Shibby

Thanks all - much appreciated!

I realise everything looks a little soft, which is down to my poor processing of the stars (the luminance layer looked fine before final tweaks).

17 hours ago, carastro said:

Very nice Shibby from another Atik460EX owner.

Could do with your skies though (I'm SE London) 

They're Bortle 5, so don't be too jealous!

12 hours ago, bomberbaz said:

I am having a go at it myself but my gear is far lower spec than yours so if I manage a quarter the detail I will be happy. 

You should definitely try it, it's a nice target for all sorts of equipment. I managed to dig out this old image I took (11 years ago!) with a Canon 450D and unguided exposures:



 

Excellent - you should be very proud of this result for your first narrowband image!

Excellent Lion - I remember that a lot of this nebula is very faint so you've got a great result for 4 hours. I suppose f/2.2 helps!

First image of the season!

I really struggled with this one, so I'm not too pleased with the result. I think a new set of flats might help - although they are recent, I may have nudged the camera assembly around when fitting a new auto-focuser.

Once combining channels, I found I had awkward colour gradients to try and sort out. I'm thinking it might help matters if I were to rotate the filters between each exposure rather than capturing a full set of each in turn? Then they might match up better?

Anyway, the details:

• MN190
• Atik 460ex
• L: 20x600s
• RGB: 3x18x300s

@wimvb Just wanted to say thanks for your comments. I have since tweaked my polar alignment and improved the guiding and I'm actually pretty happy with the star shapes. I haven't yet had a chance to a proper star test as I don't want to remove the camera at the moment!

16 hours ago, wimvb said:

Essentially, focuser tube, outer edge of secondary, and reflection of primary should be centered.

Let me clarify my question/situation. Sorry for not being clear enough, or (more likely) still not understanding properly.

So, my scope has its secondary offset towards the primary mirror (as well as away from the focuser). My understanding is that this is a "classical offset" and is common on a Mak-Newt. Therefore, the outer edge of the secondary is NOT centred under the focuser. Please see green circle in my images.

Is that wrong? I would want to be 100% certain before moving the secondary up/down the OTA. If it's not wrong, and I should leave it where it is, my question is: should the primary reflection (red circle) still be centred under focuser.

Thanks for you comments @wimvb

I was aware of the dangers of moving the secondary offset, so I have *not* done that! Having read several threads, I still can't quite figure out if my collimation as shown above is even theoretically correct. I'm thinking that, given a secondary is a flat mirror, the offset should not be affect the primary reflection, therefore that primary reflection should indeed be centred under the focuser, same as it is with an ordinary secondary. 

Anyway, I will try a star test the next chance I get.

On 28/07/2022 at 17:55, Dave scutt said:

How do you get the blue, green and red circles overlaying 

Yep, it's in the OCAL software.

You align the outer circle yourself with respect to the focuser, then the inner circles remain concentric to help you collimate those elements.

Can anyone answer the question: Should the primary be centred to the focuser OR the secondary??

My MN190 hadn't been collimated for a long time - it's a somewhat daunting task, so I recently bought an OCAL to help out.

The collimation, as far as I can tell, was actually still pretty good but I did end up making a small tweak. However, I may have made it worse - my star shapes aren't as round as they used to be, however I can't 100% rule out my tracking/guiding as the cause.

With the help of some screenshots, can someone tell me if I have done this OK?

In image 1, you can see the initial collimation. You can see that the secondary is not centred under the focuser. My understanding is that is by design on the MN190 and you should not move it up/down the OTA.

In the above, you can see that the reflection of the primary is not quite centred either. This is where I made the (possibly incorrect) decision to tilt the secondary slightly to re-centre it. However, I can't quite get my head around whether it should actually be centred or not based on the fact that the secondary isn't centred??

Below, you can see the final collimation. [Note: The circles appear to expand a little as I change the focus]

A rare sighting!

Don't we always feel that way about our own images...

Looks to me like you may have some good data there. I would say the colour balance is strange - very green. Also, the image looks clipped, possibly at both ends of the histogram. This may be a symptom of using GIMP, though - does GIMP still only have 8bit curve adjustments?

I like it a lot. Great detail and you haven't over-processed it, leaving a "natural" look - if you can say that about narrowband images!

Superb! I'd say you've managed to preserve all those details while also achieving a nice colour balance.

As I have the same 'scope, your image gives me something to aim for!

Nice - the seeing will of course be worse the lower the altitude, but you're lucky - it only reaches 25deg here!

Wow - incredibly sharp detail. I look forward to seeing it with more data!

Very impressive structure your image is showing off - great work!

15 hours ago, wimvb said:

Excellent! Once again, a 190MN delivers.

Thanks very much! Yeah I've been very happy with the 190MN ever since I got it. It's difficult to imagine ever swapping it for anything else (unless I come across a massive windfall!) I decided to re-collimate it recently, though, using an OCAL and think I've had a negative effect. I'll post a separate thread about that.

It took me several nights to pull together enough data for this one. I've still had to push the luminance quite hard to reveal the fainter parts, but a fresh set of flats helped a lot. I'm a little disappointed I haven't revealed a bit more structure in the outer arms.

I went looking for interesting facts about this galaxy. Couldn't really find any so here a couple of mildly notable facts

• It is not part of a group, which is relatively uncommon.
• It has an unsually high number of globular clusters - 300 or so.
• Although arguably flying, it's not unidentified. It was discovered by Herschel in 1788, although of course nobody knew what "spiral nebulae" were for sure until Hubble figured it out in the 1920s!

Image details

• 190MN
• Atik 460ex
• L: 22x600s
• RGB: 3x17x300s
• Total: ~8 hours
• Processing: DSS, Photoshop
• Scale ~1.4 arcsec/pixel

Thanks for looking

Wonderful image! The 2 stars of the show are handled fantastically, but I also love the detail on show for all those many, many, little background galaxies.

15 minutes ago, almcl said:

I have had stacks of 25 in which DSS failed miserably to remove hot pixels, despite quite large dithers every frame and just the other night it failed to Sigma clip a single satellite trail from a stack of 70

This surprises me greatly. I've never had this problem.

I can actually see the galaxy in your sub, but DSS can only detect 1 star so can't align your stack. I don't know much about CMOS sensors, but you had the gain set to 0 which might be too low for 30s subs?

One solution is to process each linear sub individually to brighten it up and safe it to TIF before stacking.

11 hours ago, almcl said:

They look like hot pixels.  

If you are not tracking, the stars progressively move across the frame and when each frame is aligned the hot pixel appears to move.

You might be able to eliminate them with a Kappa-Sigma clip stacking algorithm, but if you're using DSS you will probably need a good deal more than 20 frames for this to be effective.

I believe 16 is the "magic" number, so stacking 20 should work OK with a sigma clip stack.

9 minutes ago, SamAndrew said:

Using a filter wheel? it's possible the filter hasn't gone back to the same position when you've gone to take the flats?

Hi Sam, I thought about that but some of the dust is on the sensor window (present with all filters) and was also out of alignment.

3 hours ago, david_taurus83 said:

Trouble as in dust particles don't line up or the stacking software says they are not the same pixel count?

All the dust rings in the flats don't line up, but once nudged everything lines up perfectly. The pixel count is exactly the same, I can't explain it!