Which would be sharper, this Tamron zoom (at 560mm), or a Canon 400 f/4L DO + 1.4TC at 560mm (either a ii or iii TC)?
I know that particular Canon is supposed to be less contrasty because it's a "DO" but it's not supposed to be soft...it's supposed to be fairly high in resolution. The images I've seen from it, look extremely sharp to me...far sharper than the 100-400L. And none have lacked any contrast that I would want to add to.
Just debating whether to rent a 400 DO...they intrigue me. It weighs about the same as this Tamron...and is f/4 at 400mm, rather than f/5.6. I know it costs a lot more, but used (and refurb) prices have been known to dip down quite a bit below the full retail (might even get below $4k sometime). And it can be rented for 4 days for around $200.
It gets a pretty scathing review by TDP http://www.the-digital-picture.com/Reviews/Canon-EF-400mm-f-4.0-DO-IS-USM-Lens-Review.aspx
The image quality with 1.4x TC looks poor there.
I don't see the "scathing" part of the review. Also don't see a sample where it's combined with a TC.
Bryan usually writes about lenses in glowing praise. But this is what he writes about the 400/4 DO, quote:
"The apparent sharpness of this lens is not in direct relation to its price. The Canon EF 400mm f/4 DO IS USM Lens is reasonably sharp at f/4 and very sharp when stopped down to f/5.6. But it is not as sharp as the Canon EF 300mm f/2.8 L IS Lens (few lenses are). The 300mm f/2.8 L IS with a Canon 1.4x Extender attached (yielding a heavier but less expensive 420mm f/4 IS lens) is similar to the 400 in sharpness. The Canon EF 500mm f/4 IS L Lens is sharper as well (similarly priced but nearly twice as heavy). The much smaller, lighter, slower (max aperture) and far less expensive Canon EF 400mm f/5.6 L Lens and Canon EF 100-400mm f/4.5-5.6 L IS Lens compete very well with the DO in sharpness at f/5.6 and are even sharper in the corners (and one of them is a zoom).
Contrast is the Canon EF 400mm f/4 DO IS USM Lens' optical shortcoming - which also hurts the apparent sharpness performance. I found that most of my shots needed a healthy contrast boost in post-processing (or a positive in-camera contrast setting). I could easily tell which image was taken with the 400 DO when looking at comparative shots on a monitor. The 300 f/2.8 IS has much better contrast than the 400 DO. Even the Canon 100-400mm L has better contrast when the vignetting in the full frame corners at 400mm does not get in the way. Low contrast is my most-significant disapointment with the 400 DO - fortunately it is something that post-processing can help."
(Note the comparison with the 300mm f/2.8 is with the less sharp series I lens, which does not take 1.4xTC as well as the series II does).
And, here is a direct comparison of the 400mm DO with a 1.4xTC vs the 400mm f/5.6 at 560mm, with the DO stopped down to the same f/8 of the older lens. The 400mm f/5.6 is significantly sharper http://www.the-digital-picture.com/Reviews/ISO-12233-Sample-Crops.aspx?Lens=338&Camera=453&Sample=0&FLI=3&API=3&LensComp=278&CameraComp=453&SampleComp=0&FLIComp=3&APIComp=1