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130 PDS focus fix


Bottletopburly

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Right here's the problem with the 130pds ,the draw tube has been cut down by i think 18mm measuring the length against the 200pds draw tube assuming they are the same length, now what is causing the problem is as you wind the drawtube out the two small stainless rollers are loosing contact with the tube  so there is a few possibilities to fix this 

1/ move the two rollers further up the tube by approx 20 mm (there is four rollers holding tube .)

2 extend tube dont know if that's possible tube dia 56mm

3 source a stock focuser and change the draw tube 

 

I think the tube has been cut as a modification but i don't know what the mod was haven't found it yet had a look on Sgl couldn't see it so do not know what was trying to be achieved by cutting down .

Any ideas, comments please 

 

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Edited by Bottletopburly
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I would just be looking for a second hand focuser. I have no idea why it's been cut down as it wouldn't affect anything like the back focus. Someone's always upgrading, so they come up fairly often, we'll keep our eye's open. Maybe someone on her has one they don't need anymore?

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I have no idea what was trying to be achieved ,thats why  i was wondering if it was a mod,so i could see what went wrong 

 

 

 

 

 

 

 

 

 

 

 

 

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I can only assume it was to do with a focus travel issue, but as the top end is threaded, they might have bodged it right up. Both scopes are really good. What are you looking to do with them?

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My thinking too - shortening the focal length for some reason. Could be to do with the gear he was attaching - any combo of coma corrector, filter wheel, long back focus camera, T-ring spacers, etc could've lengthened focus too much. Or maybe even using binoviewers, barlow, GPC, etc to get focus. Might be worth giving him a bell and asking just outa curiosity. :)

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2 minutes ago, Brantuk said:

My thinking too - shortening the focal length for some reason. Could be to do with the gear he was attaching - any combo of coma corrector, filter wheel, long back focus camera, T-ring spacers, etc could've lengthened focus too much. Or maybe even using binoviewers, barlow, GPC, etc to get focus. Might be worth giving him a bell and asking just outa curiosity. :)

Yes maybe that will solve the puzzle quicker i will fire off a PM

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That's what I was thinking Kim. To get a 130PDS to focus with a DSLR you needed to move the primary up the tube by 2cm. Now maybe it was done by someone who didn't know the principle and tried to decrease the focuser tube length for some reason.

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20 minutes ago, Doc said:

Has the primary mirror been moved up the scope?

i dont believe so 

IMG_0259.JPG

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3 minutes ago, Doc said:

That's what I was thinking Kim. To get a 130PDS to focus with a DSLR you needed to move the primary up the tube by 2cm. Now maybe it was done by someone who didn't know the principle and tried to decrease the focuser tube length for some reason.

Is that really required as the PDS was meant to be tuned for astrophotography ,i have Pm the seller see if i can shed some light 

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17 minutes ago, Doc said:

I have found the answer. Check out this thread.

 

https://stargazerslounge.com/topic/239937-150pds-focuser-modification-required/

Bingo Doc,

would say 18mm has been cut off but that's about 6mm too much ,i may be able to fit a stop on end of tube so it hits on roller if i can still get focus using the baader cc which i know he had and sold ,the sw corrector is a 0.9 reducer as well so stops this issue without modding scope ,so all i need to do now is find someone with a 130 pds that is using a baader cc what the measurement is from the underside of the plastic collar to the top of the white focuser when its at focus that will determine if fitting a stop will work ,basically the tube sticks out leaving stars like they have a chunk out 

IMG_0260.JPG

Edited by Bottletopburly
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So if anyone is using a 130 pds with specifically a baader CC and a dslr what is the measurement from the underside of the black collar to the top of the white of the focuser ?

55 minutes ago, BAZ said:

I can only assume it was to do with a focus travel issue, but as the top end is threaded, they might have bodged it right up. Both scopes are really good. What are you looking to do with them?

well i was going to get a 130pds but opted to get the 127mm mak so moon and planets covered longer FL,the 200pds now replaces the 200p and the 130pds will give me a wider FOV so no more scopes required  

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4 minutes ago, BAZ said:

You can really only get those £50 American imports! :whistle:

I think i can save it but i need the focus measurement first , 

plan A i can fit a stop 

plan B i can move roller and fit a stop , but all rests on the focus measurement using a Baader CC and a dslr 

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I reckon it was an imaging mod. Probably wanting to cut down on draw tube intrusion into the primary light path when a coma corrector is fitted, depending on the camera the draw tube may have had to be racked well in to focus and they saw the tube sticking into the light path?

Which as most of us know doesnt really affect much but some folks with OCD want every photon.

 

If you can reach focus with all your accessories then the cheapest option would be fitting a stop

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4 minutes ago, philjay said:

I reckon it was an imaging mod. Probably wanting to cut down on draw tube intrusion into the primary light path when a coma corrector is fitted, depending on the camera the draw tube may have had to be racked well in to focus and they saw the tube sticking into the light path?

Which as most of us know doesnt really affect much but some folks with OCD want every photon.

 

If you can reach focus with all your accessories then the cheapest option would be fitting a stop

I have had a reply off the chap this is exactly why he had it shortened after taking advice off sgl ,he had professionally shortened but cant remember by how much i think it was 18mm ,so im hoping the stop will solve it may need a tweak or two 

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Of course if you really get stuck you could always get a new draw tube made for it.

That is if you know someone who could do it for you ;) ;)

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I have considered this for my Newts, but decided against it and just blackened the outside of the drawtube instead.

The original silver drawtube can create a 5th spike on brighter stars.

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5 hours ago, Graham said:

Of course if you really get stuck you could always get a new draw tube made for it.

That is if you know someone who could do it for you ;) ;)

That sounds a better idea graham anyone in mind ;)

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