Schmidt and Maksutov Cassegrain

[Meneldil]

Further to my telescope buying intentions - I've been reading up on subtypes of Cassegrain telescope. It seems that the Schmidt and Maksutov patterns are the ones actually being manufactured today, and they differ by the kind of secondary mirror that they have.

But what practical difference is there? What would you notice if you had one of each, both with the same aperture, trained on the same object?

And might there be other types of difference, like one kind is more likely to be knocked out of alignment from being carried into position?

[brianb]

Maks tend to be much longer focal ratio, great planetary scopes but not so good for DSOs. And they're easier to collimate, there's no adjustment for the secondary because, being a spot on the corrector plate, it can't get misaligned. The thick Mak corrector plate makes the scope slower to reach equilibrium temperature than the thinner Schmidt plate. But there's very little, if any, difference between the optical performance of a good example of either type which has been correctly collimated & allowed to cool to equilibrium temperature. Same applies to Newtonians ... refractors tend to have slighly more contrast because of the lack of the obstruction caused by the secondary mirror, but may be subject to "false colour".

Newtonians are significantly cheaper & can have very low focal ratios though, if so, the collimation can be very hard to get right. Those with truss tubes are also very prone to collimation changes, to the extent that they have to be recollimated every time they're used. Refractors give least maintainance worries as well as great performance, if they're ED or triplet apochromats from a reputable maker, but good ones can be very, very expensive.

As usual, price / performance is far from a simple equation.

[John]

The schmidt-cassegrains (SCT's) have larger secondary mirrors than their maksutov (Mak) cousins which has a slightly negative effect on sharpness and resoloution although I've had my finest views of Saturn with an 8" SCT. Mak's tend to be favoured for high power, planetary and lunar viewing. SCT's tend to be F/10 wheras Mak's seem to be F/12 or more.

As for differences between them in use, this review is quite informative:

Orion 127 Mak Cass Vs. Celestron C5 SCT - Shootout

I guess a SCT is perhaps more of an "all rounder" but with a few compromises as you might expect.

John

[Whippy]

The main difference between the two is the corrector plate and the secondary mirror. It used to be the case that Mak-Casses had a flatter field normally at the expense of a longer focal ratio but both Meade and now Celestron have aplantic SCT's that have a flat field and in the Celestron HD's case, apparently eliminates coma too.

Is there a huge difference? Probably not a huge one but when you start getting bigger Maks (7" and up), they get expensive. So if you're planning to go 'big, I think a SCT is your choice.

Maks tend to be much longer focal ratio, great planetary scopes but not so good for DSOs. And they're easier to collimate, there's no adjustment for the secondary because, being a spot on the corrector plate, it can't get misaligned.

Brian, the Intes (now Bosma) Maks have seperate secondaries that can be collimated and most of the are at f10 too, just like SCT's.

HTH

Tony..

[Meneldil]

Thanks everyone, these were just the sort of answers I was hoping for.