Say Cheese

Barlow Lens Reversed:idea:
Not long ago I purchased a CCD camera for my telescope. I have not had a lot of chances to play with it. However, what few chances I have had show that my expectations will out shine the actual results.

For one thing, I am pushing the camera beyond its capabilities. The camera is designed to work with telescopes that have at least a 1000 millimeter focal length. My scope has a 450-millimeter focal length. The focal length is the base magnification of a telescope. Even with this drastically shorter focal length the camera should work well for getting images of the Moon and the Sun with an appropriate Sun filter. However, at its base level it is not going to let me get shots of various planets such as Jupiter or Saturn.

I recently purchased an inexpensive device to help me deal with that. It is called a Barlow Lens. It is a form of lens trickery. The Barlow Lens is a long barrel that fits in the eyepiece socket, between the socket and the eyepiece itself. It has a few lenses that extend the focus point of the light from the telescope itself, essentially pushing the point of focus further away. The eyepiece is placed at the opposite end of the Barlow Lens tube, and receives the new, extended focus image, which in effect makes the focal length of the scope longer. I purchased a 3x Barlow, which turns my scope from a 450mm focal instrument to a 1350mm focal instrument.

If you have ever played with a magnifying glass, you may have an idea of what a Barlow Lens does. The way you are suppose to use a magnifying glass is to place it close to your eye, which in turn lets you get closer to the thing you are looking at, while still allowing your eye to keep focus. But I’m sure you have also pulled the magnifying glass away from the object, and your eye away from the magnifying glass, and found a point where the things you were looking at appear huge. It may also have been a bit distorted around the edges, but it was certainly bigger. In pulling things away, you extended the focus point. You basically created a Barlow Lens, making the magnifying glass magnify a little larger than it is actually designed to do. The result is a bigger image, but with a bit of distortion.

The problem with the CCD camera on scopes with small focal lengths is that objects like planets are so small, they do not put enough light on the CCD device for it to produce an electrical charge, and thus an image. It isn’t that the image doesn’t shine on it. It just doesn’t shine on enough of it. It is like an underexposure. The image is just too dark. My hope with the Barlow Lens was that it would increase the size of the object enough that it would excite enough of the CCD for it to open for an exposure.

I have not had a lot of opportunity to try this, it having been rainy lately. But I have had one quick opportunity to test it, and my first desire seems to be realized. The Barlow does make the objects, in this case Jupiter, large enough to allow the CCD to create a charge and expose. I cannot yet speak to the quality of the images, or whether I will be able to obtain useful images. That will take more experimentation.

In that experimentation, I have also started experimenting with taking pictures with my standard camera, a Sony Cybershot, directly through the telescope eyepiece. Much to my surprise, this may yield more useful photos with my short focal length telescope. This has to do in part with my standard camera being a much better CCD style camera than the cheap one I purchased for the telescope. It will expose at much lower light levels. Additionally, this approach attempts to take pictures of what is magnified by the eyepiece of the scope itself, whereas the cheap camera I purchased for the telescope takes pictures through the eyepiece socket, with no eyepiece involved at all. In most telescopes, the eyepiece is the major magnifying device.

There are simple, inexpensive mounts that allow standard cameras like my Cybershot to be attached to a telescope for casual picture taking. I may look into one of these as my experiments go forward. While I do not have any useful pictures at this time, I will say that I am really enjoying my telescope, and I hope I can take images so I can share with you some of the wonders that I view.

About Sifu Keith Mosher

My new book, "Astro Boy, Sensei, and Me" is available now, as is my Sci-Fi joy ride, "On a Sphere's Edge". I have a Bachelor of Media Arts degree from USC. I have been an Audio Producer / Engineer, a Law Office Manager, and I am currently an Author and a Martial Arts Instructor.
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