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Skywatcher 9x50 Finderscope as a guidescope


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After doing a little scanning of the internets, I have seen that this is a rather popular method of obtaining a guide scope. I'm at the very beginning of this and have notice that much of the crucial detail is left out of all of the tutorials I have seen with all the obvious stuff left in. The way I want to do this:

  • The kit must function as both a finder and a guide scope (after the necessary dis/reassembly, of course)
  • Use a webcam as the sensor placed into the guide scope via a 1.25" eyepiece barrel (that will be glued onto the webcam casing)
  • Use an eyepiece adapter in place the finder's crosshair eyepiece (this obviously needs to be detachable if the first requirement is to be met)
  • Preferably have some kind of sensor focusing so the primary focus can be left in the same position for both purposes.

So, in order to achieve this, I need to know (but can't seem to find anywhere else):

  • The focal length of the finderscope's primary lens (this might determine whether or not it would be worth getting a helical eyepiece focuser to add to the train)
  • The thread type at the end of the tube or if there are any attachments I can buy that would allow a 1.25" eyepiece to replace the original crosshair eyepiece
  • Where on earth I can buy some 1.25" eyepiece barrels. Seriously, I've looked everywhere! How else could I attach the cam sensor to the guide/finder scope?

 

If anyone else has tried/is trying this your advice would help immensely! (Tried adding photos but the site says that my 220Kb and 223Kb files are too big! - ???)

Thanks

Lewis

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Maybe one of these might help?
http://www.modernastronomy.com/product-category/accessories/finder-guider-adapters/
Though quite WHICH may take a bit of research? ;)

Personally I got my friend to "turn down" a standard 2" to 1.25" adapter, cut off an 
appropriate amount of finder tube (with angle grinder) and just "whacked it in"!... :p

But I sense such things DO exist. Might be worth giving Bern @ Modern Astronomy a ring?
(Not sure there will be room for a (unneeded?) Helical Focuser, without a fair bit of surgery!)

Edited by Macavity
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Googling uk skywatcher guider conversion came up with this link

http://www.rothervalleyoptics.co.uk/rvo-finderguider-adaptor-skywatcher-to-c.html

However looking at prices selling yours and buying this might work out cheaper - not sure about mounting but it does come with a decent holder. It might mean sawing of the base of a bracket and attaching it some how.

http://www.365astronomy.com/ZWO-60mm-Finder-and-Guide-Scope-60280.html

They also do the adapter - probably cheaper than the other link

John

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Thanks for the responses, guys.

I had considered selling the finder and going for an all-in-one kit. Some are very reasonably-priced. Unfortunately, there are various issues in attaching most of the cheaper kits to the top side dovetail bar of the OTA which, for the sake of brevity, I won't bother going into.

I decided to buy some throw-away used eyepieces and just unscrewing the barrels. This actually turns out to be rather cost-effective if a little wasteful.

As for the finder attachments, I still can't find any details on the thread gauge of the tube, so am taking the vendor's words on trust that the attachments fit the onto the finder tube.

I gave ModernAstronomy a go (which was very helpful - thanks for the pointer, there) and found these:

The helical eyepiece focuser is needed to bring the sensor to focus. There are non-rotating alternatives for roughly the same price but not with a female T-thread on the scope side, adding the need for more adapters and thus extra cost.

I'll post updates once it's fully assembled.

Thanks again

Lewis

Edited by lewis_riches
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If you are using a computer, you don't need to use an eyepiece as well as the camera for guiding (if I am reading your thread correctly), you can see what the finder is looking at on screen.  Saves a lot of bending and squatting, and saves having to swap over the eyepiece and camera and re-focus.

Got mine from Modern Astronomy, system is brill, finderscope on screen, lovely jubbly.

Carole

 

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Not putting an eyepiece in the train for guiding. My mistake, should have said "helical eyepiece FOCUSER". I have updated the comment.

Sounds good. I'll be using a Raspberry Pi for the guiding calcs, operating the mount over GPIO and controlled by an Android phone via Bluetooth but the idea of having a video feed from the guidecam sounds like something I'd like to add. So, this bit is the easy part!

Lewis

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As I am slowly collecting bits for AP I bought one of the ZWO one's I linked to. I've a lot to sort out first. May as well mention here as using it will be a bit diy.

Nice and light. Pleased about that as finders can be pretty heavy.

Things lock up nicely.

Having looked through a lot of optics I reckon I can get a good idea using them terrestrially. Nice and bright and very sharp even with a 10mm eyepiece and then a 22mm Vixen. 280mm fl. If the sky ever clears I'll see what stars look like but strongly suspect it will be ok. I was bit dubious when I saw that there were no baffles in it.

It will focus with an eyepiece in it but a televue plossl wouldn't unless it was pulled out about 6mm. Distance around 30m. Another old Vixen was ok. So due to looking how much the focus was sticking out I thought I might get away with a 1 1/4 diagonal in it. No. Might be able to by modifying one but doubtful. There is some scope for modifying by making new bits for it where this could work out - with a lathe. The fact that this one has a rotating focus doesn't seem to be much of a problem to me. It certainly isn't with an eyepiece in it and I can't see it being much of a problem with  a guide camera either.

It's a nice holder with 3 adjusting screws that can be locked on each ring but it sits on a short Vixen dovetail. Small holders for these are available but making one or adapting would be a lot cheaper.

So, wont focus with one eyepiece so I could send it back legit but o/all think I will keep it. I was surprised just how light it was given it's 60mm objective. Pity about the work needed. The focus adjustment could have been longer. May well not be a problem with a cross hair eyepiece but it would benefit from an eyepiece focal length that maximises the field of view, say 32mm giving a mag of just under 9x :smile: the edge of the field  might be a bit colourful using a 1 1/4" eyepiece like this. It's only intended to be used over a small sensor.

Then there is the work needed to make some sort of camera par focal with an eyepiece.

John

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