Focal Train Help!!!!!

[Peakedge]

Over the last few weeks I have aqcuired some new bits and bobs; ZWO120MM-S and ZWO manual filter wheel. I'll be using these on my SW200PDS, having a go at a bit of lunar and planetry stuff. I also want to have a go at basic deep sky with this kit and possibly try cooling the camera. For any of this, will I need to use my SW F5 coma corrector? My issue is that I cannot work out which order to put all the bits and how to attach the coma correctorto the filter wheel. Obviously the camera and filter wheel have 1.25" adapters whilst the CC has 2". I really dont know the thread sizes for the internal or external threads of any of them or the adapters needed. Im also concious that the CC has 55mm backfocus.

Any help would be very muchly appreciated. Guess I've got time to sort this before we next have clear skies.

David

[Dr_Ju_ju]

This is what I have, working outwards from the focuser tube to the camera(s)

1. coma corrector, 2. OAG (with guide camera if fitted), 3.filter wheel, 4. main camera

hope this helps

[Peakedge]

Thanks Julian.

I don't have the OAG but makes sense. What do I need to attach them together? The threaded extensions with ther filter wheel do not fit the CC.

 

David

[david_taurus83]

You need an adapter with male threads both sides. Did a thin adapter come with the filter wheel? It enables you to screw the camera directly to the filter wheel.

[Peakedge]

I've managed to connect the filter wheel to the camera but not to the CC.

David

[david_taurus83]

How have you connected the camera to the filter wheel? With the 1.25" stuff?

[Peakedge]

2 minutes ago, david_taurus83 said:

How have you connected the camera to the filter wheel? With the 1.25" stuff?

With the thin adapter you mentioned above. It originally had the all sky lense attached.

[david_taurus83]

Does the CC not screw into the other side of the filter wheel?

[Peakedge]

14 minutes ago, david_taurus83 said:

Does the CC not screw into the other side of the filter wheel?

No. The filter wheel hole is about 8mm smaller than the CC.

[david_taurus83]

Ah. So the Skywatcher CC is an M48 thread? You need an M48 to M42 adapter. Is the thin adapter you've already used about 2mm thick? So 12.5mm camera face to sensor, 2mm adapter, 20mm filter wheel, 0.5mm for filters, that leaves you 20mm short for the optimum 55mm back focus.

 

You could get something like below and a 10mm M42 or M48 extension and that will get you pretty close.

[Peakedge]

3 minutes ago, david_taurus83 said:

Ah. So the Skywatcher CC is an M48 thread? You need an M48 to M42 adapter. Is the thin adapter you've already used about 2mm thick? So 12.5mm camera face to sensor, 2mm adapter, 20mm filter wheel, 0.5mm for filters, that leaves you 20mm short for the optimum 55mm back focus.

 

You could get something like below and a 10mm M42 or M48 extension and that will get you pretty close.

Could do the trick. The ring I used allows the filter wheel to sit flush to the camera so suppose 12.5mm plus 20mm for filter wheel and 0.5mm for filters (do you also add the filters on since they inside filter wheel?) I take it the adapter is 10mm so all together that makes 43mm, 12mm short. So suppose some sort of extension tube?

[david_taurus83]

12 hours ago, Peakedge said:

 (do you also add the filters on since they inside filter wheel?)

Glass refracts light slightly so it adds to the back focus. They say you should add on about a third the thickness of the filter. So if you count a filter and say the glass screen above the camera sensor you could simply add 1mm there or there abouts. That leaves you 11mm short then. Another 10mm spacer and some delrin shims maybe. The 55mm optimum isn't always perfect. It depends on different setups. A millimetre or so either side is usually close enough. Try and source an adapter (get confirmation on the M48 thread as I'm only assuming) and spacer and see how that works. The sensor is small on that camera so it might just be enough. For lunar and planetary you don't really need the CC at all. But no harm getting it right from the start anyway.

[Peakedge]

25 minutes ago, david_taurus83 said:

Glass refracts light slightly so it adds to the back focus. They say you should add on about a third the thickness of the filter. So if you count a filter and say the glass screen above the camera sensor you could simply add 1mm there or there abouts. That leaves you 11mm short then. Another 10mm spacer and some delrin shims maybe. The 55mm optimum isn't always perfect. It depends on different setups. A millimetre or so either side is usually close enough. Try and source an adapter (get confirmation on the M48 thread as I'm only assuming) and spacer and see how that works. The sensor is small on that camera so it might just be enough. For lunar and planetary you don't really need the CC at all. But no harm getting it right from the start anyway.

Thank you for all this info. It all makes (sort of) sense now. Have ordered the adapter and extension ring as pretty sure the thread is M48. What do you use for smaller sizes such as 1mm? Should I invest in these https://www.widescreen-centre.co.uk/baader-t-2-ajustment-spacer-rings.html or can something else be used?

David

[david_taurus83]

Their expensive for what they are but yes, you could use those. Those ones are a bit of a struggle to fit over the M42 threads. I've used them myself! If it was me, I'd try without them first.

[Peakedge]

Just now, david_taurus83 said:

Their expensive for what they are but yes, you could use those. Those ones are a bit of a struggle to fit over the M42 threads. I've used them myself! If it was me, I'd try without them first.

That's what I thought. Guess could use anything as a shim if I needed to. I'll let you know how it goes when my order arrives and we get some clear skies!!!!!

Thank you for all your advice.?

 

David

[Peakedge]

On ‎29‎/‎12‎/‎2018 at 11:43, david_taurus83 said:

Their expensive for what they are but yes, you could use those. Those ones are a bit of a struggle to fit over the M42 threads. I've used them myself! If it was me, I'd try without them first.

On ‎29‎/‎12‎/‎2018 at 11:46, Peakedge said:

That's what I thought. Guess could use anything as a shim if I needed to. I'll let you know how it goes when my order arrives and we get some clear skies!!!!!

Thank you for all your advice.?

 

David

Got the adapter and ring and used metal clips from a garden clip for the remaining mm or two. Fit nicely around the threads!

Eventually had a gap in the clouds on Sunday and fired up the camera and took the following comprised of 2 mins of frames, stacked in AS2 and wavelets in Registax.

Many thanks for your advice.

 

David

 

[Astro Imp]

Nice image David, well done.