Canon 7D Star Trail Photography

Star Trail photography using a Canon EOS 7D camera and Canon 10-22mm lens

Cemlyn Bay on Anglesey in North Wales, Wylfa nuclear power station is on the right hand side

The Barn Owl Centre in Gloucestershire

St Bartholomews Church in Churchdown, Gloucestershire

Initially the Canon 7D produced some slightly disappointing results with gaps clearly visible between the individual 30 second exposures. The stacked exposures have been processed by the freeware software StarTrails

It appears that each 30 second exposure was taking 32.6 seconds to complete. This 2.6 seconds delay between frames was giving the gaps in the Star Trails.

This test image of 25 exposures looks good at web resolution

but at full resolution gaps are clearly visible between exposures

Checking on the Flickr StarTrails and Photography-on-the-Net forums gave me some pointers and after turning all the noise reduction functions off, disabling Silent Shooting mode I have be able to reduce the delay between each thirty second exposure so that when this image of 74 exposures

is viewed at 100% the gaps are significantly less.

Further testing on the Canon 7D has shown that the 30 second exposure setting on the camera is actually opening the shutter for in excess of 31 seconds.

The sequence below is of a clock on my laptop with the 7D programmed for  continuous 30 second exposures which illustrates the length of the 30 second exposures. What should of taken 8 x 30 seconds** took 8 x 30 seconds plus an additional 19 seconds.

** plus a small time for the mirror and shutter to recycle between exposures, maybe 8 x 0.25sec

[Show as slideshow]

Some tips I’ve picked up that work for me

1. I use the stacking method for star trail photography. In light polluted areas the technique allows me to get a good exposure of the stars and sky and allows me to ‘paint’ the foreground with light or flashguns to highlight something of interest in the foreground. If I used the single long exposure technique the sky would end up very overexposed from light pollution.
2. Typical sessions will consist of 200-300 30 second exposures taken at iso 200 f4 using a wideangle lens on the Canon 7D.
3. Use the aperture to define how many of the distant stars appear in the final image and also how much of the image is in focus. It is worth calculating what the optimum hyperfocal distance is for the aperture you are using so that you know infinity is in focus and some of the foreground will also be sharp. With wideangle lens focussed at 10 metres you will get a DoF from 5m to infinity with the lens stopped down one or two stops (f4-F5.6).
4. When you have the right aperture use the shutter speed to control any light pollution; close to cities you can use shorter exposures without losing the stars being captured, in darker regions you can use longer exposures.
5. I try to keep the iso setting to 400 or less to minimise the sensor noise
6. Always take dark frames before AND after you do the main sequence of images. Adding the dark frames into the star Trails program will reduce the effects of sensor noise.
7. I normally shoot in RAW mode to give me the control over the quality and finish of the image. Using JPG mode is fine and certainly means less post processing of the files but it has some limitations. Using RAW also means the White Balance can be adjusted later in the RAW processing software. I do manually set the camera White Balance to 5800k so that it is constant through the sequence.

This site contains a lot of very useful information and is well worth a visit