R&P focuser trouble

cahullian · #1 25-07-2005, 05:51 PM

My cheap and nasty r&p focuser is giving me grief. When I star test I can unfocus anti-clock wise (closing the focuser) but clock-wise(opening the focuser) I run out of room to turn before the star is little more than a blurr.

I am thinking of unscrewing the large bolts that hold the primary mirror in place and seeing if the extra few mm in focal length will make any difference.

Any help in this would be much appreciated.

Gazz/Irish

janoskiss (Steve H) · #2 25-07-2005, 06:26 PM

Plug-n-Play focuser? (check thread title)

As a workaround, how about pulling the eyepiece out just a little?

cahullian · #3 25-07-2005, 06:30 PM

`I will try that but I never used to have any trouble with it before.
Fixed the P&P also lol

RAJAH235 · #4 25-07-2005, 09:24 PM

Has something moved? Like the primary!

Unless someone says otherwise, I wouldn't be loosening/adjusting the *large* main mirror screws just yet. What happened re; the collimation?

L.

rmcpb (Rob) · #5 26-07-2005, 08:20 AM

How have you been collimating the primary? If you adjust all screws eventually the mirror changes position up or down the tube. Try adjusting the primary toward the base of the tube by adjusting all of the collimating screws then recollimate and, if that works, in future only use the two closest screws to collimate and keep the third as a reference "depth guage".

Good luck

gbeal · #6 26-07-2005, 09:08 AM

I'm off in a different direction.
If nothing is loose, and little has changed (which doesn't sound correct from your post) then I would use it as is, but with an extension tube. I use them all the time, as the infocus for imaging is just not there normally.

ving (David) · #7 26-07-2005, 09:41 AM

with one of my EPs i have to pull it out a touch to focus. is it with just one EP?

RAJAH235 · #8 27-07-2005, 04:02 AM

This is a new DOB we're talking about, is it not? To start with, do these DOBs have lock screws? My Meade doesn't.( just heavy springs). Anyone? Correct info. here please. If so, then I would back them off completely, then tighten the collimation screws right down CAREFULLY & SLOWLY, in turn, till they 'bottom out'. Then give each one 2 to 3 turns out, ie; loosen, collimating as you go. When done, just nip the lock screws up a 'little' more than finger tight. Not too much. This way, you have max tension on your springs.
Am open to correction. But this works fine with mine. Haven't needed to collimate for 18 mths or more, only after cleaning.
HTH.

L.

asimov (John) · #9 27-07-2005, 03:50 PM

I'd be just doing as janokiss suggested. Or make up a ring to slide on the EP before putting it in the focuser..

ballaratdragons (Ken) · #10 27-07-2005, 03:56 PM

The rubber 'O' ring trick works fine with this problem! Just place an 'o' ring on the EP barrel and it will stop in the focuser wherever you place the 'o' ring!

asimov (John) · #11 27-07-2005, 04:12 PM

Top idea Ken.

ausastronomer (John Bambury) · #12 27-07-2005, 04:24 PM

Quote:

Originally Posted by gbeal

I'm off in a different direction.
If nothing is loose, and little has changed (which doesn't sound correct from your post) then I would use it as is, but with an extension tube. I use them all the time, as the infocus for imaging is just not there normally.

Gary Beal,

I collimated and star tested Irish's scope at the June Kulnurra star party. I had plenty of travel either side of focus, after fighting the focusing knobs. I think the eyepiece I had in was Louie's Tak LE. The scope has an outstanding mirror for a mass produced mirror. Since that time Irish has removed the mirror to center spot it and then re collimated the scope himself.

One of several things has happened since I tested and collimated the scope:-

The scope had the worst focuser I have ever used on any telescope, I could hardly turn the focusing knobs but when I finally fought it to where I wanted it there was plenty of in/out travel. The focuser was not right, something was definately broken or very badly adjusted/aligned with it. I told Irish he needed to pull it apart and clean it and check it all out in the daytime as I wasn't going to do it in the middle of a paddock in the dark. The problem with the focuser could well be a damaged or burred tooth on the rack or the pinion and through use this has caused further damage which is now restricting the amount of travel in the focuser itself. I think this is the most likely cause of the problem. If thats the case, it may be able to be fixed or the focuser may need replacing under warranty.

The 2nd possibilty which a couple of others have suggested is that through repeated collimation adjustment the mirror has crept up the tube and now restricted the outtravel. That's easily fixed by re-collimating the scope with the primary lower in the tube, or higher, whatever is needed to compensate for the focuser travel problem.

Gaz (Irish),

If you want me to look at your scope prior to the next Kulnurra observing night (6/8/05) I would be happy for you to come to my house early to mid Saturday afternoon. I can do this in my workshop where I can see and have the necessary tools. I can pull your focuser apart and fix/adjust it as necessary. I can't do this at the observing site in the dark.

I live about 25 to 30 minutes east of Kulnurra so its not too much of a detour from Sydney.

CS-John B

ausastronomer (John Bambury) · #13 27-07-2005, 04:26 PM

Quote:

Originally Posted by ballaratdragons

The rubber 'O' ring trick works fine with this problem! Just place an 'o' ring on the EP barrel and it will stop in the focuser wherever you place the 'o' ring!

Ken,

That idea is great when the focuser travel issue rests with the eyepiece/scope combination but in Gary's case I think it would be just putting a band-aid on a problem that needs to be addreessed, refer to my post above.

CS-John B

ballaratdragons (Ken) · #14 27-07-2005, 04:39 PM

Yep! It could be more than a simple EP prob. I do use the 'o' ring method when I use my Huygenians but that is all I have ever needed it on.

asimov (John) · #15 27-07-2005, 04:51 PM

That would definately explain the problem then John B.

elusiver · #16 27-07-2005, 05:12 PM

gaz check out this

i got mine from this guy. it's gso.. fits perfectly on the 8".. cost was $119 inc shipping at the time. Thing is with his auction just bid $69! don't bid more. He's a shill bidder, he put in a fake bid to see if i bidded higher and raise the value but cause i only bidded $69, he ended up winning his own auction.. but then he sent me a second chance offer with my highest bid($69) within a couple of minutes

el

RAJAH235 · #17 27-07-2005, 11:11 PM

Sounds like you already know what the fault is, John. All that work, was not mentioned in the original post...... I feel like deleting all of what I just wrote.

L.
ps. Surely, these t'scopes are properly designed, with the correct length collimation screws, NOT to let the primary tooo far up?? I can just see it now, someone is collimating away, & the main mirror cell falls out. NO WAY!!!
Commonsense must prevail.

rmcpb (Rob) · #18 28-07-2005, 08:33 AM

If the R&P focuser is no good and warranty is a problem I have one just sitting on the shelf looking for a good home.

Cheers

cahullian · #19 28-07-2005, 09:46 AM

Thanks for the offer John, but Louie is going to sell me A Crayford style focuser. I hope to never see my R&P again after that lol. I had one of the Science teacher at the high school have a look at it and he agreed with what John said (worst focuser he has ever came across, and it was stuffed from the get-go ) I have had a chat with Lee at Andrews and he was happy to have it fixed for me but that meant having no focuser for a few weeks and seeing I was on a two week break from work I didn't want to part with it. Now that Louie is selling me a crayford I will install that and then send Lee the R&P just incase I ever need it again(hope not).
Once again thanks a lot ppl for all your much needed input. You guys are the reason this is the best forum site on the web.

Gazz/Irish

cahullian · #20 28-07-2005, 09:50 AM

I have had to collimate a few times as my scope does get knocked around a fair bit.

I always turn the screws in the same direction. so today if I get time im going to unscrew them most of the way back and start again lol

That should make life a little easier for the next few weeks.