Now have a 10" GSO Dob

[Scoper]

Finally got a 10" dob from Andrews: sent on monday and I received it wednesday; great service!
Very impressed. The scope arrived almost fully collimated, just slight adjustment of the secondary mirror was needed. Having once owned a 6" f/4 telescope I am well versed in collimating fast newtonians.
The secondary holder was spot -on centred in the tube and the primary was fully adjusted, you can check the primary collimation two ways: 1 by using a sighting "eyepiece" in the focusser and 2 by tilting the scope and looking down the tube at the secondary and its image in the primary; with one eye you then match the secondary just within the outline of its image; any slight misalignment of the primary shows up like the proverbial dog's wedding tackle.
The offset in the secondary was almost spot-on, Just minor adjustment needed here (I also have two methods I use to check this).

As for first light, well it was cloudy wednesday night (of course) but thursday I was able to check the optics using magnification of 166x and 270x. No sign of spherical abberation (must allow mirror time to cooldown for this check as mild undercorrection occurs during cooling); no zonal errors that I could see, essentially the same diffraction pattern either side of focus and no astigmatism noticeable including pinched optics. The claim of 1/12 wave accuracy must be pretty close.

Jupiter was a real treat. Also indulged myself in an orgy of gazing at some well known DSO's: Sombrero, ngc 5128, ngc5139, Sag/Scorpiuos region etc. Wonderful!

Got 4 eyepieces with the scope: 4mm,9mm,20mm and 25mm Plossls. All but the 4mm are reasonable, the 4mm is actually quite useless. Already have a 15mm gso superview and an old 20mm erfle. All the eyepieces (barring the 4mm which will remain redundunt) work fairly well at f/5 but a vast improvement is noticed at the edge of field by using them with a 2x Barlow. I suppose this is why some high cost eyepieces work so well, they employ a built-in Barlow. I must comment that the 15mm superview does give a ghost image so better for dso's than planetary.

Am impressed with the price and performance of this scope--optical quality at a reasonable price has certainly improved. Very pleased and congrats to Andrews for good service and products.

One problem is the dob base being a little too stiff despite the central bolt not being tight, may need extra teflon pads close to the bolt.

Another concern I did have was the size of the secondary mirror--at about 60mm it is 1/4 the size of the primary! However judging by the views of Jupiter this should not be a problem---I've come to believe that the supposed "destructive effects" of the central obstruction in reflectors is grossly exagerated( but Have yet to test the 10" against my 8"f7.4 which has a secondary mirror 1/6th that of the primary diameter).

Am I happy? You bet! GSO are the best thing for amateur astronomy.

Thanks to those Iceinspacers who convinced me.:thumbsup:

Cheers Malcolm.

[Dujon]

Yes, Malcolm, I can but agree with your comment regarding the GSO products. They have allowed me to enter the realm of larger 'scopes.

Congratulations on your purchase, I hope that you have many, many hours of pleasure using the thing. 'Twas interesting to note your comments regarding the eypieces. With a wee bit of luck I'll be in the market for a Barlow in the next week or so (I only have 26mm, 15mm and 9mm eyepieces at the moment). So, what Barlow are you using? I was considering a TeleVue 2x, but the Orion is nearly half the price and price unfortunately is a critical factor for me.

I've been reading the various contributions to this site on the subject and am still confused. If you are keen enough then confuse me further.

As Robbie Burns said so many years ago, "The best laid schemes o’ mice an’ men / Gang aft a-gley". Which means, of course, that my intention to purchase a Barlow will undoubtedly founder on the rocks of fiscal necessity.

[xelasnave]

Work out the area of your secondary and subtract it from the area of the primary..there is not much in it. Its the outer rim that picks up the area impact.
You will find you have made a good choice, they are excellent value for the money and if not doing astrophoto work who needs an EQ mount..
Congratulations now go out and convert some non believers to the faith
alex

[Starkler]

The secondary is actually 63mm minor axis, and the holder contributes maybe another 3mm making for a total obstruction of about 26%.
One could go a size smaller, but I dont think theres much to gain other than loosing illuminated field on that 31mm nagler ;)

I would be interested to know how your 8" compares on Jupiter, as I've been tossing around the idea of building a long f-ratio 8" planetary scope using premium components.

[Scoper]

I use a "no name" Barlow, John, that I bought from York Optical in 1996, never gave me an ounce(gram?) of trouble. Just a 2x cemented doublet; Cost me $50 then. No ghosting and does not introduce other abberrations. Tested it against a Meade air-spaced barlow some years back and the only difference was that the Meade barlow gave a slight but noticeable reduction in brightness.
Don't have experience with the Teleview or Orion Barlows though the Teleview may be superior to the Orion (and to mine). Be wary of advertising claims though! The Orion or other cheaper brand Barlows should be perfectly adequate--you could buy the Orion now and get the more expensive Televue later if necessary. Hope this helps and doesn't add to the confusion.
By the way, this is my second attempt at posting a reply. I'll get used to it one day.

Cheers
Malcolm

[mickoking]

Malcolm, glad to hear your enjoying your new Dob, GS do make great telescopes :thumbsup:

[Dujon]

Thanks, Malcolm, I've put your thoughts into the mix.

All the best with your equipment. I've only had mine for a month or two and, because of the cloud (and at times other commitments), it's not been outside all that often.

Cheers,