relationship between how contrasty a lens is and CA?

kuuan · Expire: 2014-12-26

please compare the following three images,
all taken wide open against the sun, on Sony NEX5n as RAW, imported to LR + one click on 'auto' which mostly adds 'black' and which enhances the differences

Would you please be so kind, be sport and share your observations? if not obvious, the title of the thread gives away what I am wondering about Wink

I shall tell you which lenses had been used, my observations and ask more questions, if interested will add more samples of the same scene taken with some other lenses more.

thank you, cheers, andreas

Attila · Expire: 2025-11-18

I vote for third one

kds315* · Expire: 2021-03-09

Nope, I don't see a logical connection between contrast and CA.

But I prefer also - of course - #3

kuuan · Expire: 2014-12-26

haha, ok!

here 100% crops of the above images in the same order:

reviewing these a simple thought had struck me:
typically CA shows around high contrast lines between dark to very bright areas. Now if a lens has less contrast, the difference between dark and light is less pronounced, there is less CA.
Certainly reality is more complex than that, but wouldn't that thought also make sense?

marcusBMG · Joined: 07 Dec 2012 Posts: 1318 Location: Conwy N Wales

As this page explains

http://toothwalker.org/optics/chromatic.html

CA is an inherent property of a lens and will be more or less pronounced depending on the lighting, f-stop, subject. You can perhaps construct a relationship with contrast since that also is inherent to a lens but it's not really whats going on is it?

kuuan · Expire: 2014-12-26

thank you Marcus, specially for the link.

I accept that technical knowledge says that there is no relation between how contrasty a lens is and how much CA it produces and therefore won't try to argue in favor of the notion. However I must admit that for myself only I will take away my own conclusions from this test, I had taken the same shot not only with the three lenses shown but with a total of 8 lenses of the same focal lengths.

I had not yet mentioned, the three samples shown had been taken with 3 different copies of a Canon LTM 1.8/50mm ( noteable oof highlights have the same shape in all three pics, those taken with other lenses look different ) First has an inner element with strong haze, the second has an inner element with little haze and the last copy is clear.

Specially Canon LTM 1.8/50 and 3.5/100 but also others are notorious for an inner element that is hazy, milky, and it is difficult to get a clean copy. If not the intended purpose this thread at least shows what to expect from a lens with a milky element.. Differences of takes not taken against light of course aren't that dramatic, to note that, if using a mirrorless cam, focus peaking will show less readily when using a 'hazy' lens.

Nordentro · Expire: 2015-01-29

Interesting, also interesting to see with and without haze Wink

leonAzul · Joined: 12 Mar 2014 Posts: 17

dnas · Joined: 14 Nov 2008 Posts: 488 Location: Japan

Or, another way to look at it, CA shows itself where the transition between light and dark is high. IF there is CA, then you get a colour fringe. (purple)

If you have a lens that is less contrasty, the transition between light and dark is less, so the CA is still identical, but the contrast of the CA colour purple is reduced.

So for example, if you take an image with CA, and you reduce the contrast in Photoshop or reduce the saturation then you can't see the bright purple as easily, even though the CA is still there. (if you reduce the saturation so it's B&W, then the purple is less obvious Wink

)

kuuan · Expire: 2014-12-26

thank's for the input.

You guys say that "high contrast scenes reveal whatever CA has been there all along, just make it more obvious" and "If you have a lens that is less contrasty, the transition between light and dark is less, so the CA is still identical, but the contrast of the CA colour purple is reduced."
To my simple mind there is 'more CA if I see more" and "less CA if I see less". Even though you mean to contradict my notion I feel that 'actually', by that I mean 'only referring to what is seen', you are rather backing it Wink

But again, I am not a technical guy and don't want to argue about this!

cheers, andreas

Nordentro · Expire: 2015-01-29

Andreas has a point. CA is produced in contrasty areas, isn`t it? So less contrast would make less CA?
Would the CA come back if you adjust contrast in post if it`s not any visible CA there? Of course not...

bernhardas · Expire: 2017-05-23

edited

Lightshow · Joined: 04 Nov 2011 Posts: 3666 Location: Calgary

I have low contrast lens with lots of CA, also have high contrast lens with lots of CA, I also have lenses that have high /low contrast but with no CA, I have to conclude that it can be in any lens if it's not been corrected for it.

leonAzul · Joined: 12 Mar 2014 Posts: 17

Nordentro · Expire: 2015-01-29

This look more like spherical aberration with a dash of chromatic aberration, what lens is used?

kuuan · Expire: 2014-12-26

leonAzul · Joined: 12 Mar 2014 Posts: 17

Nordentro · Expire: 2015-01-29

poilu · Expire: 2019-08-29

Tedat · Joined: 08 Nov 2011 Posts: 800 Location: Berlin/Germany

Could there also be a relationship with the coating? I get the feeling most of the older single coated lenses doesn't suffer from CA this much as lenses with stronger MC do.

leonAzul · Joined: 12 Mar 2014 Posts: 17

y · Joined: 11 Aug 2013 Posts: 308 Location: EU