Focal Length and Barlow Question...

[Shaun_Astro]

I've been wondering what the advantage is of buying a specific "planetary" scope is, like a f12 Mak, when sticking a 2x barlow on a f6 Newt does "the same thing".

If a barlow all it does it literally double up the focal length, what bother getting a long focal length scope, when you can use a F5 newt for widefield, and slam a 5x barlow on it for planetary, but you can't get a 5x focal reducer. Surely there must be some disadvantages?

Thanks!

 

 

[Peter Drew]

It's the same on paper, but in the real world the native longer focal length of a given telescope makes it easier to figure the optics to a high standard. There may not be a great deal of difference but the long native focal length usually wins. 

[orion25]

I agree with Peter; native long focal length scopes have the edge. I have two Maks and a reflector. For a given EP,  the reflector with Barlow yields a slightly less detailed image than the Mak of comparable aperture, and on very bright objects I can sometimes see a hint of the effect of the spider veins. For the casual observer, this probably won't matter too much. I'm stuck on Maks for planetary, lunar and bright DSO observing: the detail is stunning, and without the light dispersion of any additional glass. But the wide field of a reflector is a beautiful thing, and to be able to plug in a good, quality Barlow to switch to "planetary mode" is very convenient!

Reggie

[ollypenrice]

Another to agree with Peter. Faster optics are harder to make and to collimate. In refractors colour correction gets much harder. Pound for pound you'll do better with slow native optics if you don't need the wide field possibilities of faster ones.

Olly

[Shaun_Astro]

Ok, thanks for the answers. I would still like to image a planet using a Skymax 130 and my 130pds with a barlow, and see if anyone can spot any difference! I'm sure it would look better, still can't understand why too much