Williams Optics GT81 balance probs?

[Jimtom]

I'm looking at getting an 80ED of some sort, it's not easy to pick one that will fit my budget and my needs, they all look good in their own ways

I've started on the venture of AP with a 6" SCT and am getting on OK with that but want a wider FOV so 80mm is the place for me.

After much deliberation, taking into account optics, build quality and focuser I am seriously looking at the WO GT81 but have heard that balancing them can be a pain. Is this correct? I'm using a Celestron AVX mount.

Is a triplet worth the extra dosh for someone like me who, to be honest, is a beginner or would I be better off getting a good doublet like the faithful SW Evostar and learning the ropes with that? I sometimes wonder if the extra expense is justified with the English air and LP!

Thanks for looking.

Jim

[MattJenko]

It depends on your budget. For GT81 prices (+ flattener), if it was me, I would buy the Star 71 instead. No flattener needed, proven and a wider field of view. If it is 80mm +- 1 or bust, then the TS PhotoLines looks lovely (same as Altair Astro ones I believe) and the Skywatcher Esprit seems rather nice too at a little more. I have the ED80 + flattener and like it and don't regret it, but given the extra funds, it would be the Star 71 for me.

As for if they are worth it, it depends again If a cheaper OTA means you can get a better camera sooner, then I would do that (it is what I did).

As for balance, there is very little a longer dovetail cannot sort out.

[Jimtom]

Thanks for the f/b Matt, yes, the Star 71 does look good with no need for a flattener plus it's fast. In even more of a quandary now. The SW80ED plus FF is in budget for me, the triplets aren't really but ........... Well , it is Xmas coming up

[Demon Barber]

Hi ,you will not have any problems balancing the GT81,i have had one since they were released,just take you time with which ever scope you go for,

Regards

Mike

[Jimtom]

Hi ,you will not have any problems balancing the GT81,i have had one since they were released,just take you time with which ever scope you go for,

Regards

Mike

Thanks Mike, do you use a DSLR or CCD on it? Were there any probs with back focus etc? I've heard that spacing of FF is critical on fast refractors like this.

[Demon Barber]

I have used both and not encountered any problems,both with a canon 500d and an Atik16osc ccd.

Regards

Mike

[Jimtom]

I have used both and not encountered any problems,both with a canon 500d and an Atik16osc ccd.

Regards

Mike

Thanks Mike.

[ollypenrice]

I'd have the Star 71 any day if it's in budget. Fast with a big flat field and great colour correction from the images I've seen.

You can always balance a scope provided you have a long dovetail on which to offset it in Dec. It may be necessary to mount the OTA upside down or at an angle in order to get at the focus lock and other focuser bits but the lenses are round so no worries!

Olly

[Erquy]

hi,

i have the gt81 on avx and love it, great combo, easy and portable in/out garage on few meter (all together, included camera), and more than happy on what i get with the sx694/mini fw/ lodestar and 0.8 FF, it is indeed difficult to balance using the original short vixen type dovetail as supplied, the camera/ff/fw is heavy and while extending to 7cm the focuser, it makes it back 'very' heavy if one use the original dovetail. you simply need to buy a longer dovetail (no need to 'replace' the original dovetail, simply add it under, there are screws under the original -in fact need as well if you want to reach easily the locking screw on the focuser -if you do not want to turn it-. otherwise consider ring set up. below example in narrow band and rgb

https://www.astrobin.com/201680/C/

https://www.astrobin.com/full/202339/0/

i cannot comment if you may face problems with only a dslr at the back without any FF

[JR1987]

hi,

i have the gt81 on avx and love it, great combo, easy and portable in/out garage on few meter (all together, included camera), and more than happy on what i get with the sx694/mini fw/ lodestar and 0.8 FF, it is indeed difficult to balance using the original short vixen type dovetail as supplied, the camera/ff/fw is heavy and while extending to 7cm the focuser, it makes it back 'very' heavy if one use the original dovetail. you simply need to buy a longer dovetail (no need to 'replace' the original dovetail, simply add it under, there are screws under the original -in fact need as well if you want to reach easily the locking screw on the focuser -if you do not want to turn it-. otherwise consider ring set up. below example in narrow band and rgb

https://www.astrobin.com/201680/C/

https://www.astrobin.com/full/202339/0/

i cannot comment if you may face problems with only a dslr at the back without any FF

I have a gt-81 on order so im glad this has come up.

Could you possibly post a photo of your gt-81 and how you have got it balanced correctly adding the extra dovetail? I want to have this sorted before it arrives so im not stuck! 

[salas]

I really need to try the longer dove tail bar option, I've been adding various objects to the front of my GT81 to balance it using bungee straps - including a can of Fosters, which is a well deserved beverage as a bonus after a hard night imaging! 

Just beware if you buy a new dovetail bar to screw straight through it in to the bottom of the scope ring it will need to have countersunk holes in the bottom to accommodate the Alan head screws or it wont fit in the mount saddle, as I discovered the hard way.

[Erquy]

here it is

[JR1987]

Thanks for that, Ill look into getting an extended dove tail..

Makes me laugh how these companies want £50+ for a small block of metal with some holes in it.