Which sct ?

[JamesF]

2 minutes ago, Merlin66 said:

There are more performance differences due to collimation and tuning in typical SCT’s than  between brand names.

That makes me wonder...

Do typical SCTs and Maks (Meade/Celestron/Skywatcher, say) perform better (or perhaps "best", whatever we take that to mean) at the stated focal length?  For example, will a 127Mak perform best if the optical train is arranged such that the focal length genuinely is 1500mm, or a C9.25 be best if the optical train is similarly arranged to be 2032mm?

James

[MarsG76]

I recommend the C8 on a CGEM or equivalent mount and you won't regret it.

[northwalesparry]

Wow , thanks for all you input , I think I'm swaying towards celestron . Just one question but what is the difference between the 8se and CPC versions . I know one has a duel fork arm but is that it ? 

[johninderby]

The OTA is the same although on the SE it is mounted using a standard dovetail so can be removed and fitted to another mount, On the CPC it isn’t removable.The SE mount just barely manages to cope with the weight of the OTA wheras on the CPC 8 is rock solid.

The 8SE is light and portable and can be carried complte but the CPC is far heavier and not as easy to carry about. You really want to carry the tripod seperately.

The Evolution 8 is another version worth considering. Single arm with removable OTA and seems to be a sturdier mount.

Edited September 23, 2019 by johninderby

[Stu]

28 minutes ago, johninderby said:

The Evolution 8 is another version worth considering. Single arm with removable OTA but a much sturdier mount than the SE.

The Evolution actually looks to be a very good compromise between the other two.

[Cosmic Geoff]

There is also Meade's new LX65 series, with ACF optics and a single arm mount that can mount two scopes.  An 8" model costs about £1300.   There are some reviews of it online.   

Is ACF the equivalent of Celestron's Edge HD?  An 8" Celestron Edge HD costs around £1300 without any mount.

[Merlin66]

James,

This was discussed in a recent thread.

I have never found it significant.

with my spectroscope mounted behind an f10 SCT I actually end up around f11.

Also, many users add a focuser to the rear cell to minimise the mirror slop, this adds at least 80 to 100 mm to the back focus, then add the OAG, the filter wheel and finally the camera. So we are well away from the design focus.

I don’t hear any complaints about performance.

 

[johninderby]

Too many get stressed about how adding anything that affects focal length of an SCT or Mak is going mess things up when the changes in focal lengt are actually a very small percentage that will only have a minimal effect. A bit of a non problem unless you are using a binoviewer which can introduce it’s own problems.

Relax and just use the scope. 🙂

Edited September 23, 2019 by johninderby

[daslolo]

The lx65 is a great concept and the optic is fab but some units are very buggy so you end up with goto that goes under the horizon or above the maximum elevation, denting the case and stressing the gears, also some have mechanical problems (I got all the above, someone else none) so buy it from a vendor that does return.

Edited February 21, 2020 by daslolo

[daslolo]

I had a 9.25 ages ago, very solid mount, my eye wasn't as discerning

 new lx65 - stellar optics, garbage mount and software.

Based on this large sample base I'd go new Meade optic and some other mount

Edited March 11, 2020 by daslolo

[joe aguiar]

Ya I'm not getting into a who better in fact I have both and both are equally good. I cant even say one is better than other

It comes down to what u want

8se lighter portable 

8lx90 more stable with dual fork arms

That's pretty much it

joejaguar 

[Louis D]

On 23/09/2019 at 05:48, JamesF said:

That makes me wonder...

Do typical SCTs and Maks (Meade/Celestron/Skywatcher, say) perform better (or perhaps "best", whatever we take that to mean) at the stated focal length?  For example, will a 127Mak perform best if the optical train is arranged such that the focal length genuinely is 1500mm, or a C9.25 be best if the optical train is similarly arranged to be 2032mm?

James

Yes, hypothetically each performs best at the design's optimal distance.  However, most eyes won't be able to discern the difference, but a high resolution camera might, so this is mostly an imaging issue.  Here's a nice description on CN of the spot size variance in a standard SCT as the back focal distance is varied above and below the optimal distance of 100mm for the hypothetical design that was ray-traced.  The EdgeHD would have a much flatter set of curves due to much better off-axis correction.