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Thread: How to achieve proper focus of stars at night?

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    How to achieve proper focus of stars at night?

    I would like to take some photos of stars at night. I have found the location. No problem. I have to keep an eye on the alligators while I am doing this because the location is in the Everglades. No problem. The only problem I am facing is that I have hard time focusing at the stars because the viewfinder is black. (It is 1:00am at night after all.... )

    I manually focus at infinity and the stars are out of focus.

    I have tried to use the screen in video mode after increasing ISO. No luck. Even the screen on the back of the camera is dark so I am not be able to see the stars for proper focusing.

    My question: How do you focus in total darkness? Did I miss something?

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    Re: How to achieve proper focus of stars at night?

    Live view - zoom in on a star in live view and adjust focus manually so that the star is as sharp as possible. It depends upon the camera's live view as to how easy this is but this is how most of us do it these days.

    You can't rely on infinity focus on the lens but it's a good starting point.
    Remember: adventure before dementia!

    As Oscar Wilde said, "my tastes are simple, I only like the best"

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    Exclamation Re: How to achieve proper focus of stars at night?

    Quote Originally Posted by GrahamWelland View Post
    You can't rely on infinity focus on the lens but it's a good starting point.
    I was not aware that 'infinity' was a variable distance.

    Any lens that does not properly focus collimated light when set at the infinity stop belongs in the trash can.

    Set your lens at the infinity stop. End of story.

    - Leigh

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    Re: How to achieve proper focus of stars at night?

    Leigh

    Good luck with that. I can tell you definitively that if you rely on the infinity mark, assuming that you hit it at night, you are not guaranteed the sharpest stars. Some lenses, especially AF lenses, will focus past infinity to the end stop to handle thermal expansion etc, not to mention that even if you do select exact infinity on the lens that your sensor is absolutely in the right place.

    Theory is one thing, practice is another!
    Last edited by GrahamWelland; 8th September 2014 at 04:47.
    Remember: adventure before dementia!

    As Oscar Wilde said, "my tastes are simple, I only like the best"
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    Re: How to achieve proper focus of stars at night?

    Quote Originally Posted by GrahamWelland View Post
    Theory is one thing, practice is another!
    And the laws of physics are yet another.

    The i'net is full of statements about how one or another physical law does not apply in a particular situation.

    Yes, a few lenses will focus past the mechanical infinity mark, which should be properly positioned for "normal" temperatures.
    These are commonly long focal-length lenses where ambient temperature can cause the mechanism to expand or contract.

    If the lens in question is one of these, then additional measures would be appropriate if and only if the ambient temperature is extreme.

    If there is a concern, set the focus ring slightly short of infinity.

    Depth of Field at infinity focus is rather large. If the true focus is off by a few parsecs (impossible), it won't matter.

    - Leigh

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    Re: How to achieve proper focus of stars at night?

    Leigh

    I shoot a lot of night exposures using many systems and what you are talking about is all fine in theory and I repeat, not practice. If you want sharp stars then you need to focus for them. Period.
    Remember: adventure before dementia!

    As Oscar Wilde said, "my tastes are simple, I only like the best"

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    Re: How to achieve proper focus of stars at night?

    Quote Originally Posted by GrahamWelland View Post
    If you want sharp stars then you need to focus for them. Period.
    Last time I checked, the distance to the nearest star and all further ones defined infinity.

    If your lens doesn't focus there, it's defective.

    - Leigh

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    Re: How to achieve proper focus of stars at night?

    Leigh,

    I can only surmise that you've never actually shot star fields at night using real camera equipment.
    Remember: adventure before dementia!

    As Oscar Wilde said, "my tastes are simple, I only like the best"

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    Re: How to achieve proper focus of stars at night?

    i have had several lenses that, when in actual focus at an "infinitely" distant object were either not at the rotation stop or not at the inf marker. lenses from
    schneider, Rodenstock and most recently, the Canon 17mm TSE (this was a surprise).

    it isn't physics we are talking about, it is a mark on the lens. read about shimming the alpa cameras, for example.
    http://www.luminous-landscape.com/re...c_review.shtml
    a lens that is set "beyond infinity", the buzz lightyear setting, will have everything out of focus, no depth of field compensation will help, only an acceptance of relative out of focus/sharpness. it is surprising how the image goes to hell overall once you get the lens too close to the sensor
    Last edited by jlm; 8th September 2014 at 03:34.

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    Re: How to achieve proper focus of stars at night?

    Quote Originally Posted by GrahamWelland View Post
    I can only surmise that you've never actually shot star fields at night using real camera equipment.
    Surmise what you wish.

    My wife is an astronomer who has traveled worldwide shooting such subjects.

    I'm a professional camera repair tech who knows how to assess lens performance.
    And I have the proper equipment to make such assessment.

    - Leigh

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    Re: How to achieve proper focus of stars at night?

    Well, like I said, back in the real world ...
    Remember: adventure before dementia!

    As Oscar Wilde said, "my tastes are simple, I only like the best"

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    Re: How to achieve proper focus of stars at night?

    And, in addition to almost all newer lenses focusing beyond infinity, especially the autofocus variety, there's also curvature of field that so many lenses have in abundance, that will let you focus accurately only in one part of the frame or another but never on the entire frame, infinity or not.

    Graham is correct here in paraphrasing Yogi Berra.

    Haring - What specific lenses are you using? Live View focusing is the best and most accurate way to go, using something like a Hoodman loupe on your LCD.

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    Re: How to achieve proper focus of stars at night?

    Haring, I'm not sure I understand all the thrash in these comments.

    Anyway it's simple, prefocus your lens on infinity sometime during the day. Tape the lens.

    Alternatively if you're OK with it then mark the lens when focused so that you can realign it at any time (with a flashlight) so that you don't need to keep tape on it.

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    Re: How to achieve proper focus of stars at night?

    I believe that part of the problem with the animosity and misunderstanding in this thread is due to the fact that "astrophotography" or "sharp stars" is a rather broad subject and the degree of difficulty is greatly dependent upon the focal length of the lens (or telescope). Hyperfocal technique or merely focusing at a terrestial object at "infinity" might work for wide angle images of the Milky Way, but this becomes more challenging and critical as focal length is added in the equation. Achieving sharp stars is not "simple" in such a case, which is why the OP posted the question. Even focus peaking is not a perfect solution, even if that particular feature is available on the camera you are using. I would believe those espousing their "simple" techniques a little more if they also provided example images that they had produced using their techniques.

    The real answer is to use a Bahtinov Mask. These are fairly easily made:
    http://www.getdpi.com/forum/new-or-i...ars-night.html

    These are made to fit over the lens (or telescope) to which your camera is attached.

    A secondary answer (aside from achieving perfect focus) is to use stacking software that has been fed multiple images of the same star field. Obviously, the better the focus of each subexposure the better the stacked result will be, but stacking can help to sharpen the end result of a set of less-than-sharp subexposures, also. Examples of such software are DeepSkyStacker and Registax.
    Last edited by pixelsmithy; 4th January 2016 at 20:17.
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    Re: How to achieve proper focus of stars at night?

    http://www.getdpi.com/gallery/files/..._2k_framed.jpg

    Well this was shot using A7RII with 16-35 @ f/4 using the live view focus technique. I certainly wouldn't rely on focus peaking because it doesn't really work well at identifying pin point focus and true infinity. This isn't an ideal shot because even at 15s and 42mp at 16mm I'm seeing trailing but at least the short trails are sharp.

    Agreed that if the full milky way was the real objective then a star tracker and/or multiple stack images would be better but this was a single shot.
    Remember: adventure before dementia!

    As Oscar Wilde said, "my tastes are simple, I only like the best"
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    Re: How to achieve proper focus of stars at night?

    if anyone has used this method on a camera I would like to hear your comments

    http://www.astropix.com/HTML/I_ASTRO...METHODS.HTM#HM

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