Tiny Clanger

I guess you are thinking of the Heritage dobs rather than a full size one ? A full size dob would be extremely awkward on a balcony, and a table top dob would be smaller but still quite awkward - and require a very steady table, box, or something to stand it on too. I love my 150 heritage dob, but agree with M40, a mak would be better. The 127 mak is great for planetary & lunar, and crucially for you, the tube is only about 30cm long , so easy to use in a confined space. The main negative with maks is that they need to cool down from room to outdoor temperature to avoid internal air currents churning around and messing up your view, but a balcony is presumably a pretty secure place to leave one to cool ! Dew build up on the glass corrector plate can be a pain too, but on a balcony off the ground that might be less of a factor ... and dew shields are cheap and easy to make anyway.

Before buying the Bresser 'frac I'd tried white light solar with my ST80 and a DIY Baader visual filter, I expected more from the larger aperture/better focuser 102s, but that orange Bresser filter really let it down. Fortunately I'd made my 80mm filter carefully from the edge of the sheet of Baader film, which is slightly smaller than A4, and had enough film to make another for the 102.

The included Bresser ep is just a normal plossl . I had a 102s and it had the same warning about eyepiece use. BTW, I thought the Bresser solar filter very poor in terms of the view it gave compared with a DIY one of Baader film, well worth £25ish and some cardboard and tape to make one.

This page may help https://www.firstlightoptics.com/ed-pro/sky-watcher-evostar-72ed-ds-pro-ota.html and if it doesn't , an email to FLO will get an authoritative answer https://www.firstlightoptics.com/contact.html

The Castor works far better with a 102 f7 'frac for me than my AZ5 does. No slo mo, and I have to be aware at high alt. to shift the tripod legs so the OTA doesn't clash with them. I bought my Castor used, it came with a second clamp & counterweight bar, but I don't often use a counterweight, because while it gives some improvement in az smoothness I don't feel the need for grab & go purposes. On the odd occasion when I do add a weight it goes in the second clamp (with a home bodged wooden wedge countersunk bolted to the weight) or in the form of my 72ED ! Because I want this to be the most portable 100mm grab & go possible for a lazy person (me), I have the setup on a carbon fibre tripod*, which makes the tripod/Castor combo come in at under 4kg. It works very well for me, is light and compact enough to carry out in one go, capable of extending high enough to use standing up when needed, and is easy to close the tripod down and lay the whole thing across the back set of the car for a speedy nip out to a darker site. For me the inevitable vibrations are not noticeable below 100x mag. and perfectly acceptable up to around 140x . If I find conditions look like they will allow higher mag than that, I'll take my 127 mak out, which works fine on an AZ5 (on a metal photo tripod) as the slo mos come in useful and the mak's short OTA does not provoke horrible vibrations on the AZ5 as the longer 'frac does. * one of these https://www.amazon.co.uk/INNOREL-ST324CF-Professional-13-158cm-Upgraded/dp/B08F2GJ8D6 I much prefer lever locks to collar locks on tripods, there are many very similar tripods available, but that's the only one I could find with levers. Others with collar locks may be cheaper, it's the 32mm largest tube diameter that's important, another £100 or so and a beefier but hardly much heavier cf tripod would be even steadier.

There's a reduced price BST 12mm at FLO https://www.firstlightoptics.com/bst-starguider-eyepieces/bst-starguider-60-12mm-ed-eyepiece.html , or keep an eye out for a used one, typically BSTs go for £35 ish second hand.

I'll have a guess that it's a Bresser 'scope with included plastic-y solar filter ? I had the same thing included with a 102 Bresser refractor I bought. I'd already had a little experience of white light solar with a smaller 'frac and Baader film/home made holder, and was so deeply unimpressed with the fuzzy low contrast image and orange cast with the Bresser filter, that the thing went straight back in the box, never to be seen again until I got the packaging down from the loft when I sold that 'scope. I made a filter from the Baader visual film I already had, it really is streets ahead. I don't think Bresser's included orange filter is a danger to eyesight, but it's a poor substitute for the good stuff !

In memoriam:

Try https://archive.org/details/manualzilla-id-7345459

It gets more complicated than just magnification though ! There's also exit pupil (essentially the diameter of the circle of light a 'scope/eyepiece combo presents to your eye) which affects what you can see : a mid range mag. eyepiece might seem pointless but it can help get a good contrast between the perceived brightness of the deep sky object you are looking at and the background sky around it. Your eye also has an exit pupil range it can accommodate, which varies from person to person. There's plenty of explanation to be found about this, I'd start here : Heather

I mention the specific type of strip in that comment. Online search saved me ferreting through the shed !

I've had a look through the photos I've uploaded before, here are some showing where I put the finder this angle shows the RACI is located so it parks neatly between the RDF and focuser when the 'scope is closed. If I can find the package I'll let you know what brand I bought.

Me too, but I managed to do it on my heritage 150 with no problems. Took the primary out (I marked the orientation of the collar with masking tape so I could replace the cell the same way, hoping to reduce the re-collimation. It hardly needed more than a tweak .) swathed the secondary in j cloths & a plastic bag plus more masking tape, obviously with the front section opened out. Marked the holes needed on yet more masking tape, drilled with a brand new metal bit - it was my first go drilling anything metal - turned out to be easy. In order to decide where to place the RACI I temporarily fixed the shoe on the 'scope tube with double sided foam glue strips - the sort of thing used to stick number plates on cars. I cleaned the surface with isopropyl alcohol first, and the strips held so firmly the shoe took the weight of the RACI easily with just a little give (because of the elasticity of the foam) . The location I chose worked well, and the foam pads were so good that I left them doing their job for a few months while I worked up the nerve to drill. Heather

I'm not 100% sure about the AZ4, not owning one, but I think it uses a 10mm bolt from the tripod. The AZ5 I know has a 3/8" photo standard tripod to head bolt fitting. Check which your tripod has ( skywatcher make both types) , you might have to get an adaptor if there's a mismatch . For M10 tripod to 3/8" head there are £39 astro essentials adapters available from FLO, but the other way round, 3/8" tripod to 10mm head adapters seem to be rare creatures ...

https://apod.nasa.gov/apod/ap200722.html is simply explained. https://www.wired.com/2013/03/why-is-a-comets-tail-curved/ includes some mathematical modelling .