- This topic has 6 replies, 2 voices, and was last updated 10 years, 2 months ago by
.
-
Posts
-
Here’s a shot of the Milky Way taken in South Africa! I went outside after dark, and was simply amazed by all the stars that were visible! The sky there must be a lot clearer than where I live! Anyway, I couldn’t resist, so I got out my tripod, and tried to capture as many stars as possible.
Shot with a Canon EOS Rebel T3
Shutter Speed: 25 sec.
Aperture Value: f/3.5
ISO Speed: 800
Focal Length: 18mmNOTE: I pushed the exposure in Lightroom exactly +3.00 stops to bring out the fainter stars.
- This topic was modified 54 years, 11 months ago by .
Attachments:
As I was shooting the stars (pardon the pun), I had the idea of testing my camera’s sensor sensitivity abilities. So I set my camera at a 25 sec. shutter speed, f/3.5, 18mm, and ISO 100. I then took a picture at every ISO level, in this sequence: 100, 200, 400, 800, 1600, 3200, 6400. The only thing I changed was the ISO speed, all other settings are identical. I can’t post all of the sequence here, but I’ll show a very interesting observation that I made!
I took the image shot at ISO 800, and compared it to the one taken at ISO 6400. Obviously, the ISO 800 one will be darker. Then I figured out the number of steps difference it was, 3 EV difference. So I popped it into Lightroom, and “pushed” the exposure 3 stops to make it as bright as the one taken at ISO 6400. To my surprise, when I compared them, I could see very little difference! I would have expected the “pushed” one to exhibit a lot more noise. Now I can tell that there is more random ‘color’ in the “pushed” file, but other than that, I can’t see much difference!
Attachments:
Wow, that sky is full of stars! I’m surprised there’s not much difference between the two pictures you compared. That’s very interesting; an experiment I’ve never done myself. I’d be curious, did you conduct an experiment with a fluctuating shutterspeed/aperture to keep the same exposure only at varying ISO levels?
I don’t know if you spent any time processing the first picture you posted, but you certainly have something worth really enhancing. This PDF Guide to astrophotography in Photoshop and this article on Star Color Enhancement, might be of interest to you.
“did you conduct an experiment with a fluctuating shutterspeed/aperture to keep the same exposure only at varying ISO levels?”
No, I did not. I knew that changing the aperture was out, as that would darken the image so much that many of the stars would be invisible. But actually, come to think of it, I should try with varying shutter speeds at least, because the length of the exposure does affect the noise visible in the image. The longer the shutter is open, the more random noise you are liable to get. For example: A picture taken at 20 sec. with an ISO speed of 1600 would (theoretically) have more noise than a picture taken at 5 seconds at ISO 1600. Of course the number of stars would be greatly reduced in the second picture due to the much shorter exposure time, and if you “push” it in post, it would surely be more noisy than the first picture. My object in this picture was to avoid star-trails, I wanted detail, not trails, that’s why I kept the shutter speed to 25 sec.
Attached is a picture taken at the same location. Notice how bright the sky is! Over 72 minutes, any small light levels can add up immensely!
There was a city nearby with lots of light pollution, but the camera was pointed away from it at a 90 degree angle.Shutter speed: 4320 sec. (72 minutes)
Aperture: f/3.5
ISO speed: 100
Focal Length: 18mmFor comparison’s sake, here’s one taken facing the same direction, but from the top of a nearby mountain. Now you can see the city lights, but look at the light levels in the sky! This shot was a stack of 84 exposures:
Shutter speed: 20 seconds per frame, (1680 sec. total) (28 minutes)
Aperture: f/3.5
ISO speed: 1600
Focal Length: 18mmFrom now on, all my long exposures are going to be stacked shots! Stacking means that all the random noise will be removed, as it is averaged out, allowing me to use ISO 1600, which in turn, allows me to capture FAR more stars than ISO 100. There’s also less chance of ruining your picture when the camera runs out of battery and shuts down. I’m sure it would try to save the long exposure before doing that, but if all it has is a bunch of 20 sec. exposures, they’re already saved to the card, and you’ll only lose the last one. It has never happened to me, I’m just theorizing, but it certainly isn’t an impossibility. The one thing that I don’t like about it, is that you will be increasing the number of shutter actuations of your camera much faster than normal. Although, I don’t know, it might be better to wear out the shutter, than to overheat your sensor!
Attachments:
Very interesting!
If your camera runs out of battery and shuts down, it will not save any exposure it was recording. Like, if a 60 minute exposure is running and the camera shuts down at 59 minutes, none of the exposure is saved to your camera at all. At least, this is my experience. Make sure you have a full battery and know how long it will last!
So, how did you stack the 84 exposures?
- This reply was modified 54 years, 11 months ago by .
Oh, I was going to mention that, but I forgot! The image was stacked using StarStaX. I don’t know much about it, as I’m just learning to use it myself, but in my opinion, it does a very good job! It’s quite fast too!
As for battery shut down issues, I think any of the more modern cameras will save your exposure before they shut down. I’m quite certain that my Rebel T3 will. I would suspect that the older cameras like the 40D and so on may not, but I have no way of testing that!
I have not really had any long-exposure battery problems. I can take several hours worth of exposures with my Rebel T3 without draining the battery. According to snapsort.com, the Rebel T3 has nearly the longest battery life of any entry level DSLR, and I would certainly believe it!
A note on battery life: Just before I left for Africa, I purchased a new batter for my T3 as I had no idea if we would be able to charge them while we were there. That brought me to a total of 3 batteries, the OEM Canon one that came with it, a Chinese no-brand one from Ebay, and the last one, a slightly more expensive Opteka brand from Amazon.com. I figured that since it’s been almost 2 years since I got my camera, the batteries were probably starting to wear out. During the first 3 weeks, I hardly used my camera, although I did do a few star shots, but nothing more than 5 minutes. As far as I can remember, the battery lasted till we started traveling through the Etosha Game Park, where I took several hundred pictures. All of a sudden, the battery was dead. Oh well, I have two more “freshly charged” batteries! The next battery lasted for no more than 200 frames when it too was dead! Now I was starting to worry, I only had one “fresh” battery which had been charged 3 weeks ago the night that we left for Africa. I started trying to cut down on battery use as much as possible, I turned off the Image Stabilization for the lens, limited the time spent viewing pictures, and turned it off whenever possible. By the time we left the park, that battery too, was blinking red. I started to suspect my new lens as the cause of the sudden battery drain. Come to think of it, I never noticed that my batteries were starting to “deteriorate” till I got the new lens. I can often hear “clicking” and see the viewfinder jump, especially when turning the camera on/off.
We stayed in South Africa for a few weeks afterwards which was where I took the pictures posted above. During that time, I took several long exposures, and the battery held up just fine.
So, learn a lesson: I strongly considered buying a 12V DC battery charger (for use in a vehicle) along with my new camera battery, but it cost all of ~$25 dollars, and I finally decided against it. I wish now that I had! What is $25 compared to pictures from a country that you might never visit again!
Thanks again for your experiential insights, @buddingphotographer! There’s nothing more nerve wracking than to be in a prime shooting location with the threat of no battery power.
You can experiment with your camera to see what would happen if you ran out of battery power in the middle of a long exposure by removing your battery in the middle of a multi-second exposure. On my 5Dii, no image is saved if I remove the battery during either the exposure or during the wait-time after the exposure during Long Exposure Noise Reduction.
- This reply was modified 54 years, 11 months ago by .
You must be logged in to reply to this topic.