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Why do the t5i have chromatic aberration disabled by default?

jbodine74
Contributor

I bought this camera about a month ago with the 18-135m stm kit lens. My pictures have looked out of register the whole time. I kept reverting to the factory defaults, I looked at buying a new lense, taking it back to the store, etc. until I enabled chromatic aberration in the camera menu. My pictures are awesome now. For the past 3 years I had a t1i and never even heard of chromatic aberration. Why is this not on by default CANON?

9 REPLIES 9

Skirball
Authority

A lot of photographers prefer to control such things in post, as opposed to having the camera manage them.  Usually default settings will limit such things - CA, sharpening, noise reduction, shadow boost, etc unless you tell it otherwise.   If you do them in camera, and the camera over does it, there's no going back.  If you do it in post, you have control over the amount of the effect, on each individual photo.  Not saying that's how you should do it, just a likely explanation as to why it's not default.

Thanks for the quick response. Now I understand why some people prefer it off.

One more thing:  you can use any decent photo editing program to remove the CA from your older photos. 


@jbodine74 wrote:

Thanks for the quick response. Now I understand why some people prefer it off.


And just to be sure you're clear on the concept, chromatic aberration is the problem, not its cure. It's a phenomenon common in many lenses and is difficult to design out. It's the correction for CA that's disabled by default.

Bob
Philadelphia, Pennsylvania USA

TCampbell
Elite
Elite

I shoot in RAW so I only get the real data -- a chromatic aberration (CA) adjustment wouldn't be applied to a "RAW" image (if it were, then it would no longer qualify as a "RAW" image.)  But it's easily applied in software.

 

Chromatic Aberration is a dispersion problem created by the prism-like effect of the lenses.  As light passes through the edge of a lens, the lens shape behaves like a prism and starts splitting light into it's constituent wavelengths (it starts to create a rainbow).   Light traveling right downt the center axis of the lens is going through "flat" areas of the glass and don't get this effect... but the farther off center axis, the greater the effect.  

 

Blue light (shorter wavelengths) bends more easily than red light.  If you were to photograph a white spot on a black background (position the spot to an extreme corner of the lens) then you'll tend to get a blue fring on the inner edge and a red fring on the outer edge.   If you reverse tings and shoot a black spot on a white background then the fring will reverse.

 

It's actually VERY easy to correct this in software.  Ultimately you need to imagine that whe the camera takes a photo, you're sort of capturing three photos ... a "red" photo layer, a "green" photo layer, and a "blue" photo layer.  The red layer represents the light has bent the least, the green layer is just a very tiny bit smaller (imagine shrinking the image by about 1 pixel) and the blue layer will be the smallest (imagine shrinking the image by about 2 pixels.)

 

It turns out if you separate the image into color channels in Photoshop, resize them, and then re-combine them, you'll fix the CA problem.  That is, of course, a manual process and a bit tediuous and since CA is a well-understood (and easily correctable) problem, many of the better photo editing apps have a tool specific to CA correction so there's no need to go through the more time-consuming Photoshop color-channel approach.

 

Higher end lenses are designed to minimize the CA.  This involves the use of higher end materials to formulate the glass to create low-dispersion glass.  There are many variations on this, but nothing seems to work as well as fluorite.  There are two downsides the fluorite from a manufacturing perspective...  it doesn't form in nature in large enough pieces to be useful as a lens -- so it has to be synthetically "grown" in a kiln.  If it's grown too quickly, you end up with imperfections.  It has to be done slowly to create crystal large enough and pure enough that it could be ground into an optical element.  THEN of course there's the grinding problem.  Fluorite is very fragile and easily chipped.  So even that process is time consuming and requires special care (far more than ordinary optical glass.)  The results, however, are worth the effort (just not fast nor cheap.)

 

See:  http://cpn.canon-europe.com/content/education/infobank/lenses/fluorite_aspherical_and_ud_lenses.do

 

 

Tim Campbell
5D III, 5D IV, 60Da

ebiggs1
Legend
Legend

Chromatic aberration is prevalent throughout the zoom range on this lens, exceeding one pixel width mostly. These high levels of CA can pose problems. You will see it in images with high contrast more than photos with less contrast.  It is fairly common in the consumer or "kit" line of lenses.  It is easy to correct with software such as Photoshop Elements.

EB
EOS 1DX and 1D Mk IV and less lenses then before!

Thanks for all the tips. I am a graphic designer for a printing company and know photoshop inside and out. Would upgrading to a L series lens like the EF 24-105mm f/4L IS USM be good? I'm looking to get really sharp images.

 

The EF 24-105mm f4 L IS USM is a best buy in the Canon "L" line.  It is very much better than the kit lens you already have. EFS 18-135mm.  Plus it is a constant aperture another plus in my opinion.

EB
EOS 1DX and 1D Mk IV and less lenses then before!

ebiggs1
Legend
Legend

However, while on the subject, since you know PS inside and out, it is still a best practice to use it.  How I shoot is to use RAW and bring up the RAW photo in ACR.  I do lens correction which ACR already has for the EF 24-105mm.  It will recognize it and apply the necessary corrections with a simple click.  All lenses need this procedure, BTW!  From ACR, open in PS and do whatever you do.

 

The old saying, a great photograph is 1/2 made with the lens, 1/2 made with the camera and 1/2 made in Photoshop.  I am sure there is "logic" there, somewhere.

 

 

(ACR = Adobe Camera Raw, it is part of PS.)

EB
EOS 1DX and 1D Mk IV and less lenses then before!
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