LX 200 focusing fixes

[h0ughy]

After speaking with Mick Pinner and others i found this item
for the LX200
Primary mirror stabiliser and lock
Reduces mirror flop and focus drift on 10",12" and 16" models - $25.79 (£13.60 - €19.04)
This simple spring-loaded shunt screws in to the main mirror support from the rear of the LX200 through the transit screw hole, and provides a controllable thrust tension to the mirror. The stabiliser will reduce mirror flop/sag and image shift during focusing, and provide a more positive action to focussing by reducing sluggishness. All components are precision turned from aluminium, acetyl and stainless steel. Simple fitting in less than 10 seconds with full instructions included. Based on a design suggested in the MAPUG files.

[atalas]

Mr Gadget ! there is one other issue that hasnt been mentioned .

How do you know the main mirror is squared of to the corrector plate ?

Looks good though .


Louie:D

[h0ughy]

good question Louie?

Haven't a clue but I will be chasing it up as soon as I can. Sound good though!:)

BTW you are so cruel calling me Mr Gadget. :sad:

[Orion]

Hey someone is paying out on H0ughy for a change!..........sorry of the subject.:D

[h0ughy]

I also found some more information here
Its a bit long but should be OK. Rodstar may need to take note as well.

http://www.isomedia.com/homes/cvedeler/scope/mirrorlock.htm

Subject: Mirror Stabilization Bolt --part 1 of 3
From: Chris Vedeler

As I'm sure most of you know, a SCT focuses by moving the primary mirror up and down inside the OTA. The mirror is mounted inside an aluminum or steel mirror cell that rides on the central tube (where the light comes through) inside your scope which you can easily see. This mirror cell is moved by screwing up or down on the focus knob. As far as I know, there are only 2 points of contact with the mirror cell, the central tube and the focus screw. Since the central tube is a nicely machined match for the mirror cell hole, and they use special grease the mirror cell doesn't move from side to side much at all, but it still moves a tiny bit (giving a slight image shift). There is an inherent slop in the focus screw that can only be improved upon by machining a better focus screw. When you change direction with the focus knob, you have to make up a tiny bit of slop in the screw before the top of the teeth of the screw engage with the bottom teeth in the mirror cell or visa versa depending on the direction of the focus. If you have ever played with a bolt and a nut from the hardware store, you know that there is a tiny amount of play when the nut is screwed onto the bolt. The same thing is happening inside your SCT.

When your 10" or 12" SCT first arrived from Meade, the mirror cell was locked down to avoid problems during shipping. This is done by moving the mirror all the way to the back of the OTA and screwing in a 1/4" screw through the hole right next to the focus knob. When this is done, the mirror cell can not move at all (which is what you want when shipping in case UPS drops it). When you are focused using normal eyepieces and cameras, the mirror cell is actually about another inch or two deeper inside the OTA. The original shipping screw that came with your scope is not long enough to reach the mirror cell now. The mirror (inside the aluminum or steel mirror cell) is now "floating" on the central tube and is adjusted by a screw mechanism that is controlled by the focus knob. Given the design of this type of focusing mechanism, a little movement is inherent and unavoidable.

I got my idea for my mirror stabilizer from Randy Rubis:
<http://www.look-inc.com/rrubis/mir_loc1.jpg>
All I really changed from his design was adding a compression spring in between the wing nut and the spacer. In theory what you are doing is locking down the mirror cell just like you would for shipping, except the mirror is not moved all the way down to the bottom of the OTA. This requires a longer screw. It takes about a 2" or 2.5" screw just to reach the mirror from this hole. The reason you need to use a 6" screw is so you can clear the focus knob (i.e. about 3 .5" outside the OTA). It is necessary to have a nice tall spacer so that you can turn the wing nut above the end of the focus knob (imagine trying to screw a wing nut between the focus knob and the back of the OTA.)

I've tried to remove the backlash per Meade's instructions as well, and it really didn't do anything either. Unless it is really, really bad, I wouldn't bother. I put pictures on my webpage:

<http://www.isomedia.com/homes/cvedeler/scope/mirrorlock.htm>
Clicking this link should evoke a new browser window.

Subject: Mirror Stabilization Bolt --part 2
>Okay, I have some pretty simple questions. Sorry if these are rehashed questions, I just need some clarification.
>To make my mirror stabilized, I need the following?
>1) one (1) six inch long, 1/4 inch thick, 20 thread bolt.
>2) one (1) wing nut for the 1/4 inch bolt.
>3) two (2) one inch tall nylon spacers.
>4) one (1) three inch long, 1/4 inch internal diameter compression spring.
>
>Then, I assemble them like this?
>1) Take 6" bolt and thread on wing nut.
>2) Sleeve on one nylon spacer
>3) Sleeve on the compression spring
>4) Sleeve on the second nylon spacer
>5) Screw the entire assembly into the focus locking bolt hole one to
> two and a half turns. Is this correct?
You almost have it. One thing I did different. The spring goes between the wing nut and the nylon spacers, but I guess it would work your way too as long as you clear the focus knob. I've used just one 1" spacer with some success as the spring is anywhere from 3" to an inch depending on how compressed it is. I got the other spacer just in case. Ultimately the spacers are just a way to clear the wing nut past the focus knob.

> Okay, I'll assume this is correct. Now what?
> Do I focus as usual and then, when I've gotten as close as I can get,
> I screw in the bolt assembly inorder to stabilize and then make minor djustments?
Once it is installed (remember, don't thread it in more than a turn or two into the mirror cell!) with the spring uncompressed you focus as normal. Once you get close to focus, screw down the wing nut until you compress the spring to about one-half it's original size. This puts a gentle and controlled pressure on the mirror cell that keeps in place. Then do the final focus. You will find the focus behaves much more predictably, smoothly and stops on a dime (the way it should from Meade, but doesn't). If you move the focus a whole lot (add a barlow, different camera adapter, add focal reducer etc.), make sure you watch the spring, as you don't want to compress it all the way or you could damage your focus mechanism (just like you don't want to try and move the focus when the shipping screw is installed). The spring makes this a lot safer, but you still want to be careful.

> Or, do I just begin the night by screwing in the bolt in 1 to 2.5
> turns and let the spring take the tension away from the mirror when I focus?
If you aren't changing focus drastically, you can just leave it in all night. One thing though, I do remove it when I am packing the scope up for the night. It does stick out a ways (3" or 4" from the back of the OTA), and is directly connected to the mirror cell inside the OTA. I'd hate to bump it and do damage to the mirror or mirror cell!

> This brings me to my final question. Does this bolt thread into the
> locking bolt hole, or does it just slide into the hole?
The locking bolt hole is not threaded, it is just an access hole to get to the mirror cell female threads inside the OTA.




Subject: Mirror Stabilization Bolt --part 3 of 3 (Mirror Locking Bolt's Effect on Collimation)
From: Bruce Dickson <bdicksonmweb.co.za> Date: Sep 2003

I did some experimenting with a mirror locking bolt (as originally proposed by Chris Vedeler).

I've been doing some planetary imaging using a webcam, and based on comments by Thierry Legault, I decided to check my collimation just before I started up the camera.

I was quite surprised - although the mirror lock bolt kept my mirror static, it twisted so much that the collimation was rubbish. I found that I achieved far better planetary images without the "stabilised mirror". Although I tried, I wasn't able to achieve acceptable collimation with the bolt in place.

I've also found that the mirror "flop" was sufficiently repeatable that provided I _always_ focus in a clockwise direction, the object will return to the centre of my webcam's field of view, even at f/45. (The direction might is different for the 7", 8"and 10" LX200s.)

That's not to say stabilising isn't useful for _long_ exposures, it's just that for high resolution imagery on low contrast objects, perfect collimation is far more critical.

[rumples riot]

Houghy you can test for this really easily, just use a collimation tool and insert it into the rear of scope and look in. You should see the mirrors' ringed and non should be cut off on the outside. Second then do a star test and if you had good collimation before then it should be still good. If it is bad then you know that this has affected collimation.

So do the rings test first. If that is fine then do the collimation test. If collimation is out then readjust collimation. If the first test fails, then I would reconsider using this product.

However, I would think that this product has had good reviews and works fine.

For my interest is this only for use on a Standard LX200 or can it be used on the GPS version? The GPS version has a mirror lock knob but it does have that little hole in the same place.

[h0ughy]

Not sure yet Rumples, I am looking into that one!

BUt I am sure I have found a fix for my 12" classic

[Rodstar]

Who is the supplier HOughy?

You have got my full attention.

[h0ughy]

rodstar

the original contact is here


Contact us
For enquiries relating to products or orders, please contact Metal Planet using any of the following methods:

Telephone: +44 1353 699 859
(24 hours call back service in operation during out-of-hours)

Fax: +44 1353 699 996

E-mail: sales@metalplanet.us

Postal address:

Metal Planet
The Gatehouse
Straight Furlong
Pymoor, Ely
Cambridgeshire
CB6 2EH
UNITED KINGDOM

For the latest news from Metal Planet join our mailing list. We'll keep you posted on all the latest additions to our product line along with other exciting astro developments.

but the american link is as follows. I think the exchange rate is better with the US.

http://www.digitecoptical.com/ae-accessories-meade-lx90-lx200.htm

[rumples riot]

I got my weight set from metal planet, they are good guys and their gear is very good, well engineered. Good stuff.

[Rodstar]

Thanks HOughy and Paul H. I'm going to place an order this weekend with Metal Planet if they can confirm that it can be used with an LX200GPS.

[atalas]

So Mr Gadget is out !and Slick is in. I shall try and be more sensitive Dave, and good work hunting down all that info.


Louie:)

[h0ughy]

I don't think I was really offended. the slinging off is quite a complement, and besides you have no Idea of what i didn't take to Kulnurra!:D

this is a shot of what the gadget really looks like from metal planet

[h0ughy]

I have recieved the "gadget" and will proceed in the near future to fit it.

Rodstar - FYI the order came in quickly and after reading the instructions - quote "Althought the device will fit the same apature versions of the LX200 GPS, we do not consider it worthwhile as the GPS already has a solution to the problem of primary mirror instability in the form of a mirror lock and zero shift micro focuser."

[atalas]

Hey Mr Gadget ! why don't you come and show us in person on Saturday!

Louie:D

[h0ughy]

Sorry Louie,

I have some bonus points to redeem myself from last night when i came home from the viewing night for the Merewether High Students. i basically wasn't interested in keeping a meaningfull converation with my wife, so I am in the doghouse:D

next week might be different.

PS I have just arranged to get a second hand Kendrick SCT 2" laser collimator from the US, Should have it in a few weeks!:cool:

[atalas]

It will be interesting to see how well It works Houghy!not sure why you would want one?SCT are so easy to collimate.

Louie :)

[Rodstar]

HOughy, I am very interested to see how the stabiliser works...hopefully we can catch up on the long weekend viewing night. Glad I didn't place an order, if it does no more than the functions I already have with the LX200GPS.

[h0ughy]

Sure Rod
be happy to see you there next weekend. I hope the weather keeps up the great skies