200mm Macro Lens

[steve_rasmussen]

One problem I've noticed with using the shorter macros is that they can be so close to the subject that they scare insects away that I would have rather been in the picture. I'm talking about flowers with bees, butterflies etc. What I need is a 200mm macro with f/64 capability and Double Gauss design. APO color correction would be nice as well. BTW, I called Pentax and asked if they can modify lenses to be able to stop down further and they said no. SR

[bill baker]

This may seem a tenuous 35mm/MF comparison, but you'd think Pentax

might take a hint from the phenomenal sales (for a prime) of the Nikon

105mm macro due to its exceptional performance as both a tele-macro and

portrait lens. The specific optical design you're describing, Steve,

would that be optimized for an ultra-flat focus field? I gather that

some portraiture mavens don't prefer an ultra-flat field, but I'd give

it a whirl.

[steve_rasmussen]

All photographic lenses that I've seen are flat field. The Double

Gauss type is but one of them. If there were a curved field lens, then

you would need to have spherically curved film to capture the sharp

image. This is not practical. Flat film must be used and therefore the

lenses must have no(or very little)curvature of field.

Non-photographic refracting and reflecting optics are the only types

that I know of that have a curved field. SR

[bill baker]

I thought all lenses had some degree of spherical abberation, and that

the correction for it was usually optimized for one subset of its focus

range. I'm probably mixing up optical concepts. All I'm really asking

is if the specific macro design you're throwing out would detract from

using it for portraiture, on the theory that Pentax would be more

likely to market a tele-macro if they think it has multi-use appeal.

[steve_rasmussen]

Bill, spherical aberration and curvature of field are two different

things. But you are right that spherical is usually figured for a

certain distance depending upon the lense's intended use. My proposed

design would be good stopped down for macro work and good for

portraits as well. The design would be optimized for spherical

correction at 20 feet so stopping down for would solve the spherical

aberration problem in macro work.