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Checking Manual and
Autofocus of Modified Camera:
Replacement with Baader
filter: Since the
Baader replacement filter used for the 450D and 1000D modifications
is the same thickness as the original Canon IR filter that was
removed, the manual and auto focus operation of the modified camera
through the viewfinder remains unchanged, but it is good to check
anyway to be sure no problems were created during the mod procedure,
such as a misplaced shim. For a Full Spectrum modification with
an Astronimik MC Clear Glass replacement, reshimming or sensor
adjustment is required and focus tests should be made. For any
type of modification to the 500D or 550D, the focus tests should
be made since there are no fixed positions for the imaging sensor.
Replacement with other filter
or optical glass: If a different thickness replacement
filter or optical glass is used instead to replace the original
IR filter, calculations would need to be made to correct the focus
point to that of the original unmodified camera. The thickness
of the original Canon 450D IR filter is 0.57mm, much thinner than
the 300D IR filter. This is because of the stacked multi-filter
arrangement of the self cleaning filter/imaging chip assembly
that can be seen Here. The calculations
for determining the amount of shimming that would be required
if a replacement filter or optical glass of a different thickness
from the original IR filter are discussed Here
for the Canon 300D. The location of the shims needed to be added
or removed for the 450D are shown in Step 35 Here.
A procedure for re-shimming the imaging sensor for a Full Spectrum
modification with the Astronomik MC Clear Glass replacement is
Live View Focusing:
The Canon 450D has a "live
view" feature that uses the image recorded directly by the
camera's CMOS imaging chip. Using "live view" focusing
achieves the best focus if it can be done accurately. The "live
view" image can be displayed for focusing on the camera's
display or a computer display using a USB connection. "Live
view" focusing works well for astronomy since the object
being imaged is stationary and can be magnified (zoomed in) to
check for precise focus . There are two "live view"
focusing modes on the 450D, "live view manual focus"
and "live view auto focus". For true "live view
auto focus" operation, the camera's custom function setting
Fn-8 (AF during Live View shooting) should be set to setting "2.
Live mode". The Canon owner's manual states Live View Auto
Focus can fail to achieve focus for the following: "subjects
in low light", "night scenes or points of light",
"extremely small subjects", or "subjects strongly
Traditionally, focusing of SLR
and DSLR cameras has been through a viewfinder by eye. A diagram
of a typical DSLR camera can be seen on Leon Goodman's site Here.
The light path from the camera lens to the viewfinder's focusing
screen needs to be the same as the light path to the imaging chip
in order for manual or autofocus to be accurate. There is the
rub....if the light paths differ, focusing will be inaccurate.
Early versions of the Canon Rebel such as the 300D have an Autofocus adjustment screw for
correcting any discrepancy in the focusing light paths. It appears
that the Canon 450D and the 40D do not have such AF adjustment
screws. The only way I see at this time to adjust for proper focusing
when not using the live view mode would be to disassemble the
camera and re-shim the CMOS imaging chip. The location of the
shims are in Step 35 Here.
Focus Check: To check if the modified camera is achieving
perfect focus, the camera's focus can be easily tested. For testing
my camera after the modification, I used the procedure
by Bob Atkins on photo.net. Mr. Atkins also provides a focus test
if you wish to use it as I did for the focus tests below.
You may want to check the focus
of your camera before doing the modification and if focus is out
of the Depth of Field, return it for repair.
For the test setup I used:
Pre-Modification: First test the camera's focus by using
the liveview mode feature. Use the camera's time delay setting
of at least 2 seconds to avoid any blurring from camera shake.
Aim the camera so that the center line of the focus test chart
is well centered. Use the 10X magnification mode in liveview to
zoom the image of the line. Manually adjust the focus of the lens
for precise focus. Take a few images while refocusing between
exposures. Compare these images using a slideshow program to be
sure that they are consistent. Select one of these images as the
"control" focus test image. Since you have focused the
test chart using liveview, which shows on the camera back LCD
display exactly what the imaging sensor is capturing, this is
the best focus that can be achieved with that lens.
Manual focused test image
using liveview at 10X magnification:
Next, change the camera lens to
Auto Focus. Make sure the camera's "AF Points" setting
is set to use the center AF point only. Take a test image. Switch
the camera lens back to manual focus and rotate the camera's focusing
ring past focus, on the other side of focus. Switch the lens back
to auto focus and take an image. Repeat this process a few times
so that you have a collection of test images that were taken with
the camera lens motor trying to "Auto Focus" in both
clockwise and counterclockwise direction. Review the test images
using a slideshow program. The test images will show how well
your camera and lens returns to the same focus point.
Auto focused test image:
Comparing the auto focused test
image above with the manually focused liveview "control"
test image taken earlier, shows that the pre-modified camera's
autofocus function is working well.
Post-Modification: The above tests should also be made
after the modification is completed and examined for any front-focus,
back-focus or tilt issues. My post-modification test results are
The test images above show that
good focus and tilt has been maintained in the modified camera.