Alnitak, Flame and Horsehead 30 Jan 2019 Manche, France

[The Thing]

I think the Revelation 1.25" UV/IR filter installed as close to the camera sensor has done it's job a bit too well and cut the Hydrogen Alpha wavelengths limiting the red on the wall around the Horsehead. However it caused minimal halos around the bright stars which is an improvement. The sky had variable transparency and the streetlights were on for 2/3 of the subs.

128 mins in 120s exposures Gain 120, Offset 30, Temperature -20C
Image date, time and location:   2019-01-30 21:25 - 00:02 CET Manche, France
Telescope aperture and focal ratio:   TS1506UNC f4, TS Komakorr
Camera and filters used:   ZWO ASI294MC Pro, Revelation UV/IR 1.25" filter
Processing applied:   DSS 4.x, Startools

[Carole]

Wow, well I don't know what to say about Alnitak, that's probably the biggest amount of star rays I have seen from Alnitak, is that the result of your UV/IR filter arrangement.   Shame about the Ha though.

Ignoring those two aspects there is a lot of detail coming through,  particularly in the nebula below the HH and the flame.

Carole

[The Thing]

Yeah, I seem to have a lot of extra diffraction going on somewhere! The dust is amazing though and the detail in the nebulas, light and dark. My scope and camera seem to like dust.

BTW Should have said -  No Calibration applied.

[Carole]

No Calibration applied.

None at all, inc darks?

Carole

[ApophisAstros]

Is that ampglow on the right side a little down?
That is where the ampglow shows on this camera , on my one its on same side but halfway down,
Usually Darks take it out.
Roger

[The Thing]

It was going to be a quick DSS stack to look at the data so no calibration:) the darks would have taken care of the amp glow, well spotted Roger. Pretend IRS a bright star just off the side!

[The Thing]

Btw There may be a reprocess in Pixinsight today...

[MarkS]

Nice one!  It shows great potential.

The diffraction from Altinak looks crazy but that's the name of the game.  You also seem to have a purple to green colour cast in the background dust.  The calibration frames will probably fix that.

Mark

[ApophisAstros]

I see you used gain 120 , just wondered how you decide on gain is it length of subs/target/Lp/filter choice or all of the above .
BTW i know mines a Mono and yours is colour so would imagine that might favour a different setting.
Roger

[The Thing]

I just use unity gain as it has huge dynamic range and low read noise. 120s is about the limit for not having too many saturated pixels while lifting the histogram off the left end. I've tried higher gain and that's nice, longer and shorter subs. This combination seems to produce data that's not too hard to process while keeping stars tight without guiding being critical. PE is more important. Also fewer subd are lost due to planes, clouds etc.

I would love a method of optimising gain, sub length and offset for a given target. NINA gives an estimate for sub length based on sub's taken. SharpCap tries as well but it told me to use 0.0001s sub's at unity gain!

[NoelC]

Mindblowing!
I just love the preponderance of colour.
I suspect it would give some purists kittens, but in terms of relating what you see through an eyepiece to the nebula in the background it has a huge amount to recommend it.
Any idea why Alnitak has 8 diffraction spikes?

Noel

[The Thing]

HI Noel, No idea on the number of difraction spikes except it possibly has something to do with the very cheap £12 Revelation IR cut filter I tried. Going for the expensive £20 1.25" Ostara Skyglow filter tonight for comparison.

I must confess I'm not a fan of the leery astrophoto but a while back I had complaints there was not enough colour...

[Hugh]

I think 'leery' gives it a bit of character!

Like it.

Hugh

[RobertM]

Looks like a great image Duncan.  Alnitak is an interesting one with those diffraction spikes.  I can understand the thin spikes being the spider vanes but the thicker ones look like they could come off mirror retainer clamps - are there three or four ?  As for the blue 'mist' around the star, could that just be UV pass through and reflection off the Revelation filter ?  I think you can work out the distance to the offending surface to see where it's coming from.  It was a bit like that on the Christmas tree area too.  Have you a Bader Neodymium or something a bit better than the Ostara (transmission curve looks a bit all over the place at UV wavelengths) to try ?

Robert

[The Thing]

Thanks Robert. I've only seen that many spikes since trying cheap £10 1.25" filters close to the cmos window using the adaptor provided. 2" filters e.g. neodymnium can be screwed to the far end of the komakorr corrector but they cause even worse flare around bright stars. Time to buy a quality 1.25" uv/or cut, luminance filter and or maybe a small neodymnium. They'll  be useful for planetary as well. I'm toying with the idea of the latest IDAS LPS filter as a dual bandpass option for OSC, its been discussed on Cloudy Nights and seems an interesting way to enhance images, the Horse head image has very little Ha.