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The struggle with M 101


Eastman

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It took me a few weeks to see M101 towards the end of last year.

I used an 8" dobsonian.

 The trick is to use an eyepiece that results in a large exit pupil.

I used a 32mm at F6, 37.5x, which gave me a 5.33mm exit pupil. 

Viewing at the zenith made M101 a direct vision object, albeit a faint one.

At exit pupils of 4mm or below, M101 was not visible to me.

I'm in a border zone Orange to yellow (Bortle 5).

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Take a look also for the companion galaxies for M101, there are several, notably NGC 5474 and NGC 5473, which can sometimes be mistaken for the Pinwheel. Quite reasonable when at zenith and if dark adapted (transparency is good etc). Exit pupil probably will play a role, largish as mentioned, but not too large. M101 is of course of low surface brightness, my own observations have been with an exit pupil of around 4.5mm, in approx 21.4 mag skies.  

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