I took a series of test images using a new Canon T4i (650D)
for comparing to test images of other Canon DSLR 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 T4i along with tests and comparison
What camera features are new?
These are the main features Canon added to the T4i model that
the T3i model does not have:
What camera features are missing?
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 T4i model if you plan to do regular photography
or infrared photography with a modified camera. The Canon models
tested and compared here were all non-modified. A Full Spectrum
modified camera using the Astronomik MC Clear Glass, that replaces
the anti-aliasing filter, would provide sharper images with increased
detail as explained HERE.
Touch Screen Display:
This is the first time Canon has added a touchscreen feature to
a DSLR model. The articulating screen is similar to that used
on the T3i and is the same size and resolution. The touchscreen
is contact sensitive as opposed to being pressure sensitive. I
have been using Canon DSLRs for many years now on nearly a daily
basis and prefer using the camera buttons over the touchscreen.
I'm sure that is due in part to not having prior experience with
using the touchscreen feature and that I also have large fingers.
For astro imaging one might think there is an advantage of using
the camera buttons instead of having to look at the display, but
even with the buttons you need to check the display for the feature
you are changing. One button that was left off the T4i model is
the Display (DISP) button and I use that button very often on
the other models. For the T4i you can turn the display off by
using the INFO button as a toggle switch. The touchscreen feature
can be disabled using the camera menu.
As with the T3i model, the articulating screen feature can
be a very useful one for those using the camera back display,
as opposed to a computer screen for astro imaging. This avoids
having to bend into awkward positions to see the camera back display
or cricking your neck. If the camera is mounted in a telescope
focuser, piggybacked on a telescope, or tripod mounted; the display
screen can be easily flipped out to the side and pivoted up or
down 270 degrees. The display screen can be positioned outward
in its normal position on the back of the camera as with non-articulating
screen models or completely turned facing inward, so the LCD display
is not seen. This is a good feature to avoid errant light emitted
from the display at dark sky sites and also to protect the LCD
display glass from scratches.
Kit Lens: The T4i camera kit can be purchased with the
EF-S 18-55mm f3.5-5.6 IS II zoom lens that Canon has been providing
with the T3i model. Canon is also selling the T4i as a kit with
a new EF-S 18-135mm f/3.5-5.6 IS STM zoom lens. The "STM"
designation stands for stepper motors used in the lens for autofocusing,
that is silent and faster than with non-STM lenses. The STM feature
has little use for astro imaging but is very useful for non-astro
video because other non-STM lenses make a lot of focusing noise
when capturing audio with video. I purchased an external mic for
my T3i camera and still had a lot of focussing noise recorded
when taking video using the 18-55mm kit lens.
The T4i body is basically the same size and weight as the T3i.
See the table below. The T4i and T3i, because of their larger
size over previous models will not fit inside the Whole
Camera Peltier Cooler if built to the dimensions on my web
T4i and T3i compared side by side:
In the first photo above, notice that the T4i (on left) has
two built-in microphones on the camera flash. That is for stereo
audio recording. The T3i has only one built-in monaural microphone
but the external jack can be used for stereo. Also notice in the
T4i photo, the top selection dial now has three positions: Off,
On and Movie. For previous Canon models this selection switch
has two choices, Off and On, as can be seen in the photo of the
T3i. When using the T4i camera for the first few times, when I
used my thumb to turn the camera on, I was moving the selector
past the "On" position and instead all the way to the
Movie mode. I found that frustrating, but it was caused by force
of habit. Also notice that the display (DISP) button is missing
on the T4i as discussed earlier.
The chart below has some key specifications for the T4i that
can be compared to six other Canon models popular for astro imaging
at this time. Notice that the T4i has the same number of effective
pixels (18.7 million) and same pixel size (4.3µm) as the
T3i. The T4i is now using a Digic 5 image processor as opposed
to Digic 4 used in the T2i, T3 and T3i models. The T4i camera
continues to use the same LP-E8 battery.
For planetary, lunar and solar imaging, the Canon camera model
that has stood out because of its special "movie crop mode"
is the T2i (550D). In movie crop mode, only the center 640 X 480
pixel area of the CMOS imaging sensor is captured at a speedy
frame rate of 60 frames per second. The movie crop mode provides
a 7X fixed zoom without video interpolation. This feature is not
available on the T3i. Instead, a similar feature "Video Digital
Zoom" is a function of the T3i that captures the center of
the imaging chip, in a cropped zoom mode that is adjustable from
3X to 10X magnification. A drawback of the Video Digital Zoom
feature for astro imaging is that the capture rate is limited
to 30 frames per second, half the capture rate of the T2i. As
an example, if imaging Jupiter with a 2 minute video, the T2i
at 60 fps can capture 7200 frames from which to select the most
detailed frames for stacking. Using a T3i at 30 fps would capture
3600 frames. I have an example of Jupiter taken with the T2i movie
crop mode here.
The T4i model has dropped both of these handy crop video modes
so loses some functionality of the previous models especially
for planetary, lunar and solar imaging.
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
that I have done for the 450D, 500D, 550D, 600D, 1000D and 1100D.
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 550D, 600D and 650D camera dark frame test images
Below are the
histogram displays using Canon's Digital Photo Professional software
for the initial 5-minute ISO 1600 dark frame exposure of all seven
Canon models for comparison.
As seen in the
above graphic, the 450D continues to have the lowest initial 5-minute
dark frame noise with the 1000D having 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
The image below compares the initial 5-minute ISO 1600 dark
frames of all seven 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 600D image appears to have 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 seven Canon models and are
displayed in the graph below:
for three 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. Surprisingly, the 650D model maintains the lowest
dark frame noise level at the end of the two-hour period based
on the histogram display. Between the three 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 three 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 less noise in the 650D 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 all three 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 seven 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
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. 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 70-300mm 1:4-5.6 IS
USN Lens was used at 300mm 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.
screen dumps from Canon's Digital Photo Professional "thumbnail
with information" view:
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:
Based on the stamp
images above, the 650D image is slightly brighter than the other
two and has a less noisy appearance. If you look closely at the
date "2006" on the stamp, it appears to be a little
smoother than in the other two images. 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
For the above
dark calibrated comparison images, again the 650D appears to have
the less noise.
As would be done
for astro images, for the above dark calibrated images I adjusted
the color balance using levels 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.
Based on my review
and testing of the T4i (650D) and earlier Canon camera models,
these are the key T4i features I found most applicable for astro
What I didn't like:
Check back for test results of the T4i (650D) compared to other
camera models with peltier cooling.
Additional test results for comparisons
of the Canon Digital
Rebel 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.
For my low cost astro & infrared
modification service for your Canon DSLR camera CLICK
DSLR Astro Imaging Guides on CD-ROM by Jerry Lodriguss HERE......