KP82

Thanks for the review. I've got the 26mm to use with an erecting image diagonal and Altair 72EDF for daytime and widefield sweeping. At f/6 and with an erecting prism I can only find image deterioration in the extreme outer edge of the view. Very impressive for £20.

As you probably have access to really dark skies in some remote sites in the Alps, you could really push for high mags with your scope. I'd go for something around 7 - 9mm with a 2x or 3x barlow. You may also want something to fill the gap between the N31T5 and your high mag ep, something like a 14 - 18mm.

Beautiful scope. Looking forward to your first light report.

Use the following to find out: https://astronomy.tools/calculators/guidescope_suitability

I've seen quite a few HEQ5 popping up on UKABS. Maybe you want to keep an eye there.

The same could have been true for the 72ED before the price increase. Being an ED it would also do well at high power should you need to. Someone might say he/she has other scopes to for that, but it's unlikely for him/her to carry multiple scopes on a holiday. But with the latest price of £339 for the 72ED, ST80 is of much better value.

I'm aware that you only need to pay the VAT once. For EU goods less than £135, you pay EU VAT. Otherwise the VAT should be waived off during checkout and then paid at UK rate upon delivery. The prices listed on TS website already exclude EU VAT the last time I checked, so I don't think it would work out to be much cheaper than Altair. And thanks for explaining about the difference in duty between scopes imported as a whole and assembled from imported parts. This will certainly help in choosing where I can order my future astro gears.

All of these Chinese APOs are imports. I remember I've read it somewhere if an item was manufactured outside EU and then imported into the EU, there would be an import tax. Before Brexit this was an one-off charge and already covered by EU retailers (e.g. TS), so ordering from UK the customer wouldn't need to pay it again. However after Brexit the customer now needs to pay both the UK VAT (the scope costs more than £135, so EU VAT waived off) and import tax upon delivery.

Yes mount upgrade will be needed. I've been pushing the limit on my HEQ5 with the APM 115. During a calm night I could still guide at sub 1 arcsec, but the wind would really mess it up. I'll be replacing it with an AZ-EQ6 once the stock are back.

Unless the OP has some specific needs, Kstars/Ekos for macOS should be fine.

Go with EQ6-R or better AZ-EQ6 if you're already planning for bigger scopes.

Tecnosky is another one of the rebranders just like Altair and TS Optics. These guys along with Astro-tech, Stellarvue (used to be) and William Optics (sometimes) all source from the same factories in China but with each of their own minimum specifications. It's very difficult to describe the actual difference between FPL51 and 53 in words except for listing out their dispersion characteristics measured in Abbe number (51 = 81.54, 53 = 94.66). The performance of the final product lens also depends on many other factors including the figuring of each lens element and the type of mating elements. But generally speaking a good fpl51 doublet at f/7 or slower should be pretty much indistinguishable from fpl53 doublet at low to medium high mag. It's only at extremely high mag (usually used for splitting tight doubles) where the difference can be seen. For anything faster than f/7, fpl53 or a triplet is more desirable.

Agreed. My settings were aiming for about 15 - 16pix dithering. But if the new mapping is correct, then my previous settings were actually producing 32pix dithering (way more than required).

This BYEOS dither aggressiveness mapping is different from the one I've seen before. However without knowing the official numbers I can't say which one is correct. Based on this mapping you will need BYEOS "2" and PHD2 "5" to achieve the 5pix dithering for guide camera which translates to 12pix for the main camera with your guide to imaging ratio.

Use the following page to find out your guide to imaging ratio: https://astronomy.tools/calculators/guidescope_suitability The setting in BYEOS doesn't affect your guide to imaging ratio. It's a multiplier for PHD2 dithering.

I use BYEOS too. I've read somewhere on CN before that the dithering setting in BYEOS works like this: 1 = 0.5x, 2 = 0.75x, 3 = 1x, 4 = 1.25x and 5 = 1.5x. I've set my dithering to 3 in BYEOS and 7 in PHD2. This is to tell PHD2 to dither 7 pixels (1 * 7) for the guide camera. And my guide to imaging ratio is slightly above 2, so it's effectively doing 15px dither for my DSLR.

I concur with the choice of an 102ED f/7.

The Rowan AZ100 + encoders + tracking/GOTO motors are going to be the ultimate heavy duty alt-az mount. The only downside could be its cost, probably going to be close to £3k.

The 80ED-R is a FPL53 doublet with a rotatable focuser whereas the Ascent 102ED uses FPL51 and non-rotatable. FPL53 ED glass is slightly superior to FPL51 in terms of dispersion characteristics. The difference matters more to astrophotographers than visual users although if budget allows, 53 is always more desirable than 51 assuming the rest of the spec is the same. I remember there is a recent review of the Ascent 102ED in the user equipment review section here. You may want to have a read on that.

TS Optics, Astro-tech and Tecnosky offer similarly spec'ed 4" f/7 ED doublets as they all share the same source manufacturers (KUO, Longpern, etc.). The difference between them is usually the focuser, rotatable vs non-rotatable or 2" vs 2.5". So go with whichever is the cheapest. But beware of the import tax if you're going to order from TS Optics in Germany directly for example. Yes, AZ5 works well with a 4" f/7. Get the mount head only and attach it to either a heavy duty photo tripod if you already own one or the SW 1.75" steel leg tripod.

Binoculars are a good way to start especially if you're worried about equipment safety in some public parks in London. Some of these 4" f/7 ED doublets are actually in stock unlike many Skywatcher & Celestron stuffs which are still months away from reaching the shore of UK. But since you also need a mount, you won't be able to get the full kit in a couple of months.

For high mag views of the planets, tracking or at least some forms of manual slow-motion control is a must for me personally. I'm not a fan with nudging my dob (often overshoot) and often use my refractors on a tracking EQ mount for planets despite slightly less resolution. I'd imagine for a 16" dob the nudging will be even more difficult.

I kind of agree. I'd also be skeptical about spending nearly a grand on something I have zero experience with at all. My first scope was a cheap Tasco 60mm gifted to me by my aunt. On the other at hand the portable aperture size we're talking about at the moment (5" or less), nothing beats an apo refractor for views.

WO like to add 1 extra mm of diameter to the final spec of their refractors for marketing reasons and paint their OTA in flashy colours to distinguish them from the competitors. Many of their scopes are essentially the same as Altair, TS Optics, AT, etc. counterparts. Those reviews on the other brands are often equally valid for the WO equivalents. This is not to dismiss WO. I owned a Megrez 90 before (bought 2nd hand) which was solid and I do love some of their latest innovations such as the Redcat and the saddle handle (I bought one for my Altair 72EDF). But personally I wouldn't pay extra for some of their scopes only for the 1mm extra aperture and flashy colours when I can get the same model quite a bit cheaper from another brand (e.g. £599 for Altair Starwave 80ED-R as opposed to £799 for WO ZS81).

For a standard refractor, the physical length of the OTA has to be shorter than its focal length. Usually at least 100 - 135mm shorter to accomodate a star diagonal, but often much more (180mm - 220mm) on premium models to allow bino-view. If you go with an Altair or TS Optics ED doublet, you will also need to price in a star diagonal, a finder and a couple of eyepieces as the scope itself is sold OTA + tube ring + dovetail bar only. As you said you would also need a mount. These extras + the mount will probably add about another £400 to the total cost.