<blockquote>
  <p>Next to the eyepiece there is a screw that you can turn loose and if
  you make it as tight as possible the focus knob won't focus the image
  but when it is a little loose it starts to focus it</p>
</blockquote>

<p>Sounds like the lock screw. If that's what it is (your description is a bit vague), it's designed to lock the focuser in place, like when you're doing prime focus photography with a heavy camera, and you don't want the focuser to move around and lose focus.</p>

<p>If it's the lock screw, don't mess with it. Don't tighten it, you don't need that for regular observations. Keep it comfortably loose. If it's a bit tight, it could be rubbing against the drawtube (or whatever moving part it's designed to stop), and then it would make that noise - and you don't want that.</p>

<p>I have a very heavy <a href="https://i.sstatic.net/bkIMk.jpg" rel="nofollow noreferrer">30mm 82deg Explore Scientific eyepiece</a>, and even with that thing (bigger than a soda can, and weighing about 1 kilogram) I don't need the lock screw - and this is on a regular mass produced two-speed focuser, not some fancy precision hand-crafted MoonLite. Visual observations are all about moving the focuser around, hunting for the best focus, and changing eyepieces for the best view. Let the focuser move easily.</p>

<p>Unless it's moving too easily, but then you have a problem with the focuser.</p>

CC BY-SA 3.0
2015-07-16T06:02:23.060Z
2015-07-16T06:13:38.960Z
2015-07-16T06:13:38.960Z
Florin Andrei
<p>I'm not sure whether I should ask this question here but I'll give it a shot. I have a XT8 Dobsonian Reflector telescope and it works fine. But recently when I use the focuser to focus the image when I change eyepieces it focuses fine but it makes a scratching noise that is really loud and it doesn't sound right. Now I don't know what this screw that I am about to explain is neccesarly for because I am no where near a telescope expert. Next to the eyepiece there is a screw that you can turn loose and if you make it as tight as possible the focus knob won't focus the image but when it is a little loose it starts to focus it, but it keeps making a scratching sound and a high pitched rubbing sound that doesn't sound right.  I know I explained this pretty vaguly but any help would be helpful! So far I could not find anything on the web for this weird problem. </p>

<p>UPDATE:</p>

<p><img src="https://i.sstatic.net/ljZxZ.jpg" alt="the eyepiece,screw is on the left"> </p>

CC BY-SA 3.0
2015-07-14T15:06:29.417Z
A picture of your focusing apparatus would be nice. It doesn't sound like a typical rack and pinion setup. https://www.google.com/search?q=rack+and+pinion&ie=utf-8&oe=utf-8#q=rack+and+pinion+focuser
Wayfaring Stranger
CC BY-SA 3.0
2015-07-15T00:44:07.530Z
@WayfaringStranger Ya that's what it is. I will update my Description with the picture.
Dashboarrd
CC BY-SA 3.0
2015-07-15T12:31:09.073Z
Have you tried removing the locking screw entirely. It may be pushing on a little rod, which in turn pushes on the eyepiece tube to hold it firmly in place. If the little rod, which is supposed to be loose, has gotten jammed, that could make a nasty noise. There might instead be a rubberized pad involved to supply pressure on the eyepiece tube. Can you take the eyepiece tube out entirely to have a look see?
Wayfaring Stranger
CC BY-SA 3.0
2015-07-15T19:45:51.410Z
@WayfaringStranger I have removed the lock screw and nothing changed. But I will try what you suggested and remove the eyepiece tube entirely to see.
Dashboarrd
CC BY-SA 3.0
2015-07-15T20:05:58.530Z
@WayfaringStranger So I took out the eyepiece tube and saw the little rod that you were talking about and that is what it seems to be. Do you know how I could fix it by getting it unjammed? Thank you!
Dashboarrd
CC BY-SA 3.0
2015-07-15T22:53:23.630Z
Manuals are online: http://www.telescope.com/Product-Support/Telescopes/pc/191/com/241.uts I'm not seeing a focuser that looks like your pic, and the manuals they do have seem a bit skimpy on design detail as well. Product support phone, chat, or email may be your best bet: http://www.telescope.com/custserv/custserv.jsp Be sure to include the exact model name/number.
Wayfaring Stranger
CC BY-SA 3.0
2015-07-15T23:40:07.553Z
@WayfaringStranger Ok, thank you so much for your help!
Dashboarrd
<dobsonian-telescope>
Problem with Dobsonian reflector telescope
Dashboarrd
# Problem with Dobsonian reflector telescope

(Asked by: username_0 on 2015-07-14)

I'm not sure whether I should ask this question here but I'll give it a shot. I have a XT8 Dobsonian Reflector telescope and it works fine. But recently when I use the focuser to focus the image when I change eyepieces it focuses fine but it makes a scratching noise that is really loud and it doesn't sound right. Now I don't know what this screw that I am about to explain is neccesarly for because I am no where near a telescope expert. Next to the eyepiece there is a screw that you can turn loose and if you make it as tight as possible the focus knob won't focus the image but when it is a little loose it starts to focus it, but it keeps making a scratching sound and a high pitched rubbing sound that doesn't sound right. I know I explained this pretty vaguly but any help would be helpful! So far I could not find anything on the web for this weird problem.

UPDATE:

![the eyepiece,screw is on the left](https://i.sstatic.net/ljZxZ.jpg)

**Tags:** dobsonian-telescope

> **Comments:**
> **username_1**: A picture of your focusing apparatus would be nice. It doesn't sound like a typical rack and pinion setup. https://www.google.com/search?q=rack+and+pinion&ie=utf-8&oe=utf-8#q=rack+and+pinion+focuser  
> **username_0**: @username_1 Ya that's what it is. I will update my Description with the picture.  
> **username_1**: Have you tried removing the locking screw entirely. It may be pushing on a little rod, which in turn pushes on the eyepiece tube to hold it firmly in place. If the little rod, which is supposed to be loose, has gotten jammed, that could make a nasty noise. There might instead be a rubberized pad involved to supply pressure on the eyepiece tube. Can you take the eyepiece tube out entirely to have a look see?  
> **username_0**: @username_1 I have removed the lock screw and nothing changed. But I will try what you suggested and remove the eyepiece tube entirely to see.  
> **username_0**: @username_1 So I took out the eyepiece tube and saw the little rod that you were talking about and that is what it seems to be. Do you know how I could fix it by getting it unjammed? Thank you!  
> **username_1**: Manuals are online: http://www.telescope.com/Product-Support/Telescopes/pc/191/com/241.uts I'm not seeing a focuser that looks like your pic, and the manuals they do have seem a bit skimpy on design detail as well. Product support phone, chat, or email may be your best bet: http://www.telescope.com/custserv/custserv.jsp Be sure to include the exact model name/number.  
> **username_0**: @username_1 Ok, thank you so much for your help!  

---

## 1 answers

### Answer by username_2 on 2015-07-16. Score: 1 | Accepted answer

> Next to the eyepiece there is a screw that you can turn loose and if
> you make it as tight as possible the focus knob won't focus the image
> but when it is a little loose it starts to focus it

Sounds like the lock screw. If that's what it is (your description is a bit vague), it's designed to lock the focuser in place, like when you're doing prime focus photography with a heavy camera, and you don't want the focuser to move around and lose focus.

If it's the lock screw, don't mess with it. Don't tighten it, you don't need that for regular observations. Keep it comfortably loose. If it's a bit tight, it could be rubbing against the drawtube (or whatever moving part it's designed to stop), and then it would make that noise - and you don't want that.

I have a very heavy [30mm 82deg Explore Scientific eyepiece](https://i.sstatic.net/bkIMk.jpg), and even with that thing (bigger than a soda can, and weighing about 1 kilogram) I don't need the lock screw - and this is on a regular mass produced two-speed focuser, not some fancy precision hand-crafted MoonLite. Visual observations are all about moving the focuser around, hunting for the best focus, and changing eyepieces for the best view. Let the focuser move easily.

Unless it's moving too easily, but then you have a problem with the focuser.


---

