60mm or 70mm Refractor for Star Adventurer?

[Steve789]

Which would you choose for DSLR astrophotography with a Skywatcher Star Adventurer? The Altair Astro 60 EDF F6 weighing 1.5Kg https://www.altairastro.com/60EDF-ED-R-Refractor-Telescope.html or the Altair Starwave 70 ED F6 (using a 0.8x Flatenner/Reducer will be F4.8) and weighing 2Kg? Both cost about the same and have similar focal lengths, the 70 ED being slightly wider at 336mm.

Currently I'm favouring the 70 ED mostly because of the faster F-Ratio but also because it comes with some nice little accessories like a case and red dot finder (I know the accessories shouldn't sway me but they do). I'm just a bit worried about the extra weight - I know it will fall well within the max payload of a Star Adventurer but I like to have plenty of room for adding extra stuff later. If any of you are already using this scope or similar with the Star Adventurer I'd love to hear of your experience with it.

I assume the 60 EDF has better quality glass as the blurb seems to make a fuss about S-FPL 53 glass but I don't know what that means to be honest.

Thanks in advance for your comments and by all means jump in with a "I wouldn't choose either of those I'd choose..." answers. My budget is around the £500 mark including a flattener.

[Mr niall]

I’ve owned a 70ed and can recommend it. I like the accessories makes it a versatile travel scope too. 

[jimmyjamjoejoe]

I had my heart set on a william optics ZenithStar 61 until earlier today, until i found the altair 60 edf. I'd be interested to hear opinions if anybody has used both. 

A 2kg scope is definitely pushing it for the SA. By the time you've added the scope, camera, finder?, and attached them (ballhead?), and counterweight - You'll be around 4KG, which will already lead to lost subs, that's before you take into account the longer focal length making things tougher. The common wisdom is anything above 300mm will want guiding, which will add even more weight. For that reason, I wouldn't want to try the 70.

 

[Steve789]

Yeah I was thinking about the WO 61 until I saw the Altair 60EDF but then I saw the 70 ED and realised with the right Flattener/Reducer I could have a faster scope.

Hopefully the 70 ED will be alright cos I just ordered one from Altair. Focal length shouldn't be an issue as I'm getting the 0.8x Reducer/Flattener which will bring it down from 420mm to 336mm. We'll see if I can get away without guiding - the whole point of this setup is to keep it simple and quick to use. One of the reason's I stopped imaging with my old kit (HEQ5, CCD,Laptop, Autoguiding etc)  was because I got fed up with spending over an hour to set-up only to get 5 minutes imaging time before clouds rolled in. I don't know if it's because I live near an estuary in Cornwall but that used to happen a lot!

I'll try and keep this post updated with my results for anyone interested although it might take a while. I haven't even got the Star Adventurer yet. I have the Star Adventurer Mini which I'll probably put the 70 ED on just for giggles while I wait for it's bigger brother to arrive 

[SteveNickolls]

On 17/10/2018 at 18:26, Steve789 said:

I'll try and keep this post updated with my results for anyone interested although it might take a while.

Please do, and good luck.

Cheers,
Steve

[Steve789]

As an update I have the Star Adventurer and Altair Astro 70ED set up in the spare room. The 70ED is much bigger than I envisioned - I think I may have ordered the wrong scope... Naturally I've weighed everything as I've loaded it up onto the Star Adventurer. With the 70ED, Reducer, 6D, L bracket and counterweight I'm coming in very close to the max payload of the Star Adventurer - never a good idea for astrophotography! I can save a couple of hundred grams by using my 1100D instead of the 6D but I really want to be able to use both.

In order to get everything balanced I've had to flip the supplied dovetail base so it's facing backwards and the counterweight is at full extension. I'm already planning in my head ways of mounting any future guiding set-up on the end of the counterweight bar and replacing the counterweight.

There's potentially some clear skies tonight so hopefully I'll get a chance to test it. Not sure my tripod is stiff enough though.

[Steve789]

Last night was first light with the Star Adventurer and Altair Starwave 70ED.

First lesson learnt was to make sure you've got good batteries in the SA! I thought I'd overloaded it and spent ages trying to get it balanced and double checking PA only to find the old batteries I'd put in had run out of juice. Once I had new batteries in it performed as well as I could have hoped. I managed 1 minute subs of which 90% were keepers. I'm already sourcing a better tripod as my carbon Benro photographic tripod is too bendy with that much load. I'm thinking about getting an old EQ tripod. I'm sure with a better tripod I can improve the PA and push the subs a bit longer.

Here's a very quick stack of Andromeda using the Canon 6D, uncropped with very little editing done. I need to investigate the spacing for the field flattener because as you can see it's not doing a very good job with heavy vignetting. This may be because I'm using a full frame camera. If anyone can tell me why I get hollow stars with DSS I'd love to know (I may start another thread about this).

Currently I wouldn't recommend this set-up for someone starting out with the SA. Balancing the scope is right on the limit with the 6D attached so much so that you have to have the L bracket mounted so low on the SA that you can't use the illuminated polar scope with the L bracket attached. In hindsight I wish I'd gone for a 60mm scope...

 

[SamAndrew]

Promising results! Thinking about a similar setup myself to get back into imaging after a long hiatus. I don't think you'll find any doublet refractor that will deliver a flat field for a full frame camera, so you may be better off with the 1100D which will save you some weight as well.

[Steve789]

I did ask Altair Astro if the scope and flattener would be suitable for full frame before purchasing and their reply was "Yes just!" which gave me a clue that some cropping might be necessary. I'll give the 1100D a try but I think I'll be disappointed with it's sensitivity.

I'm thinking about a 100D if I can find a cheap one. I believe it's the lightest DSLR canon do and the sensor seems pretty good for astro. I imagine it'll be easy enough to mod.  I've done 3 DSLR mods in the past.