Optical sighting system for big telephoto lens bird photography

Red dot sight setupAfter investing in a more serious telephoto lens setup for bird photography, I learned that acquiring and tracking birds in flight can be one of the trickier aspects for getting good BIF (Bird In Flight) images.  If you consider 500mm lens on a camera with a 1.6x crop factor and a 1.4x teleconverter to boot, then you end up dealing with a magnification of about 22.4x when normalized to a 50mm lens on a full frame 35mm equivalent camera.  Trying to acquire a bird flying by through your lens at this magnification, and then tracking it such that you can maintain focus lock can be quite a challenge.  A gimbal head for your tripod definitely can help, but I figured that after such an investment that perhaps something more could be done to help.  

That is when I noticed that some hunters use what is called a red dot optical sight.  This is similar in appearance to a normal scope, but shorter and typically with no magnification.  Instead of cross hairs, you have a small LED illuminated red dot focused at infinity at the center of the sight.  Because there is limited or no magnification, it is has a wider field of view and relatively easy to find your target while viewing through it. Both have the same objective of try to acquire and lock on to a target in-flight.  If it can work for them, then why couldn’t the same capability be adapted for the camera instead of the gun?   

After going to a few sporting good stores, I decided on a Tasco 42mm sight that mounts on to a rifle using a standard weaver scope mount with a cost of about $65.  There are cheaper ones out there, and more expensive versions as well, but this one struck me as being of sufficiently quality (all metal construction) and having a relatively wide field of view.  Weaver mount adapterThe next step was to figure out how to adapt a weaver mount to my camera rig with the big lens attached while on a gimbal mount.  So at the gun store, I also purchased a weaver mount adapter plate designed for attachment for various rifles.  I was not sure how I was going to make it work, but at about $10, I figured I would come up with something after getting home and tinkering around in the garage.  

Hot shoe weaver mountAt first I explored the idea of mounting the sight on the hot shoe of the camera.  Going on the internet and looking for hot shoe adapter brackets, I also learned I was not the first to come up with this idea, and that in fact someone has a business of selling weaver mounts that lock into your camera’s hot shoe.  It is called "Xtend-a-sight" and I ordered this from Photosolve (it cost about $25), but after trying it I was not satisfied with the results.  The way this attached to the hot shoe was not sufficiently rigid. It also tended to bend the camera hot shoe bracket outward to create enough tension to hold it in place. But no matter how much tension I applied on the locking allen screw with this bracket, it would continue to wobble with the red dot sight attached. It seemed like a bad design to me, and caused me concern that it could eventually cause permanent damage to the hot shoe on my camera body if I continued to tighten it further.  

Through the sightI then settled on the idea of using a right-angle flash bracket that screws into the 3/8” mounting hole at the bottom of the camera.  I already owned one and noticed that it seemed to be sufficiently rigid and heavy duty in construction, and speculated that one could be retrofitted to hold a red dot sight instead of a detachable flash head.  So I ended up purchasing a lower end cheap chinese knock-off for about $15 for this purpose that was of sufficient girth to support the weight of the sight and not wobble or bend out of alignment too easily while in use in the field.  

The next step is to replace the hot shoe at the end of the right-angle hot shoe bracket with a weaver mount adapter plate instead.  This ended up being relatively easy to do:

  1. With the flash bracket in a vise, drill out the rivets holding the hot shoe plate and remove it.  In my case, I was able to use these rivet holes as the basis for mounting the weaver mount adapter plate.  Two holes at a minimum will be needed, but if you have the space, three would provide more stability.
  2. Manually align the weaver mount adapter plate on the flash bracket the way you would like to see it positioned with the red dot sight attached while in use with the camera.  As a general guideline, you should position the back of the sight roughly at the same distance to the viewer as the back of your camera.
  3. Once you have this aligned to your satisfaction, place marks with a pencil on the weaver mount adapter plate through the holes of the flash bracket where you will drill.
  4. Acquire 2-3 fine machine screws (black anodized would be nice) with locking washers and nuts that will be used to mount the two pieces together. The heads of these screws also need to clear the red dot sight bracket hardware when it is attached.
  5. With the weaver mount adapter plate in a vise, drill the marked holes in step #3 at a diameter to accommodate the machine screws acquired in step #4.
  6. Connect the two pieces together with the machine screws, using the lock washers and nuts, and viola!  

You have a red dot sight based setup for high performance bird photography.   The total cost for this project was about $100.  You could build it even cheaper by settling on a lower end red dot sight, but I am not sure I would recommend that.  

The next step is to calibrate this setup and put it through some field trials.  The first thing I realized is the importance of having spare batteries. The Tasco sight has no auto-off and I had apparently left the red dot sight “on” while stored in my bag or from the last time I had been experimenting with it.  This model uses a standard CR2032 battery and lasts about 4-8 hours according to the gun shop owner.  So on my 2nd trip after purchasing some spare batteries to have in the bag, I was off again to one my favorite birding locations.  

Rear view of sight setupSet this up by screwing it into the mounting hole at the bottom of my camera as a last step after first attaching the telephoto lens onto the camera and attaching the whole thing on the gimbaled tripod mount.  To sight align this setup, first lock the camera down with the gimbal head on a target at about the same distance you expect to be taking most of your BIF related photography from.  Rough left-right (windage) alignment should be achieved by simply loosening the bracket mount to the camera and pivoting in either direction, and then tightening it down.  Fine adjustment should be done by unscrewing the elevation and windage adjustment protective caps on the sight itself, and then tweaking the adjustment screws until the red dot matches the target that you have set for the center focus mark as seen through the viewfinder of your camera. If you don’t have a screwdriver with you, a dime or a penny can work pretty good. This alignment exercise needs to be applied after every setup, but should only take about 5 minutes to complete.  

Now that I may have gotten some folks excited about this, I must now confess: The results of this effort have not been as positive as I was expecting. Although it is now much easier to acquire a target through the red dot sight and track it across the sky, one challenge has been the magnification disparity between my 500mm telephoto lens setup with the 1.4x teleconverter is too much with respect to the red dot in the sight.  The area covered by the red dot in general is much larger than the area of the center focus mark as seen through the viewfinder of my camera at this magnification.  Even when you think you are locked on the target, it may still not be close enough for the camera focus lock using the center focus sensor only.  I have found that this disparity is not as bad without the teleconverter attached to the lens (i.e. just 500mm), but also the need to use this sight diminishes accordingly.  Perhaps part of the issue is that personally over this same time, I have gotten more experienced and skilled in the tracking of birds through the big lens without the need for the red dot sighting system (see my Bird Gallery).  I have found in critical situations I tend to put more trust in my ability to acquire the bird via the camera viewfinder than through the red dot sight.  Another factor is that my current camera setup is based on a Canon 50D.  The new Canon 7D has a better auto-focus capability that almost seems designed specifically for birding related photography.  From what I have read, the 7D supports a focus mode that allows you to use a smaller cluster of auto focus sensors grouped toward the center together.  I would expect this to be much more friendly for matching up to the area of uncertainty covered by the red dot via the separate sight and acquiring focus lock.  Another suggestion that could help is to get a red dot sight that has a slight magnification to it.  Perhaps something in the range of 2-4x would be a good compromise between having sufficient field of view to find your target, but magnified sufficiently to properly align the red dot to your camera’s auto focus sensor?  

Stay tuned for further results in the future…  

If others have additional inputs or learnings on this, feel free to send me an email I will append them to this article (Sorry I currently don’t have a blogging capability with this web site, as I am new to web development and learning to do this as I go).