Focuser options for an SCT

[ChrisM]

I'm looking to upgrade the focus system on an M14, by locking the mirror and fitting a motor-controlled Crayford or rack & pinion style focuser. I don't know what traps there might be for the unwary, but I am sure that others must have been down this path before. I wish to continue doing both visual observing & get set up for imaging too.

Feather Touch have several 2" models - either crayford or R&P (eg. FTF2015BCR-RP), and I gather that the R&P is better due to its inherent design and higher price. They also have some 2.5" models which would be a bit beefier, although the large ones appear to have the same load capacity.

Optec have their TCF-S, with a slightly higher load capacity.

MoonLite offer a large variety of options in 2" and 2.5" crayford-style with various types of motor controller. I'm not sure how much of a benefit it would be, but the Moon Lite focuser can be specified to carry a focal reducer inside the draw tube.

So, are there any others brands or models that could be recommended, or are there any other considerations?

Any advice or suggestions welcome.

Chris

[Astro_Bot]

The JMI range (I think it's called Event Horizon) would be worth a look.

Baader Steel Track is a good focuser allegedly, but not sure about motorised options.

The benefit of the Moonlite draw tube-fitted FR is that it maintains the back focus distance to the imaging sensor no matter what focus adjustments you make. Whether that's of particular use to you is a personal decision.

"M14" = Meade 14" SCT? Is that ACF optics or standard SCT? If ACF, be careful with selecting a suitable FR - although my research is not complete, so far only the Optec Lepus 0.62 Telecompressor and Astro Physics CCDT67 look promising.

[icytailmark]

im about to order a Feathertouch crayford focuser for my celestron c14. They are suppose to be the best for imaging.

They also make one for meade sct telescopes.

http://starlightinstruments.com/store/index.php?route=product/product&path=37_49&product_id=51

http://starlightinstruments.com/SCT-adaptersl/index.cfm

This is a rear cell focuser so you wont get any image shift when focusing.

[asimov]

I've been using a JMI Crayford for 6 years now & can't fault it in any way.

[ChrisM]

Thanks Astro Bot. I had forgotten about JMI and hadn't heard of Baader focusers, so will check them out. The JMI SCT models seem to have only 1/2"of travel. I'm not sure if that's enough, although I guess that the mirror could always be reset to a new position to achieve focus.

Yes - I adopted the term M14 as in C14, and it is an ACF model. I have also read that the Lepus and AP FRs are the go.
thanks, Chris

[ChrisM]

Thanks Mark. Getting rid of image shift is one of my objectives! I've also read that FT might have the edge on the competition, but they are pricier too.
Chris

[ChrisM]

Thanks John.
Do you use the JMI manually or is your focuser automated? Also, is it on an SCT?

Chris

[Stardrifter_WA]

I have JMI focusers (with motor focus) on two of my scopes, one being an 8" SCT. I like the JMI focusers as the focus motor sits discretely under the focuser and doesn't hang off the side like other focusers on the market. On my 8" SCT is has a relatively low profile. The best JMI focusers are the JMI Event Horizon series.

I highly recommend them if you are just using it for visual focus and not wanting it connected to a computer for auto focusing for astrophotography, as the JMI aren't suitable for auto focus from a computer.

Cheers Peter

[asimov]

Yes Chris, I use it on my C11 SCT. Actually the focuser is motor driven but these days I just use it manually.

[AstroJunk]

You could always consider the Meade zero shift microfocusser that plugs into the scope focuser port and is controlled by the Autostar. Mine works a treat. Rather depends on the $$$ and I haven't looked them up. I'm amazed it didn't come with one - or did you go for an OTA only?

[ChrisM]

Thanks Jonathan, I got the bare bones OTA and plan to control focusing from a PC eventually. As soon as I got the OTA, I replaced the Meade focus knob with an FT two-speed micro focuser, which is good, but, there is still a lot of image shift and backlash with this arrangement. I always intended to lock the mirror and go to a crayford or R&P system of some sort, so that's what I'm researching now.

Cheers, Chris

[AstroJunk]

Which ever option you take, the mirror lock is a big help in stopping that mirror (mostly) flopping about. I'm working on a mirror stabilising solution at the moment as I am currently primarily using the standard focusser with hyperstar which is a very poor focussing solution as you are well aware! Unfortunately the well published tweek using the transport bolt doesn't work on the 14" :(

I have not tried the Meade unit with any of the autofocussing solutions yet, but it is ascom compliant and I drive the whole scope remotely using the superb PemPro Meade handbox emulator which makes focussing easy.

[PRejto]

I do not men to hijack this thread, but I have a FT 2" RP focuser on my 12" Meade ACF. Seems to work great as does the Starizona motorized focusing system.

But, I noticed something a bit upsetting the other night. Locking the mirror down changes the collimation. Is this normal? I suppose once the mirror is locked down at a certain point a recollimation is possible and hopefully would not need to be repeated very often, but this did surprise me. Cannot say I was happy.

Peter

[Starblazer99]

Got 2 moonlight units one 2” for meade 10 acf and a 2.5” for 14” EDGE HD with focal reducer one downside is they are heavy 2” with the longer flange for focal reducer fits meade reducers 6/3 & 3/3 if you use a Optec Lepus 0.62 won’t FIT in the moonlight flange, Adaptor is sold separately to fit camera & 2” eye piece does and not fit in moonlight flange other than that they are very well made remote control works well with the high resolution motor and mini controller

[AstroJunk]

Provided the mirror stays in collimation between locks you are ok. The process of clamping the mirror the central baffle may indeed change the optical alignment, especially if it was collimated pointing anything other than straight up.

Lock it, adjust it and it should be fine.

[allan gould]

I have a moonlight focuser on my 10" Meade SCT with stepper motor. It's great and I have the option of putting a FR in the draw tube. Works brilliantly.
I would contact moonlight and send an email outlining your exact requirements and they will give you all options. They now have a new FR attach,ent regime which works well.
Allan

[Poita]

I use the Optec and love it. The temp compensation works a treat and it is as solid as a rock. I have a moonlite as well, but it has sat on the shelf since I got the optec. Nothing wrong as such with the moonlite, but the Optec has proven to be more reliable in my setup.

[ChrisM]

Thanks Brian - Thanks for the feedback, and that's interesting re the Lepus FR not fitting.
Chris

[ChrisM]

Thanks for the report Allan. I believe that the guy at MoonLite is very helpful too.

Chris

[ChrisM]

Thanks Peter. The Optec TCF-S seems to get good reports with its temperature compensation, although I note that at least one of its competitors also has TC via an external probe. I'm not sure how these things work - ie. do they autonomously re-focus if the temperature changes?

Is the Optec easy enough to use in 'manual' mode? That is, for visual observing do you just have a couple of buttons (in/out) to use?

Chris

[allan gould]

Chris
I use a stepper motor controller with temperature compensation using the Sequence Generator Pro software with my moonlight focuser. Works a charm. Automatically re-focuses on a filter change and with every degree drop in temperature. Wouldn't be without it. The controller is in the DIY section of IIS by David Trewin in the UK.
Allan

[ChrisM]

Thanks Allan,
I'll check out controller too.

One other general question: Is there any compelling reason to go for a 2.5" focuser? I note that the diameter of the visual back on the Meade (and Celestron too I think) is 3" or 3 1/4 inches. I was thinking that a 2.5" focuser would be stronger, but with a downside of being heavier.
Chris

[Astro_Bot]

3 1/4" on: C11, C14, EdgeHD 925 > 1400, Meade 10" > 14"
4" on: 16" Meade

IIRC, the Meade 3 1/4" is actually 3.27" x 16tpi while Celestron is 3.29" x 16tpi (but someone might have to double check that).

As for the focuser width, for visual, there's no advantage I can see of 2.5" over 2" since 2" eyepieces are the widest you can go*. For imaging, I don't know ... thinking out aloud, with the distinct possibility of being completely wrong ... I suppose it depends on the sensor size, but that'd have to be a big sensor, and probably a short focal length tube, to produce a light cone that needs 2.5" at the base of the focuser. ... and come to think of it, the ID of the SCT baffle is ~51mm in Meade SCTs, at least in ones I've seen.


* Just make sure you're using the 3 1/4" flange, as using the 2" SCT threaded adapter will vignette the image (for widefield 2" eyepieces) due to the ID being only about 40mm in Meade and 38mm in Celestron.

[ChrisM]

Thanks Astro Bot. I found a page on on the Starlight Instruments web page giving recommended FT focusers for various types of SCT. For the M14, the FT2015 was listed (for a GEM); otherwise a much shorter draw tube was prescribed. I have also asked them if a 2.5" dia focuser would be of any advantage.

Chris

[Starblazer99]

2.5" Moonlight on a EDGE 14 with reducer only one flange available on A 2.5 large format focuser