Clarkey

I don't think you will have an issue at that sampling rate. My FMA180 is much higher with the ASI1600 and I didn't recoil in horror at the pictures. Being wide field it is slightly less critical. Another option might be the SharpStar 76EDPH f/5.5 Triplet ED APO Telescope with flattener reducer. Very similar but standard triplet and slightly cheaper once import duties are included. In terms of real world experience I can't comment. I think both would be good wide field astrographs.

I don't know about Exeter specifically, but if there is a local village somewhere with a playground or green space? Other than a few dog walkers these places are generally empty after dark but not in the middle of nowhere. May not be as good as Dartmoor for dark skies, but may be less anxiety inducing.

Another option is the RisingCam IMX571. Yes it is from China and I guess this gives an element of risk. However, there are lots of users who seem very happy. It is the same camera but < £1100 with duties. I have one and I am waiting for some decent darkness to try it out.

As has been said above, likely to be the moon but might be light pollution from local town / house. I would suggest that 5 minute subs is probably a lot longer than necessary with the 2600 unless you have very dark skies. Probably 1 or 2 minute subs would give a better result.

If when you check it in real life there is still some backlash, you might need to adjust the end float of the worm gears. (This is the two rubber caps covering the end of the bearings). I had to make my own tool to adjust these, but you can use circlip pliers or something similar. Again, there is a risk of overtightening so you need to be careful.

Yes. That is what I did.

My HEQ5 was similar. It turned out I had marginally over-tightened the worm drive end float bearings. This sounds similar. I have actually just changed all the bearing on my HEQ5 and it is a similar age to yours. To be honest only the worm drive bearings needed changing, but as I was dismantling everything I decided to do them all.

You will need a triplet or well corrected doublet. I can vouch for the SM90 but I suspect it is a bit over budget. The Askar FRA300 and 400 seem good and there are a couple of the small Sharpstar scopes that might suit. I think it depends on FL and budget really.

You need to add your scope to the telescope settings in Stellarium. From memory, from there it is quite simple although I am using a EQDIR cable not USB.

Ok, I understand now. I used to get the same problem. A plastic storage crate with the laptop inside was my solution, then a long cable into the warm, now a remote fanless PC which generates plenty of heat.

Why not use a dew heater? Alternately a quick blast with a cool hair drier is probably better than a heater. However, for planetary imaging it is probably less of an issue.

If your anything like me you will never be completely happy. I regularly go back and reprocess images that are just 'wrong' somehow. APOCD - a new SGL acronym 😆

As I said above I probably needed to clarify my original query. Such as for the same sensor size.

Yes, I understand this from the other explanations and I appreciate the differences. It would be a lot cheaper though😀

Thanks for the guidance. From the multitude of different answers I don't think I made myself too clear but I think I now get it. In effect, there is one primary ray that is effectively straight and not refracted. All the other light needs to be aligned to the same focal plane. Just to add to my confusion, cameras have a fixed distance to the focal plane but can have any focal length lens. You could have one scope with multiple lenses😁 I think if I had drawn a diagram my query would make more sense, but I'm on holiday and using my phone.

I understand these bits but it does not answer my initial question regarding WHY the focal length defines the FOV. At least the water is no muddier🤣

There are really lots of options, much of it down to personal choice. I'm sure the FRA300 is ok, I have no personal experience. I would maybe consider the FRA400, which is a similar design but you can get a reducer to give F3.9 at just under 300mm FL. Maybe more flexible? There are other similar scopes and I would not worry about using a flattener or reducer. As for the mount I can't really comment. I have an heq5 which is about the minimum you want for a 'proper' scope. I think the AVX is similar. Maybe a used neq6 or similar might be a good option? For the camera I would seriously consider mono. The initial outlay is more, but it gives more flexibility and improves light polluted photography. I thought I would not really use narrowband when I brought my kit, but now the bulk of my widefield imaging is NB. Also helps with the moon. The ASIAIR is a fair choice but does limit you to ZWO products. I use a mini fanless PC to run my set up so I was not tied to one company. Yes it needs a fair bit of set up, but gives you the choice of other kit. (I have a risingcam imx571 for the cost of a 183. Autofocuser is fine. I use senso Sesto just because the are neater and easier to install. But with the ASIAIR..... Power - probably go bigger than you 'need'. Nothing worse than running out of juice. Finally, get a couple of good books before diving in. Mistakes are costly! I will warn you, if you get hooked it is a slippery slope to poverty 😆

I have been pondering a though which I am sure has a very simple answer. However, my old and naddled brain is not coming up with the answer. (Physics was never my strong point). Why does focal length dictate the FOV of a scope? For example, a simple refractor of a given focal length will show a certain amount of sky. Why could you not alter the lens shape to focus the same area of sky at a different point? Same with a mirror system. Any guidance to put me out of my misery would be appreciated. (Be aware, I do have a penchant to miss the glaringly obvious 😀).

I have used stellarium without issue. If the mount starts in the home position it is normally approximately right for the first slew. I think the alignment positions are held in EQMOD when synched. As more stars are synched it gets more accurate (normally). Maybe the data is not clearing from EQMOD? Do you shut your PC / Stellarium down between uses?

I would check, but I think this may be what you are looking for. https://www.firstlightoptics.com/skywatcher-focusers/astro-essentials-2-dual-speed-low-profile-crayford-focuser-for-newtonian-telescopes.html I think the hacksaw option is the 'standard' route.

Not something I can agree with. I have PI, but I find it like playing pass-the-parcel with boxing gloves on😁 I assume your camera is not modified. This would really help picking up the Ha signal. But if you have good stars at 300s that's good. I would not bother with darks with the 200d as it will probably add more noise than it removes, especially with 4.

Not sure I would try threading anything made out of cheese.

I would agree. Adjust your back focus until at least one corner is right. After that it is probably tilt. Looking at the image, I think if you get it close enough you probably won't notice any tilt unless you pixel peep.

I had just started a reply. Beat me to it! 650nm is a very low cut off point. Not only loosing Ha and SII but half the red spectrum. Strange for an astrocam?!

No. The IR/UV wavelengths are removed by the NB filters. You only need this for normal OSC imaging.