SingAstro

Good morning all,

Just got myself a 2x gso barlow.
What I notice is that the image can't seem to get focus and brightness suffer abit.
On 20mm ep still ok but once on 10mm ep the brightness and focus become poorer.
What can I do to improve it? Pls advise. TIA.

Congrats on the purchase!
Unless the barlow is severely defective, its unlikely to be the Barlow per se.
The 2 issues you raised are brightness and poor image. With regards to brightness, this is only to be expected because by doubling the magnification, you are also halving the exit pupil. Hence the image must get darker. Generally, the brightness of your barlowed 20mm should be equal to your "naked" 10mm. The barlowed 10mm, of course, will be even darker.
With regards to image quality, a few things are possible. Firstly, you are using an f/10 scope which means that the exit pupil is right at 0.5mm, the minimum recommended size before floaters and irregularities in your own eye become significant. Secondly, at 5mm you are pushing 50x per inch aperture, which is the max recommended for good quality optics. Finally, at 227x significant atmospheric effects can cone into.play, particularly if your target is lower in the sky.
If you want to find out if its the Barlow causing issues or your scope/atmospherics, simply borrow a 5mm eyepiece and see if the image is any different

cloud_cover wrote:Congrats on the purchase!
Unless the barlow is severely defective, its unlikely to be the Barlow per se.
The 2 issues you raised are brightness and poor image. With regards to brightness, this is only to be expected because by doubling the magnification, you are also halving the exit pupil. Hence the image must get darker. Generally, the brightness of your barlowed 20mm should be equal to your "naked" 10mm. The barlowed 10mm, of course, will be even darker.
With regards to image quality, a few things are possible. Firstly, you are using an f/10 scope which means that the exit pupil is right at 0.5mm, the minimum recommended size before floaters and irregularities in your own eye become significant. Secondly, at 5mm you are pushing 50x per inch aperture, which is the max recommended for good quality optics. Finally, at 227x significant atmospheric effects can cone into.play, particularly if your target is lower in the sky.
If you want to find out if its the Barlow causing issues or your scope/atmospherics, simply borrow a 5mm eyepiece and see if the image is any different

Thanks message well note.

Hi,

bern wrote:Good morning all,

Just got myself a 2x gso barlow.
What I notice is that the image can't seem to get focus and brightness suffer abit.
On 20mm ep still ok but once on 10mm ep the brightness and focus become poorer.
What can I do to improve it? Pls advise. TIA.

The magnification for the 10mm with 2x barlow is too high for your scope especially for an uncollimated newtonian.

Have a nice day.

weixing wrote:Hi,

bern wrote:Good morning all,

Just got myself a 2x gso barlow.
What I notice is that the image can't seem to get focus and brightness suffer abit.
On 20mm ep still ok but once on 10mm ep the brightness and focus become poorer.
What can I do to improve it? Pls advise. TIA.

The magnification for the 10mm with 2x barlow is too high for your scope especially for an uncollimated newtonian.

Have a nice day.

talk about collimate, think I need to have it done. my 10mm don't seem to be as shape as my 20mm.
how should I go about with this collimating thing? my scope is only 2 weeks old, should I send it back to Astro Scientific centre to let them have a check?

Need some help here.

I had send my telescopes into astro scientific to do collimation. but just now I bring down to look at saturn the focus totally worse than before. where else can I go to for collimate my scope?

TIA

Hi Bern,
If you had it recollimated at AstroSci, perhaps you might want to bring it back and get them to re do it as well as do an on the spot test?
If not, you can try to ask some of the dob owner for help.

cloud_cover wrote:Hi Bern,
If you had it recollimated at AstroSci, perhaps you might want to bring it back and get them to re do it as well as do an on the spot test?
If not, you can try to ask some of the dob owner for help.

Ok tomorrow I'll go down and see how again, thanks

bern wrote:

weixing wrote:Hi,

bern wrote:Good morning all,

Just got myself a 2x gso barlow.
What I notice is that the image can't seem to get focus and brightness suffer abit.
On 20mm ep still ok but once on 10mm ep the brightness and focus become poorer.
What can I do to improve it? Pls advise. TIA.

The magnification for the 10mm with 2x barlow is too high for your scope especially for an uncollimated newtonian.

Have a nice day.

talk about collimate, think I need to have it done. my 10mm don't seem to be as shape as my 20mm.
how should I go about with this collimating thing? my scope is only 2 weeks old, should I send it back to Astro Scientific centre to let them have a check?

They will probably ask you to do it yourself. Have a search thru the net and you should find yourself with loads of information

I had send my telescopes back to astro scientific this morning. hope they do a good job this round.

but I don't have the proper tools to do the job myself.