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Faint glow in pictures with Nikon AF-I lenses


avishek_aiyar

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<p>Hello, <br /> I recently acquired a Nikon AF-I 300mm f2.8 lens in pristine condition and started noticing that some of my shots wide open and most of my shots wide open (f4) with a 1.4TC have a faint glow....almost like a soft focus effect. I am very confident that the lens does not have haze/fungus etc. <br /> I then compared images taken with an AF-I 600mm f4 lens with a 1.4xTC (belongs to a friend, but he took the images for me) and I saw the same glow signature on his images as well. <br /> I have attached the cropped and uncropped images taken with the 600mm f4+1.4TC shot at f5.6 (wide open) to illustrate what I mean. <br /> Uncropped: http://www.flickr.com/photos/42959534@N08/8578151983/in/photostream<br /> Cropped: http://www.flickr.com/photos/42959534@N08/8578153013/in/photostream<br /> It isn't as noticeable without the TC, but with the TC, it is quite clear........and I don't think its the TC, since me and my friend used 2 diff. TCs and it would surprise me if both have haze. <br /> Has anyone noticed the same? <br /> I am not sure why it is this way. <br /> I would appreciate it if anyone has any insights into this. <br /> Thanks.<br /> Avi<br /> P.S.: THE PICTURES WERE NOT TAKEN BY ME.</p>
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<p>Just a guess...most lenses are not optimized for maximum sharpness wide open, and are often soft at their widest aperture. Most sharpen up when closed down 1-2 stops. I think that is what you are probably seeing.</p>
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<p>Just because it is an expensive lens does not mean it has magical optical properties. No lens is at it's best wide open. When you use a TC it takes your expensive lens and degrades it to the optics in the TC. Use the lens without the TC and see if it does not look better. Stop it down and see if it does not look better.</p>
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<p>It also looks like the head of the eagle is slightly out of focus, which will contribute to this "glow". It appears the pine needles are sharply in focus, while the eagle is behind the plane of focus.</p>

<p>That being said, some of these older lenses do have a "glow" wide open.</p>

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<p>The photograph posted is clearly front-focused, so the main subject is slightly out of focus and the "glow" (which is familiar to those who use soft focus filters, etc.) is to be expected. There is no EXIF information, so this may be "operator error" or an autofocus accuracy issue. My 300 f/2.8 AF-S VRII also initially showed this "glow" when used with the TC-20EIII - which I also identified as front-focusing. The combination required AF tuning, which can be done in-camera with the D300 and the other "higher spec" Nikon bodies. This is not unusual with the long tele + converter combinations. The two lenses that you are discussing should both be sharp wide open.<br>

It's also worth bearing in mind that with longer-range shots the atmosphere can intervene to give a "soft focus" glow also - one of the reasons why you so often hear the opinion that a certain super-telephoto lens is "soft at long distances or when focused at infinity."</p>

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<p>Avi,<br>

My lens/converter combination is much better after focus tuning, although it is still a little soft unless I stop down to f/8 - at which point it's just fine, and can produce super-crisp results if I get my technique right. It is absolutely worth checking the focus - try taking a few shots of a fixed target with fine detail (with tripod and adequate shutter speed to eliminate any camera shake) using AF normally, then repeat using "live view." If the live view shots are sharper, focus tuning is indicated. Try an online search for "printable camera focus target" and you should find something useful - and free - to get you started.<br>

I should have stated that the two lenses should be sharp wide open <strong>without teleconverters fitted</strong>. The teleconverter - fitted lenses definitely benefit from closing down a stop or so, although among the current converters the TC-14EII is noticeably better than the TC-20EIII.<br>

<br />Good luck!</p>

<p> </p>

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<p>First image posted has EXIF data - shot was taken from 70m (200ft+) away. I doubt that one can diagnose "front-focusing" at that distance - it might just simply be a mis-focus with the AF sensor being influenced by something other but the eagle's head. I have no experience shooting a 600mm with a 1.4x TC attached - but would expect the same results when shooting with a 300/4 and TC-17EII when shooting beyond 1000ft or thereabouts - the optical quality isn't there anymore and atmospheric issues compound the problem. My advice - get closer and things will likely improve dramatically.</p>
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<p><em>First image posted has EXIF data..</em> <br>

You are quite right - not accustomed to how Flickr presents that information. If you download the image, the EXIF is stripped away.<br>

<em>I doubt that one can diagnose "front-focusing" at that distance - it might just simply be a mis-focus</em><br>

Also correct - which is why I mentioned "operator error." However, the image is clearly front-focused - the question of whether this is an equipment issue or human error is pretty simple to test. The shot was also taken "wide open" which is not advisable, but understandable in circumstances where f/5.6 only gave 1/60sec. Small focusing errors (of both types) can be masked by smaller apertures. I agree with the observation about working distance. My 300 f/2.8 gives much better results with the TC-20EII at ranges of less than 30-40m. With the "bare" lens or with the TC-14EII, I have no such concerns.</p>

 

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<p>I looked at the photo at 2048 pixels. I think the needles in the front left foreground show the best focus in the image, and I think the eagle head and other foliage are slightly out of focus. This has to the the source of the glow. The eagle head is in the middle of the frame where the lens is at its best.</p>

<p>Check your focus. Do a test with a clean subject and known focal point. I'll bet the problem goes away.</p>

<p>I've shot the late-model 300 f/2.8 wide open, and I think it produces really excellent images. </p>

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<p>Glad I was not the only one who noticed the potential focus issue.<br>

I've found on my D800 it really needs to be dialed in to get the best image quality. With AF glass that means tuning it and with MF glass it means live view. Film was way more forgiving of slight focusing errors, but digital is totally not.<br>

Still, some of my older glass does have a bit of glow even when focused properly.</p>

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<p>Andrew is right. It's an aberration, resulting from a lens with older coatings being used with a modern camera. Pixel density has a lot to do with this, as higher MP cameras tend to show this more. The lens was also designed for film, and there is more contrast with most films than with most digital sensors, so that makes a difference too.</p>

<p>Since a TC is basically a magnifier, it will magnify those flaws as well.</p>

<p>Your mileage may vary, but my experience with high-end lenses with high-end 1.4 TCs is that you generally need to stop down one step to get the same quality. In other words, setting that lens at f/4 with the TC should give you about the same quality as 2.8 without it. Of course you're also losing a stop to the TC itself, so you're really at f/5.6 as your widest "regular" aperture, and f/4 if having the shot is more important than how that shot looks.</p>

<p>Unfortunately, that's a problem with almost all non-modern lenses. I really like the colour rendition of older lenses a lot more than the new ones, and I think that the look of these photos is just great. But I do find that older lenses always need to be stopped down a step. One stop is usually all it takes, but I've only used a few lenses that didn't have some degree of what you're getting with digital cameras, and it wasn't always the more expensive ones.</p>

<p>I remember using an old short telephoto lens that was still going for some $600 on eBay just a year ago, and getting problems all the way down to f/8. Unfortunately, the older lenses just do that.</p>

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