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I have a Nikon D7000 and don't know whether my 50mm 1.4 or 17-55m 2.8 lens would be better. I was automatically going to go with the 50mm lens, but then I was reading up on how I can use a longer exposure with the wider lens and still not get star trails.

Could I get a lower ISO with the 2.8 lens and longer exposure, or with the 1.4 lens with a shorter exposure?

Both lens are sharp wide open, and I'm not too worried about capturing less of the sky with the 50mm at this time.

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Actually just did a ton of research on this myself and found this great article: http://www.lonelyspeck.com/lenses-for-milky-way-photography/

It give's you the run down of the different lens options and what actually goes into taking pictures of the Milky Way. Just got the lens I ordered for this the other day. Got myself a Sigma 30mm f/1.4 which, was very cost effective at $500. Took a few test shots last night and it blew my mind the amount of detail in the stars with just a 15 second shutter.

To build on my answer a bit, using a 50mm lens the maximum exposure time that you won't get star trails for is around 10 seconds for a full-frame camera, and for an APS-C camera it is around 7 seconds. The only way to avoid that is by tracking, so not sure how you can not get star trails with a longer exposure. With my 30mm and my canon APS-C camera the max time is around 15 seconds, and if I zoom in all the way I can see a slight star trail. In the end... the shorter the focal length the longer the exposure time that you can have without getting star trails. Obviously also the lower the f-stop the better.

If you read up on the astro score, your 50mm f/1.4 lens gets a better score then if you shot at 17mm f/2.8. In your case since you have both lenses, go outside and try them out and see which pictures come out better. That is really the best way to tell. Also, whenever I am taking astro pictures the first thing I do is set my ISO to 100 because I would rather have less noise in the picture with slight star trails than a really noisy picture.

As a side note, I was messing around with my pictures post-production with my new Sigma lens and bumped the clarity to 100 and it honestly didn't add that much more noise to my shots. So all-in-all if you are willing to spend $500 I would strongly suggest the Sigma. Was probably the best astro lens I could find for the price.

Here is one of the shots I took at f/1.4 ISO 100 http://i156.photobucket.com/albums/t14/ajtawil/Fall%202014/IMG_5831-2_zps8e8c26be.jpg~original

Hope this helps!

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  • Welcome to the challenging field of astrophotography (Google this and get a lot of usefull info). One way or another, you'll run quite quickly into the effects of a rotating earth. Don't spend too much money too quickly. For example the barn door tracker (see link in @Adjit's answer) is a $ 15 hobby project which gives you a great price/performance ratio. Also visit a local astronomy club. Astro geeks there are probably very helpful. Piggybagging your camera on a tracking telescope will also yield great results. – agtoever Dec 11 '14 at 8:32
  • As a quick comment... Starting from 30s exposure you will begin to see the rotation of the earth... What you could do (but I have never tried it myself), is to take several images at ca. 10-15s exposure and then merge them in PP (Post Processing)... Google is your friend for tuotirals :-) – Umberto Dec 11 '14 at 11:46
  • The Rokinon lenses are usually the best bang for your buck. They are mechanical lenses and have no electronic connections to the camera, but the 14 and 24 mm lenses go down to f/2.8 and 1.4 respectively and have some of the highest optical ratings in the industry for a fraction the price of other lenses. However, if you are trying to get zoom in pictures of nebula's you may want to go with something in the range of a 70-200mm lens and for that you will also want to be able to mount the DSLR/lens combo on a tracking mount. – Jon Dec 11 '14 at 14:40
  • @Jon was looking at the Rokinon as well, but for me it wasn't the right choice for me since it wasn't auto-focus and I wanted to be able to use the lens for other things than astro without worrying about whether the picture was in focus. – Adjit Dec 11 '14 at 14:47
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    That is totally understandable. I use my Rokinon lenses more than I do any of my electronic and much more expensive wide angle lenses, but I enjoy the challenge of doing everything manual and as you might suspect, sometimes the focus is not correct and I do not find out about it until after the shoot. But as a point of interest, I have found that at low focal ratios the focus required to get pin point stars is so precise that you have to manually focus the lens. – Jon Dec 11 '14 at 14:50
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The two lenses differ by two stops wide open. That means that at a constant ISO, you can shoot with the f/1.4 at four times shorter exposure than with the f/2.8.

This is commonly referred to as the exposure triangle. You get the same exposure for all combination where aperture * aperture * shutter time * ISO is constant.

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