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clouddancer
Post subject: Focus  PostPosted: 08.07.2011 01:17



Joined: 19.06.2009 Posts: 440

How does one focus in the dark? Maybe my eyes just won't adjust (I could be being impatient), but looking the eyepiece isn't terribly useful unless there's something "light" I'm trying to photograph. Is this the time to use the "live view" function on my camera? The skies were clear tonight and I had some inspiration to photograph one of the dippers (I never remember if its the big one or little one), and while I did get stars, its a bit fuzzy like its out of focus, so I'm wondering how to get things in focus in low to nonexistent light. I have heard about a so-called infinity focus, but I have no idea where to find it or how to use it. Thanks for any information.
CD
 
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Kestrana
Post subject: RE: Focus  PostPosted: 08.07.2011 01:30
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On your lens you will see markings along the focus ring that usually correspond to the distance away that you want to be in focus. Infinity focus in basic terms is when you want everything far away from you to be in focus. So if you're manually focusing, turning the ring to the infinity symbol (on our lenses that's usually all the way to the right) sets the focus to infinity.

I'm assuming that you're using a tripod and a long exposure to take your night sky pictures, because obviously the focus is going to be off if you're holding the camera during a longer exposure. It's hard for auto focus to determine what the subject is when you're taking a picture in the dark or of the night sky since so much of your subject is just black, so switching to manual focus is probably best. orionid says using Live View can be helpful too - you can zoom in on your view on specific stars to tweak the manual focus. I usually use it for macro photography where depth of field is difficult to determine through the eyepiece, but you can also use it to minimize vibrations on your tripod and keep yourself from having to stoop over to look through the eyepiece.

If you're having a hard time seeing in the dark, before you go outside, spend some time in a dimly lit room to start the adjustment period. Then when you go outside close your eyes and hold them closed for 10-15 seconds at a time over the course of a few minutes. Every time you open you eyes, you should be able to see a little bit better.

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Last edited by Kestrana on 08.07.2011 01:32; edited 1 time in total
 
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Farktographer
Post subject: RE: Focus  PostPosted: 08.07.2011 01:32



Joined: 27.02.2011 Posts: 671
Location: Manchester, UK
Ditto what Kes said - if you're shooting stars, or something fairly far, it's easy to just set to infinity. When you've got something closer, it's harder to focus in the dark - you just need to let your eyes adjust.

/Edit to say: I've taken to carrying around a laser pointer with me if I'm shooting in low-light so I have something to focus on before I click the shutter. I guess the same could be said with a flashlight - you can shine, focus, turn off the light, then take your image.
 
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Kestrana
Post subject: RE: Focus  PostPosted: 08.07.2011 01:34
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Joined: 10.09.2009 Posts: 1750

I also had a thought too - the fuzziness could be noise from your sensor. If your ISO is set high to make your shutter speed faster, the resulting noise will make your images look fuzzy. Keeping your ISO low and using a tripod to hold the camera for longer exposures will make your images clearer if that's the case. For stars you can put the camera in bulb mode and expose for minutes if there's little or no surrounding light pollution. You'll wind up with pictures of stars you can barely see with the naked eye.

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CauseISaidSo
Post subject: Re: RE: Focus  PostPosted: 08.07.2011 01:53
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Joined: 13.07.2010 Posts: 1600

      Kestrana wrote:
So if you're manually focusing, turning the ring to the infinity symbol (on our lenses that's usually all the way to the right) sets the focus to infinity.
OK, please school me if I'm wrong, but it's my understanding that turning the focus ring all the way to the end sets the focus "beyond" infinity and is there to adjust for environmental extremes, Under normal circumstances, infinity is set by aligning the infinity symbol with the focal length mark like so:



Now that's just what I remember reading somewhere, so please correct me if I'm wrong.

Also, another possible source of bluriness in stars can be if you have too long of an exposure. I've found that after as short as 30 seconds or so, they've moved enough to start to blur.
 
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clouddancer
Post subject: RE: Re: RE: Focus  PostPosted: 08.07.2011 02:00



Joined: 19.06.2009 Posts: 440

I'm either dense, or its not there, but I can't find the infinity symbol on either of my lenses. My lenses are: EFS 18-55 mm (the kit lens) and EF 75-300 mm, both Canon, and the camera was purchased September 2010.

I'm done with work soon anyway, so I'll be heading back outside again to see what I can put to use.

Edit: Also, is this a situation where I want a low f/stop or a high f/stop?
 
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CauseISaidSo
Post subject: RE: Re: RE: Focus  PostPosted: 08.07.2011 02:15
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Joined: 13.07.2010 Posts: 1600

Sorry, I just looked at those lenses on B&H and it appears they don't have a focus indicator. In that case, I'd guess that Kes is right in that you want to move the focus ring all the way to the end, but also use orionid's suggestion to zoom in and use live view to tweak the focus.

Regarding f/stop, it depends on the body you're focusing on (moon is obviously quite different than stars), but for stars you'll likely want to use the widest aperture (lowest number f/stop). That way you get the most light and minimize the possible bluriness I mentioned previously from stars moving during a long exposure. Lower f/stops have a shallower DOF, but that's not a problem when all of the subjects you're interested in are at infinity focus.
 
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ennuipoet
Post subject:   PostPosted: 08.07.2011 08:46



Joined: 14.01.2009 Posts: 1192

Also, and especially if you are shooting in camera jpeg on long exposures, there is a setting called "long exposure noise reduction" in the menu. You should turn that on prior to doing any shot over 1-2 seconds. If you are shooting RAW it doesn't matter so much, but the in camera processing of a jpeg gets noisy without LENR turned on.
 
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caradoc
Post subject: Re: RE: Re: RE: Focus  PostPosted: 08.07.2011 10:52



Joined: 15.12.2006 Posts: 871

      clouddancer wrote:
Also, is this a situation where I want a low f/stop or a high f/stop?


Most lenses are sharpest somewhere in the midrange - and for most APS-C sensors, f/11 is the limit at which you'll start seeing diffraction effects.

I usually try for f/5.6-f/8 with my f/2.8 glass (Tamron) when shooting for sharpness within DoF limits.

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clouddancer
Post subject:   PostPosted: 08.07.2011 12:51



Joined: 19.06.2009 Posts: 440

      ennuipoet wrote:
Also, and especially if you are shooting in camera jpeg on long exposures, there is a setting called "long exposure noise reduction" in the menu. You should turn that on prior to doing any shot over 1-2 seconds. If you are shooting RAW it doesn't matter so much, but the in camera processing of a jpeg gets noisy without LENR turned on.


Found it. Thanks for pointing that out! I never would have looked in the "custom functions" otherwise. If the skies are again clear tonight, I'll attempt again. The last few I got I think came out pretty good for a first try at this, way better than the ones I got earlier. There was some noise, perhaps a tiny bit of camera shake, though I'll set to a 2-second delay when I go again to minimize that bit. I will be looking into getting a remote shutter release in the future. It seems Canon has them on Amazon for around $30, so that shouldn't be too hard to get.

Thanks for the input, Kes, CISS, orionid, Farktographer, Caradoc, and ennui. I do appreciate it muchly.
 
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CauseISaidSo
Post subject:   PostPosted: 08.07.2011 12:59
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Joined: 13.07.2010 Posts: 1600

CD, you're welcome for the input, and here's some more...

While I try to buy genuine Canon stuff for most things, a shutter release is a really simple mechanical device and it doesn't matter much who makes it. For example, here's one at B&H for $9.49. I don't know if it's compatible with your specific camera, but if not there will be another one in that price range that is.

Bottom line - go cheap on the wired shutter release. Even if it ends up failing prematurely, you can buy 3 of them for the same price as the Canon.
 
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CauseISaidSo
Post subject:   PostPosted: 08.07.2011 13:07
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Joined: 13.07.2010 Posts: 1600

Oh, and I just thought of one more thing to try to minimize blur/shake - mirror lockup. You'll need to verify that the Rebel (that's the camera you have, right?) has this. If it does, it'll be another custom function.

What it does is this:
1) There's a mirror that sits between the lens and sensor and redirects the image that the lens sees to your viewfinder.
2) When you click the shutter, that mirror springs up out of the way so that the lens image now goes to the sensor to take the picture.
3) The action of the mirror springing up can cause slight camera shake.

In mirror lockup mode, you compose your shot through the viewfinder and then click the shutter button once which moves the mirror and locks it there (no picture is taken at this point). From there on, further shutter button presses take the shot without moving the mirror. You can read about it general on wikipedia and of course you'll want to review your manual for specifics for your camera.
 
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lokisbong
Post subject:   PostPosted: 08.07.2011 13:23
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Joined: 21.04.2007 Posts: 1323

If CD has the Rebel Xs I can say from experience that it does indeed have mirror lockup. been using that feature myself on star pictures.

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caradoc
Post subject:   PostPosted: 08.07.2011 15:48



Joined: 15.12.2006 Posts: 871

      CauseISaidSo wrote:
Bottom line - go cheap on the wired shutter release. Even if it ends up failing prematurely, you can buy 3 of them for the same price as the Canon.


I get mine from dealextreme.com for $5ish each - and I buy them in lots of five, since I seem to kill two or three cables every year slamming them in car doors when it's time to run away from the storm.

This looks like the right cable for Canon but I could be wrong.

Shipping is usually free, but it sometimes takes a month or two for the boat to get here.

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Last edited by caradoc on 08.07.2011 15:48; edited 1 time in total
 
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clouddancer
Post subject:   PostPosted: 08.07.2011 15:48



Joined: 19.06.2009 Posts: 440

Ok, here's the result of last night's stargazing. It's a bit fuzzy if you view full size, but better than the previous attempts in the night.



Full size here: http://i141.photobucket.com/albums/r69/clouddancer19/nightsky.jpg

Not fantastic, and definitely room for improvement, which should be easier now that I have a little direction thanks to you all. Smile
 
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