Long Exposure Star Trails Question

Tamron SP AF 28-75mm f/2.8 XR Di for Canon

05/22/2005 05:09:20 AM · #1

I got an ML-L3 remote for my D70 and just had a go at taking long exposures of about 5 minutes.

I tried a star trail, but Im rather disappointed with my first results.
I used ISO 200, F20, Bulb with Remote, In-camera Noise Reduction and a 70-300mm Nikkor at 150mm.

click the link below to see my result. (approx 1.5Mb)

My problems -
- There is noticable blue, red and white dots on the image (these can't be stars or they would have trailed like the main ones)
- there is a purple over exposure in the top left corner

Anyone had much success with Star Trails and long exposures? Am I doing anything wrong?

Any help would be great, thankyou,
Jarrad

Click here for 6 megapixel, 1.5Mb file

tazza

Canon EOS-350D Rebel XT

05/22/2005 05:22:06 AM · #2

I've had a look but I'm a bit confused, looks like you've only got 2 trails and lots of fixed dots... So I guess the trails must be satellites and the dots (white red and blue) are the stars? The thing is, at 5 min. exposure, the stars should have trailed, so I don't know... Unless you're using a telescope mount to track ?

marbo

Nikon D5000

Nikon AF-S DX NIKKOR 18-200mm f/3.5-5.6G ED VR II

05/22/2005 05:30:26 AM · #3

All the dots are hot pixels.
For best results you want a wider lens say 18mm to get in lots more stars.
Also try f8-f10 or lower.The purple is probaly heat from your camera.

Message edited by author 2005-05-22 05:31:36.

05/22/2005 05:43:45 AM · #4

Any way to avoid the purple 'heat' problem?
I'll have another go with a wider and aperture and my 18-70mm

Does anyone else have a D70 with 18-70mm, and can post a shot of star trails that they've taken?

05/22/2005 05:46:32 AM · #5

The thing is you are only using a five minute exposure. Digital is not the best for shooting the stars because you need more like 30min to an hour for a nice exposure where you get alot of long lines. Five minutes is not enough, that is why the stars are stationary in your picture and only satellites and planes are leaving streaks.

Hint: When you are at the end of your exposure open your lens up for about 10-30sec and then you get a starburst at the end of your streak. Great for pinpointing constallations.

Message edited by author 2005-05-22 05:47:53.

05/22/2005 06:03:06 AM · #6

Im 100% sure that in the photo I submitted that there is only about 2 stars to be seen (due to my telephoto zoom)

Tycho

Nikon AF-S DX Zoom-Nikkor 18-70mm f/3.5-4.5G IF-ED

05/22/2005 06:10:41 AM · #7

Instead of shooting one very long exposure, therefore ending up with an extremely noisy image, you can shoot several (sometimes up to 30) much shorter exposures and then stack them on top of one another. There's also a nice little software called Image Stacker which simplifies the stacking process. Here you can find more info on the software and a gallery of star trail pictures produced by stacking multiple images with it.

05/22/2005 06:11:55 AM · #8

no there are plenty of stars there to get streaks. The like five streaks you have are satellites and planes. The problem is the time. Look at the photo marbo submitted. It was a 27min exposure and even then nis streaks arent that long... You need a longer exposure, this gives the stars time to move. The benefit of using a shorter lens is that you can add a stationary object into the foreground to add visual interest.

05/22/2005 06:19:19 AM · #9

or just do it the old fashion way of film. A nice b&w film like Ilford fp4 or panf, or a slide folm like any fuji slide other than velvia (major repricity failure) works great... The lower iso films show much less grain despite repricity failure. Its kind of like pushing a 125 to 400. The grain is still pretty tollerable.

If you are near an outlet you can plug in your d70 and then shoot on iso 100. Then you can run a 30min exposure if the d70 has that capability.

05/22/2005 06:22:56 AM · #10

funny thing is with that image stacker is that the original pic on there site looks better in my opinion than the stacked image. Pretty cool program though, could have alot of uses...

hyperfocal

Nikon D7000

Nikon MF 105mm f/2.5 AIS

05/22/2005 06:24:16 AM · #11

I agree with mrmojo, digital is not the medium of choice for star trail photography. Below is a older shot I took on film with a 45mm lens. Exposure is 2 and 1/2 hours @ f5.6. Not a exposure suitable for digital.

The dashed line (if you can see it. sorry for the small image) is an airplane with a flashing light that flew through the image area during exposure.

Tamron SP AF 28-75mm f/2.8 XR Di for Canon

05/22/2005 06:26:40 AM · #12

Here is my second attempt. Its obvious that there is both stars and Blue, Green and red noise in the photograph. This was:
ISO 200, 20mm, F8, 5 minutes

You can see the coloured dots in the palm trees of my back yard

Click here for the second image (2.1Mb approx)

tazza

Canon EOS-350D Rebel XT

05/22/2005 06:34:03 AM · #13

You're right, on this one it's obvious the dots aren't stars! they really looked like stars on the first one, fooled me all right. I can't believe how bright these dots are...

TomH1000

Olympus E-3

Olympus 14-54mm f/2.8-3.5 Zuiko Digital Zoom

05/22/2005 06:53:22 AM · #14

Originally posted by Jarrad:

That one is much better. Does your camera do what is called "dark frame subtraction". My E-1 does this and I am pretty sure most of the Canons dl also. The way that works is if you take a 5 min exposure the camera will take another 5 min exposure but block the CCD so no light gets to it. Then the two images are combined and anthing that is left on the dark frame image is subtracted from the real image. You can do this same thing in Photoshop also. Another option is to take many short photos one right after the other and overlay them in Photoshop.

Hope this helps.

Panasonic LUMIX-DMC ZS100

05/22/2005 08:34:54 AM · #15

thanks TomH1000, thanks everyone, I'll keep at it

wheeledd

Canon EF 24-105mm f/4.0L IS

05/22/2005 09:46:37 AM · #16

Jarrad,

I took a close look at both your images. They have exactly the same pattern of specks in them. These are clearly hot pixels - pixels in your sensor that turn on even in the absence of light with the long exposures you are using.

TomH suggested "dark frame subtraction." This is standard technique for digital astrophotography. When you take a five-minute exposure, take another one immediately after but put the lens cap on. In Photoshop, reverse the "dark" image to make it a negative and then use it as a mask to block the hot pixels.

The fact that you got the same pattern in both your images suggests that you may be able to take a single "dark" image and use it to correct all your star trails images - including the ones you have already taken.

I don't know whether the number of hot pixels you are getting is excessive for your D70. Maybe you could get one of the other D70 owners to take a "dark" image at the same exposure and compare it to what you are getting.

BTW, some of the digital cameras designed for astrophotography have built-in cooling systems to reduce the temperature of the sensor. Digital has become the medium of choice for astrophotography but both temperature reduction and dark field subraction are necessary for top-quality work.

--Dan

jab119

Canon EOS-70D

Canon EF-S 18-135mm f/3.5-5.6 IS

05/22/2005 10:46:01 AM · #17

as others have mentioned the best way to get star trails with digital is to take 60 or 70 1 to 2 minute exposures and stack them or combine them together. Just make sure you dont let more them 20 or 30 seconds pass between exposures.

If you remote has a timer function that would be great. My canon remote can be programmed to take 100 photos @ 1 minute each with a 3 second pause between exposures, just as an example.

James

Arcanist

Nikon D810

Nikon AF-S Nikkor 28-300mm f3.5-5.6G ED VR

05/22/2005 10:52:20 AM · #18

Um yeah, Although I haven't tried anything close to a 5 minute long exposure (we Northerners can get star trails with a 30 second exposure by aiming at Polaris). I have never seen that level of hot pixelation on my Nikon.

Nikons do have the in-camera noise reduction (darkframing) but I have found it to be weak compared to Noise Ninja.