First light - Esprit 120

[Craig_]

Got my Esprit 120 out for first light last night. Guiding was not great, likely because the guiding rig I used on it was totally inappropriate for an OTA of that size/weight/focal length. (A 50mm guide scope in the findershoe, works OK on an Esprit 80, less so on the 120...)

Due to aforementioned bad guiding I had to keep subs short but managed to scrape a small amount of data up before high cloud blew in and ruined it. This is about 90 minutes only, which at f7 isn't much that's for sure.

EQ6R, ASI533, Esprit 120, ZWO UV/IR Cut.

[John W (John Wilkinson)]

Shows promise Craig. Well done.

[Fernando]

That is beautiful. Congratulations and have fun with the new scope.

[Craig_]

Thanks both, it’s certainly a meatier challenge than the Esprit 80 is!

[Robert_T]

well I'm impressed, a lot of detail and highlights balanced and beautifully framed in that square sensor. After my struggle guiding the 550mm of the espirit 100 I dont think I'm ready yet for the challenge of 840mm :-)

[Zuts]

A great image, the colours really pop and the stars look nice and round.

I am thinking of getting an Esprit 100 or 120. Is that FL 840 mm with the reducer. What guiding RMS error do you get and what guidescope are you using?

[Craig_]

Originally Posted by Robert_T

well I'm impressed, a lot of detail and highlights balanced and beautifully framed in that square sensor. After my struggle guiding the 550mm of the espirit 100 I dont think I'm ready yet for the challenge of 840mm :-)

Thanks, guiding this was definitely a challenge. I bought a ZWO OAG, but that has it's own problems with the Esprit line that I've unfortunately discovered after making the purchase...

Originally Posted by Zuts

A great image, the colours really pop and the stars look nice and round.

I am thinking of getting an Esprit 100 or 120. Is that FL 840 mm with the reducer. What guiding RMS error do you get and what guidescope are you using?

Cheers. It's 840mm with the included flattener yes; it does not serve as a reducer (the flattener that comes with all Esprit telescopes is only a flattener.) You can buy various reducers to suit, but out of the box it's 840mm at f7.

My guiding RMS wasn't fantastic on this evening, but also not terrible - about 1" RMS. This is too high for this scope as my imaging scale is 0.92" with the 533. However, in longer subs I was getting oblong stars and even in many shorter subs. I think the problem is that the guide scope I was using (Orion 50mm Mini) has a 162mm focal length and on a guide camera with 3.8 micron pixels (120MM Mini) this gave me a guiding pixel scale of about 4.8" against an imaging pixel scale of 0.92" - more than a 5:1 ratio. I just don't think this setup was adequate to actually guide it well at all, compounded by the fact I had it mounted in the findershoe (this guide scope doesn't offer any other way of mounting.)

I bought a ZWO OAG as mentioned above, but unfortunately it doesn't play well with the Esprit line, at least not without buying custom adapters from Precise Parts. Basically the M48 adapter (comes with telescope) that sits on the end of the field flattener (which delivers 20mm of required backfocus on this telescope) has quite a deep thread, such that this thread actually strikes the stalk of the OAG and does not screw in all the way, adding undesired backfocus to the imaging train. An expensive custom replacement for this FF-M48 adapter can be ordered from Precise Parts that should solve the problem, but this is just chucking more money at the issue. I am thinking I might just buy a better guide scope and mount it on the top dovetail, which should give me a good improvement in guiding performance, and just re-sell the OAG.