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Lunar Focusing Issue

moon imaging astrophotography
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#1 Ibuprofen200mg

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Posted 01 October 2020 - 09:14 AM

I ran into a surprising issue last night an was hoping someone here has some insight. Here's a rundown of the gear I was using:

 

Nikon D3100

AT72ED + ATR8 0.8x/FF

3D printed Bahtinov mask

 

In the past when shooting the moon with my old scope (Orion 100mm F6) I would just zoom in via live view on a heavily cratered region and adjust the fine focus until sharp and start shooting. Last night using the setup detailed above however, I was not able to use live view to focus as the image on screen was fully blown out (assuming this could be that faster f ratio of the new setup?). To my knowledge there is no way to adjust the live view exposure on the D3100. So instead I used a Bahtinov mask to focus on Altair, panned over to the moon, and starting clicking away. Since I used a mask I didn't even bother to check the focus of the images before loading them into pipp and As!3, but I was definitely surprised when the stacked image (and individual frames) were a fuzzy blobs. I checked all through all the individual frames and surely enough they are all out of focus. I am sure my focus did slip during imaging as focuser was securely locked down. Images attached. Any ideas would be appreciated!

 

Bahtinov mask focus check

Altair.JPG

Single Frame 

Mun.JPG

Stacked and edited 

Mun_1.JPG

 

 



#2 happylimpet

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Posted 01 October 2020 - 10:01 AM

Things move, expand, contract, slip, bend.

 

I would never focus on anything other than the target itself, unless there was absolutely no other option.



#3 Peregrinatum

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Posted 01 October 2020 - 04:46 PM

I use a similar method, I slew to a nearby starfield and do an autofocus run, do this about every 30' or so, then slew back to the moon and continue

 

pLTl6gLl.jpg



#4 Kiwi Paul

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Posted 01 October 2020 - 05:12 PM

I favour focusing on the target too. Why not do your focus with the mask and then visually check (onscreen) that it looks ok. I would think if it was way off as you describe you should be able to spot that. Well worth that little extra discipline than waste an hour or two imaging?
Cheers Paul


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