focal length/eyepiece queries

[squeak (Andrew)]

i have a celestron powerseeker 127,with a claimed focal length of 1000 mm.the max distance that i can measure, from the primary mirror to my eye,is 500 mm. could someone please explain this (apparent) discrepancy ? also, the eyepieces that came with it are "k 20" and "sr 4" . what do the letters stand for? ( my 10" dob, f/l 1200 mm, does measure 1200 mm from primary mirror to eyeball) thanx.

[jjjnettie (Jeanette)]

I think there may be a built in 2x barlow in your scope.

K = Kellner SR = Super Ramsden

[Poita (Peter)]

Originally Posted by squeak

i have a celestron powerseeker 127,with a claimed focal length of 1000 mm.the max distance that i can measure, from the primary mirror to my eye,is 500 mm. could someone please explain this (apparent) discrepancy ? also, the eyepieces that came with it are "k 20" and "sr 4" . what do the letters stand for? ( my 10" dob, f/l 1200 mm, does measure 1200 mm from primary mirror to eyeball) thanx.

It has an internal Barlow lens, which is a bit of a rip-off really.

Out of the box the collimation tends to be horrible too, you may want to sort that out to get better images.

I'm guessing the K stands for Kellner 20mm, the SR for Symmetric Ramsden 4mm, a truly horrible eyepiece for that scope, with zero eye relief (you almost have to place your eyeball inside the eyepiece to use it).

-Peter

[Poita (Peter)]

Ha, JJJ beat me to the punch!

There is an extensive thread on your scope here:
http://www.iceinspace.com.au/forum/s...ad.php?t=27116

[squeak (Andrew)]

thanx. its all a bit clearer now.( unlike the view thru a powerseeker 127!) glad i never read that thread before buying it. probably wouldnt have. glad i did, tho, it has taught me a lot. seems like most people reached the same solutions ( cement in legs, plastic shims, etc.) i also changed both mirrors so that they are pulling onto (with springs) the adjusting screws. i have a bad familial tremor, and this made collimating a lot easier. trying to use a phillips can be tricky (to say the least), and the way my head bobs around, im amazed that i can see anything thru the eyepiece ! still, as dodgy as the scope is, it did open my eyes to the heavens. no looking back, now!