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Author Topic: Astrophotography - which camera?  (Read 11409 times)

jrista

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Re: Astrophotography - which camera?
« Reply #15 on: April 12, 2014, 10:59:29 PM »
Wonderfully explained!

Conclusion: a 200mm lens is wwwwwwwway too short for the ISS. It's hopeless, meaning, that even if you capture it perfecty, you will have a hard time spotting it in the final image. And for streak images, 70 is wwwwwway too long.

So, the question is not "which camera" but rather "which lens". The answer is: No lens at all, you will need a telescope for that. So if you plan to get into astrophotography, there just is no other option than getting a telescope. Fortunately, compared to EF glass, telescopes are rather cheap. They are basically mirrors, after all.

It isn't quite that simple. Most telescopes are designed for visual observing. The ones in the range of a few hundred dollars to about a thousand are not really ideal for use as "astrographs". As it actually stands, a lot of people, including myself, price Canon's telephoto EF lenses like the EF 600mm f/4 L II as telescopes due to their superb optical quality as refracting telescopes. A good refracting telescope, such as an AOP Triplet, STARTS at around $1500, and the price can reach as high as $15,000 for a very good APO quadruplet or quintuplet.

Regarding reflector-type scopes. There are some newtonian astrographs, and they tend to be the cheapest, but you are still going to spend around $1000 for one. SCTs, or Schmidt-Cassegrain Telescopes, usually start around $1500 and can reach many thousands of dollars. You usually get a lot more aperture (physical aperture) with an SCT than with a Refractor, and they are usually optically superior to Newtonians. RCs, or Ritchy-Chretiens, are also "cassegrain" type reflecting telescopes, and are generally the preferred type of OTA design for "astrographs". It is actually pretty easy to get a good quality RC astrograph for a good price.

Specifically, the best entry-level one is the Astro-Tech 6" AT6RC, which is a 6" diameter aperture (same diameter as the EF 600mm f/4 L II lens) with an f/9 focal length (1372mm, to be exact.) If you want to get an actual telescope for doing astrophotography, and don't want to spend a lot of money, the AT6RC is only four hundred bucks:

https://www.astronomics.com/astro-tech-6-inch-ritchey-chretien-astrograph_p19910.aspx

The AT6RC will make the ISS 100 pixels in size on the 7D, without any additional accessories. If you slap on a 2x barlow lens, then you have 2744mm of focal length, and the ISS will be 200 pixels in size. Keep in mind, if you push your focal length that much, you are going to need a VERY, VERY, VERY STABLE mount, because the smallest amount of shake will completely obliterate any detail you might otherwise resolve. You will, most likely, also want an equatorial tracking mount with the ability to use custom tracking rates other than sidereal or king, and the only mount I know of that can do that easily (for ~cheap) is the Orion Sirius (~$1000) or Orion Atlas (~$1400), because these mounts support EQMOD (which allows you to download and utilize custom tracking rates, and there are premade profiles for known satellites and the ISS that you can simply download). You would need a tracking mount for the AT6RC strait up, let alone with a barlow.

If you want to go larger/longer, you could look at the AT8RC, which sells for about $900. You would definitely want the Orion Atlas, so the total cost of the mount + OTA at that point is around $2400, however the larger aperture will allow you to resolve MUCH finer details on the ISS than a smaller OTA (resolving power and smallest resolvable magnitude of astronomical objects, including satellites and the ISS, is directly related to the physical aperture diameter).

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Re: Astrophotography - which camera?
« Reply #15 on: April 12, 2014, 10:59:29 PM »

Don Haines

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Re: Astrophotography - which camera?
« Reply #16 on: April 12, 2014, 11:38:10 PM »
Wonderfully explained!

Conclusion: a 200mm lens is wwwwwwwway too short for the ISS. It's hopeless, meaning, that even if you capture it perfecty, you will have a hard time spotting it in the final image. And for streak images, 70 is wwwwwway too long.

So, the question is not "which camera" but rather "which lens". The answer is: No lens at all, you will need a telescope for that. So if you plan to get into astrophotography, there just is no other option than getting a telescope. Fortunately, compared to EF glass, telescopes are rather cheap. They are basically mirrors, after all.

I think the real question is "which tripod"... Astrophotography can be of very small objects that require LARGE telescopes, it can be of wide images like the milky way, or it can be anything in-between... but for all of them you need a decent tracking mount. I have an 8 inch telescope that I use for planetary imaging and I also mount my DSLR onto the tripod for imaging nebulas and the night skies...

If you do not have a tracking mount, you will be limited to short exposures and you will have streaks of light on them.... The tracking mount comes before any camera/lens/or telescope in your wish list.
The best camera is the one in your hands

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Re: Astrophotography - which camera?
« Reply #16 on: April 12, 2014, 11:38:10 PM »