Which telescope to buy?

My needs
1. Terrestrial picture taking like birds and stuff
2. Celestial bodies like planet, moon, sun, eclipses, comet etc

I want to try my hands on wildlife and astro photography as a biginer and i'm on a tight budget of around Rs8000, ie. 70-130 $. Till now i'm dawdling between 3 products

1. Celestron travel scope 70 (400mm)

2. Sigma 70 - 300 mm F4-5.6 DG

3. Celestron C90 MAK (1200mm)

I will use it for observation( not the lens of course ) but my primary objective is picture taking

In round numbers, the image size of the Moon on your chip will be about 1mm for every 100mm of focal length. With the most common DSLRs that means a 1300mm focal length lens would have the Moon filling almost the entire frame in one direction. 650mm would have the Moon filling about half the space between top and bottom of an uncropped horizontal photo.

Of the scopes you've mentioned, I'd go with the C90 for the Moon.

It's going to have a narrow field of view, and you'll want an extra sturdy tripod and a head with smooth action for it.

Something a little shorter is apt to be easier to aim for birds.

You can take images of the Moon and for that matter brighter planets without a tracking mount as they're reasonably bright sunlit objects. For planets the usual method is to shoot a video and process it in Registax. For planets you want much more focal length. I typically shoot planets at focal lengths above 4000mm.

Comets are really in the same category as deep sky - they're pretty dim so you'll need an exposure that's long so you'll need an equatorial tracking mount. The least expensive mount up to that task is going to be several times your target budget. Inexpensive mounts tend to use small bearings and aren't stable enough for time exposures.

Before you buy anything, it really makes sense to find a local astronomy club and attend some of their observing events. Ask people to tell you about the equipment they have. They're usually quite happy to share the view with visitors. You might even find someone who will let you use your camera in their scope for a few minutes.

Here's a link to some of my astro photos. The one of M42 was shot with a Sony Nex 5 dslr. I've also taken similar shots with a Nikon D70. The planets were shot with a dedicated planet camera. (each of the planets is a separate photo - I merged them together to save space on the page) The other deep sky shots were taken with an SBIG dedicated astronomy camera. M101 isn't really purple - a plane flew through one of my green exposures and I decided purple would make a nicer neck tie. (I have Zazzle make ties with my images)

< http://www.holden-insurance.com/bmasho13.pdf >

Any telescope will do for birding, but they are clumbsy when attaced to a camera and want to pan and follow focus. A lens like a 70-300 mm VR or 300 mm d/2.8 is best for this purpose

Shooting the moon, planets and deep space is wholly different.

For that you need a computer controlled telescope so that it can adjust for the rotational movement of the earth, the movement of the earth around the sun. If shooting star fields, your telescope still needs to constantly adjust for the earths movement.

I have used a Meade LT8 Telescope telescope when shooting planets and star fields. Since I'm a photographer, not an amateur - astronomer, I spend all my money on camera gear, so beg my friends to use theirs

Tight budgets are NOT for those who want a hobby in either photography or astronomy.

My amateur - astronomer bud has over $12,000 invested in his telescopes and single camera.

He has what is called a Heat Reduction system added to his Nikon dSLR to keep the heat buildup on the cameras CMOS sensor from causing noise when he is taking exposures longer than one minute

All my money is tied up in camera bodies, lenses and high speed computer gear

Pick your hobby and then start throwing money at it. Only wives, boats and aircraft are more expensive.