wwp@yahoogroups.com:
Re: Sigma 8mm
Hans Nyberg 2006-Jul-13 16:36:00
On 13/7-2006, at 17.53, Eric Anderson wrote:
> I am trying to get some information of a lens choice. I have read a
> lot of the reviews and specs of various wide angel lenses but I need
> some input from folks that use the lens. I have a Tamron 11-18mm and
> find it a very fair lens. I am thinking of either replacing it with a
> Canon 10-22 or adding a Sigma 8mm. I read somewhere that the image
> from the Sigma 8mm on a Canon 20D is not centered. Is this true? What
> are the issues creating panoramas with the Sigma 8mm using PTGui? Is
> it easy to correct the lens with PTLens?
NO lenses are centered on digital SLRs
Or said in another way, almost all sensors are not centered but
displaced by usually 5-20 pixels vertically and horizontally.
When you know that 20 pixels is less than 0,1mm this is very
understandable.
Also the sensors has to be able to move a little due to temperature
differences.
It is usually easy to compensate for this as PTGui and PTMac can
optimize for it.
Doing this with the Sigma or any other fisheye where you can see the
circle in the image is actually very easy as you can directly measure
it.
With an image which fill all the sensor you have to take some images
which you can optimize it after.
The only thing you have to think of when using the Sigma 8mm with PTGui
is that you have to download a special panoramatools version which
supports 180 degrees.
You should also know that RealViz is in a few days releasing a new
version which has support for fisheyes.
Regarding the Tamron I believe it is just as good as the Canon but you
have to do some test for the correction.
Most of the 10-11 mm rectilinear lenses has a distortion which needs
special correction.
Hans
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