Need of a small scope

[Dob]

Hi people,

As the topic title says, i need a small and a compact telescope, something that i can easily assemble and disassemble. The thing is, i do have an 8" Dob but it (i like to call it "Little 8") is not very compact nor transportable, considering that i live in an apartment on the 4th floor. So I've moved "Little 8" to my countryside house which is approx. 15Km from city in which i live. From there i observe M's and NGC's (just started systematic galaxy hunt in Big Dipper up to 12th mag. ).

...

What i now need is a telescope for casual planetary and lunar views from my apartment's window, that will not take much space in my room.

The best choice would probably be Mak 127, but the limiting magnitude here are the financial funds.

So far i've considered SW refractor 90/900 and 130/900 reflector. Both second hand. What worries me about 130/900 is the spherical mirror, but yet, it gathers more light than the 90/900.

Would the spherical aberration be a big problem for planetary and lunar observations?

Thank you for your respond.

[Cornelius Varley]

A small mak would be the prefered choice. Spherical aberation shouldn't be a big issue with the 900/130, it only becomes more apparent at apertures over 6".

[michael.h.f.wilkinson]

Have you considered hunting for a second-hand Mak127, or C5 or C6 SCT. These come up second hand quite frequently, and are way more compact than the Newtonians.

Whether spherical aberration is a problem, or even visible depends on aperture and focal ratio. In a 6" scope, SA is evident at F/8 in spherical mirrors, whereas in smaller mirrors F/7 may still be fine. The reason is that if the diameter of the mirror is small enough for a given focal length, a spherical surface and a parabolic surface are within a fraction of a wavelength of light from each other. If that fraction is small enough, they become optically indistinguishable

[happy-kat]

Will you be observing through a window inside your apartment?

Would a small refractor be more sympaphetic to this?

Say ST80?

I have a small mak and it is poor through a window images wobble loads.

[Dob]

I did consider Mak 127, but there are no any second-hand ones currently. I live in Croatia.

i've read somewhere that the minimum f number for 130mm spherical mirror should be F7.5, while 130/900 f number is f6.9.

[Dob]

Will you be observing through a window inside your apartment?

No, the window should be opened...

[michael.h.f.wilkinson]

With a window open, I find thermal currents ruin seeing (apart from increasing the heating bill ). If there is a sufficiently open space outside to look, that is always preferable.

[Kirscovitch]

Maybe a C90?

[happy-kat]

What do you prefer looking at?

DSO, planets or say clusters and stuff.

[Dob]

Planets as i said earlier. I have 8" Dobs at my countryside house for the DSO's.

Anyway, 130/900 is ruled out due to spherical aberration issues, sharp image on planets is my priority,
90/900 too, the seller decided to keep it.

I will probably get a Mak 102 and mount in on a photo tripod, although don't know when exactly.