Alley in Pisa, Italy

by Lars Kotthoff

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I am trying to find out whether my Nikon 18-55 mm (f/3.5-5.6G VR) kit lens has something wrong with it since I'm getting a whole lot of "fogginess" in the pictures I take as compared to my other lens.

Here I have taken two pictures at the same focal depth (35 mm), same aperture (f/5), same shutter speed (1/100) and slightly different ISOs (900 and 1000) (VR off, AF on), AF is on the bottom of the Kestine box.

The problem isn't as clear here as it is in some of my other photographs but I still consider it a problem. Can anyone give me a clue as to what, if anything, is wrong with this lens or give me further advice for troubleshooting this kind of problem?

enter image description here

enter image description here

originals at imgur

ps. The other lens is a Nikkor 35 mm f/1.8 lens.

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If you kept everything the same but then changed the ISO you have changed the exposure. What do you mean by 'fogginess' ? –  JamWheel May 19 '11 at 11:32
    
Did you use a tripod in both cases? –  ElendilTheTall May 19 '11 at 11:44
2  
Could you post the images somewhere which preserves EXIF data, or post that somewhere? –  mattdm May 19 '11 at 12:45
    
I will take new pictures, unfortunately I do not have a tripod, but I'm sure I can find something similar. I will also try to take more pictures demonstrating the effect, with a higher aperture and in better lighting. I did a photo run the other day and had to throw away practically every picture because of this problem... I have a hard time defining it better than "fogginess", but I will try to take some pictures to show the effect. –  Stefan Thyberg May 19 '11 at 17:10
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@JamWheel a 10% variation in ISO won't unduly effect the results of this experiment, the f/stop and t/stop will vary a small amount between lens designs even if the ISO was the same. –  Matt Grum May 20 '11 at 12:19
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2 Answers 2

The lower of the two images is not as sharp. I would have to see more to know for sure what the cause is, but I think this is just inherent in the lens design.

Although the settings used were the same, there are a lot of differences in the lens design. The key difference here is that at f/5.0 the 35mm is stopped down a full 3 stops from it's maximum aperture, whereas the 18-55 is almost wide open. This makes a big difference in the sharpness, because in general, a lens will be sharper when stopped down a bit. You might want to try finding the "sweet spot" of your 18-55 (I would guess around f/8) and see if you notice a difference.

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I think the blurrier one is also focused a bit further back, but it's hard to tell. –  mattdm May 19 '11 at 12:46
    
Another issue is simply that the 18-55 kit zoom has to have a lot more compromises, not just because it's a zoom, but because it's got to be cheap, even with must-have-to-sell features like VR. –  mattdm May 19 '11 at 12:47
    
Yes, not to mention the fact that A) prime lenses are inherently sharper than zooms and B) the Nikon 35mm is well known for being very sharp, especially when stopped down a little. –  ElendilTheTall May 19 '11 at 13:33
    
see, the 18-55 is a pretty sharp lens. mtf charts on nikonusa.com; I had a quick look and it seems in the center (both at the wide and at the tele end) it's even sharper than the 35mm. using both of these lenses quite often, this doesn't sound so strange to me. so it's hard to tell. –  MattiaG May 19 '11 at 15:22
    
Looking at mtf charts only tells you the performance of a lens wide open in lab conditions (See imaging.nikon.com/lineup/lens/mtf.htm). While this can be useful, it is not readily applicable to the situation as stated here since we are not comparing images that are taken wide open in both cases. –  chills42 May 19 '11 at 16:39
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Looks like the bottom picture is mis-focused. The box is not as sharp as in the top picture. Have you tried turning on the VR and see if it makes a difference?

Thanks

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