How to photograph the Milky Way

[hobsey]

I guess this is a good enough place than any to post this, admin please move if not.

I was looking for tips and advise on settings for wide field photography of the Milky Way and came across this site, been written with novices in mind and very easy to understand.

Thought I would share it,

http://www.lonelyspeck.com/how-to-make-an-amazing-photo-of-the-milky-way-galaxy/

[scoobee]

Best site I've seen, many thanks

[RichM63]

Bookmarked.

Nice find.

[cockney]

thanks for posting i bookmarked it,will have a good read later

[SnakeyJ]

Excellent guide - cheers for sharing.

[sheldondave]

Hi

Just what I've been looking for.

Dave.

[Sandraj]

Thanks for sharing, will defiantly be reading it later.

[rob0971]

Bookmarked for later. Many thanks!

[MND]

That's a really good guide, many thanks.

[jgs001]

That's a good guide (although from my experience, the exposure time calculation is wrong to avoid star trailing... I see what it's doing, it's working out the equivalent exposure time, but from a static tripod with a 50mm, you cannot go much beyond 8 seconds, and 56 seconds is going to produce noticeable trails). If you're looking at capturing a widefield and ignoring the landscape also, then you can bring stacking into the mix... Which also allow you to turn off noise reduction, and use a  set of darks... (you can always use the landscape from a single exposure and layer it over the top).

http://stargazerslounge.com/topic/36308-basic-widefield-with-a-camera-and-tripod/

The rule of thumb for static tripods to avoid trails... 400/fl in seconds (for APS-C, or 600/fl for full frame).

[hobsey]

That's a good guide (although from my experience, the exposure time calculation is wrong

I had also noticed this but just above it, it says:

'Use this calculator to determine a good starting exposure for your astrophotography depending on your equipment.'

So unless he means use them exposure times to start off with then work it out from there.

[jgs001]

Yeah I read that, but the numbers don't work for pinpoint stars... with a 50mm on an APS-C you'll get trailling at just over 8 seconds... the calculator recommended 56 seconds with a 50mm at f/4, that's going to produce some significant trailing in the end image. I don't believe star trailing is taken into account. And that time difference is quite significant.

[nicks90]

or does he mean those exposure times are good total exposure to get a good result - and you can use that as a guide for how many smaller subs you would need... perhaps?

[jgs001]

He might do, but I'd want to capture at least 10 to 20 exposures, and that's 80 to 160 seconds at 50mm. 

[lonelyspeck]

Original writer of the article here! Saw the referral from this thread and I wanted to chime in on the exposure calculator and see if you guys had any questions about it. 
 
All the calculator tries to do is output an exposure of EV -8.

In my experience, EV -8 will usually pull out details from the Milky Way (like the galactic center, Rho Ophiuchi, etc.) into a "neutral" area of the exposure. This means it should result in an exposure where most of the important image data is centered on the image luminosity histogram. This makes the exposure easier to push and pull in post processing. 
 
If you enter in the aperture and ISO limits such that it's not possible to expose EV -8 with a short enough shutter speed to prevent star trailing, it will compensate with a longer exposure and output a warning: "*Notice: This shutter speed may result in star trailing. Higher max ISO or lower f/number lens recommended." Try it out. 
 
Now with a 50mm that jgs001 mentioned, he limited the lens to f/4 and found that the suggested shutter speed was 56 seconds.  If you enter in something faster like f/2 or f/1.4, or increase the ISO limit, it will bring that number down until it converges to 7 seconds, just about the limit at which you'll start to see star trails. So the trick of the calculator is to find the lens f/number and ISO limit combination that doesn't pop the shutter speed warning. Untracked astrophotos, of course, are usually best with lenses with low f/numbers. 
 
I use this calculator for calculating the single exposures for stacking images too. Below is a photograph using a (median filtered) stack of 16 exposures from an APS-C 35mm/1.4 at f/1.6, 8 seconds, ISO 6400. For reference, my calculator outputs nearly the same exposure: 10 seconds, f/1.6, ISO 6400. I reduced the shutter time to 8 seconds to further eliminate a little bit of star trailing. I usually find that 16 exposures is a good practical limit for untracked photographs. More is better but after 16, you start noticing diminishing returns (signal to noise ratio varies with the square root of total exposure time).

Of course, if you're using any kind of motorized equatorial mount, I recommend lowering the ISO limit, stopping down and using the longer exposures that the calculator outputs. Stack as many exposures as you see fit. 

Hope that helps. Let me know if you guys have any more questions. 

[hobsey]

Welcome to sgl and well done on a fantastic guide.

[Pete Presland]

thank you for the link and thank you to lonely speck for the guide, fascinating reading!

[lonelyspeck]

Thank you all for the warm welcome! I've been having fun browsing around here in the last few hours!

[jgs001]

Hi, and welcome to SGL. Thanks for the explanation on the calculator, that makes a lot more sense now.

How do you find the noise and dynamic range with the ISO so high? The result looks good viewing it on my phone.

Sent from my GT-I9300 using Tapatalk

[lonelyspeck]

jgs001, The cool thing about the night sky is that the dynamic range is rather narrow compared to typical daytime shooting so the shots don't really seem suffer in the DR department when using high ISO. The reason that I prefer a brighter image is because it's generally better to pull (make darker) an image in post processing than push (make brighter) one. A lot of this idea stems from the concept of ETTR: http://www.luminous-landscape.com/tutorials/expose-right.shtml

Noise is definitely always the biggest problem but honestly the default noise reduction built into Adobe Lightroom can make a huge difference. For the best results, I always stack multiple exposures (at least 4 separate exposures) to reduce noise. 

[jgs001]

Gotcha, although there are quite a few objects that have a huge dynamic range (M42 for example). For normal photography I do agree with you on ETTR, and tend to do that as much as possible, especially when using high ISO, as pulling the exposure back a bit, does wonders for the ISO noise , and the NR adjustments in Aperture are good for normal images. I tend to stick at ISO800 (and occasionally ISO400) for Astro.. there's a lot of discussion around about it, and I'll be honest I cannot remember the specifics of the arguments for this level, but 400 to 800 seems to be about the best option for general performance with Astro.

I tend to limit the number of shots I take on a static tripod to avoid field rotation effects creeping in, the stars around the edges smear, and whilst you have plenty of detail in the MW, you do have what look like field rotation effects in the image. Having said that, whilst it's not coma, it might be optical issues from having the lens at f/1.6, the stars in the corners look elongated, but with a central bulge (best way I can describe it)... I know that the 50mm's produce hideous coma wider than f/4 (well the 1.8 and 1.4 versions, although from what I've read the L is no better for Astro). The only lens I've tried that produced good results wide open is a macro lens (Sigma 150mm f/2.8 Macro and that requires tracking).

I like to aim for at least 12 images to stack (that way I can use statistical stacking methods to also remove things like planes and satellites).

[kalasinman]

Temperatures of astro objects run to the extremes. Space is near absolute zero and stars ...well can be quite hot. Magnitudes can vary widely from the limit of the scope, for example 12-13 to -1.46 (not counting the moon) a huge range. So I disagree that DR is less in astro. I notice at least one badly blown out star in your image, as an example.

[wxsatuser]

I tend to limit the number of shots I take on a static tripod to avoid field rotation effects creeping in, the stars around the edges smear, and whilst you have plenty of detail in the MW, you do have what look like field rotation effects in the image. Having said that, whilst it's not coma, it might be optical issues from having the lens at f/1.6, the stars in the corners look elongated, but with a central bulge (best way I can describe it)... I know that the 50mm's produce hideous coma wider than f/4 (well the 1.8 and 1.4 versions, although from what I've read the L is no better for Astro). The only lens I've tried that produced good results wide open is a macro lens (Sigma 150mm f/2.8 Macro and that requires tracking).

I like to aim for at least 12 images to stack (that way I can use statistical stacking methods to also remove things like planes and satellites).

I can understand what the author is about re the exposure, but!

As John points out you don't want to get a good exposure and ruin the whole lot with lens abberations.

The smeared stars are imo sagital astigmatism, star point flared to both sides, all stars rotating around the centre of frame

and effect tailing off towards the frame centre. I don't see coma as such, thats a different pattern.

[lonelyspeck]

jgs001 and kalasinman, I agree that we can have lots of scenarios with astro where the dynamic range is really high but for these really really wide shots with short lenses, most of those bright objects (like M42) are pretty small in the frame. 

Below is an image of Orion made with a full-frame camera and 50mm lens (the same field of view as the Rho Ophiuchi image) and you can see that M42 is really small. It's also completely blown out to white, just as you guys would expect. My intention for the shot was to try and capture Barnard's Loop so I didn't mind blowing out M42 since it's so small in the frame.

I think that DR becomes much more of a concern once we start shooting with lenses that are 100mm or longer or pretty much dedicated astro scope where objects like M42 take up more significant part of the frame. So for beginners just getting into shooting the night sky with nothing but their DSLRs and a tripod, I think it's easier to start with high ISO shots. 

The photo of Rho Ophiuchi doesn't have field rotation, it's actually just lens aberration, sagittal astigmatism, just as wxsatuser pointed out. A lot of these fast prime lenses (like the Fujinon 35mm f/1.4 that I was using) have pretty bad aberration when wide open. The solution, of course, is to stop down to a higher f/number, and rely on stacking multiple exposures to boost the signal to noise ratio lost from the reduced aperture size.

[lonelyspeck]

Here's the shot I forgot to attach from above post: 

Sigma 50mm f/1.4 @ f/4.0, 5 minutes, ISO 3200, Vixen Polarie.