Astigmatism Factor?

[Toggerman]

I've recently switched my gear over from Canon to Nikon, and one of the things I like to do is run the gear through Reikan Focal and see what's what.

I'm confused however by the Astigmatism Factor charts. All of my previous Canon lenses have been a very low percentage so I've never really looked into it before. Most of my Nikon ones are fine too, but my Tamron 70-200 VC and Nikon 300m PF are off the charts. The Nikon lens has an Astigmatism Factor Range of 40%+ on all of my bodies, but only when stopped down. At f20 or wider on the D500s the number drops to 8%, and less than 1% wide open, the same happens on the D750 but from F9 and wider. The Tamron on the other hand is 30%+ on both D500s, dropping to ~10% at F4 and again being less than 1% wide open. On the D750 the Tamron only has an AFR of 9%, dropping to 3% at f22 and wider.

So going by what Focal says my lenses sound like they're decentered, correct? But then why is the Tamron ok on the D750 and not the D500s? Could it just be bad test method even though other lenses were done at the same time and were fine?

 

[GHP]

The problem with extensive testing with something like Focal is that it will highlight "defects" which had previously never been noticed in normal use.
I did the same. Bought Reikan Focal, tested all my lenses, and found many were way off, according to the programme.
In the real world however, they were fine.
What I'm saying is don't test unless you are having a problem in the day to day operation of the camera/lens combination.
The only lens I had the need to adjust with Focal was my 135 Dc lens. It is a notoriously difficult lens to get sharp, and Focal certainly did the job.
As for all my other lenses, unless I am having focus problems during normal use, then why bother?
The other downside to Reikan's testing is getting the tests consistant.
Any minutely tiny variation will cause a swing in the result. (especially the lighting)

 

[sk66]

It doesn't surprise me that a PF lens would have a lower rating in astigmatism or CA. It doesn't mean the lens is de-centered (but it could). I would suspect it's just a characteristic of the fresnel lens design... related to the mirror lens like bokeh characteristics.
I can't recall the last time I've taken an image at an aperture of f/22 or smaller... I wouldn't worry about that range.

 

[Toggerman]

I did the same. Bought Reikan Focal, tested all my lenses, and found many were way off, according to the programme.
In the real world however, they were fine.
What I'm saying is don't test unless you are having a problem in the day to day operation of the camera/lens combination.

I always put anything new through Focal as I like to know the ins and outs of it, aperture sharpness, focus consistence, just out of curiosity. But I've never really paid attention to the astigmatism before. I've had a lens that has been decentered but was still under 10% according to Focal.

TBH I'm not too worried about it as I tend to use lenses wide open, when they are stopped down in the ranges that seems to be problematic it's for something like motorsport panning, and I've seen nothing wrong with the images so far. Both lenses are also sharpest wide open and I don't want to upset that. I just want to try and understand what Focal is telling me or if it's just messed up.

It doesn't surprise me that a PF lens would have a lower rating in astigmatism or CA. It doesn't mean the lens is de-centered (but it could). I would suspect it's just a characteristic of the fresnel lens design... related to the mirror lens like bokeh characteristics.
I can't recall the last time I've taken an image at an aperture of f/22 or smaller... I wouldn't worry about that range.

Same here, I'll touch f22 at times when panning in sunlight, but mostly I'm wide open where it's at its best. I did wonder if it was something to do with the Fresnel lens but I'm not familiar enough with the technology.