Tips on imaging with a Newtonian

The flocking was done as my very first imaging session was a disaster zone as there were internal reflections all over the place and a very noticeable 'doughnut of doom' that no gradient removal tool nor flats wanted to correct. The flocking and painting has totally eliminated that now and the data has no discernable gradient, once calibrated.

After reading your post I just realised I've been exceptionally dim…..I hadn't actually fitted the MPCC when I took that image (it's still attached to my DSLR!) so that is just the raw mirror in all it's glory!!

Hopefully will get a clear night soon and try again with the MPCC but I agree a better CC will be a future purchase….focuser first though!

Collimation tools I have are a decent cheshire, an OCAL that got given to me and a very, very poor laser that is probably just e-waste.

What about on the fly collimation using a defocused star? It seems counter intuitive to collimate then attach the imaging rig that causes different flexture of the tube/focuser etc.

Not sure on the stability of the primary cell either I'll see how that pans out. Given how cheap the scope is it's probably not great but I'm looking at this as a long term project as the primary is a rather nice mirror.

Much appreciated on the suggestions!

Clear skies.

I think your flocking is a good idea if you had that many internal reflections. Normally I flock a 12” square directly opposite my focuser and if I’m ambitious 12” at the primary end and call it good. Like you just touched up ss screws/nuts and so forth.

As far as a focuser goes I’m with @andrea tasselli I use a Moonlit on my 12” newt, but have heard good things about the Badder one that they sell, but have no experience with it.

Coma corrector? Well there are many of them with pros and cons and both Andrea and I have put in our 2 cents worth on another thread here on AB. I’m going to refer you to that thread. It may help you and give you more suggestions other than what Andrea and I would tell you. Here is the link: https://www.astrobin.com/forum/c/astrophotography/equipment/good-coma-corrector/

Collimation: yes collimation is important for sure! I use a Cheshire and then a laser collimator to do what I call a bench collimation. Once thats done and I mount it I then put everything in place and then do what you had mentioned by defocusing a star and do my best to get is as close as I can. Once thats done I then move to MetaGuide for an in focus collimation. That will get you closer than anything else in my personal opinion, however others may disagree. I’ve used it many times and once you through the learning curve you’ll be happy you took the time to do it!
FWIW, MetaGuide is actually a guiding software but it has a collimating tool in it that monitors the airy disk of an in focus star and once you get your setting right you just make it so that the red dot stays in the center of the focused star. Here is the link to the free software if your interested.  https://smallstarspot.com/metaguide/

Hope this helps.

Dale

Thank you for the advice, Andrea! I understand that a mask reduces the reflecting surface, hence counterproductive. But what makes flocking irrelevant? Can you elaborate more on that?

Yanko

Flocking works in some instances to improve contrast by remving diffuse light from, normally, a corrector element that defines the inlet pupil of the system (wiz. a SCT). In standard, properly designed newts the inlet and exit bupil is at the the primary so, unless the inner surface is signficantly reflective (but I can't recall this to be the case for the SW scopes I've seen namely the Quattros) then flocking isn't going to win your day. Flocking (or painting with a highly opaque paint which should be preferred as stick-on flocking materials tend to degrade when exposed to the elements for years) the area just behind the secondary as seen from the focuser is a better option in my opinion. This said in my 3 newtons I never had reflections and they are just run-of-the-mill tubes with no flocking ever done or even thought about.

The use of a proper dew-shield is to be recommended and it is the proper tool to avoid unwanted reflections from the outisde and near getting onto your image plane. The same goes not allowing light to filter from the back of the focuser onto the secondary and shielding away (shower-cap) the back of the tube.

andrea tasselli:
I'm thinking the first 3 mods were either irrelevant or counterproductive (mask) while the last is probably a deal-breaker.

Thank you for the advice, Andrea! I understand that a mask reduces the reflecting surface, hence counterproductive. But what makes flocking irrelevant? Can you elaborate more on that?

Yanko

An aperture mask is definitely worth it. I can testify from personal experience on my Skywatcher Quattro 250 and 8" goto dob. A mask blocks the extreme edge of the mirror (cuts in a few mm), which can be slightly curved (more so in the "budget" mirrors)  so the light from that region focuses further than the rest of the mirror. Plus adding a mask meant the diffraction-inducting effect of the mirror clips is eliminated. I could visually see the improvement with my 8" goto dob (my visual scope) on a bright star. Any reduction in the light gathering capacity of the mirror is very minor at best and somewhat irrelevant because the overall performance of the mirror is improved.

A proper mirror is always chamfered around the edge to avoid any ill effect from a turned-down/up edge so I'll discount the "edge" effect even from "budget" scopes such as my TS Photon. If I were to add a mask to it, it would need to cut into the free diameter by 4 mm which would reduce the actual light gathering area by ~5% and I'd rather not. At the end of the day the scattering mainly happens at the secondary spider (or rather because of) so it is a secondary concern for me. But, of course, if you are so very concerned with the aesthetics of the PSF then a primary mask is one way to ameliorate things. Or an apodization mask.

To all of you.

Thank you so much for all of your engagement, tips and advice. Lots to mull over and digest here.

I've ordered the Baader Steeltrack focuser and next up is finding a decent laser such as a Howie Glatter, struggling to find an autocollimator in stock here in the UK but I really like the principle behind them. Also like the idea of the software based collimation, something I will try while hunting down a good laser.

I'm in the middle of a multi night project with the babyscope (Do, do, do do) at the moment and then I'll be focusing on the Newt!

Clear skies to all you wonderful knowledgeable people!

Rich