Need Opinions on 8" SCT vs 8" F6 newt/dob

kayheem · Post by **kayheem** » Sat Jun 02, 2007 11:54 pm

Hi,

I need opinions from Singastroians who have tried out both before.

Which is better for DSOs? An average 8" SCT or a mass produced 8" F6 or 10" F5 dob (e.g. from GS or Skywatcher)? (Assuming both are well-collimated and under the same seeing conditions)

I know that the SCT has a larger obstruction, giving less contrast, blah, blah. But how do they compare under similar actual observation conditions?

I am looking for actual comparisons and not theoretical pros and cons.

I am thinking of selling my SCT and building (another) 8" or 10" light dob.

Kay Heem

ariefm71 · Post by **ariefm71** » Sun Jun 03, 2007 12:14 am

I've owned three 10" dobs and six C8 SCTs. The dobs outperformed the C8s on DSOs, no contest here. Planetaries/lunar are more difficult to judge except for better contrast on the dobs. Quality aperture rules.

On the other hand, the C8 is the largest aperture scope you can actually carry onboard an airplane. Try that with a dob

Arief

Post by **acc** » Sun Jun 03, 2007 12:19 am

I have used many SCTs and commercial dobs of various apertures, sometimes side-by-side. Provided you don't get a lemon (and I have not come across one), a mass-produced dob will easily beat an SCT of equivalent aperture: the difference in contrast, sharpness and brightness is quite apparent to even a novice observer. For visual stargazers (ie no astrophotography), once you get accustomed to the image from even a run-of-the-mill dob, you will never like what you see through an SCT again

cheers
cc

Post by **acc** » Sun Jun 03, 2007 12:30 am

Oh while dobs are big, setup is incredibly fast and easy. Just plonk the OTA on the base and you are done. No messy tripods and alignment processes. The only disadvantage optically is the presence of diffraction spikes on bright objects. However, its a minor issue that manifests only on the brightest objects. During planetary use, I (or rather my eyes) quickly learnt to ignore the spikes. Even with the spikes, planetary images is a cut above SCTs (noticeably better contrast and sharpness).

jiahao1986 · Post by **jiahao1986** » Sun Jun 03, 2007 12:35 am

So how do the dobs perform on DSOs when using low power under Singapore condition? For fast dobs low power eyepiece should give large exit pupils and hence the field of view may be too bright to be contrasty due to light pollution ?

Post by **VinSnr** » Sun Jun 03, 2007 12:50 am

No contest between the 8" f/6 dob and the 8" SCT. DSOs on the 8" f/6 is more contrasty than the 8" SCT. The difference is noticable.

If you can build a 10" f/6. That is a true winner.

kayheem · Post by **kayheem** » Sun Jun 03, 2007 7:33 am

Anyone wants to buy my 8" SCT? :-)

Post by **VinSnr** » Sun Jun 03, 2007 1:22 pm

kayheem wrote:Anyone wants to buy my 8" SCT? :-)

aiyoh..I just bot one...but it's the 8" LX200R OTA. Want to see what is so rave about the flat field of these scopes.

Post by **weixing** » Sun Jun 03, 2007 4:13 pm

Hi,

So how do the dobs perform on DSOs when using low power under Singapore condition? For fast dobs low power eyepiece should give large exit pupils and hence the field of view may be too bright to be contrasty due to light pollution ?

It's the same with any scope type if you use a low magnification until it give a large exit pupil... just that a SCT may require a focal reducer to reach such low magnification. The key is large exit pupil, not scope design.

aiyoh..I just bot one...but it's the 8" LX200R OTA.

How big is the Central Obstruction??

Anyway, if you don't have any transportation issue, a decent visual Newtonian will always perform better than a decent SCT. I love my Newtonian, but I'll have big problem if I'm going to bring it to Mersing due to it's size...

Have a nice day.

jiahao1986 · Post by **jiahao1986** » Sun Jun 03, 2007 4:40 pm

weixing wrote:Hi,
So how do the dobs perform on DSOs when using low power under Singapore condition? For fast dobs low power eyepiece should give large exit pupils and hence the field of view may be too bright to be contrasty due to light pollution ?
It's the same with any scope type if you use a low magnification until it give a large exit pupil... just that a SCT may require a focal reducer to reach such low magnification. The key is large exit pupil, not scope design.

Hi weixing,

I'm not refering to comparing the two designs. I just want to know whether light-pollution significantly affect the view of DSOs when using low power on a fast dob under Singapore condition. Thanks.

Jia Hao