Optical quality

[Scoper (Malcolm)]

Hi fellow observers,

I am considering buying a GS 10" dob from Andrews, they advertise their optics as being 1/12 wave, have any of you been able to verify this? I have owned an 8" f7.4 dob for many years, (home-made tube assembly and commercial optics) this 'scope provides very good images. The 10"dobs are f5 which means a shorter tube and less bulk than my current scope and as i'm not getting any younger the 10" would be easier to lug around plus more light gathering. Greatly appreciate any info on the optical quality of gso 10" dob (are they at or close to 1/12 wave, seems too good to be true for the price)

[janoskiss (Steve H)]

I don't know if anyone actually quantitatively tested the optics in these scopes. I would be surprised if it's 1/12 wave all the way to the edge of the primary. Mine don't look it from star test, but I'm not experienced and only comparing what I'm seeing with textbook examples, so maybe I'm reading the star test wrong.

[mickoking]

G,day scoper

I currently own both 250mm and 300mm GS Dobs and their optics are VERY good particually at the price (possibly regardless of price). As they are fast optical systems just ensure they are regually collomated to get the most from the optics and use good quality eyepieces.

Cheers Mick

[Scoper (Malcolm)]

Thanks for the reply,

But are you happy with the mages you're getting? I guess i'm being abit fussy;It's just that you can't "try before you buy".

Anyway cheers

[Scoper (Malcolm)]

Yes, thanks,
I've found a barlow very usefull on fast scopes even though you increase the magnification and, you're right, the correct eyepiece choice is vital.

Ta

[Starkler (Geoff)]

If you do buy one, check out my GSO newt checking how-to here.

In short, their optics are much better than their assembly procedures, which can be easily fixed

[ausastronomer (John Bambury)]

When they claim 1/12th wave, this is P to V which equates to 1/6th wave at the wavefront. This is still a very good mirror and equates to a strehl ratio of about .9. Diffraction limited is 1/4 wave at the wavefront.

I have looked through a lot of these scopes (in excess of 30) and all have been good to very good, with 3 samples outstanding. The quality of these optics really is excellent considering there price point and the fact they are mass produced. I have been observing a long time and also have access to some high end equipment and I am very happy with the performance of my own 10"/f5 GS dob. I did get very lucky and got an outstanding mirror, but I am yet to see one of these scopes that didn't perform well. There were a couple which had astigmatism issues but those were easily resolved with 10 mins work on the secondary holder and I don't believe this is an issue with scopes of more recent manufacture.

I am sure you would be more than happy with the optical performance.

CS-John B

[ving (David)]

as for comaparitive bulk of the 10" f5 vs your current 8" f7.? you will find they are about the same FL... the 8" may still be shorter.

8" gso mirrors are quite good i am happy with its performance

[Robert_T]

Hi Scoper, it's a subjective thing, but I do know that high resolution planetary imaging is along the most demanding activities on opitical quality. With this as a benchmark, you only need look at the planetary images produced and posted here by Mike (iceman) and David Pretorius who both use a 10inch F5 reflector (I think both GSO too). Both are producing truly world class images. The proof of the pudding and all that...

[mickoking]

Originally Posted by ausastronomer

I have looked through a lot of these scopes (in excess of 30) and all have been good to very good, with 3 samples outstanding. The quality of these optics really is excellent considering there price point and the fact they are mass produced. I have been observing a long time and also have access to some high end equipment and I am very happy with the performance of my own 10"/f5 GS dob. I did get very lucky and got an outstanding mirror, but I am yet to see one of these scopes that didn't perform well.

Good point. my 250mm could be regarded as very good, my 300mm I would consider outstanding. Money well spent.

[Scoper (Malcolm)]

Thanks all for your advice and info; you've convinced me-the proof of the pudding and all that-will get a 10" dob probably next pay if I can convince the Mrs that it's a dire necessity. The 10" will only have 125cm focal length compared to 148cm for my current scope and I could sit in a chair to observe--nice. Thanks again.

[astro_nutt]

Hi Scoper,
I own a 10" f/4.9 Saxon dob, (Chinese optics), and more than happy with it's images..especially using 2" eyepieces..a 26mm is fantastic to use on Star clusters and Nebulae!!