Long lenses, crop factor, and tele-extenders

I’m tossing around the idea of buying a long telephoto lens to shoot in some local wildlife refuges and other nature reserves. I’m not a birder, but I am familiar with the birds, plants, and animals in my state. My goal is to capture subjects in unique compositions (at least not dull looking).

My question concerns the camera sensor crop factor and using tele-extenders. Is there a maximum amount of magnification (telephoto) before an image subject would loose quality, such as sharpness, etc.?

If I buy the EF 500mm f/4L IS USM and use it with a 1.6 crop factor camera and then add a EF 2x II tele-extender then 500mm becomes 1600mm at f/8, right?

I’m just wondering if using 1600mm is going to invite concerns that I may find too difficult to be able to handle without fully understanding the limits of my equipment.

Thanks for any and all help.

Telextenders will magnify the inherent shortcomings of a lens. 2x a good lens shows up good, but worse when you have 2x a poor lens! So for that reason the general rule is that most people who don't want to greatly magnify the lens' sins will stick to a 1.4x telextender.

Your math is correct... 500 * 1.6 * 2 = 1600mm equivalent lens on a FF camera at f/8 (which your 20D would no longer autofocus!)

Thanks Wilt. Those are two things I should think about.

Your 20D is the limiting factor if you're going to use the 2x TC w/ the 500 f4. Canon's big guns (300 2.8IS/400 2.8IS/500 4.0IS/600 4.0IS) we're designed to work very well with TC's, even stacked 1.4x/2x.

In good light, I can still get very good results with the 10D+300 2.8IS+2x+1.4x. My AF still works since the camera only sees the 2x.

2x on a 500mm f4 with 20d means you will lose autofocus which is a pretty big deal. Manual focus is not fun with wildlife.

A 500 f4 is going to probably need about $700-$1,200 in tripod equipment to make the magic happen for wildlife.

I'm guessing you would want to use the 500 bare or with a 1.4TC much more than a 2XTC

PhotoScout wrote in post #2207651
If I buy the EF 500mm f/4L IS USM and use it with a 1.6 crop factor camera and then add a EF 2x II tele-extender then 500mm becomes 1600mm at f/8, right?

I’m just wondering if using 1600mm is going to invite concerns that I may find too difficult to be able to handle without fully understanding the limits of my equipment.[

Just to clear up a technical (but important) point - if you put a 500mm lens on the front of a 2x extender, the focal length becomes 1000mm regardless of the camera you put it on. The maximum aperture would be reduced by the equivalent of two stops.

You can say, however, that that combination will provide the same field of view (angle) as a 1600mm lens used on a 35mm film (or "full-frame" digital) camera.

Focal lengths (and all other characteristics of lenses such as aperture ranges, etc.) do not change when you affix the lens to camera with different film/sensor sizes.

This is important for newbies to understand which is why I bring it up here. The new folks read these threads and even if you fully understood what you were referring to, they may not. Thus I like to step in and make sure they completely understand the real facts .