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Imaging Refractor please help me choose one

Kai

By Kai
in Discussions - Scopes / Whole setups

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FLO

FLO

Posted
Posted

I figure you won't need the huge flat field of the Pentax as the chip on the Atik is tiny in comparison.

Tony makes a good point, unless you plan using a large imaging sensor then you won't exercise the Pentax to anything like its full potential.

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ngc2403

ngc2403

Posted
Posted

hey,

just had a look at that image again and thought that i would make clear the thing that i thought made the Pentax non-apo.

this three pictures are crops out of the main image

9332_normal.jpeg

(click to enlarge)

9333_normal.jpeg

(click to enlarge)

9334_normal.jpeg

(click to enlarge)

the colour in this images is quite bad IMO, and shows me that the pentax although it maybe the best flat field first as an spo it is second best.

i would of used the images from Ian king site however they have been compressed for the web site and it hides the colour.

the sky 90 is one of the refractors i too would like to have, and i know someone who has one, they speak highly of it :undecided:

ally

p.s. It is called and apo by pentax not steve at FLO or Ian King

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Ben Ritchie

Ben Ritchie

Posted
Posted
As Ben is a member on SGL i hope he might catch this thread and give me his opinion.

Eventually...! :undecided:

I've PM'd, but in the end I went for the Borg 77ED rather than the Pentax. As a bit of background, i'm looking at a long-term purchase here that must perform with a STL-11k sized CCD (not that i'm in any danger of being able to afford one any time soon!). I felt that the corner performance on the Pentax images I could find - as highlighted by Ally - was unacceptable for the price, both in terms of colour correction and sharpness. The focuser and some of the adapters required were secondary considerations.

The Borg system is a complete swine to understand (it's like doing some bizarre form of Soduku), they're idiots for making it so complex IMHO because it must put lots of people off. But, once you start to get to grips with it, it's a very versatile system. For similar cash to the Pentax 75 you can get the Borg 77ED II + 0.85x reducer + feathertouch focuser, which gives you point stars with a big-chip CCD (some vignetting in the corners, but should be fixable with flats) and a decent focuser, you can also move to f/4 although it's not cheap. Fancy a 4" refractor instead? Just swap over the objective. Right now that's all hypothetical - don't have the cash - but the basic performance looks very promising compared to the Pentax.

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Ben Ritchie

Ben Ritchie

Posted
Posted

Oh, as for the Tak choice, I've owned a FS-60C(SV) and they're lovely 'scopes, but not really directly comparable with the Pentax because they're cetainly not optimised for flat-field performance. However, they *are* flat across a 285-sized CCD, but any larger than that and you're looking a the Tak flattener + adapters - not cheap. Focus travel is very limited too, so you need a good selection of extension tubes etc. which can cause problems with tilt/sagging. Properly setup though they're really nice.

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