M83 with 6RC

[Todo43]

Hi all,


Having acquired a 6RC many months back, I have finally gained the confidence to collimate it (still rather badly however), and image with it. First (proper) image is M83. Guiding was very terrible as I think I need to use a guide scope rather than an OAG due to the lack of stars that are appearing in the guide field of view.


Stars are in the best focus I could achieve and I still feel they are quite bloated. FWHM on Pixinsight says 7.133px. Not sure how to change that to arc seconds (pixel size was 3.76, focal length ~1370mm). I definitely need to improve that somehow.



60x90s exposures
6RC
ZWO533MC Pro
NEQ6

[AstroViking]

Hi Lachlan,

You've got good colours there, and good detail in M83's arms. As you said, a bit better with the guiding, focus and collimation, and you'll be onto a winner combination!

[oska]

Hey Lachlan. That's a great result given the constraints. What are you using for acquisition? Are you using any focusing aid?

Technically you only need one star :) perhaps you can rotate the oag to find some better stars? If you're losing guiding then you're loosing guiding and more stars wont help, coz clouds. I'm on the tweezer @ 2000mm at the moment and have 4, 1 ok and 3 so-so. The seeing is giving me poor results and I'm needing to binx3 to clean it up, but on good seeing I don't.

Looking forward to more :thumbsup:

[Todo43]

Thanks Steve and John.


I am using NINA to try and do auto focus using an EAF. Its a very dodgy focus curve as I haven't sorted out the backlash or anything on the focuser. Any tips would be great. Yes I hadn't though of rotating the OAG. When you said you were binning 3x3, is that on the guider or the main scope?


Hoping to get many more images out of this setup. Its really fun going deep compared to my normal 90mm refractor setup.

[oska]

The easiest way to set up the eaf in NINA I've found is to set the backlash to overshoot and use 120 in either backlash in/out box but not both. Too much is fine in this mode but too little wont work properly.
Bad curves can be for the usual reason, clouds, but also if you have any slop in the focuser, so keeping it tweaked up (travel & tension) is crucial. Setting your steps too small can look like that too, try doubling your steps to see. Just as an example reference for steps: On the EON85(R&P) I use 15, on the 8" sct (crayford) I use 100, on the BT200(R&P) i use 50 (I think, that pc is not up). I use 3 offset steps but I started with 5 until I got it sorted(ish).

I think RC's focus like SCT's so you will need to set you movement direction in the driver such that the final move is "in", given the "overshoot" sequence. See NINA discord for an explanation/animation of overshoot.

Once it's sorted you can set your R^2 threshold quite high, mine's 0.95 on the refractor & newt and 0.9 on the sct.

And the Hocus Focus plugin, I think I've used the built-in once, ages ago.

NINA has the HFR history panel which I find indispensable. HFR is basically half FWHM, at least roughly, and along with star count become the session quality meter. I pair it with the guide panel in NINA but just periodically check the guiding and monitor the HFR/stars graph normally

A bahtinov mask is great, perhaps essential, for confirming focus, especially while you're learning how the EAF do.

I am/was binning x3 in PI to tidy up the bad seeing, probably, ok definitely, too poor for the sct. I was just mentioning it to give a reference for the very poor seeing, yet the singular(ish) guide star was working fine.

[Todo43]

Thanks John for the thorough information. I will try that next time I image (which might be a while). Should the exposure time be very long? I have it set to 20s currently, however when I had the EAF setup on a 90mm refactor, I was only needing approximately 5 or 10s exposures. Is it worth binning the auto focus?



I have managed to get a guidescope setup for if some reason the OAG doesn't work again next time, I have the backup guidescope that I can use. It also solves my polar alignment issue. Being so deep, its really hard for sharpcap to find any stars to align to so hopefully the guidescope will help with that as well.

[oska]

I use 6s exp for focus, I think it was the default.

On the longer focal length binning for focus can help but that's usually an indicator the seeing is not good enough to get a good image. Fine for experimenting :)

I polar align in NINA using the Three Point Polar Align plugin and it uses the main camera. Quick and easy even if you can't see the pole.

From what I've read the guide scope to main scope focal length ratio needs to be no more than 1:4 eg 1370/4 = 343, so at least 350mm

[Todo43]

Yeah I use 6s on my refractor.



I think any guide scope will provide better guiding than I was getting on Saturday night so I am happy with a guide scope at the moment. Might have the OAG on the imaging train, test it, and if it doesn't work, use the guide scope next clear night.



I have thought of binning while imaging some times just for that extra sensitivity, because I can then drizzle in stacking. I have tried the Three Point Alignment, but find it clunky as you have to wait each time for the plate solving where as Sharpcap is immediate.