Jump to content

Banner.jpg.b89429c566825f6ab32bcafbada449c9.jpg

Primary Mirror Locking Screws

Deacon

Recommended Posts

Deacon

Deacon

Posted
Posted

Hi

I have a SkyWatcher 200p Dobsonian which is a great scope. After I have collimated the primary mirror I always tighten the locking screws afterwards.

My question is do you need to tighten the locking screws or not? If not is there any danger of the mirror moving or falling in the tube!!

Will I damage the mirror by tightening the screws?

Sorry for these daft questions but any information to dispel this confusion would be great.

Best

Deaky

Link to comment
Share on other sites
stevetynant

stevetynant

Posted
Posted

i was told recently not to bother with the locking screws. it might need collimating more frequently but this isn't a problem as i usually collimate before observing anyway.

Oddly enough I just replaced my locking screws with some bobs knobs and only at that point did I realise the locking screws don't actually screw into the mirror assembly at all but rather press up against it - I can only imagine they press up against some spring loaded mechanism which is exerting downward pressure on the mirror itself.

I might have got this totally wrong but I'll soon find out when I take it apart on the weekend to begin the flocking process - hopefully someone with more knowledge in this process can confirm for us

Link to comment
Share on other sites
Moonshane

Moonshane

Posted
Posted

I feel that locking screws on newt mirror cells are superfluous. if you remove them there will be no detrimental effect and you really need to collimate your scope every time. in fact leaving them in mand too tight might (and sometimes does) cause temporary astigmatism until they are loosened off again.

one way to combat mirror moevement is replacing the springs with stronger ones and/or tightening the main collimation bolts to within one full turn of tight as this makes the spring tension hold the mirror in place more effectively.

Link to comment
Share on other sites
Richardisgreat

Richardisgreat

Posted
Posted

Yep i tighten mine but only to the point of the slightest bite from the allen key, i was advised not too over tighten, also when i tighten mine i do one screw a little bit then move to the next and so on to the next just a little at a time, i find it doesnt knock the collimation out too much if i do each screw a little at a time.

Link to comment
Share on other sites
brantuk

brantuk

Posted
Posted

The mirror cell sits on the springs and when you screw the collimation screws into the miror mounting it pulls it downwards (compressing the spring). This is the action that sets the mirror in place and collimates it. Then you lock it off by turning the locking screws upwards till it meets the mounting - this only needs to be "finger pinch tight" just enough to hold the whole assembly in the set position (ie collimated position). :)

Link to comment
Share on other sites
  • 1 year later...
Staraddict

Staraddict

Posted
Posted

Hi,

Today I collimated my Skywatcher Heritage 130p for the very first time and it should be fine now, but it was not totally painless. Two of the primary mirror bolts came off and I was able to screw them back in, but they had a rubber ring and I really don't know why but I was not able to screw them back in with the rubber rings. What is or was the function of the rubber rings? The bolts seemed to come off pretty easily. One of them though was always too tight. The locking screws were normal/at a normal level of tightness (at least I think so), so I am not sure why the bolts caused all those problems. I was really scared (actually terrified!) the primary mirror would come off too and break, but luckily it didn't happen. Now they are screwed in of course, but I was just wondering if others have experienced the same problem while collimating.

Thank you for your opinions!

Link to comment
Share on other sites
Ally8446

Ally8446

Posted
Posted

+1 for tightening just until you feel the bolt touch.

Although I do agree with Shane, I only use them because they're there. You really should check collimation EVERY TIME you are going to use your scope. Pretty much everytime I use my 200 dob the primary needs a little tweak.

Ally

Link to comment
Share on other sites
itmo

itmo

Posted
Posted

I usually collimate my scopes by using 2 screws that are nearer to the focuser to avoid moving the mirror up and down, then i will tighten the screws so that they touch the mirror frame and stay there, but not too tight. just so they touch. 

Link to comment
Share on other sites
Avocette

Avocette

Posted
Posted

Hi,

Today I collimated my Skywatcher Heritage 130p for the very first time and it should be fine now, but it was not totally painless. Two of the primary mirror bolts came off and I was able to screw them back in, but they had a rubber ring and I really don't know why but I was not able to screw them back in with the rubber rings. What is or was the function of the rubber rings? The bolts seemed to come off pretty easily. One of them though was always too tight. The locking screws were normal/at a normal level of tightness (at least I think so), so I am not sure why the bolts caused all those problems. I was really scared (actually terrified!) the primary mirror would come off too and break, but luckily it didn't happen. Now they are screwed in of course, but I was just wondering if others have experienced the same problem while collimating.

Thank you for your opinions!

Hi Staraddict. The neoprene O rings actually act as compression springs against which you tighten the collimation screws. So as you adjust the screws, you squeeze the rings between the mirror cradle casting (that holds the mirror) and the tube end casting. I found this to be a bit of a problem on my Skyliner 200p Dob since the torque needed to adjust against the neoprene rings was quite high and the adjustment didn't feel very precise. So I replaced the crosshead screws, allen screws and O rings with 'Bob's Knobs and Springs' and now collimation is much easier (no tools required).  

Link to comment
Share on other sites
Avocette

Avocette

Posted
Posted

Can anyone suggest suitable replacement springs for the 200P (explorer black diamond in my case, though suspect this cell is common to the skyliner's).

Hi Jake. Bob of Bob's Knobs fame sells springs. I originally also made my own springs by buying compression springs as available from ironmongers or hardware stores (usually about five times longer than needed) and trimming three pieces of the correct length using heavy duty electricians cutters which were certified for cutting piano wire. 

Link to comment
Share on other sites
Staraddict

Staraddict

Posted
Posted

Hi Staraddict. The neoprene O rings actually act as compression springs against which you tighten the collimation screws. So as you adjust the screws, you squeeze the rings between the mirror cradle casting (that holds the mirror) and the tube end casting. I found this to be a bit of a problem on my Skyliner 200p Dob since the torque needed to adjust against the neoprene rings was quite high and the adjustment didn't feel very precise. So I replaced the crosshead screws, allen screws and O rings with 'Bob's Knobs and Springs' and now collimation is much easier (no tools required).  

Thanks for the explanation. I might do the same, as I don't think they worked very well with my telescope either. Meanwhile I managed to put them back in place, as they obviously  do have a purpose!

Link to comment
Share on other sites
Staraddict

Staraddict

Posted
Posted

Why do I have to focus further out after collimating? It is my first night of viewing after my first collimation (not 100% perfect, the secondary mirror is not perfectly aligned, only about 95%). I don't recall having to focus so far out before... I guess it also has to do with weather conditions? I am a bit worried. :( Thanks.

Link to comment
Share on other sites
Staraddict

Staraddict

Posted
Posted

What worries me a bit is... will it hold a universal camera adapter (which I don't have yet) + a camera? The camera would be a point-and-shoot one, I have already been told that the helical focuser of my scope would probably break with a DSLR camera. Being so far out makes it a bit unstable. Is there a way to push the mirror just a bit further down? I have tried, but it is the same.

Link to comment
Share on other sites

Archived

This topic is now archived and is closed to further replies.

Go to topic listing

  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.