Crayford-style focuser for LX200

[Rodstar]

For all those LX200 (and other SCT) owners out there, I would appreciate your comments.

I have been fairly non-plussed with the image shift problem with the coarse focus knob, and I find that the microfocuser is too slow and cumbersome for visual work. I don't do any imaging yet....just enjoying getting to know the sky and exhausting (NOT) the GOTO catalogue.

Non-SCT peers (especially Mike) are always commenting on how crappy the coarse focuser is on my scope - too abrupt, hard to get a sharp focus, and prone to heavy mirror shift. I also have noticed the huge difference when comparing with some Dobs with a crayford focuser which are so much easier to focus, much more subtle, etc.

Last night I had a turn with Louie's new Williams Optics crayford style focuser in my LX200. No more mirror shift! It was fantastic. You just screw it on in place of the microfocuser. Sometimes you need to use the coarse focuser to move the image to a point where you can then have enough travel to use the crayford focuser, but that is easy to master. One other issue that arises is that the attachments are so long that the OTA cannot point to the zenith without hitting the bottom of the fork. I am aware that I can program my scope not to do that...so no need for any advice on that (yet).

I am just interested to know if anyone else has come to the same conclusion as me, and is using a crayford style focuser on their scope? If so, I'd be interested to know what type of crayford focuser you use, and how you have found it for pinpoint focusing. What did you pay? :shrug:

[beren]

Yeah Rod ive been thinking about it for a while and pondering the WO or other aftermarket types , its a shame Meade didnt come up with a manual adjustment on the microfocuser . Ive toiled with a mod that helps make the coarse focuser a tad easier to use but its still a pain , thanks for the post sometihing to think about .

If you have a wedge pointing at Zenith wont be a problem just transfers the problem when pointing south :P

[[1ponders]]

Hi Rod.

I felt the same as you about the meade microfocuser so when I bought my new 8" I got the JMI NGF CM Motorized Crayford type focuser. Its focus travel is only about 25mm so you still need to coarse focus, but its a sweet little focuser. And from what I remember of the meade, the JMI doesn't stick out quite as far.

It is a two speed focuser, simply hold the button and after a few seconds the second speed kicks in. It comes with manual focus knobs, so you can use it manually, but if there is one thing I would pick as a negative for this focuser this is it. To use it manually you loosen a thumbscrew on the bottom of the housing which lowers the motor and disengages the gears. Unfortunately you have to pretty well unscrew it the whole way after doing it the first time. After loosening it the first time and then tightening it up again I don't feel that the motor housing seats back into the same place. The motor focuser still works fine and the gears mesh nicely, but at a slightly different position than originally. Its not hard to hold the drive gear out with you thumb while you screw in the screw to get it back to its original position, but I though I'd better mention it to you.

It also has less backlash than the Meade Microfocuser which I found a pain when trying to get accurate focus using a focusing program.

it's about $500 bought in Aus and about $350 US I think if bought OS. Warning though, when I received mine and opened the box it had a bend focusing shaft on the manual knobs. Luckily I bought mine in Aus and was able to send it back to get repaired. It still worked fine bent, but that was beside the point. Oh there was no obvious damage to the box and the box had not been opened by my supplier here in Aus, so it was originally shipped that way.

Last point. The JMI NGF CM can be used to autofocus when you use a program like DSLR Focus. The meade can as well but the backlash is much more of a problem

Hope thats helped

ps. If you're don't want the motorization, then the manual focus is pretty sweet on its own

[Striker]

I have the identical Focuser as Paul has just said....I actualy find I dont need it...I dont find the mirror shift that bad and due to this I dont use my Electric JMI....

It may be up for sale soon.....Virtualy brand new and used about 4 times.

Model is JMI NGF CM

[[1ponders]]

Keep it Tony. If you ever decide to go the whole hog and get a dedicated CCD astrocamera YOU WILL NEED IT.

[Rodstar]

Thanks guys for the comments. I think I'll get a manual focuser to begin with - the Williams Optics one is very good, cost through Frontier Optics about $260.

I have noticed in the glossy Meade catalogue that came with my LX200 that Meade does have these focusers, but for refracting scopes. Maybe they could be compatible...hard to tell from the brochures.

I wonder if the design of the RCX400 has addressed the issue of image shift? If it hasn't, then someone at Meade needs to sit down and sort it out.

[[1ponders]]

The JMI focuser will fit to refractors. I've used mine briefly on my 4" just to confirm. I still had to rough focus with the R&P and then finish with the JMI. The JMI comes with the required adapter. But you should already have it. Its the SC adapter that comes with the microfocuser that is used to attach focal reducers etc. Just remove the 2"-1.25" adapter from the 2" focuser of the refractor and slip the SC adapter in, in its place. Works a treat.

[beren]

Rod what about trying this before outlaying the cash

http://www.scopestuff.com/ss_foc1.htm

or a homemade type

http://www.users.bigpond.com/lansma/proj_focuser_mod.htm

i find it helps

[Rodstar]

Beren, they look like great ideas for finer control, but are still susceptible to image shift.

[iceman]

It's true, I have :D I just never felt comfortable using the focuser on Rod's scope.. every time you touch it the image shifts back and forwards and there's no fine control so it goes from in focus to out of focus really quickly - I never felt confident that I'd achieved the crispest focus.

I know the microfocuser is there, but Rod has a bias against it since he broke it in the first week of owning the scope :) The crayford he used on Saturday night was a 100% improvement. A fine focuser would be even better, but at a cost of course.

I'm not sure whether moonlite do one for SCT's - they talk about refractor focusers (http://www.focuser.com/cgi-bin/dstore.cgi?category=Crayford+Refrac tor+Focusers) but they don't mention LX200's.. does anyone know if they would fit?

But their dual speed are tops, that's what I use.

Anyway i'm glad you're gonna get it sorted out Rod, you'll be very happy you did.

[Rodstar]

I'd almost forgotton than incident Mike!! Look like the moonlight brand are no cheaper than Williams Optics...better the devil you know....I've placed an order with Daniel (Frontier Optics)

[[1ponders]]

A couple of the moonlight focusers for refractors will fit (can't remember which ones).

[rumples riot]

Hmm, interesting Idea. I have noticed that image shift has got worse in the last 6 months or so. Probably because I have the scope under tarps outside permanently now. However, something like that focusor would be better than the iritating coarse focusor.

Given me some ideas.

[atalas]

Guys I had read somewhere that the grease on the shaft the mirror moves on needs better grease and replacing after a while,thats why the mirror shift gets worse. If cleaned and replaced whith better grease you can reduce the image shift to nearly nil. Don't know how true this is never tried It .


Louie :)

[[1ponders]]

Here's some information from Ron Newman from Moonlight Focusers re SCTs

Quote:
MoonLite CS model SCT Focuser Installation and Maintenance
Features
Both models, the CS1 (single rate) and CS2 (dual rate) 2” Crayford style focusers are designed to be used with SCTs. The ¾” travel drawtube along with the 5 lb load rating makes the focuser ideal for visual and photographic use. The no backlash, no image shift, Crayford design combined with the high polished aluminum surfaces gives the focuser incredible smooth focusing action. The extreme fine feel of the 8:1 reduction unit is due to an all ball bearing preloaded planetary drive design. It is of the in-line type and features high tech (gearless), no backlash operation. The reduction unit comes in 2 versions, a 2 knob (course on one side, fine on the other) and the new tri-knob version (course on one side, course and fine on the other.) Note: Dropping on, or a hard hit on the slow motion side knob could damage the reduction unit.
Aluminum thumbscrews for the 2” draw tube and 1 ¼” adapter are standard on the regular CS1 and CS2 focuser models, however Brass compression ring style draw tube and 1 ¼” adapter are also available if heavy loads are going to be used in the focuser. The 2” to 1 ¼” adapter is an extra deep version that is threaded for 2” filters.

Installation
There are 3 different thread size interface adapters that allow the focuser to bolt on to a variety of SCT threads on the visual back. The standard 2 inch SCT thread works with all SCTs and the larger 3 ¼” Meade thread fits the visual back on larger 10” Meade SCTs and up. We are also making a large thread version for the Celestron 11” and larger scopes that have the large 3 ¼” Celestron visual back thread. Installation is just a matter of threading the focuser on, finding the desired knob position then snuging up the nylon tipped setscrews in the interface adapter. Note the 2 inch thread version has 3 setscrews and a rotating ring. The large format interface adapter has only one set screw and no rotating ring, so it requires that the focuser be screwed on the whole way then rotated back to the desired position the tighten up the set screw to lock it in position.

Adjustments
The drawtube pressure can be adjusted to each user’s preference. Increasing the pressure increases the load capacity (vertical lifting capacity) of the focuser. Decreasing the pressure lowers the load capacity but gives the focuser a smoother focusing action. We set the focuser at approximately 3 lbs. at time of assembly; however, you can adjust it to be less or more depending on your specific needs. The ideal setting is to have it adjusted so the focuser can hold the heaviest load presented without slipping and requiring no additional force. This will give the focuser the best feel and still provide the vertical lifting capacity required. Just turn the (fine adjust) aluminum thumbscrew located between the two setscrews on the bottom of the focuser to make a small increase in pressure to your liking. Or do a course adjustment by turning the 2 set screws a small amount located on each side of the fine aluminum thumbscrew. Note only a very small amount of a turn is required on the 2 set screws to increase pressure. 1/20th of a CW turn is plenty to increase load capacity when using heavy loads such as CCD imagers etc. A 5/32 allen wrench is required. Note: A small increase in the pressure adjustment is normally required after the focuser breaks in.

Maintenance
To maintain the CS focusers performance, keep all bearing and shaft riding surfaces clean. All Crayford style focusers require a clean bearing to drawtube surface for smooth operation. The drawtube has been polished to remove all machine marks and hard anodized resulting in the action having a super smooth feel. Keeping the surfaces clean will keep the focuser operating at optimal performance. Dual rate focuser owners may want to break in the 8:1 reduction unit by running it up and down when first receiving the focuser. It is adjusted fairly tight at the time of assembly and requires a little use to come up to peak performance. No maintenance should be required on the reduction unit as it is packed with lithium low temperature grease for the life of its operation.
End Quote:

Prices range from $245 - $345 US

[Rodstar]

So Paul, are you going to take the plunge and buy one? I have already placed my order with Frontier Optics :)

[[1ponders]]

Don't think so Rod. Not after buying the JMI. Though I did seriously think about it, but I wanted a motorised focuser to use with either DSLR Focus or StarMate.

[xstream]

Boy! Sure is tempting.

I wonder if she'll allow it? :prey:

Have to be careful here, SWMBO is now a member. :scared3:

[Rodstar]

John, you are truly blessed to have Anna. If only my wife would catch the astro-bug!

[xstream]

Yeah, I know Rod she is a wonderful woman and it's a pity there is not more like her, but she still holds the purse strings. :D Unless I get there before she does. :rofl: But then again I keep forgetting it is Anna's scope. :whistle:

[Rodstar]

John, if it is Anna's scope, then I think you need to do some balancing of the finances with Anne, and explain that she has already spent thousands on the scope, so the least she can let you do as a matter of equity and fairness is buy a measly focuser....one that will actually benefit her more than you because, as we have said, it is her scope....

[xstream]

Keep going Rod, hopefully she'll read this thread. :rofl:

[Starkler]

Interestingly , I beleive the WO crayford is the exact same one sold by Guan Sheng fitted to the GS dobs. Anyone who owns a GS crayford will notice that the main body attaches to the base with grub screws. I beleive the crayford is designed to fit different bases for different applications.