Improved focuser for 130P reflector

[nigelbeaumont]

I've been given a Skywatcher 130P reflector (650mm FL one with parabolic mirror), and I'd like to replace the cheap and nasty plastic rack and pinion focuser with a better quality one so I can use it for imaging. Any ideas where to source one that can be fitted with minimal mods to the OTA? Given a new 130PDS is £159 from FLO, I want to spend less than that. My initial thought was a Borg helical type from Teleskop Express. I'm only going to use it with an Atik 428EX CCD with about 13mm back focus and a relatively small chip, so I only need a 1.25" focuser and I don't think I'll need to move the primary up the OTA to achieve focus

[beamer3.6m]

As I understand it you are stuck with the stock focusser on the 130p.

The 130pds has the craford however dont under estimate the rack and pinion as whilst not the best it is also quite solid.

[nigelbeaumont]

The rack and pinion is not bad, but it's one speed - I'm hoping to get some form of fine or two-speed focussing eith a Bashtinov mask for imaging

[Uranium235]

Unfortunately, its not good news....

1) The 130p tube is longer than the 130pds, so the focus point for a camera is shifted inwards - meaning you may not be able to come to focus. The only way around that is to shift the primary up the tube.

2) The 130p has a 1.25" focuser, so a coma corrector is out of the question (and yes, you will need one with your choice of CCD camera - there is no getting away from it)

3) There is no replacement focuser for the 130p or pds, you are stuck with what you have. You could maybe bodge a 2" crayford pds focuser on to it - but you may as well buy the whole pds telescope.

4) The secondary mirror on the 130p (I think) is smaller than the 130pds, so you will have more vignetting.

In the grand scheme of things, £159 is pretty much a rock-bottom price for an AP capable telescope. You could easily spend half of that just tooling up to mod the 130p - with no certainty that it will work as you wish.

[nigelbeaumont]

I was rather hoping that I wouldn't need to move the primary - the back focus on the 428EX is 13.5mm and i have to wind the draw tube out more than that to achieve focus, so I was assuming that there was enough inward travel to achieve focus with the CCD (not going to use the DSLR with it).

Im also surprised I need a coma corrector for the CCD - it's only 8.8 x 6.6 mm, so a lot smaller than the APS-C sensor in my DSLR.

I might just give it a go and see how accurately I can focus - also I have a spare 2" Crayford focusser off my 200PDS, and I might get a local engineering shop that gives me very good prices to quote for a flange to fit it to the smaller diameter OTA - the only downside is having to cut a larger hole for the larger diameter draw tube

[beamer3.6m]

Why not buy a skywatcher motor focuser to give fone foxus control. It also stops the focuser from sliding under the weight of a camera.

[ronin]

There does not seem to be a great deal in the way of upgrading the focuser on the 130P, or I half guess anyother that is a 1.25" only unit.

TS have a number of focusers but nothing is really an improvement.

As to the need of a CC no idea but try it out without one for now as you say.

[Uranium235]

Trust me, you will need a coma corrector with that chip size. I tried it with an Atik 341L and an f5 150p (identical chip size 8.9x6.7mm) and got coma (been there, tried it, brought the t-shirt). You could crop the image, but if youve gone to all the trouble of buying a CCD - you dont want to be throwing pixels away.

[nigelbeaumont]

[removed word] - more expense....... and 2 weeks without clear skies now, so my chances of a Veil Nebula mosaic with my DSLR are rapidly receding. Am I grumpy? Best ask my wife......

[Scott]

[removed word] - more expense....... and 2 weeks without clear skies now, so my chances of a Veil Nebula mosaic with my DSLR are rapidly receding. Am I grumpy? Best ask my wife......

Frustrating as it is Nigel, the veil is around a little bit longer and if you miss it this yr, there's always next

[Uranium235]

If Nigel already has the CCD camera, then he already has the gear needed to get the Veil (depending on how much of it you want). The 428 (assuming its mono) and the ZS71 (with reducer) should comfortably cover the broom and wisp in 4 panes to a fairly good standard (maybe 2 panes at a squeeze). To cut the capture time down further, just skip the green channel (the veil responds well to synth green). Even better if he had NB filters, then all thats needed is two channels per pane.

I think that DSLR needs to go into retirement

[nigelbeaumont]

I've started playing around with the CCD, doing darks and bias frames and setting up Sequence Generator Pro, but was going to wait until the nights lengthen before starting the CCD learning curve. I have found that waiting until nearly midnight before beginning imaging is not conducive to efficient learning, so I was continue with the DSLR for the time being.

The camera is a mono one, and I have NB filters as well as LRGB ones, so the Veil is high on my hit list once I have got the hang of CCD imaging. Took me about 6 months to get reasonable images out of the DSLR, and I have a great deal to learn about CCD imaging and processing

[Andyfx]

Upgrading your focuser would be a tricky job. I posted a thread a couple of years back when i refurbished an old Orion optics 150. It had a standard r&p focuser and I upgraded to a TS 2" crayford, this meant having to carefully mark the Ota after removing the original focuser, cutting into the tube, smoothing painting drilling etc. The end result was very good but, as already mentioned, due to time spent and cost you'd. Be better off buying a 130pds.