Lotusm50 wrote:
Look at how much more out of focus the center dryer is. That is some obvious curvature of field.
It has nothing to do with curvature of field. The sharper corners are due to mechanical vignetting. The iris of the aperture isn't circular when looking through it from the corners of the sensor/film plane, and thus its size is also smaller. This makes the DOF larger in the corners, and it is very common with fast lenses. The reason is simply that the front lens element isn't large enough to achieve a round aperture for light hitting the corners of the sensor. Of course, this gives quite alot of vignetting too.
Edit: With wide angle lenses, you can see a similar effect due to the "cosine^4 rule". At large angles of view, the aperture is non circular when seen from the corners of the sensor. If you cut a circular hole in a piece of paper, you will understand why when you view the hole from a large angle. This also gives larger DOF in the corners and natural vignetting (no matter how large the front element is), but not as bad as seen above.
Makten wrote:
It has nothing to do with curvature of field. The sharper corners are due to mechanical vignetting. The iris of the aperture isn't circular when looking through it from the corners of the sensor/film plane, and thus its size is also smaller. This makes the DOF larger in the corners, and it is very common with fast lenses. The reason is simply that the front lens element isn't large enough to achieve a round aperture for light hitting the corners of the sensor. Of course, this gives quite alot of vignetting too.
The proper term would be optical or artificial vignetting (in the terminology used by Sid Ray). Theoretically, optical vignetting increases corner DOF, but since this type of vignetting only occurs at large apertures its DOF effect is opposed by oblique lens aberrations which lower the corner DOF relative to the center DOF. The aberrations normally win. Fortunately DOF plays no role in the evaluation of a generously blurred background, and you are perfectly right that optical vignetting results in a reduced corner blur. However, we cannot exclude an additional contribution of field curvature to Lotus' observation, although aberrations are ill defined for out-of-focus parts of the image.
Apart from possible curvature of field, there also seems to be curvature of the dryers themselves. Is the 50/1.0L saddled with such conspicuous barrel distortion?
Jonas B wrote:
Some images are not showing any more. If you want to post something but don't have a long term host PM me and I can host it for you, unless the image is very very ugly of course...
Cheers,
--
Jonas
lol
Thanks for all your work on this Jonas! Truly generous and gracious of you.
I can offer hosting as well (an account on my site is all you need). Simply post your own thread or create "communal" threads in either of the galleries and attach your shot(s), then hot-link to them. On my site, they'll appear like http://forum.cogitech.ca/viewtopic.php?f=2&t=29 and you can use just the standard img tags to hot-link them here.
cogitech wrote:
Thanks for all your work on this Jonas! Truly generous and gracious of you.
I can offer hosting as well (an account on my site is all you need). Simply post your own thread or create "communal" threads in either of the galleries and attach your shot(s), then hot-link to them. On my site, they'll appear like http://forum.cogitech.ca/viewtopic.php?f=2&t=29 and you can use just the standard img tags to hot-link them here.
Thank you for commenting on my hard work (at slow times at work only... but anyway).
I had a look at your forum and the feature you implemented for submitting images. How nice it works!
Cableaddict wrote:
Rob, you just HAVE to explain how you did this shot!
I moved the zoom ring quickly during a slow (1/6 sec) exposure. The secret is to move the zoom ring smoothly, so you get an even blur. I was on a tripod too.
Thank you for commenting on my hard work (at slow times at work only... but anyway).
I had a look at your forum and the feature you implemented for submitting images. How nice it works!
