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FORUMS Photo Sharing & Visual Enjoyment Astronomy & Celestial 
Thread started 01 Sep 2017 (Friday) 12:18
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Milky Way...Canon 17-40 f4 versus Canon 40/2.8 Pancake

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Sep 01, 2017 12:18 |  #1


I'm a wildlife shooter and not a landscape photographer, but I will be in Algonquin PP in Canada over the weekend and would like to try shooting the Milky Way. I've watched a few tutorial videos to give me some idea of what to do. I'm sure I'll screw it up, but I want to try anyhow!

I have a Canon 1Dx which I will be using. I also have a 17-40 and a 40mm f/2.8. Should I use the wider lens, or the faster? And what is the 500 I divide 500 by the focal length to get a suggested shutter speed? That would give me roughly 30 seconds at 17mm and 12.5 seconds at 40mm. Sound correct?

Any tips, I'm all ears!

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They have pills for that now you know.
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Sep 01, 2017 12:24 |  #2

For milky-way, I would think that the wider, the better. The milky-way is gigantic carving a swath across the entire sky.

Not sure why, but call me JJ.
I used to hate math but then I realised decimals have a point.
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Post edited 6 months ago by MalVeauX.
Sep 01, 2017 12:33 |  #3


There's a lot more to milky way (wide field astro) than just focal-ratio speed and exposure time to avoid star trails from a static mounted camera (tripod; no tracker). Coma is a big deal. Zooms tend to be very poor at wide field and the shape of stars and the coma can really wreck a wide field and make it look like a swirly oblong weird star mess.

The 40 F2.8 is pretty good. It will show some CA wide open on really bright large stars, but it handles coma decently for what it is, and is fast enough to work with. Coma gets worse the faster you go sometimes; depends on lens design. The 1DX can easily do ISO 6400~12,800 and with a 40mm, you can expose for 10 seconds, so you can get what you need to work with. Exposure of the sky is not the same as exposure on terrestrial subjects. Your histogram is in a good place if you see a single spike about 1/3rd into the histogram from the left. Any further left (1/4th) and you're underexposing likely. Any further right (1/2 histogram) and you're overexposing and will get a lot of sky glow, and you're not getting more signal from it, but just more problems. So do a test run on getting your settings in to get you to 1/3rd histogram fill and you'll be good, regardless of what lens and settings you use for wide field milky way.

The 17-40 at 17mm is awful. Even stopped down a little, it still has a lot of coma issues, and bright stars have a weird shape due to glare and stuff.


40mm F2.8 STM @ F2.8 (ignore most things, just look at coma quality and CA as this is wide open); there's a little CA going on, but its not too distracting at this scale. I have a little blur from either vibration or too long of an exposure (ignore my times, I'm not static). But the idea is to see how it is wide open.

IMAGE LINK:​TM  (external link) IMG_5171 (external link) by Martin Wise (external link), on Flickr


Here's a cheap ancient Tamron 28mm F2.8 manual lens (adaptall2 mount) that costs $40~50 on Ebay for reference to compare, also wide open at F2.8. You'll notice the coma is much stronger and see the shape of the stars and more CA is noticeable.

IMAGE LINK:​pD  (external link) IMG_5164 (external link) by Martin Wise (external link), on Flickr


Here's the 17-40L at 17mm and F5 (stopped down just a little bit to help with the awful coma and distortion). It's not super bad, but it's bad. Forgive the really bad star spikes, was trying to mask how bad the glare and shape of the big stars were due to the awful coma of the lens at 17mm. Also, this was cropped, it's 17mm on APS-C, and the edges were really bad, so this is a cropped FOV from even the original so you won't see how bad it was on the edges, but it was bad enough I cropped it out (worse than the adaptall2 old lens above).

IMAGE LINK:​4X  (external link) MilkyWay17mm_07082016 (external link) by Martin Wise (external link), on Flickr


Ideally on a full frame, you may want to be at 24mm or 28mm for galactic core milky way on full frame. Going wider just gives you more room for landscape foreground stuff or a lot of cropping room. You don't want to be at 17mm unless you're incorporating a foreground most likely.

If you have a 24mm prime laying around, that would be a good start.

If you just have the 40 STM and the 17-40L, you could try the 17-40L at 24~30mm and stop it down a little (F5, etc) and just push ISO harder (that's totally ok!). Or just use the 40 and focus on the galactic core where the interesting stuff is anyways and do 10 second exposures.

Very best,

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Post edited 6 months ago by Nogo.
Sep 01, 2017 12:37 |  #4

What's wrong with using both? One is wider and one is a 2.8. There is advantages to both.

I would also take multiple shots of the same scenes. Then later if you really get into it you can merge the shots to get even more detail.

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Sep 19, 2017 00:49 |  #5

That 40mm STM is damn impressive actually. I may have to pick one up since I already have an iOptron.

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Sep 27, 2017 10:48 as a reply to  @ 01Ryan10's post |  #6

So envious of those Milky Way pictures. When we were without power for Irma, I figured I'd just go try some night sky pictures, and NOTHING turned out.

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Oct 01, 2017 21:33 |  #7

GESWhoPhoto wrote in post #18461431 (external link)
So envious of those Milky Way pictures. When we were without power for Irma, I figured I'd just go try some night sky pictures, and NOTHING turned out.

OK so expand on the bolded part

what camera, lens, settings etc
tripod ?


A picture is worth 1000 words ;)
Canon 5D3, 6D, 700D, a bunch of lenses and other bits, ohhh and some Pentax stuff ;)

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Milky Way...Canon 17-40 f4 versus Canon 40/2.8 Pancake
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