How Big Should It Be?

[SBGemini]

G'day folks, wonder if somebody could advise briefly. I've not done much observing over the summer? Due to light nights or cloud! Last night I glanced out the window and saw that Jupiter was big and bright so decided to dust off the mak and take a peek. Really disappointed at the size of the image in the scope considering how clear and bright Jupiter was. EP used was Bader Hyperion clickstop zoom and the full range was used. The image appeared to be approx 6mm circle in the FOV. Would using my 2x Barlow bring any improvement? I am partially sighted and struggle to see detail in small images. Any advice appreciated!

[John]

A 2x barlow would double the magnfication that the zoom eyepiece is giving across it's zoom range - so it, in effect, becomes a 4mm - 12mm zoom.

However, with your scope, at it's 8mm setting (no barlow) you are getting 187x which is a fine magnification for Jupiter - I was using 150x last night with a 120mm refractor and seeing reasonably good detail when the seeing conditions allowed.

I feel the barlow, while giving you the larger image that you seek, would "overpower" the scope and not deliver sharp, contrasty images.

I'd keep observing with the zoom on 8mm and you will find, over time, that your eyes do start to pick out the details.

[SBGemini]

Cheers for reply, think I just need to persevere and try a few combinations of EP and Barlow!

[hemihaggis]

hi there , i love the mak scope , best way i found was to find a mag that was still nice and sharp ,and study it for a while .

[brantuk]

Try this for a free download - it'll give you image sizes for eyepieces and/or camera if you put your equipment specs in:

The New CCD Astronomy Home Page

Or this one for an online fov calculator:

http://www.12dstring.me.uk/fov.htm

[ollypenrice]

Work out your magnification by dividing scope focal length by eyepiece focal length.

The useful range is about 180x to 250x and for 250 to be an improvement on a lower power you need an exceptionally STABLE night, not an exceptionally clear or transparent one. You need 'good seeing' with little mirage-like turbulence in the atmosphere.

You also need to respect a rule of thumb that says, Don't exceed 50x magnification per inch of telescope aperture.

Olly