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Thanks, Wim. I suspect there will be some trial and probably quite a lot of error while getting to grips with this. On the positive side my 190MN has proved remarkably stable as far as collimation goes, must be all those nice baffles and the corrector plate keeping everything in position 🙂so once an accurate collimation is dialled in it should hold it for a while.

Not sure of the answer to that, Vroobel, but as regards camera sensor tilt, there's a fairly long thread here which goes into detail about how to measure chip tilt in the camera, independently of scope/lens &c amd also how to correct it. Might take a bit of reading as it's grown to 7 pages now,

Just as you say, Wim. I wonder if all I would do using the Tri-B mask would be to collimate out the camera tilt which is sometimes quite large according to ASTAP (I mis-typed above - it's ASTAP I use for SQM and tilt). I found a thread on Cloudy Nights (here) which referenced a Tri-Bahtinov grabber on Github (here) which, although a bit quirky, seems to give understandable results. Here's what it made of image 5 in the sequence above: I haven't worked out yet how to relate the channels to collimation screws (there is an assist diagram available but not sure how it works yet). Also not sure if I want to collimate for tilt at set-up every time (= lost imaging time) or whether 'close enough' is sufficient? Perhaps something to have a play with during the next two months of Astro twilight?

Short unexpectedly clear evening gave me a chance to test my 'cut-out-of-thin-card' Tri-Bahtinov mask last evening. Set up using my normal method of conventional Bahtinov and APT's Bahtinov aid, got us down to a very small error, shown in the first image. I then substituted the Tri-bahtinov and got image 2. (not quite right but not too bad) Racked the focusser out about 0.15 mm (approx 10th turn of fine focus knob on the Moonlight focuser) and got image 3. The spikes have shown some movement. Then reacked the focuser a similar distance back past the original position to get image 4. Again the spikes show some change. Lastly I tried returning to the in-focus point - image 5. From these images it appears that collimation isn't too far off, although I would appreciate any comments/observations on this. Two things struck me while doing these tests, one was how much camera tilt we had and how this would affect the result. (ASTAP gave a figure 8% tilt on an image shortly after the mask was removed.) The other was how easy adjusting the collimation screws to correct any perceived mis-collimation would be in the dark. Perhaps a Tri-Bahtinov grabber (think I've readof this somwhere on CN) would help. For the moment I think I'll stick to Concenter and Cheshire in daylight - which doesn't seem to have put collimation too far out?

Thanks for that, WIm. Much appreciated. We still have some astro dark left so if the clouds clear I'll use a freshly made mask (with all the slots cut out this time!) and see how my in-focus and defocussed spikes look. I'm strictly a manual focusser using a conventional Bahtinov and APT's Bahtinov assistant. My collimation is done by eye with Concenter and Cheshire, so it will be interesting to see what the tri-Bahtinov makes of this.

Hi Wim I had a go at making a tri-bahtinov out of dark card a couple of years ago and its been kicking around the workshop gathering dust ever since. I can't now remember if I got any results with it - apparently I got bored with cutting out the slots and may have tried to use it in its partially cut-out state - but can't find any images of the result. If I did use it, it would have been on the 190 MN. But looking at your images, how are they interpreted? In the 2nd image, I see that the 9 o'clock - 3 o'clock spike is reasonably symmetrical, while the 1 o'clock - 7 o'clock and 11 o'clock - 5 o'clock are much less so. Does this show a focus problem, a collimation issue or something else altogether?

May have misunderstood this, but if it's the Skywatcher Extension tube (pics below) then the top mounting bolt includes a ballrace/washer arrangement that allows azimuth adjustment via the adjusters on the north peg, even when the head is tightened down quite severely. My experieence is that both this and the north peg need to be as tight as reasonable (don't strip the threads!)

Don't have any experience with the EQ6-R, but have been using my Az-Eq6 for almost 8 years now and it just works. On nights of good stability it guides down below half an arc second (it did this evening in a gap between the clouds). It lives in an unheated shed and has been carrying my SW 190 MN which weighs something over 14kg as assembled, without any problem. I did have to replace one leg extension lock bolt a little while ago when it seized and the head sheared off when brute force was applied and the counterweights need repainting every now and then, but otherwise that's about it.

No greatness this year, I am afraid. All captured with SW 190 MN, ASI 2600mc mounted on AZ EQ6 GT. M20 M16 M8 NGC6781 M86 and friends

Many thanks, Han.

I have not used a Polemaster but I do have a guide scope and a ASI 120mm. Using this combination with one of the three polar alignment routines built into PHD2 usually gets me sub 5' polar alignment error which is more than adequate for my mount (AZEQ6) and scope (F/L 1000 mm). That said, the polar scope often gets us within 10' and sometimes closer. Not sure if a Polemaster, which seems quite expensive, would see much of an improvement?

Got it to work! Thank you, Han. I hadn't thought to reload the images after the batch solve... but now I have, the column is filled. The values look a bit unusual but that's a minor issue.

Can't answer your question directly, but when Juan Fierros sold me an Astro modded Canon 700d some years ago, he fitted a replacement filter, I think a Baader BCF1, in place of the Canon original. This lets through a lot more IR but, with a custom white balance means the camera is still good for day time terrestrial use. In fact it has now retired from Astro in favour of a 2600MC but is still much in use for terrestrial. Unfortunately, I don't think Juan is still doing this work, and not sure if a screw-in filter of the same transmission characteristics is available, but if you're up for a re-mod? There are a couple of example images about three quarters of the way down the thread here which show how the filter performs

Thanks Han. Unfortunately the first time I did that I get this message: The second time, it ran but the column was still blank. I ran analyse and organise, and still nothing. I may have missed a setting soemwhere, but not sure which?

I think it might be top right, 95 Arethusa, that Steve is referring to?