Short term ideas

[Powdergnome86]

Good evening all,

I currently own a 102 Mak Cass with its 25mm stock plossl.

Coming in the mail I have an ES 24mm 68° ep and an ES 2x focal extender.

However, after much thought, I also went a bit bonkers and bought a GSO 200mm classical (2436mm FL, F/12) Cassegrain which will hopefully turn up in the next day or so. Now this scope only comes in the box with its focuser (2" with 1.25" adaptor).

Now down the road I'm thinking I will invest in a Baader T2, so I can change the nosepiece and EP holders to suit whatever size I need.

But for now, even the 25mm makes for a small FOV and 100x power. In time I will invest in a 50mm (2") EP to help widen/lower. I only have a 1.25" diagonal available, so I was thinking of getting a 40mm super plossl (apparently a 52°) to help bridge the gap in the mean time. Then a ES 16mm 68° ep

I think these will also help the 102. For the time being these are both visual scopes.

Am I on the right path or are there other options that could be more beneficial? 

Thank you for reading my saga, and for any feedback.

Cheers and clear skies,

Gary

[KP82]

Cats are for lunar and planetary views primarily. It's kind of a waste to go wide field on them. Even with a 55mm 2" plossl (max fov in 2"), they are not going to give you the same spectacular wide views of extended DSOs like newts or fracs do. BTW 32mm plossl already maxes out the fov of the 1.25" barrel, so 40mm will only give you a bigger exit pupil at lower mag.

If I were you, I'd replace the 102 Mak with a 6" dob or 4" refractor for wide field. Keep the 8" CC for the planets.

[michael.h.f.wilkinson]

14 minutes ago, KP82 said:

Cats are for lunar and planetary views primarily. It's kind of a waste to go wide field on them. Even with a 55mm 2" plossl (max fov in 2"), they are not going to give you the same spectacular wide views of extended DSOs like newts or fracs do. BTW 32mm plossl already maxes out the fov of the 1.25" barrel, so 40mm will only give you a bigger exit pupil at lower mag.

If I were you, I'd replace the 102 Mak with a 6" dob or 4" refractor for wide field. Keep the 8" CC for the planets.

The classical Cassegrain is a reflector, not a catadioptric. My C8 can get 1.33 deg true FOV which is fine for most DSOs, after investing in a 2" visual back and is my main visual scope for moon, planets, and most DSOs (planetaries, galaxies, globulars, etc). The classical Cassegrain may however have issues off-axis, as (like the Newtonian) it is only perfectly corrected on axis.

However, not all cats are based on the Cassegrain design. Mak-Newts and my own 6" F/5 Schmidt-Newtonian have a beautiful wide fields (3.3 deg at 24.5x), with considerably less coma than a regular Newtonian

[johninderby]

The f/12 Classical Cassegrain has less field curvature than an SCT and being a planetary specialist the off axis performance isn’t that important and it has better on axis sharpness than an SCT. The SCT is a better all rounder but prefer the CC for lunar / planetary. Horses for courses as they say. 🙂

[Louis D]

Do Newtonian coma correctors work in classical Cassegrains?

[michael.h.f.wilkinson]

Just now, Louis D said:

Do Newtonian coma correctors work in classical Cassegrains?

Unlikely, the main optics are very different.

[Louis D]

45 minutes ago, michael.h.f.wilkinson said:

Unlikely, the main optics are very different.

So, are there dedicated correctors for classical Cassegrains?

[johninderby]

Doesn’t need a corrector. 

From the TS website.

”Large corrected and illuminated image field due to parabolic primary and hyperbolic secondary mirror with less field curvature than with SC telescopes.”

[Louis D]

So no off axis coma then?

[johninderby]

Not a problem with coma.

Nice little review here.

https://astronomytechnologytoday.com/2020/01/03/gso-eight-cassegrain/

[KP82]

5 hours ago, michael.h.f.wilkinson said:

The classical Cassegrain is a reflector, not a catadioptric. My C8 can get 1.33 deg true FOV which is fine for most DSOs, after investing in a 2" visual back and is my main visual scope for moon, planets, and most DSOs (planetaries, galaxies, globulars, etc). The classical Cassegrain may however have issues off-axis, as (like the Newtonian) it is only perfectly corrected on axis.

However, not all cats are based on the Cassegrain design. Mak-Newts and my own 6" F/5 Schmidt-Newtonian have a beautiful wide fields (3.3 deg at 24.5x), with considerably less coma than a regular Newtonian

My mistake for using the wrong shorthand. I was too focused on cassegrain and completely forgot that CCs do not have corrector plates. The "Cats" I was referring to were the general standard SCT and Mak. Yes Mak-newts and schmid-newts can provide wider fov with less coma, but they are also more expensive, heavier, taking longer to cooldown and requiring dew shield than comparable sized regular newts. A coma corrector can easily remove the comas and be used on any future upgrades. 

True you can get 1.33 deg fov on a C8, but why bother when the OP gets to have two scopes? If the CC was going to be his only scope, then yes he would benefit from some wide fov eyepieces. As it stands now, his 102 Mak is completely redundant. If portability is important, a ST102 or better ED80 will do the job.

Edited January 28, 2021 by KP82