Purple fringing - the cause?


OldTaffy

Link Posted 01/10/2011 - 17:29
I know that the problem of purple fringing has been mentioned again and again in these forums. Almost always, it is in the context of a particular lens, and there are one or two lenses that are regularly criticised for this fault.

My question is provoked by several recent publications that seem to be shifting the 'blame' onto the camera sensor, or even the firmware. For instance, in Wikipedia 5 alternative causes are suggested. Several authors whose books can be (partially) read in Google Books are suggesting that PF originates in the microlens structure, or some other factor, in the CMOS or CCD sensor. See, for example: Langford, Freeman and Long.

What do the experts on this forum think? It can't be all in the sensor, surely, if some lenses are regularly condemned for the fault.

(I hope that the long URL addresses in the links above will work)

Martin
A few of my photographs in flickr.
Lizars 1910 "Challenge" quarter-plate camera; and some more recent stuff.

ChrisA

Link Posted 01/10/2011 - 17:45
OldTaffy wrote:
It can't be all in the sensor, surely, if some lenses are regularly condemned for the fault.

Some lenses are, without a doubt, much worse than others for this. In my experience, the Sigma A400 F5.6 (non APO) and the Tamron 70-300 are very susceptible.

I tried to get to the bottom of this several years back, but gave up.

Axial CA (not lateral, which gives purple on one side and green on the other) is probably a large contributor when there's a clear difference between lenses (in particular the Sigma 400mm is much less bad when stopped down which is indicative of CA), but whether there's any sensor effect as various references have suggested, I have no real idea.
.
Pentax K-3, DA18-135, DA35 F2.4, DA17-70, DA55-300, FA28-200, A50 F1.7, A100 F4 Macro, A400 F5.6, Sigma 10-20 EXDC, 50-500 F4.5-6.3 APO DG OS Samsung flash SEF-54PZF(x2)
.

davex

Link Posted 01/10/2011 - 17:46
With a lens like the Tamron 70-300 one can induce PF whenever required, providing the light is bright enough. Typical example would be a tree branch against a blue sky. Have not heard of this with a DA* 200 or 300 lens, even my DA 55-300 exhibits much less tendency to produce pf.

The scenario above can be duplicated with most wide angle zoom lenses, pf is usually always less with a prime.

For me it has to be the lens.

Davex.
K5 + 8mm-500mm zooms and primes
Please feel free to play with any images I post.
My flickr: link

Anvh

Link Posted 01/10/2011 - 18:22
http://toothwalker.org/optics/chromatic.html
Stefan


K10D, K5
DA* 16-50, DA* 50-135, D-FA 100 Macro, DA 40 Ltd, DA 18-55
AF-540FGZ

ChrisA

Link Posted 01/10/2011 - 19:44

Well yes, this is the clearest explanation of axial CA as a cause for PF.

But note the paragraph at the end - it all gets very 'arm-waving' as soon as anyone talks about whether the sensor's contributing. I'm far from convinced that anyone understands that aspect properly.
.
Pentax K-3, DA18-135, DA35 F2.4, DA17-70, DA55-300, FA28-200, A50 F1.7, A100 F4 Macro, A400 F5.6, Sigma 10-20 EXDC, 50-500 F4.5-6.3 APO DG OS Samsung flash SEF-54PZF(x2)
.

lemmy

Link Posted 01/10/2011 - 23:40
davex wrote:
Typical example would be a tree branch against a blue sky. Have not heard of this with a DA* 200 or 300 lens
For me it has to be the lens.
Davex.

I have a 200mm f2.8 and I can tell you wide open especially, it PFs in spades.
lemmy
My Home Pages, Cartoons and Videos

OldTaffy

Link Posted 02/10/2011 - 15:48
Thanks friends! The opinion on this forum, at least, seems definitely to lay most of the 'blame' on the lens. I have just added PF to the Wikipedia entry for photographers' abbreviations. I wonder whether to edit it more firmly towards the 'lens defect' explanation.

Cheers.

Martin
A few of my photographs in flickr.
Lizars 1910 "Challenge" quarter-plate camera; and some more recent stuff.

MarkTaylor

Link Posted 02/10/2011 - 17:53
IMO the difference between a good lens and a bad one ('good' or 'bad' meaning specifically with respect to CA/PF) on the same camera and similar situations is so obvious and striking that it would be madness to blame anything other than the lens as the primary culprit.
My Flickr Pentax K-5 K-5 II Sigma 8-16mm F/4.5-5.6 DC HSM Tamron SP AF 17-50mm F/2.8 XR Di II LD ASL SMC Pentax-DA* 50-135mm F/2.8 ED [IF] SDM SMC Pentax-DA 55-300mm F/4-5.8 ED SMC Pentax-DA 18-135mm F/3.5-5.6 ED AL [IF] WR Vivitar 100mm F/3.5 Macro AF Metz Mecablitz 58 AF-2

ChrisA

Link Posted 02/10/2011 - 18:08
MarkTaylor wrote:
IMO the difference between a good lens and a bad one ('good' or 'bad' meaning specifically with respect to CA/PF) on the same camera and similar situations is so obvious and striking that it would be madness to blame anything other than the lens as the primary culprit.

This is very much the obvious conclusion.

There's a very simple experiment, of course, which would confirm it, if anyone has a suitable lens, and still uses a film camera as well as digital.

The Tamron 70-300 would be a good candidate if it doesn't vignette too badly (I can't remember if its image circle is big enough for 35mm) - take a picture of some twigs or TV aerials against a bright sky, verify that it PFs on digital, and then take the same picture on film.

If anyone's up for it, I'm more than happy to scan the neg for them on my Nikon 5000 scanner if it helps.
.
Pentax K-3, DA18-135, DA35 F2.4, DA17-70, DA55-300, FA28-200, A50 F1.7, A100 F4 Macro, A400 F5.6, Sigma 10-20 EXDC, 50-500 F4.5-6.3 APO DG OS Samsung flash SEF-54PZF(x2)
.

andrewk

Link Posted 02/10/2011 - 19:47
ChrisA wrote:
There's a very simple experiment, of course, which would confirm it, if anyone has a suitable lens, and still uses a film camera as well as digital.

I've been thinking about doing this for a while.

I have a XR Rikenon 300mm f4.5 APO lens which is really quite sharp - but on my K200D generates lots of purple/blue fringing at most apertures. It does go away a bit at f11 and onwards - but it's more than enough to put me off using it with a DSLR. The fringing is a bit more blue than purple ........

I posted this 100% crop in a thread about the lens, some while back. The fringing is pretty obvious on the bike.




As it happens, I also have a Ricoh KR10 Super which might well be the camera the lens was originally made for. I might even have some rolls of Fuji Reala in the fridge (but they've been there for maybe 3 years).

Andrew
Flickr photostream
Last Edited by andrewk on 02/10/2011 - 19:47

PierroJ

Link Posted 04/10/2011 - 13:23
I have a couple of lenses that exhibit this effect, but i wouldnt simply not use a lens because of it. Something like the PFK plug in ( action ) for Adobe PS sorts most of my CA

Here's the action on the above pic. It took longer to open Photoshop than it did to remove the CA, which is just a 1 click job and done



K-7 + some other stuff
Bird Gallery 1
Bird Gallery 2
Last Edited by PierroJ on 04/10/2011 - 13:23

andrewk

Link Posted 04/10/2011 - 16:32
PierroJ wrote:
Here's the action on the above pic. It took longer to open Photoshop than it did to remove the CA, which is just a 1 click job and done

I know it's not that hard to remove - but it might be a bit harder than you are suggesting where the fringing is primarily blue rather than purple. This was the full frame.




Although I don't use the Rikenon in anger (at the moment), I have no intention of selling it. It's way too good to give away - and also quite rare.

Cheers
Andrew
Flickr photostream
Last Edited by andrewk on 04/10/2011 - 16:37

PierroJ

Link Posted 04/10/2011 - 16:42
Yes, I agree it would take a little more effort as you say, but still not difficult in CS. But like you, I would keep a decent lens, despite a small flaw here and there.
K-7 + some other stuff
Bird Gallery 1
Bird Gallery 2
Last Edited by PierroJ on 04/10/2011 - 16:43
Add a Comment
You must be registered or logged-in to comment.