John

The F/9 will not be held steadily by an AZ-3. The F/7 would be pretty marginal as well I'm afraid especially if you try and use the sort of magnifications that these scopes are capable of. An AZ-4 would be much better.

If the objectives are figured to a similar quality (which is likely) then there won't be a lot of difference, just a touch more false colour around bright objects and possibly the F/9 might be able to handle higher powers wiht a touch more aplomb. I have a 102mm ED doublet that works at F/6.5 which I think uses an FPL-51 element but the false colour is not intrusive at all. A well figured F/7 ED doublet is a very versatile scope being able to handle both high powers and deliver wide fields of view at low powers

I believe the TS 102mm ED (non-Photoline) uses an Ohara FPL-51 glass ED element. What type of glass the mating element uses is not defined. The F/9 100 ED uses an Ohara FPL-53 element mated with a Schott glass element. The levels of false colour visible in the F/9 are very low indeed from what I recall when I used to own one. The TS 102 that uses FPL-51 will be a lot better in terms of colour correction than an achromat of that aperture and focal ratio but is likely to show a little more false colour than the F/9 Skywatcher. As Stu says, the F/7 will enable a wider field of view to be delivered and the focuser is likely to be better than the Skywatcher. Depends on your priorities I suppose ?

A decent quality barlow lens, on average, reduces light transmission by 1-3%. That is less than the variation in light transmission that is found across different eyepiece designs / brands without a barlow lens in play.

I use the Baader T2 Zeiss prism with my Takahashi FC-100DL and it works very well. I also have a couple of Tele Vue Everbrights and an Astro Physics Maxbright which I also think highly of. The Baader T2 suits the slim lines of the Tak very well but in all honesty I've yet to see any optical difference between it and the Tele Vue and Astro Phiysics mirror diagonals when I've swapped them about on my refractors I have read BillP's reviews as well, more than once I have to say - they are good reads

These are all the flanges that Moonlite do for various refractors. My suspicion is that they won't have one currently with the Bresser AR127L name on it but one of the others is probably the right one, either a Meade or an ES probably because those brands have had strong connections with Bresser products. The question is which one precisely ..... https://focuser.com/refractorflange.php If you can get the flange sorted out, the rest is easy

The Skytee II should handle an ED127 triplet OK if it is on a sturdier tripod than the stock 1.75 inch one. A 2 inch steel tube legged tripod or even better a Berlebach Uni should be investigated. Even then you would probably have some vibrations to deal with at higher powers I reckon.

In my opinion a 100mm ED doublet would have the edge over an ST120 for white light solar observing with a wedge. I use my Lunt wedge with my Vixen 102mm ED and Tak FC 100 and the results are really good. On double stars I think it would be a close run thing but personally I feel that good ED doublet refractors have provided the most satisfying views of double stars of any scope types that I have used. On lunar observing, again it would be a close run thing between a good ED 100mm doublet and a 127mm mak-cassegrain.

A quick "bump" for this heads up. More info on UK observation here: https://www.popastro.com/main_spa1/transit-of-mercury-2019/

The trouble is that the GOTO function eats up a lot of a £350 budget leaving proportionaly less for the scope itself wheras without GOTO that budget would get you firmly into the 200mm aperture class. It's a tricky decision I grant you.

Interesting thoughts Doug Lots of clouds and rain do tend to prompt this sort of review. That, and lots of equipment tinkering ! The only thought that I have to offer currently is that refractors seem to get quite a lot larger and harder to mount steadily when they exceed 120mm in aperture.

Yes, with an eyepiece. I've not actually used one though but I've read about the need for quite a lot of inwards focuser travel with this coma corrector frequently.

That still looks quite a large CO though ?

I agree with Dave - for purely visual observing I would always prefer to have that additional 22mm aperture.

Do you include imaging as a potential application for the scope ?

I don't feel the need for a coma corrector but I have read that the ES one requires 38mm of inwards focuser travel which has caused issues for some users.

Upgrading to the 1.75 inch steel tube legs tripod (who ever you buy it from) makes a lot of difference to the stability of the EQ3-2 mount I found when I had one. That alloy tripod is the weak link for sure.

Well, what do you know ? - the sky is clear !!! So the AZ100 is outside, has the 130mm F/9.2 refractor on board and I'm letting the scope cool for a bit before giving it a go

I won't know for sure until I actually use the mount but I'd guess that it would handle a 200mm F/5 pretty easily, also maybe a 250mm F/5.

More rubbish weather this evening so I've removed one of the dovetail clamps and installed the counterweight shaft and counterweight to see how that fits together. Four M6 bolts fit the C/W shaft to the axis once the dovetail clamp is removed. The C/W shaft mounting plate perfectly matches the full diameter of the altitude axis of the mount. The shaft itself screws into mounting plate with an M12 screw thread and that end of the bar is also enclosed in a snugly fitting 15mm deep sleeve. Its much more solid than I thought it might be and handles the supplied 5.2kg counterweight as if there is nothing on there ! The dovetail clamp is Losmandy fitting and a really nicely executed unit in it's own right. It is drilled with holes that fit a number of mount types in M6 and M8 sizes. I was pleased to find that it bolts straight onto the 35mm spaced M6 holes provided the Giro Ercole and Skytee II mount arms. With no scope to balance the counter weight the motion of the mount around both axes was just as smooth as it had been without the shaft and weight fitted. I'll actually get out and use the mount as soon as the clouds and rain relent. I'm very optimistic about it's likely performance from what I've seen so far Here are some photos of the mount with and without the counterweight shaft and weight fitted plus the rather lovely dovetail clamp:

I've read that a few times recently but I still see new designs with relatively large apertures coming on stream that use it so I guess reports of it's passing were exaggerated.

I suppose this topic also begs the question, what is serious amateur astronomy ? Someone at my astro society reckoned that you need to be an active member of the BAA to be considered a "serious" amateur. Maybe thats for a different thread though.

It's the small cheap scopes on e.bay that are labelled "Pro" than put a wry smile on my face Behind closed doors professional astronomers are all using those, of course

One thing that I've found about the dob mount is that they are really steady, in terms of vibration / shake control, when using high magnifications. Goodness knows what an alt-az or eq mount that would hold my 12 F/5.3 inch dob steady would cost or how big it would need to be but the simple plywood dob mount that Moonshane made for my scope a few years back holds it really solidly even when using 400x or more.

None of mine are serious - its a hobby for me and I do it for fun So Peter is probably right in that respect - it depends on the approach and attitude of the owner rather than the scope. When a look back at all the years of observing that I've done though, it's when I've been using my larger aperture scopes that I've been able to go deeper, look futher and see things that I otherwise would have found harder or not been able to see at all. So I guess currently my 12 inch dob is the nearest I have to a "serious" scope despite my lovely (and somewhat more expensive !) refractors.