Bresser or GSO for a 12" inch dob

[dweller25]

The Bresser appears to have a single speed focuser, the GSO/Stellalyra have a two speed focuser.

[Mr Spock]

2 hours ago, thegopieffect said:

Hi, thanks for your response. Have you tried astrophotography with the GSO’s focuser? I mean any workaround? 

I'm not sure what you mean by workaround.

It holds my D500 ok. I can't imagine any astro camera being as heavy as a D500!

 

[Chandra]

3 hours ago, thegopieffect said:

How about the primary mirrors on both? Do you think it’s good equally? With Bresser’s I’m definitely getting the fan. 

I have read in different publications that OSG uses state-of-the-art manufacturing and test lines on their mirrors which ensures diffraction limited performance, with a surface quality of at least 1/16 wave RMS, and often better, i.e. optical performance with virtually no light dispersion. Supposedly, the image produced by their mirrors is above the standard, however they are manufactured in a material (borosilicate N-BK7) with a coefficient of thermal expansion greater than that of the optical glass used in the manufacture of Bresser mirrors in this category, whose material is H-PZ33, with similar specs to Pyrex. 

Considering that the cooling rate of a mirror is proportional to the square of the thickness of a mirror, and the thickness depends on the aperture (for the surfaces of the primary mirrors to be undeformed and stable, the thickness-diameter ratio must be at least 1/6), with a diameter of 10" the mirror must be at least 40mm thick. That is a very considerable mass of glass to cool, which will require a long time to reach (almost) thermal equilibrium. Perhaps this is the reason why the OSG incorporates the cooling fan, to accelerate the thermal balancing process of its mirror, since due to the material in which it is constructed, it therefore has a higher linear expansion coefficient. In the acclimatization process, which in these mirrors of considerable size will hardly take less than 2 hours (depending on the thermal gradient to be overcome), the figure of the Bresser could possibly be somewhat better than that of the OSG. Of course, once both are there. acclimatized, the figure of the OSG will supposedly surpass that of the Bresser, if we trust the quality data of its surface.

Anyway, it is likely that I have not clarified anything, but I wanted to make the point, since we have been talking perhaps more about the accessories, the focuser and the quality of the mount (aspects that are obviously very important), than about the optical quality (which it also is). I must admit, however, that in this case the best thing would be to test both tubes in parallel and under the same conditions in a real observation, and it is likely that no one here can say that they have done it...

[Chandra]

2 hours ago, bosun21 said:

If you are serious about astrophotography then you are buying the wrong telescope completely. Buy a refractor.

It wouldn't be unreasonable to do "serious" astrophotography with a Newton, but then he would have to mount it in an equatorial configuration, get a coma corrector and above all invest a lot of money in a sturdy support, which would undoubtedly enormously exceed the initial budget... In the end, it is clear that a small APO refractor ends up being cheaper...

[bosun21]

56 minutes ago, Chandra said:

It wouldn't be unreasonable to do "serious" astrophotography with a Newton, but then he would have to mount it in an equatorial configuration, get a coma corrector and above all invest a lot of money in a sturdy support, which would undoubtedly enormously exceed the initial budget... In the end, it is clear that a small APO refractor ends up being cheaper...

Exactly. Plus he would have a insanely steep learning curve with a 12" Newtonian as a starting point for AP 

[paulastro]

Some good points about both scopes.  I think you'd probably be pleased with either.

 One other point which may be an issue for you.  A while ago I had Bresser 8inch Newt tube and mounted it equatorially.  It was noticeably heavier than any other 8 inch I have used with the same focal ratio.  There was hardly enough room on the counterweight shaft for all the weights I needed.  For this reason I didn't keep it very long.  A shame as it was a good scope.  If you're buying the 12inch Dob version you might want to check the weight first.

[alacant]

9 hours ago, Mr Spock said:

It holds my D500

It may hold it, but locking it in place -using the locking screw- tilts the focuser. Certainly on the five or so which we've witnessed.
Cheers

Edited May 23 by alacant

[Mr Spock]

13 minutes ago, alacant said:

It may hold it, but locking it in place -using the locking screw- tilts the focuser.

I don't use the locking screws. In addition, I sometime use the 4x Powermate too.

I'm not sure what you are suggesting here.

[alacant]

13 minutes ago, Mr Spock said:

I don't use the locking screws

There is only one locking screw. If you don't use it, you won't see the tilt when you do! The second screw adjusts the Crayford spindle tension.
It probably doesn't matter if the OP is simply going to look through the telescope. Holding a camera for hours on end is a different matter.
Cheers and HTH
 

Edited May 23 by alacant

[Mr Spock]

You wouldn't need to hold the camera for hours on a Dob. They aren't made for long exposure imaging 

Works fine for planetary imaging though.

[alacant]

4 hours ago, Mr Spock said:

They aren't made for long exposure imaging

The Bresser is designed to be easily adapted to do so. The OP also expressed  interest in doing so. Perhaps my fault for suggesting a suitable mount!
HTH

Edited May 23 by alacant

[John]

The 12 inch Bresser seems to have quite a light tube for a 12 inch. It seems to be made of GRP which probably accounts for it's weight (or relative lack of it). 

[bosun21]

16 minutes ago, John said:

The 12 inch Bresser seems to have quite a light tube for a 12 inch. It seems to be made of GRP which probably accounts for it's weight (or relative lack of it). 

It's still only 600g less than the GSO .

The Bresser is 18.9kg with accessories and the GSO is 19.5kg also with accessories. I suppose the tube rings will contribute to to the weight of the Bresser, but then it's finder scope is made of plastic, probably to save weight.

Edited May 23 by bosun21

[John]

49 minutes ago, bosun21 said:

It's still only 600g less than the GSO .

The Bresser is 18.9kg with accessories and the GSO is 19.5kg also with accessories. I suppose the tube rings will contribute to to the weight of the Bresser, but then it's finder scope is made of plastic, probably to save weight.

My OO 12 inch F/5.3 was about 17kg inc accessories. Aluminium tube. 

 

[bosun21]

9 minutes ago, John said:

My OO 12 inch F/5.3 was about 17kg inc accessories. Aluminium tube. 

 

The O Optics aluminium tubes do appeal to me. I was considering buying a 10 or 12" OTA when one of each size were recently advertised in the classified section. I was thinking of putting it on my AZ-EQ6. I then realised that this would be pointless as I already had a 10" Synscan dob. I really do need to keep myself in check when browsing the for sale astro sections!