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Hi,  I have an astromaster 130eq, the focus wheel seems a bit sticky and when using a higher powered ep like a 8mm when turning the focus wheel in one direction to the other direction the image I a trying to focus on moves across the view in the ep, even when the focus wheel is moved very slowly. Hope what I've stated makes sense and is this normal?

thanks

Tim

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Mine is quite solid, don't know about stiff but certainly not all loose.

What you may find about your object moving across the EP, especially an 8mm is that the earth is rotating at 0.25 degrees every minute. The 20mm EP is 1 deg FOV and the 10mm is 0.5 deg FOV so the 8mm will be slightly less.

Also what you may find is that as you try and focus is that you are actually moving the scope itself, this will be far worse with the higher mag EP.

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Hi Tim, not quite sure, but you may be describing 'slop' in the focuser tube.  Can the focus tube be 'waggled' around when you hold it ?

That could cause the image in the focuser to shift as you turn the focus wheel.

You may find that any slop can be adjusted out (or greatly lessened) by some careful DIY.  

Go very carefully if not sure. Cleaning out the old grease and tiny amounts of good quality new grease may help.

Apologies if I've misunderstood what you are saying.

Hope you sort it, Ed.

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It is rack and pinion focuser?

Focuser tube is a bit wobbly in the housing?

When you reverse the direction of rotation of the handwheel, the focuser tube changes it's angle slightly - hence the movement in the eyepiece.

Had similar problem in another scope with worn r&p focuser.

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Thanks all for your psts

NGC 1502, think you've hit the nail on the head. the focus tube does wobble a littleand the issue i am having (the way the object is moving in the ep) would be explained by this. Sorry to be a pain but you referred to some careful DIY, does this involve taking the focus tube off? Is there anywere will a description on how to do this. 

Thanks in advance

Tim

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First thing to do - search SGL forum.

This problem is common and has been discussed before, for example here

Next google it - plenty of useful info there.

For example, adjustment shown in this

might help?

I have adjusted my sloppy focuser by using piece of shim plastic between focuser housing and tube, like so:

IMG_7743.jpg

(red piece of plastic is the shim material) - it may take some experimenting with both thickness and type of plastic.

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I did watch a video recently where someone just put a layer of insulating tape on the barrel, one piece each side.

However I wouldn't think that this would be a good long term solution as I would expect the tape to wear as it goes in and out of the main barrel.

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Yes... the piece of plastic I have used is actually engineering shim material.

Insulating tape would be too soft and there is also an issue of gooey sticky stuff on it, which might make things worse.

I agree with you that this is not long term solution.

I didn't have to stick it - it just stays there retained by friction.

Some focuser can also be shimmed behind the rack, but that means taking it out and apart (not everybody's cup of tea).

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Thanks all for your psts

NGC 1502, think you've hit the nail on the head. the focus tube does wobble a littleand the issue i am having (the way the object is moving in the ep) would be explained by this. Sorry to be a pain but you referred to some careful DIY, does this involve taking the focus tube off? Is there anywere will a description on how to do this. 

Thanks in advance

Tim

Hi again Tim, sorry I'm late back to this, been busy all day.

This http://www.youtube.com/watch?v=xj38CUnwId8 from post # 6 could work.  If you need to put tape on the focuser drawtube, it needs to go opposite to the focus wheels.

You could use sellotape.  It may wear out after a while, but it's easy to replace.

You may need a bit of trial & error.  If you can greatly reduce the wobble, maybe best to quit while you're ahead, rather than get frustrated going for perfection. A tiny bit of play is acceptable.

Hope you sort it, Ed.

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