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Focuser upgrade?


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I have this lovely old 8" Orion Optics UK newt that I've had for, probably 12 or 13 years and it was second hand when I got it.  Its a fantastic scope with brilliant mirrors, so I'm in no rush to change it.

 

However, the focuser let's it down badly!  It the original steel r&p focuser and it's just dire.  It's barely workable for visual and a nightmare for planetary imaging.

 

As its so old, I'm wondering what would be my best plan of action to improve it?  Should I replace the focuser completely and; if so what with?  Could I get something with dual speed that might be a pretty straight swap?  I don't really want to drill or cut the tube if I can get away with it.

 

Alternatively, would I be better just getting an electric focuser for it?  Budget is tight, so the cheaper the better!

 

Thanks in advance

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I feel your pain with this one I have had two old scopes recently which were otherwise superb scopes let down by rusty old 1.25”  focusers.

I think the chances of you fitting a new focuser without having to drill the tube are close to zero unfortunately. You may be able to fit a focus motor to it if you could fabricate a custom bracket, but then you’d still have to deal with backlash in the rack and pinion (if it’s there?)

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I thought I'd seen a similar focuser replaced but it was a later model with 4 screw holes. You would most likely need to add the extra holes and widen the hole for the focuser tube as well as per this.

Before thinking about a focus motor it might be a good idea to see if you can strip the focuser and replace anything worn or simply adjust anything loose.  A motor won't fix a loose or slipping focuser.

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CraigT82 is correct. You would have to drill holes. Hard choice to make, but if it were my scope with great optics and so well preserved I would do the upgrade. It would be like having a brand new quality instrument for the price of a high end focuser. You can consult Startlight or Moonlite instruments for an opinion and they can help you determine which focuser is the best fit. I know a few friends who have done this to dobs with bad focusers but good optics. Good luck.

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Another new focusser vote.
I have changed focussers on newts before. Nothing major involved. Just a bit of thought and planning.

I know where you are coming from as the OO newts I have owned had great mirrors.

While you have the scope apart (I would remove both mirrors before drilling) think about anything else.
Different finder holes, flocking or better black paint for example.

Depending on how the new focusser fits, you may wish to make an adapter plate.

That can give a tidier upgrade. Possibly the opportunity to avoid new drilling if it really bothers.

Let us know how you get on.

David.

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7 minutes ago, StevieDvd said:

Is it a 1.25" or 2" focuser - it looks small in the images? And perhaps you should measure the hole for the focuser tube from inside to get a better idea of your replacement options.

It's just a 1.25" focuser.

Thanks for all the posts.  I think a new focuser is the plan, I'll just have to 'bite the bullet' and drill new holes!  The suggestions about giving the whole scope a bit of a tdiy up whilst I've got it apart are quite genius too.  Thank you all.  I'm off to trawl the web for a suitable replacement.  May as well go 2" as well, while I can... 

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I'm a bit late to this conversation, but I would add a few words of encouragement.

I updated a 10-inch OOUK Newtonian several years ago and replaced the focuser and the secondary holder. Changing the focuser required the drilling of a new fitting hole plus screw holes. As you can see in the photo, I used a Dremel drill and cutting wheel to cut the new mounting hole.

New_hole_web.thumb.jpg.b327f024d294e7d591fbd181be1a43d2.jpg

The ragged pieces of metal were the remains of the previous owner's attempt to cut a hole for a focuser. Note the use of a marked-up card to provide a template.

Here is the new focuser in place. It is a Skywatcher focuser which was surplus to requirements. 

New_focuser_web.thumb.jpg.a919e134934cd9754176d5c592a83b1e.jpg

To get good collimation, you should align the new focuser with the tube. I did this by determining the point on the inside of the tube exactly opposite the centre of the new focuser hole. This point was marked on a card fixed to the inside of the tube, enabling the focuser pointing to be adjusted using a laser.

On_the_spot_web.thumb.jpg.b9a26a635370fd5231c26fa9e9718353.jpg

I then flocked the tube with Protostar flocking.

The original OO secondary holder was a simple device which gave ugly diffraction spikes.

OO_secondary_web.thumb.jpg.70b2b4ebe714eec3bbf9280f1267ad83.jpg

 

I replaced this with a set of curved spider vanes, which resulted in a telescope giving some beautiful visual views.

 Tube_spider_web.thumb.jpg.13336bcb9656e0567dffe2a8c0d30e6a.jpg

 

By the way, I would not recommend curved spider vanes if you plan to use the scope for deep sky imaging, but they are great for visual and planetary.

David

 

 

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11 minutes ago, Second Time Around said:

David, I'm probably being thick but could you explain how to determine where the point opposite the focuser is?

Many thanks.

I’m inexperienced and in no way to be advising anyone if anything here but if it was me I would mark the center point of the focuser hole and run a line oarralle to the end of the tube (sky side) then measure the longest therefore widest distance which should then be the opposite point runs line down the inside of the tube with tape and a pen then when the new foxuser is in run a simple laser collimator through the focuser and make sure it matches that line and is true if not shin it so it all lines up ?? Maybe I’m over thinking this ?? 

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19 hours ago, Moon-Monkey said:

I’m inexperienced and in no way to be advising anyone if anything here but if it was me I would mark the center point of the focuser hole and run a line oarralle to the end of the tube (sky side) then measure the longest therefore widest distance which should then be the opposite point runs line down the inside of the tube with tape and a pen then when the new foxuser is in run a simple laser collimator through the focuser and make sure it matches that line and is true if not shin it so it all lines up ?? Maybe I’m over thinking this ?? 

Pretty much.

Once you have cut the new hole, measure the distances from the top edge of the tube to the top of the hole and the bottom of the hole. The average of these two values gives the distance of the centre from the top edge of the tube.

Stick some sticky-backed paper around the top edge of the tube. Use a set square to find where the centre line through the hole intercepts the top edge and mark it. Now cut a band of paper with a length equal to the tube's circumference and fold it in half.  Mark the half way point. Now lay the band of paper around the top edge of the tube with the join aligned with the centre line of the hole and mark on the sticky-backed paper where the half way mark comes. 

Paper_band_web.thumb.jpg.8202bc0998ab95120d4ccdd745848518.jpg 

 

Stick a piece of card to the inside of the tube opposite the hole. Mark a line parallel to the top of the tube at a distance equal to the distance of the hole centre from the top. Transfer the position of the halfway point to the card and draw a line down the tube using a set square (small carpenter's square).

 

🙂

P.S I record almost everything I do with photos. They sometimes come in useful for talks. 

 

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19 hours ago, Moon-Monkey said:

I’m inexperienced and in no way to be advising anyone if anything here but if it was me I would mark the center point of the focuser hole and run a line oarralle to the end of the tube (sky side) then measure the longest therefore widest distance which should then be the opposite point runs line down the inside of the tube with tape and a pen then when the new foxuser is in run a simple laser collimator through the focuser and make sure it matches that line and is true if not shin it so it all lines up ?? Maybe I’m over thinking this ?? 

I've recently done this with a new focuser and I'll try and explain how it's done. There was a great thread here years ago with pics that showed how to do it but I can't find it now.

This process assumes the new focuser will be centred in the existing focuser hole.

Remove the secondary and focuser.

Take a piece of thin card, a couple of inches wide and a couple of inches longer than half of the tube circumference.  Hold the card tightly inside the tube with one end on the edge of the focuser hole, ensure it lays flat against the curve of the tube and mark the tube with a pencil at the end of the card.  Repeat this on the other side of the focuser hole. You'll end up with two pencil marks opposite the focuser a few inches apart, find the centre of these marks and you have a centre line directly under the focuser.  I did this by holding the card next to the two pencil lines, marking the lines on the card, folding the card in half, marking the centre and transfering the line to the tube.

That's one dimension, now you have to find the centre of the focuser hole in the up / down direction of the tube.

Measure the distance from the tube end to the near side of the focuser hole, call this A. Measure the diameter of the focuser hole, call this B. The distance from the end of the tube to the centre of the hole equals A + (B/2). One you know this, measure down from the tube and mark with a pencil, you should end up with a cross of pencil marks exactly under the centre of the focuser hole, I then marked this with Tipex so it was more visible.

Fit your new focuser and use a Cheshire or other sight tube to ensure that your focuser points exactly at this point.

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