telescopes

[jeanie]

hi all, i'm not sure if i can post a 'help me' thread here for getting telescopes.moderators, please feel free to move it to wherever is appropriate.
sorry for inconvenience.

I would like to purchase a reasonably good telecsope for photographing the moon and maybe a start to astrophotography.
can someone please recommend me where to buy a good telescope so that i can attach my nikon?
i heard of celestron.may i know an indicative price for a average piece?
and other than the shop in science center, where else can i get telescopes?

i did wiki and read i shouldnt get telescopes from camera or deparmental stores.

appreciate all advises.

TIA!

 

[jeanie]

when i read the specs for some celestron, when it shows 600mm, is this equivilant to our dslr lenses of 600mm?

are we able to view the rings of saturn here in sgp?

i'm sorry if the questions are extremely noobish.

 

[dOlBy]

when i read the specs for some celestron, when it shows 600mm, is this equivilant to our dslr lenses of 600mm?

are we able to view the rings of saturn here in sgp?

i'm sorry if the questions are extremely noobish.

I had viewed Saturn in Singapore before, but you got use a barlow magnifier with eyepiece. For photograpy it it better to have a longer focal length I recommend the 127mm maksutov with a focal length of 1500mm and it has a shorter tube length of 330mm very easy to carry around.http://www.skywatchertelescope.net/swtinc/product.php?id=83&class1=1&class2=108

 

[ArchRival]

yes can see Saturn. Can even see the cassini division.

 

[jeanie]

yes can see Saturn. Can even see the cassini division.

how many mm was that taken with?
is that the best that a telescope can do?or can still go nearer?

 

[Ryonpepper]

Hi Jeanie,

You can check with the expert from the Singastro forum. I believe they can guide you along with Astrography.
http://www.singastro.org/

For Astrography, If I can rem correctly, it's better to use lower f no telescope(focal length/aperture), and not based on the focal length. Just like in photography when we term fast lens... for faster exposure.
Magnification is then based on telescope focal length divide by the eyepiece focal length. So the longer the focal length of your scope, you should have more magnification. Correct me if I'm wrong la... hee.

There are specialize telescope for taking photo called astrographs, normally comes in small f no., f/5 n below. There's even 1 from Takahashi at f2.8.
http://www.astro.com.sg/telescopes/takahashi/astrographs.php

Or these big mama of astrographs:-
http://www.optcorp.com/ProductList.aspx?uid=1-599-635

Check out from the friendly guys from singastro.... they are one of the most active group of astromoner here in Singapore.

:thumbsup:

 

[ArchRival]

how many mm was that taken with?
is that the best that a telescope can do?or can still go nearer?

Taken in '03 with a Celestron C102 achromat. Think now the equivalent model is a Celestron XLT 102 or somethin.

The optical tube assembly has 1000mm focal length with four inches aperture, hence a f/9.8 system. 2x barlow was used. The camera was a modified webcam with 640x480 res. i was pushing the resolving limit of the system, so for the 4" aperture that's about the maximum. Even so you can already do funky things like this

Just so you know how much to spend, this setup (OTA, mount, tripod, finderscope, diagonal and 20mm eyepiece) went for $999 sgd new at one time.

If you are looking to photograph moon and planets, go for a longer focal ratio instrument, eg a schmidt-cassegrain (~f/10) or maksutov-cassegrain (f/15), or a long-tube 1-meter instrument like the 102. Moon and planets are bright enough so you can use a slower system. Exposures of 1/30s work for planets like Saturn and Jupiter, and even faster on the moon.

For DSOs, get a fast instrument, eg. short tube newtonians (f/5), high-quality semi-apochromats or apochromats (f/6.3-f/7). f/4 apochromats are usually expensive and difficult to find. People do take DSOs with f/10 schmidt-cassegrains too. There is something called a focal-reducer that reduces the f/10 to f/6.3 on a schmidt-cassegrain. You can get a 8" schmidt-cassegrain for less than $2k nowadays, tube only.

A good choice will be the 5 inch (127mm) maksutov-cassegrain. It has a camera mount so it can be used on regular camera tripods like the manfrotto 055 with a gear head. I believe a 127mm mak-cas will set you back $800+ nowadays. Gear head is $400+??

Camera lenses are specced according to f-ratio and focal length, since zoom is important. For telescopes, aperture is important, hence they are specced with aperture and f-ratio. eg C102 means 102mm of aperture. A 127mm mak means 127mm aperture.

I don't profess to be any expert, maybe the astro gurus here can give better advice.

 

[jeanie]

thanks so much for the information.
seems like astrophotography is another big field of it's own.
PHEW!

 

[Redsun]

wow cool!just look at saturn!!

 

[weixing]

Hi,
Welcome to the world of Astrophotography!

The below are a list of Singapore vendors other than Astro Scientific that sell telescopes:
1) Astro-Bargains - http://www.astrobargains.com/
2) StarOptics Scientific - http://staropticsscientific.com/
3) StarMatrix - http://www.starmatrix.biz/ (not sure whether still in business)

Anyway, basically any scope can be use to shoot the Moon, but avoid those "fast" achromatic refractors (faster than F8)... which usually had very serious chromatic aberration. Also, take note of the focal length... the Moon is too small if the focal length is too short and too big to cover in a single frame if the focal length is too long (unless you want to shoot parts of the Moon). The full Moon is usually around 0.5 degree in angular diameter, so you need to do some basic calculation. Below is a formula to calculate the field of view (FoV) base on the scope's focal length and camera sensor size using prime focus (DSLR connect directly to scope):
FoV = 2 x arctan [sensor size / ( 2 x Scope Focal Length)]
FoV in degree, sensor size and Focal Length in mm.

For example, a scope with focal length 1000mm using Canon 450D (sensor size:22.2mm x 14.8mm):
FoV (Width) = 2 x arctan[22.2/(2x1000)] = 2 x 0.636 = 1.27 degree.
FoV (Height) = 2 x arctan[14.8/(2x1000)] = 2 x 0.424 = 0.85 degree.

Note: If you want the whole Moon to fit in a single frame, don't use a scope with a specified focal length that will exactly fit the 0.5 degree of the Moon, because:
1) the Moon angular diameter is not fixed due to changes in distance from Earth,
2) the specified focal length of scope is not the actual focal length... it's a nominal focal length especially for Schmidt-Cassegrain Telescope (SCT) and Maksutov-Cassegrain Telescope (MCT), and
3) the Moon is not a stationary object, so you'll have problem in framing the whole Moon if there is no allowance especially if you are using a non-tracking mount, such as a camera tripod and head.

Have a nice day and happy shooting.