Purple Fringing

[mkh]

My new Tamron 70-300mm apears to be sharp but has some problems with purple fringing. This seems to be most noticeable in things that are hevily backlit (i.e. distant trees).

SHould I exchange it? Is the fringing something that is simply part of the way this lens is designed? Would it vary from lens to lens?

[gasrocks]

Could be part of that lens. What settings, which part(s) of the frame?

[DavidEB]

the purple fringing is probably Chromatic Aberration, which ocurrs because the lens bends different color light by different amounts. Same phenomena that makes rainbows. CA is generally more of a problem with longer focal length lenses. Also seems to be worse at edges than at center of image. CA is less in lenses with high index of refraction glass (sometimes called "low dispersion glass").

The only lenses I know of without CA are the diffraction optics jobbers from canon.

Overall the Tamron is probably a pretty good piece of glass for the price. The only reason I sold mine was for the extra f-stops provided by the Sigma 70-200, so I could shoot indoor sports.

These links might help you. The first one is a direct test of your lens against sigma & canon.
http://photography-on-the.net/forum/showthread.php?t=78099
http://www.e-fotografija.com/artman...ticle_306.shtml
http://photography-on-the.net/forum/showthread.php?t=75863

[Dante King]

Any sample pics you can post? PSCS has CA compensation tools that might be a good investment.

[ron chappel]

This seems to be completely normal with this model lens.
I just did a lens comparison test and found the same as you-the tamron is amazingly sharp and contrasty for the price but does give moderate to strong purple fringing and odd 'double vision' background blur.

Personally i much prefer the sharpness (over the other available consumer zoom options*) and happily put up with some minor problems like these

*Just a side note-the sharpest consumer zoom may possibly be the sigma 70-300 Apo macro super II but ONLY if you get a good example !
The canon 100-300usm is easily the most consistant allround performer

Here's a test i did,unfortunately it shows little or none of the flaws of the tamron
http://www.photo.net/photodb/folder?folder_id=456157

[ron chappel]

Here is an image from a different test which shows the odd bokeh and some purple fringing
http://gallery.photo.net/photo/3452295-md.jpg

[I Simonius]

My new Tamron 70-300mm apears to be sharp but has some problems with purple fringing. This seems to be most noticeable in things that are hevily backlit (i.e. distant trees).

SHould I exchange it? Is the fringing something that is simply part of the way this lens is designed? Would it vary from lens to lens?

Heavily 'backlit' white shirt - well, his back is heavily lit! :D

The CA is much more obvious on the RAW file - see 100 crop
50 mm 1.4 @ 1.4

[Dew]

That kids been eating his ready brek!
Could be a sun/detergent/UV type thing going on there?

[ron chappel]

Wow that's serious!

I've tried some correction techniques in photoslut with some success.In images where you can circle the offending area and reduce blue channel saturation i've found to be easy.This method is useless with the tree branches against sky though.
One interesting idea i've read is that ,because the problem is due to colours hitting the sensor at a different magnification....one should seperate the image into seperate RGB then recombine after slightly reducing the size of the blue image.I'm not sure if it works well but it's certainly different!

[I Simonius]

Wow that's serious!

I've tried some correction techniques in photoslut with some success.In images where you can circle the offending area and reduce blue channel saturation i've found to be easy.This method is useless with the tree branches against sky though.
One interesting idea i've read is that ,because the problem is due to colours hitting the sensor at a different magnification....one should seperate the image into seperate RGB then recombine after slightly reducing the size of the blue image.I'm not sure if it works well but it's certainly different!

Blagh! Too complicated for me!
I might do that if the image was an absolute stunner, buit what a hassle otherwise! :evil:

That was a very white shirt in direct midday sun, actually I quite like the effect, reminds me of the 70's! Oh wow man -look at my far out shirt :lol: :lol: :lol:

[ron chappel]

That kids been eating his ready brek!
Could be a sun/detergent/UV type thing going on there?

Maybe the pic could bring big money for a detergent add;) :D

[I Simonius]

Maybe the pic could bring big money for a detergent add;) :D

OH NO!

I mean OMO!

[mkh]

My fringing wasn't that bad as it only seem sto show up in backlit situations of small things (i.e. tree branches). Other than that the sharpness has been great.

I can't post an image as I don't have a place to host it.