Simple Astrophotography (Part Four)

Two months ago I write three articles (here, here, and here) about some simple and easy ways to use little more than a digital camera and a tripod to get some pictures of comets, the stars, and the ISS as it flies by overhead.

Last month I gave everyone a heads up about Saturn and the moon being near each other in the evening sky, making Saturn easy to find for even the novice backyard astronomer. I took a bunch of pictures that night (of course!!) and wanted to share with you, especially since a similar viewing opportunity will be coming up in mid-July.

First I was simply taking pictures of the waxing gibbous moon using my Canon Rebel Xt DSLR and a Tamron 70-300mm telephoto zoom lens.

(Click on any image to enlarge & see the full-sized image.)

A telephoto lens of this size won’t let the moon fill the frame, but it’s more than big enough to let you see considerable detail. It’s critical to get your focusing correct. You can try to let the camera autofocus to get you in the ballpark and I’ll take a few pictures using autofocus, but I always try to take most of my pictures focusing manually to get it perfect.

You’ll need to bracket a number of pictures to get the exposure correct on the moon. Remember the rule – “Digital photographs are CHEAP!” The moon will be far, far brighter than your camera thinks it is, while the camera’s light sensors will try to average over the whole frame to set the exposure if you’re in full automatic mode. So full automatic mode will give you pictures of the moon way, WAY overexposed, just a huge white blob.

For example, on this night the camera on full automatic mode wanted to do exposures in the 1/30  second and 1/60 second range. I shot bracketed exposures all the way down to 1/500 sec and then double check, only to be amazed that they were still seriously overexposed. This picture was taken at 1/4000 sec at f5.6, the fastest the camera will go.

You may be photographing an object in a really dark, black sky, but it’s really bright, especially as you get closer to full moon.

 

I tried to take pictures of Saturn with this lens, but at 300mm it’s just not big enough to show any detail. Saturn here is the bright dot just above center, but the only thing making it look like it’s bigger than a dot is a slight vibration in the camera during the 1/3 second exposure.

 

So, given that 1/4000 sec was good for the moon and 1/3 sec was good for Saturn, how does one go about taking a picture of the two of them in the same frame?

Unless you’re using Photoshop, it’s tough. Getting Saturn to show up at all will guarantee enough glare from the moon to wash out the frame, while exposing for the moon will leave Saturn lost in the gloom. Also, for most lenses, if you put the moon anywhere near the center of the picture you’ll get horrible ghost images from the internal reflections in the lens. The lens flare seen above is one thing (think JJ Abrams!!), multiple ghost images across the frame are another.

The next step for me is to try to go beyond “simple” astrophotography into what we might call “intermediate” astrophotography, using telescopic gear that the average person won’t have just lying about. We’re not talking about tens of thousands of dollars in gear here – it’s absolutely amazing what you can get for $1,000 or less, telescopes that would have cost twenty or fifty times that just twenty years ago. Still, it’s not “simple”.

I hope we’ll get to that later in July.

One final extremely simple astrophoto that you can take, which I spotted at the Angels game on July 4th. If you go out just after sunset these days and look to the west-northwest you’ll see a really bright object sinking toward the horizon an hour or two behind the sun.

That’s Venus.

 

Way above the roof of Angels Stadium you see two big, blobby, ghostly images – those are reflections of the lights under the roof. But just a smidgen above the center of the roof, right over a green stanchion or support sticking up, you can see a clear, bright pinpoint.

Voila! Even in the glare and lights of a fully illuminated baseball stadium, you can spot (and photograph) Venus.