Aramcheck

Found an interesting reply last night on the SGL on the thread linked below from @emyliano2000- I will have to check the alignment of the focuser I think before trying to cut the mirror free.

Cheers
Ivor

I finally got a couple of spells of clear-ish nights. With the back focus set to 60mm the coma looks much reduced. I've also adjusted the Dec backlash after watching a few youtube videos (Martin's AP, Cuiv The Lazy Geek and Astrobloke). This helped PHD2 to complete the calibration / guide assistant process, although I haven't yet tried binning... On the 12th I thought everything was going ok , but the stars still had a triangular shape. On the 13th I made sure that the primary locking nuts were not touching the mirror cell & took a few shots of Vega whilst varying the focus. (The full sequence can be seen here: https://youtu.be/KuIURZ9u1p8) I also took a set of 10s exposures in addition to my regular 180s ones for a couple of targets - M27 & another near zenith. These also show triangular stars. I didn't bother to dither on either night, to maximise the amount of data I could collect.

I presume the next step will be to cut the primary mirror free & to try again with the sealant. Am I missing anything else?

Photo of the stacked/unprocessed 10s M27 subs with a STF applied.

Thanks again for all the help!
Ivor

PHD2_GuideLog_2022-09-13_220027.txt PHD2_GuideLog_2022-09-12_213448.txt

Thanks @Clarkey - It looks pretty daunting, but I guess I'll have to attempt it soon.

Much appeciated

Ivor

Did you follow any particular instructions / video for the AZ-EQ6?

Cheers
Ivor

Thanks @alacant & @michael8554 - much appreciated.

@alacant :- I do have a 130pds, but only tend to use that if it's too windy for the 200pds. A  better coma corrector is something I probably will look into when finances permit. Not sure what the advantage of a Losmandy plate are, but I do intend to put a 2nd bar on the top of the OTA, as you've suggested in other posts.

@michael8554 :- Thanks - the tip about moving North before calibration is a great suggestion. I'll also try guiding with binning x 2. Since moving over to the OAG I haven't managed to get PHD2's guide assistant to run successfully, due to Dec backlash not giving enough movement South. Normal calibration has also been hit & miss, but even using the 50mm finderscope for guiding it wasn't uncommon to get calibration warnings about large Dec backlash. On the Dithering I was working on the assumption that with the OAG the guide camera & imaging camera had the same pixel size then I should use a setting of 1 in Astro Photography Tool. I'll try increasing that, although I haven't noticed much fixed noise.

Another suggestion I read about, was to increase the size of the box around the guide star in PHD2. When the scope is pointing at lower altitudes I sometimes get large deviations which make subs unusable... I'd put these down to wind/glitches/cable snags, but I think now that it's occuring when the guide star randomly moves outside of the target box in PHD2, presumably due to the larger atmospheric thickness at lower altitudes. Something else I'll need to look into.

Cheers
Ivor

Thanks @alacant I'll try increasing the back focus to 60mm.
On the primary mirror I just let gravity do the work & left it on a flat surface for a couple of days, until the separate test blob had cured ok. (i.e. no pushing was involved!) I've attached a couple of pictures showing the amount of sealant used & one of the rear 'after' shots.

I must apologise too, as I'd forgotten that the M27 I posted was a combination of some 2021 data and from the 19th Aug 2022. The 2021 data set was at a vastly different angle & only overlaped a central band, so that's why the diffraction spikes look odd.

 I've attached an unprocessed M27 image with just the 19th Aug 2022 data & a STF applied.

Cheers
Ivor

I've recently bought a ZWO Off-Axis Guider v2 & carried out the Primary Mirror sealant/spring modification  to my SW 200pds & fitted a Baader Steeltrack focuser.

Subsequent results over the last couple of months haven't however been good & last Thursday's session was absolutely dire... Part of the problem has been in getting the 57.5mm back focus which Baader specify with the MKIII M48 configuration. Initially I made the mistake of thinking I had to get 55mm & had been trying various spacers without much success. The best result over recent weeks was a go at M27, where I'd used the 21mm spacer that came with the camera & a (notionally) 1mm Baader spacer ring. This still had bad coma, but at least the central stars didn't look too bad...

I then realised that I needed a 23.5mm extension (The ZWO 2600mm has 17.5mm from face-plate to sensor & the OAG spec says it's 16.5mm, so that should mean I need to add a 23.5mm). On Thursday I tried using a Baader varilock set to 23.5mm, but even with 10 / 30 second exposures, the stars are distorted throughout the field.

For polar alignment I use an iPolar to align the AZ-EQ6 GT Pro mount, and that all seemed fine... My initial pre-focus 5 sec shot shows I think reasonable out of focus stars in the centre of the frame & what I presume is the effect of coma evident at the top right/left. On the 10 sec, 30 sec and 180 sec exposures the star eccentricity doesn't seem dependant on exposure time.

Also on Thursday, the satellite trails also have a high frequency oscillation, which follows the RA/DEC axes. I read that this could be caused by vibration from the camera fan or the mount gears. I did think the fan was a bit noisy, but I'm not 100% sure. Checking previous datasets, I've not had this problem before except for a couple of nights earlier in August, which had the same issue but much less severe. Last week's M27 session doesn't exhibit this issue & aside from re-calibration I don't think I've changed any of the PSD2 settings. (Earlier in the month I had tried reducing the guide period from 3s to 2s).

The only difference between the M27 image and last Thursday is the swapping the 21mm Ext + 1mm spacer with the Baader varilock.

Sorry this is a bit incoherent - I'm pretty much at my wits end trying to figure things out. Tonight looks like it may be clear, so I don't know whether to ditch the OAG & revert to using the finderscope for guiding, or try again with the Varilock.

Any ideas much appreciated!

Ivor

PS: Prior to trying the Varilock, I'd also bought a set of Astro Essentials spacers. These gave bad coma too, but I realised yesterday that one I used had a hole in the side and so was tilting the assembled tube...

PHD2_GuideLog_2022-08-25_221319.txt PHD2_GuideLog_2022-08-19_225352.txt

1 minute ago, iapa said:

Does it not come with a tool to fit? Mine has.

It does, but I couldn't loosen it with the supplied tool. I should be alright now the 2 x trainer method has loosened the rings up...

Thanks
Ivor

Thanks @david_taurus83 I didn't think we'd have any trainers, but I found an old pair of my wife's... I put some clingfilm over the heels & it worked!

Many thanks!
Ivor

6 hours ago, david_taurus83 said:

Have you tried the 2 trainer technique?

Sorry - I've no idea what that means!
Cheers
Ivor

I recently bought a Baader Varilock extension tube in the hope of solving problems I've been having setting back focus with my Baader MPC III coma corrector + ZWO OAG v2 + ZWO 2600 MCPRO camera.

My initial attempts to use the Varilock were hopeless, as trying to adjust everything & keep the OAG from obscuring the camera chip proved impossible.

I think I've now figured that I need to have a 23.5mm extension (to get the 57.5mm required from the coma corrector (with collar ring removed), as the OAG has a width of 16.5mm and camera's sensor distance of 17.5mm)... BUT the Varilock is currently locked solid & I can't loosen any part of it.

Any ideas on how to loosen it so I can set it to the required distance? Can I use WD40 or a light oil?

Many thanks

Ivor

On 06/12/2021 at 08:05, bottletopburly said:

due to the base design this allows light leakage under the plate into the ota which was quickly remedied by cutting two strips of foam that housed the focuser in packaging box and glued to underside of base blocking light...

note I did find a site with a 3D printed spacer that fits under the verabase which looks a neat soloution pity baader never thought of that https://en.rbfocus.net/product-page/adaptador-200pds-para-enfocador-baader-diamond-steeltrack

@bottletopburly I don't suppose you remember the dimensions for the foam fix & which bit of the packaging you used? I'm in the middle of fitting the baader to my 200pds...

I thought about the adapter you listed but with shipping it worked out at 70 Euros, so I'd much rather try the foam solution!

Cheers
Ivor

What is the length of the springs used on the 200 dps?

Cheers
Ivor

For my CMOS OSC camera I just use darks which match the exposure time (& temperature) of the light frames & a second set which match the exposure time (& temperature) of the flats.

The darks are taken with the camera by itself (not attached to the scope) with the cap on & then integrated into a Master Dark for the lights & a Master Dark Flat for the flat frames. (And as I had a coma corrector fitted at the time I used some aluminium foil over the top of the plastic coma corrector cap). The darks were also taken in a dark environment, though I doubt that made any difference. I've not had any problem with light leaks...

Best of luck!
Ivor

I don't use WBPP but the ImageCalibration process worked fine on the single file I tried. Any reason you haven't taken Darks or Bias frames?

Cheers
Ivor

Thanks for all the advice - much appreciated. Last night I figured out the hard way why the guide camera focus didn't appear to change... When I'd set up PHD2 it had, of course, defaulted to the 2600 MCPRO instead of the 120MM.... Took me awhile to figure out why I couldn't save any images with APT.

Haven't managed to get any images yet, as cloud rolled in shortly after, but hopefully I'm on the right track now.

One thing that's worrying me a bit is all the weight hanging off the focus tube. I have a compression ring fitted but even though it's tightened as much as I can, it always seems to have loosened slightly. I think I'll be saving up for a SteelTrack & Clicklock clamp next...

Thanks again
Ivor

I'm experimenting with using a ZWO OAG (mkII) with my SW 200dps + Baader CC (mk III) & a ZWO Mini 120MM as guidescope. So far I've got it all connected & have set up PHD2 with the calibration assistant.

The only way I could connect everything was with a 21mm M42 extension tube between the camera (ZWO 2600MC PRO) and OAG; & using the M48 OAG adapter to fit the Baader CC, which then inserts into the focus tube.

In order for the OAG prism to be clear of the camera sensor the camera orientation is limited, so I suspect it'll be a case of keeping it one position in relation to the guidescope. The first question then is, if I want to rotate the whole assembly to either obtain better target framing, or to find a guide star, will I have to redo the guide calibration? As I've previously used a finderscope for guiding I always redo calibration each night when setting up, but with the OAG will I have to re-do it a second time if I have to rotate the assembled camera/oag/guidescope in the focus tube?

Also - last night after focusing the main camera/scope, the guide camera distance didn't seem to make much difference to the view of the star in the guide camera or star profile image in PHD2. I understand that it should be set parfocal with the main camera, but how critical is the distance & how do you tell if I can't see it very well in PHD2?

Many thanks!
Ivor

PS: I'm aware that the 120MM may not be the best, but current budget didn't extend beyond the OAG & Helical focuser.

Anyone know what the 'eye' like object is in the upper left of the APOD? I searched on SImbad & found a planetary nebula at about that position (M51 29), but I'm not sure I got the right thing!

2 hours ago, BrendanC said:

  

Could you provide a link please? There are lots of options!

I don't have the original email/details but it would have been this one:-

https://kitronik.co.uk/products/polypropylene-sheet-05mm-x-1050mm-x-750mm?_pos=1&_sid=81be08b7f&_ss=r

Ideally I would have picked black, but during lockdown they only had white in stock - that worked ok as it was easy to mark on the bits to cut out & black marker pen on the edges worked ok. Once you've cut the polypropylene sheet to the correct OTA length I inserted it into the OTA & then marked the overlap position at either end. That made it easy to get the correct width, so that it fits in the tube of its own accord (i.e. no tape needed)

For the 200 dps the length wasn't quite enough to go to the end of the OTA, but I figured that the nearer the primary it wouldn't make much difference. In another thread on the SGL somebody recommended using hair-spray on the flocking material to help prevent it shedding fibres. I'm sure that helped, but it doesn't eliminate the problem entirely. (I'm about to give the mirrors a rinse & attempt @alacant's suggestion of replacing the primary mirror clips with blobs of neutral silicon sealant).

Cheers
Ivor

I used 0.5mm thick Polypropylene sheet from kitronik.co.uk. Worked fine on both the 200dps and 130dps.

Example of the 200dps process in the attached pdf.

Cheers
Ivor

flocking.pdf

Thanks @ONIKKINEN , now I understand why some folks have fans attached to their primary! I'll have a go with hanging a weight onto the cheshire (or my poorly collimated cheap laser) - good suggestion!

Cheers
Ivor

Thanks for the comments/suggestions. @ONIKKINEN The scope is kept in a storage area which is near ambient & is only moved a small distance. I re-checked collimation yesterday but I don't have a collimated laser, so could only do so with a cheshire (& obviously without the coma corrector). I took a few pictures with the scope at different orientations, roughly mimicking the positions during the last imaging session, but there could be some focuser slop once the 2600 camera is attached. Why should tube currents create the elongation in one direction?

@michael8554 The session 4 guiding had a four big blips in RA whilst imaging & a drift in Dec at one point. The figures reported in the PHD2 log are calculated on the whole period with these outliers & if they're removed from the calc then the RA/Dec rms is approx 0.44 / 0.41 arcsecs, respectively. Between session 4 & 5 there was only a 9 second gap, when I re-selected the main guide-star, so there shouldn't have been a big difference, aside from the 'blips'. Thanks for the tip on the RMS vs imaging scale & flexure!

@alacant Thanks - I know you're a strong advocate of replacing the mirror clips with neutral silicone sealant, but I've not been able to find any video or pictures of the process (other than the completed result). The only video I've found of someone removing a SW primary:- https://youtu.be/7fIkC9GukrM?t=1073 has the cork attached to a paper disc. I think mine has the cork attached directly to the metal ring. Do you put the put the sealant onto/around the cork & at the outer edge? One old thread advocated using a coin as a spacer, but presumably if the Cork is left in situ then there is no need to do so? (Also should the sealant be Low or High modulus?)

I'll have a look into the Losmandy & a second bar on the top for additional rigidity. I presume it's the longer length that helps? Also I think I need to either go down the OAG route or a top-mounted guider. The converted finderscope was all I could afford originally. Odd that only this dataset seems to have the problem though. With Pixinsight I've blinked through a few, including all the recent sessions since the last collimation, and it's only this one that is showing this particular issue. On this session I did have the camera at a different angle compared to what I usually do & I suspect that the guidescope wasn't aligned properly with the main scope.

Thanks again for the help!

Ivor

guide.xlsx

I'm a bit puzzled by the shape of the stars I've recently been getting & what to do to improve them. I'm using a SW200dps & ZWO ASI2600MC-PRO with a 50mm dia converted finder scope/ZWO120MM for guiding, which just sits in the finderscope shoe. I also have a Baader MK III coma corrector.

Last Wednesday night I got 43 x 3min subs on NGC3938 & then a further 15 on the Draco Triplet. Guiding for the most part seemed ok (*), but the stars have small tails which look like tadpoles. In PHD I'm using multi-star guiding, but it's possible that the chosen guide star was outside of the main image frame. The scope has recently been collimated. The shorter 10s subs I used whilst plate-solving look like they don't have the same problem, or at least not to the same extent.

Any suggestions/help much appreciated!

Cheers
Ivor

(*) In the attached log, Section 4 + 5 was on NGC3938, with a pause while I stopped guiding & reselected the star. Section 6 was on the Draco Triplet.

PHD2_GuideLog_2022-06-01_225109.txt

From last Thursday/Friday night (28/29th May)... SW 200 dps + ZWO ASI2600MCPro & Bortle 8. I wanted to have another go at M101, so that I could compare with the DSLR image I took in May 2020.

Forecast on Thursday looked a bit hit-n-miss & proved to be mostly cloudy with the odd clear spell. 71 x 3min Images taken between 22:54 and 03:00. Neighbours insecurity light didn't come on until 1am & then was triggered at regular intervals for the duration. Friday night I got a further 70 subs (22:54 to 02:52). Sky quality was much better, but the insecurity light was on up to 16 times an hour, although after 1am the frequency was much reduced.

On the attached plot of PSF Signal Weight, you can see how the sky brightness at the start & end of both sessions degrades the images & also how the insecurity light was affecting the quality on the Friday night. (It also similarly makes the guiding accuracy worse).

The good news is that my wife's had a word with the neighbours & they'll adjust the light angle & reduce the sensitivity, so hopefully things will improve!

Image processed in Pixinsight...

Cheers
Ivor

I've only tried it on one OSC (small) galaxy image so far, but it did a good job in comparison to my regular noise supression methods (MLT + ACDNR/TGVDenoise). I also tried comparing with an old copy of Topaz DeNoise & results were much better with NoiseXterminator.

It is very easy to over do it though & takes some trials to avoid the over-sharpened plastic look.

Cheers
Ivor