GSO 12" OTA newton. F5 or F4?

[shaggles (Shag)]

Some background info....

When I was a youngster of ~13 (27 yrs ago) after many a lawn mow and extra house hold duties, I got myself a little 4&1/2" newton. It looked much like this, but white and probably was exactly the same : someone elses on this site

That telescope & I spent many nights together from sun down to sun up. I remember I could make out the cassini division, the bands on Jupiter with the red spot, ice cap on mars... impressive for such a wee mass produced scope I think.

As the years went by it was used less, lent to a friend and eventualy donated to a local Astronomy club. A club which I have still to even visit.

Anyway, here I am much older and considering a new one.

As the title says, I'm looking at a GSO 12" OTA. They have 2 versions, the f5 and f4. Size isn't an issue so it comes down to whats better over all. If I get a new scope that I actually use, it will eventually end up with a semi home made equilateral mount or similar. Maybe a dobson mount just to get me going with the proper mount being a project to work on later.

What's peoples thoughts on these two models with their pro's and cons? I suspect it'll be mostly hands on viewing but a camera option would be nice... I got told the f5 has issues with getting a camera to work without modifications unlike the f4?

Any info on these appreciated.

Cheers.

P.s. I tried to sign up to the cloudynights forum but was rejected as a possible spammer. Crazy yanks

[multiweb (Marc)]

TBH if you're looking at a 12" newt F/5 or even F/4 I'd look outside of the GSO brand. The mirrors aren't half bad but a 12" primary is starting to weigh a little and I don't think the cell will be designed well enough to hold collimation out of the box if the 8" is anything to go by. Unless you're into DIY and not afraid to do a bit of work to stiffen things.

[rustigsmed (Russell)]

Hi Shaggles,

F4 is 'better' for photography, and therefore i'd recommend getting the f5 if you plan visual use. You will need to use a coma corrector for the f4, but you can get away not using one at f5 - well i don't mind especially visually.

I have a 12" GSO tube (f4) and a 12" Skywatcher goto dob (f5). I agree with Marc that you may want to atleast consider another brand unless you don't mind making modifications to it the scope to make it useable.

I had to buy stiffer springs for the GSO and with the skywatcher i could get away without buying stiffer springs - in fact i haven't upgraded them and are happy as it is. collimation is easier in the SW too. I also plan on buying an upgraded spider vane for the GSO as it is quite soft and moves very easily.

of course if you are planning on putting it onto an eq mount in the future at 1500mm in length the f5 will be pretty hard to look through.

I had no issue on my f5 SW goto dob for astrophotography.

http://www.flickr.com/photos/80336656@N07/ although i did find a coma corrector was needed for deep space stuff.

some people like tinkering and upgrading parts so it might depend on what type of person you are.

You might want to consider a 12" f5 dob, then buy an 8" f4 newt for photography- they go pretty cheap.

All the best

Rusty

[Allan]

Hi Shaggles,

I also had that Tasco telescope. When I upgraded to that from my first telescope, a 60mm refractor, I felt like a king. I still have fond memories of Halley's Comet and my 4.5" Newtonian.

My advice for putting a 12" OTA on an equatorial mount is, don't do it. There are a few people who have done it, but they normally keep such things permanently set up in an observatory. It's probably not something you want to move around, because the setup will be massive and heavy. You will need a ladder to observe, because the mount will put the eyepiece very high. I sense you are leaning towards this setup for imaging, but you should consider something smaller than a 12" that will make your life easier.

Now for visual, which you say you will be mostly doing, Dobs have taken over the world. I would definitely recommend a 12" Dob. They are quite easy to move around, setup and use. Get one of these first, and worry about a second scope for imaging later.

I've used GSO, Skywatcher and Orion Dobs. The optics are all similar, but the telescope design and build quality differ a lot. I have an Orion Dob. It is very well engineered and works all the time just the way it is supposed to, and gives great views. The Skywatcher scopes are also just as well made. Pick one of these 2 brands for years of happy observing.

f/4 mirrors can be problematic. You will need a Paracorr with a f/4 mirror. Some premium mirror makers won't make mirrors under f/4 because of the difficulty in achieving an acceptable end product. Longer f ratio mirrors are easier to make, so you may end up with a better mirror at f/5. A 12" f/5 is not particularly long, and you will be able to view through the eyepiece at zenith comfortably with your feet on the ground.