130PDS Focuser mod test

[Uranium235]

Here are the first resutls from the modified 130PDS, which has been converted to all threaded connections and an internally housed corrector. I haven't quite got the spacing right yet (need to lose 1mm) so the stars arent quite 100% perfect towards the corners, but its not far behind what the 80ED used to deliver in terms of flatness. Just a wee tweak and it should be perfect. Once I receive the T2-M48 male adaptor it will open up threaded collimation too, so im expecting that to contribute towards the overall result.

The unintended side effect of being slighly over is that spacing distance is that my f-ratio is now approximately 4.38 (570mm), not bad - but its really showing up my 1.25" filters now!   (despite using flats)

Also, another handy consequence of having an internally housed corrector is that the focuser now has to be racked out a fair bit - so far in fact that it now hardly intrudes into the light path! (so no need to hacksaw... phew!)

Addendum 23-11-14:

Please refer to the MkII mod for a more secure mounting method, the short threads of the original TS M54 adaptor were not found to be suitable for repeated mouning/removal of heavy imaging equipment (almost fell off one night!).

http://stargazerslounge.com/topic/215645-skywatcher-focuser-mod-mkii/?hl=%2Bfocuser+%2Bmod#entry2311103

Just testing, an hours worth of exposure on each, the sky quality was rubbish and it was near enough a full moon.

 

 

[nightfisher]

very nice, looks good

[Uranium235]

Cheers

Just a shame I cant do much about those two dark corners, those same corners were a bit dark at f6.38 - but at this speed they're hard to work with. So I need to experiment with my flats a little, anything that will delay the onset of 2" filters! (owwww my poor wallet!).

Edit: For pixel peepers, the fullsize uncropped versions are here:

http://farm3.staticflickr.com/2847/10912684633_330123d8b5_o.jpg

http://farm8.staticflickr.com/7340/10912941983_6c370c8e77_o.jpg

[Coco]

You've done a superb job here...

[davew]

I've just been and looked at the price of that scope. That's outrageously good for the money and plain old very very good at many times more !

Have you done a write up of the mods ? If you have I've missed it.

Is the filter slightly out of line if it only shows in two corners or is that a flats fault ? What the heck, just crop a bit

Dave.

[Uranium235]

davew, on 17 Nov 2013 - 11:08 PM, said:davew, on 17 Nov 2013 - 11:08 PM, said:davew, on 17 Nov 2013 - 11:08 PM, said:

I've just been and looked at the price of that scope. That's outrageously good for the money and plain old very very good at many times more !

Have you done a write up of the mods ? If you have I've missed it.

Is the filter slightly out of line if it only shows in two corners or is that a flats fault ? What the heck, just crop a bit

Dave.

Cheers

I didnt do any write up because I wasnt sure if it would work, but its much better than the compression ring that was there before it. Oh, the filters are I suspect - slightly out of centre, I put that down to the filter wheel not placing the filters not quite in the middle of the M42 apeture (BS astro filterwheel). Its only been an issue since I got the bigger chipped camera.

Basically, the procedure is this:

1) Get the TS M54-T2 focuser adapter, it incorporates an internal M48 thread for the CC - also get a T2 female to M48 male while you are there (so you can thread on your collimator)

2) First problem to be overcome is the Skywatcher coma corrector, the collar cannot be screwed off and therefore has to be cut off if you are to fit it into the drawtube.

3) Stuff a lens cloth into the scope side of the corrector and replace the 2" protective cover, do the same to the camera side of the corrector - but dont replace the endcap (or it will get in the way). That is the end that must be face-down, on a thick(ish) wedge of paper - or folded newspaper (what I used).

4) Next, get a small square of wood to spread the pressure from the G-clamp evenly over the corrector barrel (the end that is capped).

5) Tighten up the G-clamp until its steady enough for cutting, and that a good seal is provided at the base (between the M48 thread and the newspaper).

6) Brace yourself, then make 8 cuts. The first four are the longest (and toughest), cut so you have a squared circle, then cut the four corners straight across. After that, what little is left is easily dealt with using a file. You can probably get away with leaving about 1 or 2mm of it left, just measure it up against the M54 adapter to get a better idea.

I need to add that after each cut, you must remove any loose metal with a dyson or something with a bit of power. Also, allow the CC to cool down a bit between each cut, it can get quite hot. Once the cutting and filing is complete, ensure that all debris (including that on you) has been removed.

7, Release the G-clamp, remove the cloths and check the optics for any bits of metal. If there is any, blast it away with the rocket blower (do not attempt to wipe it off).

8, Now screw the M48 thread of the CC into the M54 adapter, then screw that directly to the focuser drawtube.

9, There ya go, one internally mounted reducer/corrector! (you can paint the bare metal at your leisure)

With the skywatcher CC, the distance between where the collar was - and the base of the t-thread on the M54 adapter is 9mm. So you have a gap of 46mm to play with - its a bit tight, so its only really suitable for CCD cameras.

[davew]

After reading that lot I'm even more impressed.

Sounds like a job for a mini lathe and home made anodising bath !

Dave.

[Uranium235]

No need for special tools mate

Just a G-clamp, hacksaw, file and plenty of elbow grease!

Thats what I love about this hobby, youre often forced to come up with DIY solutions that can cost next to nothing, but work extremely well.

All i need now is a bit more clear sky!

[davew]

No need for special tools mate

Just a G-clamp, hacksaw, file and plenty of elbow grease!

Thats what I love about this hobby, youre often forced to come up with DIY solutions that can cost next to nothing, but work extremely well.

All i need now is a bit more clear sky!

That was aimed at Gina but she may not take the bait

Dave.

[Shibby]

Very nicely done Rob. The bright stars are looking much better than they did before! The coma still seems well corrected to me, too. Although tempting, don't think I could bring myself to such drastic measures

[Mark72]

Looks great Rob, especially the Trunk, M27 is a bit small for this set up.

Mark

[Uranium235]

Thanks guys

Mark, I did M27  as it sits in a reasonably populated starfield, and its the corners I was looking to test. Ive since managed to shave another 0.5mm off the spacing, so Im hoping for improvements tonight. Its going to be a bit tight though, Ive got literally 15min to set up before I have to put the dinner on (or risk having a hungry 3 year old on the rampage!). I've also done a threaded collimation too, so im hoping for some crisp results.

Lewis, is might be worth having a go someday should you ever get another corrector, I have two - so operating on one didnt put me at risk of having nothing should it have gone wrong. But it had to be done, because as it stood - the compression ring was unuseable for any serious AP.

Have to decide what to go for tonight though, Im thinking of a quick mosaic - just to test how well the panes stitch together (curved fields make it difficult).

[Chris]

Just awesome! I miss my 130pds!

[sulaco]

Hi, Having a re-jig of my imaging kit and been following all of these threads on the 130pds as it's been a choice between this or the Ed80.

I'm thinking of stocking withe the reflectors as I have the coma corrector but I wanted to know if this mod would be applicable for dslr photography or is it more to suit the Atik that us being used in your thread.

Thanks

Campbell

[bluedandelion]

At f/4.38 the 1.25" filters will be tight with the Atik. I went with 36 mm. Still the images look great.

Ajay

[Tinker1947]

That's a good result.....

[theo]

Well it sure looks like the work is paying off - great results!!

Pete

[Uranium235]

sulaco, on 22 Nov 2014 - 4:07 PM, said:sulaco, on 22 Nov 2014 - 4:07 PM, said:

Hi, Having a re-jig of my imaging kit and been following all of these threads on the 130pds as it's been a choice between this or the Ed80.

I'm thinking of stocking withe the reflectors as I have the coma corrector but I wanted to know if this mod would be applicable for dslr photography or is it more to suit the Atik that us being used in your thread.

Thanks

Campbell

For a DSLR (assuming its a Canon), it can work - but it would be quite a squeeze. It involves getting an ultra-short M48-EOS adaptor (about 1.5mm) since youve already lost something like 44mm from the camera mounting flange to the CMOS sensor - that leaves you with 10.5mm to play with.

So as you can see, that with a DSLR it will just about fit (in terms of spacing) -  there is absolutely no room for adjustment - which is why its suited more to CCD cameras where you have a lot more room to play with.

For a DSLR I would first suggest drilling and tapping a third M4 thumbscrew hole, in terms of difficulty - its pretty easy. But you do need access to a bench drill and something to clamp the part with - dont try drilling it by hand for gawds sake!   The M4 tap set can be gotten from B&Q for about a tenner.

[Uranium235]

Important

I need to add that this particular mod was done using the old TS M54-T2 adaptor. Which I later found to be less that reliable in keeping the enitre assembly attached to the focuser (it almost fell out once!). Problem was that the M54 thread is way too short, and ater a while it begins to strip the focuser thread.

The super-beefed up-overkill-built like a tank version is here:

http://stargazerslounge.com/topic/215645-skywatcher-focuser-mod-mkii/?hl=%2Bfocuser+%2Bmod#entry2311103

But that requires quite a bit more work, but its major advatage is that is can be adjusted to take out any tilt in the imge.

[Tinker1947]

For a DSLR (assuming its a Canon), it can work - but it would be quite a squeeze. It involves getting an ultra-short M48-EOS adaptor (about 1.5mm) since youve already lost something like 44mm from the camera mounting flange to the CMOS sensor - that leaves you with 10.5mm to play with.

So as you can see, that with a DSLR it will just about fit (in terms of spacing) -  there is absolutely no room for adjustment - which is why its suited more to CCD cameras where you have a lot more room to play with.

For a DSLR I would first suggest drilling and tapping a third M4 thumbscrew hole, in terms of difficulty - its pretty easy. But you do need access to a bench drill and something to clamp the part with - dont try drilling it by hand for gawds sake!   The M4 tap set can be gotten from B&Q for about a tenner.

One of these will save your fingers....

[lensman57]

After reading that lot I'm even more impressed.

Sounds like a job for a mini lathe and home made anodising bath !

Dave.

Yep, time for my 1947 Myford ML7 to earn it's keep.

A.G