Live Webcam Focusing

Canon Digital Rebel

by Gary Honis

UPDATE: For more accurate webcam focusing using an Olympus Varimagnifier/webcam setup CLICK HERE.

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.

What I have put together is an easy to make adapter mount for attaching a Philips webcam to the viewfinder of the Canon Digital Rebel. The viewfinder of the Canon 10D is the same as the Rebel and I guess other Canon DSLRs. The webcam can display the view through the viewfinder 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 can be easily placed on and removed from the camera's viewfinder as needed.

Here is the Philips Vesta Pro webcam attached to the Canon Digital Rebel:

For the adapter mount I used a plastic pill bottle. A slot was cut in the lid of the bottle with a razor knife. The slot was cut to the size needed by using the viewfinder eyepiece cover on the camera strap as a guide. The top of the plastic bottle was cut off at an angle as shown below and a hole was cut using a razor knife for a 1/4 - 20 knob used to attach the webcam using the tripod socket:

The nylon washer fills a gap between the bottle and camera tripod socket.

For a solid connection I epoxied the cap to the bottle. This adapter mount allows the lens of the webcam to be rotated for best focus of the viewfinder image. This crude adapter fit surprisingly well on the camera and snapped securely into place. As a first test, I used the camera with a telephoto lens on a backyard bird feeder.

I used GUIDEDOG as shown below in focus mode. Note the webcam image is upside down, since I mounted the webcam so that the camera's LCD display is fully visible. Focus was fast and easy; I used a sun glint on the bird feeder to focus.

Live Video Focusing:

This is the image taken:

I removed the webcam and checked focus with the Olympus varimagnifier and it looked good.

From the above test, daytime focusing works well with the setup. I will try next with imaging through an h-alpha PST scope. Solar focusing has been tough; there are no star images for software like DSLRFocus to lock onto. For infrared and deep sky imaging, if a brighter viewfinder display is needed, I plan to use the SC modified Vesta Pro webcam that can do long exposures. Even if one or two second exposures are required while focusing, the immediate feedback of live video focusing, should make focusing easy and quick.....I hope........testing will tell.

Modification of Canon Digital Rebel Pages:

Part 1: Removal of IR Cut Filter for Astrophotography & Infrared Imaging

Part 2: Plans for Peltier Cooling



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