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Purple Fringing in New Nikon 20mm f/1.8G


derek_thornton1

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<p>Derek, the image of Bruarfoss that you linked to doesn't seem to have any pixels which are clipped in the highlights as far as I can tell (I could not find any pixel where any of the R G B values is 255). So it's not overexposed in the sense where the sensor would start causing issues with abrupt transition to white. I may have images which have white parts of the sky after the image has been edited, but it is more common to get that kind of color fringing when the image is overexposed in camera. I can of course check if I should be photographing trees against the sky some day with the 20mm. But I haven't noticed this lens to be prone to that effect.</p>
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<p>Gosh, I just ordered that lens about four hours ago. This is not particularly encouraging, but I have seen worse purple fringing.</p>

<p>I do think that there are some lighting situations in which purple fringing is almost inevitable. Even so, have you tried shooting it with exposure compensation down 1/3 or 2/3 stops? Then push it in post to bring it back up (if you are shooting raw) and see if it is any better. Will that work? I have no idea, but it might be worth a try. I would certainly try before sending it back.</p>

<p>Then again, as I recall, pushing film can cause more color distortion. What works in digital? Does anything work? I really don't know, but I would experiment with exposure compensation if I were you just do see what the possible effects might be when "pushing" or "pulling" with digital. If it sounds as if I don't know what I am talking about, that would be because I don't--but I do know that trial and error can work, provided that it is done in a systematic matter.</p>

<p>In that same vein, have you tried shooting at different f-stops? Sometimes it is surprising what works and what doesn't, but purple fringing can be resistant to the usual fixes--or so I am told. What Dieter has done looks pretty good to me.</p>

<p>Try using the Nikon software, as someone suggested. I will be back to see what you get, so that I will know what might work when my copy arrives in a couple of days.</p>

<p>--Lannie</p>

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<p>Lannie, I wouldn't worry about it. As I said, once I pixel-peep the corners of an image captured with the 17-35mm/f2.8 AF-S at 17mm, with a similar setting with branches in front of a bright sky, I saw the same type of purple fringing as well. Very few-super wide-angle lenses are perfect deep into their corners.</p>
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<p>First, I see Landrum touching on it, but with my 135 2.0 dc, if I stop down to 3.2 I am pretty much rid of any fringing and what is left is easily controllable in post. I generally am stopped down to that anyway to get a dof that is reliably going to get in focus what I need. The bokeh is still like budda. I'm not sure what the dynamic range of your camera is, but you could take a spot meter of the highest value in the sky and safely decrease shutter speed 2.5 stops reflecting about a 5 stop detail range. You probably have better. Were you shooting near wide open? If not for control of dof but rather to get adequate shutter speed because of low light, how about raising iso so you don't have to open up as much? </p>
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<p>How about this situation, mountain laurel on a cloudy day? Easily noticeable on leaf in center and under branch near top of frame.<br>

<img src="http://d6d2h4gfvy8t8.cloudfront.net/18336430-lg.jpg" alt="" /><br>

Really, all I would like to know is if I got a bad copy or is this normal? Is it even possible to get higher CA in a bad copy? I only have a couple more days left to send it back, what would you do?</p>

<p>Appreciate the help.<em><br /></em></p>

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derek-thornton.artistwebsites.com
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<p>Derek, I don`t have your lens but I tend to think it is normal. It is very easy to find this issues on many lenses, at least on mine (I have a cabinet with dozens of lenses). And BTW, I don`t think there are that sample differences as it may seem while reading on internet forums.<br /> I have just checked an image provided by photozone, the one with threes as the left row, eighth frame (1/250" - f8). I see yours has been taken at f8, so aperture is close.<br /> If you enlarge the image a bit over 100%, you will notice similar fringing. <br /> And the review says <em>moderate</em> CA issues, while corner sharpness is very good (but not excellent) at the corners. Just shoot a contrasty line or border and the CA will be there, even more noticeable if overexposed.<br /> To your question, I`m not qualified to give an answer, but I`d be surprised is there is a wide aperture f1.8, 20mm lens capable of doing it better. Maybe a slower one (or a $$$$ Leica M... ).</p>
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<p>Derek, having looked at the forest image (not a crop) at 1000 pixels wide, I'd say I was not pixel peeking. Still there is fringing - way too much. I suppose that the mountain laurel image is a medium crop, but not nearly at 100%. The fringing is clearly visible. When you know it is there, at least you will see it and notice it.<br>

If you keep that lens sample - you will start hating it very soon. (If I had known I would have returned my, then current, version of the 20mm lens as the focus plane was tilted - the right 1/3 of the image needed clearly different focus setting compared to the rest of the image.)<br>

As with everything, especially with manufacturing and assembly there are tolerances and eventually some samples are produced that are at or beyond acceptability limit. Outliers are bound to happen. Tests after the assemby are not done to every unit produced except for the high end special lenses.</p>

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<p>Just thinking aloud...<br>

Could you perform a decentering test?<br>

Have you checked this issue on a different camera? <br>

Have you noticed this on other, bright day, perfectly exposed images?<br>

It could tell if there is certainly something wrong with your lens.</p>

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