smr

8 hours 21m 
HEQ5 Pro
ZWO 2600MC Pro
3 Minute Subs
Darks
Dark Flats
Flats
 

Delighted to unveil my image of the of Veil Nebula in the constellation Cygnus. I've finally finished processing it after photographing this on Holiday in Norfolk last month. The total exposure time is 3 hours and 20 minutes. This is one of my favourite objects in Deep Space, it's a supernova remnant from a Star which was 20 times more massive than our Sun, and exploded between 10,000 and 20,000 years ago. This part of the remnant is called the Witches' Broom, and below it, Pickering's Triangle. The emissions are made up of Hydrogen, Sulfur and Oxygen and it's 2,400 Light Years from Earth.

Acquisition > Skywatcher HEQ5 Pro Rowan Belt Mod - ZWO ASI 2600MC Pro - L-eNhance Dual Narrowband Filter - Altair Starwave 50mm Guidescope - PHD2 Guiding - DSS Stacking - PS Processing - 3h20m x 180 second subs, 50 Darks, 20 Flats, 20 Dark Flats.

Imaged over three nights, this is my North American & Pelican Nebula image.  The total exposure time is 8 hours and 12 minutes, consisting of 164 Lights. Calibrated with Darks (-10), Flats (from one night, along with dark flats). I omitted taking any after the first night, I did take flats after the second and third night's but I hadn't realised that I had ran out of disk space just as APT was taking flats on the morning after the third night - so I calibrated with just one set of flats from the second session, which seem to have worked alright. 

Gear Acquisition
William Optics Zenithstar 73
ZWO 2600MC Pro
HEQ5 Pro Rowan Belt Mod
PHD2 (Multi-star guiding)
APT

Stacked in Deep Sky Stacker and processed in Adobe Photoshop. 

Thanks for looking.

Joel

8 minutes ago, Elp said:

Your flattener has a back focus distance from the bottom of it's thread of 54.8mm, the distance from the front of your camera to the front of the sensor is 17.5mm, so 54.8-17.5=37.3mm should be the blue line distance.

Thanks, yes just measured it, it is 37.3mm.

This is how the flattener came.

30 minutes ago, Elp said:

Just to confirm the spacer rings you are using, do they measure 37.3mm total length (bottom of thread connected to flattener to camera face)?

That should eliminate the spacer issue.

Do you mean this ... ?

25 minutes ago, symmetal said:

It does look like a tilt issue. The right side corners look pretty reasonable while the left corners have elongated stars pointing generally inwards. This implies that the left side of the image, particularly the bottom left is closer than the optimum FF distance. Here's a CCD Inspector analysis

It's worth building a test jig as several others have done using pieces of wood and a cheap laser pen as shown here. Trying to adjust tilt by analysing star image tests is a never ending nightmare. If the camera doesn't have tilt adjustment then a tilt adjuster can be fitted in the image train before the camera, or the filter wheel if a mono camera, and the camera, filter wheel and tilt adjuster mounted together on the jig.

Alan

Thanks. I'm not that brilliant at DIY stuff but if this is the only way to do it I'll have to give it a go. Is there anything obvious in the image above which might be contributing / causing it?

31 minutes ago, Elp said:

If the stars at the edges look like they're radiating out from the centre of the image it's likely your camera is too close to the telescope focal point. Have you tried adding in another 1-2mm into the backspacing to see if it makes a difference?

What field flattener are you using? There's also a chance due to sensor size and the flattener being used it may cause elongation at the edges.

Thanks for the reply. Here's a pic of what I have... it's the WOZ73 1:1 Field Flattener with spacers...

I haven't been happy with the Stars in my images for some time and really want to get to correct it so that I can take images where the stars are round in all corners.

Take the FITS image attached. If you zoom in on it you can see the Stars are pulled in different directions in each of the corners...

Top Left

Top Right

Bottom Left

Bottom Right

Middle

Any ideas as to what this is ? Is it Tilt? 

 

L_2022-07-27_00-40-07_Bin1x1_180s__-10C.fit

On 30/06/2022 at 10:33, tomato said:

Very nice, Altinak really well controlled. Is this an RGB image rather than a dual band filter?

It's a bit of both, some with the L-eNhance and some subs without.

Maybe my video might help

https://www.youtube.com/watch?v=j66cVp_B_Cg&t=24s

Thanks all. The Gain was 100 and Offset 50, a mixture of subs, from 3 - 5 minutes.

Hi,

Here's my image of the Horsehead & Flame Nebula, taken last Winter and I've just got around to processing it in June.

19h27m - 374 Lights
2600MC Pro 
William Optics Z73 Refractor
HEQ5 Pro Rowan Belt Mod
 

5 minutes ago, vlaiv said:

Just measure it.

Your exposure length needs to be such that background / LP noise is at least x3-5 times larger than read noise.

Simple as that.

Take one sub - measure LP levels, convert to electrons, take square root and compare to published read noise values for the gain you are using.

Increase sub length accordingly (depending on measured ratio - mind the difference between signal and noise which is square root of signal).

How do I go about this? Have you heard about the 'Brain' feature in Sharpcap? I've just learnt of it and started reading about it - that might help me by the sound of it 

8 minutes ago, Budgie1 said:

The last time I imaged the Iris was with my astro modified DSLR and I used ISO 800 at 180s exposures and it came out fine, picking up lots of the black dust.

With the sensitivity of your ASI2600MC, you should be fine using 180s and if the focus goes off or there's high cloud then you're loosing less exposure time for each sub.

Cheers Martin, your Bortle 2 skies must be stunning. I'm stunned by Bortle 3/4 skies - such a difference to 5/6 at home. 

Is there any benefit in going for 5 minute subs ? My data isn't clipping on 3 minute subs (data is off the LHS of the histogram in APT) and I'm shooting with a 2600MC Pro, Z73 in Bortle 3/4. 

But I''m wondering if 5 min subs would be better as I'm imaging the Iris Nebula - and there's lots of dust there

Attached image to show histogram 

Hey guys, wondering if you can help me pick a target for tonight as it looks like the stars will align... I'm at my holiday home on the coast and have Bortle 3/4 skies here. Ideally I would like to image a nebula, thinking perhaps the Iris Nebula. I have the 2600MC Pro and Z73, also have the l enhance with me if any Ha targets, Northern Hemisphere. Other than that, any galaxies, could go Bodes and Cigar, any suggestions welcome. I think with New Moon and bortle 3/4 here the Iris might image nicely? Cheers! I am excited! Hope it is clear skies tonight! 

I'm pretty sure my 2600MC Pro has sensor tilt. 

I've had a look at remedies for this and can see that there are two options - one is to adjust the tilt of the Camera at night whilst imaging, and I can imagine this is extremely frustrating - or is it ? Has anyone tried it? 

The other is to build some sort of DIY laser device setup to correct tilt indoors - which I can't say I'd be confident of trying.

So, I was wondering if there are any astrophotography stores which can do this ? 

Just changed some settings in Deep Sky Stacker, experimenting to get better image quality, one thing I'm not sure of is whether to choose Bilinear or AHD interpolation.

Just now, Chefgage said:

So for example then for two nights of imaging you would use group 1 and group 2 tabs and then process as normal. If say a couple of weeks later you get another night on that same target would you then re-stack everything i.e. put the first nights lights,darks,flats,bias in group 1, second in group 2 and the new data in group 3 and then re-stack?

Yes, and save the file list after each time you add to a new group so you don't have to add everything from night one.

With regards to taking flats, is it OK to take them indoors against a white wall? It's just that I haven't got a flat panel and sometimes the next morning it might be patchy cloud which I understand isn't ideal for pointing the scope at to take flats (with the t shirt covering the scope)

What I do is name a folder 'Horsehead and Flame Nebula' for example and then within that folder make sub folders for each night - named by date, ie. 28-01-22, within that I make sub folders, Lights, Darks, Flats and Dark Flats

I then put all those images from all four sub folders into Group 1 in DSS, and for the next night of imaging I'll put all the images from that night into Group 2 etc.

This also explains why my total stack on the Horsehead Nebula came out the same way as the 2nd image in my OP - the image with flats but no darks applied.

In my longer stack of the HH, I've got a blend of 3 and 5 minute exposures, and only a master dark for the 3 minute exposures. I haven't got any darks for the 5 minute subs. So I'm just taking some 20 x 300 second dark frames now, I'll integrate them into DSS tomorrow and see if I can get a nice stacked image. 

Ok thanks guys, and wrt darks, how often do they need renewing?

The ones I am using are from Feb last year.

Ok, looks a lot better with the Dark frame. I didn't realise that Dark frames were so necessary with flat frames. I'm sure I've read a few things where some people say they don't bother with dark frames and just dither etc.?