I have been doing astro and infrared imaging with a modified Canon Digital Rebel. My preferred method of focusing has been using an Olympus varimagnifier that fits on the viewfinder of the Canon DSLRs. I have tried the focus assist software programs DSLR Focus and Images Plus for focusing that assure perfect focus. But, I found the USB transfer speed of the Canon Digital Rebel to be much slower than that of the 10D, which I also use. It takes a lot of time to achieve focus using the slow USB transfer rate of the Rebel. I missed the live-view focus capabilities of the Olympus C2000 series digital cameras that I had been imaging with before the Canon DSLRs.
I have also done a lot of imaging over the years with webcams. I have a few Philips Vesta Webcams including an SC Modified Vesta Pro for long exposures.
My first live webcam focusing setup consisted of an easy to make adapter mount for attaching a Philips webcam to the viewfinder of the Canon Digital Rebel. The setup and test results can be seen HERE.
UPDATE: A better setup, that results in more precise focusing, involves using the webcam with an Olympus Varimagnifier. The Olympus Varimagnifier is a right angle finder that attaches to the viewfinder of Canon DSLRs and has a switch that provides a 1.2X and 2.5X magnification. I made an adapter to attach the Philips Vesta webcam to the Varimagnifier as follows.
The completed unit on Canon Digital Rebel:
Modified Canon Digital Rebel with Sigma 55-200mm lens and color correcting filter at full zoom used for all tests
The webcam can display the view through the varimagnifier in real time using any webcam software. Focus is achieved by looking at the webcam display on a computer monitor and adjusting focus using this live video display. The webcam/varimagnifier can be easily placed on and removed from the camera's viewfinder as needed.
Parts used for the adapter:
I had a black plastic pipe that had an inside diameter very close to that needed to slip over the eyepiece end of the Olympus Varimagnifier down to the knurled section. I filed it with a round file a little until I had a secure fit. The parts were assembled as follows:
Assembled unit attached to the Digital Rebel viewfinder:
With this setup, the Varimagnifier/webcam can be used in both the 1.2X and 2.5X modes. The 2.5X mode provides a dimmer viewfinder image and requires an increase in webcam gain. I made these tests near dusk on an overcast day with an unmodified Philips Vesta webcam using its slowest shutter speed of 1/25 second. Below are the "full frame"screen dumps from my notebook for four configurations. I used the software K3CCDTools to display and adjust the webcam settings on the 1024 X 742 notebook display. It has a 100 percent and 200 percent zoom mode, so I used both for the 1.2X and 2.5X varimagnifier settings.
1. Varimagnifier at 1.2X and Notebook Display image at 100 percent zoom:
2. Varimagnifier at 1.2X and Notebook Display image at 200 percent zoom:
3. Varimagnifier at 2.5X and Notebook Display image at 100 percent zoom:
4. Varimagnifier at 2.5X and Notebook Display image at 200 percent zoom:
Here is an image taken using the above focusing setup with the Varimagnifier at 2.5X:
I found all four configurations above to work well for achieving focus, but my preference was the Setup No. 4 which provided the greatest magnification. There is no second guessing the best focus point with the large live magnified image that appears on the notebook display. The first step in focusing is to adjust the small diopter wheel on the Canon DSLR so that the AF points (7 squares with dots) appear sharp and well defined on the Notebook display. Then adjust focus of the camera lens or telescope until best focus is achieved.
It is important to verify that your camera is focusing properly through the viewfinder; see Page 9 of my modification instructions for testing and adjusting focus.
For astro-imaging, which involves focusing on stars of very dim images, I plan to use an SC modified Philips Vesta webcam that is capable of long exposures. Exposures of one or two seconds in length should provide sufficiently bright star images for focusing.
The immediate feedback of live video focusing makes focusing easy and quick.....will report next on results for astro imaging.
Gary