Uranium235

If its a bit stubborn , id probaby go (very carefully) with a cotton bud dipped in IPA first (then a toothbrush).

Inspect your flats, a normal one (albeit my example is mono) should look something like this (vignetting amount will differ between optical/camera setups), but it should measure 1/3rd of the histogram - or/and have a healthy ADU reading, over 16bit that would be reading of about 21,000.

But the previous suggestion of inspecting all your lights should also be done. If you have Ps, then you already have all the tools you need to process the image correctly (after calibratrion and stacking). Dont rely on software to correct vignetting, the only sure way is with proper calibration. If you have a gradient after applying flats, that is best dealt with using a Ps action/filter - or you can create your own gradient map in Ps (a poor mans version of the DBE found in Pixinsight).

Also, if you want to simplfy your data for now - just convert it all to mono (including your flats), see if you can get anything out of it that way - I find mono is far easier to work with if youre trying to rescue some data.

8 hours ago, LooseFur said:

aaah ok - Yes, I am using full frame so you are not using the edges of the lens that I am...

In my experience, there are very, very few lenses or telescopes that can cover a true full frame (35mm+) with pinpoint stars. And those that do, cost a lot more (thousands).

2 hours ago, LooseFur said:

yes, same lens but I am on full frame so I am not sure how much of the lens area you are using with your camera ? Is it full frame?
Though I am very new to all this so I have a lot to learn! 
I opened a thread about this on CN actually (https://www.cloudynights.com/topic/734450-issue-with-asymmetry/). I can't seem to get both corners sharp (top right, bottom left)

Im using the KAF8300 sensor - its just very slightly smaller than APS-C

On 13/10/2020 at 13:01, LooseFur said:

cool! I am struggling to get good stars across the image of my modded canon 6D at f/4. I can get the lower left corner good, but the top right suffers, and vice versa. Painful!

You have the same lens? Try 2/3rds, but moving the star towards the affected corner.

8 hours ago, ollypenrice said:

Cor blimey, Rob, that doesn't look like a lens image! The stars are tiny.

I can safely say that I'm very impressed!

Olly

Might have something to do with the Astrodons   and a bit of processing magic.

@StamosP wow.... newtons rings.... ive never seen that before in a reflector!

https://en.wikipedia.org/wiki/Newton's_rings

http://www.365telescopes.com/how-to-deal-with-newtons-rings-in-cmos-imaging/

It only usually affects solar H-alpha images, so Im a bit clueless as to why its appearing in a DSO image. Remove the corrector and try imaging again, if it disappears - youve found the culprit.

1 minute ago, Coriorda said:

Thank you, I think 1000mm will take some time and deep pockets ! I see you are local .. is the WAS meeting again do you know ?

I dont attend any local astro society meetings (work commitments etc), but @michaelmorris (I beleive) is still involved.

1 minute ago, HunterHarling said:

I started with an SCT at 2000mm, and I must say it was difficult ;) I think either of those scopes would be great, you should be able to get excellent images with those short focal lengths.

lol... 2 metres... you'd have to be stark raving bonkers to start at that FL

You should be fine at 250mm, it will be very forgiving when it comes to guiding/tracking. It only gets especially tricky at 1000mm and beyond.

17 hours ago, LooseFur said:

Very nice, what aperture did you set the lens to? 

This was wide open at f4, using the 2/3rds focusing technique (not focusing on a centrally placed star, but moving it out 2/3rds towards the edge of frame).

3 hours ago, Davey-T said:

Looks pretty darn good Rob, did a bit of pixel peeping and can't fault it.

Have you tried any RGB with it yet ?

Dave

Havent tried RGB yet Dave, that will be my next box to tick being as M45 is now coming into view from my back garden (a bunch of very bright stars should be a good test).

Well, its been a couple of weeks before I was able to go out and grab some OIII for this one (always a challenge due to localised LP) - but its now in the bag and I've spent the morning processing it (still feeling pretty tired though.....lol).

So, the million dollar question - can this lens make a pretty photo?  Yeah, I think so

Had to crop a little bit out because of a medidian flip on the OIII, but I didnt lose that much. While I was there I also topped up the Ha luminance layer for a bit less noise in the outer regions.

One other note though... being as the lens body is almost entirely made of metal (and can hence get quite cold) - you do need to go out and adjust the focus after about 45 min from the session start... nothing unusual or different from any other telescope or lens really.

19x900 (Ha_L), 8x900 Ha_R, 8x900 OIII_G&B  - Modified cannistra biclour process

Askar ACL200, QSI6783, NEQ6

Thanks for looking!

Ha luminance layer:

11 hours ago, Backyard Space Dude said:

Good spot! I’m very aware of the weird shaped squiggly stars, I can’t figure out a good way of reducing the stars either before or after adding them back in to the starless layer. I did use some fairly heavy noise reduction with Topaz labs and photoshop so maybe that’s where the pixelation is happening. I’m fairly sure I uploaded the tiff to Flickr and then shared from there to here, so perhaps that has something to do with it, too? Though the original doesn’t look great either haha

For NR, I personally use the normal reduce noise filter in Ps set to 7 or 8 strength, with preserve detail at about 85-90%. Then on the final step, its noise ninja at a very low setting (Strength/Smoothness set to 3 or 4) - and sometimes selectively apply it (using a layer mask). That avoids processing artifacts or the "vaseline" look.

If you want to reduce stars, you can do it in two steps. Firstly by using a layer mask about 3 curves into the stretching - ie: do three curves, then set that image aside as a copy, stretch the original more until the stars are getting too big for comfort (usually another 2-3 curves later), then paste in the one you set aside using a layer mask (so you are compositing the stars only, not the nebulosity). Then, as you are approaching the end of processing, use noels "make stars smaller" action... but only twice at most, otherwise you might get dark halos. Bit hard to explain in plain text...lol, it needs a practical demo.  But either way you need to keep a close eye on the details to avoid those dark halos.

When it comes to reducing star sizes, layer masks are your friend 😊  oh, and noels actions (if you are using photoshop) 

5 hours ago, Adreneline said:

I'm afraid I used the "cheating method". I took the image into PixInsight, inverted the image and applied the SCNR process normally used to reduce green in an image. I then reinverted the image and the magenta halos have been removed. I am sure there are fancy methods involving PixelMaths and masks and all manner of things but the cheat method seems to work and I honestly can't see it has changed anything else.

Adrian

Seems a bit labour intensive for such a simple thing..lol..

My method: load into photoshop, call up saturation, select magenta, move slider left to remove magenta.... done   

If you inspect the sensor, do so under a very bight light... better, a headtorch set to full power - that will show up pretty much anything that shouldnt be there.

You just cant beat f2 eh?   If you do get any new optics...  dont sell the Samyang!!! (you will regret it).

Ive often wondered how a 490ex would perform on this lens.... and... its pretty blummin good.... if not the perfect combination.

Once you do have enough for an AP setup, things will open up nicely in hydrogen alpha which is fairly immune to LP  (being as most of our galaxy is comprised of Hydrogen!). Depending on the local LP (whether LED or not), and if - like me you have a very tall street light just 25 yards away (I put up a screen to block it out and create a "shadow" for my gear to operate in).

1 minute ago, Davey-T said:

Had similar problem with one of mine and think I traced it to the power connector, doesn't seem to be a very good fit, I presume its a standard 2.1 pin but only had to breath on mine and it disconnected, squirted some contact cleaner on it and now use it with power cable wrapped around USB cable to keep some sideways tension on it, hasn't disconnected since then but may just be a coincidence, lost a couple of hours subs one night when it first did it.

Dave

Yep, if I velcro all the cables up and dont look at it or breathe on it - its usually ok   Maybe some nice right-angle connectors would help there (looks better too!).

10 minutes ago, SyedT said:

Thanks for the feedback! I was aiming for 600 second subs as a minimum since that's what I tend to go for in NB, but a combination of poor seeing and therefore bad guiding meant I couldn't do that and had to settle for 300 seconds. I guess the next step would be to take a bunch of longer subs and add them on. 

Ahhh yes, guiding can also limit your sub length. As well as having one of those nights where the sky can be very on/off. Next time its a perfect sky, just get out there and hammer it with Ha as that will carry most of your luminance and contrast 

At first glance, its pretty good! Especially the crescent.

However   (lol) being the pixel peeper I am, ive had a real close look at it and maybe there is something up with the way the image has been saved off because there is quite a lot of pixelisation going on in the surrounding neubulosity:

Probably an easy fix, just have a fiddle with the export settings or try a .png file to see if that makes any difference. If its present in the .tiff file, it may be caused by a noise reduction routine somewhere along the processing workflow.

4 hours ago, peter shah said:

wow thats stunning Rob

Thanks Peter, I reckon I could push it up another notch if I add three more hours in Ha, then a bit of OIII for some cannistra colour. Ive not used an OIII filter with the Askar yet, so it will be interesting to see how it turns out.

The humble 80ED, still punching well above its price tag all these years later  

Looks good, but to kill that noise - I would personally opt for subs which are much longer than 300s.

You are using a CCD, so your exposure time is only limited by the brightess of your target, or the local LP - neither of which should come into play in narrowband. So ramp it up to 900s and replace some of the data captured under "less than ideal" conditions, if you keep bad data in the mix it can sometimes bring down the end result... a case of quality over quantity perhaps, but ideally its quality and quantity.  It will take a while since you may need to manually inspect all of your subs and toss "bad" ones into a separate folder.

If you can push it further than 900s, do it. Higher risks yes, but the rewards are worth it   (but 900s is a good benchmark to start off with).