Saturday, October 20, 2007

Discussion of Extenders for Canon DSLRs

This is in response to Abraham Lincoln's question about extenders to boost the range of his 70-200mm F4 L lens. First off there is no choice but to buy Canon in this case. Canon has a list of which lenses their extenders will work with. In some cases extenders will actually not physically fit the wrong lens, but in many it is that although they will fit, optical performance is unacceptable. It is generally accepted that one should buy extenders designed for a specific lens. I have been down the generic brand route before and it has never worked well.

The second point is somewhat controversial, but most consider the 1.4X to give acceptable results. I have found it to work well on the 70-200mm 2.8L and it is also recommended for the F4 version. Using the extender makes the lens about one stop slower. According to a chart I found, the 70-200mmF4 becomes a 98 -280 5.6 lens which equals a 156-448 mm film camera lens once one factors in the digital rebels 1.6X multiplication factor.

Most do not recommend the 2X extender. I have never tried it on the 70-200mm, but did extensively on the 500mmF4 early on and only got a few acceptable photos. It seemed I could get better results by using the 1.4X and cropping more severely in photoshop. Two seasoned photographers advised against buying it and I wouldn't listen.

Now for the confusing part. This test is by no means scientific and one must bear in mind the quality of pictures is hard to judge at the size we use them on the internet. The acid test would be to print them out.

A flock of Eastern Wild Turkey came into the meadow between 200-250 yards from me. (I still think of distance in a rifleman's terms) and I conducted this impromptu test with the Canon 40D and the 70-200mm 2.8. The birds were continually moving about but they stayed about the same distance. I didn't try for correct composition on the uncropped shots, but basically centered them. Images were shot in RAW and sharpened in Photoshop CS3 along with tweaking
levels. Everything was optimized for the best possible images: ISO 100, tripod, remote release and of course good lighting. Exposure was 1/500 f4.5 without extender and 1/350 f4.5 with extender.
200mm No Extender

200mm 1.4 Extender

200mm Cropped in Photoshop

200mm and 1.4X- Cropped in Photoshop

The bottom line is that it is hard to tell from these pictures if the extender is of value or not as the image holds up well to the cropping in both cases. Personally I wouldn't want to be without one. Although I don't use it often, it does come in handy. Perhaps the biggest lesson to be learned from this is that a photograph can be cropped quite tightly when a good lens is used and conditions are ideal.

Another possible option is the 100-400mm Canon L Zoom. I don't think it can be cropped as severely as the 70-200mm or the 500mm, but it is a very powerful lens which on the Rebel is 640mm 35mm equivalent on the top end. This is about a $1,400 lens. "Salty" is using mine at present and is quite happy with it. I know two other superb photographers who use it as well and all are pleased with it. On the down side it is a push-pull type zoom and gets longer as you zoom in, it also is not as sharp as a prime L lens and has only a 5.6 aperature when at maximum zoom. Its' big pluses is that it has IS, is reasonably sharp, and is a very powerful lens in a relatively small package. It is listed as being compatabile with the 1.4 extender, but it doesn't hold up too well with it and I prefer to avoid using the extender with it.

Here are some links for further information: All are to B&H Photo in New York.

1.4 extender

2x extender

Canon 100-400mm


Anonymous said...

I think you have made a good argument for the 1.4 extender. I have the 70-300mm lens at f5.6 but it doesn't have IS so I have not been able to use it without a tripod and the remote shutter release. I something think I can still do it but I shake or move too much now and just can't get it sharp.

I do appreciate your efforts and links and all of the effort just to answer a question or two. Not many take the time. I try to help folks, like you did me, but sometimes wonder if it helps or not. In my case, and your info, it has helped me a lot. Thanks.

Old Wom Tigley said...

It is good to see this kind of thing going on, lets face it helping each other will only make the whole blogging experiance better for all.