12" Binte/Adrews/ or 6"achro

miki63au · #1 27-07-2008, 05:18 PM

Hi everyone.
My cass. scope project going slow, and I need something right now.
I tossing between Bintels white 12" dob or Andrews GSO dob.
What is the different between them?
(I like the Bintel becouse its white...

)

Also Andrews Com. selling the 6" achro OTA for about the $800 as well.
How is the Chinese refractors would compare to?

The 6" achro used to be legendary because of higher contrast than mirror based systems (for equal price). How is nowadays the quality of this doublets? Would Andrews Com. exchange it if optically compromised, like spherical aberration or astigmatism?

Any opinion?

Matty P (Matt) · #2 27-07-2008, 05:30 PM

I'm pretty sure that there is no difference between the 12" dobs except the colour and a couple of extras. They are both GSO scopes except Bintel have renamed them.

Satchmo · #3 27-07-2008, 05:59 PM

Quote:

Originally Posted by miki63au

The 6" achro used to be legendary because of higher contrast than mirror based systems (for equal price). How is nowadays the quality of this doublets?

Miklos, If you put a 6" off-axis aperture stop on a 12" Newt you'll see superior images to a 6" F8 Chinese refractor. I have two 6" F8 Achromats and consider that the star images are looking soft and distinctly yellowish with a 12mm eyepiece, due to Chromatic Aberration.

A stopped-down Newt has no such limitations. Its great to be able to remove an aperture stop on a larger Newt, when you want to see some detail in deep sky objects.

GrahamL · #4 27-07-2008, 06:01 PM

I dont know if you get a choice in the colour .. the white ones do look very scientific

.. but mine at times had a habit of catching a bit of stray light around the focuser and bounceing it into your eye ..so I painted the top bit black

.. more annoying than a big problem..they are both the same though.

miki63au · #5 27-07-2008, 06:17 PM

Quote:

Originally Posted by Satchmo

I have two 6" F8 Achromats ... .

Fair enough, but I read everywhere that 6" synta not bad for the money.
Just need a bit of luck to get a well corrected one tho.
You have two ? Have you tried to optimise it by changing the spacers?

AlexN · #6 27-07-2008, 06:17 PM

I have a saxon 6" achro and I can say the views are nice untill you go to something very bright, or you use too much magnification....

As has been mentioned, the Andrews/bintel 12" are the same unit. whichever takes your fancy at the time.

Satchmo · #7 27-07-2008, 07:27 PM

Quote:

Originally Posted by miki63au

Have you tried to optimise it by changing the spacers?

These Synta refracters are air -spaced I would assume optimally. Even 30 years ago an F8 6" achromat would have been a rarity, becasue of its camparatively poor color correction. if you are used to Newtonians with good optics, a 6" achromat loses its appeal after the initial thrill of contrasty views of bright star clusters at low power with them wears off.

toyos · #8 28-07-2008, 12:08 AM

Quote:

Originally Posted by miki63au

Hi everyone.

Also Andrews Com. selling the 6" achro OTA for about the $800 as well.
How is the Chinese refractors would compare to?

Any opinion?

$800?? They were $599 last month. I bought one just to find out more about it and sold it again after 2 weeks. The images were contrasty (as expected) showing good definition and fairly sharp for an achro but the chromatic aberration was apparent and some star images did look quite yellowish. The CA also affected the apparent sharpness to some extent. Compared side by side to unmodified 12" GSO & 10" Skywatcher dobs, the contrast of the refractor was way better. I tried putting an aperture stop on the unmodified 12" GSO dob and the result was nowhere as good as the 6" refractor (chromatic aberration aside). Overall, despite the false colours, I'll choose this refractor over an unmodified budget 10" dob.

kinetic (Steve) · #9 28-07-2008, 12:14 AM

Quote:

Originally Posted by miki63au

Hi everyone.

(I like the Bintel becouse its white...

)

Any opinion?

Hi,

the Andrews GSO 12 that I got about a month ago is
white.....looks beautiful.

See here:
http://www.iceinspace.com.au/forum/s...ad.php?t=34116

Steve

miki63au · #10 28-07-2008, 08:21 AM

Quote:

Originally Posted by toyos

$800?? I bought one just to find out more about it and sold it again after 2 weeks. .... . Compared side by side to unmodified 12" GSO & 10" Skywatcher dobs, the contrast of the refractor was way better. ....nowhere as good as the 6" refractor .... Overall, despite the false colours, I'll choose this refractor over an unmodified budget 10" dob.

way did you sold it? what you mean "unmodified" dob?

I like the idea of having a 6" refractor, but the 12" dob if the mirror is ok
probably more useful. I think both system cop out around 200 mags unless
it's exceptionalY good sample. Actually I want both of them, use the refractor for wide field and the 12" for fainter DSO...

AlexN · #11 28-07-2008, 08:53 AM

a 6" F/8 refractor wont give wide field views....

it will have a focal length of 1200mm, the 12" reflector will have 1500mm..

For widefield shots you really want less than 1000mm.. something in a 6" F/5 would be great at 760mm FL.

Satchmo · #12 28-07-2008, 10:21 AM

Quote:

Originally Posted by toyos

I tried putting an aperture stop on the unmodified 12" GSO dob and the result was nowhere as good as the 6" refractor (chromatic aberration aside).

If you found an effectively unobstructed 6" F10 reflector to be inferior to a 6" F8 refractor then you must have a really poor quality mirror.

toyos · #13 28-07-2008, 01:06 PM

Quote:

Originally Posted by Satchmo

If you found an effectively unobstructed 6" F10 reflector to be inferior to a 6" F8 refractor then you must have a really poor quality mirror.

That's what I thought - poor quality mirror, but I star tested the scopes inside & outside focus, they seemed okay (acceptable). Did you fully flock & baffle your 12" GSO dob? I never bothered modifying my dobs (I don't even have enough time to use them) and I've sold them anyway, even my supposedly 'low-contrast' SCT's always showed better contrast than the dobs in spite of the larger CO's.

This is the reason why doubling the horsepower of your car does not make it go twice as fast. There are many other factors that affect it.

Ian Robinson · #14 28-07-2008, 01:46 PM

It's a no brainer.

Go for a 12" reflector.

You can see more.

AlexN · #15 28-07-2008, 06:50 PM

Else - Spend more money and buy a 12" APO

anj026 · #16 28-07-2008, 09:14 PM

At the risk of going off topic, wouldn't a 15 or 16 inch aperture newtonian be required to achieve an un-obstructed 6 inch aperture with an off axis mask?

miki63au · #17 28-07-2008, 09:57 PM

Good point Andy,
how is your 6" f15 ? Is it a D&G?

Anyone had a chance to see a 6" Chinese achro with "chromacor" ??
The thing is that a GSO 12" mirror is about the price range of the achro,
so my logic is we should compare it to that. Zambuto quality is not fair...
I think the average 12" and the achro will top out at 200 mags.
The mirror is because the lack of figure and polishing, the achro is too
fast and possibly not well corrected. Still, 6" and no obstruction....

toyos · #18 29-07-2008, 12:04 AM

Quote:

Originally Posted by anj026

At the risk of going off topic, wouldn't a 15 or 16 inch aperture newtonian be required to achieve an un-obstructed 6 inch aperture with an off axis mask?

That's right, you can turn a 12" dob into a roughly unobstructed 4.8" reflector. Alternatively, you can make a multiple aperture stop with 2-4 holes which kind of re-introduces the central obstruction but could slightly increase contrast (by darkening the background) & sharpness. Both methods didn't work that great for me. Also keep in mind that multi-coated lenses transmit more light than combinations of mirrors, for some reason most people don't seem to take this into account when comparing refractors to reflectors.

anj026 · #19 29-07-2008, 12:08 AM

Hi Miklos, my scope uses a D&G lens in a home made tube. It is a lot of fun but not practical for everyone.
I have not used either a 12" dob or a 6" f8 achromat but they both seem like great value for $800 and I expect you could use one for a year or so and then sell it on for more than half what you paid. If you prefer deep sky go for the dob.

tnott · #20 30-07-2008, 09:04 PM

Quote:

Originally Posted by miki63au

Good point Andy,
how is your 6" f15 ? Is it a D&G?

Anyone had a chance to see a 6" Chinese achro with "chromacor" ??
The thing is that a GSO 12" mirror is about the price range of the achro,
so my logic is we should compare it to that. Zambuto quality is not fair...
I think the average 12" and the achro will top out at 200 mags.
The mirror is because the lack of figure and polishing, the achro is too
fast and possibly not well corrected. Still, 6" and no obstruction....

You will see more detail with the 12" (if the seeing allows) central obstruction or no.

http://www.skyandtelescope.com/howto...tml?c=y&page=5
http://legault.club.fr/obstruction.html

Portability, cool-down time and convenience are other important considerations though.