Improvement advice (72ED, ASI224MC, EQ5)

[rob_r]

Hi,
Finally I got around to my first imaging run with the new Evostar 72ED paired up with the ASI224MC, this is more a widefield image run than previous (mostly planetary imaging) runs with my Mak. The learning curve has been tricky using the 72ED as opposed to my Mak127, I'm guessing it is due to the wider FOV and shorter focal length. Additionally, so I can use the same T-rings and eyepieces I got a Baader 2" to 1.25" adaptor but I'm unsure if that is suitable for imaging. To gain focus with the ASI224MC I needed an 2" extension tube which needed to be just... not quite fully inserted into the adaptor (see photo of my setup). I needed another 10mm or so. The images below are with 70 lights at 30secs on a EQ5 GoTo mount. Star trailing is clearly evident on a quick post process on the resulting stack via DSS. I like to think I'm fairly decent at polar alignment but I guess only a second pair of eyes could tell me otherwise.  The stars appear stretched at the edges too as well being incredibly bloated. The next couple of nights look promising here despite a moderate breeze so I am going to retry this target again, hopefully I'll remember to add the IR cut filter next time too. Any advice would be welcome please. Plus, I have a couple of questions. I read that realistically the EQ5 tracking can only do a maximum of a 30 second single exposure...?

For the data, I was disappointed that the lights were all in mono but then had that light bulb moment of de-bayering the data to get the colour. I know far more data is needed even the colour image looks dirty and quite noisy. But, despite the lack of data some detail is starting to come through. Maybe try and up the resolution too on the camera if I can.

So a couple of questions please:

• Will the 2" to 1.25" adaptor cause any issues with the data collected? Would I be better just getting some 2" fittings for the camera(s)?
• Can I achieve focus using another method without the extension tube?
• Do I need a field flattener?

Any advice would be great how to better the tracking and quality please.

Many thanks, Rob --

 

 

 

[Elp]

The t ring adaptor may introduce tilt if I think its what it is and doesn't screw in. The last time I used my 224mc I used m42 extension rings to get the right backfocus to the camera sensor. A field flattener helps with flat field but the sensor resolution is quite small so I don't know whether it will help. At the moment you just have to fine tune your backfocus and make sure the PA is as best as possible. I found the camera quite noisy and couldn't expose for more than 30 seconds or so. My stars are quite bloated too could be a sampling issue:

Edited April 22, 2022 by Elp

[rob_r]

Thanks for the reply. The T-ring doesn't screw in, it just slots in and it is all tightened up by the 2" to 1.25" adaptor brass ring so some tilt may well have been introduced. I'll have a look into getting a M42 extension ring, a 10mm extension may be all I need. I may have to find a better alternative to ASIImg too as I prefer to have finer control over the exposure and gain settings. The weekend didn't pan out as expected so will have to wait for another opportunity to retry. Thanks again.

[Elp]

Flo sell two m42 sets which I've bought which are both quite useful, the smaller increment one is more useful think it's 4, 5, 6, 7, 8, 9mm set, the larger one is in increments of 5mm. Both sets have their uses.

For software try Firecapture, sure there's a pc version. I tend to use an Asiair or astroberry so no need for a pc (though astroberry displays better on a pc sized screen).

[Elp]

Just checked, this ones out of stock atm:

https://www.firstlightoptics.com/adapters/astro-essentials-t2-m42-extension-tube-set-4mm-5mm-6mm-7mm-8mm-9mm.html

 

[tomato]

First off, congratulate yourself on a nice first image of M51, you have both colour and detail there.

As you have already established, a screwed together imaging train will help no end, particularly if you are dismantling and setting up each time. I started out by attaching the camera into the focuser with an extension tube and it was hit and miss as to how much tilt was introduced each time.

Are you focussing with a Bahtinov mask? This aid will ensure good focus each time, templates are available on line for all sizes of scopes if you want to make your own.

Your imaging scale is 1.84 arcsec per pixel if I have entered your kit correctly into the calculator, so that’s fine. Get your PA as good as possible (use the drift alignment method if you do this by eye) and limit your subs to 30 secs or less and take lots of them.

Finally are you calibrating your data with darks, flats and dark flats? It’s important to capture these at the same camera temperature as your lights, but it won’t take long with sub minute light subs.

[rob_r]

Thanks @tomato . The 2" to 1.25" has a thread too so screwing any additional extenders in should not pose an issue. I only have a Bahitinov mask for my 127 Mak at the moment so I will get or make up a smaller mask for the 72. I just focussed in on Alkaid on this particular run as it was the nearest identifiable star to M51 for me. I took about a dozen darks and bias frames too. The camera and scope should be a good pairing according to various calculators. I'll read up on the drift alignment method as it seems complex at first glance but I guess some Youtube videos may help me understand the process better. 

[tomato]

You can drift align with your camera with some cross hairs superimposed on the image.  You basically see if the star is drifting up or down over time and adjust the alt/az on the mount accordingly. There was a really good how to guide on drift aligning on Ian King's website , I don't know if it found its way on to FLO's resources page when he joined them.

[rob_r]

I had another go last weekend, everything was screwed in.
71x lights at 30 seconds, 15 darks and 15 bias.

Still having issues with the backfocus despite the extension rings which added another 49mm on top of the other extension tubes. I tried different combinations but focus is a struggle. The cam seems so far away from the scope. The Bahtinov mask helped and spikes crossed over, but still the stars have come out bloated.

I see if another opportunity presents itself very soon.

[WolfieGlos]

Are you still having issues with tilt? If so, I’d recommend changing your connection to the focuser from the terrible skywatcher 2-screwed clamp to a screwed version like this: https://www.firstlightoptics.com/adapters/astro-essentials-m48-adapter-for-sky-watcher-newtonians-and-72ed-refractor-m54-with-10mm-backfocus.html

This will connect directly to a Stellamira flattener (but not the skywatcher one), but if you’re still imaging without a flattener then it might be worth checking with FLO if you’re unsure what adapter you’d need. When I bought my 72ed I had terrible issues with it, and that adapter alone brought down my tilt from 60% to 25% if I recall correctly (measured in ASTAP). There’s a topic on SGL somewhere with @AstroNebulee, myself and others trying to solve it. You will also see we had various ranges of backfocus; mine was in the range of 61mm for a DSLR with a flattener, and I think he had a ZWO camera but can’t recall how much backfocus was required. 

Good luck with it!

[AstroNebulee]

6 hours ago, WolfieGlos said:

Are you still having issues with tilt? If so, I’d recommend changing your connection to the focuser from the terrible skywatcher 2-screwed clamp to a screwed version like this: https://www.firstlightoptics.com/adapters/astro-essentials-m48-adapter-for-sky-watcher-newtonians-and-72ed-refractor-m54-with-10mm-backfocus.html

This will connect directly to a Stellamira flattener (but not the skywatcher one), but if you’re still imaging without a flattener then it might be worth checking with FLO if you’re unsure what adapter you’d need. When I bought my 72ed I had terrible issues with it, and that adapter alone brought down my tilt from 60% to 25% if I recall correctly (measured in ASTAP). There’s a topic on SGL somewhere with @AstroNebulee, myself and others trying to solve it. You will also see we had various ranges of backfocus; mine was in the range of 61mm for a DSLR with a flattener, and I think he had a ZWO camera but can’t recall how much backfocus was required. 

Good luck with it!

@rob_rI can't find the thread @WolfieGlos an I were discussing, at the moment but will look. I have my back focus set to 60.5mm using all screwed connections. I've attached my diagram of the connections I use.

Maybe that adding a FF, either a Stella mira or ovl (as I use) would help your issues atall? 

I'm not sure of all the previous lengths you have now but generally from what I've seen on the 72ed the back focus is around 60mm or a shade more. 

Lee

Edited May 21, 2023 by AstroNebulee

[rob_r]

Apologies for the late reply. This is all great advice so thank you both. The diagram is a great help. When I got the 72ED I didn't account for the 2" focus tube as my Mak uses 1.25" accessories.

At the moment, I am using this which looks like it may not be all that suitable from your suggestions to help reduce the tilt, https://www.firstlightoptics.com/adapters/baader-2-to-125-reducer-adapter.html and this is the set of extension rings I got, https://www.firstlightoptics.com/adapters/astro-essentials-t2-m42-extension-tube-set-4mm-5mm-6mm-7mm-8mm-9mm.html . 

So the recommendation would be a FF perhaps.  I was considering the SW one, https://www.firstlightoptics.com/ed-pro/skywatcher-85x-reducerflattener-for-evostar-72ed-pro.html but maybe go for this one instead and everything screws together, https://www.firstlightoptics.com/stellamira-telescopes/stellamira-2-0-8x-reducer-field-flattener-with-m48-adapter.html . The price is a welcome bonus too. 

Thanks for the help as ever. I'll get there hopefully!

Edited May 25, 2023 by rob_r

[WolfieGlos]

Hi Rob,

I have recently upgraded to a Starfield 102 f/7, and the flattener https://www.firstlightoptics.com/starfield-telescopes/starfield-08x-adjustable-reducer-flattener-for-90102mm-refractors.html is an adjustable one which removes the need for those extension tubes to get backfocus correct. It won't be compatible with the 72ED, but it made it so much easier to get backfocus correct. In fact, it was actually bang on 55mm for my DSLR.

So if you are looking to get a flattener, then perhaps consider an adjustable version such as this: https://www.firstlightoptics.com/stellamira-telescopes/stellamira-2-adjustable-field-flattener-with-m48-adapter.html - but please check with FLO if it is compatible with the 72ED.

I have both the skywatcher 0.85x reducer and stellamira 1x flattener for the 72ED, and I had to constantly play about with extensions and spacers to get backfocus correct. Even then, I still suffered with eggy stars and tilt on both so I gave up in the end. 

[rob_r]

After seeking further information from FLO, I got the following purchases.

• ZWO M42-M48 Extender 16.5mm Long
• StellaMira 2" Adjustable Field Flattener with M48 Adapter
• Astro Essentials M48 adapter for Sky-Watcher Newtonians and 72ED Refractor (M54) with 10mm Backfocus

They said the flattener is a great match for the 72ED plus the ASI224MC and the 600D. With the above extensions, plus another set of M42 extensions which I already have the imaging train should all screw directly into the focuser tube with the correct backfocus required.

Fingers crossed and thanks for all the advice. I'll keep you updated on progress.

Edited August 9, 2023 by rob_r

[AstroNebulee]

58 minutes ago, rob_r said:

After seeking further information from FLO, I got the following purchases.

• ZWO M42-M48 Extender 16.5mm Long
• StellaMira 2" Adjustable Field Flattener with M48 Adapter
• Astro Essentials M48 adapter for Sky-Watcher Newtonians and 72ED Refractor (M54) with 10mm Backfocus

They said the flattener is a great match for the 72ED plus the ASI224MC and the 600D. With the above extensions, plus another set of M42 extensions which I already have the imaging train should all screw directly into the focuser tube with the correct backfocus required.

Fingers crossed and thanks for all the advice. I'll keep you updated on progress.

All sounds great Rob. The field flattener will definitely help you indeed. You may still get some bloating of the stars, I think most skywatcher 72ed scopes have this to some degree. 

I'll look forward to your reports on the improved imaging train. 

Lee