Ricochet

I think that selection will work well. The only issue you might have is that the sct baffle might vignette the field of the 30mm. People who own the scope will be better able to advise on this.

Excellent. Clicklocks improve every scope.

You could pop over to Tring Astro and see how big an 8" dob is in the flesh, as their website says they are now open for prearranged visits.

Sounds like coma, that's what the additional coma corrector is for. If they all point to the centre, your collimation is correct. I use the FLO premium red cheshire for collimating my secondary. It slides in all the way up to the part where the top widens for the angled face. Seeing the edge of the secondary/primary will just depend on how far out the cheshire is. However, lining up the crosshairs with the doughnut is the important bit. For primary collimation I use one of the short cheshires with the crosshairs removed as the angled face is brighter than using a collimation cap.

Yes, so far it seems to work really well. Consider the placement of it before you commit to sticking it to the tube. Most people pair it with a RACI finder so you have to make sure that they don't impede each other.

I don't have any photos of how I made it, but for some reason my dob had quite a few extra flat pack furniture connectors included with it. I basically copied the method in which the base fits to the upright sections. However, I did not find a single balance position that worked at all altitudes. At low altitudes the tube had to be shifted back to balance with my heaviest eyepiece or binoviewers, but at high altitudes it would swing up and so a more forward balance point was required. To counter this I have added a bungee cord as shown in the photo below. At different altitudes the bungee is stretched by different amounts and so exerts a different force. The silver part at the rear of the base consists of a skateboard wheel bearing with repair washers either side to act as a guide. Moving this part up and down the rail changes the distribution between the force pulling the telescope up at low altitudes and down at high altitudes. The rail just above the base allows me to adjust the total force exerted by the bungee. Since adding this device, the telescope is stable at all altitudes and with any eyepiece or no eyepiece without the need to add any additional weights to the tube. Unfortunately, the current balance position is still just low enough that I don't think I could have used it without the extension.

A drop of threadlocker should stop the parts unscrewing, or you might find that if left alone for a decent period they seize up naturally. I'm not sure why you replaced the standard Bresser reducer with a normal Baader one though? A 1.25" Clicklock would only be a little bit more expensive.

Actually, the pds scopes are all designed for astrophotography, they just have longer focal lengths than the standard beginner scopes of a 130pds or 80ED. An eq5 with motors and an heq5 are not the same thing. In any event you should start with at least an heq5, but if you choose the 200pds and get into astrophotography you will most likely want to use it for that too so you should start with an eq6 class mount. If you think that you will only ever use your initial scope for visual then I think you would be better off with an alt/az mounted solution (dob for 8") as a Newtonian on an eq mount is quite unwieldy and subject to focuser rotation as the mount tracks the sky.

When you say rotating, do you mean turning the whole focuser or so you mean turning the knobs that make the focuser draw tube move in and out? Assuming that it is the second, does turning the focuser knobs no longer move the draw tube in and out? If so then it is likely either you have the focuser lock thumbscrew engaged, or the tension grub screw has come loose and needs tightening. The picture below shows a similar focuser, but I believe the standard focuser may have fewer adjustment screws. Having said that, the usual reason that people cannot focus with skywatcher telescopes is by having the incorrect number of adaptor/extension pieces fitted. Please post a photo of your focuser, as you have it set up, so that we can advise on this.

Divide the focal length of the telescope by the focal length of the eyepiece.

In this case it sounds like the cap is at fault, not the focuser. A replacement cap might solve the issue, so I wouldn't touch the collimation of the scope at this stage.

Ignore the mirror clips. Align the doughnut in the centre of the primary mirror with the cross hairs at the bottom of the cheshire/sight tube by adjusting the secondary. You should do this with the focuser extended to roughly the same position that is required to focus eyepieces. When you say off centre, are they not pointing at the doughnut, or are they not centred in the cheshire? If you rotate the cheshire in the focuser, do the cross hairs stay pointing at the same spot or do they prescribe a circle?

Get the secondary so it appears centred under the focuser and the offset will take care of itself. It is probably oversized so you don't need to worry about that too much. The next step of aligning the secondary to the primary is the important secondary adjustment.

I tested this a few weeks back. I put a fingerprint on the mirror and then cleaned it with Baader fluid. The fluid cleaned off the fingerprint (which was only there for minutes), but left streaks/spots as it dried. I think you would want to clean the mirror in the normal manner after cleaning it with the Baader fluid.

So it's in collimation every 360° and varying amounts out at all other angles? It sounds to me like the focuser is eccentric, personally I think I would talk to your supplier about getting it replaced. Before, you do though, take the collimation cap out and reinsert it at a different angle to check that the fault is with the focuser, and not the collimation cap.

When you don't have the focuser fully in, is there play in the focuser such that it can move to where it looks collimated? In this case perhaps the standard modification of ptfe tape on the threads will help. Alternatively, as you turn the focuser, does it drift in and out of collimation depending on the angle that the focuser has been turned? (i.e. One full turn from fully in it is in collimation again. )

This is true when using a normal barlow in front of the binoviewer and when using scaled eyepieces with short eye relief on the short focal length eyepieces. I would hope that a Baader GPC has been designed to correct aberrations from the binoviewer prisms such that further narrowing of the light cone is unnecessary for better correction. Additionally, if you can afford to binoview with Delites, I think that you could happily use short focal length Delites too. It will depend on the focal length of the barlow compared to the light path of the binoviewer. Different barlows will give different magnification factors when used with a binoviewer. With my binoviewer I use the nosepieces two "2X" barlows. One gives 2.1X, and the other gives 3.1X when threaded to the nose of the binoviewer.

I don't think you will find any in the UK. It isn't a standard part, it is a custom part made specifically for converting a binoviewer like yours to T2. (Assuming that is the right thread for your binoviewer)

You need to take the photo through the Cheshire.

I believe the H100 stand has a 3/8" thread on the underside of the base. If this is the case, then any decent photographic tripod where the head can be removed to reveal the 3/8" bolt will fit.

If you purchased a new one there should be an additional spacer ring that can be fitted between the eye lens and eyecup. Have you tried this combination? Also, what sort of blackouts are you seeing? Are parts of the view going black or is the whole view going black because you are not keeping your eye centred over the exit pupil of the eyepiece? If it is the second then I would try lowering the tripod so that you can sit to observe instead of standing. Sitting is more stable and will help you to hold your head in the correct position more easily.

Good choices, that foam looks like it should work to me.

Firstly, I think you should forget those maximum magnification numbers. They are based on long focal ratio refractors (which your scopes aren't), scientifically splitting tight double stars (which you're not doing), and without taking into account the atmosphere (which will heavily impact on at least the C9.25). For planets and star clusters your optimum will max out at about half that, and for extended DSOs, about a quarter, and that still doesn't take into account the atmosphere. You want to concentrate on the C9.25 and planetary viewing so I am going to make a suggestion that only applies to that, and not the small Newtonian: get a binoviewer. Using two eyes will show you more detail (and I think allow a slightly higher magnification), than using one eye. You also don't need to buy really expensive eyepieces to go in it. I suggest that you look at getting the Baader maxbright 2, possibly one of their T-threaded diagonals, and a GPC that will give you about 150X when using 32mm Plossls or 25mm Orthos. If you want full disk lunar, you'll need a variation that gives around 100X, but I don't know if that is possible. I think there is a specialist SCT GPC, but I don't remember the specifications.

My order would be: DIY light shroud. I don't think there is any downside to having one,so go for it. 5mm BST. Jupiter and Saturn are in the sky now, so you will want to get this before they are too low in the sky to observe. In addition, as it will give you a 1mm exit pupil, this focal length should give you a high power option for viewing star clusters. Increasing magnification to this level will significantly darken the background sky, whilst star brightness should be pretty similar to lower magnifications. 12mm BST. A 2.5mm exit pupil is a good option to have. Under light polluted skies it might be less used than "normal" but it will still be a good option to have. The 15mm is reportedly not as well corrected as the 12, so the 12 is the option to go for. With regards to the barlow, a 2X might be useful as it would effectively give you 4mm and 6mm options, which may be useful as the planets are so low this year and the atmosphere will limit the magnification that can be used, however, I'm not sure that it is essential. Light pollution filters are mostly aimed at sodium lighting, with the increase in LED lighting, they are generally becoming less effective. Good ones might make a very small difference on some targets, cheap ones are likely to be pretty much useless. UHC and OIII filters are useful on emission nebula, but the same rule applies, cheap ones with a bandpass that is too wide will not perform as well as they should. Under heavily light polluted skies I think the narrower bandpass of an OIII filter is more useful so that is the one I would look at, although I expect you would only find it useful on the Orion, Ring and possibly Dumbbell Nebulae without going to dark sites.

I would say yes, but you have to remember that aperture is very important. Increasing the aperture gives you both more light grasp and more resolution. Given that you already have a 70mm telescope, I don't think that you should go any lower than the 130mm model. 100mm probably won't be enough of an improvement that you will think it is worth spending money on.