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Is a 127 Mak good enough


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Hi all,

I'm looking to upgrade my OTA from a 90mm Mak to a 127mm. I love the Mak's for the clarity, but DSO's are hard to spot with a slow scope with a small ap. I'm not a refractor fan. So is a 127mm enough to see some DSO's?

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I have a 127 mak not really fast enough for DSO's better on planets, for DSO's a reflector of about F5 is better but even then they look like a smudge but attach a camera and image you will see more detail. You can buy web cams that have been converted for deepsky or even a cannon dslr off ebay which will do the job at a minimum cost if you really want to see DSO's in all there glory.

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This 5" f/5, and a bit more manageable, would serve for both visual and imaging...

http://www.firstlightoptics.com/reflectors/skywatcher-explorer-130p-ds-ota.html

The Cassegrain family of telescopes, particularly the Maksutov, were created in the desire for a long-focal planetary refractor, but folded within a tube roughly a third its length.

A rough rule of thumb: f/10 to f/16 for planetary; f/5 and faster for deep-sky. 

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A rough rule of thumb: f/10 to f/16 for planetary; f/5 and faster for deep-sky. 

The rest of your post I agree with but I'm not sure I agree with that "rule" !

My refractors are F/6.5 and F/7.5 but do really well on the planets and deep sky, for their aperture. My dobsonian is F/5.3 and does fantastic in both fields as well.

A 5" mak-cassegrain will show deep sky objects just as well as any other 5" class scope but the field of view will not be as wide as it would be with a faster scope. Many deep sky objects (most ?) will fit within a 1 degree field.

That said a 5" scope is not going to be as good as an 8" scope on deep sky objects whatever it's design - "aperture rules" for deep sky objects.

Back to the OP's question, a 127mm aperture scope will show deep sky objects better than a 90mm one because the light gathering area has increased quite a bit. 127mm is still not a lot for deep sky objects though and, if those are a priority for you, a similar investment could get you a significantly larger aperture scope of the dobsonian type.

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i could be wrong but i would of through it would just be a case of field of view being smaller in a slower scope. if thats the case it would be worth getting eyepieces with as widefield view as  your wallet will allow

With the widest field eyepieces in the 1.25" fitting the 127mm mak-cassegrain will show a 1.1 degree true field of view. I don't think the design allows for 2" eyepieces to be effective so that is the max field of view.

1.1 degrees is enough to fit both M81 and M82 in the same field of view with a little room to spare.

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as others say go for the dob, great scope, it sounds like you want the best of both worlds, planets and dso the dob would do that. also you can upgrade eyepieces as you go along. my favourite eyepiece is my 24mm Explore Scientific 82° eyepieces. it gives great widefields of view in my st120 short tube refractor and my 350mm dob

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The OP has asked about the mak so presumably there are reasons why he has not considered dobs, perhaps space or the need to transport it easily?

Perhaps the OP could indicate any budget limitations and size requirements?

I wonder whether a small (5 or 6") SCT may be worth considering with the shorter focal length (f10 vs f12) for a little bit more fov.

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The old rule of thumb was, "the best scope you have is the one you use the most"! For this reason, there is a lot to be said for having a portable scope if you have a light polluted viewing site, and Maks and SCTs are very portable compared with reflectors!  Clearly, we would all like a 30" observatory class telescope in the back garden, but unfortunately practical considerations intervene for many of us....

Chris

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A 127mm is still a 127mm immaterial of the scope design, you will be getting (127/90)2 as much light collected. So very close to 2x the collection.

The "problem" is the design, it being intrinsically a long focal length so you get "high" magnifications and this means reduced brightness and reduced fields of view.

Really I would say it means selecting eyepieces with a bit of thought, a 10mm or even 12mm will not of great use for DSO's, a 25mm or 32mm will. If you say that 1 degree is sufficent then a 30 or 32mm plossl 25mm BST/X-Cel will deliver that and that will squeexe M45 and M42 in (just).

Since many other DSO's are smaller in size then you can start to drop in 20mm, 18mm, 15mm as suitable.

So it is a 127mm scope and use of it will require the application of a little thought.

It is however something you are used to, and it is compact for transport.

I will also say that 5" and 6" SCT's and Maks are very popular scopes (at one club there seem to be 80% of the ones in use) so they seem to fit the requirements for a wide range of use.

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