Please could you post this message to the CVNet community?
We are trying to obtain lenses which are very well corrected for chromatic
aberration over the wavelength range 400 to 1100 nm (to measure the
reflectance spectrum of the tears); ordinary achromats (which are designed
to have equal focal lengths at 2 wavelengths) have a variation of about 0.5%
over this range, but 'apochromats' (which are designed to have equal focal
lengths at 3 wavelengths) should be considerably better. We need lenses in
the focal length range from about 50 to 150 mm. Does anyone know a source
of such lenses, or someone who could fabricate them (hopefully without
charging an arm and a leg)? Melles Griot make "Dapromats" which include
diffractive optics, but I doubt if they would do a good job of concentrating
light into the principal focus over such a wide wavelength range. I think
that some camera lenses are designed as apochromats, but their
antireflection coatings may not work well in the infrared (they would
presumably have many surfaces compared to a 3 element, cemented apochromat).
Another possibility might be to use (off-axis) mirror optics, but this would
introduce other aberrations, particularly astigmatism, unless special
mirrors were used (off axis paraboloids or toric surfaces).
Any suggestions on any of the above would be most appreciated, bearing in
mind rather limited funds available (say $500-$1000 per lens).
With thanks,
Ewen King-Smith, (614) 292 3939, FAX (614) 292 7493
College of Optometry,
338 W 10th Ave.,
Columbus, OH 43210