Clarkey

I have had a very quick play and got the image below. There is certainly some good detail in there, but the background gradients need some work to remove.

The back focus is the distance from the flattener to the sensor - not normal focus. For most flatteners this is 55mm. (I am assuming you are using a field flattener with the 72ED). For a 600D this is normally the Canon T-ring plus the distance from the front of the camera to the sensor. But it is always approximate and may need extending by a fraction. (You can buy M42 and M48 spacers such as these Astrodymium Colour Coded Fine Tuning Spacer Rings for M42 Threads (12x) | First Light Optics). Ideally to avoid any tilt try to get screw fittings. Any sort of compression fitting is likely to introduce tilt.

Looking at the subs, I would say a combination of backfocus from the flattener and a bit of tilt.

I can't remember the exact size, but the ones I replaced on my 200p were M3 or M4 from memory. If you take one out and measure it.... As for purchase, standard thumb screws are cheap as chips online. Try to get a similar material to the existing ones to prevent galvanic corrosion. As for the washer, personal preference really.

Great first result with PI. I was 'converted' last year after lots and lots of videos. I was imaging last night and my guiding was all over the place. I put it down to the wind. Sometimes you just need to ignore the numbers and worry about the result.👍 M106 is worth adding a little Ha to the mix.

Meridian flips simply prevent your telescope from crashing into the tripod or pier. If you don't do it, eventually the scope will hit something. (Yes, there are exceptions - but as a general rule). HFR is simply a statistical measure of the size of the stars. In theory stars should be point sources covering one pixel only. However, seeing, poor focus and optics can all make this worse. By getting the HFR (or FWHM) as low as possible this is the 'best focus'. The number will always vary from day-to-day and scope-to-scope, but it just needs to be the lowest possible.

Amazingly I managed my 3rd imaging session of the year last night. Despite being windy and the guiding being a bit rough, I was not going to miss this rare opportunity... This way a combination of data from a 115mm triplet with my trusty 1600mm pro for luminance, and my RC8 with the IMX571 Rising Cam for RGB. About 5 hours imaging with each. Processed in PI. Given the poor conditions, it has not turned out too badly. For once the refractor was giving poorer stars than the RC, probably due to a bit of more play in the HEQ5 mount and the gusty winds. Critical comment welcome as always.

Nina works on the guide camera so you need to work out your pixel scale for both scopes and adjust accordingly. I would recommend using multi-star guiding in PHD2 - looks like you are using single. Also, you make want to adjust your dither settle times / accuracy as the guide scope is still adjusting when the next image is starting. (This mat also explain the walking noise and soft stars). You also need to put your scope and camera details into PHD2 to get an error in arc secs. Currently this is reading zero. The RMS value you have is all in px, so slightly meaningless. HTH.

I think I must be the only person on SGL that likes RC scopes. I'll be burnt as a heretic next! 🤣

As I said, I seem to have got a good one. Because they are built to a price point, I am sure the quality varies from one to another. New focuser is a minimum for all of them. I have heard the horror stories - it made me think twice about buying one. For once I seemed to have got lucky! I agree to a point. However, when imaging natively at <0.5 arc secs /px I found the results better with a reducer and bin2 (giving about 1.3"/px) compared with bin3 at 1.5"/px. The reducer also acts as a flattener too. Just some 'fine tuning' really.

This is the reducer I use. As it is a variable reducer depending on distance, I don't reduce the full 0.67 as I find it better at around 0.75. At F6 and bin 2 it gives a relatively 'fast' system. CCDT67 & 27TVPH (astro-physics.info) I know there are people who have really struggled with the RC's. I may have just been lucky and got a 'good one'. If I get the secondary perfectly aligned with the focuser, the primary can just be adjusted with a star test. Generally, the primary adjustment is so small it does not need any more than this. I do have a 6" F4 newtonian which I find more difficult to get perfectly collimated than the RC. I think this is down to the flex in the system that does not exist with the RC. I'm not sure they are that heavy for the FL and aperture. Having said this, the 8" would be at the limit of the mount. I have used mine on my HEQ5 and it will just do it - but the guiding was not that good. I have just checked the C8 weight and I was surprised how light it is. Maybe the SCT with reducer is the way to go? The reason I raised this was down to the pixel scale. For my set up this gives about 1 arcsec/px which is about as low as I can go (and probably lower than I should). A 910mm FL with a 0.8 reducer would give a similar scale with a bit of extra 'speed'. Ultimately, unless you have unlimited resources, whatever option you go for will be a compromise in terms of aperture / FL / mount limits.

I must admit to feeling a bit like this at the moment. I think it is largely down to the weather. I have spent a similar amount (maybe a bit less) on masses of kit and it is sitting doing nothing at the moment. Not only this but I have had nothing from Spain in the 3 months since Christmas. Depressing indeed. I have just decided to keep the kit I have (no spending😬) and wait until next season and see what happens. If it as rubbish as the last 12 months, who knows.......

I'll give my opinion - but it is only that.... APO - yes they are good but pretty large for the mount. I had a 130mm photoline but had to sell it as it did not quite fit my mini observatory. I was planning on putting it on the AZ-EQ6. I think 'speed' for galaxies is slightly less of an issue due to the concentrated brightness. RC - great scope for the money and my main galaxy scope for the last 3 years. It will almost certainly need a new focuser (I use a Steeltrack). Mine is reduced to F6 and I bin2 which gives pretty good results. I have been lucky with mine as the mirror optical axis seems pretty close to that of the focuser, so collimation is not too much of any issue. Also, it only needs doing occasionally. Newt - As you say, lots of scope for the money, but a little more 'faff'. I am currently considering an F4 250mm to give me a fast a system as I can currently afford. Again, you may well need a new focuser. The standard Baader MPCC or Skywatcher coma correctors are fine at F5 so not too expensive. SCT - I have no experience, but your comments seem valid enough. One other possible option I'll throw in the mix is the 115mm refractor. I have the Altair version with FPL51, but the correction an imaging is excellent. Slightly lighter for the mount. I use it with a bog standard 1x field flattener from Stellamira which gives good results. There is of course an FPL53 version which would be better in theory. (I now combine my RC8 and 115mm for galaxies) HTH's.

You might improve resolution with a barlow, but at the cost of much more time. The set up as it is gives a pixel scale of around 2.2 arcsecs/px which is fine for widefield imaging. It is probably a little bit undersampled for galaxy imaging, but not excessively. With UK seeing you cannot get more detail than the atmosphere will allow. I image with an RC8 with a reducer and bin 2x2, which gives a scale of 1.3 arcsecs/px which I find is about right. Either use the scope as it is and crop out the sky - or get more focal length. For a 294 something around 1000mm would be ideal.

Mmmm. 60+ hours. This would be about 3-4 years with normal spring weather here..... Here is my old image of the area. I think my current processing would give better results - but I was happy with the result back then. I might have another go at processing, now I know what I am doing (sort of).

Now we just need some weather worth forecasting!🤣

Second rule: if you can't see a reflection you are either a vampire or you need to clean the mirror😁

Blimey, that will fill your hard drive quickly!

Hopefully not. Although a little tricky, I think the fear of RCs is worse than reality - unless you get a really bad one. My collimation is based on the DSI guide. I also got some good information from @fwm891, which I may need when I clean the mirrors in the summer.

I dismantled mine to replace what I thought was a noisy fan. Turns out it was just a bit of a rattle from the cooling fins. I replaced the fan anyway for a better one. Anyway, I digress... The internals looked fine in mine. No obvious evidence of cutting corners.

I have an RC8 which I am a fan of. Collimation is a bit tricky, but once set it hardly moves. I probably only collimate once a year, even when it was regularly moved. With a small chip and the RC6 I think collimation will be fine. FWIW, I did change the focuser on mine, but I was using a cooled mono camera with filter wheel. Getting the primary mirror and focuser aligned on the same axis is fairly critical for good collimation. Fortunately mine was very nearly spot on. (I purchased the tilt plate but never needed it). If I get the secondary perfectly aligned with the centre of the focuser, I just need to tweak the primary with a star test. I have a recent M101 in the deep sky imaging section which will give you an idea of what the scope will do.

Doesn't sound too bad for the repair. I'm glad it worked out ok as I have a RC imx571 too. (Probably on your recommendation)🤣

Normally, yes. But why? What did you have in mind?

With the weather being so awful, I have been going over some of my old data from a few years ago, when I had no idea what I was doing. Now I have a vague idea of what I am doing, and the new imaging software tools, the difference can be quite amazing. This is a re-process of about 9 hours of HaLRGB data from April 2021, using an RC8 and 1600MM pro, processed in PI. I am quite pleased with the amount of faint information has come out in the spiral arms. Also, the small messy NGC5477 galaxy also shows some detail. In case it is not obvious, the first image is the new one! Critical comment welcome as always.

Great widefield image with some good detail👍 30 hours is more than I have managed all winter☹️