hotnews - 16 inch GS dob coming soon

[ausastronomer (John Bambury)]

Originally posted by RAJAH235
Will be interesting to see the 'new' DOB when it is released, & the actual optics they pick. Surely they would have to use 'PYREX' for that size! L.

Thats exactly what I would have thought.

BK7 (Borosilicate Crown) is an optical glass that was originally designed for making refractive light transmitting elements, not front surface reflective optics. In terms of Newtonian mirrors it is way better than plate glass but certainly not quite as good as pyrex or the more exotic materials in terms of its thermal expansion co-efficient. In smaller mirrors up to 12" it does a very good job and GSO have produced some outstanding BK7 mirrors considering they are mass produced. When you get to a 16" mirror the thermal properties of the glass become a lot more critical than they do in smaller mirrors, this also applies to grinding the mirror as well as observing with it. On the basis that GSO would be ordering a large number of these 16" mirror blanks I would have thought the minimal additional cost of going to pyrex instead of BK7 with mirrors of this size would be well worth it.

I am not sure whether or not the 16" truss scope will ever happen, truss scopes is an area GSO have never gone before, but I would like to think that it can happen. I do know that an Aussie, very experienced in designing and building truss scopes is currently providing them with a lot of design input for such a scope.

CS-John B

[Rodstar (Rod)]

16 inches......sounds good to me, HOughy!

I'm just trying to think of what explanation I can give to The Other Half about why I need to buy ANOTHER scope.

Wouldn't it be nice to have the option of a stand-by 16" light bucket, just in case you have trouble seeing something at the limits of your ordinary scope??!! Would my dear wife swallow that line? (Methinks NOT).

GS have produced some pleasant surprises with some of their other products (especially EPs). Maybe this scope will carry on that fine tradition. I for one am very interested to learn more.

[MiG]

Originally posted by h0ughy
MiG

if you can get to sydney in a 1972 datsun (plate glass), or you can get there in a well for arguement sake lets say a GMH 2005 monaro(BK7), what woud you take. ( no sentimental the datsun would be an experience answers accepted!)

Since what matters is coefficient of thermal expansion and heat diffusivity, it's more like a comparison between a 1972 Datsun and a 1978 Datsun with a flashy paintjob. BK7 isn't much better for mirrors than plate glass.
So it comes down to the price difference. If they're roughly the same price you take the slightly newer Datsun that looks nice. Otherwise you don't bother.

[gaa_ian (Ian)]

Good call starkler ...
I will be watching this one with interest too ..
The upgrade from a 10 to a 12" is not inviting enough for me ... 16" of aperture though !
I can think of 100's of DSO's I would love to see through that size scope.
Beam me up scotty ... the universe awaits

[h0ughy (David)]

nice to see a bit of passion from the dato' owners out there. Personally the 1600 with all the trimmings was a goal of mine when I was way younger.

Personally I started with a 80mm tacso refractor when I was 18, then went to a 8" celestron (no dec motor) when our first child came on board, went to a 10" meade (no dec motor), then bought a meade etx 90RA from a NZder, then won a meade 12" lx200 buzz click whirrr, then a celestron 4gt (i sold the etx), then for solar a PST ( really wanted to 90mm Coranado), now who says I suffer from aperture fever!!!!

But to get something reasonable like 16" for the price has got me hooked.

[dhumpie]

A cheap 16" fast newt. Oh that's going to be very tricky to pull off. At those fast focal lengths, you probably need hand figuring in addition to the general figuring they do with machines. I wonder how GS is going to pull that one off for a low price. And if they are going the way of the truss, I would think the price to be more along the lines of Discovery (maybe a little bit cheaper). Just my 2 cents.

Darren

[slice of heaven]

Yes Darren
I hope they've got something up their sleeve to pull off that trick.
I finally had the chance/time/energy to directly compare the gs12" to the Parks 12".
The Parks definately has the edge over the gs in contrast and sharpness but I have to admit the gs still gives a fantastic view. There is definitely nothing nasty about the gs optical performance.
The optics are the heart and soul of any scope. It's the one place you cant take shortcuts.

Slice

[ausastronomer (John Bambury)]

Originally posted by slice of heaven
I finally had the chance/time/energy to directly compare the gs12" to the Parks 12". The Parks definately has the edge over the gs in contrast and sharpness but I have to admit the gs still gives a fantastic view. There is definitely nothing nasty about the gs optical performance.

Slice

Geoff,

20 years ago Parks and Cave scopes were at the top of the tree. For the mass produced 12" GS scope to even get close to a high grade scope like the Parks is praise in itself.

CS-John B

[slice of heaven]

Yes Aus I was surprised myself.
One thing I didn't mention was the Parks probably does need its mirrors recoated. But I cant tell how much this difference this would make until I actually have it done. The surfaces dont show any obvious major marks or blemishes but time has to take its toll on coatings. It maybe 20yrs old.
Regardless of that, the absence of anything 'nasty' that I could see has to give the gs scope it's strongpoint.

Slice

[bytor666]

Plate glass? pyrex? Bk7? I think for a nice cheap 16" light bucket the figure of the mirror itself matters much MORE than the substrate used .
If it is cheap, I'd lay down my money for a nice size scope like this because it would mainly be used for "deep sky" work anyways.

People need to not be so fussy about what the mirrors are made out of, heck even the older 100 inch mirrors were made out of PLATE GLASS with bubbles all inside of it and those were amazing telescopes.
------------------------------
Mark
12" gso scope

[Orion]

I agree. We spent some considerable time figuring my mirror and it is an 18" f4.5 (30mm plate glass) If I would have brought a Pyrex blank I wouldn't have had the money to build the telescope.

[MiG]

Originally posted by bytor666
People need to not be so fussy about what the mirrors are made out of, heck even the older 100 inch mirrors were made out of PLATE GLASS with bubbles all inside of it and those were amazing telescopes.

But the Hooker telescope is kept in an insulated dome so that there is little temperature variation. This is slightly impractical for us. Stargazers don't want to have a two hour cooldown time after bringing the scope from indoors. Pyrex will still have a long cooldown time, but the strains during that time are less than half of plate glass so the distortion won't be as bad.
Of course, once equilibrium is achieved the figure is what matters.

[slice of heaven]

Spot on MiG
The figuring of the mirror is the greatest concern.
At the moment the current sized gs mirrors are well made and affordable and that's their strongpoint on these scopes.
Up the price and reduce the quality of the optics and that would be the downfall of a larger mirrored gs scope. Regardless of how bad/good their ot and base design is, if the optics dont cut it, they'll only be bought by the desperates or unwary.

slice

[h0ughy (David)]

Slice

are you call'n me desperate or unwary????

Damn, I hate when the truth comes out.

[Starkler (Geoff)]

Originally posted by bytor666
[B]Plate glass? pyrex? Bk7? I think for a nice cheap 16" light bucket the figure of the mirror itself matters much MORE than the substrate used .

Too right, and if cool down is an issue, add some fans to scrub the thermal boundary layer.

[slice of heaven]

Sorry to let the cat out of the bag Houghy. lol

That was 'if' the optics dont cut it. Hopefully they wont take a shortcut in that area.

The substrate stated originally in the first post was bk7.

Then you still have to worry about the ot assembly and base.
They dont have a good track record in those areas.
By the way. I've noticed a few upgrade packages available in the states for their bases. Side braces...cross supports....thicker base plates...to remove the shakes and wobbles.

Slice

[h0ughy (David)]

will have to just wait and see

[h0ughy (David)]

I have just had another discussion with Andrew's, the 16's were due for delivery in September of this year, but he doesn't expect them until christmas of this year.

Now I am busily collecting aluminium cans for $crap, robbing pensioners, slealing the tuck shop money from the kids and saving for this expected delivery date!

[MiG]

People might also need to save up for the station wagon or ute to carry the scope

[h0ughy (David)]

But it would be worth it. I think it would fit in the subaru with the seat laid down. The car is pretty full with the LX200 stuff, so the 16 inch will be ok