Advice on SCT Focuser

[E_ri_k]

Hey guys. I'm thinking of buying a GSO RC 10" or 12". I'd like a good motorised focuser, because I have heard that the standard ones aren't fantastic. I am under the impression that the Moonlight and JMI are good. Anyone using one of these, or is there anything else I should be looking at?
Thanks
Erik

[trent_julie]

I own the RC8 and I replaced the focuser with a moonlight, I haven't looked back. I found the fitted focuser to be a bit sloppy.

Trent

[roughy]

I too have a Moonlite on my RC8. Rock solid and worth every penny.

[E_ri_k]

Awesome, I have been thinking really hard about the moonlight over the weekend, and I think its the way to go. Thinking of adding the Hi-Res stepper and micro controller to it also. Does it thread straight onto the back of the OTA? No need for adapters, etc?

Erik

[allan gould]

I have a motorized focuser (Moonlight) on my GSO 10" RC and it's beautiful. But be aware that the new moonlights have a DC motor option which is NOT controllable from a PC only by a hand paddle.

[allan gould]

If you purchase the focuser and controller at the same time all fixing threads for mounting are present in the focuser base plate to accept these motors. The high res stepper is the way to go for PC control.

[Poita]

I have a moonlight and a TCF-S (http://www.optecinc.com/astronomy/catalog/tcf/tcf-s.htm)
and I prefer the TCF over the moonlight for photgraphic work by a considerable margin.

[E_ri_k]

Thanks Allan. I looked at the different options, including the DC manually controlled motor.

Peter, what is it that makes you prefer using the TFC-S over the Moonlight for photography?

Erik

[Poita]

I find the temperature monitoring makes a big difference with my setup, and I find it much easier to achieve perfect focus with it. It is a far more compact unit as well compared to my moonlight, but I'm not sure if that is the case with current models.

[E_ri_k]

Thanks Peter. The current Moonlight I am looking at also has temperature compensation. I looked at the Optec focuser, and it also look very nice, and as you said probably a bit more compact, in regards to the where the motor is fixed. And for pretty much the same price, I'm stuck between the two! I imagine they would be pretty similar performance wise. I think I'm leaning towards the moonlight at the moment.
Maybe a silly question, I understand how temperature changes affect focus, but how does the temperature compensation operate with these focusers? I am assuming there is a temperature probe, and the software knows the expansion/contraction properties of the Aluminium and adjusts the set focus by measuring the temperature differences, and calculating how much the focus may have changed by?

Erik

[Poita]

If you want to borrow my Optec, just drop me a line and I can box it up and send it to you.
As for the compensation, you effectively 'train it' and store the parameters in the controller. I have mine setup and trained for my two different scopes.

From the manual:
"A simple learning procedure is used to find the temperature coefficients specific to the user's telescope system. The TCF-S and TCF-S3 systems allows for two different coefficients (corresponding to two different f-ratio configurations) to be calculated and stored in the controller memory. Once learned, either coefficient can be selected with a simple slide switch. A manual mode allows the user to set the focus manually at any time. At the end of an observing session, the TCF-S focuser remembers the last temperature and position. When the unit is turned back on for a new session, the TCF-S computes a new position using the current tube temperature and moves to that position. Assuming no changes to the optical configuration, the object will snap into sharp focus."

http://www.optecinc.com/pdf/tcf_technical_manual.pdf

My moonlight unit doesn't have that capability, the newer ones might. The model in your Picture is for PC control only and doesn't have a hand controller as far as I know.

[E_ri_k]

Thanks Peter. That is a very generous offer. I am heading overseas in a couple of weeks, for 1 month, so I might give it a miss for now, but I'l certainly let you know when I come back.

Erik

[PeterM]

Unless you are using an LX200 GPS in which case a 3.5 mm jack cable can plug straight into the LX200 panel and then be controllable through SKYX.

[Poita]

Sure thing, the offer will still stand when you get back :)

Where are you off to?

[Sirius1066]

Very interesting thread guys.

I have just started thinking about getting a motorised focuser for my new 8" LX90. But I know less than nothing about them. Any tips?

E

[Poita]

For visual or photogrpahic work?

[Sirius1066]

I'm really only into visual work at the moment, but will be starting to have a look at astro imaging in the near future.

[E_ri_k]

Thanks Peter. heading to Sweden with my wife and 1yr old, to visit my mum. will be nice. looking forward to the european summer!
Erik.