Horrible purple cast, not a new species of robin

Yes, I know. I agree it's not ideal. I'll experiment with the other techniques when I get a chance; meanwhile I'll save up for some Pentax glass...

Question:

Has anyone experienced this purple fringing thing with film, rather than digital? Everything I read seems to focus on digital.

Just curious. But since taking up SLR photography in 1984 with the Super A and ME Super, and quite a few not-at-all-Pentax-SMC-lenses, I never saw it with film.

Not even once.

It's not much of a problem with film as lenses are well corrected and as film has a flat surface it is happy to accept oblique light rays.

You can see the effect in abundance if you use a colour film in an old box camera with a lens only corrected for Ordinary Film (blue sensitive only).

As an aside, if you want sharp pictures with a box camera and panchromatic film, use a blue filter.

To remind those younger than 100 years old:
Ordinary Film was sensitive to blue only
Orthochromatic film is sensitive to blue and green
Panchromatic film is sensitive to blue, green and red

Found this detailed explanation of CA and Purple Fringing.

http://www.vanwalree.com/optics/chromatic.html#ref14

Near the bottom of the page it deals with achromatic lenses and the purple and green fringing ( both both of which are evident in ChrisA's "cropped top robin" photo). Could that be the problem? Also the paragraph below that, titled Purple Fringing: Lens or Sensor? it points out that in film vs. digital photography it is much easier to be critical of lenses when easily viewing the output in digital at 1:1 magnifications. In the Reference section there are a lot more links with a lot more interesting reading.

In my Googling (is that a word yet?) I also found, this product for correcting PF. http://www.shaystephens.com/ca.php

There is certainly no shortage of information on the web about Purple Fringing, just a shortage of agreement on the topic that's all.

"We've heard that a million monkeys at a million keyboards could produce the complete works of Shakespeare; now, thanks to the Internet, we know that is not true."
- Robert Wilensky


Drew

An achromat is a lens corrected for two wavelengths of light, blue and green.

An apochromat is corrected for three wavelengths and would be the preferred option.

But bear in mind also that to a large extent you get what you pay for and a Sigma APO and a Leica APO may have very different degrees of apochromatic qualities...

Yes, he suggests that it's a symptom of axial, rather than transverse CA (see my earlier post quoting that link).

I haven't had a chance to test his assertion that if it is axial CA, the fringing problem is less when the lens is stopped down.

Thanks for the Shay Stephens link.