Arps a-plenty

[AKB]

The chance to actually observe something last night was so exciting that I nearly scuppered the whole thing by starting to move the mount (remotely) before opening the observatory roof!  Cut the power to the mount just in time and went to see the damage.  Fortunately, just the flexible dew shield had crumpled against the observatory roof and stopped short of the camera sticking out of the corrector plate.  A close thing, and not a great start, but it got better...

I'm trying to quantify the the tradeoff between my previous Hyperstar/mono camera combination and the current RASA/colour OSC one, so I'm targeting some of my favourite, er,  targets - Arps -  starting with big and easy, and then getting smaller and tougher.  So last night, I managed the following, all 1 minute subs and generally 10 of them.  Due to Jocular's feature of splitting OSC images into separate mono ones, a ten minute grab shows as a 30 minute one in the annotations.

• Arp 337, aka M82.  Also M81 through an almost complete accident... I had chosen the wrong ROI for the camera (ASI294-MC) normally using about a quarter of the available field, but this time it turned out to be a 2:1 aspect ratio – perfect for this combination!
• Arp 85, aka M51. 
• Arp 26, aka M101.  Not much colour on show here.
• Arp 214, with an inverted mono image to examine the structure more closely
• Arp 317, the Leo Triplet, looks very soft... I refocsed after this.
• Arp 320, Copeland's Septet, also a Hickson grouping
• M109, this isn't an Arp, but it was nearby, so didn't want to miss it, and all its friends which are labelled in the eyepiece view.
• Arp 104, Keenan's system.  The key here is to observe the bridge between the two galaxies, an inverted image helps.

It's going to take some time and effort for me to assess the differences between these and my previous versions, but qualitatively I would say:

• The OSC isn't a significant handicap, compared to a mono, but...
• ...still mulling the benefits of colour.
• I'm struggling a bit to get a good colour balance with Jocular
• There are no calibration frames here at all. I definitely need to get the bad pixel map working for colour (any pointers @Martin Meredith ?  I know that OSC is not top of your list!)

It was a complete blast to have a romp around Ursa Major and Leo on a relatively clear (although not ideal) night.

Hope there's something of interest here for you too.

Tony

 

 

 

 

 

 

 

 

 

Edited March 7 by AKB
Updated Leo Triplet image

[PeterC65]

All nice clean and sharp images. I expect that's due to the 11" of aperture (my largest scope is 8") and the longer sub exposure time (I'm limited to 15s with the mount in AZ mode).

Interesting that you're moving from mono to colour. I've been thinking about getting a mono camera to add to my existing colour camera for those faint galaxies, and maybe emission nebulae with a Halpha narrow band filter.

 

[bosun21]

2 minutes ago, PeterC65 said:

All nice clean and sharp images. I expect that's due to the 11" of aperture (my largest scope is 8") and the longer sub exposure time (I'm limited to 15s with the mount in AZ mode).

Interesting that you're moving from mono to colour. I've been thinking about getting a mono camera to add to my existing colour camera for those faint galaxies, and maybe emission nebulae with a Halpha narrow band filter.

 

Is there a benefit of using mono against a colour camera capturing in mono? 

[PeterC65]

2 minutes ago, bosun21 said:

Is there a benefit of using mono against a colour camera capturing in mono? 

Because the mono camera doesn't have a Bayer matrix it should capture three times as much light. That's the theory, but I'm not sure what that would look like in practice when observing a faint galaxy.

The extra sensitivity of a mono camera could also be "used" to allow observation with a very narrow band filter. My colour camera probably wouldn't work well with anything narrower than 10um in front of it.

 

[AKB]

1 minute ago, bosun21 said:

Is there a benefit of using mono against a colour camera capturing in mono? 

Well, technically at least, there should be two advantages of mono:

1. captures more photons, since the Bayer matrix of a colour camera limits any one pixel to R, G, or B. 
2. better resolution, since the synthetic L from a colour camera is made up of three or more pixels.

In practice, however, that's exactly the question to try and answer.  It appears that modern debayering algorithms are quite good at preserving resolution.

9 minutes ago, PeterC65 said:

Interesting that you're moving from mono to colour.

Almost an inevitability with a RASA, since whilst I love EEVA, it's main use is likely 'proper' imaging, and you're not going to be swapping cameras all the time between mono and colour, or swapping filters, really.

[Steve in Boulder]

What a great set of views!  That RASA/294MC combo works nicely.   I’d guess the SNR advantage of mono over OSC would be about sqrt(3), or ~ 1.73 times.  But color has information too, like the H-alpha filaments in M82 you captured so nicely.  

One other consideration is that a 294MM would give a pixel scale of 0.77”, twice what you’re getting with the 294MC, so depending on seeing you might get better detail.  Even a 533MM/2600MM (or MC) would give a 1.25” pixel scale, which might be a good match for your seeing.

[AKB]

1 hour ago, Steve in Boulder said:

One other consideration is that a 294MM would give a pixel scale of 0.77”, twice what you’re getting with the 294MC, so depending on seeing you might get better detail.

Thanks for that.

Interesting, I’ve never used my 294MM in that mode (which would also receive four times fewer photons), but always binned x2.  

Everything's a trade off!

Tony

[Steve in Boulder]

18 minutes ago, AKB said:

Thanks for that.

Interesting, I’ve never used my 294MM in that mode (which would also receive four times fewer photons), but always binned x2.  

Everything's a trade off!

Tony

At f/2 you might be able to afford less photons per pixel!

[Martin Meredith]

Great results, especially considering the OSC->RGB approach isn't really optimised. I'm not sure why hot pixel removal isn't working for you but it might be to do with the 3-for-1 sub proliferation. Maybe try setting the successive subs value to 1 rather than 3?

 

[AKB]

1 hour ago, Martin Meredith said:

it might be to do with the 3-for-1 sub proliferation. Maybe try setting the successive subs value to 1 rather than 3?

Good thought, but apparently not.

I was wondering, perhaps, whether it's the debayering, which spreads a hot pixel into multiple ones and may cause detection to fail.