Night sky photo focus suggestions

[chuck]

<p>When I attempted to take photos of the night sky, the scene is too dark for either phase detection AF or for LV to detect anything. Is there any other clever way to obtain sharp focus, except through focusing by distance scale and a large dose of trial and error?<br>

Nikon AF lenses do not seem to focus to infinity right where the focus scale says infinity.</p>

<p> </p>

[SCL]

<p>Doesn't need to be trial and error. Before total darkness just focus on the moon or a bright planet or star, or an object a mile or so away. As a rule of thumb, optical infinity is described as somewhere between 2-5000x the focal length of the lens. In practice, the DOF takes up the slack. The only problem I've encountered in using this method is where there is significant thermal change from the time of initial setting until time of exposure, in which case you have to punt with your eyes fully adjusted to darkness (20 minutes or more) use manual focusing and your viewfinder.</p>

[rodeo_joe1]

<p>+1 to Stephen's suggestion of focusing on the moon. I'll add that autofocus is rubbish for astro-photography, so forget AF. Manual focusing and Live View are your friends here. With AF disengaged, zoom in to maximum magnification in LV and you can focus using a bright star or planet to minimise its blur circle. With a wide-angle lens your only option is probably the moon though. Once focus is optimised, leave the focusing ring severely alone. Taping it in place is probably a good idea to prevent it being accidently nudged out of position.</p>

<p>You could then make a mental note (or take a picture) of where true infinity is on the lens's focus scale - if it has one! A better solution might be to buy an old MF only Ai-S Nikkor that has a hard infinity stop. Used MF lenses are cheap enough. And some of the old IF-ED Nikkor telephoto lenses have a locking ring on their focus.</p>

[ilkka_nissila]

<p>I focus on the stars by first turning the camera to maximum ISO and setting the lens initially wide open at infinity focus. Then I look at live view and scan the field of view for stars. Once I find one I focus manually until I've minimized the blur. Then I make the exposures.</p>

[Keith S in Arizona USA]

<p>Stephen, Rodeo Joe, Ilkka, all terrific inputs.</p>

<p>Many lenses will focus beyond infinity. One older Canon zoom I have does this, they claim, to compensate for focus changes (lens length expansion / contraction) when used in very cold to very hot temperatures.</p>

<p>As stated, MANUAL focus is the only way to go.</p>

<p>My eyes are not what they used to be. To that end, here is what I have done to solve my own nighttime astro-photography focus issues:</p>

<p>I apply two pieces of masking tape on the focus ring and the un-moving barrel. Then, with my camera in a MANUAL focus mode, I focus in daylight on an object at infinity and mark across the two tape pieces to set the infinity focus.</p>

<p>At night, I use a penlight to re-align the marks if necessary and I am good to go. Any slight focus error has never shown up in my photos, so I would not worry at all about focus error unless you are in EXTREME hot or cold with a susceptible lens. Unless you are using a very long lens to photo moon craters or such, there should be no focus error issues.</p>

[Mary Doo]

<p>Just a suggestion: If there is something in the foreground that can make a composition more interesting: e.g., a barn, a tree,... lit it up for a while, or use a flash light to "paint" it into the image. If it's a peak that artificial light cannot reach, make a longer exposure for it to combine with your night sky. Brighten the peak in post-processing, etc.</p>

[chuck]

Hi, thanks. Prefocus is a good idea. The night sky is really too dark for manual focusing as well.

 

Mary, yes, merging two shots with different exposures for foreground and background sky is great idea. In some recent

attempts at shooting the sky in Yosemite I found exposing properly for the foreground overexposed the sky, and also

cause star trails. Merging two shots would solve the problem,.

[confindelmundo]

<p>I have a Nikon system. I had problems with AI-S lenses at night, very difficult to find focus except with 85mm 1.4. I also bought a Samyang 14 mm 2.8 Manual, never had any problem using exact inifinity for astrophotography (night shots), all shots sharp focus at infinity.</p>

[rodeo_joe1]

<p>Daniel, are you saying that your Ai-S lenses had incorrect infinity stops? I've always found that Nikon's old primes were bang-on with their infinity focus. Unless they were very well used and worn. If you're talking about the IF-ED telephotos that focus beyond infinity, they have a lockable secondary ring that can be set to "click" the focus on a preset point. The locking ring only needs setting in daylight to give a hard infinity stop for use after dark.</p>