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Achieving focus with a DSLR

astrophotography
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9 replies to this topic

#1 claudioarchi

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Posted 14 September 2018 - 01:01 PM

Hello,

 

I must warn you I'm totally new to astrophoto.  I'm able to operate my 6inch Newtonian on a German Equatorial Mount (celestronAVX) as well as my DSL via BYE.  I  live in a very light polluted sky so the live view of my camera does not show any star on which I can focus. So I have to go by try and error (roughly 15 images until I'm satisfied). My DSLR has a SkyTech CLS Canon EOS Clip Filter which it's giving good results. My question is: Is there a technique on how to achieve focus if no star shows on the camera's live view? Can I try to point the telescope/camera to a brighter star, visible in the camera's live view and then move to the target that I want to shoot?

 

My equipment :

6N Celestron

Canon 450D EOS

SkyTech CLS Canon EOS Clip Filter

Stellarium

Backyard EOS

Deep Sky Stacker

 

Attached is my first image of M31 Total exposure time 22 min (lights, not enough darks, and flats) BTW this is a post-prod image in PSD in order to get more detail only

Attached Thumbnails

  • M31_20180912_BackYard.jpg

Edited by claudioarchi, 14 September 2018 - 02:22 PM.


#2 Jeff Struve

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Posted 14 September 2018 - 01:06 PM

Yes... you can focus on a brighter star then move the scope... the only caveat wiuld be if you were using an SCT w/o mirror locks where the mirror could move



#3 droe

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Posted 14 September 2018 - 01:17 PM

I have used this technic that works well for me. I use BYN, I take a test image of my target and zoom into a very close double (separated by just a few pixels). Then I focus until I see the best possible gap between the 2 stars. I can always find at least one close double in my targets image frame. This is also good so that when I am imaging, I can check the gap between the 2 stars and if the gap start to deteriorate I know it is time to refocus. I seem to be able to see changes in the gap quicker then I can see changes in star focus.

 

Hope this helps.

Attached Thumbnails

  • focus_example.jpg

Edited by droe, 14 September 2018 - 01:57 PM.


#4 astrolexi

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Posted 14 September 2018 - 02:09 PM

Using the camera's live view never worked for me (and my Canon cameras on a 80/480 refractor and a AVX).

If you use BYE you could try focusing with a Bahtinov mask.

 

With a little practice and using the serial mode in BYE finding the exact focus will be very easy.

If you can't find a bright star near your target find one that is not too far away.

 

I would recommend to insert an initial step into your workflow:

Point to your target, take some images and choose the right orientation of your target in the frame by turning the camera.

At this step it is not necessary that the focus is at 100%.

Then continue with your workflow.

 

Hope this helps a little.

 

Best wishes

Klaus



#5 Stargezzer

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Posted 14 September 2018 - 02:11 PM

After I get good polar alignment I back out and go to named stars and pick a nice bright one. I focus the scope and take a test shot then adjust if necessary. I then use a B- mask and take another test shot. I usually get the focus I want within a couple of test shots, Remove the B-mask and slew to your target, I always take a couple of test shots of my target to make sure It is centered and if I need to change the ISO or exposure time. You shouldn't have to do any more focusing the rest of the session unless you bump something. I ran almost 3 hours the other night on two targets and the focus was excellent for both



#6 Hesiod

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Posted 14 September 2018 - 03:18 PM

I use the Bahtinov mask too, but sometimes (e.g. with short lenses) just focus on the landscape and then move to the target/s.



#7 claudioarchi

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Posted 14 September 2018 - 03:35 PM

Using the camera's live view never worked for me (and my Canon cameras on a 80/480 refractor and a AVX).

If you use BYE you could try focusing with a Bahtinov mask.

 

With a little practice and using the serial mode in BYE finding the exact focus will be very easy.

If you can't find a bright star near your target find one that is not too far away.

 

I would recommend to insert an initial step into your workflow:

Point to your target, take some images and choose the right orientation of your target in the frame by turning the camera.

At this step it is not necessary that the focus is at 100%.

Then continue with your workflow.

 

Hope this helps a little.

 

Best wishes

Klaus

Hi, Klaus Thank you for your answer. I'm not familiar with the serial mode un BYE. Can you explain what that is?

 

Thank you



#8 claudioarchi

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Posted 14 September 2018 - 03:36 PM

WOW thank you guys for the support I really appreciate. I'll try it and see if that works for me

 

cheers



#9 astrolexi

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Posted 14 September 2018 - 04:31 PM

Sorry for causing confusion. It's my broken English...

 

Just use the loop function at the lower right in BYE.

Choose an appropriate pause between the exposures so that you can adjust

the focus.

 

Best wishes

Klaus


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#10 Ken Sturrock

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Posted 14 September 2018 - 07:57 PM

I must warn you I'm totally new to astrophoto. 

 

No problem. That’s why there are fora out there for talking about imaging. 

 

Moving to the DSLR Forum.




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