Jump to content

SkySurveyBanner.jpg.21855908fce40597655603b6c9af720d.jpg

Skywatcher finderscope RFT conversion


Moon-Monkey

Recommended Posts

Hey gang so I need a little bit of help here I’ve been eying up the Astro tech AT50 from the states but they won’t ship here sadly and I’m really after a tiny scope to fit in a small bag to go travelling etc perhaps on a plane etc now I have a short tube 60 but that’s still far too big IMO I want / need something smaller so here we go … I have a straight through 8x50 (I 🤔 think) skywatcher finder and a 50mm tasco F10 refractor (real bad plastic lenses stopped down to 20mm) 🤣 so I wnat to put the optics from the finder in the other tube cut it down 3D print a female focal back and then put an 1.25” diagonal in to be able to (albeit rough) focus a 1.25” EP here’s what I’ve got any suggestions ??? Oh and before it’s asked the focuser on the tasco is .965 which is fine I have some great vintage circle t ep’s but there going to be horrible in such a fast scope so there out suggestiij lovely people before I start cutting tubes 🤣🤣🤣BE03B413-7883-49B1-9CEA-891A5225DCAA.thumb.jpeg.57af4b5362249bcca93ed14bf3e4ded5.jpeg

Link to comment
Share on other sites

I think that main issue is lack of back focus on that 50mm finder.

Focal plane on it is roughly where black tube ends.

You can check that by unscrewing that simple eyepiece on finder end - and you will find that it has cross hair where focal plane is (so it is in focus when you look thru the finder).

Info online about sky watcher finders is that it has 180mm of focal length.

Now if you measure that focuser you have on tasco scope - you will find that focuser + diagonal will have about that much optical path give or take (diagonal alone is something like 60mm)

In another words - what you thought of doing probably won't work.

What might work would be to get one of these:

https://www.aliexpress.com/item/4000923397029.html?spm=a2g0o.store_pc_allProduct.8148356.19.58015d4a4bsY1f&pdp_npi=2%40dis!EUR!€ 44%2C60!€ 23%2C64!!!!!%40210318c916678562655543276e8a99!10000011178628951!sh

And 90 degree prism with very short optical path.

When you combine those two - you might get short enough optical path to be able to fit it behind the 50mm lens and use that as RFT

Alternative to that is simply to DIY small scope

Get 50mm lens from AliExpress - this might be good option:

https://www.aliexpress.com/item/4000933374862.html?spm=a2g0o.store_pc_groupList.8148356.23.531b2be1TQQwvq&pdp_npi=2%40dis!EUR!€ 15%2C24!€ 12%2C95!!!!!%400b0a050116678564622867697e415c!10000011286156697!sh

That is 50mm aperture 360mm FL lens.

You'll need some aluminum (or PVC) tubing. You can 3D print lens cell and any adapters needed. Add that helical focuser and diagonal - and you have nice scope (with less CA than the finder).

 

  • Thanks 1
Link to comment
Share on other sites

  • 2 weeks later...

Vlaiv is right about the 50mm finder.  There is almost no backfocus and CA is atrocious.  Here is a pic of one in video finder mode with helical focusser and ZWO120MM.  It only works because the ZWO120MM has its sensor at the end of a long snout that reaches a long way forward.  Even then you have to remove the objective lock ring and screw the objective cell right the way in.  If the helical focusser is M42 then you will need to also get an M42 adapter that replaces the eyepiece plate and screws into the OTA tube.  They are available (can't remember where I got mine!), but added to the cost of the helical focusser it all adds up.   Its quite acceptable as a finder but probably not what you are after - why not a  pair of observation binos ?

Simon

P1460084_small.jpg

  • Like 1
Link to comment
Share on other sites

5 minutes ago, windjammer said:

Vlaiv is right about the 50mm finder.  There is almost no backfocus and CA is atrocious.  Here is a pic of one in video finder mode with helical focusser and ZWO120MM.  It only works because the ZWO120MM has its sensor at the end of a long snout that reaches a long way forward.  Even then you have to remove the objective lock ring and screw the objective cell right the way in.  If the helical focusser is M42 then you will need to also get an M42 adapter that replaces the eyepiece plate and screws into the OTA tube.  They are available (can't remember where I got mine!), but added to the cost of the helical focusser it all adds up.   Its quite acceptable as a finder but probably not what you are after - why not a  pair of observation binos ?

Simon

P1460084_small.jpg

Hey Simon thanks for the confirmation there buddy I may be on the road to nowhere … ok so my plan was this … 

I saw on CN a thread and on the 60mm telescope club that the Astro tech AT50’s were great little scopes now being a small apeture freak and loving a challenge I wanted an AT50 to ply with do some solar and take out and about on holiday etc as it’s so super small etc that was my thought train with it being on a budget doesn’t help or I would have ordered a Borg 50 but hey ho I’ll find a way even if I have to buy a lens cell and make everything else 😀😀

Link to comment
Share on other sites

43 minutes ago, Moon-Monkey said:

Hey Simon thanks for the confirmation there buddy I may be on the road to nowhere … ok so my plan was this … 

I saw on CN a thread and on the 60mm telescope club that the Astro tech AT50’s were great little scopes now being a small apeture freak and loving a challenge I wanted an AT50 to ply with do some solar and take out and about on holiday etc as it’s so super small etc that was my thought train with it being on a budget doesn’t help or I would have ordered a Borg 50 but hey ho I’ll find a way even if I have to buy a lens cell and make everything else 😀😀

Maybe this would be solution to your needs then?

https://www.teleskop-express.de/shop/product_info.php/info/p13750_TS-Optics-50-mm-f-4-ED-travel-refractor--spotting-scope-and-guiding-scope-with-Crayford-focuser---perfect-optics.html

It is a bit expensive for my taste, but it does all you want it to do.

  • Like 2
Link to comment
Share on other sites

3 hours ago, vlaiv said:

Maybe this would be solution to your needs then?

https://www.teleskop-express.de/shop/product_info.php/info/p13750_TS-Optics-50-mm-f-4-ED-travel-refractor--spotting-scope-and-guiding-scope-with-Crayford-focuser---perfect-optics.html

It is a bit expensive for my taste, but it does all you want it to do.

Hey buddy I think this is a great option a bit above what I wanted to spend honestly as you say a bit expensive for my taste too however I may find one on the second hand market at some point 🙂🙂🙂 thanks for making me aware of it though Vlaiv 

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.