Stacked Converter IQ?

[Marvin T. Smith]

I've been experimenting with stacked teleconverters and want some feedback. What do you think of the image quality on this uncropped image? I know I need to remove the out of focus branch, etc., but I just want an honest opinion on image quality. Thanks. Manual focus is a problem with my glasses, but the focus beep apparently works so I am focusing as much by ear as by sight.

Canon 7D, 300 2.8 with both 2x II and 1.4X II teleconverters. If my math is right, this gives me 840mm.
Gitzo tripod and Mongoose head. Early morning light. 1/800 f8 ISO 800 AV manual focus

[Marvin T. Smith]

I apologize. For some reason the link I copied from Flickr (twice) is not working. I forgot to preview my post before submitting. What do I do now?

[Marvin T. Smith]

http://www.flickr.com/photos/89283016@N08/12417408193/

One more try!
Marv

[Doug West]

Looks pretty good to me.

Here's mine: http://www.thebirdphotographer.com/p763290844/e1066f9cc

Mine was captured with a 600 NON/IS lens with the 1.4x and 2x on a Gitzo
with a Wimberley. Manual focus of course.

So it can be done. Normally the people who say something is 'impossible'
haven't actually tried it or don't have the technique.

Doug

[Tim Harding]

Focus and sharpness looks good to me as well. Good job with that much magnification.

[Randall Farhy]

Seems to work well enough if the situation calls for it, is it my eyes or do images taken with stacked converters have more contrast?

[Diane Miller]

Looking at the full image reduced for web presentation doesn't tell you much (at least not what I want to know). Zoom in to 100% to compare.

Two different shots in the wild also won't compare well. Set up a test target -- tape a magazine page with small, sharp type onto flat cardboard and shoot it straight on. Put it in the shade and set ambient light to be way underexposed and use flash to get a very fast shutter speed. Shoot from a tripod with your best technique from the same distance with the bare lens, 1 TC and stacked TCs -- then shoot again moving away each time to frame the same sized subject. Look at them at 1:1 in LR or ACR. That tells you what your best result can be. You will have other issues (camera shake etc) getting sharper shots as the telephoto length increases.

I would expect the stacked converters to show noticeable degradation and you would be just as well off with the equivalent cropping. Would be interesting to find out otherwise, but that's what I've found.

[Marvin T. Smith]

Thanks Diane. This is exactly what I wanted to know. Would I be better off stacking extenders or simply cropping more? You have given me your opinion and a valuable test to try.

[Diane Miller]

I'll be interested in your results. When you go to longer focal lengths you have more issues with stability, but when you crop more you have more issues with noise. And optically, converters are designed to maximize IQ as much as possible with that single converter, but stacking two adds optical issues they weren't designed to deal with. And there is a reason they don't sell a 3x or 4x. There are lots of compromises in lens design.