The Hidden Galaxy

[Stefan B]

This is rather a test shot than a dedicated project. It was the first light for my upgraded imaging train now containing a GPU coma corrector and an OAG instead of a Baader MPCC and a guide scope. Furthermore the filters are now applied via a filter drawer instead of being threaded in front of the coma corrector.

The weather conditions were pretty bad, especially for the Ha data. It was basically shot through clouds and is thus pretty blurry. I also introduced a bit of tilt to the coma corrector in two of the sessions since I tried to compensate the weight of the camera etc dragging the focuser down...slightly overcompensated

The OAG needs a bit of tweaking, too. I had to adjust DEC aggressiveness in PHD2 since the mount seemed to wave at me once it started to make corrections in DEC. It always was too much correction which was then counter corrected too much again, getting worse and worse. Sometimes I am also surprised at what simple things are confusing me. I was doing guided test shots and saw tilt. I wanted to know if the newly applied weight of the OAG and camera standing out was the reason. So I rotated the camera together with the OAG and tried to do guided test shots. Guess what, the guiding was horrible and I was totally clueless... until it dawned on me that I have to recalibrate the guiding after rotating the camera since the FOV of the OAG also changed and right and left meant now totally different things than during the initial calibration...

But overall I am quite happy with the first try.

See https://www.astrobin.com/m7lfhd/ for details.

It is also pretty convenient to change filters with the drawer instead of taking out the camera and threading the filters in front of the coma corrector with readjusting rotation and focus again

Regards
Stefan

[Startrek]

Hi Stefan,
That’s a great Galaxy image from your upgraded set up.
A really nice target
Well done !!
My only observation is maybe slightly over saturated with Color in main body of galaxy and the Star field which detract from fine details. The stars seem a bit too colourful but that’s only my opinion ?
The TS GPU is an excellent coma corrector, however it did introduce some Vignetting into my image train which is easily resolved with flats.I have 2 of these GPU , the original model which has a brass sleeve and the latest model without the sleeve which is much better.
Have you ever tried PHD2 PPEC algorithm? I haven’t used Hysteresis for 4 years now and get good results from PPEC ( my mount is not PEC trained either )
With these EQ6-R mounts ( I’ve had 2 now ) the key to good guiding is a few easy adjustments -
1/ Adjust Ra and Dec axis thrust bearing tension ( Synta tend to tighten them up too much before they leave the factory )
This allows really precise Dec and Ra balance.
2/ Adjust Dec and Ra worm gear free play ( takes a few nights fine tuning but well worth the exercise in minimising backlash.
3/ Adjust Ra and Dec drive belt tension ( 2 to 3mm of belt flex at the centre between the pulleys is enough )

Good luck with the new set up, especially going OAG , I’m a bit lazy and use guide scopes on my 8” and 10”

Cheers
Martin

[dx_ron]

I like that quite a lot Stefan. (I'd do up the colors the same way, so maybe I'm also usually missing some fine details )

Never used an EQ6, so just wondering aloud: could your dec oscillations be from way too much backlash compensation? Maybe try setting the compensation amount to the minimum (20ms) and let PHD2 figure out how much is needed.

[fmeireso]

Very nice startcolors Stefan, and nice image overall!

Just wondering, why did you switch to OAG? I guide my 130 mm F/7 refractor with a guidescope without problems, at least sofar. I do use a ASI 290 mini cam, bit more sensitive then a 120 mini and a 60 m guidescope with F=280 mm.

[Stefan B]

Thanks, guys, really enjoyed your feedback!

My only observation is maybe slightly over saturated with Color in main body of galaxy and the Star field which detract from fine details. The stars seem a bit too colourful but that’s only my opinion ?

I agree on the stars being too colorful, Martin. But the galaxy gained details with more saturation in my eyes. Since there's so much dust in front of the galaxy the details appear blurred but increasing the saturation helped revealing the galaxy's structure.

Since I try to avoid selective processing the treatment of saturation was the same for galaxy and stars. Though it probably would have been easy to decrease saturation of the stars.

The TS GPU is an excellent coma corrector, however it did introduce some Vignetting into my image train which is easily resolved with flats.I have 2 of these GPU , the original model which has a brass sleeve and the latest model without the sleeve which is much better.

We've already discussed your usage of the GPU. Your opinion on it was one of the reasons for me to upgrade I haven't seen vignetting yet. My understanding is that it should be fine for APS-C but not so good for full frame.

Have you ever tried PHD2 PPEC algorithm? I haven’t used Hysteresis for 4 years now and get good results from PPEC ( my mount is not PEC trained either )

I'll have to look into that. Haven't used it until now.

With these EQ6-R mounts ( I’ve had 2 now ) the key to good guiding is a few easy adjustments -
1/ Adjust Ra and Dec axis thrust bearing tension ( Synta tend to tighten them up too much before they leave the factory )
This allows really precise Dec and Ra balance.
2/ Adjust Dec and Ra worm gear free play ( takes a few nights fine tuning but well worth the exercise in minimising backlash.
3/ Adjust Ra and Dec drive belt tension ( 2 to 3mm of belt flex at the centre between the pulleys is enough )

Thanks so much for your helpful and knowledgeable comment! I am not very handy when it comes to mechanics. I guess I have messed up my EQ3-2 with such adjustments But I guess my EQ6 came out of the box pretty fine. Using the guide assistance in PHD2 two years ago the result was that there was basically no backlash. And guiding is in the 0.5'' range with the guide scope and the OAG. So I don't know if I want to risk messing that up.

Good luck with the new set up, especially going OAG , I’m a bit lazy and use guide scopes on my 8” and 10”

Did you notice any flexure or frequently bad frames although your guide graphs says everything's fine? Mirror flop?

I like that quite a lot Stefan. (I'd do up the colors the same way, so maybe I'm also usually missing some fine details )

Thanks, Ron, much appreciated!

Never used an EQ6, so just wondering aloud: could your dec oscillations be from way too much backlash compensation? Maybe try setting the compensation amount to the minimum (20ms) and let PHD2 figure out how much is needed.

Maybe, I will try that! Silly question: How does PHD2 figure out how much is needed!?

Very nice startcolors Stefan, and nice image overall!
Just wondering, why did you switch to OAG? I guide my 130 mm F/7 refractor with a guidescope without problems, at least sofar. I do use a ASI 290 mini cam, bit more sensitive then a 120 mini and a 60 m guidescope with F=280 mm.

Thanks, Freddy! My problem was that I frequently had bad subs although my guide graph looked perfect. Maybe flexure. Sometimes the stars were pretty long streaks. Maybe mirror flops. I already heard of that from different youtubers (e.g. recently Cuiv) and they solved the issue with OAG. My stars already looked much more consistent from sub to sub. I even think I noticed pinched optics at the start of the night while it seemed to get better when temperatures dropped. I probably didn't notice because the slightly oblong stars did hide that problem Refractors are probably much easier in that regard.

Regards
Stefan

[dx_ron]

How does PHD2 figure out how much is needed!?

Just the computer equivalent of trial and error. If a direction-changing correction undercorrects, it adds a bit more backlash comp time. Once it starts overcorrecting it backs off. I had to use compensation when I had a CEM25P - I always found that using the value suggested by the Guide Assistant way overestimated the actual backlash.

[Stefan B]

Thanks, Ron! I see, I will try that! Though decreasing DEC aggressiveness from 100% to 70% already led to a guide error of ~0.5''. I also had to adjust the exposure time from 1 to 2 sec. I had the impression that I was chasing the seeing (also with multi star guiding) which might be expected since now the focal length is 750 mm instead of 165 mm while the pixel size stayed the same. So the pixel scale is much smaller and seeing becomes a bigger factor I guess.

Regards
Stefan