HarryLally
03-04-2013, 04:18 PM
I tend to agree with you2....i.e. I don't understand either. Why would changing a physical aperture on a lens change the point of focus? Does anyone know the mechanism for this?
Quote:Why would changing a physical aperture on a lens change the point of focus? Does anyone know the mechanism for this?http://toothwalker.org/optics/spherical.html
Quote:You could of course suggest instead that the camera refocuses when you finally press the shutter button. However, that would probably lead to some sort of shutter lag.There already is a lag time, due to setting the aperture. I once tried to measure the aperture movement speed of the Canon 50mm f/1.8 and concluded it was a little too slow for the full fps of the 7D. I don't know how much aperture settling time they allow, but possibly the minor focus nudge could be done in that time with minimal impact.
Quote:The macro performance is not all that hot at 70mm @ f/4
Quote:From the review:
The lens is designed so that you extend the lens PAST 70mm when attempting close focus shots. I wonder if the softness at f/4, 70mm, and close focus would be solved by turning the zoom ring further toward the "Macro" mark. This seems too obvious to be the case, but I thought I'd bring it up in case something was overlooked.
The complexities of including the Macro feature probably account for some of the asking price, and make Macro somewhat of a headline feature for this lens. Therefore it seems odd that there were so many problems with the Macro mode. Did you take any "real life" sample shots that really exercise the Macro mode? It would be nice to see how the curiosities seen in the lab translate into real life experience.
EDIT: The Tamron 24-70 seems similarly soft wide open, but this wasn't really mentioned as a problem in that review. Is there a functional difference between the performance of the Tamron at 2.8 and the Canon at 4? Is it because the Canon is labeled a Macro lens? I'm trying to decide between the on-paper flexibility and compact nature of the Canon and the wider aperture of the Tamron, and the RSA/LoCA sections of the two reviews show very similar performance characteristics.
Quote:however i don't see why Canon can't put in compensation no matter which mode (Tv, Av) the camera is in, if the camera and therefore lens knows what the correct exposure is, it can then put the comp in for the aperture, no? ... but to do this the manufacturer would have to admit that my lens has a problem...Wow, the overhauled forum software is not without its bugs... Took me 6 tries to get this part quote correctly (well, I have not posted it yet, so it might still be wrong.. and then I can't edit the post anymore...).
Quote:...... How bad is the focus shift in "normal" use? And how bad is the focus shift in macro use? And does it occur over the entire focal range?