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06-27-2019, 12:21 AM   #1
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Astro - Pentax 14mm 2.8 or Sigma 17-50mm 2.8?

Hi all!

I'm looking at going to take some pictures of the Milky Way this weekend since the moon will be mostly dark. I'm looking at renting the Pentax 14mm 2.8 from a local store for the weekend, but I'm wondering if it would be worth my $40. I have to imagine that a prime (and a wider one at that) would be better overall for astrophotography, but I read a few reviews saying the lens didn't meat their expectations.

What do you all think? Would it be worth my time?

Thanks in advance!

06-27-2019, 05:55 AM - 1 Like   #2
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Have you considered doing a stitched panorama? Over in the astro group SunValley posted a really nice one a little while back. This may be a better option to get the wide view you want.
06-27-2019, 07:12 AM - 1 Like   #3
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I've used the Pentax 14mm 2.8 for astro. It works quite well, other than some comma nearer to the edges of the frame.
You'd get better images with one of the Rokinon/Samyang wide angles. Or, the new Pentax 11-18.
MossyRocks suggested a stitched image, but I think that you would ideally need an astro tracer to do that.
06-27-2019, 07:31 AM - 1 Like   #4
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For Milky Way images aperture is the the important factor. Faster is better. Since both are f2.8 it's not going to matter and the difference between 14mm and 17mm is minor so it's a toss-up. My personal preference for night work is a prime. If you already have a 17-50 2.8 I'd use that one. If you have to rent either lens I'd use the 14mm.

06-27-2019, 08:08 AM - 1 Like   #5
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QuoteOriginally posted by gifthorse Quote
For Milky Way images aperture is the the important factor. Faster is better. Since both are f2.8 it's not going to matter and the difference between 14mm and 17mm is minor so it's a toss-up. My personal preference for night work is a prime. If you already have a 17-50 2.8 I'd use that one. If you have to rent either lens I'd use the 14mm.
I bought the Rokinon 14 2.8 for astro work after it was highly rated on an astro-photography site. I haven't been able to try it out yet.
06-27-2019, 10:17 AM   #6
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So I actually just managed to snag an SMC DA 15mm F4 ED AL Limited for $50 (the guy was originally selling it for $25, I don't think he knows what he was selling!) so I will likely just bring that and my 17-50mm 2.8 and try them both out this weekend. Thanks for the feedback!
06-27-2019, 12:21 PM - 1 Like   #7
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QuoteOriginally posted by Qman Quote
MossyRocks suggested a stitched image, but I think that you would ideally need an astro tracer to do that.
Not really. Astrotracer would give you longer trail free exposure but one could get some nice pinpoint stars going up to 10s with the 17-50mm at 17mm or 15s using the 14mm. With astrotracer with either of those lenses one could probably go out to 2 or 3 minutes without much issue and get some really nice stars. If you had foreground you wanted that would get blurred using astrotracer. The solution to that is then to shoot that separately and let the stars trail and then just blend the sky images with the foreground image.
06-27-2019, 12:27 PM - 1 Like   #8
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QuoteOriginally posted by MossyRocks Quote
With astrotracer with either of those lenses one could probably go out to 2 or 3 minutes without much issue and get some really nice stars.
Just the function provided by the O-GPS-1 unit or internal GPS on APS-C cameras provides that much longer exposure time for the stars?

06-27-2019, 12:36 PM - 1 Like   #9
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QuoteOriginally posted by ehrwien Quote
Just the function provided by the O-GPS-1 unit or internal GPS on APS-C cameras provides that much longer exposure time for the stars?
That also depends on the focal length but that (2-3 mins) is generally true for wide-angle lens. I have tried 2 min at 16mm with O-GPS1 to get trail free images and it worked pretty well.
06-27-2019, 01:34 PM - 1 Like   #10
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QuoteOriginally posted by ehrwien Quote
Just the function provided by the O-GPS-1 unit or internal GPS on APS-C cameras provides that much longer exposure time for the stars?
If you have a Pentax DSLR with the built in GPS, or the O-GPS1 with compatible ones, yes you can get much longer trail free astro shots. It is dependent on focal length, as well as where you have it pointed in the sky. The estimates it gives you are highly optimistic for what I typically do but may work well if going for the no noticeable trails in a printed picture or as a computer wallpaper metric. I regularly shot 30 second exposures of stars and deep sky objects with a 300mm f/4 lens using astrotracer (K-3 + O-GPS1). I want to do some wide angle stuff but the weather never wants to cooperate as I have a 28mm and 17mm fisheye that I want to play with when getting some Milky Way shots. Neither are new being M42 mount, so they are pretty slow thus using astro tracer would be a good option to make up for lack of aperture. I have done a 10 second shot without astrotracer one night from a rest stop as I didn't have the O-GPS1 with me as it would have just been another piece of gear I was hauling around all day that I didn't need. The clearing of the sky at night was just by chance and was only brief there.
06-27-2019, 01:45 PM   #11
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The Samyang 24mm f1.4 gets good reviews for astro work
06-27-2019, 03:05 PM   #12
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QuoteOriginally posted by MossyRocks Quote
one could get some nice pinpoint stars going up to 10s with the 17-50mm at 17mm or 15s using the 14mm
My concern was that between shots the stars would move quite a bit and might make blending the shots more difficult. I haven't done it, so I'm curious if this is a problem. Also, I'm wondering if a lens with significant comma would result in a strange looking blend.

QuoteOriginally posted by roberts_camera Quote
I actually just managed to snag an SMC DA 15mm F4 ED AL Limited for $50
Good deal!
06-27-2019, 04:49 PM   #13
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QuoteOriginally posted by Qman Quote
My concern was that between shots the stars would move quite a bit and might make blending the shots more difficult. I haven't done it, so I'm curious if this is a problem. Also, I'm wondering if a lens with significant comma would result in a strange looking blend.



Good deal!
It's not a problem. The stars don't move that much Particularly with a wide angle.
18mm. 6 20 second exposure landscape frames stitched in Lightroom.


28mm. 4 ten second exposure portrait frames stitched in Lightroom.


28mm. 10 eight second exposure portrait frames stitched on Lightroom.
06-27-2019, 05:40 PM   #14
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Everyone is correct when they mention "where you have it pointed at in the sky" being a determining factor of exposure length trail free. For example, in my experience with the area I shoot at and where I point the camera an exposure of 1min 30sec using Astrotracer, ISO 800 @ f/3.2 on samyang 10mm f/2.8 lens will get fairly nice images, but when you start zooming in, there are still trails... to remedy this, I would need to drop the exposure time to 1min 10sec for completely trail free stars, where pointing the camera in another direction would require a different exposure time. But unless you're going to view or print the images at 100%, 1m 30s does just fine as a dummy starting point for astrotracer exposures just trial and error afterward to reduce any trailing.
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06-27-2019, 09:13 PM   #15
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QuoteOriginally posted by ehrwien Quote
Just the function provided by the O-GPS-1 unit or internal GPS on APS-C cameras provides that much longer exposure time for the stars?
I've gotten 60 seconds with a 55-300 PLM, stretched out to 300mm, with astrotracer.
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