Checking Manual 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.
Gary
Continue to Page 10: Daytime Testing with Color Correcting Filter