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FORUMS Photography Talk by Genre Astronomy & Celestial Talk 
Thread started 14 Feb 2018 (Wednesday) 03:01
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Focusing!

 
Jocce
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Feb 14, 2018 03:01 |  #1

So, I'm new to the Astoscape Photography.

One of the hard things is to get the focus correctly.

Right now I am using live-view and 10x magnification and trying to get the focus correct.
But this is REALLY hard when it is pitch black outside and just looking at a small single star in the live view.


So, any more tips about this?


(Using a Mark IV and Samyang 14mm/2,8)


/Jocce



Feel free to correct my English. I'm from Sweden ;)

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DesolateMirror
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Feb 14, 2018 05:47 |  #2

Some people focus the lens during the day and mark it with tape or just tape it in position but changes in temperature can throw that out a bit. Some focus on a bright object in the distance.

Considering the hyperfocul distance for your setup should be about 7.62 ft, focusing anywhere past that (but not past infinity, which these lenses can do) should get the stars in focus, but the lenses aren't always made with the best quality control and the focus ring can be a bit off with the measurements.

This blog recommends 10ft: http://intothenightpho​to.blogspot.com.au …ng-rokinon-14mm-lens.html (external link)

I've never been too fussed with foreground elements being in focus so I use the liveview with the lcd brightness turned up and zoomed in all the way, you really have to point it at a big bright star or bright cluster otherwise it can be a bit painful.




  
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Left ­ Handed ­ Brisket
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Post edited 3 months ago by Left Handed Brisket. (2 edits in all)
     
Feb 14, 2018 06:15 |  #3

When trying to focus on stars, rather than slowly trying to dial it in to perfect focus, I usually like to rock back and forth between front focus and back focus. This lets me get a feel for not just where my hand will land, but what sharp focus will look like on the screen.

As said, DOF with a wide lens will be enough that I wouldn't worry about it too much. I usually don't use hyperfocal distance though unless there are foreground elements within 20 feet or so from the lens. When the main subject is the stars, it is best to push focus as close to them as possible.


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gjl711
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Feb 14, 2018 07:10 |  #4

Run tethered to a laptop running EOS Utility. It's much easier to see.


Not sure why, but call me JJ.
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Jocce
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Feb 14, 2018 07:50 |  #5

gjl711 wrote in post #18563477 (external link)
Run tethered to a laptop running EOS Utility. It's much easier to see.

But a lot more work to bring out in to the woods...


/Jocce



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TCampbell
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Mar 01, 2018 14:07 |  #6

Pick up a focusing mask... like the SharpStar2 by Lonely Speck.

It makes it much easier to focus. I will say this works better with longer focal lengths. The shorter the focal length, the dimmer the stars will appear to be and the more difficult it is to focus. To deal with that... just take a longer test exposure.

But the idea behind the focusing mask is that it causes the stars to throw diffraction spikes... but it's a pattern of three spikes. Two spikes create an "X" shape and a third longer spike is a vertical "|". If the lens is focused, the spikes all converge at a common center point.




  
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Celestron
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Mar 01, 2018 16:53 |  #7

Jocce wrote in post #18563398 (external link)
So, I'm new to the Astoscape Photography.

One of the hard things is to get the focus correctly.

Right now I am using live-view and 10x magnification and trying to get the focus correct.
But this is REALLY hard when it is pitch black outside and just looking at a small single star in the live view.


So, any more tips about this?


(Using a Mark IV and Samyang 14mm/2,8)


/Jocce

Very few if any focus the way I do . I have a hard time focusing the way most here are suggested . First I tripod my camera or place on my scope camera mount . If using a zoom lens I zoom in all the way . I put the lens on auto-focus and set my focus area to center focus so that direct center red light is the only focus point . Make sure my camera is in manual mode and set to bulb . I use a remote switch while shooting so I can expose long as I want .

If the moon is up I point my camera at the moon and do a quick focus on it usually close to the edge of the moon . Snaps to focus quick using the shutter button and watching for a steady light on the green focus light inside the viewer . When focus sets and have a steady light I let go of the shutter button and carefully move the lens auto switch to manual focus . Just never touch the focus ring or bump camera hard .

I have focused this way on the moon and bright stars that are easily seen like example Rigel in the Orion constellation or Sirius in Canis Major constellation just below Orion . Those show up easily in a zoomed in lens . If i'm shooting WF say with a 70-200mm lens i'll zoom in , focus , and zoom back out . If your careful not to touch the focus ring and don't bump the camera I usually get good images after this focusing .

I tried live view . Didn't work for me but many others do and swear by it . But what ever works best for you , that's the way you should do it . Clear Skies !




  
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legoman_iac
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Apr 29, 2018 06:26 as a reply to  @ Celestron's post |  #8

One thing to also try, if you don't have many bright stars, is when using live view, is to crank the ISO all the way up (just while you're focusing). It took me a while before I realised my 50D's live view shows more light this way. As you get into focus you might see fainter stars, which help let you know you're close.

- Daniel S


2x 50d: with 17-85mm f4-5.6, 100mm Macro USM, 50mm f1.8, 2x Sigma 30mm f1.4, 55-250mm (kit lens), Canon 100-400mm L, Tamron 200-400mm f5.6, Samyang 8mm. 480mm refactor with HEQ5. Home made beamsplitter stereo rig.

  
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