Canon 7D at night

fishing4sanity · Feb 19, 2015

I made my first attempts at night time photos, stars and Milky Way, with my 7D - it was a flop. Just wondering if some of you have had good success with night shots? After looking at some YouTube videos on photographing the Milky Way, I tried to mimic them, but to no success. I was using a Sigma 18-50 at f/2.8 and a couple different ISOs and 30 sec. shutter, outcome just wasn't like the videos at all. Also, does the 7D have any 'long-exposure noise reduction' settings in the menu? I couldn't find anything.

UjaiDidida · Feb 20, 2015

Hi there.

For a Milky Way shot, I think 30 seconds is just too long. At 18mm I will only shoot at 15 seconds or faster. There is a calculation for that to avoid star trail. Keep everything in focus while the aperture wide open. The ISO speed is usually around 1600. The sky condition must be very clear, very dark which means no light pollution at all. Can you share us your shot so we know what you can do to improve it?

Cheers.

ronlane · Feb 20, 2015

I have not shot stars with my 7D yet (Only got it in November), but UjaiDidida is correct about the star trails.

I would be interested in seeing examples of your work.

Noise reduction is in C.Fn II-2 High ISO speed noise reduction.

TCampbell · Feb 20, 2015

30 seconds is too long. By the math, if you use the "rule of 600" designed for 35mm and full-frame digital cameras, you have to adjust that by the crop factor (1.6). 600 ÷ 1.6 = 375. Now divide that new base (375) by your focal length (hopefully you were using the widest 18mm focal length on that 18-50mm lens). That works out to 375 ÷ 18 = 20.83.

That means you don't want to shoot any longer than about 20 seconds (15 seconds if you want to be conservatively safe.)

Long exposure noise reduction only applies to JPEG. The camera actually takes two frames... one with the shutter open (a normal "light" frame) and one while leaving the shutter closed (activates the sensor for the same duration and ISO setting... but does not actually open the shutter. This is the "dark" frame. It's purpose is just to capture noise.) The "dark" frame is then subtracted from the "light" frame in the hopes of reducing some of the noise. Some noise will be random. But some will be "pattern" so while this won't perfectly eliminate noise, it will reduce some noise.

Anyway... for these sorts of shots, you'll be dealing with a lot of dark and very dim stuff. JPEG doesn't deal well with that sort of thing. It tries to normalize pixels that have insignificant levels of difference (differences it thinks your eye won't notice) by just making them the same. Once these are the same, it can achieve better compression for storage (which is why JPEG files are so much smaller than RAW or TIFF.)

But there's a problem when you apply this to astrophotography -- which is that you'll need to work the image to bring out the detail. We call this "stretching" the image. This is THE weak spot in the JPEG format. It has extremely poor adjustment latitude.

If you were in fantastically dark skies then the Milky Way actually does look like that amazing thing you see in these photos. But if you're in suburban skies, then the light pollution from all the street lights will illuminate the entire "black" sky to a dull gray (or orange depending on if it's Mercury vs. Sodium, etc.) The problem is... the stuff you're trying to photograph is already a dim gray with hints of dim reds smattered about. So when the sky is being lit up to a dim gray, there's practically no difference between the background brightness of the light polluted skies... and the brightness of the stuff you're trying to image. Basically you are trying to shoot a dim gray object on a dim gray sky and you end up not seeing much of anything. This is why we encourage you to only do this on a moonless night AND get as far away from the cities and town and any source of light as possible. If you're so far from civilization that you're worried you might be eaten by a bear... you're in the right spot (btw, some guys bring protection against such hazards.)

JPEG can only deal with tiny amounts of adjustment. The more you try to adjust exposure / levels / curves / highlights & shadows / etc. the more you start to see that the detail is lost because of the compression algorithms involved. That detail is precisely what you need to be able to "stretch" the image (I'm not talking about physical image size... I'm talking about exaggerating the differences between tonality in the image to bring out the the detail in the Milky Way.) JPEG is appropriate only for images which won't require much (if any) adjustment. Deep sky photos definitely DO require aggressive adjustment and are not candidates for JPEG format.

You want to shoot these only in RAW (and convert them only after you've finished performing all the adjustments.)

fishing4sanity · Feb 22, 2015

Thank you for the advice. The first attempt was bad enough that I just deleted everything, but with the info shared I'll give it another try. Thanks again.