MBS Astronomy » astrophotography

CCD Cameras and Frost

Captain Ippei — Fri, 11 Sep 2009 08:50:32 +0000

A couple of years ago after owning my SBIG ST2000-XCM camera for about 10 months, I ran into a situation that puzzled me. I was at Anza and started imaging M42 so I decided to start with 5 minute subs. The first shot looked pretty good. No field of view rotation, guiding looked good, in focus…a perfect start to a nice night of imaging, right? Wrong.

Each subsequent frame started to slowly degrade from the edges in. Nebulosity started showing where it shouldn’t be and stars were starting to diffract every which way just like the unprocessed shot to the left.

Since this was something I had never seen before, I kept taking a couple more shots until the last shot clearly showed the culprit…FROST! It was like looking through a window in the dead of winter with the center of the frame still fairly clear but with crystal like spider veins on the edge of the frame.

M42 Frost, -5C

Well, for frost to form, two things need to be present. A surface at or below freezing, and moisture. Now, what could I do about the moisture? Nothing at all. I could do something with the temperature level of the CCD Chips though. I was running at -5 degrees Celsius, so I decided to raise it to 0 degrees Celsius. I know what you’re gonna ask, 0 degrees is still freezing so why not go to 5 degrees? Well, the chip itself is at 0 degrees at the back surface but the front surface is just slightly warmer due to it being exposed to the air inside the camera body.

After letting it warm up for about 30 minutes, I started taking shots again and could clearly see a difference. Most of the frost had melted and is evident in the stars at the left, bottom and right edges. M42 itself is a bit sharper and the nebulosity isn’t artificially enhanced. What is also evident is the amount of noise from the increase in temperature. Eventually all of the frost disappeared and the rest of the shots I got that night were usable.

M42 Less Frost, 0C

After I got home, I immediately read over the manual and followed the direction on how to recharge the built in desiccant. Fortunately SBIG’s design of the ST2000-XCM desiccant plug is very simple. It simply screws out of the body, replace it with a dummy plug to prevent anything from getting in the camera and recharge it following the recommended procedure.

This happened almost after a year of use and in the fall, right after our monsoon season which makes sense since it was so humid. So here are a few tips to follow to minimize the chance of your CCD Chip frosting over.

Store your camera in a cool, dry place
Throw a pack of silica gel or other type of desiccant inside your camera case when not in use
Recharge your desiccant plug (if applicable) on recommended intervals or before big imaging trips
If frost forms during an imaging session, set the temperature regulation to 0 degrees C or above

SBIG Desiccant Plug

Dummy Plug

Astrophography with a 1 1/4″ focuser

fuadramsey — Sat, 14 Mar 2009 06:02:20 +0000

If you are like me, you are amazed by all the wonderful photos people are getting with their telescopes. Yes it does take a while and is not easy, but there are things you can do to try it out. We’ll focus on the types of astrophotography you can do with a telescope that has a 1 1/4 focuser.

The type of focuser you have determines the type astrophotography you can do with your telescope. Since my first telescope was the Celestron Omni XLT 150 (6″ reflector), I was not able to mount a DSLR camera to the stock focuser for two reasons: you need a 2″ focuser for the proper connections, and the camera will be too far away from the optical tube assembly (OTA) to reach focus.

So unless you are mechanically inclined, stay with the stock focuser. (Here’s how I replaced mine:

http://tinyurl.com/br852t

That does not mean you can’t do photography though. You have several options available with a 1 1/4″ focuser.

1)Eyepiece
You can simply get a point and shoot digital camera and hold it over the eyepiece. I got my first astro photo this way. You will need to use a wide field eyepiece and hold the camera steady. Orion makes a cool adapter that lets you attach your camera to an eyepiece. You just attach the adapter to the eyepiece, and then attach the camera to the adapter. Make sure to use a shutter timer if your camera has one. Use manual settings if you got them on your camera. You’ll also want a small and light camera here.

2) WebcamYou can attach a webcam to the eyepiece and take images of Mars, Jupiter, Saturn and Venus and the Moon. Webcams are great for planetary shots. You pretty much just take a movie of the object and “stack” the images. The end results can be quite amazing. This is one of the preferred methods for imaging the planets. To do this remove the lens from a webcam, attach an empty film canister to the body of the webcam, and insert this into the eyepiece holder on your telescope. Now you capture the image with some software and stack the images from the AVI movie you captured.

3) Piggyback
If your telescope has a tracking motor you can attach a DSLR to the telescope. Celestron’s Omni XLT 150 has a bolt on the tube ring that allows for this. With this technique you can get amazing wide field photos. But your success depends on a decent polar alignment, focus and how dark your skies are. One of my best photos so far was using this technique. It’s also one of the most forgiving techniques. You will always get good results if you aim towards the Milky Way.
Give these techniques a try. There’s a lot to learn with these techniques that will carry over to other types of astrophography like using the manual settings on your camera, using your camera in the dark, and getting a good polar alignment.

Once you have mastered these things, you will be ready for the next step. But beware it’s not easy and it’s very contagious.