HCG 68 Framing Check seeking comments.

[DaveS]

Just 2 hours of 300 sec Luminance subs, calibrated and given a basic stretch. As I wasn't sure about this target, and with the moon quite close, I wasn't going to spend more time on it.

As expected the galaxies are *very* small in the field of view, so much so that I'm debating whether to continue. The centre is also way off from what I thought I had set, something for me to check.

Rotated so North is up.

Comments and suggestions please. What do people think? Is the off-centre framing disturbing or a "happy accident"? The light streak in the upper border is coming from an 8.35 mag star just out of field.

Edited April 10, 2022 by DaveS

[DaveS]

That blazing searchlight in the middle of HCG 68 is mag 6.45

And there are a *lot* of even fainter fuzzies in the background.

[Craig a]

I like these kind of images from these huge distances the light has travelled, I would carry on and leave the framing as is as it’s different to the norm, and looking at all them faint background galaxys they will pop with more time added, it could be a fantastic image in the end 

[DaveS]

Thanks Craig. It's going to need a heap more data though. May turn out to be yet another multi-year project.

[juno16]

I agree with Craig. It’s a very pretty image already. 
I would keep going with the current framing. 
Looking forward to seeing the final version!

When you do finally post a final version, please include this image for reference.

 Thanks and good luck!

[DaveS]

Thanks Jim

OK, so that's two votes in favour of continuing.

Will have another look when the moon's out of the way.

[wimvb]

With a group of small galaxies such as these, I research the surroundings in Aladin. Usually there is more interesting stuff in the fov, and I adjust the framing to include this extra.

You have ngc 5390 just outside the fov to the left (you'd need to rotate the camera 90 degrees), and a distant (3 billion light years) cluster of galaxies just to the south.

http://simbad.cds.unistra.fr/simbad/sim-id?Ident=%402210954&Name=NSC J135404%2b394427&submit=submit

http://aladin.unistra.fr/AladinLite/?target=13 54 25.134%2B40 05 24.38&fov=1.09&survey=P%2FDSS2%2Fcolor

[DaveS]

thanks Wim. I'll check again in Stellarium, and check the coordinates I wrote down, and what I typed into the target page in Sequence. maybe by pushing the centre a little I can get both. And lose that annoying streak.

[wimvb]

To get the galaxy cluster you may need to take new flats. It looks like you have dust bunnies that gåhave shifted between lights and flats capture.

Anyway, good luck!

[DaveS]

Yes, a new set of Luminance Flats are on my to-do list.

[DaveS]

@wimvb

With new Luminance calibration, and a deeper stretch. I cannot get rid of those diagonal shadows which are from the ODK spider vanes. The streak of light is from a 8.35 mag star just out of field. I may stump up for an OOUK carbon fibre dew shield.

 

[wimvb]

3 hours ago, DaveS said:

I cannot get rid of those diagonal shadows which are from the ODK spider vanes.

Problems with spider vanes, or rather, diffraction spikes, is why I invested in a SkyWatcher 190MN. But I've never seen them cause shadows like this.

[DaveS]

Well, the ODK spider is machined from the solid, so the vanes are thicker than the usual 0.5 mm or so, so more likely to cast a shadow. I had thought that the problem was down to dodgy focus (Which I did have in the early days), but the focus is dead on, and the Flats were taken at the same focus as the Lights. So I'm as mystified as you.

[wimvb]

Are the shadows visible on uncalibrated lights? You can stack all lights without flat correction (but do use darks) to get better signal to noise ratio. If the shadows are absent, it’s the flats that are to blame. (what does a stretched flat look like?)

How do you take flats? A light box on top of the scope can cause priblems.

[DaveS]

OK, I'll try that, thanks. I'm using T-Shirt flats with either a completely blue or light overcast sky.

[wimvb]

1 hour ago, DaveS said:

OK, I'll try that, thanks. I'm using T-Shirt flats with either a completely blue or light overcast sky.

That should be ok. I've only heard about people having trouble with weird things going on if they put a flat panel / led panel on top of the scope. Light can get reflected off surfaces where it otherwise wouldn't.

[tomato]

I’m a bit late to the thread, but I think it’s a great image worthy of some more integration, but then galaxies and galaxy clusters are far and away my favourite imaging subjects.

[DaveS]

I did a trial stack without Flats, and a stack of the Flats last night, but didn't get round to posting, will put them up this morning.

[DaveS]

OK, as promised:

Stack without Flats. Given a slightly exaggerated stretch

And the Luminance Flats, calibrated with Dark Flats

The filter looks off-centre, don't know why . Not a cheap wheel.

Dur...That's HCG 44, which I had been working on. Still, it shows the problems.

Edited April 14, 2022 by DaveS

[DaveS]

Take Two.

Shifted the centre so I now have NGC 3590 and possibly the very distant cluster that @wimvb mentioned.

BUT...

The sky background is so bright that I really had to hammer it down. My fault, as I was setting up in a hurry since the sky had cleared just as I was going to bed and just grabbed a likely exposure file, and decided to live with the 600 sec subs. If I had more time I would have set up one with 300 sec. Far too much moon for 600 sec.

Options: Use a camera with a bigger sensor, IMX 455 to get more FOV, Yeah right, like I have a spare £5k or so. Or use a camera with a smaller FOV ASI 533C and just go after the HCG with nothing else. Probably a no-brainer.

 

[DaveS]

I'll add that turning the camera by 90 deg as was suggested above is a non-trivial operation involving rotating the entire focusing train in its seating on the back of the ODK then rebalancing around the RA and OTA. ASA mounts are *very* finicky about balance in all three axes. The focuser doesn't have a camera rotator (Despite being a FT), and I'm still looking for a 68 mm rotator.

 

Edit: I did find a pair of Baader quick release dovetail adaptors but they are £243 together, and eat 25mm of  already tight back focus.

Edited April 19, 2022 by DaveS

[DaveS]

I managed to get a bit of RGB last night. Not nearly enough for a finished image, but enough to give an idea.

By rights I should reframe yet again, but I'm rapidly running out of astro dark. Will leave the framing here, and at some point revisit HCG 68 on its own with an ASI533.