Stargazers Lounge Uses Cookies

Like most websites, SGL uses cookies in order to deliver a secure, personalised service, to provide social media functions and to analyse our traffic. Continued use of SGL indicates your acceptance of our cookie policy.

Welcome to Stargazers Lounge

Register now to gain access to all of our features. Once registered and logged in, you will be able to contribute to this site by submitting your own content or replying to existing content. You'll be able to customise your profile, receive reputation points as a reward for submitting content, while also communicating with other members via your own private inbox, plus much more! This message will be removed once you have signed in.

  • Announcements

    sgl_imaging_challenge_banner_jupiter.jpg

     

  • entries
    6
  • comments
    11
  • views
    684

First light, first fail

Filroden

204 views

The weather started to promise some clear spells throughout the day with increasing areas of blue sky visible. The forecast suggested the clouds would thin at lower levels with some high haze until late evening when a new band of clouds would move over. So I took the chance and decided to do a full set up and trial run at aligning the new Celestron AVX. Having already set it up once, though without connecting any of the electronics, I decided to work from my memorised check list.

Moving all the gear outside and setting it up, with all gear fully connected took 25 minutes. The ground at the other end of the garden was also level to within a degree, so other than marking the patio stones for future set ups, there is little more I can do to speed up the process. Marking the counterweight bar saved me time. The addition of the StarSense did little to the balance in RA but I did need to move the scope a little more forward to get near to balance in dec. The bar on the Esprit just isn't long enough to reach full balance so I will either have to get an extension or add a little weight to the front of the scope.

I found focus with my L filter and I could see Polaris within the field of view. This gave me comfort that I had the mount very roughly aligned.

Goto alignment

I decided to try StarSense in full automatic mode. I've always used the manual mode because I had such a limited view (partly obscured by houses and partly limited in altitude to below 60 degrees). Taking a closer look, I could see almost down to the horizon to the west (Venus could be seen just to the right of the house) so the houses only block about 100 degrees. Automatic worked a charm, never slewing to an area blocked by houses or fence. It seemed to follow a different pattern than for an alt/az mount, with some images taken just degrees apart from earlier ones. There must be a different optimal set of image spacings needed to model the EQ mount compared to the Alt/Az mount.

I forgot to add an additional calibration image (which is recommended in the manual). In fact, it's so easy to use, I should probably be adding a few additional calibration points, particularly in the area I will be imaging.

Polar alignment

Now the moment I was dreading - polar aligning the mount. I used the polar alignment routine on the StarSense, choosing Betelgeuse as my alignment star (it was close to the meridian). I had a mild panic as the mount, which was almost pointing in the right direction, started to slew in the other direction. I wondered if I'd somehow got my north and south mixed up when setting up. Panic over, Betelgeuse must have just passed the meridian and the scope was coming at it from the other side. It did give me confidence that the mount could manage cable wrapping, as it always pivots around the north. I will still need to tidy up the cables as I caught them trying to catch on the tripod leg, the hand controller holder, and anything else around the scope.

At this stage I think I also missed a calibration step. I think i skipped this and went straight into polar alignment mode. 

I loosened off the mount knob so there was enough rotational play for the azimuth knobs to move it and, with my laptop showing a loop of 2s exposures binned 2x2, I slackened one knob and tightened the other a fraction to see which way the star would move. Once I got the right direction, I continued to slacken one and tighten the other, always 'pushing' the star, until I had it on one of the cross hairs. I tightened up the loose knob so it could no longer move.

I repeated this in altitude though it wasn't quite as easy. Loosen one side and tighten with the other to push. Once the star was getting close to centre I increased the screen magnification to 200x and continued to fine tune. There was some play between the axis as I had to make a final small adjustment in azimuth to get the star completely central. Once centre I tightened up all the adjustment knobs and also tightened the mount, making sure this didn't move the star.

Overall, I have to say this was very easy. Much easier than I imagined. It was very similar to how you aligned a star for goto alignment, just using the physical adjustment knobs rather than the handset controls to centre the star. The goto and polar alignment probably only took 5-10 minutes. I then completed another StarSense automatic alignment (as I'd moved the mount). This should give me a good indication of my polar alignment.

Bad news

It again quickly ran the alignment routine and I brought up the polar alignment error. 46' in RA and 6' in dec! And now clouds were starting to build, so I decided I wanted a few test shots. I slewed to NGC2239 and expected to see the usual pattern of stars on the laptop. Nope. The scope seemed to be pointing in the right direction but nothing in the 2s exposures seemed familiar. I increased the exposure length and it still wasn't recognisable. As the clouds were really starting to build, I decided to take a few test shorts at increasing exposure, starting at 15s and working up to 240s. I swapped to my Ha filter as the Moon was nearby.

After the first two exposures (15s and 30s) SGPro started to give download failure messages. I'd seen this once before and the only solution was to close SGPro and open it again. I saved my sequence and new profile and reloaded SGPro. Clouds were now starting to cover the area around Betelgeuse so I would soon not be able to see anything. The area around Procyon was still clear so I slewed there. No bright star in the field of view (though again it was still roughly pointing in the right direction). I did manage to take 30s, 45s, 60s, 120s and 180s exposures before the clouds had closed completely. Enough for me to plate solve and diagnose my alignment issues.

A quick inspection of the stretched images showed trailing in everything above 30s. Not surprising given the error reported by the handset.

Good news

I plate solved the 30s exposure of "NGC2239" and found I was a single field of view away. I also found that images were oriented 90 degrees to how I expected them to be (based on the Alt/Az mount). I had captured 8 (epsilon) Monoceros at the lower (west) side of the frame and just clipped into the Rosette on the top (east) side of the frame. I still did not know what I'd done wrong. I thought it might be because I tried one manual StarSense alignment before doing the automatic one, but the sky was still too bright to find enough alignment stars. I assumed that in trying to solve this and then running the automatic, that I'd somehow corrupted the model.

NGC2239_H_30sec_2017_03_04_191902_1x1_20C_fpos_5906_0001_Annotated.thumb.jpg.aecf4f578901ad6f2fe47398412a2e99.jpg

The answer was much simpler and came to me this morning. I'd set the date wrong!

So next time I need to:

  • set the right date (mm/dd/yy)
  • add some additional calibration points when doing the initial goto alignment
  • add one additional calibration on the star I'm using for polar alignment
  • sort out my cables

So now:

  • My confidence set up will be easy in comparison to alt/az: 7/10 (+3)
  • My confidence extra effort will result in improved images: 8/10 (no change)



0 Comments


There are no comments to display.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now