[opendtv] Re: Line Pairs/millimeter vs. Price vs. Image Format Area
- From: "Albert Manfredi" <bert22306@xxxxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Sat, 02 Jun 2007 19:40:05 -0400
Craig Birkmaier wrote:
We are NOT talking about lenses for consumer still photo cameras
Bert. We are talking about high quality lenses for professional HDTV
cameras.
Read the series of articles i posted Bert. For some reason I trust an
expert like Larry Thorpe more than I do you.
Dan Grimes wrote:
Be careful about comparing still lenses and video lenses. Still lenses
are designed for a static moment so they are optimized for certain
qualities (resolution, contrast, MTF, bokeh, etc.) but other qualities
can become second priorities in the design (focus breathing,
linearity during zoom, edge distortions during zoom, fixed front
element, etc.) Video lenses must be designed for performance
during live operation. A still lens can have all sorts of errors and
distortions that don't show up in a still picture.
There are two topics intertwined here. How are movie camera lenses different
from still camera lenses, and what does it take to be a good HDTV camera
lens. The articles Craig posted *only* cover the latter topic.
Everything I've been able to find online on the first subject, i.e. how 35mm
SLR and 35mm movie lenses differ, has, if anything, said that the SLR lenses
have to be *optically* better, but the movie lenses may have to be faster
(bigger aperture) and have to have all the extra mechanical servos for the
zooms. I have also read that since the 35mm movie lenses are marketed to a
different segment of the economy, i.e. professionals rather than amateur
photographers, they are priced differently.
None of the articles Craig posted says anything that contradicts this, nor
do they consider 35mm movie lenses explicitly. In fact, they only make the
point that small lenses are demanded for small and light cameras, and that
they are not optically as good as the bigger ones. (That being the case, the
cheaper price is not be hard to understand.)
And those articles also spend a good deal of time explaining how well a lens
has to measure to be considered for HDTV, and compare this with SDTV lenses.
But what it takes for HDTV is not optically that impressive, COMPARED WITH
the qualities of 35mm lenses. The MTF arguments are included, and the Sigma
site I showed does have MTF graphs associated with the 55 to 200mm zoom. It
shows that this $139 lens, at 30 lp/mm (that's 1.5 Mpel equivalent for APS
size, so keep that in mind), provides contrast between lines of 0.75 to 0.7
throughout most of the frame. This seems more than competitive, as far as
optics goes, if you compare with the MTF in the first and second articles
Craig lists.
I found discussions about conversions of movie lenses into lenses for still
photography. The upshot has always been that this only makes sense if the
movie lens was acquired on the cheap. One guy claimed that the movie
Angenieux 180mm/2.8 lens was not as good as the Canon EOS equivalent.
I read several commenting on the fact that movie lenses don't have to cover
the 24mm X 36mm frame, although that too is not always true. Let's not
forget VistaVision. Then again, it seems that 35mm movie lenses are
typically designed to cover the 24 X 36mm format anyway, according to other
comments.
I've yet to find any authoritative source that explains what *optical*
compromises have to be different between 35mm still and 35mm movie. I did
see claims that 35mm movie lenses and 35mm SLR lenses are derived from the
same optical designs, however. So if that is true, then it stands to reason
that these larger lenses, for HDTV, would NOT be more expensive due to
*optical* considerations. They might be more expensive for the stronger
servos required, and they no doubt would require a bigger a tougher camera
that the 1/2" lenses.
Craig continues to imply that something in the articles he posted makes some
sort of claim to dispute what I say, but this is simply not true. As always,
he is invited to read the articles, first, and to provide factual proof to
back his opinions.
As far as I can tell, providing HDTV lenses and sensors that are based on
35mm lens designs and frame sizes should, by all rights, REDUCE the cost as
far as the *optical component* of cost goes. And as far as I can tell,
meeting the requirements of 1080p HDTV should be quite achievable. But
please, Dan and Craig, do point to something factual I can read that tells
me why I'm all wrong.
Bert
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