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Skywatcher 250PX Dob Mods


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New low profile focuser, moonlight do them. Skywatcher also do a lowprofile crayford which may suit the job...if your planning on using i for astrophotography.

Will also need a coma corrector, you can get away with it to a certain extend but tbh, it annoys me seeing coma >..<

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I would definitely vouch for a new focuser, I bought a 2nd hand Antares dual speed crayford for mine for £65 and it works so much better than the standard rack and pinion I had originally.

I wouldn't say that a coma corrector is really necessary as most people can live with it and it is only really troublesome when using the scope for astrophotography which you won't be if you have a dob, unless you also have an eq mount for it. Also a lot of eyepieces these days correct coma to a certain extent and improve the view, it's only with the cheap eyepiece that coma can be a REAL problem.

Flocking the OTA would be a worthwhile endeavour as it dramatically reduces the amount of scattered light inside the tube and hence improves contrast in the final image. This material is relatively cheap to buy (£30 from telescopepartsuk) and can be installed quite easily on a spare evening.

I would also suggest fitting a telrad red dot finder to the tube to help finding objects easier. The unit superimposes three rings onto the night sky at 0.5, 2 and 4 degrees to aid with star hopping. And maybe a RA finder would be useful also to stop you from getting an aching neck.

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The mods don't cost that much.

BASE

I cut up a plstic milk container to make a disc of platic to put between the ground board and the telfon disc around the central nut.

SECONDARY

I also put one between the secondary holder and spider to help avoid turning the mirror as I collimated. I found the collimation screws pitted the metal of the holder and they tended to get stuck in the pits. To address this I glued a metal washer onto the holder base as the washer doesn't get pitted as easily.

I also replaced the secondary collimation screws with bobs knobs which allow you to adjust without the allen key.

OTHERS

Totally agree about the flocking, red dot finder and fan. I mounted the fan on a piece of neoprene and used velcro around the back of the mirror with holes for the knobs. I thought the neoprene might isolate any vibrations from the fan.

The mods are about just making it better, rather than fixing things that are wrong.

Brian

Edited by irishbloke
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Feel a right dummy asking this but I have to to make sure lol

I take it you have it pointing upwards into the scope to cool it down rather than otherway around to cause a draught of air to just reduce moisture?

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Maybe a 120mm Xtreme PC fan (I have 4 in my PC) they are low noise and move a lot of air.

Right sounds like I need to focus on the base stuff first. I also read the side bearings can squeak?.. have any of you found this, and how to get round it?.

Thanks

Rob

Edited by Rob
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Now I understand theres some short comings on these dob's and mods are required?. Any advice would be great thanks.

Cheers

Rob

Not required just optional. Works out of the box but can be improved.

Milk bottle washers around central bolt. I found the teflon pads on both my 200P and 250PX were complete garbage. They had been stapled to the board but the staples were protruding from the teflon. I ripped them off and fitted new teflon with countersunk screws. Also added some Ebony Star formica for the teflon to run against. Much better.

On the altitude i added some teflon mouse tape around the lugs that the tube sits in. And ripped off those red disks on the side. Used more teflon tape instead.

The tube was pretty well balanced, so always had the tensioners there as handles only.

Also did the bits the others have said. Added a zero power finder to compliment the optical finder but changed the optical finder to a right angle. I found the single speed Skywatcher was actually better than the Antares/GSO etc. So never changed it.

Edited by russ
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  • 4 weeks later...

Forgive my lack of knowledge. I hope members are still keeping an eye on this thread.

What do you do with the bearing? Is it just fixed between the ground board and lazy susan? How do you know what size to get? will the bearing not be thicker than the existing teflon pads and so cause rocking???? With regards to the fan I see from the bottom of the scope there are 4 holes for a fan to fix to. Is there not a SW fan available as an accessorie that just screws straight into the fixing holes?

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interested in hearing about more mods for this scope, getting closer to winter and clearer skies now and I wanna get mine modded a bit.

i'm especially interested in modding the base and the altitude swivel because they are quite stiff and I often end up moving them way too much cause it jerks when you move it, so some explaination on what the best way to do this would be and how to do it would be awesome ;-; thanks

Edited by Sunwind
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my mods on the Orion Optics 12" (which has a better constructed base than the SW etc) have been as follows :

  • BASE
  • friction brake*
  • OTA
  • dob knob
  • dual speed focuser*
  • telrad*
  • right angled finder*
  • flocking
  • painted any shiny screws matt black
  • added tool free adjusters for secondary and primary
  • added side fan and rear fan
  • weight system for counterbalancing heaviest eyepiece*
  • additional tube ring to maintain tube position if I ever have to turn scope and add balancing ballast*

I will be undertaking a similar series of mods to the 6" in due course.

As Russ says, you don't have to make these mods and the scope will work fine without them (i.e. be optically pretty much the same) but the experience will be more enjoyable and flocking in partic will enhance the contrast of the images. The ones I have starred can of course be transferred to another scope should I ever sell this one. :D

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flocking is black matt material. there are some which are branded like Protostar

BTW here's a link to the threads with pics showing most of the mods I mention

http://stargazerslounge.com/members-equipment-gallery/97917-dob-has-landed.html

http://stargazerslounge.com/diy-astronomer/109577-latest-dob-mods-fan-balancing-weight.html

Edited by Moonshane
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flocking is black matt material. there are some which are branded like Protostar

BTW here's a link to the threads with pics showing most of the mods I mention

http://stargazerslounge.com/members-equipment-gallery/97917-dob-has-landed.html

http://stargazerslounge.com/diy-astronomer/109577-latest-dob-mods-fan-balancing-weight.html

right, but what is this black matt material used for exactly?

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