Celestron 6inch SCT V's Skywatcher 127mm Mak Cass

[John]

Hi,

Has anyone owned or tried these 2 scopes and can comment on their relative planetary performance ?. I'm wondering if the smaller secondary in the Mak would compensate, at least to some extent, for the reduced aperture against the SCT which I think has a significantly larger secondary.

I'm interested in contrast and resolution - I assume that the SCT would win on light grasp.

I'm thinking of getting a longer focal length compound scope to complement my 102mm F6.5 ED refractor. An alternative might be the new Skywatcher 6inch F8 newtonian I suppose but the tube length is a bit unwieldy. Can't go above 6 inches aperture I feel as the scope has to sit happilly on my EQ3-2 mount.

All thoughts welcome.

Cheers,

John

[Cloudwatcher]

Can't comment on the Celestron John, never owned an SCT but I find the 127 Mak excellent for Luna and Planetary viewing. It's lightweight,nice and managable too. Indeed I have used it on my EQ1 as a kind of 'Grag n Go' without any problems.

CW

[GazOC]

I've never owned 6" SCT (I've owned 8" and 10" models) but I've owned a couple of 127mm Maks. I'd be VERY surprised if a 5" Mak wasn't a better planetary scope than a 6" SCT.

[John]

I've never owned 6" SCT (I've owned 8" and 10" models) but I've owned a couple of 127mm Maks. I'd be VERY surprised if a 5" Mak wasn't a better planetary scope than a 6" SCT.

Thanks Gaz (and CW for the earlier reply), - that's what I would think as well but I've not owned either. Does anyone know how big the secondary (diameter) is on the Skywatcher 127mm Mak ?.

John

[GazOC]

Its ~33% but I think I remember reading that the baffle on the 127mm is oversized and stops the effective aperture down the 121mm.

[PJF]

Even allowing for your fast ED Vixen not being the final word on colour correction, it's still a better device for viewing the planets compared to these two 'scopes you're considering. Four inches of quality unobstructed aperture will easily see off the 4.7 inches of so-so 33-35% obstructed aperture of the Maksutov. Even the significantly larger six inch SCT (37% obstructed) will have to be very good to come close. Since you already own the better option, my advice is to save the money. And I say this despite having a nice example of the Mak I'm getting ready to sell - so you know I mean it.

The central obstruction on the "127mm" Mak is about 40mm (the mirrored spot is 38mm but the baffle behind is slightly larger). The clear aperture of the 'scope is 120mm (and this size is what Synta and co would describe this 'scope as being if they weren't indulging in naughty marketing). A Maksutov corrector (front glass) diverges the incoming light rays, so the primary mirror needs to be bigger than the corrector in order to receive all the light. On the Synta "127mm" Mak the mirror is the same size as the corrector (127mm), so it is only receiving light from the central 120mm of the corrector.

rgds

Peter

[GazOC]

Does the 6" SCT have an oversized primary? SCT correctors also diverge the light rays....

[GazOC]

Does the lack of an oversized primary act as an aperture stop or just mean you don't get a fully illuminated field? I think its the latter......??

[John]

Even allowing for your fast ED Vixen not being the final word on colour correction, it's still a better device for viewing the planets compared to these two 'scopes you're considering. Four inches of quality unobstructed aperture will easily see off the 4.7 inches of so-so 33-35% obstructed aperture of the Maksutov. Even the significantly larger six inch SCT (37% obstructed) will have to be very good to come close. Since you already own the better option, my advice is to save the money. And I say this despite having a nice example of the Mak I'm getting ready to sell - so you know I mean it.

rgds

Peter

Thanks Peter - I'm not planning on parting with the Vixen ED, just mulling things over

If I got a 2nd scope it would probably make more sense if it was an 8 inch dob or similar for DSO's.

John

[russ]

Owned both the 127 and C6. The 127 was a cracking scope but not up to the task of beating an ED100. While the C6 was slightly disappointing on the lunar/planetary side but strangely good on the deepsky :? I preferred the views through the SLT102 when viewing Jupiter and the Moon, despite the little bit of false colour in the SLT. There could have been some cool down issues with the C6 or it being more adversely affected by the atmosphere?

Bottom line.....Having owned the Vixen 102M achromat and seen what that could do on Saturn compared to the C6, I'd eat my hat if either (C6 or 127) could provide a better view of the planets than your Vixen. Your plan B of the 8" dob sounds a good one.

[The Warthog]

Even allowing for your fast ED Vixen not being the final word on colour correction, it's still a better device for viewing the planets compared to these two 'scopes you're considering. Four inches of quality unobstructed aperture will easily see off the 4.7 inches of so-so 33-35% obstructed aperture of the Maksutov. Even the significantly larger six inch SCT (37% obstructed) will have to be very good to come close. Since you already own the better option, my advice is to save the money. And I say this despite having a nice example of the Mak I'm getting ready to sell - so you know I mean it.

In considering the obstruction, we are talking area, not linearity. The 33% obstruction comes down to about 10% when you consider area, and the 4.7" Mak, even with its large obstruction, has the light grasp of a 4.4" refractor. (all figures approximate) The influence of the obstruction on contrast is another matter, but the effect of the obstruction on light grasp is less than commonly believed. In a Newt, it's about 5%.

[PJF]

"In considering the obstruction, we are talking area, not linearity.

..

The influence of the obstruction on contrast is another matter..."

Contrast is the joint primary attribute that John mentioned in his original post, so it's the 35% linear obstruction that is relevant to his enquiry.

.

[FLO]

Spare a thought for comfort

Contrast and resolution are important but so is focal length as it determines the eyepiece required for a given magnification. The Skymax 127 Mak' and Celestron C6 SCT both offer 1500mm focal length (over double the f6.5 refractor) so can achieve the high magnifications necessary for planetary observing without resorting to short focal length eyepieces.

[John]

Spare a thought for comfort

Contrast and resolution are important but so is focal length as it determines the eyepiece required for a given magnification. The Skymax 127 Mak' and Celestron C6 SCT both offer 1500mm focal length (over double the f6.5 refractor) so can achieve the high magnifications necessary for planetary observing without resorting to short focal length eyepieces.

That was one of the main things that was leading me down this path Steve

John

[FLO]

I have actually bought a Celestron Nexstar 6 SE for my own use but haven't got around to using it. I wanted an easy to setup back-garden scope that was good at observing objects less effected by light pollution - lunar, planets, globulars and brighter deep-sky-objects like the Ring and Dumbell. It also has enough aperture for use with a Baader Neodymium and will make a fine solar scope when fitted a full-aperture solar filter. I had considered the Skymax 127 but was swayed by the SE GOTO mount (which will also accept a short wide-field refractor via a standard Vixen/Synta dovetail) and by all the positive feedback the C6-S is generating. I'll let you know how it goes

[MartinB]

I haven't compared these 2 scopes but have had plenty of viewing of Saturn through an ED120 and a C8 often side by side.

The first thing I found was that the differences between the views weren't as marked as people had led me to expect. The colours are a bit more vivid through the refractor and the extra bit of contrast made the features stand out a little more clearly - "little" being the important word. In poor seeing I think the refractor gives the more pleasing view since the resolution advantage of the larger scope doesn't make itself felt. In good seeing although the refractor view still has the advantage in terms of contrast - Cassini is that bit blacker, the SCT is able to show significantly more detail because you can crank up the magnification to a higher degree than with the frac.

Lunar views with the frac are lovely and crisp with really dark shadows but when swapping to the SCT tiny details spring up that just aren't there with the frac. All in all though the views aren't that different until you go up to high powers in good seeing when the SCT wins out.

So it's very much personal preference. Now there's over 3" difference in aperture between my 2 scopes so the resolution advantage of the 6"SCT over the 5" Mak is likely to be less. You really have to try to have a look yourself. I don't think you'll be disappointed by either.

Just be careful about the subjective views of others, we all see things differently and have differing tastes and biases

.