Is 5x minimum focus distance covering all distances?

Question

In the Shooting Guide three distances are recommended:
1 x minimum focus distance (32 cm)
2 x minimum focus distance (64 cm)
5 x minimum focus distance (160 cm)
I have added the actual distances for my 24-70 mm set-up.
In the lensprofile these distances are interpreted very differently - and most off at the shortest distance (this has been discussed earlier, and I corrected the data in the lcp-file).
When the profile is opened in LC, the focus distance is shown like e.g.: 24mm, f/11, 1,6m, raw.
99% of my images were shot at a focus distance longer than 5 m. Of course I will choose the 1.6m option, because it's the closest, but at the same time the number seems a bit esoteric. I think that >1.6m would be more intuitive. Not all users are making there own profiles.
Question: I guess the profile is much the same at any distance longer than 5 x minimum focus distance?
Br, Eigil

Answer 1

Hi Simon,
at a distance of 1.2 m the image of my A1 size target covers about half of the frame width and I can get a good distortion profiles from 9 shots according to the recommendations of the user guide. But this distance is not what I want because I normally take images from landscapes. Increasing the number of shots does not seem to be a good solution for the problem. With a reasonable number one cannot increase the distance to a satisfactory value and I have not seen a proof that the method works well with a very large number of very small images of the target. (Small residual mean errors shown in the profiles are no proof, I got these with apparently wrong profiles) . Therefore I suggest a different method for producing a distortion profile based on two considerations. The first one is that distortion is a property of the lens and its settings, not of the objects before the lens.That is, only the focus setting of the lens is important, not the distance of the target from the lens. The second consideration is that distortion of a good lens in essentially independent of the aperture, otherwise one would get blurred images with open aperture. This means that I can choose any aperture to create a distortion profile which is good for all apertures. Consequently I take 9 shots at a distance of 1.2 m with the focus ring of my lens set to infinity at an F-number of 22. The images are fairly sharp, the ALPC has no problems finding the corners. The result is similar to the one I got with 25 images at a distance of 2 m which is still marginal.
I think, the chromatic aberration profiles obtained for very high F-number are also good for small F-numbers, the vignetting profiles certainly are not. One would not need the complex procedure with many images for creating vignetting profiles, one image of a white uniformely illuminated target taken from any distance should be sufficient. I hope that Adobe will share my opinion and separate the creation of vignetting profiles from the creation of distortion profiles in ALPC. So far I will manually correct vignetting of my few images taken with small F-number.
Helmut