Different color, different focusing depth

[zydeholic]

I've been hearing about how different frequencies of light will focus at different focal lengths. This is why lenses have coatings, to bend them back to the same plane.

I've heard this happens with pinhole, but no way to rebend the light. Just wondering if the resulting images might be of different sizes too, i.e. the red image might be just a little higher and wider than the green image, etc.

Just thinking that I might be able to retweak things in photoshop by changing the height and width of the resulting image for each color channel. I know, off-the-wall question.

 

[2F/2F]

With a pinhole, it is really a non consideration, IMO. If you want the most sharp and technically sound picture, use a lens. If you must, you can throw whatever wavelength you want into the "ideal" hole diameter equation in order to favor any one color over another. The standard is 550nM (green-yellow), as it is pretty much in the middle of the visible spectrum.

 

[zydeholic]

I was thinking more about correcting color abberations over sharpening, but bottom line, my gadgety mind was wanting something to chew on.

 

[Ole]

I've been hearing about how different frequencies of light will focus at different focal lengths. This is why lenses have coatings, to bend them back to the same plane...

No, that's not why lenses have coatings. But it is why lenses have more than one element.

A pinhole has no chromatic aberration, but it can still show a little bit of colour fringing due to the differences in diffraction of different wavelengths. The only way to get rid of this is to use a monochromatic filter.

 

[Allen Friday]

Ole is on top of the question. If you are really concerned about the different wavelengths, use a cut off filter. Allow only one wave length to enter the pin hole. I remember there was an article several years ago in Phototechniques where a high school student compared shaprness of photographs taken with an old, uncorrected (non-APO) lens with no filter and with a cut off filter. The ones with the cut off filter were sharper. I suppose the same would work with a pin hole. But, the filter will affect the distribution of tones, which may or may not be desirable.