First test of L-Enhance tri-band Filter

[Stub Mandrel]

On Wednesday evening I had a first try of my Optolong L-enhance filter with my ED66 and modified, cooled Canon 450D.

This is one of the relatively 'new' tri-band filters that actually has two pass bands that encompass Hb & OIII at the overlap of blue and green and Ha in the red. Broader than narrowband filters, they still exclude most of the visible spectrum including all the main light pollution lines.

Unfortunately I was shooting almost straight up and a large dust bunny or two fell onto the sensor, moving between some frames making elimination with flats impossible. There was also a tilt in the imaging train giving poor stars AND PHD2 stopped talking to my guide scope a few times which also impacted the star shapes with long subs. Add some poor framing and relatively few subs and the resulting images are not really the fairest test of the filter but I have learned a few things.

I used super pixel mode so there was no bleed through of data between colours. I did little more than stretch in FITS liberator, to PS for a background balance and another stretch then denoise in PS or Astra.

1 - the images are easy to process using 'super pixel mode', balancing the background generally gives white stars. This gives a very pure, deep red Ha signal.

2 - The filter is very powerful at removing light pollution, normally my 300s subs would be washed out with skyglow. I could easily go to 10 minutes, except brightest stars would blow out.

3 - Blue and Green were, as expected, very similar with slight bleed through of the brightest patches of Ha.

4 - In targets with a lot of OIII, this comes out very well in a blue-green colour (Veil).

5  - It accentuates Ha very nicely on the red channel.

6 - It reduces stars, but not as much as a narrowband Ha filter.

7 - where there is a blue reflection nebula, this didin't really come out at all, just a fainter Ha signal, nothing in blue or green (NGC7822).

8 - where there is are secondary OIII signal I expected to get, nothing strong appeared although the Ha was very good (Heart nebula).

9 - I am guessing this will work very well for planetary nebulas and targets like the Rosette where elements of the ordinary OIII signal are clear even in an OSC image.

10 You could use this as a powerful anti-pollution filter for things like clusters, but don't expect to get lovely star colours.

Here are the example pics, blame my impatient settup and lack of monitoring rather than the filter for the poor results. You can see a few patches where I have tried to clone stamp the dust bunnies out and a few spots where I didn't bother...

Veil, 30x300s:

NGC7288, 14 x 300s

Heart, 16 x 300s :