Problem image sample.

[hefyjefy]

Hi all,

Just getting started here, I have an Orion EDT80 refractor on an Orion SkyView Pro mount and a Canon SL1 camera with an Orion off-axis guider, although I am not using the Auto Guide feature - yet.

I am fairly happy with the results so far but close inspection of my last effort shows an artifact that I can't explain.  (See attached) 

Bright stars are OK, nice discs, but faint stars appear to be circles with a "hole" - what sort of tracking/focus problem might cause this?

I am getting quite good numbers for focus using BYE (< 4.0) - I have not yet figured out drift alignment, still relying on careful use of the polar scope, but this doesn't look like an alignment problem.

The image is from a single 10 sec exposure at iso 1600.

Any ideas on where to start looking are very welcome.

Many thanks

Geoff

[Leveye]

Looks to me like a focus issue. If your live view has a magnify feature use that to assist in tighter focusing.

[Aeseir]

Focus. Get yourself a bahtinov mask or make one through the generator (just search) and you will be sweet. Had same problem, and your bright star there will shrink.

[Knight of Clear Skies]

I agree it's a focus problem. When focussing you want to make the stars as small and sharp as possible.

[hefyjefy]

OK guys thanks - I do have x5 option in live view, I will give it another shot (when the clouds permit!)

[jtlandreneau]

Get a Bahtinov mask for sure - inexpensive if you don't want to make one yourself, very easy to use

[hefyjefy]

OK, much better!  It was the focus I think - I have noticed that the focus also changes over time (temperature?) - 'nother image attached.  And another question: 

I noticed that the two components of Albireo look very slightly hexagonal, not circular, is this caused by the camera iris?  I am using BYE and a Canon SL1

Geoff 

[jtlandreneau]

Cool Alberio! I haven't tried taking a picture of that one yet...

The rule of Thumb I read was check your focus every hour, though I don't know how practical that is. I suppose its all dependent on how perfect you want your pictures to be. Temperature will definitely affect it, I've noticed too that large movement will also affect it - I default now to focusing on the nearest bright star next to my target.

As for the hex, could be a bunch of things - I don't really see it in your picture though

[hefyjefy]

OK - yes, could be my imagination, if you look at stars for a long time you start seeing things!

G

[MartinB]

Looking at your out of focus stars I noticed that there also seemed to be some obstruction to your light path ? Your oag.

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