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 .

It's a really useful little book, I bought a second hand copy (via amazon, I don't recall who the actual seller was) for under £10 ages ago, and when I saw one going for £5 locally I snapped it up for friends. I'd not pay £28 though, I'd prefer a copy I wasn't worried about using at the telescope where it is bound to get damp. Wait a bit, keep an eye on Amazon and Abe books etc, a second hand one will be on offer at a sensible price eventually. Meanwhile, if you've not already done so, the free downloadable Virtual Moon Atlas can be set to show you your 'scope view, the phase, and lists the interesting features near the terminator https://sourceforge.net/projects/virtualmoon/files/latest/download I use VMA and the book, they complement each other.

It would be polite to state the sources of the material, crediting Gary Parkerson and Wolfgang Rohr at the very least. I note the copyright symbol the latter has added to his photos, so it should not be reproduced, just linked to.

Me too, I've got 'The New Challenge of the Stars'(1977, the £4.95 sticker still on the cover) and 'Hardyware, The Art of David A Hardy' from 2001, well worth hunting down if you don't already have it. I was unreasonably pleased to find he lives a few miles from where I did before leaving for uni. still going strong, he must be well into his 80's now. He has a good website https://www.astroart.org/ ,

Yep, if I was buying my first mak now (instead of during lockdown when the things were rare as rocking horse manure) I'd prefer the Bresser 127. The only reservation I have with the Bresser refractors is the non-standard finder shoe (and comically bad supplied optical finder) but it looks as if their mak comes with an RDF, which is all you need to point at the Moon anyway.

I think it's a variation on L.G.M.

As Bosun21 said, a mak. The advantages are that they are physically short, while having a long focal length, which makes them both lighter and easier to securely mount. I have a skywatcher skymax127, not wildly expensive and it weighs just a shade over 3kg. I can use up to a 6mm eyepiece with it giving somewhere around 250x magnification before eye floaters are too intrusive. What mount and tripod you choose to put it on will be the greater part of the overall weight, mine works well on an AZ5 (comes in at under 3kg) and a sturdy photo tripod , making the whole setup under 8kg.

If it's the mount & tripod that you have identified as the main weakness in your setup, get that sorted out first. I assume that your current telescope has a standard dovetail rail ? A new mount compatible with a standard Vixen type dovetail will be less delicate to pack into a rucsac than a telescope, and many photo tripods close down into short, compact packages. I'd suggest as well as upgrading mount and tripod you could consider adding one of the Baader filters that reduces chromatic aberration to make your current 'scope work better for you https://www.firstlightoptics.com/achromat-semi-apo-filters.html A filter would be certainly be easier to pack than a new 'scope ! You've not said what country you live in, or what country you are visiting, or how much you have to spend, so it's difficult to be specific about exactly what you might choose to buy, but photography equipment shops are more common than astro ones, so you will probably be able to see some tripods on display, maybe even handle them. Most quality photo tripods can be bought without a photo head, and have a 3/8" protruding screw to fix a head to. A lot of alt az heads with an under 8kg carrying rating use that 3/8" screw fitting too. As to heads which fit those photo tripods, I've used a 102 refractor a similar size to yours on a skywatcher AZ5 and found it vibrated too much, the same for a premium alt az head with a similar tall vertical arm arrangement. I've had far better experiences with the more compact alt az mounts which hold the OTA out at the side of the head, like this https://www.firstlightoptics.com/alt-azimuth-astronomy-mounts/berlebach-castor-ii-altazimuth-mounting.html and even this, which was rather strained and very close to the stated carrying capacity with a 102mm f7 on it, but OK at lower magnifications, and very much improved by use of a counterweight https://www.firstlightoptics.com/alt-azimuth-astronomy-mounts/omegon-az-baby-mount.html I've not owned one of these, but read that they have been used with 100mm fracs, and have the advantage of slow motion cables (which you can easily remove to pack) https://www.firstlightoptics.com/alt-azimuth-astronomy-mounts/sky-watcher-az-pronto-alt-azimuth-astronomy-mount-wo-tripod.html Import regulations, taxes and fees vary enormously from country to country, you need to check your home country government advice on personal imports from the specific country you are visiting. Taking it out of the box certainly won't negate any fees, it might avoid them, or it might get you in trouble if an inquisitive customs officer notices you are trying to evade paying ...

You need to remove the mirror cell from the tube to get to the clips which hold the mirror in the cell. If the clips are pressing on the mirror, the glass distorts, there needs to be a tiny gap between the mirror surface and the side of the clip that faces it. It sounds scary, but if you are very careful it's not hard to take the cell out (best mark the outside of the scope tube and the edge of the cell before you start with some masking tape or similar, to help get it lined up exactly the same way round when put back together to minimise any collimation loss) I've managed it with a 250 newt and I'm a weedy ham fisted fool. The usual advice is there should be a gap big enough to allow a sheet of paper between the glass and the clip.

Plenty to read here : https://stargazerslounge.com/forum/185-getting-started-with-observing/

Can't help you decide, but can point out a returned starfield with a reduced price available : https://www.firstlightoptics.com/offers/offer_starfield-102mm-f7-ed-doublet-refractor_431919.html