How to Focus Astrophotography Camera (for Free!)


I finally got a nice clear night to play around with a new scope, so I have some more info to share. One of the first challenges you face in astrophotography is focusing your camera. You may be used to point and shoot auto focus kind of thing, but it obviously does not work here. Even if you have a sharpest eagle eye you most likely will fail to get a good focus manually. While there is special software which will help you do it, usually you have to pay for it, plus you have to pay for laptop (if you don’t own one already), plus you have to pay for accessories to connect your camera with a laptop (remote shutter to computer cable can easily cost ~$75), shortly speaking — you have to pay :-) When people are short on money, they start to think and mr. Bahtinov came up with a cool device which will get you a sharp focus in a matter of seconds.

This is how bright a bit overexposed star looks on photo with Bahtinov mask on the telescope. I took this picture on my front yard, feel free to redistribute ;-)

This is how bright, a bit overexposed star looks on photo with Bahtinov mask on the telescope. I took this picture on my front yard, feel free to redistribute ;-)

This is the idea: you make a special telescope mask and shoot a bright star with it. You will see 3 lines coming through the star. Top and bottom lines do not depend on focus, but the middle one moves up and down if you change focus. Take a picture, check where the middle beam is, if it is not in the middle — change focus a bit, shoot picture again. Rinse and repeat until you get the middle beam right in between the other two (like on the photo above). This method will probably give you the sharpest focus you can get without computer help. Mine Bahtinov mask looks like this (my wife made it for me :-)

Simple Bahtinov mask made from the burger cardboard pack. Feel free to share this picture.

Simple Bahtinov mask made from the burger cardboard pack. Feel free to share this picture. Paint it black if you want to look professional, in my case I have street lights shining right into my scope, so black paint is just breadcrumbs comparing to it :-)

Pattern depends on your telescope exact specification (clear aperture and focal length), but kind guys already created a nice Bahtinov mask calculator which will generate pattern for you. In my case slots were too thin with default setings, so I tweaked a “slot width” parameter a bit and it worked like a charm!

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2 Responses to “How to Focus Astrophotography Camera (for Free!)”

  1. Chad (HoseHead78) Says:

    Fantastic! I would love to see a before and after photo side by side.

    Thanks again for the post!

  2. Chicago Astronomer Joe Says:

    Ivan,

    I have always wanted to try this type of focusing mask for my Canon S3/scope combo.

    Yours, has encouraged me to try a version of it.

    Thanks for sharing!

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