Beginning Astrophotography

[starscream59]

Astrophotography is something that has long since peaked my interest. I've always wanted to attempt it, but I'm unsure where to start. I currently have a Nikon D7000, but I was looking for rather inexpensive telescope that would allow me to get my feet wet and experiment with the concept. I was wondering if anyone had any suggestions where to start? I've seen reflector telescopes starting from very inexpensive all the way to several thousand dollars.

 

[qleak]

Astrophotography is something that has long since piqued my interest.

Click here to learn some vocabulary

I think it depends what sort of astro-photography you want to practice. Just saying generally you want to do all of it is not practical unless you have a NASA or NSF budget.

So what do you want to shoot? The moon, the planets, galaxies, the sun, star trails etc...

I'd say start with one objective and if you want to do more, expand later. Unless of course you have government funding

 

[WayneF]

Astrophotography is something that has long since peaked my interest. I've always wanted to attempt it, but I'm unsure where to start. I currently have a Nikon D7000, but I was looking for rather inexpensive telescope that would allow me to get my feet wet and experiment with the concept. I was wondering if anyone had any suggestions where to start? I've seen reflector telescopes starting from very inexpensive all the way to several thousand dollars.

I suggest starting here: Astronomy Club of Akron

Don't ignore the need for a dark sky. Far away from populated areas and lights, where you can at least see the Milky Way. Like Wyoming. or well up into Canada. At least for anything more than the moon and close planets.

Then just a wide angle lens on the camera can produce some stunning shots.

The problem:

 

[ruifo]

First tips:

• Get an ultra fast lens, with little coma aberration wide open, like the manual focus Samyang/Rokinon/Bower 24mm f/1.4 Aspherical lens. Or the manual focus Samyang/Rokinon/Bower 85mm f/1.4 Aspherical lens. These are the least expensive ones, they have little coma and being manual focus is better for focusing at infinity. Keep them focused on infinity and at f/1.4.
• Wide angle lenses, like the 24mm, will be better for the Milky Way shots. Tele lens, like the 85mm, will be better for deep sky details, like nebulas, or distant galaxies.
• You will want to be in the countryside, at least some 20mi away from any city lights, in dark evenings, with no full moon whatsoever, and no clouds, and no moisture, haze, humidity etc. So watch out for the weather forecasts.
• Full frames cameras are better, but your DX can work as well. With DX, the f/1.4 lenses become even more needed.
• Download the Stellarium free software - Stellarium - once it will provide you with precise astronomical bodies and night sky location for planning your shots.
• Always shot in RAW with uncompressed 14bits, if available in your camera. Get Lightroom or another similar post processing software and learn how to develop your RAW shots.
• Always close, block your viewfinder for long exposures, to avoid light leak into the sensor. This is important. And buy a tripod and a shutter release cable to prevent shake while shooting.

This is the basic for starting to shooting with DSLR. Read and watch the materials linked below, for further reference. They will help you to understand the gear factors, and techniques you need to use.

Astrophotography Without a Telescope

How to Pick a Lens for Milky Way Photography – Lonely Speck

Best Lenses for Milky Way Photography: Nikon Astrophotographers – Lonely Speck

https://docs.google.com/spreadsheet/lv?key=0AomVJ2lbrwb1dDRGeHJOaVZfYnlFR2ZDTFNlSnk2emc#gid=2





Good luck!

 

[pgriz]

Well, as mentioned already, it helps to know what you want to achieve.

To shoot the Milky way and star-scapes, you need a really dark sky, and a wide angle lens. If you want to go "deep" you'll also need a tracking mechanism to counteract the Earth's rotation..

To shoot the Moon, a telephoto lens (probably minimum of 200 mm), and if you want lots of detail, then you'll need a telescope with a sturdy mount and tracking ability, plus the necessary hardware to connect your camera to the scope.

To shoot the planets, you'll need good magnification, and (these days) a video camera from which you will extract individual frames to stack. Also stacking and registration software, and image-processing software.

To shoot the galaxies, nebulas and other faint critters, you'll need a telescope with lots of light-gathering power, plus tracking ability. Usually for these types of objects, the camera of choice is a dedicated astrocamera with cooling capabilities and filters built in. Then after you've acquired the image(s), there's a lot of work with software to bring out the details.

There are a number of members here who do astrophotos - and they will probably give you an idea of what you need once you've identified what you're really interested in.

When it comes to astronomy gear, "inexpensive" usually means ineffective, unless you really know what you're doing. The most under-rated part of a telescope is the stand (tripod, pier or other), as a wobbly/jiggly stand makes observing next to impossible. Second most important element is the tracking mechanism or mount, as without the ability to orient and track the object you're shooting, you will be severely limited by the exposure duration you can use. Third element is the light-gathering ability - telescopes are also called "light-buckets" because their main purpose is to gather enough light to allow you to see/image the faint objects. Magnification, which everyone focuses on, is the least important attribute, and certainly is useless unless you have the other three things working for you.

Here's one guide on buying a telescope: How to Choose A Telescope for Astronomy

 

[astroNikon]

All great advice.
As mentioned darkness is key. then the light gathering ability of the scope. That's why SCTs (mirror scopes) are common as they are less expensive than other scopes for their light gathering ability vs cost.

I recently upgraded from a Meade 125etx to a Meade 10inch SCT.
Wow, quite a difference.

The more light gathering you have the more detail you can see with similar magnification.
What I see on the 10inch of just the moon was not even visible on the 5inch for "smaller" craters.

But you have to start somewhere. So a budget is always good to work with. The budget to include the adapters needed to connect your d7000 to the scope.
I also have a d7000, so it's a good start. I then upped to a d600 FF which is even better.

 

[KmH]

. . . When it comes to astronomy gear, "inexpensive" usually means ineffective, unless you really know what you're doing. . .

+1.

Reflecting telescopes, which use a mirror as their main light gathering element, are easier and less expensive to build than refractor telescopes that use a lens as it's main light gathering element.
A basic entry level 5 inch reflecting telescope, w/manual equatorial mount, and a decent tripod will cost $400 to $500.
A basic 5" reflecting telescope w/manual equatorial mount, and a decent tripod will cost about 2x more - $800 to $1000.

Like camera lenses telescopes also have a 'speed' or f-number.
Telescope focal length divided by telescope aperture = the telescope's f-number
'Fast' reflecting or refracting telescopes are generally f/5.

 

[TCampbell]

I've gotta run (ironically I'm running off to present a couple of planetarium shows this afternoon), but the short answer is:

1) You need a GOOD equatorial mount. The mount is often more important than the telescope itself.
2) Refractors are good instruments for astro-imaging but these come in two classes (and they look the same, so you'd have to read the specs).

As light passes through the glass, the glass itself will tend to split the light into it's constituent wavelengths (like a prism). The effect is called "dispersion". You notice dispersion especially when you inspect the corners of the image and notice the stars have color fringing... red on one side and blue/violet on the other.

a) An "Achromatic" refractor will be the least expensive. These typically have two front elements. One is a somewhat traditional lens shape, the second has a concave front side to it. The second lens attempts to correct for dispersion but you WILL still notice color fringing around the edges of the image.

b) An "Apochromatic" refractor (often abbreviated "APO") typically employs three or more elements (although there are two element models that use low dispersion glass). These do a considerably better job controlling the dispersion. Not all apochromatic scopes are equal though... you'll even find some quality variation here.

You'll notice a very obvious price difference between the two. And of course bigger tends to be better (we're talking about diameter... not the focal length). Larger diameter scopes provide the ability to resolve finer amounts of detail... but of course that just adds even more to the price tag.

 

[TCampbell]

Now that I'm back I can add a few more comments...

"wide field" shots are definitely easier to shoot than narrow field shots.
"bright" objects are definitely easier than dim ("faint fuzzies" as we often call them.) objects.

Add that up and high-magnification, narrow-field, dim objects are REALLY hard. But bright wide-field images are really easy. There is a continuum from easy to very very very (you'll lose all your hair learning this) level of difficulty.

Obviously we suggest you start with the "easy" stuff first and work your way up.

A camera on a non-stationary tripod can shoot wide-field images but it helps to have a wide-angle lens... the wider the better. Also you want dark skies... WELL AWAY from any cities or towns, and also you want to do this on clear MOONLESS nights (check your calendar for the "new moon" or nights which are reasonably near the new moon. On those nights the moon is technically up during the daytime ... not at night.)

Assuming a DSLR with an APS-C size sensor (the vast majority) use "400" as a baseline value and divide this by the focal length of your lens. The result is the number of seconds that the camera can safely image the sky and NOT have stars beginning to elongate (growing a tail because of the rotation of the Earth.) E.g. if you have a 10mm ultra-wide angle lens then it's 400 ÷ 10 = 40 seconds. Now suppose you have a 200mm telephoto lens... with that it's 400 ÷ 200 = 2 seconds... anything longer than 2 seconds and the stars already start growing "tails"... so you can see why a nice wide-angle lens buys you more time.

Taking a photograph of the moon through a telescope is also fairly easy although you'll need a piece of equipment to to mount the camera to the scope.

Chiefly you'll need:

(1) a "T-Ring" designed to mount to YOUR camera type. e.g. for your Nikon you'll need a T-Ring designed for Nikons. It's a simple ring that has the Nikon style bayonet mount on the camera-facing side and industry-standard "t-threads" on the telescope facing side.

(2) a camera "nose piece". This is either a 1.25" or 2" barrel (the exact same barrel size as a 1.25" or 2" diameter telescope eyepiece) but it has an industry standard t-thread. You thread the "nose piece" and T-Ring together. With this attached to your camera, the camera can now be inserted into the telescope just like an eyepiece.

Here are some links so you get the idea:

Amazon.com : Celestron 93402 T-Ring for Nikon Camera Attachment : Celestron Adapter : Camera & Photo
Amazon.com : Celestron 93625 Universal 1.25-inch Camera T-Adapter : Telescope Photo Adapters : Camera & Photo

Those two devices together are still only around $20. Any Canon shooters reading this would need to substitute the T-ring for Nikon with a T-ring for Canon EOS.

ALSO... the 1.25" nosepiece is ok for APS-C size sensor cameras, but if you shoot with a full-frame DSLR you may have an issue with vignetting in the corners of the frame and may need to use a 2" diameter nosepiece (and of course you'd need a scope that can accept 2" diameter eyepieces.)

Not all telescopes are suitable for imaging. Many newtonian reflectors don't have enough focus travel in order to allow the camera to come to focus. The sensor plane is far back inside the camera so usually you have to rack the focuser in and you eventually may hit a point where the focus is in as far as it can go but the imaging was only beginning to come to focus... you'd need a few more millimeters of travel. This is generally never a problem for any refractor style scope nor for catadioptric telescopes (Schmidt Cassegrain scopes or Maksutov Cassegrain scopes).

When shooting through a telescope, the moon is your easiest object and looks best near the 1st or 3rd quarters although the 1st quarter moon is up right after sunset while you've got to get up in the early pre-dawn hours to shoot the 3rd quarter moon (so my vote is for shooting 1st quarter moon so I can sleep in.) This is because the sun is lighting the moon from the sides so you get excellent highlight/shadow details on the mountains. If you shoot at or near the full moon the moon is lit with the sun "at your back" and you don't see any shadows... the moon looks flat and 2D.

The exposure for the moon could be the same as the exposure for the day... the "Sunny 16" exposure (f/16 and set the shutter speed to the inverse of the ISO). But there's a problem... the moon has EXTREMELY low surface albedo (reflectivity). It's about as reflective as a black sidewall tire or freshly laid asphalt road. So we open up one stop and they call it the "Loony 11" rule. It says you can use f/11 and then set the shutter to the inverse of your ISO speed (e.g. at ISO 100 use 1/100th sec. At ISO 200 use 1/200th sec.) and you'll nail the moon every time. When shooting through a telescope however, you don't have an adjustable aperture and that means you'll need to look at the telescope specs to get the focal ratio. I have an f/5.6 scope (560mm with a 101mm aperture) so that's 2 stops open from f/11 that that means I need to speed up my shutter by 2 stops to compensate. But I can also shoot through a 2x barlow (I use a 2x Televeue Powermate) and that takes my scope up to f/11 natively.

...

And then there's the "hard" stuff.

Here's one of my attempts to image the Dumbbell Nebula (Messier 27)

To get this image, my camera is connected to a telescope (which in this case happened to be a 14" Celestron C14 -- an f/11 telescope) and my camera took 16 images of the object. Each image was 4 minutes long. So that's a bit over an hour's worth of data.

But there's a catch... I use a modified camera designed for astrophotography. It's about 5 times more sensitive to Ha light than a conventional camera. To gather this same data with a convention camera I'd have needed to shoot 20 minute long exposures (everything you see in "red" in this image is in the Ha wavelength.). So that's a bit over 5 hours worth of imaging just to collect the data.

The "data" that comes out of the camera looks like mud. It needs a lot of work to process it. It also needs "flat frames" to compensate for the vignetting of the telescope (illumination is never even and while it normally doesn't look bad, when you do astro-imaging you'll do a lot of "stretching" of the data to bring out the detail you want. When you do that you will MASSIVELY amplify the uneven lighting of the field. The "flat" frames are taken so that the computer can adjust to create even lighting across the frame.

And then there's the "dark" frames. The "light" frames generate a lot of "noise". The computer can process that noise out (not completely... but it can knock it back quite a bit). This is, in part, why you need so many "light" frames. The ability to knock the noise back is the square root of the number of "light" frames that you shot. So if you shoot 16 frames you can knock the noise back by a factor of 4x. But you also get "pattern" noise and to knock that back you need to shoot "dark" frames. Those frames are taken at the same physical temperature as the "light" frames, but you keep the camera covered so no light can enter. The "rule of thumb" says you should take at least half as many "dark" frames as the number of "light" frames. The "dark" frames do need to be at the same temperature, ISO setting, and exposure duration as your "light" frames.

Through all of this, the Earth is spinning and that's going to ruin your images. So you need a mount that can "track" the movement of the Earth as we spin... it needs to be a GOOD MOUNT (no being cheap on this purchase.) I consider about $800 to be rock-bottom pricing for a tracking mount and frankly while people "make it work", it's better if you can spend more. I went through three mounts before I found one that I really liked (a Losmandy G11 mount with a Gemini II computer to control it.)

With all of that you'll still need some magic to process the image. This is a skill that can take years to learn (and frankly, I'm not that good at it.)

Oh... and this is one of the EASIER deep-space objects to shoot. Many of them are much more difficult.