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09-12-2017, 10:43 AM   #1
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Focus issue

I was in Manitoba last week and was presented a show of the Northern Lights. I mounted my trusty K3ii on a tripod and tried to focus my 18-135 lens. I have been advised that the trick is to focus on infinity and back off a tad, but there is no infinity mark or stop on the lens so focusing was just shear luck, not something I'm overburdened with! Any advise? A different lens would be better, but not practical at the time.

Another time I tried to find the milky way, but a full moon ruled out longer exposures, plus, how do you know where to look?

Any help greatly appreciated.

Tuggie76

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09-12-2017, 10:54 AM   #2
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Sometimes chimping is the way to go.

Google's skymap app will help you find what's up there.

I'm sure others will chime in with more sophisticated advices.
09-12-2017, 11:16 AM   #3
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Trial an error is the way to go, unless you can make out the stars in live view magnification. Also, if the moon is up you can "cheat" by focusing on it first.

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09-12-2017, 11:23 AM   #4
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Ranked in order of best to worst:

1. Focus on the moon or a bright star using live view and electronic zoom to magnify the distant object. (Spot meter mode can help the live view of the moon not be blown-out)

2. Focus on distant city lights, radio towers, buildings, etc. using live view and then electronic zoom to magnify the distant object.

3. Focus at infinity on some high-contrast horizon object during the day time and tape-down the lens or carefully mark/memorize the location.

(Note: older primes do tend to have reasonably reliable infinity marks although they often aren't quite good enough if you use the lens wide open for astrophotography. Zooms tend to be really bad about the location of the infinity mark and infinity can vary with the zoom setting, too.)

09-12-2017, 01:46 PM   #5
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I have been using the 18-135 with a K5 and tried to focus with live view on bright stars and trial and error, but it was an exercise in frustration. I could not reliably find the stars on live view and on zooming in the stars and noise worked together to cause even more confusion. I have not tried the ' focus during daylight on infinity and taping the lens ' method, but it robs you of using the lens during the best part of the day and the throw is so short on the focusing ring that it would go out of of whack easily. I settled on using an manual focus 50mm F2 Pentax lens on infinity stop and it worked fine, but without the wide angle of the 18mm. If your really serious and need the wide angle ( don't we all?), I would go for a manual focus like the Samyang 16 or 14 mm, but it seems that you need to calibrate the focusing as well

Good luck
09-12-2017, 03:37 PM   #6
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I think you already know the answer...that really isn't the lens for the job. It's really not designed for manual focusing at all, let alone in these circumstances.
09-12-2017, 04:35 PM   #7
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I don't have much to share on the night sky shooting, but I do some city landscape at night and to get infinity focus at night, I would use manual focus on live view and do 100% view at the brighter part of the house see on the lower right hand. Make sure the white wall is in focus that should give me the infinity focus.
K3II (I have K3) LCD is pretty good. the live view at 100% should be able to help you nail the focus at night even at darker part of the hous in your image.
Even "if" the house is not in the infinity distance on your lens, it would be interesting to have a forground object in focus as a point of interest in the image, IMO.

Last edited by pakinjapan; 09-12-2017 at 04:59 PM.
09-12-2017, 09:19 PM   #8
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Tuggie, I find the easiest way is to use manual focus, go to Live View, hit the magnify button, and search for a bright star anywhere in the sky. Turn the focus dial until it is *minimum* size.

09-12-2017, 10:09 PM   #9
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Similar to what others have said, find the brightest star in the sky, then zoom-in with liveview and manually focus until the star is as small as possible. Use a distant water tower or radio antenna if you can't find a bright enough star.

Resort to trial and error when you can't find any star or ground feature bright enough for live view. Focus at maximum distance (beyond infinity for some lenses), take a test photo and review it, focus tiny bit closer, take another photo and review it, repeat until the stars look sharp.
09-13-2017, 10:54 AM   #10
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Thanks for all the advise, I would have changed lenses, but it just wasn't possible at the time. On a different night I had my 10-17 on and that worked fine by setting to infinity and backing off a bit, but the moon was too bright to get long enough exposures.

Tuggie76
09-13-2017, 03:45 PM   #11
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QuoteOriginally posted by tuggie76 Quote
the moon was too bright to get long enough exposures.
Just an idea on this, since you already on a tripod, It might be a good idea to do image stacks. One for the dark sky and another one for the moon. then put it together in post process.
2 Days Ago   #12
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QuoteOriginally posted by Quartermaster James Quote
Sometimes chimping is the way to go.

Google's skymap app will help you find what's up there.

I'm sure others will chime in with more sophisticated advices.
There's an app called Google Skymap? I cannot find it - at least not for iPhone.
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QuoteOriginally posted by dula.george Quote
There's an app called Google Skymap? I cannot find it - at least not for iPhone.
No, it's an android app...hell would freeze before Apple allowed a competitor into their lair.
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