| review: SLR Canon EOS 20D for long time exposures and astrophotography (appr. € 1500,- body only) |
Introduction
The Canon EOS 20D is a semi-professionel Single Lens Reflex digital camera with a true bulb mode.
The capabilty for changing the lens, i.e. by a telescope, and the exposure times up to 30 minutes and more is making it very interesting for astrophotography.
Many excellent reviews have been written about the fantastic day light capabilities of the 20D.
This review will focus on the long time exposure capabilities and the usage of the 20D in astrophotography.
Technical specification
- 3504 x 2336 pixel
- Pixel size: 6.5 x 6.5 uM
- Chip size: 22.7 x 15 mm
- Read out noise / Dark current: very low for an uncooled CMOS chip. Built in software noise reduction.
- Better than the appr. 25% overall quantum efficiency of the 300D as measured by Christian Buill
- One-shot colour with a filter relation of RGB of 1/2/1
The CMOS sensor and micro lenses
The 20D has a new CMOS chip with a 50% smaller gap between the micro lenses compared to 10D or 300D.
In addition there is less transistors in the pixel sensor which increases the light collecting area.
This all will increase the quantum efficiency compared to former models.
Noise generating electronics
A new amplifier for readout will decrease the readout noise.
Canon states that the ISO 1600 of the 20D has the same noise than the ISO 400 of the 10D.
Therefore the ISO 3200 should make much more sense than in the modified 10D or 300D models which is comparable to almost 2 full stops.
In my 300D the red/magenta amplifier glow at the right side of the chip was very present.
In the 20D the amplifiers will be be powered down during long time exposure.
Next to a drastically reduced glow there is also the benefit of increasing the life time of the batteries.
Dark frame subtraction
The 20D allows to switch on an automatic dark frame subtraction mode.
I do already know that from my Minolta Dimage 7i.
No doubt, this is an excellent way to reduce noise without losing sharpness or any other image infomation.
The price to be paid is: 5 minutes of exposure will take 10 minutes of time.
But that is for sure worth the effort.
This feature might in deed lead to a new dimension in "consumer" SLR astrophotography.
Other improvements
The camera now comes with USB 2.0 support.
The download speed of images to the PC is therefore about 10 times faster than 300D.
The mirror-lockup feature will prevent long telephoto lenses from shaking like my 300D did.
Good for imaging planets and the moon.
The 20D is capable of doing more frames per minute than the older models.
Still slower than a WebCam, but worth a try for the planets.
Darkframe of 20D compared to 300D
All darkframes were taken at room temperature and exposed for 5 minutes.
The images are 100% resolution and taken from the right part of the frames where the amplifier glow is at it's maximum.
As you can see the switched of amplifier is not generating the redish glow known from the 300D.
The right most dark is showing the dark with dark subtraction.
It renders the remaining noise when the noise reduction feature is switched on.
| 300D dark |
20D dark
with noise reduction off |
20D dark
with noise reduction on |
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Conclusion
The Canon 20D seems to be a big improvement for astrophotography.
Search photos taken with the Canon EOS 20D
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