Comparing macro lenses using MTF - Part VII - Tube lenses

Miljenko · Post by **Miljenko** » Mon Oct 15, 2018 2:05 am

Lou Jost wrote:Miljenko, can you explain what the CA numbers mean? Unlike the resolution numbers. I suppose they are nonlinear with respect to anything that photographers can easily interpret. This means that it is difficult to know if the difference between, for example, 0.50 and 0.55 is large or small. The scale range from 0 to 1, right?

Nope. According to Imatest tutorials: CA (area): Chromatic aberration area in pixels. An indicator of the visibility of CA. The area between the channels with the highest and lowest levels. In units of pixels because the x-axis is in pixels and the y-axis is normalized to 1. Explained in the page on Chromatic aberration. Measured in along the axis indicated by Profile on the upper-left. Meaning: Under 0.5; insignificant. 0.5-1: minor; 1-1.5: moderate; 1.5 and over: serious.
Norman Koren explained this area concept in detail here: www.imatest/docs/sfr_chromatic/

Lou Jost · Post by **Lou Jost** » Mon Oct 15, 2018 6:32 am

Thanks Miljenko, that is very helpful! There is both an area measure and a normalized percentage measure, thanks for reminding me that these were areas, based on the pixel size of your particular camera. That makes them pretty easy to interpret.

Miljenko · Post by **Miljenko** » Fri Aug 23, 2019 1:39 am

Hi Lou,
sorry for the very slow reply. Norman Koren, the author of Imatest software explains it here: http://www.imatest.com/docs/sfr_chromatic/
I am measuring what he calls "area chromatic aberration". There is obviously no upper limit for this value.
Regards,
Miljenko

Lou Jost · Post by **Lou Jost** » Fri Aug 23, 2019 6:50 pm

Thanks Miljenko, that's helpful.

Miljenko · Post by **Miljenko** » Sun Aug 25, 2019 1:22 am

Lou, excuse me for doubled reply. This is my first post since October 2018. Just tried to catch up but didn't noticed I replied earlier to your question. Last winter I was unexpectedly stopped with my lens testing due to life threatening health issues. It took me this long to get well again and now I'm fully functional, working and getting back to my hobbies.
In the meantime some new lenses arrived waiting in a cue for lab testing. Currently I got Laowa 25mm 2.5-5x borrowed from distributor, just finished testing yesterday. Now I'm sorting results and preparing for upload. There are some interesting findings :-)
Hoping to be regular on this forum again!
Regards,
Miljenko

Lou Jost · Post by **Lou Jost** » Sun Aug 25, 2019 6:31 am

I am sorry to hear about your health problems, but I look forward to your return as an active member here!

I have that Laowa and I like it at its lower end. The "zoom" ability is really helpful. At the higher end of its magnification range there are better alternatives but it is still very useful because of that ability to change magnifications so easily.