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Focus issues with ASI290mm mini as main scope camera for WO Z73

beginner astrophotography
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#1 ngprime

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Posted 02 August 2020 - 02:54 AM

Hello all! Been loving the forums here for a couple weeks now as I bootstrap an understanding of the hobby.

This last week I finally got the components for my first imaging rig together: an HEQ5 mount and William Optics ZenithStar 73mm telescope.

For a camera I made the somewhat unusual choice of selecting the ZWO ASI290mm mini, with the idea being that I could learn the ropes on that cheaper camera, and then use it for a guide scope once I’m ready to upgrade.

So far I’m off to a rocky start and have been unable to find the focus point the last two nights. Tonight I spent the whole session pointed at various terrestrial stuff as a sanity check and still couldn’t pull it off.

Is this just an innately poor pairing of telescope and camera or is my luck bad? I tried the full range of the focus knob repeatedly and added the eyepiece extender that came with the camera as well. Maybe I just need more extension?

Any help that anyone more senior that me (read: anyone on here haha) can offer would be much appreciated. Thanks!

Edited by ngprime, 02 August 2020 - 02:55 AM.


#2 Stelios

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Posted 02 August 2020 - 03:34 AM

How short were your daytime exposures? They should only be a few ms.

 

It’s also possible you need an extension tube. If so, you should see focus improving as you back off out of the focuser (slowly) and hold the camera “in the air” behind the scope.

 

Or, if you by some chance were using a diagonal, you may need to remove it. 

 

Basically you need to determine in which direction focus improves.
 



#3 Tapio

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Posted 02 August 2020 - 03:44 AM

With a refractor and camera you need either diagonal or extension.

#4 OldManSky

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Posted 02 August 2020 - 06:51 PM

Tapio has it right -- you're going to need an extension.  Without the field flattener designed for the ZS73, its focus point is way, way, WAY back -- in order to focus an eyepiece with a diagonal.  You'll need to add at least 40mm or so of extension (or use a diagonal) to get it in focus.


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#5 ngprime

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Posted 02 August 2020 - 10:17 PM

Thanks for the advice, all!

Managed to get some tree leaves in focus earlier today by holding the camera in the air behind my maximum extension. So that’s the issue—got two extenders on the way now so hopefully those’ll do the trick.
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