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

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.


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About the author

Cory Schmitz

Co-founder of PhotographingSpace.com, co-owner of several telescopes and mounts, too many cameras, and not enough hard drives, Cory is an American expat living in South Africa with his wife, Tanja Schmitz.

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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