WO GT81 and Esprit 80 for AP

[Andyb90]

Hi Everyone,

I've been reading up on these scopes here and on other forums. 

They have similar f/ratios and focal lengths (when 0.8x reducer is used with GT81) and both seem to get good reviews.

Their flatteners/reducers also appear to be specifically matched to the scopes.

I would be purchasing from FLO. I'm really keen on the check and tune offered.

Do you think there is anything to choose between them for AP?

Andy.

[Pig]

ooops wrong widow

[Skyline]

I think I would be slightly more inclined to buy the skywatcher esprit 80 due to it been faster then the GT81.

[Andyb90]

I'd use the gt81 with the 0.8x reducer. So it would be f4.7 compared to f5 for the esprit. So very little difference between them.

Andy.

[Uranium235]

Do a spot of research first to see which one has the largest corrected field (I'm inclined to go with the GT81 in that respect).

[Andyb90]

I found some info in the Esprit manual:

The Sky-Watcher ESPRIT 80 Field flattener has been specifically designed for your

telescope. It guarantees excellent field flatness across the entire 33 mm imaging plane

and ensures full illumination with extremely minimized halation and zero color fringing

even on bright objects

The only reference I've found to the gt81 imaging circle is on a site called cyclops optics, where it states 40mm. It doesn't say anything about correction though.

Also looking closer at the Esprit 80 I can't see if the mounting shoe is removable. I'd want to mount the scope with tube rings on a losmandy plate. I would then have a dovetail bar on top of the tube rings with guide scope rings bolted to it.

I also see the Esprit 80 dew shield is fixed, so even if I can remove the mounting shoe the tube rings would be quite close together. I think I'd prefer to be able to spread them a bit further apart for more stability.

Andy.

[Andyb90]

I'd more or less made up my mind to get the gt81 with 0.8x reducer.

But I input the scope, reducer and the asi1600mm cool camera, which I just ordered, into the ccd suitability tool.

The result is 2.05"/pixel with OK seeing, which the calculator says is borderline under sampling.

Would this be okay or could it be a problem?

Andy.

[ronin]

2" is pretty reasonable. It seems that there are many idea of the ideal arcsec to pixel ratio. I have read anything form 1" per pixel to 5" per pixel. On that basis 2" seems reasonable. I think SBIG say 1" per pixel. The area of arcsec:pixel seems "flexible".

[DaveS]

2" per pixel is fine. Pinpoint reported 2.04 for mine and I've never had any problems.

[Andyb90]

Good to know there shouldn't be an issue with under sampling.

The GT81 reducer is push fit and it looks like the scopes focuser has 2 compression screws. I'm wondering if that will provide a solid enough connection with spacers, filter wheel (SX USB) and camera (ASI1600mm cool) connected. Or should it be okay?

The only other option I can think of would be moving up to the Esprit 100 ED, with the flattener that has an M48 thread. So potentially the whole lot could screw together. Although I'm still unsure then how the camera could be rotated for framing. I assume some kind of additional adapter would be needed to rotate the camera?

I must admit moving to the Esprit 100 would push my budget to the limit and it seems quite a drastic option.

Any advice on the above would be greatly appreciated.

Andy.

[Andyb90]

I contacted flo about the push fit connection with the gt81 and it will be fine.

Does anyone know if the gt81 or Esprit 100 have tilt adjustment?

Or is such a feature not necessary as I see FLO sell tilt adjustment adapters.

Andy.

[Andyb90]

I'm now considering the WO FLT 98 as a possibility too. It's a bit lighter than the Esprit 100 and has a 3.5" R & P focuser. There is also an adapter to form a threaded connection to the WO reducer/flattener 4. The f ratio with reducer looks good at f5. The scope also gets very good reviews from what I've read so far.

Would be good to hear of anyone's experience imaging with the scope and reducer.

Andy.

[Andyb90]

After much consideration I ordered the FLT98, but unfortunately it's been discontinued 

So I'm now considering the options again.

Originally I liked the WO gt81 but was a bit put off by the push fit connection to the focuser. I prefer a screw fit connection.

Has anyone used a gt81 with a Baader Steeltrack Diamond focuser? I see the one for refractors that FLO sell has an adapter with T2 thread.

https://www.firstlightoptics.com/baader-diamond-steeltrack-focusers/baader-steeltrack-diamond-rt-for-refractors.html

So I'm wondering if this would enable me to achieve a threaded connection with the gt81.

Andy.

[steppenwolf]

FLT 98 discontinued? WO must be nuts! This was one of their finest products .........

[Andyb90]

2 hours ago, steppenwolf said:

FLT 98 discontinued? WO must be nuts! This was one of their finest products .........

Yes, I'm absolutely baffled. I've not seen a negative comment about the scope.  

Andy.

[morimarty]

I'm really suprised to here the Flt98 is discontinued, its not that long ago it was revamped with the excellent 3.5" rack and pinion roto-lock focuser,very strange decision to my mind. If I was you Andy, I would ring Flo to see if they can in some way manage to get there hands on one for you. If not the price of mine as just trebled.

[ronin]

Maybe not quite so overly strange, although the FLT98 has a big reputation, but WO also produce the GT102 which is another FPL-53 triplet. That is in a way one company producing 2 scopes that are only 4mm difference and the general specification is very similar.

The WO shop does not list the 98 in the FLT series, just the 132 and 151, and the GT 102 is listed as Out of Stock - note this is direct from WO so retailers may/probably will have stock of the 102's I would half expect.

Likely someone will still have an FLT-98, try Ian King, Widescreen and then ones like TS and AST Optics.

[Andyb90]

On 03/09/2016 at 15:28, ronin said:

Likely someone will still have an FLT-98, try Ian King, Widescreen and then ones like TS and AST Optics.

Really want to order from FLO, especially with the check and tune being available. I'm currently re-considering the Esprit 100. Also I'm checking with FLO if I can use a Steeltrack focuser with the gt81 to achieve a threaded connection between scope and reducer.

Andy.