[Stu Littlefair]

That's great, thanks. It's only 650mm, so from what I read anything longer than 32mm is likely to show the secondary?

Perhaps; what matters here is the size of the secondary mirror in the "exit pupil plane" compared to the size of the eye's pupil. The secondary is about 30% of the diameter of the telescope, so will also be 30% of the exit pupil.

A 40mm eyepiece will give an "exit pupil" of 8mm, which is a good match to the pupil size of a healthy dark adapted eye. At 30% of this, the secondary shadow will be 2.4mm, and you shouldn't notice the secondary. However, if you look through it in daylight, when your pupil is much smaller, it will be obvious. It will also be apparent if your pupil doesn't dilate much, or when you first go outside.

32mm is a nice choice though; it will give you 20x magnification, which with a 80 degree AFOV would give you a 4 degree field; a nice match for objects like the Pleiades and Andromeda (which are ~2 degrees across). Maybe stick with that and be safe. A 26mm will be OK, but the view of larger DSOs might be a bit tight?

Don't get too paralysed by choosing an eyepiece; most modern eyepieces are excellent, and you know what forums are like for spending time getting hung up on pointless minutia! I'd start with 2, something around 32mm, something around 5-7mm and see if you feel there's a gap missing after that.

Do you have the book "Turn Left At Orion"? It has lots of ideas for things to point your scope at. Don't miss out double stars. Albireo is one of my favourite things to look at; https://earthsky.org/brightest-stars/albireo-finest-double-star

[Johnny Brown]

Ok thanks, that's useful.

I got a decent view of the Pleiades last night with the 25mm but they did fill the view. Doesn't seem to be much choice of longer eyepieces in 1.25" though? Suppose I'll pop over to Rother valley and have a look at a few.

Was also looking at Cygnus last night, shame I didn't know which star to go closer on!

Yes, that book is on the xmas list...

[Johnny Brown]

Update: so six weeks or so on I've been getting a lot of use out of the scope. Have made a couple of trips out to darker spots at Stanage and Ringinglow but these seem more prone to cloud, so mainly in the back yard.

Did a lot of research on eyepieces. The ES 26mm 26degree (£97) I went for is great for widefield. It gives I think the max TFOV possible (2.5 degrees at 25X) and a really great view - Pleiades look fantastic. Feels like a premium piece.

Also got a 6mm Baader classic ortho (£50new / £30 used). If I was buying again this is the first upgrade I'd suggest, gives 108X. I haven't had a problem with the tight eye relief and the limited glass makes for sharp, contrasty views. Tiny and light. Effectively parfocal with the 26mm, which makes a nice combo.

Did a bunch of mods, in order:
Made collimating cap from 35mm film case.
Flocked light shield.
Greased focuser threads with chapstick.
Made full light shield (telescoping tube) with eva foam and sticky-backed plastic.
Cleaned primary in sink (carefully!)
Drilled and tapped a second hole on dovetail rail to take an arca rail to mount on tripod. A big ballhead slacked right off works surprisingly well as a alt/az mount.

Also bought a couple of other eyepieces - Baader 8-24mm zoom. It's great quality but pushing it weight-wise on this scope, it also requires a lot of in-focus which makes it a bit of a hassle swapping with other EPs. I'll hold onto it as it's great on the moon and wide pairs, and I suspect will be better on a longer fl scope.

4mm Nirvana 82 degree (£75). These Nirvanas are touted as the best bang-for-buck EP out there. I like it - 82 degree gives the 'spacecraft window' effect where you swivel your eye and can barely see the edge, but at 4mm it needs good seeing and is a bit dim and lower contrast compared to the ortho.

Stu, any beta on the best star atlas? Found a decent free PDF and prompted by your Albireo suggestion have been ticking my way through the best 200 doubles list. Cosmic train spotting as Varian put it is about right, well it's better than tv. Waiting for the new edition of Turn Left, looking forward to planets being better positioned. Not bothered looking for DSOs as the view of Andromeda from the backyard is underwhelming to say the least.

[lagerstarfish]

Me and the kids have been making do with a 1970s USSR 33T20x50 telescope taped onto a camera tripod. Having fun, but would like something "better"

based on the info in this thread (thanks!) I'm looking for second hand Skywatcher Dobsonians on Ebay, but not managed to score yet

any recent developments in the used telescope scene that I should consider?

cheers

[tomtom]

My telescope advice is to always check the eyepiece to make sure no one has smeared black goo or paint around it 👍

[Johnny Brown]

I'd say definitely go for a skywatcher dob. As big as is practical, the 5" is a good intro for cheaps but go bigger if you can. My small one is not getting much use if you want to try?

Since my last post on here I bought a 10" tube and then rebuilt it as a plywood and truss combo which is my main scope and much more portable. You can pick up 8" dobs in good nick for £200, or 10" for £350 ( both my scopes were ~£75 used but I spent a £300 on the rebuild. The sky really opens up with the bigger scopes, both the resolution and fainter objects. I've also got a spotting scope and a box full of eyepieces now... the included ones will get you going but budget for some upgrades.

[lagerstarfish]

nice one JB

I'll put some G4S stickers on the van and do a fake Covid Enforcement Raid on your street - we can load up the dob while your neighbours run away screaming or hide in their cellars - you can tell them that I found your mother in-law doing some illegal child minding and that she is now locked up for the duration.

[Johnny Brown]

Books...

Turn Left is great but quirky. Firstly it's massive so a bit unwieldy, but spiral bound which helps. It's all black and white, very basic artwork, and the decision to use star names and no RA/ Dec makes it a bit patronising and unrealistic, like you'll never use any other resource. But for actually finding stuff it's by far the best.

Collins Stargazing should be free with every beginner scope. Big pocket size, perfect balance of info, nice photos, great choice of targets and brilliant maps. Only fault is the maps have a few gaps when it seems with a few more they could have squeezed in a full atlas. £8 well spent.

Companion volume Collins Moongazing is dogshit. Seriously, poor maps, poor info and half the book filled with poor info on photography. I want my seven pounds back.

Collins 2020/ 2021 etc annual guides. These are great, most of the info you get in a year's magazine subscription in a slim pocketable volume. Occasionally miss big events, and not sure if the star informs the same year to year.

Collins Stars and Planets. 5th edition, £15. If you get into it you won't grow out of this one, comprehensive, essential. Might be a bit dry for kids. Some of the older used editions have even nicer maps.

Astronomy a visual guide. DK, £15, comes in a fancy moon embossed slip case. Probably the best single book for an interested teen but imho tries to do a bit much while remaining accessible.

Sky & Telescope's Pocket Sky Atlas is the proper atlas to get first. Decent size, excellent water resistant card pages and plenty of detail, likely to have most of your targets. For me much better than an app, but in combination with the internet you probably won't need another. The Cambridge one is much bigger and has flimsy paper, but their Double star atlas is essential if you get into them.

[Johnny Brown]

PS not much goes on eBay, everybody uses astrobuysell.com/uk

And check the buy/sell forum at stargazerslounge.com.

[lagerstarfish]

PS not much goes on eBay, everybody uses astrobuysell.com/uk

And check the buy/sell forum at stargazerslounge.com.

Nice one

Cheers

[Johnny Brown]

This is a great little film that might push some of you over the edge:

[Duma]

That's lovely

[Johnny Brown]

Eyepiece upgrades

I would suggest you set aside at least half your budget for eyepieces. They define the quality of the view more than the scope and the included ones are typically pretty poor. The good news is you only need two or three to start and can pick up more as you go along, plus they'll work on any scope and hold their value well. If you're not in a rush wait for them to come up used - most are in perfect nick as they don't leave the house. However the variety is baffling, a bit like popping into a West Indian record shop because you liked Legend. In my experience you can only really judge them on the stars so I wouldn't bother with a shop visit either (Rother Valley optics are hopeless, unless you're near somewhere better). So assuming you're buying on spec...

Focal length
You want something to give you the widest view possible, for big objects and finding stuff. This means a long focal length >24mm. For bigger scopes this will mean a big, heavy, pricey 2" piece, for a 1.25" focuser you have less choice - more below.
Then you want a high power eyepiece about the same length in mm as your scope's focal ratio - i.e. 5mm for an f/5 scope, 10mm for an f/10.
Double the high power and you've got your mid-power, i.e. 10mm for f/5, 20mm for f/10. This is actually likely to be the one you use most so the advice is usually to spend most here.

Apparent field-of-view (AFOV)
Expressed in degrees, typically from 50-100^o, determines how big the view appears to the eye. 60^o and up is considered wide angle, above 80 'hyper' or 'ultra' wide. You can take in about 60 without moving your eye, above 80 the edge of the view ('field stop') is increasingly in your peripheral vision, so you have to peer around to see the edges. This is often touted as a more immersive view, and it has the practical benefit that with an undriven scope you get more looking time before having to nudge it along. If you've not used an ultra wide the first time is quite a treat.

The other stuff - sharpness, contrast etc are what you pay for but harder to derive from specs. Both will improve with magnification up to a point then decline again - this is one reason your mid-range Ep will excel. Have a read of Stu's post on exit pupils above - things will generally peak around a 2mm exit pupil, i.e a 10mm eyepiece in f/5 scope.

A lot of the lower-mid price range are the same optics in different bodies. Read some reviews. I'm not convinced by zooms (I have the Baader ) - unlike photography there isn't much call for tweaking the view, more jumping to a significantly different mag, plus they have have variable AFOV which declines so you just get a bloated mid-range piece which shows a similar view bigger or smaller.

Some brands for starters.

Svbony - Russian EPs via ebay. A modest upgrade on your included ones for a few fuck-alls.

BST Star guider - usually the cheapest recommended, ~£50 a pop new.

Explore Scientific - a big range with prices and quality that go up with the AFOV. All seem very well regarded. I've got the 26/62^o, 24/68^oand 8.8/82^o.  £100-150 new, used ~70%. The 8.8mm is a gem, cost me £85 and probably my favourite but this is partly due to a ~2mm exit pupil in my scope.

Meade - a bit of a mixed bag but the 5.5mm and 8.8mm UWA 82^o are very good. I've got the 5.5mm £130.

Skywatcher Nirvana - cheapest well regarded ultrawides. £75. I've got the 4mm, its decent.

Televue, Pentax etc. The best but you won't be buying them based on my opinion. >£250. I've got one Nagler, it's almost perfect but not twice as good as the Meade 5.5 or ES 8.8mm.

The other issue is getting the widest view out of a 1.25" focuser. The alternatives are limited, same true field but as the afov increase the price and performance goes up:
32mm plossl £30 might not be an upgrade on the included
ES 30mm 52^o £70
BST 25mm 60^o £50
ES 26mm 62^o £100
ES 24mm 68^o £140 (£85 used)

There is a similar choice around 2" max view but I'll not bother unless anyone asks...

[Johnny Brown]

PS... In that moon vid your man has got a £600 Televue 100^o Ethos eyepiece operating at about 115x and a 2.5mm exit pupil. That's delivering a view of the whole moon in blistering detail but with the edge right out into your peripheral vision, like someone holding a 2m diameter model a meter away. That's why they're gasping.

[Johnny Brown]

One thing I forgot - Baader orthos. Low price, limited field of view, very sharp, high contrast. £35 used, £50 new. If you don't want to spend much a 6mm would be a good choice for your first addtional EP for an f/5 dob.

Similar 'minimal glass' EPs are popular with the beard stroking crowd for keeping out maximum detail on planets (which are all tiny even in any scope btw, except the moon), although they tend to go for pricey Japanese ones that aren't made any more. Downside is very short eye relief which takes a little getting used to and is a complete non starter with glasses.