk of spectrum it chops out. Pretty good for removing sodium glow. Next time you're in a dark location it might be interesting to image some favourite object both with and without it. 

[JohnP]

It might take a chunk of the spectrum out but it works very well... I use it all the time when I am imaging from my garden (if not using the Ha) - I even used it on my recent m81 image & that was from a fairly dark location. I think it's a great filter....

John

[MarkS]

Rick, yes, it takes out quite a chunk of spectrum but it does leave behind the most important emission lines H-alpha, H-beta & O-III.  In daylight (visually) it gives an overall blueish tint but other than that colours look quite natural. Here's a diagram http://www.astronomik.com/english/eng_cls.html.

John, it does look like it'll do the trick. I bought 1 1/4 because most of my stuff is 1 1/4.  If it works well I might get a 2" as well

[JohnP]

Hi Mark, Yep - I have both - started with 1 1/4inch but then got 2inch for DSLR - you def need it for this else look out for severe vignetting... John

[Daniel]

Just wondering, would you guy's reccommend a CLS filter over a standard UHC-S filter for Light polution blocking, Im especially having trouble picking up Ha, which i know is mostly due to my IR blocking on my camera.
.
Right now I can take about 1 minute exposure tops before my histogram is dangerously in the overexposed area

[Rick]

Rick, yes, it takes out quite a chunk of spectrum but it does leave behind the most important emission lines H-alpha, H-beta & O-III.  In daylight (visually) it gives an overall blueish tint but other than that colours look quite natural. Here's a diagram http://www.astronomik.com/english/eng_cls.html.

Good for emission nebulae, but might make reflection nebulae look a little different, then. It's interesting to see exactly what's being removed, and your spectrum photos show that really well.

[RobertM]

Hi Mark,

You might find this a useful reference to filters of different types and passbands:

http://forum.orpington-astronomy.org.uk/index.php?topic=2659.msg10430#msg10430

Cheers
Robert

[Ian]

ooh, we're getting self-referential...

[RobertM]

It's self recursion you need to watch out for ... 

[Fay]

That is really interesting Mark. To actually see the difference in the image rather than a graph.

[MarkS]

Now the moon has moved on I had the chance to perform another comparison - M42.

The top row shows a 5min exposure - F6 with ISO 400 using a 300mm lens on the Nikon D70 with and without the CLS filter and both without any processing.
The bottom row shows the result after background subtraction, colour balancing and then adjusting brightness to allow direct comparison.

After processing, the CLS version is definitely cleaner and showing more detail.  But it is not as big a difference as I would have expected.