SCT focusers are attrocious! - Page 2

Poita (Peter) · #21 07-12-2011, 08:34 AM

Whether SCT, Newt, RC or refractor, it seems in the consumer space that the standard focusing option included almost always could use replacing.
I added a cheap GSO crayford to the back of the Meade 10" and never looked back. I lock the mirror and use the crayford for fine focus and it is rock solid.

toc (Tim) · #22 07-12-2011, 09:16 AM

I agree they are pretty bad - my 12inch Meade SCT has not only mirror flop, but runaway focus - when you move the focus anti-clockwise, it will slowly drift out of focus all by itself. I suspect I need to open it and lube up the shaft. (ew, that sounded wrong)

For any sort of planetary imaging, the stock focusers on the larger Meade SCT's appear pretty useless. My old C8 focusing was great - light as a feather, and almost no mirror flop.

rainwatcher (Peter) · #23 07-12-2011, 09:34 AM

Some interesting replies here, it really does seem like luck of the draw.
As for locking the mirror there is no facility on the C8, and if you lock it how can you microfocus it, implies there is enough slop in the lock for some micro movement.
Anyway i have found that my C8 original (and of couse horribly expensive) DC dec adjuster fits and i am first going to try that just to see if it it will hold good focus. Of course its a single speed so i would have to take it off and on after rough focus.
Then i am gong to strip the back end and check the adjuster plate, connection and lube.
I am also still keen on the GSO 10:1 crayford - at $99 its a bargain and i will feel more comfortable adjusting the eyepiece than the whole mirror.

koputai (Jason) · #24 07-12-2011, 09:41 AM

So it looks like the options for my LX50 vintage Meade 10" is either the Feathertouch microfocuser upgrade to the standard system, or lock off the mirror somehow and add a proper focuser like a Moonlite/Feathertouch/etc to the back. I think I will head in that direction.

Thanks everyone.

Cheers,
Jason.

Poita (Peter) · #25 07-12-2011, 10:07 AM

I can send you my GSO unit to borrow for a week if you want to try it out.

Poita (Peter) · #26 07-12-2011, 10:09 AM

Quote:

Originally Posted by toc

I agree they are pretty bad - my 12inch Meade SCT has not only mirror flop, but runaway focus - when you move the focus anti-clockwise, it will slowly drift out of focus all by itself. I suspect I need to open it and lube up the shaft. (ew, that sounded wrong)

For any sort of planetary imaging, the stock focusers on the larger Meade SCT's appear pretty useless. My old C8 focusing was great - light as a feather, and almost no mirror flop.

On my 10" meade the standard focusing had none of those issues, but I went to a crayford for the fine control, and because it is what I am use to on the refractor anyway. It makes a nice upgrade whether the SCT has issues or not really.

koputai (Jason) · #27 07-12-2011, 02:32 PM

Does anyone have a link to a site with teardown instructions for SCT's? Or how-to's on servicing the focuser?

Cheers,
Jason.

Karls48 (Karl) · #28 07-12-2011, 06:36 PM

An other possible solution is to replace plastic washer in the focuser with trust bearing. On my LX90 it improved mirror shift considerably. I cant say if it was the bearing or re-greasing. I did use Peterson EZ focus kit but you can use just right size trust bearing.

koputai (Jason) · #29 07-12-2011, 07:40 PM

Quote:

Originally Posted by Poita

I can send you my GSO unit to borrow for a week if you want to try it out.

Thanks Peter, that's very kind of you. I think though, that with a GSO being worth under $100, the postage here and back would be a waste.

Regards,
Jason.

rainwatcher (Peter) · #30 07-12-2011, 08:11 PM

http://ngc1514.com/Celestron/disassem.htm

has a dissasembly page.

marki · #31 07-12-2011, 11:32 PM

On the LX200R/ACF tubes you can remove the original focuser knob (grubscrews in the end) and there is a nut underneath. If you do this right up then back it off about 1/8th of a turn it will remove a lot of slop from the mechanism only really leaving free play between the baffle tube and mirror to worry about but this is minimal. Only problem is that the focusing action can become very heavy and you need to find a balance between slop and focusing action which means mucking around with the adjustment for a bit. I did this when I first got my Meade with good results but have now switched to a feathertouch microfocuser and a moonlight stepper crayford. For visual the FT is ideal, for AP the moonlight takes over.

Mark

rainwatcher (Peter) · #32 08-12-2011, 11:26 AM

I am sure you must all be getting bored with this subject by now, but i have had a minor win. I stripped my focuser on the C8 and did as suggested in most of the posts, moved the object through all its travel to redistribute the grease. One thing I did notice is that the bearing on the shaft is at least 6 mm diameter smaller than the machined bore it goes in. It is located in place by the three screwed plate that locks it in. I am not sure if this is good design, in fact I know its not. However I centred it the best I could and locked up the plate. The wobble was noticeably less, still worse than my standard Newtonian focuser, but if I were only doing visual I would accept it. My main interest is photography so I will be buying the GSO Crayford.
By the way I have given up on my JMI/Celestron Dec motor option for focusing as the electronics for it are interconnected into the DC drive of the scope and I have been spectacularly unsuccessful in finding a circuit diagram that I can use to redesign. It may be surplus to requirements anyway as I don’t like it, and will be replacing it with a stepper motor system of my own design and build.
On a final note I am looking for something to de-dust the front of my C8 corrector plate and also something to clean my eyepieces, which my photography is showing up as quite dirty, one lens seems to have what looks like little water marks on it. Any advice .

Damian Couzoff (Damian) · #33 08-12-2011, 09:26 PM

I use a Bintel Crayford (2 inch) 10:1 SCT focuser on my CPC 1100-11 inch.It works very well on high power/visual planetary.The standard focuser worked well enough,but the crayford is easier to fine focus at high power.

multiweb (Marc) · #34 13-12-2011, 06:59 PM

Quote:

Originally Posted by GrampianStars

J

Here's all you need to do...........
a mirror lock..
http://www.isomedia.com/homes/cvedel...mirrorlock.htm

All your troubles will begone

This is quite clever actually. Locking the focusing arm rather than the mirror. On my C11 I have mounted 3 bolts spaced at 120 degrees that hold the mirror once in focus. It does a good job but you can tilt the mirror if you apply the slightest pressure on one side or even defocus the whole field. With practice you learn to get the mirror a bit lower out of focus then push it back up to focus with the three lock. It seems to hold better with a little pressure. It's a big chunk of glass anyway and it would take quite a lot of pressure to degrade the image quality.

In the end best focus is of course achieved at the visual back with a good quality focuser. But you can't use one with an hyperstar so having a feather touch micro-focuser attached to the primary is also a must.

koputai (Jason) · #35 13-12-2011, 07:21 PM

I've made and fitted the spring loaded gizmo, will see how it goes if the skies clear. Have also bought the GSO focuser, which I expect to be a lot better.

Cheers,
Jason.