I took a series of test images using a new full frame (1.0 crop factor) Canon 6D for comparing to test images of other Canon DSLR (1.6 crop factor) APS-C models popular for astro imaging. The test images include long exposure dark frames and also images in bulb mode to compare long exposures for sensitivity. Some info on the 6D model along with tests and comparison results follow.
6D Specifications:
In chart above are specifications for a few of the Canon models that are available for sale at this time and are popular for astro imaging. The prices are based on refurbished body only kits available from Canon, and online camera shops such as B&H Photo and Adorama. A more complete listing of models dating back to 2003 can be seen HERE.
The 6D model became available in November 2012. It was advertised as the world's smallest and lightest full frame DSLR camera for prosumer photographers. I bought my first DSLR in 2003, the 1.6 crop factor Canon 10D. The 6D model is a little lighter and smaller than it. For the 6D model, Canon did not include a built-in pop up flash but instead added built-in Wi-Fi and GPS. The advantage of having a lighter camera for astro imaging is important to most, in order to avoid extra stress on the telescope's focuser. From the chart above you can see that the sensor of the 6D has pretty large pixels and they are larger than that in Canon's other full frame models. Larger pixels usually means increased sensitivity, but testing will tell. The 6D model gets the highest rating for Canon camera sensors in testing done by DxOMark Labs.
Canon's other full frame model, the much higher priced 5D Mark III has some features that the 6D does not have. They include 61 AF points instead of 11 AF points, multiple card slots instead of a single card slot, and a built-in headphone jack for monitoring audio. Those differences don't matter for astro imaging. Other specifications of the 6D are:
One of the features of the T3i, T4i and T5i models that I do miss on the 6D is an articulating screen. An articulating screen allows the display to be easily flipped out to the side and pivoted up or down 270 degrees and avoids having to bend into awkward positions to see the camera back display or cricking your neck.
The 6D's high ISO setting of 102,400 should be very useful for liveview focusing and framing of astro images. The fastest speed the 6D can capture video useful for planetary, solar and lunar imaging is in its 1280 x 720 mode at 60 fps. One thing I noticed right away with the 6D is that it has a very quiet shutter and also has a "silent shutter" mode. For regular daytime burst imaging, the frame rate in "silent shutter" mode is reduced to 3 fps from the normal 4.5 fps when silent mode is not selected. For long exposure deep sky astro imaging, this might be a useful feature to reduce vibrations.
This review is from an astro imaging perspective and focuses mainly on camera features that are most important for astro imaging. You may want to see other camera websites for normal daytime imaging reviews of the 6D model if you plan to do regular photography or infrared photography with a modified camera. The Canon models tested and compared here for long exposure dark frame noise were all non-modified. For the sensitivity tests a Full Spectrum modified 6D camera using the Astronomik MC Clear Glass was used. The clear glass replaces the anti-aliasing filter, so provides sharper images with increased detail as explained HERE. Astronomik now has the MC Clear Glass replacement in a size that fits the 6D model. The T2i and T4i models used for the sensitivity tests were non-modified.
The 6D body is larger and heavier than 1.6 crop factor bodies, but not by much. A comparison is shown below comparing it to the T3i and T4i models.
Dark Frame Noise Testing:
My first testing with this camera model was to take a series of 5-minute dark frame exposures at room temperature and ISO 1600 over a two hour period as was done in previous testing that I have done for the 450D, 500D, 550D, 600D, 650D, 700D, 1000D and 1100D models. A 15-second delay was used between each exposure. Camera settings were adjusted to be similar to those used for other models and found to be most conducive for astro imaging. All testing was done at room temperature. The settings information from Canon's DPP for the 6D, 600D and 650D camera dark frame test images is below. Please note that the setting of "High ISO speed noise reduction" was disabled for all models tested:
Below are the histogram displays using Canon's Digital Photo Professional software for the initial 5-minute ISO 1600 dark frame exposure of eight Canon models for comparison.
As seen in the above graphic, the 450D model that was king for lowest noise is now matched or slightly bested by the 6D. The 1000D continues to have the highest level based on DPP histogram displays. The initial 5-minute dark frame noise of the 550D and 600D are similar with the 650D being slightly better. For the purpose of these tests, please be aware that the dark frame noise levels for cameras of the same model type that I have tested over time can vary from unit to unit as discussed HERE.
The image below compares the initial 5-minute ISO 1600 dark frames of eight Canon models. RAW dark frame files were converted to 16-bit TIF files using Canon's DPP software and the TIFs were then cropped at center to 300 X 300 pixels using Photoshop CS5. The 6D image has the lowest noise.
For the Full Frame TIF dark frame images, image pixel standard deviation values for luminosity of the initial dark frames were recorded using Images Plus for all eight Canon models and are displayed in the graph below:
The histograms for four camera models are shown below, for both the initial 5-minute dark frame and the last 5-minute dark frame of the two-hour imaging sessions. The 6D model has the lowest dark frame noise level at the end of the two-hour period based on the histogram display. Between the four cameras, the 600D has the highest noise level at the end of the imaging session based on the histogram display.
The image below compares the final 5-minute (after two hours) ISO 1600 dark frames of four Canon models. RAW dark frame files were converted to 16-bit TIF files using Canon's DPP software and the TIFs were then cropped at center to 300 X 300 pixels using Photoshop CS5. There is almost no noise in the 6D image:
For the final Full Frame TIF 5-minute dark frame images (end of 2-hour period), image pixel standard deviation values for luminosity were recorded using Images Plus for five Canon models and are displayed in the graph below:
For the 5-minute dark frames taken continuously over a two hour period, I recorded the EXIF temperature readings from the RAW dark frame files over the two hour period for all eight camera models and plotted them below. With each new in-camera video capture model, Canon has been able to lower the internal temperature recorded in the EXIF data and that is again apparent with the 6D.
Sensitivity Tests:
For the sensitivity tests below, the cameras were powered with fully charged batteries and the same 16GB SD card was used to store the RAW images. The 6D camera was Full Spectrum modified with a UV/IR clip filter installed and a custom white balance setting was used. The T4i (650D) and T2i (550D) cameras were non-modified with a Daylight color balance setting used. 5-minute bulb exposures were taken using a digital timer remote for all three cameras. The viewfinders were covered to block any ambient light in a darkened room. A Canon Zoom EF 28-135mm IS Lens was used at 135mm and F32 with the cameras set at ISO 1600. For all three cameras, in the Custom Functions menu item, long exposure noise reduction was turned off and high ISO speed noise reduction, highlight tone priority, auto lighting optimizer and peripheral illumination correction were all disabled. Liveview focusing was used at 10X zoom for all three cameras. Imaging was done in a dark room with a 5 watt incandescent lamp in one corner of the room. The lamp was covered to limit the amount of illumination for the testing using 5-minute bulb exposures. This was done to crudely simulate astro imaging of a faint deep sky object. Dark frames were not subtracted for the first test images.
Full Frame screen dumps from Canon's Digital Photo Professional "thumbnail with information" view:
Notice that the 6D image above has a wider Field of View because the 6D is a full frame camera as opposed to the other two 1.6 crop factor models.
For this comparison, the RAW Full Frame of each camera was converted to a TIF file using Canon's DPP, aligned, cropped and saved as a JPG file. The 6D image crop was enlarged to be the same size as the two other 1.6 crop factor cameras:
Based on the stamp images above, the 6D image is much brighter than the other two and has a less noisy appearance. Keep in mind that no dark frames were used for the above 5 minute exposures.
For the comparison below, a similar procedure as above was done, but this time each TIF image was calibrated with one dark frame using Images Plus software:
For the above dark calibrated comparison images, again the 6D image appears to be best by far.
As would be done for astro images, for the above dark calibrated images I adjusted the color balance using levels and curves in Photoshop and attempted to get each image brightness level nearly the same. There is a lot of yellow in the processed image because of the weak incandescent light that was used to illuminate the room and the room wall colors that were reflecting light.
Summary:
Based on my review and testing of the 6D camera and earlier Canon camera models, these are the key 6D features I found most applicable for astro imaging:
What I didn't like:
Additional test results for comparisons of the Canon Digital Rebel T4i (650D), T3i (600D), T2i (550D), T1i (500D), XSi (450D), XS (1000D) and T3 (1100D) can be seen HERE.
For discussions on DSLR modifications and cooling for astro imaging, please consider joining the DSLRmodifications Yahoo Discussion Group HERE.
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