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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 Here.
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 reflecting light".
Traditional Focusing:
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 chart Here 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 shown below:
The test images above show that good focus and tilt has been maintained in the modified camera.
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