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Skywatcher 150 PDS issues


AbsolutelyN
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I've just picked up a Skywatcher 150PDS in the hope I can set it up (and take it down) much quicker on less favourable nights rather than hauling out the huge 250PDS which requires a 100% good night for it to be worth the effort. On inspecting the scope the drawtube protrudes a long way into the tube and after a few googles this seems to be an issue with the 130pds/150pds which I did not spot before buying. I cant seem to figure out which coma correctors solve or exasperate the issue.  I'm using the skywatcher 0.9x coma corrector. Does anyone know if I'll need to hacksaw the draw tube for good stars?  Current conditions don't allow for even taking the scope outside.

The other issue I immediately found was balancing. Being so much smaller the imaging end with camera/filter-wheel/focus motor seems considerably heavier than the mirror end. I noted ankle weights were good for the 130pds but  suspect the 150 is too big for those - does anyone have any recommendations for balancing the 150pds?  

Any thoughts much appreciated.

Edited by AbsolutelyN
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  • AbsolutelyN changed the title to Skywatcher 150 PDS issues

I've read on several occasions that GPU CC pushes focal point further out so you need to rack out tube more - and it solves issues with protruding focuser tube.

You'll also want to mask off mirror clips for perfect stars.

https://www.teleskop-express.de/shop/product_info.php/info/p6706_TS-Optics-NEWTON-Coma-Corrector-1-0x-TSGPU-Superflat---4-element---2--connection.html

image.png.4992716a20eed49f1e8b6eedcad62bda.png

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Thank @vlaiv much appreciated. I'll be 3d printing a mask for the mirror clips but I just had not anticipated the focus tube issue. Being on a limited budget the coma corrector you mention is great but is out of budget (already have the skywatcher) and that kind of defeats the point of buying the scope as it basically costs the same as the scope itself. Perhaps I'd have been better saving for the TS 150 f/4 and that corrector ... but as is perhaps the hacksaw may the the best option. Interesting though, I dint know those properties of the TS corrector so thank you. 

Edited by AbsolutelyN
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1 hour ago, AbsolutelyN said:

Perhaps I'd have been better saving for the TS 150 f/4 and that corrector

Be ready to change the focuser too. I have just got the TS f4 Photon and then had to spend another £500 on a new focuser and Aplanatic CC as the Baader MPCC was not good enough. (Claimed to be OK at F4, but I could not get it to work).

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Thanks - yes I'd heard the TS f4 focuser was not great. I'd have gone with it but as you've found out it adds a lot of cost needing to upgrade the coma corrector. 

All the mods now done so ready for first light. 18mm chopped off the focus tube, flocked inside, aperture mask around the mirror, bobs knobs added and dovetail switched to Losmandy. Just need a clear sky to test it ... hope I've not copped too much off the drawtube 🙂 

img-1867.jpg?width=1800

 

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Get some 5mmx50 bolts with recessed heads, and move the mirror upwards in the tube. Did that with my 200PDS, works like a charm. Made 3 spacers 15mm thick, this will give room to move mirror 15-20mm. No problem with eyepieces. The drawtube is now flush with the tube when my Canon is in focus.

This mod can be reversed without the need for a hacksaw. Make a drawstring bag in some dark cloth and tie it around the bottom of the tube. Theese tubes leak light unmodified, and the rising of the mirror makes it even worse. I've not done anything regarding the three clips, but I've painted the sides and bottom of the mirror matt black.

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