Request advice OMC140 Focuser doesn't work

[cdd2455]

Hi

I purchased an OMC140C from OO and would appreciate some advice , the focus knob has no effect on focus, it's like it is not connected to anything. 

I mounted the OMC pointed first at the moon and all I saw was a large bright circle with a black centre, tried focussing a few turns one way and a few turns the other way and no change at all. 

I tried different eyepieces and pointed the scope at other bright targets ( Venus and Jupiter ) with  the same result.

I have emailed OO but no answer yet most likely as it's their Christmas / new year break.

Can anyone assist with instructions on how to remove the back plate of the OMC140 and connect  the focus mechanism is connected to the mirror.

Best Regards

Carl

[Kirscovitch]

Is it a crayford focuser?

[cdd2455]

No, it's the standard moving mirror type focuser, with a micrometer type knob sticking out of the back plate the 'scope.

[nightfisher]

How old is this 140? on the older models you had to remove the finder shoe then 3x little screws around the outer edge of back plate, but NOT the 3x hex bolts in the end of back plate, have a look at the focuser and see if there is a tiny screw to lock it to focus spindle, this might just need tightening up a touch, can you post a pic of the back end of the scope

[cdd2455]

Thanks Jules, it's a brand new OMC140C, factory fresh. I'll check and tighten the tiny screw on the focuser spindle.

Best Regards 

Carl

[Mr Spock]

If it's new, don't touch it, you'll invalidate the warranty. If it really doesn't work, send it back.

[Cornelius Varley]

It may take more than just a few turns to reach focus. Maks have a wide focus range so you may need to turn the focuser farther than you think.

[nightfisher]

It may take more than just a few turns to reach focus. Maks have a wide focus range so you may need to turn the focuser farther than you think.

That is a good point, may take many turns

[Mr Spock]

Try it in daylight with your lowest power eyepiece. You'll soon see if the focussing mechanism works.

[cdd2455]

Thanks Guys,

I tried again, there was no need to tighten the tiny hex screws, they were snugged up tight.

Using a 32mm plossl, there was no movement on the mirror that I could tell at all, the fucus knob just unwinds al the way out without having any connection to the mirror.

I still have a large bright circle with a black circle at the centre.

Ho Humm, I'll wait for OO to answer the email I sent and take it from there.

Best Regards

Carl

[nightfisher]

Thanks Guys,

I tried again, there was no need to tighten the tiny hex screws, they were snugged up tight.

Using a 32mm plossl, there was no movement on the mirror that I could tell at all, the fucus knob just unwinds al the way out without having any connection to the mirror.

I still have a large bright circle with a black circle at the centre.

Ho Humm, I'll wait for OO to answer the email I sent and take it from there.

Best Regards

Carl

Only problem with sending it back is your location, carriage there and back is gonna cost a small fortune, keep us posted as to what happens

[knobby]

Take a look at the end of this review ...

http://www.astromag.co.uk/pdfs/omc-140.pdf

[cdd2455]

Thank You White Dwarf,

That was an interesting read, now that I know it's possible, I'll be patient and wait for OO to respond.

And yes Jules,

returning the scope to OO would have been expensive and time consuming.

Best Regards,

Carl

[nightfisher]

That looks a helpful link what knobby posted, could well be the problem with yours, good luck with it

[cdd2455]

All's well now.

John ( from OO ) advised me of the fix which was straightforward.

A lovely elegant mechanism.

Best Regards

Carl

[paul07834]

I know this is an old thread, but I had the exact same problem as the OP.  A google search found this thread and I was excited to learn that the OP had solved the problem.  Unfortunately the OP did not bother to provide the solution for future readers who might encounter the same issue.  So I thought I would do so for future readers.  The following solution provided to me by John of OOUK worked for me.

"If you remove the 3 small screws going around the carbon tube into the mirror cell, all the cell will come away from the tube with a small pull. You can then see probably the mirror tube has got stuck in a position and will need moving back."

Note that my OMC140 was new in 2020 and I needed to remove about 8 screws (including those holding the dovetail bar) from around the carbon tube before the mirror cell would come out.

Paul