Mak, Cas or Frac?

[Paz]

1 hour ago, Captain Scarlet said:

Sadly the skymax does not have a small obstruction. Although the central spot and baffle on the corrector are indeed small, the CO is actually defined by the retaining ring on the primary mirror, which seems to be much larger than it needs to be. Consequently the CO comes to about 33%.

This is a good point I did not know, there are things like this to look out for. 

All other things being equal slower final focal ratios enable smaller central obstructions to be possible and if going for a Maksutov I would recommend f15 or slower. 

Skywatcher do some Maksutovs which are faster which isn't a bad thing, it is just making different choices about trade offs.

The main thing though is aperture, a 150mm maksutov and 150mm CC are in the same ballpark either would be winning.

Edited August 18, 2023 by Paz

[bosun21]

Remember that the CC has a much larger central obstruction than the 150 Maksutov. This will definitely affect contrast.

[Guest]

If it were me i would opt for the CC, just to be different. 

[Stu1smartcookie]

The point of affecting contrast is not conclusive … Razeem from Astrofarsography on YouTube reviewed the 6” and 8” versions and he saw no reduction  in contrast . 

[Captain Scarlet]

32 minutes ago, bosun21 said:

Remember that the CC has a much larger central obstruction than the 150 Maksutov. This will definitely affect contrast.

I think they’re about the same, actually. The Skymax Mak has its central obstruction defined by size of the ring that secures the primary mirror to the baffle tube. It’s much bigger than the spot and baffle attached behind the corrector plate. Very naughty, actually, because the Skymaxs were (and possibly still are in the US, at least last time I looked) marketed retail on the “small CO” basis.

[bosun21]

2 minutes ago, Captain Scarlet said:

I think they’re about the same, actually. The Skymax Mak has its central obstruction defined by size of the ring that secures the primary mirror to the baffle tube. It’s much bigger than the spot and baffle attached behind the corrector plate. Very naughty, actually, because the Skymaxs were (and possibly still are in the US, at least last time I looked) marketed retail on the “small CO” basis.

I have never considered this aspect. If I ever do decide to buy another Maksutov I’ll make sure that it’s at least f15. I think Skywatcher have made too many concessions by making them shorter focal lengths.

[F15Rules]

ED Refractor.

The End.

Dave

[Louis D]

Just to toss in another option, look at a 150mm (6") f/5 GSO Newtonian OTA.  I picked up one used for about $300 with a GSO CC.  It's light, has no cool down issues, gives sharp and color free images, holds collimation really well, can give low power views, can have a dual speed focuser (mine does), and has the eyepiece in a position easily used while sitting with it mounted on a mount with a low tripod (more stable than using a fully extended tripod with a long frac).

Here's some comparison images of the moon I recently took through several of my scopes.  Any of them except for the 6" f/5.9 achromat work well for lunar observing.  However, even to my eye, the Newtonian was showing finer details than the smaller scopes (or the achromat).  No surprise, the 90mm APO had the highest contrast images either to my eye or in a photograph.  However, that triplet takes over 30 minutes to equilibrate for high power work.

[Mr Spock]

100mm apo doublet. I take it straight from inside to outside and it requires no cooldown time. Visually it will be more pleasing to look through than any 150mm mirror based scope.

Here a single shot 'snap'

[dweller25]

22 hours ago, pbyrne said:

 

150mm Maksutov.

150mm Classical Cassegrain.

100-110mm ED Refractor.

 

I have tried all three, only the 4” refractor has remained.

In my opinion a central obstructions does have an effect on the views.

This has very good feedback from users….

https://www.firstlightoptics.com/starfield-telescopes/starfield-102mm-f7-ed-doublet-refractor.html
 

Edited August 19, 2023 by dweller25

[Knighty2112]

Cool down time for my ‘fracs (80mm & 102mm) is practically zero, so basically get them outside and start observing with them straight away.

150mm Mak and especially the 150 CC will take time to cool down and give you their best views. When I had a 6” inch CC it seemed like it took forever to get anywhere near anything like the ED ‘fracs would show me straight off the bat after setting up.

[pbyrne]

I have come across a video on YouTube from Ed Ting where he discussed the 150mm CC.

He is not a huge fan.

[pbyrne]

I came across a pair of interesting scopes.

https://www.astroshop.eu/telescopes/ts-optics-apochromatic-refractor-ap-102-1122-ed-ota/p,62910

https://www.astroshop.eu/telescopes/tecnosky-apochromatic-refractor-ap-102-1100-ed-planet-ota/p,76384

 

[nfotis]

Personally, I love my Skymax 180. It was a large jump from my Skymax 127, and it seems to offer quite contrasty views.

My HEQ5 mount can (barely) handle it, the Skymax 150 should be more enjoyable (manual focus is a bit of a pain, too much jumping and vibration - an autofocuser is very helpful at such long focal distances).

I haven't tried the GSO CC. After the initial hype, it seems that these aren't offering a big improvement, and I suspect the lack of a front glass corrector makes balancing on the mount a bit harder.

I don't notice any thermal problems, but since I need almost one hour of setting up my mount etc on the rooftop this might be expected.

[dweller25]

12 hours ago, pbyrne said:

I came across a pair of interesting scopes.

https://www.astroshop.eu/telescopes/ts-optics-apochromatic-refractor-ap-102-1122-ed-ota/p,62910

https://www.astroshop.eu/telescopes/tecnosky-apochromatic-refractor-ap-102-1100-ed-planet-ota/p,76384

 

They are probably the same scope, no mention of glass type but they do look interesting.

Your HEQ5 should be able to keep jiggles down when focusing the 1.1mtr long tube.