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Need guidance

Another short clear window in the early evening let me practise set up and alignment of the new AVX mount again. I ran through my new alignment process, including calibrating the StarSense to the OTA. I then repeated the process and the handset reported a final PA accuracy of 30" in Dec and 3' in RA. However, (and with clouds rapidly moving over) I managed to take another sequence of 30, 60, 90, 120 and 180 second shots to test tracking. Here's the 180s (which is heavily affected by high clouds), which is consistent with the others but shows the trailing best:


Q1. I roughly measure the trail to be 14 pixels, or 26.6" at my pixel scale, so 0.15" per second. If correct, my maximum unguided exposure would be 13 seconds to stay within my 1.9" pixel scale. Would a PA error of 3' give this sort of trailing?

Q2. I also noticed (or believed I noticed) that the mount seems to move when tightening the mount bolt. I think that this further tightens the accessory tray which pushes on the legs more. I noticed this when I calibrated the StarSense on Betelgeuse. Normally, my goto would then be bang on centre but when I slewed back to Betelgeuse it was a little way outside my crosshairs (using SGPro). I wonder if this is causing me problems and whether I need to attach the accessory tray at all?

Q3. I also use anti-vibration pads beneath the tripod feet. Could they also slip when adjusting the mount?

Q4. Whilst the length of trailing seemed proportionate to the exposure time, the direction was not always consistent, particularly in the shorter subs. I'm assuming this could be the affect of many things: PEC, wind, seeing. Is that right?

I did get reasonable 120s exposures the previous night, so I know it's possible. However, I'm quickly concluding that having tested unguided I now need to quickly move onto a guided set up (skipping over drift aligning though I probably should learn how!). I have a ZWO OAG and ZWO ASI224 so time to bite the next complexity bullet. As it's likely to be cloudy until Monday at the earliest I can start working on that now.


I think I've just got my spacing right for the ASI1600MM-C.


Which for my reference was 66mm for the Skywatcher field flattener plus an additional 1mm for the filter (1/3rd of the 3mm filter thickness on the Astrodon 3nm HA).

I achieved this spacing with:


The OAG has a spacing of 16.5mm and comes with a M48 adaptor so I'm hoping I can just swap out the 9.0mm FLO M48 to M42 adaptor and the 7.5mm Baader T2 extension tube.

How good does a polar alignment need to be for guiding? Would it be happy with the sort of accuracy I was achieving above or would I need to drift align and improve it further? I'm hoping that a single StarSense alignment routine will get me close enough that guiding will take over (having also read that guiding seems to like an error in PA so that it only has to correct in one direction). Tune in next week for what I expect to be a frustrating first attempt :)


The forecast was spot on for a change. Clear all afternoon into the evening, clouding over later. So it was worth a good run at fixing the issues I had with my first attempt at polar aligning the new AVX mount and maybe, finally, getting some subs.

I've noticed a few extra things this time:

  • the tripod is much lighter than the Evolution one. They share the same legs so it's just down to the mounting plate and the accessory tray being much smaller. It's a one hand job rather than two for the Evolution. It still feels as solid. In fact, it was quite windy last night and it seemed to handle it ok.
  • Likewise, the mount itself is lighter, though it's more awkward to carry. I do like that Celestron have now added carry handles to its latest mounts.
  • The mount seems to remember the time/date. It must have an internal battery clock. I have to set the time each time I used the Evolution, so this is a nice quality of life improvement.

Last night it took about the same 25 minutes to get set up and everything connected. I decided to use the USB hub and also connect the mount to the PC in the hope of testing mount control from within SGPro. This gave me even more cables to deal with. Having powered up and roughly aligned the mount using a compass, I checked my time, date and location data and set StarSense to auto align. It hung on the first slew with a message on the handset that it was trying to read the alignment. After repeating this a few times and getting the same result I restored the handset to factory settings, rebooted and tried again. This time it worked. It seems I'd saved alignments on the previous session and this was messing with the process. 

I finally got aligned and slewed to Betelgeuse. It was in the field of view so I started the Polar Alignment routine. It slewed again (as expected) but no sign of Betelgeuse in the field of view. I did a blind plate solve and I was about one frame to the west. I adjusted the azimuth bolts and finally found the star and centred it. I ran StarSense auto align again and slewed back to Betelgeuse. No sign again! I took a test shot anyway, and was seeing significant trails even in a 30s shot. Something wasn't right. I'd forgotten to calibrate StarSense.

I reset the alignment model and started again from the beginning. It seems to get a good alignment I need to complete a calibration step each time. So my new alignment process is:

  1. Roughly align the mount with a compass
  2. Set the mount to its home position
  3. Check time, date and location data in handset
  4. Run a StarSense auto alignment
  5. Select and slew to polar alignment star (close to meridian and ecliptic)
  6. Press Align to calibrate to this star, then move it into centre of cross-hairs using handset
  7. Run Polar Alignment, centring star using the alt and az bolts
  8. Run StarSense auto alignment once more

Even with this, I can't have been spot on. I slewed to IC443 (bang on) and framed it. I then took a series of single exposures from 30s to 180s to see how well the mount tracked unguided. Here's the series with the same auto stretch. The 60s and 180s show trailing but I was pleased I could get a 120s sub without trailing.

30 seconds


60 seconds


90 seconds


120 seconds


180 seconds


Having run these quick tests I wanted to gather some data so I set a sequence of 30 x 120s subs running on IC443 and went and caught up on some TV for an hour. By this time the clouds had come over so I packed up and transferred the files to the main PC for processing. After weeding out cloud covered images I found that about a quarter of the subs showed a lot of trailing. Also, between the first and last sub, the frame had moved significantly in RA and a small amount in Dec. I definitly need to spend a little more time on getting my PA right, maybe even running it twice. I also need to start guiding!

IC 443 Jellyfish (if a little wobbly)

Choosing the best 21 images (though some still showed trailing), here's a quick process of 42 minutes at gain 139 offset 21 and cooled to -20C on IC443 using the Celestron AVX mount, Skywatcher Esprit 80, ZWO ASI1600MM-C and the Astrodon 3nm Ha filter. It's noisy, the stars are elongated because of trails, but it's a image (and considerably better than the one I took on the Evolution)!



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.


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)


The mount arrives in one double-boxed package. Inside were five boxes of various sizes, designed to fill the full space. This did mean that two of the boxes were significantly over sized for their contents, but these were protected with padding. There are good unboxing videos already available such as the one below so I did not take photographs.

There are two large boxes, for the tripod (including eyepiece tray) and the mount (including hand controller in a neat little insert pocket in the polystyrene). A third box holds the counterweight and the two remaining boxes have various accessories (azimuth bolts, counterweight bar, power cord, etc).

Warning: I'd noticed in the unboxing video that the counterweight can easily fall out of its box so when I picked it up I made sure I held both sides of the box!

My first impressions of the mount were:

  • the tripod has the same sturdy 2" legs as my Evolution but because the mounting plate was much smaller and the eyepiece tray is designed to be removed between uses, it takes up much less space. I'd estimate it takes about half the volume as the Evolution tripod. This will make transporting it much easier. It will lie much flatter in the boot of the car leaving much more space for the mount and scope.
  • there are many more pieces than the Evolution. Setting up the Evolution simply means taking out the tripod, tightening the tray and then lowering the mount onto the plate. The mount is rotated so that three screws under the plate can be tightened to lock the mount in place. Done! This time, it looks like the set up will be much more involved.
  • the mount design (small base with a downward protruding altitude knob) means it is not as stable when being stored. The Evolution mount has a large, flat base so it sits solidly on a shelf when not in use. This mount will need some thoughts for storing it securely.

Set up

I'd read the manual in advance (downloading the PDF from the Celestron website (http://www.celestron.com/media/796147/Advanced_VX-Manual-F.pdf) but I took the time to go through the printed manual included in the box. The initial set up was relatively easy.

  1. I took out the tripod, leaving the legs at their shortest (it helps me keep the scope inside the shadow of my garden fence) and tried to roughly align it north using the compass on my phone. I also tested how level the mount plate was. Though not needed to be level, it does simplify adjustments to alt and az during polar alignment. The plate was within 1 degree of level which was good enough for me.
  2. I attached the azimuth bolts to the mount, screwing them in just far enough so they were secure but the didn't impede the area where the alignment peg would sit. I assume they are removed during transit to make it easier to box the mount.
  3. I tightened the RA and dec clutches on the mount (which were left loose during transit).
  4. I sat the mount onto the tripod. It fits nicely. Putting the Evolution mount onto the tripod takes a little jiggling for it to seat itself. The AVX drops in with little effort.
  5. I pushed the central mounting knob under the mount plate upwards to connect with the mount and then screwed it in so the mount was held firmly in place. I then unscrewed it a little, so that there was some play, which is needed during polar alignment.
  6. I attached the accessory tray, which helps tension the tripod legs. I did not like that the v shaped spurs of the tray looked like they could mark the tripod legs when tightened. I will have to see if this is an issue over time. The spurs on the Evolution were more rounded and fit the legs smoothly so this never concerned me before.
  7. I attached the counterweight bar then removed the safety screw and slid the counterweight about halfway up the bar before reinserting the safety screw (with one had firmly holding the weight) before tightening the weight itself. 
  8. I snapped on the hand controller holder onto one of the legs. Note: at this point the manual goes through the process of attaching and balancing the scope. It is not until the very end that the manual mentions that you need to connect the dec motor to the RA motor using the supplied short cable. Without this cable, the mount cannot drive in RA! I would have thought this step should go much earlier in the manual.
  9. With great trepidation, I then attached the scope to the mount. Even though I knew this would be secure it still feels so wrong to have so much weight being held by two lateral screws!
  10. I then proceeded to try my first balancing of the scope. I loosened the clutches and rotated the scope so counterweight bar was horizontal and the scope was parallel to the ground, locking the clutches once finished. I then loosened the RA clutch, holding onto the scope for dear life. I slowly released my hold (waiting to catch the scope as it moved) to see which way the scope rolled. Nothing. Mild panic. I tested that the scope could move in RA. Yes, there was a little resistance but it moved freely and easily. I guess I was just very lucky and I'd already put the counterweight in the right place. I tested this by sliding the weight further down the bar and tested again. This time it did roll, so I returned the weight to its original position and marked this with some tape on the bar so it would be easy to balance in the future.
  11. I then tested dec. The scope did roll this time and I needed to push the scope a little forward. I will probably have to move it further forward once I add the OAG and guide camera, and have the StarSense attached.
  12. The next step would be to connect all the electronics and testing motor control from within SGPro and via Stellarium. I had many cloudy days and nights ahead so I decided to dismantle the set up and see how a more normal set up would be.

My initial impression of set up confirmed my worries that this would take longer than setting up the Evolution. There are a number of additional steps that I need to take which might add 5 more minutes at the start of a session. However, as I would normally set up in the afternoon, this shouldn't be an issue. However, it would take a similar time to take down, when I'd also be more tired, so I will need to practice.

The biggest set up differences will be:

  • roughly aligning the tripod, hopefully to be speeded up once I've done my first PA and I can mark the paving slabs
  • attaching/detaching the accessory tray each time, though this can be done indoors if I need to do a hasty take down
  • balancing the scope, which will be quicker now I've marked the bar and will (once I have the full imaging train attached) mark the dovetail.

I now need to test the motor control and then attempt my first alignment. As it stands:

  • My confidence set up will be easy in comparison to alt/az: 4/10
  • My confidence extra effort will result in improved images: 8/10

An Evolution

Although this has been posted elsewhere I think it might be useful to show how my imaging has (hopefully) improved as I gained experience/equipment.


A Year of DSO Imaging with an Alt/Az

Well, I seem to have attempted my first DSO images in December 15 and January 16 so it's been just over a year of trying to image with the Alt/Az mount. My first DSO target was M42 which I've shared previously but my next target was the Rosette Nebula which I don't think I've shared. I thought it would be nice to see how it progressed over the year.

Image 1: Rosette Nebula through the 9.25SCT using the Canon 60D - no sign of any nebula but look at the resolution of those stars. If you find HD46150, a 6.8 magnitude star that forms the left of the middle pair of stars that make the famous rectangular shape inside the nebula you can see two companions so close they are almost touching. I think this serves as a clear example of why a long focal length SCT is not suited for DSO imaging on an Alt/Az mount!


Image 2: Now with the Esprit 80 with the ZWO 1600MM. I did a terrible job at removing the background and removed most of the nebula in the process (and still left a nasty ring of gradient). Though at least there is nebula to see now! It shows how nice the field of view of the refractor is. Whilst this image has been cropped, it retains probably 90% of the area of a single sub.


Image 3: same data as image 2 but with better processing. I was able to do a better job at removing the gradient and start to bring out some of the detail within the nebula. However, the stars are starting to dominate.


Image 4: my first attempt with a narrow band filter. I love how this image is so much cleaner that an equivalent amount of data collected with the L filter (see above). With very little noticeable gradient this was such as easy image to process.

NGC2239_20161228_v2 1 Ha mono.jpg

Image 5: my first try at adding RGB data to the Ha data in image 4 resulted in an almost monochrome tinted version. I had very little usable RGB and the luminance of the Ha data swamped it, leaving it lacklustre in terms of colour.


Image 6: with a little more data and some helpful processing advice I managed to get a better RGB version. This blends the Ha data into R and L using one of PixInsight's many scripts.

NGC2239_20161228_v2 2 HaRGB.jpg

Image 7: and with an extra 30 minutes data, and further processing improvements. This is back to being a simple HaRGB with the Ha replacing the luminance. Just a small amount of additional RGB data meant I could push it much harder and for it not to be washed out.


It seems 40% of the improvement I've seen over the year is equipment, 40% better processing and only 20% improvement in skill at actual data capture. If you'd asked me at the start of this journey I would have though capturing the data would be the hardest part. It is hard, just not as hard as processing it!

It's also interesting to see how, with each additional dataset, I've had to crop more and more of the image to remove stacking artefacts caused by rotation.

And, to set a baseline for future EQ imaging, here's my current 'best' version of the Rosette. My plan is to start my imaging with this (if the weather improves before it moves out of my viewing range) so I can compare the results.




After over a year of owning and using a Celestron Evolution mount, initially with the 9.25" SCT for visual and planetary imaging, but more recently with a Skywatcher Esprit 80 for DSO imaging, I finally took the step of ordering a Celestron Advanced VX mount, taking advantage of the ridiculous sale price at @FLO.

I'd always been hesitant to move to an EQ mount even though I knew it's advantages for imaging. Just the thought of all that extra set up gave me a cold sweat. I loved the ease of the Evolution mount. It took about 5 minutes to set up, another few minutes for the StarSense to do its magic and align itself and in short order I could be focused and imaging.

Over the course of the year I added more to my equipment list:

  • I bought the StarSense to speed up alignment. It's a luxury that isn't needed but it got me up and running so quickly.
  • I purchased PixInsight and BackyardEOS. Both made great improvements. BackyardEOS made taking images so much easier, and the quality of my processing started to improve using PixInsight (and gradually got better as I found more tutorials and guides).
  • I purchased the Skywatcher Esprit 80. This was a revelation in terms of being able to image. The SCT was great for visual and for planetary/lunar imaging but would not work for DSO imaging. The Esprit was amazing. It's much wider field of view was ideal for the targets I loved.
  • I swapped my Canon EOS 60d DSLR to a mono ZWO ASI 1600MM-C with electronic filter wheel and a set of LRGB filters. I hated the noise of the DSLR and the processing difficulties. I also didn't like its lack of red response (not bad, just not very good). I knew the ZWO ASO1600 would be great with an Alt/Az mount as it worked well at shorter exposures.
  • I purchased Sequence Generator Pro. I needed a replacement for BackyardEOS now I was using a new camera. Having tried a few options, this was the one for me. It was a little more tricky to wrap my head around the idea of profiles and sequences, but once I'd figured it out, it worked really well for me.
  • I added a Lakeside focuser to the Esprit so that I could automate focusing within SGPro.
  • I purchased an Astrodon 3nm Ha filter. Again, this made a massive improvement to imaging. Still within the 30-60s exposure lengths I could squeeze out of the Evolution mount, the image was so much better than from my LRGB filters.

I'd purchased all of the above knowing that they would work with any mount, so once i made the step up to an EQ mount, I'd be all set. I ordered a Celestron AVX mount along with the ZWO OAG (which would work with my ZWO ASI224 camera for guiding). I chose Celestron for two reasons: I already has the StarSense to aligning would be easier, and I liked that you could align on any star rather than Polaris.

I had two set up locations, at either end of my (small) garden. I have limited visibility with street lights to the north and houses blocking the view from the SSW through to the NW. However, I had a good easterly view - ideal for Alt/Az imaging as field rotation is lowest to the east and west. I would normally set up outside the kitchen which really limited my view to the south but meant I could stretch the cables through the window and sit inside in the relative warmth. If I needed a more southerly view I could move the mount to the other end of the garden but it meant also setting up the laptop there too. I tried using a remote PC but the WiFi strength was too flaky and I had yet to set up any network cabling.

I intended to continue to use both locations with the EQ mount. I would gain a wider view because I could now aim the scope above about 60 degrees altitude (the absolute limit for my Evolution mount with the refractor plus imaging train).

I finally decided to try an EQ mount for three reasons:

  • Being able to image above 60 degree altitude
  • Eliminating field rotation which was slowly meaning I was losing up to 40% of my field of view because of cropping stacking artefacts
  • The price, during the recent sale, became too attractive

I also opted for an OAG. My plan was to continue with shorter exposures but I already had a suitable guide camera and having the option of improving my tracking even over 60s and adding the option of longer subs should I choose seemed a sensible decision.

My plan was to test unguided imaging using the StarSense polar alignment routine only, hoping to get good 60s subs, then to progress to either improved alignment using the drift method (unlikely) or adding guiding (more likely).