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SimonS

Converting my SW 9x50 into a guide scope

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Hi all,

I have been starting to experiment with AP for a little while now and I have been contemplating converting my SW 9x50 finder into a guide scope using Orion Starshoot IV as an initial camera.

I have seen a few threads on SGL that talk about doing this, but one thing I have wondered about is focusing the camera.

I am currently looking at getting 2 things, an adapter that will convert the finder into a t-thread:

https://www.modernastronomy.com/shop/accessories/adapters/sky-watcher-clones-to-t-thread-adapter-for-straight-through-finders/

and a helical focuser that will hold the nosepiece of the camera and allow some movement for focusing

https://www.firstlightoptics.com/adapters/baader-t-thread-to-125-helical-focuser.html

Do you think a focuser like this will be a good choice for a guide scope? or is there another way that I can ensure focus using the camera and a fixed t-thread to 1.25" adapter?

Thanks in advance :) 

Edited by SimonS

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Hello,

The description states: "The Sky-Watcher & Clones to T thread Adapter for Straight Through Finders Connects ZWO, QHY6 and Orion SSAG cameras with the T Thread to Sky-Watcher, most Celestron and Orion 8 x 50 & 9 x 50 straight through finders. Other T thread guide cameras will be compatible if their sensors are around 10mm – 15mm below the front surface of the camera."

I don't think you are going to be able to reach focus with an additional focuser and a camera with 1.25" nosepiece. This design allows a T thread camera to be connected as close as possible to the end of the guide scope. The sensor will be then 10-15mm away from the guide scope's end. You then focus by screwing the front element. However, even with this, you may need to unscrew the front element locking ring in order to get the lens even closer to the sensor.

Are you able to detach your camera's 1.25" nosepiece?

Below the adapter there's a link showing what kind of camera you can directly screw on the adapter: https://www.modernastronomy.com/shop/cameras/cooled-ccd/qhy-cooled-ccd-cameras/qhy6/
The ASI 120 fits for sure as well.

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When i converted mine all i used was the adapter and a 5mm extension ring both from Bernard at MA, i could focus just fine using the finders focus ring.

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I did this with the RACI version and all I needed was the adapter from modernastronomy. I reached focus by adjusting the front lens.. Very easy..

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1 hour ago, moise212 said:

Are you able to detach your camera's 1.25" nosepiece?

This is the camera, the nose piece unscrews, unsure what size screw it is, measuring approx 2cm wide (is it a c-thread?)

20180112_155439.thumb.jpg.1a446b561a0f586a83fd8627b1aedf17.jpg

Thanks for the replies, I will probably just get an adapter and see how I get on. I was just a bit worried about how I would get it to stay put....

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I use one of Modern Astronomy's adaptor with my GSO 9 x 50 finder.  My Lodestar just screws straight on to the back of it via the camera's built in C-Mount thread.  I too focus just by turning the front lens of the finder.  If you have a problem with this working loose why not get the focus just tickety-boo then lock it in place with some adhesive tape?

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It might be an idea to email Bern at Modern Astronomy @SimonS and attach the picture - he can advise then.  If you need to try a helical focuser I've got one you can try :smile:

Helen

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Thanks all, I think I will give Bern an email :). When I have got things started, I will report back.

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Hi.

I use the SW Finder as a Guidescope with a ZWO ASI120MM-S.

The ModernAstronomy adapter works a treat (I bought mine from Rother Valley Optics if I remember correctly) with the ZWO ASI120MM.

The biggest problem I have is focussing the guidescope; every time I get the scope focussed and then lock off the ring it moves the focus again.

I keep thinking about buying the ZWO guidescope with helical focus unit from FLO but then I think I should persist and one day I might get the SW tightly focussed.

Nonetheless I achieve very good guiding and achieve 20 min subs with no problem.

By the way, Astrometry.net tells me the focal length is 176mm.

HTH

Adrian

5a59263adbc11_SW-FGASI120MM.thumb.jpg.469742be33533858657b936146ca73b5.jpg

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Apparently it is better to have a guidescope slightly out of focus as the software will find it easier to calculate the centroid :wink:  So nailing focus might actually make your guiding worse!!  

Helen

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8 hours ago, Helen said:

So nailing focus might actually make your guiding worse!!

Thank you Helen - I'll live with slightly out of focus and save myself some money! :)

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Thanks for the images Adrian:).

I heard back from Bernard at Modern Astronomy and he says that because the thread of my camera is slightly smaller than a C-thread, he doesn't have a suitable adaptor so may need to do a 'bodge' job to make my current camera work with the finder. I have started 'saving' for a ZWO camera so I shall wait until I have one of them before going further.

Thanks all

Edited by SimonS

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28 minutes ago, SimonS said:

I have started 'saving' for a ZWO camera so I shall wait until I have one of them before going further.

I find the ZWO works very well. I purchased the USB 3 model and with hindsight the USB 2 would have been more than adequate and perhaps easier from a connectivity point of view. I've had problems with long ( > 3m) USB 3 cables and have found the only reliable solution was an active repeater cable purchased from CPC (Farnell); I need 5m cables to connect the scope etc. to my PC.

I used a colour Altair GP-CAM IMX224 initially but I was having problems getting 'good' guiding. Advice on this forum indicated a mono would be better and I can confirm that is good advice! - it does indeed work better. As an aside the ZWO is supplied with an all-sky 'fish eye' lens which I discovered also fits the IMX224 so I've been having a bit of fun with the two - not that I've produced an image I would venture to share on here!

Good luck.

Adrian

Edited by Adreneline
Clarifiaction re. camera
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Well worth doing but I found the main problem with  my camera was having enough inward travel...then the fine focus could be achieved with winding the front lens in or out..i much preferred this to my Altair 60mm guider I have now..if Riley using as a guider,get a adapter to for the finder to camera..find out your rough focus point and glue it in..

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