AMcD

An older Losmandy G11 mount can develop an oscillation of 76 seconds in its periodic error. Having posted a PHD2 guide log on the PHD2 forum in an effort to refine my guiding, and had it analysed by Brian Valente no less, it transpires that my trusty old G11 has this dreaded 76 second oscillation. Because this 76 second oscillation is not an integer multiple of the RA worm cycle it cannot successfully be guided out (although Brian did kindly suggest some settings on PHD2 that he described as the “brute force” solution). In the circumstances, any effort to reduce permanently this non-integer oscillation in the PE has to include the mechanical element. Adjusting the standard RA worm blocks on the older G11 is difficult because of its design. The original worm block design has many elements, making it easy for those elements, and in particular the worm blocks, to become misaligned in any or all of their axes. Whilst an option is to buy an after market one piece worm block from Losmandy that eliminates the issue, these are expensive and there is currently a waiting list. So, before getting in the queue and spending money on the after market solution, I decided to try and improve things by adjusting my RA worm blocks, having scoured the Web for advice and procedures. As with all my tinkering, I only attempted this because my mount is now aging and was already second hand when I got it in the mid 2000s. Attempting such adjustments on a newer more expensive mount is a different proposition altogether. I used the following process. First, measure the periodic error to ensure you have a reference against which to measure the results of the adjustments you make. As I say, I sent one of my PHD2 logs to the PHD2 Forum for assistance with my guiding and received advice on what the periodic error looked like. This showed the 76 second oscillation: Ensure the mount is balanced in RA (the end of the process a slight East side bias to the RA balance can be re-introduced to aid more reliable tracking and guiding). Measure the side to side play in the RA axis at the end of the counter weight shaft. There should be a small amount of play to prevent the RA gear binding. The play at the end of the counterweight shaft should be slightly less than or equal to 1mm. My play measured a little over 2mm. Remove the the cover from the RA worm by backing off the two tiny hex screws. Remove the drive motor so you can turn the worm by hand in order to check the free play. Examine the orientation of the worm blocks in each axis. The gap between the back of the motor side worm block and the RA gear housing on my G11 was 0.84mm but the gap between the back of the other worm block the R.A. gear housing was 0.98mm, so we’re well out of alignment in addition to there being a lot of play in the RA axis. Also check whether the worm blocks sit flush on the RA worm base plate. If they do not then they may require shimming. There is a good guide on how to make that adjustment if you need to before undertaking the steps below at http://www.wilmslowastro.com/tips/g11gemini.htm. Clamp the worm blocks together using a small toolmaker's clamp so that they are held together when you loosen the hex bolts holding the blocks in order to adjust them. Loosen the large hex screws under the worm blocks. Using an appropriate feeler gauge placed between the back of the worm block and the RA gear housing, adjust the spacing between the back of each of the loosened worm blocks and the RA gear housing using following method. With thumb pressure press each worm block against the chosen feeler gauge before re-tightening the large hex bolt. Take care when tightening the hex bolt as this action can move the worm ever so slightly back into the RA gear, potentially resulting in binding. Re-tighten in stages with the feeler gauge in place. Test the rotation of the RA worm by hand. The aim is to make the fit between the worm and the RA gear as tight as possible (as indicated by the amount of play in the R.A. axis at the end of the counterweight shaft) whilst still being able to turn the worm effortlessly by hand on the balanced mount. Now that you have adjusted the worm blocks to a known tolerance (as indicated by the chosen feeler gauge) you can continue to make iterative adjustments, using thicker or thinner gauges, until you achieve the optimal adjustment for fit and effortless turning. I started with a gap of 0.75mm for each worm block (at which the worm could not be turned by hand at all and there was no play in the R.A. axis at the end of the counterweight shaft) and finished at 0.88mm for each block (when the worm could be turned effortlessly by hand and there was less than 1mm of play in the RA axis at the end of the counterweight shaft). Once you have achieved optimal adjustment make sure the hex bolts are properly tightened. Again, tighten in stages with the feeler gauge in place to avoid unintentionally moving the worm block. When reassembling the motor connection there is an option to install a thin stainless washer between the motor-side worm block and the Oldham coupler that connects the worm shaft to the motor, to eliminate the free play that exists at that point. Now check that there is no binding for the whole of the RA gear. Just because you can effortlessly turn the worm at the point you are at on the RA gear does not mean this will be the case on the whole circumference of an aging RA gear. The only really reliable way to do this is to reassemble the motor and run an RA slew from RA limit to RA limit, but it is better to find out at this point that the worm and RA gear are binding than during an imaging run. I found my RA gear was indeed binding at one spot so I removed the motor and, again using the feeler gauges, repeated the process above to back both the worm blocks off the RA gear housing by a further 0.02mm to 0.90mm. This solved the binding. When you replace the worm cover ensure that you have it properly aligned before tightening the set screws. As a result of this work I have managed to reduce the play in the R.A. axis from over 2mm to under 1mm. Now I have to wait for a clear night to see whether I have also achieved any improvement in the non-integer oscillation as a result of correcting the mis-alignment of the worm blocks, or at least an improvement in guiding performance more generally. More news in due course...

I think starting out with what you have and then trading up on the second hand market when your ability has outgrown your equipment is really good advice. I started out with a second hand Celestron Celestar C8 on its original fork mount doing visual astronomy, before putting the C8 on a second hand Meade LXD55 Mount with a Meade DSI camera to start imaging. After a few years I sold the LXD 55 and bought a second hand Losmandy G11 and put the C8 on it with a second hand Starlight Xpress SXV M7 mono CCD. Most recently I have added to this set up a second hand 6” achromatic refractor and a QHY8. This journey has taken nearly 20 years. AP is a wonderful, infuriating, rewarding and exasperating hobby. Building up slowly with what you have allows you to master the basics before investing further if you are still hooked. It also means that those times you want to lock the whole damn pile of equipment in a cupboard, never to be seen again, are easier when what is locked in the cupboard has not cost thousands and thousands of pounds. As for the QHY8, I really like it. It is easy to use and reliable. As another poster has said, it has large pixels so is really better with longer focal lengths. I have been using it with a Hyperstar on the front my C8 but I have now moved it to the back of the scope to get a much longer focal length and therefore better resolution on the big pixels. The Bintel Astronomy Calculator is another good tool to experiment with different scope / camera combinations (https://www.bintel.com.au/tools/astronomy-calculator/?v=322b26af01d5). The author of the calculator has a YouTube channel that offers a great selection of ‘how to’ videos (https://m.youtube.com/c/DylanODonnell/videos?disable_polymer=true&itct=CBIQ8JMBGAEiEwjdm_DOh5_vAhVUPPEFHXO3CoY%3D). The only other issue with the QHY8 is icing on the CCD. I don’t know if the QHY8L suffers from this as well but I have found that a 2” dew-strap wrapped around the nose of the camera solves the issue. Have fun...

I did my corrector plate and primary mirror this weekend and set out the process I used here: The cotton wool I used I got on Amazon: https://www.amazon.co.uk/gp/product/B0120YQQEW/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1

In an effort to maximise my time in the observatory I would like to have the option of using my TS152 achromatic refractor for solar. To that end, and having looked at the optical configuration needed to ensure the sun’s disc would be visible in its entirety within the fov, would the following set up work for photographic purposes: TS152 achromatic - x0.8 focal reducer - 2”APM / Lunt Solar Wedge - Baader Calcium K-Line Filter - Appropriate CCD camera If so, I will need to sell my Hyperstar 8 and my WO Zenithstar 66 SD APO to help fund it. Will the x0.8 reducer I currently have on the Zenithstar serve as the reducer in the above set up? Many thanks...

Have taken out my old Thousand Oaks white light solar filter for the first time in years. Seems to be a fairly quiet period for sun spots...

Since I have owned telescopes I have always adhered to the maxim ‘thou shalt not clean the optics unless it is absolutely necessary’. This is definitely the best advice and it takes a very long time to reach the stage of ‘necessary’. However, after owning my C8 for twenty years I decided this week that we had reached the point of ‘necessary’. The corrector plate was very dusty on the outside with some resin marks and, somehow, a spider had found its way inside the scope and spun a web on the back of the corrector plate. The said spider had also, like a malicious burglar, pooped on the primary mirror. I should make clear that I only attempted this cleaning because my Cat is twenty years old and even then second hand. Cleaning a newer, more expensive scope would be a very different proposition indeed. However, I found the following process, gleaned from various online sources, worked very well and resulted in a very clean, streak free corrector plate and primary mirror. I first assembled distilled water, isopropyl alcohol, washing up liquid, pure cotton wool, latex gloves, an ultra-soft brush, a blower bulb and a Philips head screwdriver. I then undertook the following staged process: (1) I mixed a cleaning solution of 1/3 isopropyl alcohol, 2/3 distilled water and a drop of washing up liquid. In another bowl I poured only distilled water. (2) Before removing the corrector plate I cleaned it on the outside by: (a) using the bulb blower to blow loose dust and particles off the optical surface; (b) using the soft brush then to gently dust further contaminants from the optical surface; (c) wetting pure cotton wool in distilled water and dabbing (not rubbing or dragging) the wet cotton wool on the optical surface to wet it all over, discarding each piece of cotton wool as it became dirty; (d) once wet all over, I dabbed the optical surface with clean cotton wool dipped in the cleaning solution, discarding the cotton wool and repeating until the cotton wool showed no visible signs of dirt; (e) once the cotton wool showed no dirt I then gently dragged cotton wool dipped in the cleaning solution over the optical surface under its own weight (no pressing or rubbing) covering the whole of the surface; (f) the next step is to dry the optical surface, again using cotton wool dragged gently under its own weight until a dry, streak free finish is achieved; (g) finally, once the surface is fully dry the bulb blower is used to blow away any remaining cotton threads. (3) I then removed the corrector plate retaining ring and then, taking care to mark (a) the orientation of the corrector by dabbing a spot of correction fluid at the edge of the plate and a corresponding dab on the plate holder and (b) the placement of the cork shims that ensure the corrector plate is centred, I removed the plate and set it on a towel (as I have a Fastar C8, I removed the secondary mirror and stored it during cleaning). (4) I wiped down the inside of the telescope tube with a damp, clean cloth, taking care not to touch the primary mirror. (5) The next stage is to very delicately clean the primary mirror using steps set out at (a) to (g) at stage (2) above in the same order as set out there. (6) Finally, I cleaned the inside optical surface of the corrector plate, again using the steps (a) to (g) set out at stage (2) above in the same order as set out there. (7) Once certain that the mirror and internal surfaces of the tube are dry, the corrector plate is then re-installed, with collimation to take place at the start of the next session. To repeat, the maxim ‘thou shalt not clean the optics unless it is absolutely necessary’ should in my view always be followed, but once there is no option but to clean your Cat, I found that this method, delicately applied, worked very well indeed.

I have owned my second hand G11 for over 15 years and it has never missed a beat. At present it holds a Celestron C8 and a TS152 refractor side by side together with cameras, filter wheel etc. and a mini PC piggy backed on the TS152. It is relatively easy to balance, stable and tracks reliably even with this load. That said, you will undoubtedly also read of some idiosyncrasies with Losmandy mounts (not least the design of their worm blocks). Many of these can be dealt with by upgrades or after-market additions. I do not know a great deal about the HGM Titan but a good place to read about one owner’s experience of a G11 is at: http://www.wilmslowastro.com/tips/g11gemini.htm

I no longer use the star alignment on my Losmandy G11 with Gemini to synchronise the mount now that I am using plate solving. I simply ‘Cold Start’ the Gemini, slew to an area of sky and then plate solve and sync using ASTAP or Plate Solve2 via SGP. I find that sets me up well for the session, with subsequent plate solves via SGP in order to centre objects generally being spot on. As well as this approach working, I find it is necessary with the G11/Gemini as a Gemini mount alignment model built using ‘Telescope Align’ (which I suspect is the Gemini version of aligning three stars) does not tend to play nicely with plate solvers when Plate solving is being used to centre objects.

I have decided to move my QHY8 back to the prime focus of my C8. When used with the Hyperstar the QHY8 significantly under samples at 3.79”/pixel (compared to a slight over sampling of 0.79”/pixel at prime focus). Coupled with the very uneven field illumination given by the Hyperstar, this makes the output difficult to process and the width of the field no longer makes up, at least to my eye, for the lack of resolution. As a result I ordered some items from Astroshop.eu as they had them in stock. I thought they might get stuck at the border or be subject to extra tax and fees but nothing of the sort transpired. They arrived in four days. And they came with a small bag of Haribo Gummy Bears😁

I have had the X shaped artefacts shown in the very roughly processed image below appear in my images from recent imaging sessions. All the affected images were taken towards the West. At the western side of the observatory stands a chrome flue attached to a hot tub. Could reflections from the chrome be the culprit? The artefacts do not appear in images taken to the South.

Fifty-five subframes of five minutes each using a Celestar 8 with Hyperstar, a QHY8 and an Optplong L-Extreme on a Losmandy G11. Captured with SGP guiding with PHD2. Calibrated with dark, flat and bias frames, stacked in DSS and processed in Photoshop. Any feedback, positive or negative, greatly appreciated as I sometimes feel that I am shooting in the dark with this hobby at the moment, not only literally but figuratively...

I have been imaging a lot over the past number of nights but have discovered that most of my data has been affected by some unusual internal reflections. I have not yet got the bottom of it but all the affected targets passed suspiciously close to a chrome smoke stack attached to our hot tub that reflects a nearby streetlight 😅 The Rosette had the benefit of being in a different part of the sky. Twenty five minute subframes taken with a Celestron Celestar 8 with Hyperstar, QHY 8 and an Optolong L-Extreme filter mounted on a Losmandy G11. Calibrated with dark, flat and bias frames, stacked in DSS and processed in Adobe Photoshop.

Thanks tooth_dr. It does look pretty tiny!

My ZWO EAF has finally arrived. It was well worth the wait. Very straightforward to install and set up on the TS152 and works like a charm with SGP. Now contemplating one for the C8 as well...

I have an SXV M7 attached to my TS152 Achromatic. Whilst setting up my new ZWO EAF this evening and calibrating the autofocus I noticed that the images being produced by the camera had stars with horizontal bands through them as demonstrated in the TIFF image attached. Does anyone have a suggestion as to what is going on? Banded Stars SXV M7.tif

Good session tonight on the C8 and Hyperstar with the QHY8. The plate solving in SGP is working a treat with ASTAP. Spent a couple of hours on the Horsehead and now closing out the night on the Flaming Star Nebula. It is meant to be clear tomorrow night as well...

This is the processed version of a stack of the images taken through the L-Extreme (I had to re-do the stack above as I had messed up the flat frames to the extent that they introduced an unwanted and complex gradient into the stack, born of the Hyperstar's notoriously uneven field illumination and not helped by its current lack of proper collimation). It is so much easier to deal with processing in Photoshop when not having to wrestle with light pollution...

First, a caveat about these two stacked but unprocessed images. The pictures do not constitute an absolute comparison. The first, unfiltered, image of the Rosette Nebula was taken on a night with a full moon. The second, L-Extreme filtered, image of the Rosette Nebula was taken on a night with a waxing crescent moon. The first image was captured on a still, cold night that had a degree of haze. The second image was taken on a warmer, windier night following heavy rain, meaning that there was likely less haze. Both pictures represent approximately 2 hours exposure time comprising 5 minute sub-frames taken using a QHY8 on a Celestron C8 with Hyperstar mounted on a Losmandy G11. The images were stacked with dark and flat frames in Deep Sky Stacker using the "average" setting for each of the light, dark and flat subframes. Notwithstanding the significant caveat set out above, the Optolong L-Extreme has immediately made a huge difference to the quality of the data I am able to achieve from my city center location, which includes an old sodium street light that shines directly into my back garden observatory. The quality of the data has also allowed me to identify that my Hyperstar assembly is urgent need of collimation!

Every now and then the postman and fate coincide, allowing newly delivered equipment to be tried out the same day it arrives. All I can say about the L-Extreme is wow! Just, wow! This was the first 5 minute sub-frame of the Rosette Nebula through my C8 with Hyperstar:

After an attempt to capture the Rosette Nebula with a OSC camera reminded me of just how heavy the light pollution is when imaging from the heart of the city, I hope this delivery from the postman today will offer some help...

Appalling picture of the center of the Rosette Nebula, dragged kicking and screaming from amidst the light pollution, BUT it represents the first time I have been able to successfully operate the observatory on a remote basis (apart, of course, from having to go outside and roll the roof off and take off the caps!)

I was born in Sudbury and grew up in Suffolk. My parents still live there. Very dark skies.

It did indeed clear after the snow clouds. Finally catching some light...