Clarkey

Good advice above, but I would add that it is very dependent on your set up. I image with a 1600MM pro and a RisingCam IMX571 colour camera and I have no problem with a standard LED panel (tracing panel from Amazon) and very short exposures << 1sec. (Not recommended with a 294 sensor). This is particularly convenient when taking NB and LRGB flats at the same time as I do not need to alter the screen brightness. Similarly, with the RC8 I remove the dew shield for the flats and it is fine. Obviously, this may not be the case with an SCT due the effect of the corrector plate.

1 hour ago, dark knight said:

In particular I need a 5.5 x2.1mm centre positive  to usb c. This will connect the mounts hub to power a mini pc (USB c input). Anyone know where to get these, I can only find pd charging cables. Who would of thought the topic of cables would cause problems

I struggled to find these too. I ended up making mine with a standard 5.5x2.1 male to male then adding a 5.5x2.1 to USB C adaptor. However, I suspect the ones in the link from @TiffsAndAstro would be OK for low wattage.

I tend to go for shorter exposures on globular clusters - maybe 30 or 60s. I then try to remove any with poor star shapes to give the crispest image I can.

Nice image. Always worth adding a bit of Ha to this one.

With Astro darkness soon to be a distant memory, here is probably my last image of the season. M3 over 4 hours evenly split between RGB using the 1600MM pro. Processed in PI. I think the processing of globular clusters is probably the most difficult to get good results - and this is OK, but I will probably give it another go later.

You can just put in the coordinates for the moon on the day you are imaging. I have done this for imaging comets.

You also need to remember that M101 has a very low surface brightness so is not the easiest target. It is relatively large, but quite dim. Many of the other Messier objects are much brighter.

Also, don't be too hard on yourself or have too high expectations. AP is difficult and things are always challenging. I have been at it for 4 years now and I only feel vaguely competent. Have high aims, but don't expect to get there instantly without throwing money at it.

Mine is the same. I use a Reego for the secondary and star test for the primary. Cheshire or Laser is well off.

In theory once you have the collimation spot on you could add a tilt corrector to get the secondary on the same axis as the primary. You could then use a Cheshire. However, I only collimate about once per year so it is not that critical.

Why not carry out the lunar imaging as a planetary image? You can then process in AS3 and Registax (or something similar). This will allow very sharp images and it won't care about field rotation or movement.

Found this online for a 14" Orion. Does not solve your problem as such, but it does show the whole assembly being dismantled. The motor appears to be spring loaded.

If the Dobs are anything like the 'normal' skywatcher mounts then the meshing between the drive wheel and the worm could be a touch tight. This is then causing the motor to stall - hence the rough sounds. On the standard mounts the worm can be adjusted in and out (mainly to allow for poor manufacturing tolerances). I'm not sure if this is possible on the Dob? Is the whole motor /gear/worm assembly moveable?

I've been using NINA for some time now and I have never had a green screen. Sounds like it might be a display issue rather than NINA if everything else seems to be working OK. In the Options tab for imaging there is a reset  button - you could try this. There is also the option to save and restore the settings.

6 minutes ago, TiffsAndAstro said:

How do you know what your seeing i

You can tell from the analysis of the star sizes. I run an auto-focus routine which gets the best focus point. This also gives the HFR (or FWHM) figure. Good seeing for me is 3-4 arc secs. Very occasionally < 3. I'm not familiar with Siril, but I suspect it will analyse a light frame and give you a FWHM or HFR value. (When close to optimum focus they are to all intense and purposes the same).

Your set up gives 2.48 arcsecs/px or 2.11 arcsec/px depending on whether you are using the standard Skywatcher flattener/reduced or a straight flattener. Given the size of your scope, you will not be able to resolve much more than this value - around 1.6 arcsec/px. For the type of images the 72ED is good for (widefield) this sampling rate will be fine in my opinion.

3 hours ago, OK Apricot said:

White t-shirt over the aperture and pointed at a white light? 

Probably your best option for now. White T-shirt and overcast sky should work - and it is unlikely you will need to wait too long🤣

11 minutes ago, TiffsAndAstro said:

i assume its 2" ish

What is your sampling rate and what kit are you using? To make drizzling worthwhile you really need to be quite under sampled. If you are getting seeing of 2 you are doing very well for the UK. I consider anything near 2 pretty exceptional and I have never got < 2 when imaging.

1 hour ago, ollypenrice said:

I'm just wondering if you were oversampled

Definitely. Native is 0.73 arcsecs/px. I normally bin2 but I might push this to 3 or 4 and see what it gives me. Worth a try.

If you are imaging, base your need on pixel scale. If an F5 scope bin2 gives you the right value, it will save you the headache of collimating at F4. I am looking at getting a 10" F4 newtonian, but only because I have a very small imaging observatory and an F5 won't quite fit. An F4 10" with a 2600 sensor will give me 1.55 arc secs/px at bin 2. This is about as much as my seeing will generally support. An F5 will give me about 1.3 arc secs/px - which would be OK if it fitted. A 200mm F5 will also give 1.55 - but less overall light gathering.

I would add that I spent more time trying to collimate my f4 6" newtonian than my RC8.

Very nice. The RASA's seem to be showing more and more 'new' stuff.

I had just finished processing an M51 using Roboscopes data. 8 hours with a 12" dobsonian. I was quite pleased with the tidal tails on mine. Then you posted this.......😧

3 hours ago, 900SL said:

I usually do manual meridian flip, as i babysit my mount. I can track 15 degrees past meridian before risk of scope/tripod collision.

I'm tucked up in bed normally😄

The image above, although cleaner looking, is heavily black clipped so you loose quite a bit of the faint detail. Don't overdo the black background.

I use PixInsight now. As I said there is quite a bit of detail in your image, the trick is learning how to extract it without pushing the data too far. I consider myself a vaguely competent imager now - and this is after 4 years. I am still learning. Getting the images is the easy bit (weather permitting) once you have a basic routine. The processing is way harder. As I said, this was a very quick bash at your data, and I think with better pre-processing there is a decent image in there. I'm not sure why the background is so patchy - something you will need to look into.

You are definitely on the right track. Keep it up👍

27 minutes ago, TiffsAndAstro said:

Ok then, after looking at your link they go down to 0.4mm. is it just a case of trial and error, slowly building up the spacers and looking at the results?

Pretty much. It is pretty common to need the odd spacer in an imaging train. Basically, you need the focus tube > field flattener >55mm >sensor. As @bosun21 says the 55mm (+/- a few mm) is totally separate to the normal focus point.

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.

1 hour ago, TiffsAndAstro said:

But now im wondering if i have to get the exact back focus right before i then move the focus knobs?

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.