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#AskPS: How can I find focus with a DSLR and a Dobsonian?

Cory Schmitz

E asked:

Way back in the days of the Virtual Star Party, you were taking Astrophotographs with a DSLR and a Dob on an EQ platform. Question, did you have issues getting focus? Did you use a Barlow to move the focus point?

Funny you should ask!

Yes, I had issues finding focus because DOBs aren’t generally set up for prime focus AP, and often require the sensor to be closer than the focuser allows (not enough “in-focus” distance).

I figured out that using a coma corrector for newts, (like this), the problem is solved with only 0.1x mag. It gave me about 10mm or a little more “out-focus” distance that was perfect for my old Zhumell 10″ Dob.

For planetary use, I used that same Dob and EQ platform, but only with either 1 or 2 Barlows, excluding the coma corrector. There was plenty of focus distance with that setup.

Cheers,
Cory

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About the author

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Cory Schmitz

Co-founder of PhotographingSpace.com, co-owner of several telescopes and mounts, too many cameras, and not enough hard drives.

An avid astrophotographer for timelapse, deep-space imaging, lunar, planetary, and star trail imagery, he is an all-around jack-of-most-trades for night-sky photography.

He is also an internationally published and commissioned astrophotographer, where his photos have been used in multiple online and print publications.

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