Question on higher magnification

[arkanovi]

Hi all,

Managed to get my first night of viewing last night ( same day as I got the telescope, is that a world first??) and the first object I looked at was saturn. I was looking through a 25 and 10mm eyepiece on my 6" dob. I was able to see the rings... but I'm after more magnification now.

Would a barlow x2 do well on my dob with a 10mm? that'll give me x240.

[John]

Hi,

Yes a 2x barlow would be a good idea - 240x should be OK with a 6" dobsonian. You will need a night of good seeing and the scope properly cooled and collimated to make the best of it but it should be OK. You will probably find that the clarity comes and goes as you observe - I've noticed that at high power the effects of any atmospheric disturbances are also magnified.

Tracking at that power with a dob will be challenging but managable.

John

[The Warthog]

A barlow is always a good idea. You know, of course, that the maximum practical magnification of a scope is 2x the objective diameter in millimeters.

So, if your scope is f/6, you would get that magnification with a 3mm ep (half the f/number.) I would suggest you get a 6mm ep as your shortest, and use the barlow on the once a year fantastic seeing night. Then you can build your ep collection, keeping in mind that you don't end up duplicating eps with the Barlow.

Your best usual magnification will probably be about 2/3 of the max, so with a 8", f/6 scope, 240x would be about right.

[arkanovi]

Heres the info on my scope.

Magnifications (with eyepieces supplied): x48 & x120

Highest Practical Power (Potential): x300

Diameter of Primary Mirror: 153mm

Telescope Focal Length: 1200mm (f/7.84)

Eyepieces Supplied (1.25”): 10mm & 25mm

So would around 180-200 be my best you think? I'll have to work out what size ep that would be

[almach]

I have the same spec scope as you with the same eyepieces. I bought a 2x barlow and is great with the 25mm. With the 10mm, it is not easy to aim because you are looking at such a tiny piece of the sky. With something like Saturn it is not so bad because it's nice and bright, but be prepared for that nice view to be out of your FOV very very quickly. If you push the scope even slightly too hard to get it back, saturn will look like a comet as it streaks across your eyepiece

I would recommend getting the Barlow, and personally I have ordered a 9mm with a wider FOV and (hopefully) better eye relief because I can't stand the one I have.

[mdstuart]

Make sure you get a good barlow, one of the "branded" ones...A celestron etc. A guy in the USA sells them new on ebay for about £25.

Glad you got out to use your new scope!

Have you got any books to guide you to the best objects...Turn left at Orion is a good starting point...

Mark (Thornbury)

[arkanovi]

I dont really mate, the nearest thing to that is stellarium. But i'm finding that a great help. Because I've been looking at that program since before my scope was even ordered I was able to know I was looking at saturn before even looking through the eyepiece

I'm having problems with collimation atm, when I look through the focuser my eye seems to be dead in the centre of the secondary mirror which in turn seems dead in the centre of the primary. However when I look at stars I can never seem to get satisfied with the clarity, they seem slighly mushy or as if they're going off at an angle.....hard to explain.

I let the scope to cool outside for up to an hour or so.... so I have no idea what it is... I just wish someone would say " Yep thats out of collimation!"

Anyway, was out earlier and saw M42 which was pretty good when the cloud was breaking up

[The Warthog]

Almach, if you have trouble finding an object with the hgiher magnification ep, start with the lower magnification, centre the object, and then pop in the higher mag ep.

Arkanovi, your best choice for a short ep would be a 7.5 or 8mm. Combined with the Barlow, that would give you your highest magnification. This sounds like a scope you could keep for a while, so consider getting better eps as you go along. The supplied eps are probably plossls or kellners, which are not bad in themselves. Consider getting wide angle eps. With the longer focal length of your tube, the scope will be forgiving of sligntly lower quality eps.

I would suggest you look at having a nice 7.5 or 8mm ep fairly soon and a Barlow. That will give you a nice range. Later you could add a 32mm, and a better quality 12mm. This would give you a range of 32, 16, 12, 8, 6, and 4mm when combined with the Barlow. Pretty nice range for only a handful of eps.