General Chromatic Aberration Numbers

All,

With the seemingly large choice of import lenses available I decided to do some software experiments and see what the difference would be in the chromatic aberration error in the different lenses offered. These are general numbers but for those who are thinking of making a large refractor using some import optics (me) I thought I would post my results.

Please understand that these are general numbers. A general guideline. There too many factors to be precise but this should give a very basic understanding of how much color (visual) one can expect from achromatic lenses of different diameters and focal lengths.

A 127mm or 152mm F/15 used to be a good standard (3X Airy disk) but with the proliferation of 150mm F/8's out there I decided to use it as the standard. The numbers represent the size of the red and blue (combined) blur circles as compared to the airy disk diameter. The color crossings of the red and blue are between the 70% & 100% zones. The current standard for decent color correction in an standard achromatic lens is 3X the airy disk. Also remember that, as in all scopes, the airy disk shrinks with aperture so this is part of the equation as well.

I am sharing this for someone like me that is thinking of building a large refractor using an import lens. The prices for such large lenses are hard to resist. The quality is still open for debate. Anyway, here goes:

150mm F750 16X
150mm F1200 7.6X (standard)
150mm F1500 6X
150mm F1800 5X
150mm F2250 4X
204mm F1200 17X
204mm F1800 9.6X
204mm F2400 6.5X
204mm F3000 5.5X
216mm F2700 6.6X
220mm F3000 6X
228mm F1800 12X
250mm F1375 25X
250mm F1800 15X
300mm F3000 11.8X

Simi-Apos or any other "special" corrections were not part of these equations. Leaning the correction torward the red or blue were not used as a factor as well.

To the professional opticians, if I am in error please let me know. I don't want to be a source of misinformation. I will pull this thread if so.

Keith