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09-26-2016, 03:49 AM   #1
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What is wrong with my night sky photos?

Hi,

I got the Pentax K1 and I was using the Rokinon 14mm wide angle lens with the astrotracer function. ISO was set at 400. But even with lower ISOs I still get this weird green thing in the pictures and I don't know what they are. I even tried the 31mm limited and same thing. Even at low ISOs.

How can I fix this problem please? I really want to take night photos. I've attached a photo showing what I mean. This one was at ISO 400 with a 2:50minute exposure time using astrotracer and the 14mm wide angle lens. I don't get these problems shooting anything else such as people, landscape etc. and my sensor is clean.

Thank you.

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09-26-2016, 03:57 AM   #2
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That is a serious case of lens flare caused by the very strong light source at the bottom left of the frame.

The following article should give you a good understanding of lens flare and how to avoid it:

Understanding Camera Lens Flare
09-26-2016, 04:28 AM   #3
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Even if you can manage to avoid lens flare completely - i would suggest going somewhere better suited for night sky photos.
Under a really dark sky without light sources shining into the lens a K100 with kit lens and without astrotracer will deliver better results than a K1 under the conditions visible in your sample image.
09-26-2016, 04:34 AM   #4
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Green thing? I think the auto focus assist is green. Maybe its on or flashing during the shot. Its hard to see from behind the camera. Next time check whats happening in front of the camera. good luck!

09-26-2016, 04:44 AM   #5
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yup, that's flare.. could even be fog on the lens too to get that hazy look (though I see you are in Antigua, so atmospheric conditions might induce fog at this time of year).

Some Pentax lenses have a reputation for green flare resulting from light reflecting off the sensor and hitting the rear element. (DA 21 specifically on APS-C sensors) - you could be suffering the same with the 14mm Rok. I suggest finding a beach you can point out into the night sky with no lights around to get used to the process - comfortable with your equipment. It will make trouble shooting these things easier.
09-26-2016, 05:44 AM   #6
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Mercury vapour lights produce light with a greenish tint, the lights at bottom could be mercury vapour.
09-26-2016, 05:46 AM   #7
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Thank you all for your advice. I will try it out. I took these pics on my roof. At night its pretty dark (not many street lights) so i thought it wouldn't be a problem. Also living in the tropics I don't think it would fog up or something like that. I might try the beach thing and see. Thanks again.
09-26-2016, 07:45 AM   #8
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It is some flare. It's like on a dark night someone shining a bright flashlight in your eyes - it washes out the rest of the view. You need to find someplace a bit darker, or at least protected from any direct lighting. There is a dark sky finder map You want to get as dark as you can. Also, starting out at about a minute at iso 3200 is a good spot.



09-26-2016, 09:18 AM   #9
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QuoteOriginally posted by ydaf Quote
I took these pics on my roof. At night its pretty dark (not many street lights) so i thought it wouldn't be a problem.
When you manage to control the flare and the direct light sources the problem will be light pollution from every light on the whole island that you can see in the general brightness of the sky and the whitish clouds.
Still it doesnt seem too bad, with some post processing (like pulling down the shadows) you still can get decent results.

Easy test for astrophotography: stretch your hand out towards the night sky.
If you can make out its shape easily its too light polluted for good results.
If you can see your hand directly better focus on daytime photography
09-26-2016, 01:28 PM   #10
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FWIW, the Rokinon 14mm and other branded variants, are notoriously prone to flare. If you look at a shot of a test grid shot with this lens you'll find it has a borderline fish eye characteristic at the edge of the frame with incredibly bad barrel distortion of around 5%. Although I own one, it's not a lens I choose to use for night sky work when there is nearby light pollution.
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