Catseye Precision Spotting Template and SW 150P Primary Mirror Woes

[AdeKing]

Last night I attempted to centre-spot the primary mirror of my SW Explorer 150P using the (very expensive for what it is) Catseye spotting template and reflective hotspot.  The template was the official version purchased from FLO and not the downloaded version from the Catseye website which is apparently not scales for accurate printing.

However, I have to admit to rushing to finish the job and didn't properly measure the diameter of the primary, assuming of course that a 6" (150mm) mirror would be 152mm in diameter (152.4mm to be precise as that is the conversion from 6" inches to mm, and is the diameter that the 6" circle on the template measured, well its actually more like 152.5mm but who can tell the difference between 0.4mm and 0.5mm on a standard ruler).

However, getting a results where the centre-spot appeared to be off-centre, I measured the diameter of the primary in my 150P and found it to actually only be 147mm in diameter (so 5.4mm smaller than the 6" diameter ring on the template).

I'm blaming nobody but myself for this, as I rushed to finish the job and didn't check everything properly first, but I was quite surprised to find that the mirror is only 147mm in diameter, as all of the Skywatcher specs state that the optical diameter is 150mm.

The problem is that I now feel that the money I've spent on the Catseye Spotting Template has been completely wasted is it doesn't have a ring of 147mm diameter, so I'll be going to staples on the way home for some acetate to make up my own template.

Grrrrr, very frustrating and I will know MUCH better for next time.

Ade  

 

[the bishop]

Hi, I'm finally building up courage to go ahead and centre spot my sw 150

as it hasn't  got one ? and have been putting it off and wondered how everything finally turned out for you ?

gra 

[AdeKing]

My centre spot is very slightly off-centre and I was too tight to pay for another reflective spot so I'm putting up with it.

I can get collimation close with the Cheshire then fine tune with a star test but the Cheshire seems to be good enough.

There is a good tutorial for centre spotting the primary on the Astro-Baby website.

http://www.astro-baby.com/TAL Telescope Rebuild/Telescope Mirror Cleaning.htm

If you use the template just size it up against the mirror and take your time to line everything up before sticking the spot down.

Good luck.