Lunar / Planetary scope - Classical Cassegrain or 4" ED

[Davesellars]

I hadn't thought about that.  A fine helical focuser at the diagonal could alleviate the issue...  What advantage does the 6" mak have over the 6" CC (with them both being f/12) ?

[nfotis]

14 hours ago, Davesellars said:

I hadn't thought about that.  A fine helical focuser at the diagonal could alleviate the issue...  What advantage does the 6" mak have over the 6" CC (with them both being f/12) ?

It's more a matter of taste and manufacturing variation for such "mass produced" items.

From my understanding, the larger Synta Maks are quite consistent, very rarely lose collimation and tend to be less fussy. These offer refractor-like views (quite contrasty), and the closed tube means less maintenance of the mirror etc (the internals are better protected against dust and humidity). On the other hand, the glass corrector in front may mean more time needed to acclimatize the scope if it's cold outside.

A well-built CC should be even better in visual acuity and quicker to acclimatize (since you don't have the glass corrector in front), a bit harder to collimate *if* it needs it. Oh, and it'll offer you diffraction spikes due to the secondary mirror being mounted via steel spider vanes. You may get more dust etc on the primary mirror in the long term.

The nice things about the GSO CC is that in the price they include an adequate Crayford focuser already, which should help with fine focusing (but the standard focuser on the Mak snaps quite clearly into focus).

N.F.

Edited February 15, 2022 by nfotis

[johninderby]

One other thing to note with the CC design is that it has a fixed primary so no mirror flop. 

[Davesellars]

So the CC would be sharper than the Mak?  I suppose this is because of the need for the glass corrector... ?

[johninderby]

Yes find the CC edges out the mak and SCT in on axis sharpness.

The optics in the CC seem to be better finished. Will take higher mag as well.

Edited February 15, 2022 by johninderby

[Davesellars]

On 15/02/2022 at 22:36, johninderby said:

Yes find the CC edges out the mak and SCT in on axis sharpness.

The optics in the CC seem to be better finished. Will take higher mag as well.

Thanks @johninderby .  I've also started considering the Bresser Messier MC-127 mak which seems a good price at around £360 - I noticed from some searching that you had this scope as well as the 6" CC - and have sold them both?  Why did you sell them? and thinking back would you still recommend the 6" CC over the mak?  The mak I think is quite a bit lighter although that's not too much of an issue if the CC really outperforms the mak on contrast and resolution and taking it higher magnification particularly for lunar observation.

[johninderby]

I sold the CC6” to help pay for the 125 APO but always regretted selling it and bought back the CC6” a bit later. I thought the 125 APO would completely replace the CC6” but it is much heavoer scope that requires a bigger mount so not very grab’n’go.

The CC6” will show more than the 127 mak but the mak is still a very nice scope and much lighter.

Edited February 23, 2022 by johninderby

[Davesellars]

Thanks John for your invaluable input!!!

[Davesellars]

Just bought the Starfield 102 ED f/7 from FLO for less than the Altair f11 I was looking at originally - I couldn't say no to that offer!    Thanks FLO!

 

[Mr Spock]

My 102 is great. I think you will be pleased. 

[Mark at Beaufort]

2 hours ago, Davesellars said:

Just bought the Starfield 102 ED f/7 from FLO for less than the Altair f11 I was looking at originally - I couldn't say no to that offer!    Thanks FLO!

 

Well done Dave I look forward to your review. You should now be set up for the Planets return later this year.

[Davesellars]

...  and the new scope has landed! 

Absolutely love the focuser... it puts the one on the 80ED to shame.

[johninderby]

Yes the ED80 focuser is a bit “low end” isn’t it compared to what is available nowadays. 🤔

Edited February 26, 2022 by johninderby

[Mr Spock]

Quality scope isn't it? Skywatchers are really basic and old fashioned by comparison.

[Mr Spock]

The only negative for me is the twist lock fitting. I've come to hate it. Fingers on the diagonal, thumb under the focuser with one hand, then twist with the other. Totally unpractical. I wish I could replace it with a compression ring fitting.

[Davesellars]

Yes, the 100mm f/9 Skywatcher is the same amount which would for me be really bad value for money now compared to this.  Having said that The SW 80ED was definitely great value many years ago - I'm glad I bought it when I did and would not sell it although it could use an upgrade to the focuser I've serviced it so it's pretty strong now.

I agree with the twist-lock fitting having played with it and also the fact that the force to do that rotates the focuser unless you have it really tight or grab on the focuser at the same time.

[chiltonstar]

On 14/02/2022 at 23:18, Davesellars said:

I've not tried a Mak however I really didn't like the mirror shift in my 8" SCT when I had it which i believe is also present in Maks as well.

You can deal with it by winding the focus knob from end to the other occasionally. I have additionally added an external focuser to my 180 Mak, which helps when imaging planets at very high mag, for which the scope is excellent.

Chris

[chiltonstar]

3 minutes ago, chiltonstar said:

 

 

Edited February 26, 2022 by chiltonstar

[Mr Spock]

27 minutes ago, Davesellars said:

also the fact that the force to do that rotates the focuser unless you have it really tight or grab on the focuser at the same time.

Exactly. You need three hands to use it 

[bosun21]

On 14/02/2022 at 07:43, dweller25 said:

The central obstruction on the CC at 58mm and primary mirror size of 153mm is a 14% obstruction. The light grasps (area of mirror or objective in a refractor) are 8167mm/sq for the refractor and the CC is 18376 minus the 14% which leaves 15803mm/sq. So from these calculations i can’t see how the 102 refractor beats the CC for contrast when it’s approximately half the light grasp.

Edited July 17, 2022 by bosun21
Spelling error

[Mr Spock]

7 hours ago, bosun21 said:

So from these calculations i can’t see how the 102 refractor beats the CC for contrast when it’s approximately half the light grasp.

When the majority of people talk about a scope's contrast, they actually mean the scope's MTF. For actual contrast, it's the difference between light and dark. All scopes will have black as black, but the white will be brighter in the larger scope regardless of the design. However, compared to a refractor, especially a good apo, something like a CC will have a poorer MTF due to the central obstruction, so it won't be able to separate close shades of grey like a refractor would. That is what people mean when they refer to a refractor having better 'contrast' - it's just a misuse of terminology.

[davidc135]

7 hours ago, bosun21 said:

The central obstruction on the CC at 58mm and primary mirror size of 153mm is a 14% obstruction. The light grasps (area of mirror or objective in a refractor) are 8167mm/sq for the refractor and the CC is 18376 minus the 14% which leaves 15803mm/sq. So from these calculations i can’t see how the 102 refractor beats the CC for contrast when it’s approximately half the light grasp.

It's more useful to think of the CC as having a nearly 38% linear central obstruction when it.comes to contrast effects. Even with perfect optics and seeing the scope is suffering from the equivalent of 1/4+ wave spherical aberration.

My 3'' refractor just edges a 96mm sct with 38% obstruction so a 6'' CC could just reverse that compared to a 102mm ED if the same quality. Maybe.

David

Edited July 17, 2022 by davidc135

[HollyHound]

On 23/02/2022 at 09:43, johninderby said:

I sold the CC6” to help pay for the 125 APO but always regretted selling it and bought back the CC6” a bit later. I thought the 125 APO would completely replace the CC6” but it is much heavoer scope that requires a bigger mount so not very grab’n’go.

The CC6” will show more than the 127 mak but the mak is still a very nice scope and much lighter.

I know it's a good few months since this comment was posted, but anyway... It was me that bought the CC 6" from @johninderby and I can confirm, it was a superb (and lightweight) scope 👍 

I only sold it (back to John again of course, as he was missing it 🤣), as I bought a Mewlon 180... any of these open tube designs (Classical Cassegrain or Dall-Kirkham) are fantastic lunar/planetary scopes. I love them because they don't suffer from dew, unlike my Mak127 or indeed refractors.

However, I've also still got both my Mak127 and C5 (SCT) and they make superb, easy to use scopes too.... we truly are blessed to have access to such fine (and relatively cheap) equipment in this modern era 😁 

[bosun21]

43 minutes ago, HollyHound said:

I know it's a good few months since this comment was posted, but anyway... It was me that bought the CC 6" from @johninderby and I can confirm, it was a superb (and lightweight) scope 👍 

I only sold it (back to John again of course, as he was missing it 🤣), as I bought a Mewlon 180... any of these open tube designs (Classical Cassegrain or Dall-Kirkham) are fantastic lunar/planetary scopes. I love them because they don't suffer from dew, unlike my Mak127 or indeed refractors.

However, I've also still got both my Mak127 and C5 (SCT) and they make superb, easy to use scopes too.... we truly are blessed to have access to such fine (and relatively cheap) equipment in this modern era 😁 

Indeed, I’ve just ordered a new SL 6” CC for the approaching planet oppositions. Like yourself not having dew to contend with like on my Maksutov and refractor is a huge bonus for me.

 

Edited July 18, 2022 by bosun21
Typo

[raadoo]

3 hours ago, HollyHound said:

I know it's a good few months since this comment was posted, but anyway... It was me that bought the CC 6" from @johninderby and I can confirm, it was a superb (and lightweight) scope 👍 

I only sold it (back to John again of course, as he was missing it 🤣), as I bought a Mewlon 180... any of these open tube designs (Classical Cassegrain or Dall-Kirkham) are fantastic lunar/planetary scopes. I love them because they don't suffer from dew, unlike my Mak127 or indeed refractors.

However, I've also still got both my Mak127 and C5 (SCT) and they make superb, easy to use scopes too.... we truly are blessed to have access to such fine (and relatively cheap) equipment in this modern era 😁 

As one of the lucky few to have such a wide range of small cats, and me someone looking to up my lunar game … which would you choose as your only lunar scope? The Mak127, C5, CC6 or Mewlon 180?

Edited July 18, 2022 by raadoo
Added option to the list.