Anyone owns a 12" or larger DOB?

Post by **VinSnr** » Sat Apr 08, 2006 8:36 pm

siahheng wrote:I too am toying with the idea of an Obsession scope!!

For big dobs, they have increased light gathering capabilites but also bring in more light pollution and the view in Singapore will not be much better. Can you guys tell me if this is true.

And, I would like to peek into a 12 inch or bigger dob if there is any around. Thanks.

Siah Heng

Are you sure the bulk and weight is gonna worth the trouble?

siahheng · Post by **siahheng** » Sat Apr 08, 2006 11:16 pm

VinSnr wrote:
siahheng wrote:I too am toying with the idea of an Obsession scope!!

For big dobs, they have increased light gathering capabilites but also bring in more light pollution and the view in Singapore will not be much better. Can you guys tell me if this is true.

And, I would like to peek into a 12 inch or bigger dob if there is any around. Thanks.

Siah Heng
Are you sure the bulk and weight is gonna worth the trouble?

Someone told me that bigger dobs will bring in not only the light form the DSOs but Singapore's light pollution as well and the DSOs will still be difficult to see.

Is this true?

Post by **acc** » Sun Apr 09, 2006 12:16 am

Its a myth, based on my observations in Singapore using scopes with aperture ranging from 70mm to 16". Just that beyond 10", scopes really start to get bulky and difficult to manage.

Canopus Lim · Post by **Canopus Lim** » Sun Apr 09, 2006 12:17 am

Well with Singapore increasing light pollution, I don't think we will be using scopes much for DSO (except the brigther ones). So might as well get a larger scope for Mersing or darker skies since we can only use scopes to see planets or moon well in Singapore; and probably we need to travel more to Mersing since Singapore skies are getting 'suckier'. But the 18inch requires a hatchback car that is for sure. Many small cars (1.6 litre and below) are sedan so that is a problem. Also, if a cab is needed, the 18inch cannot fit into it.

Tachyon · Post by **Tachyon** » Sun Apr 09, 2006 11:52 am

Not light pollution, but I have read arguments for/against larger apertures being more sensitive to bad seeing.

The problem with light pollution is contrast - leading to decreased signal-to-noise ratio of the DSO object you are trying to observe. While a larger scope will gather more light from the object, it will also proportionately gather more light pollution. However, larger apertures will increase the amount of light gathered from the DSO, and thus increase the signal - hence the ability to see the object. Note that the contrast is not improved and you will not see the magnificant details as compared to a dark site.

Cheers!

Post by **acc** » Sun Apr 09, 2006 12:06 pm

A large aperture helps to some extent in Singapore. For example, during an observing session at Dempsey, the hat shape of M104 is easily discernible in the 8" Portaball, while a 10" dob nearby shows a slightly better defined dust-lane. This same object would be practically invisible in a 70mm scope in Sg.

Post by **weixing** » Sun Apr 09, 2006 11:23 pm

Hi,
I think there may be some true on this and I think this will only happen at low magnification when the seeing and transparency is not that good.

My experience so far with this is that at low magnification the light pollution through my 120 refractor seen more serious than through my 9x50 finder scope.... and I think the view will be even worse if I'm able to use 9x on my refractor...

Anyway, may be next time acc can bring out his 12.5" to test with other smaller scope...

Have a nice day.

PS: So when are you resuming the CSN???

Post by **acc** » Tue Apr 11, 2006 9:52 am

weixing wrote:Hi,
I think there may be some true on this and I think this will only happen at low magnification when the seeing and transparency is not that good.

My experience so far with this is that at low magnification the light pollution through my 120 refractor seen more serious than through my 9x50 finder scope.... and I think the view will be even worse if I'm able to use 9x on my refractor...

Anyway, may be next time acc can bring out his 12.5" to test with other smaller scope...

Have a nice day.

PS: So when are you resuming the CSN???

My Portaball just arrived yesterday

There was a problem with the electrical system that took me a couple of hours and a few phone calls to Mag1 to fix. Now waiting for first light

Tachyon · Post by **Tachyon** » Tue Apr 11, 2006 10:09 am

Is that a 14.5" portaball??? You lucky man!

jermng · Post by **jermng** » Tue Apr 11, 2006 10:10 am

Wow! Congrats man!

Looking forward to a first light report!

and maybe a chance to look through it ...