and Autofocus of Modified Camera:
The calculations and measurements
used to correct the focus point to that of the original unmodified
camera are discussed on Page 4 above.
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
and test chart by Bob Atkins on photo.net. 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.
The test setup I used was:
For the image below, autofocus
was used to focus on the straight horizontal line in the center
of the test chart:
For the image below, manual
focusing was used to focus on the straight horizontal
line in the center of the test chart:
A number of test images as above
were taken to confirm the point of focus. The lines on the test
chart labeled 1, 2 and 3 correspond to distances of 1, 2 and 3
cm. My results were the same as for those of the camera that Bob
Atkins tested on the above referenced site.
I plan to replace the Canon viewfinder
screen with a clear focusing screen for astrophotography. It is
important to do the above test before replacing the focusing screen
to check the camera's focus point.
Terry Lovejoy, on
his site, describes a method of fine tuning the camera's autofocus
by using an AF adjustment screw located in the shutter compartment.
To access the adjustment screw you need to use the camera's "sensor
clean " feature on the camera's menu to swing the mirror
out of the way. Here is a photo of the autofocus adjustment screw
location with the camera in the "sensor clean" mode:
I did not have to make any adjustments
to this screw for my camera after modification.
The true test for astrophotography
will be confirming the accuracy of viewfinder focus for star images.
Check back here for star test results.
Continue to Page 10:
Daytime Testing with Color Correcting Filter