If you want to start out in astrophotography for DSO's (deep-sky objects like nebulae and galaxies), and want to produce good rather than average photos, then perhaps an Orion dobsonian is not the right choice because you will soon become frustrated with the lack of equatorial tracking needed to keep a camera locked onto a nebula long enough to expose the image (we're talking exposure times of anything from 30 seconds to 1 hour). The tube itself is perfect for photographing DSO's, but without tracking only short exposures are possible. [Note: Equatorial mounts specifically for the Orion Dobsonians to sit on top of, can be purchased from third-party vendors or built as a DIY project]

If you don't know it already, let me stress this point to you - APERTURE IS MORE IMPORTANT THAN MAGNIFICATION !

It's all about Light Gathering Power.

XT10 OTA TubeThe XT10 has a 48 inch (1,200mm) focal length (1200mm FL divided by 254mm Aperture = f4.7 focal ratio) which helps to keep the telescope manageable and portable, and yet it will still provide good high as well as low magnification observing.

The XT10 is one of the most popular Dobsonian Reflectors among those who want a manageable telescope with the light gathering and fields of view potential for observing many of the most popular deep sky objects. With about 920x the light gathering power of the unaided eye, the XT10 telescope provides an increase of about 1.55x better than the light gathering power of the 8" Dobsonian models.

Bear in mind that the XT10 is a big telescope for big celestial appetites! Before you buy a telescope such as this, consider carefully its overall size and weight before you buy. I am fairly strong, and even though the base has a substantial carrying handle, I find the XT10 heavy and unwieldy to carry as one unit, and you run the risk of the tube tipping in the altitude mount unless you secure it beforehand.

I much prefer to release the tube from the base, and carry the two parts separately. Independently they are lighter and far more manageable, and I feel safer doing it this way.

When transporting the scope to a dark-sky location, I put the dob base into the boot of my 4x4, and lay the tube across the back seat with the seat belts wrapped around it (the tube is almost 48 inches end to end, and 12 inches outside diameter).

If you plan taking the XT10 to a dark site, I recommend somewhere that you can get your vehicle close to the actual observation site, so that with planning and a backpack you only need two trips from and to the car.

For deep-sky objects the greater the aperture the better.

This is the main reason why you should not buy a cheap telescope basing your buying decision upon the fact the scope is capable of 750x magnification, yet only has an aperture of 2 to 4 inches.

High magnification has its place of course, but with mags above about 250x the quality of the view is greatly dependent on the "seeing", even in expensive professional quality scopes (I'll explain seeing in just a moment).

The rule of thumb for practical magnification is no more than 50x per Inch (25mm) of aperture. So a 10inch diameter mirror should in theory be capable of up to 500x. Hopefully you will start to appreciate that a budget scope with low quality optics and a 3 inch aperture will only really be good for 150x magnification - not the 750x it might advertise on the box!

 

Next section: The Human Eye - Dark Adapted and Averted Vision

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