Re: aspheric lens question


"Beaver Shaver" <noone@xxxxxxxxxxx> wrote in message
news:e7xQg.1201$nX4.46@xxxxxxxxxxxxxxxxxxxxxxx

The image intensifier has an 18mm circular screen. The CCD is a 2/3"
format which has an active image area of approximately 8mm x 6mm.

I'm currently trying to find an intensifier (2 or 3 stage MCP type) with
the CCD bonded directly to it. Unfortunately, it looks likes there are no
manufacturers in the US.

To answer your original question, the use of an aspheric lens does not
really address the problems posed by this application. In addition, you
were right to worry about the quality of the image formed by lenses intended
to be used as condensers. That doesn't mean it never could work, but there
are better approaches.

If you do decide to pursue an relay lens solution, there are a number of
possible options. In approximate order of up front cost, these are:

1. Combine two catalog simple lens elements or cemented doublets to form
the relay. The combination of two allows use of the lenses at their design
conjugates, which eliminates spherical aberration as an issue for this
application unless you need a very low focal ratio.

2. Find an existing multi-element lens that is designed to work at
approximately the correct magnification and that has a usable object-image
distance and focal ratio.

3. Combine two existing multielement lenses meant to work at infinite
conjugates.

4. There is at least one lens manufacturer that claims to maintain a large
number of lens designs "on the shelf". Since what you need has almost
certainly been needed before, they can probably help you. I don't know how
the overall cost would compare to the next option.

5. A fully custom lens design.

The problem with options 2, and especially 3, is that, in general, you won't
be able to predict their performance; you'll simply have to try them. With
option 2, if you can find something very close to what you want, you'll
probably be OK. Option 3 is much chancier -- vignetting often is too high
to be acceptable. With option 4, presumably the manufacturer can tell you
how well it will perform.

It is only options 1 and 5 that give you mechanical layout flexibility.

For 2/3 inch I use 8.8 x 6.6 mm; the diagonal is 11 mm. If you decide to
pursue this, you need to specify what relationship you want between the CCD
format and the screen. Diagonal corresponds to the diameter of the screen?
Screen fully encompassed by the CCD format? Something else?

You'll also need to figure out what focal ratio you need in the relay. You
do this by comparing the radiance produced by the image intensifier to the
irradiance required by the CCD to produce an image having adequate signal to
noise ratio.


.

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