AStigmatism

Could anyone please tell me how lens astigmatism can affect an image? All of my lenses have 'significant astigmatism' according to Reikan FoCal during AFMA but I just ignore this indication now. If I actually did have one that was suffering from this would I really be able to see any effect on images taken with it?
Thanks in advance.

LensRentals.com has written a number of great articles on aberrations, astigmatism etc. You could spend hours, probably days reading all that Richard has written over the years. However, I suspect your conclusion would be the same as mine.

There is no perfect lens. If some "defect" obviously affects your images in such a way that you are trashing good shots because of it, it is probably time to do something about it. At least look at the alternatives. If you are generally happy with what you are getting out of your lens/camera, don't worry about it and keep shooting.

Was just curious as to how astigmatism might manifest itself. Interestingly enough the worst astigmatism - at an allegedled 16% - again according to FoCal, is on my latest acquisition namely the Canon 70-200 f2.8L IS which I have found, so far, to be absolutely brilliant. I cannot see any problems with the images it makes but as I don't really know what to look for I could be missing something. As mentioned I take little notice but I am eager to learn.

There are any number of ways flaws can be seen in lenses.

If you go looking for a problem, you are sure to find one.

I'm not trying to be an ass, that's just the way I view this "issue". I have read a bunch of his articles, and from a lens science perspective I find it very interesting, but I have never once tried to prove anything with one of my lens'. I know each lenses strengths and weaknesses simply through use and casual observation.

I encourage you to read his blog, in particular there was a recent article about cinema lenses and field curvature that is particularly enlightening. Poking around there will give you much more of a sense of potential abberations, and their potential effect on the final image than what you are likely to get in a forum post ... even though we have some very smart people here.

oingyboingybob wrote in post #18548060
Could anyone please tell me how lens astigmatism can affect an image? All of my lenses have 'significant astigmatism' according to Reikan FoCal during AFMA but I just ignore this indication now. If I actually did have one that was suffering from this would I really be able to see any effect on images taken with it?
Thanks in advance.

It depends on a variety of conditions. For starters, lens aberrations may be more apparent at certain focus distances than others (i.e. near vs. far). It may affect details of specific spatial frequency more than others. Also some other aberrations can look like astigmatism so this could be some generic, catch-all bucket that the software might be using.

As a simple explanation, say you selected a small patch somewhere in the image frame, and this small patch contained repeating black and white lines. In one case, it is vertical lines and the other case it is horizontal. If astigmatism is present, the edges between black and white will be more blurred/lower contrast/less sharp in one orientation versus the other.

Perhaps a more real example would be of small foliage detail in a portion of an image where it seems like the edges are smeared/unsharp in one direction, but not in the direction that is 90-degrees/perpendicular of the first.

In addition to Poe's very good answer, one other place you are likely to really notice astigmatism is is you are needing to accurately photograph items that are round.

I have an astigmatism in my right eye, and am right eyed too. The astigmatism also gets worse as my eye gets tired. I am a very keen competitive target rifle shooter, which pretty much requires the ability to accurately align a series of concentric circles. At its worst I see a sight picture that looks like Jack Nicholson embedded that axe in to it from about the four o'clock position. Not helpful.

Alan