Uranium235

It was about 20mm, which takes it to f5.9. Not really any meaningful difference to the amount of exposure I give it. Masking off Ive found, does make collimation easier too. All it is is just a black cardboard ring, that ive stuck to the mirror clips. Simple, but effective. We all know that systems that are of a higher focal ratio have less coma, so... what about adjusting it to a slightly higher (but tolerable) FR so there is less work for the coma corrector to do - in turn giving you a larger useable field.... in this case 100% coverage of a KAF8300 (22mm diagonal). However, a complete new set of flats would be required.

Just messing around with the 130, had the idea to mask off the primary a little in order to "buy" that last corner and I think it worked! I think losing a stop hasnt hurt anything tbh: 10x450 (x2 panes) Ha 2x2bin (3.4" p/p) - No calibration

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.

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).

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

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

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.

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

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.

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).

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:

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)

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).

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!).

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.

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.