New (to me) Orion Optics SX150 f6 Newtonian - planned mods

[Moonshane]

Hi all,

I have just taken a punt on a scope of Ebay and it seems to have worked out well enough see http://stargazerslounge.com/members-equipment-gallery/167602-you-cant-always-get-what-you-want.html

It's a 20 year old scope but as as a dob owner, I cannot help myself with regard to thinking I can make any scope better and I have some plans for this scope. Below are all my plans (as Eric Morecambe would say, not necessarily in the right order).

1) Flock the interior and blacken all the shiny bits.

2) Replace current fixed finder (upright image, left right reversed) with a standard Synta QR dovetail shoe and RACI finder.

3) Add Telrad finder base

4) Add better primary collimation knobs and secondary knobs. Possibly add stiffer springs to primary.

5) make a dew shield

6) change the green LEDs on the pedestal feet for red ones

7) modify the mount to convert to ALTAZ

8) possibly make a truss based suitcase dob for holidays etc.

9) possibly change to new focuser with 2" barrel. This would give me another 0.5 degree field to 2.2 degrees overall.

10) change the metal thumbscrew in the focuser for a nylon one to prevent eyepiece scarring - done!

11) add a dob knob

12) make a solar filter

[MjrTom]

Sounds good to me

Look forward to hearing the progress

[michael.h.f.wilkinson]

Nice project. If you change the focuser, you may have to put in a larger secondary.

[Moonshane]

good point Michael. I am having second thoughts about the focuser as I don't think I really need a larger field, it's not too bad in use and the whole idea was as little weight as possible. this is effectively my wide field scope and at lower powers, I don't really need the fine focus.

I generally prefer compression ring fittings but with a alt az set up and 1.25" eyepieces I reckon I'll be fine with the hard plastic M4 screw, with which I replaced the original metal thumb screw.

[Moonshane]

here's some pics which are hopefully self explanatory!

[swamp thing]

Looks real nice Shane.

Look forward to hearing what kind of FOV you get.

[John]

Looks a nice scope Shane - OO were clearly taken with a Vixen-type colour scheme back then !.

I've not seen that approach to the secondary spider supports for a few years - it will be interesting to see if the 2 thicker vanes cause some diffraction effects.

F/6 is a really nice focal ratio for newtonians I think - I wish more of the Chinese ones (with the honorable exception of the Skyliner 200P) would go for that spec.

[Glasspusher]

Shane,

The vanes on the secondary mirror holder look a bit on the thick side to me, might be worth looking at improving this as part of the project?

John

[Moonshane]

well I got a chance to have a think and a play today so managed to get the old finder removed and instal a new QR synta shaped foot for my usual 9x50 RACI finder. will also work with a Baader Skysurfer 3 if I ever have a shootout with all my scopes.

also, cleaned and regreased the focuser but in truth there's not much improvement - it's a decent all metal focuser and still has a stiff spot in mid range. I suspect the rack is contacting the main body so may go carefully with a needle file to shave away a little and see if this helps. There's teflon pads inside the body - encouraging!

more importantly I have found a way to take the mount apart and reassemble as an alt az without major surgery in a way that will allow me to put it back to an EQ mount easily if required.

I basically turned it around and upside down and it's now like a GIRO (well almost). I am much happier with it now and will add some pics to show what I have done shortly.

thanks for the comments too re the secondary holder. I agree that I will need to check the diffraction spikes (I presume four?) are not too bad. that said, I once saw something at OOUK which suggested there's no visible difference between 0.5mm and 5mm vanes in terms of diffraction spikes produced. a 4 vane 6" spider is not expensive so it's certainly an option in due course.

[ismangil]

Shane this is excellent you got the little brother of my OOuk 200mm scope!

Exactly same design tube and mount just bigger mirror.

I will be very interested in following your mods. Especially how you made it into alt-az.

You didn't mention anything about mirror ventilation. I've done tests using in/out thermometer on my mirror, it can't keep up with the cooling of the ambient temp, always more than 2 deg difference.

I am contemplating drilling holes, or even making a new mirror cell?? Gary Seronik's design is quite interesting: http://www.garyseronik.com/?q=node/24

[Moonshane]

Shane this is excellent you got the little brother of my OOuk 200mm scope!

Exactly same design tube and mount just bigger mirror.

I will be very interested in following your mods. Especially how you made it into alt-az.

You didn't mention anything about mirror ventilation. I've done tests using in/out thermometer on my mirror, it can't keep up with the cooling of the ambient temp, always more than 2 deg difference.

I am contemplating drilling holes, or even making a new mirror cell?? Gary Seronik's design is quite interesting: A Simple Double-Plate Mirror Cell for Your Reflector | Gary Seronik.com

hi Perry - what a coincidence!

I'll put some pics up tomorrow maybe re the altaz connversion - it's just a matter of moving components around. I'll have to cut one of the stainless rods though and also for stability drill one hole through the central fixing tab and add a bolt. alternatively, I may drill and tap a hole through the mount base plate and into one of the rod housings - all will become clear in due course.

not thought about cooling yet. usually with a 6" mirror it's not an issue but I may also cut some wedges out of the end plate and then strengthen the remaining struts with 5mm aluminium. I'll have a think about the cell as mine is currently stuck with silicone (the usual three blobs) which I am not really keen on.

[ismangil]

Oh that's different cell design then. Mine is a three mirror clip design, steel. The back cover looks exactly the same though.

[callisto]

Shane,

The vanes on the secondary mirror holder look a bit on the thick side to me, might be worth looking at improving this as part of the project?

John

Not an issue at all, have these same vanes on my Orion dob and performs perfectly

Mark.

[Glasspusher]

I once saw something at OOUK which suggested there's no visible difference between 0.5mm and 5mm vanes in terms of diffraction spikes produced. a 4 vane 6" spider is not expensive so it's certainly an option in due course.

Shane, it appears you might be right. I have done a little googling and it looks like vane thickness is not as critical as might be thought!

John

[yesyes]

probably a silly question, but what are the LEDs on the base of the pier for? Are those "position lights" to stop you tripping over it?

[ismangil]

Shane, it appears you might be right. I have done a little googling and it looks like vane thickness is not as critical as might be thought!

John

I do read vane shape is important. The curved shape seems to produce most agreeable diffraction patterns. Again I'm quoting my guru Gary Seronik. He explains things so clearly and somehow discusses the things I have questions!

[Moonshane]

probably a silly question, but what are the LEDs on the base of the pier for? Are those "position lights" to stop you tripping over it?

spot on - anti trip devices.

not even sure if I'll use them to be honest.

[Moonshane]

I do read vane shape is important. The curved shape seems to produce most agreeable diffraction patterns. Again I'm quoting my guru Gary Seronik. He explains things so clearly and somehow discusses the things I have questions!

the curved vanes produce a more aesthetically pleasing spike free view but many say that they also smear the diffraction across the whole field. so you gain aesthetically but overall sharpness may be affected. I'll stick with straight ones myself.

[Moonshane]

I did another minor mod today, replacing the primary collimation wing nuts with some M6 threaded rod connectors. they make for easier and more accurate tuning of the collimation. I'll eventually replace with something more aesthetically pleasing like these DIN467 Flat Knurled Nuts maybe

I also used some teflon M6 washers which make for a much slicker turning.

I was somewhat shocked that the collimation bolt on the primary was not a countersunk M6 bolt through from the mirror side of the cell plate but a stud, screwed into the back side of the plate. It popped out while I was adjustng things.

I may redo the cell after all (or just epoxy the studs in place maybe).

Getting this short newt makes me feel much happier than having the short refractor. I am (and have probably always been) a confirmed newt man.

[Astrokev]

Hi Shane

I thought you already had a 150mm newt. What d'you hope to achieve with this scope that you can't get with your others, or is just that you like to tinker?

[Grunthos]

I think I'd be prepared to fork out £77/£112 for a second hand reflector to tinker with!

Not much to loose really.

I'll need to keep an eye out on ebay and take pot luck...

[Moonshane]

Hi Shane

I thought you already had a 150mm newt. What d'you hope to achieve with this scope that you can't get with your others, or is just that you like to tinker?

hi Kev

I do have a 6" f11 dob but this gives me a relatively narrow field of view and also the tube is 5 feet long so tricky to get in the car for hols etc. this f6 version has a much shorter tube and allows eventually a 2.2 dgree field so I can fit e.g. Pleiades in the field of my current eyepieces.

Although, yes, of course, I love to tinker!

I think I'd be prepared to fork out £77/£112 for a second hand reflector to tinker with!

Not much to loose really.

I'll need to keep an eye out on ebay and take pot luck...

sure worth picking the right one. go for it! what it does is remove the fear of a new one in terms of mods or minor damage etc when cramming it into a car.

[cotterless45]

Yo, yep really surprising what comes up on fleabay and other sites now and again. Always worth taking a punt. As a confirmed mirror man , I was pleased to get a Vixen 90 custom M for £112, still in it's original boxes and beautiful to use.

[Gina]

Oh there's nothing like tinkering I love it I like DIY too but a scope is a bit beyond me I think. At least ATM - but who knows in the future I think cheap bits from eBay with the view that if it isn't any good it's not a great loss is quite a good way to go. My latest is a perfectly good game pad for a fiver I'm pleased with that

[Moonshane]

quick update.

my original list as follows and with what has been done:

1) Flock the interior and blacken all the shiny bits. done

2) Replace current fixed finder (upright image, left right reversed) with a standard Synta QR dovetail shoe and RACI finder. done

3) Add Telrad finder base done

4) Add better primary collimation knobs and secondary knobs. Possibly add stiffer springs to primary. done

5) make a dew shield using one made for other scope

6) change the green LEDs on the pedestal feet for red ones won't be using them as I have removed the main trip risk - the large handwheels. as I am using in alt-az mode, there's no major need to level.

7) modify the mount to convert to ALTAZ - decided to use with my GIRO mount and sell the mount that came with the scope.

8) possibly make a truss based suitcase dob for holidays etc. still on the horizon.

9) possibly change to new focuser with 2" barrel. This would give me another 0.5 degree field to 2.2 degrees overall. will definitely be changing this in due course

10) change the metal thumbscrew in the focuser for a nylon one to prevent eyepiece scarring - done!

11) add a dob knob ordered but not yet received

12) make a solar filter done

here's some pics