[opendtv] Lens Performance on Small Imagers

From: dan.grimes@xxxxxxxx
To: opendtv@xxxxxxxxxxxxx
Date: Fri, 23 Jul 2010 16:41:27 -0700

In the past, there has been discussion on this forum on lens performance
and price relative to imager format.  There were also questions as to
whether the lenses that came with these inexpensive cameras could resolve
to match their imagers.

For those that are interested, I recently tested different lenses on a Sony
PMW-EX3 with a 1/2" imager while set to 1280x720p60.

The lenses were as follows:
Sony VCL-614B2X (a Fujinon 14x5.8mm lens that is manufactured for and came
with the camera, $8.3K for both)
Fujinon HS18x5.5BERM (approx. $16K)
Fujinon HSs18x5.5BRM (approx. $11K)
Fujinon XS13x3.3BRM (approx. $10K)

All lenses exhibited enough resolution for 1280x720, easily showing 600+
line pairs of horizontal resolution at both minimum and maximum focal
length.  However, the lens that came with the camera seemed to be absent of
a myriad of aberrations in the other three lenses, each costing more than
the camera and lens package:

-Both HS series lenses could not be focussed for both the center and
outside areas with the f-stop fully opened (f1.4).  Optimum and consistent
resolution was found at f4 to f5.6.
-Both HS series lenses suffered from chromatic aberrations on the outsides
when not perfectly focussed.  Usually, one side would have blue shifted to
one side and the other red.
-Both HS series lenses would breath when focussed (focal length varied when
focussing).
-The HS18x5.5BERM exhibited all the typical problems with the multiplier
in, yet still maintained very high resolution up around 600 line pairs.
-The XS series lens exhibited all the HS issues.
-The XS series lens exhibited strong pincushion aberration at wider angles.

-The VCL lens did not have strong monochromatic aberrations at any focal
length (squares staid square) and no apparent chromatic aberration when
focussed or not.
-The VCL lens did have lower contrast and lower resolution when at smaller
apetures (f11 and higher).  Optimum resolution was at f2.8 to f4.

Conclusions?  All lenses were well matched for the 1/2" imager at 1280x720P
in general resolution and contrast.  Of course, I need to go back and
repeat the test in 1920x1080i to determine if they match the full
resolution of the imager.  However, the cheeper lens that came with the
camera outshined the more expensive lenses.  Clearly this lens was
optimized for this camera either optically and/or electronically.  I am
still checking to see if there is lens data that can be used for the
Fujinon lenses in the EX3 camera.

Now, there is still good reason to purchase and use the Fujinon lenses,
namely, the additional focal length range, available accessories and
filters, and the ability to use studio controls.  But I wouldn't encourage
purchasing the more expensive lenses for image quality.

I guess what I am really getting at is don't discount the included lens
because of its price.  And perhaps those cheap lenses can match the
resolution of the imagers.

Dan
[opendtv] Lens Performance on Small Imagers

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