70-200 f2.8 problem, Decentered ?

suggs

suggs

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Harry
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Hi folks

My normally razor sharp Nikon 70-200 has developed a problem, its gone very soft at f2.8 and the higher up the image the softer it gets and has a slight ghosting/flare. At around f4 and above its pretty much fine, i use this lens constantly for shooting MX as its my job so i know when something isnt right. Ive shot thousand and thousands of images with it at f2.8 with very few duffs, but now almost all are soft.

Im not aware the lens has had a knock but its possible that ive not realised due to my working environment.

Im thinking its become decentered but what do you think ?


HPB_7192 by Harry Picturebike Lessman, on Flickr

same lens a few weeks ago

Untitled by Harry Picturebike Lessman, on Flickr
 
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I'm struggling to see much of a difference. The spokes in the first picture look pretty sharp to me, at this resolution at least.

If you're really worried about your lens, I think you need to be carrying out controlled tests in reproducible settings.

Decentring usually causes images to be softer in one corner, or on one side, than the other corners/sides. There's an easy way to test it though.
* Pick a high contrast target in good lighting. A car number plate or something like that is good.
* Position yourself close enough to be able to focus on it accurately, but far enough that moving the target from the centre of the frame to the corner doesn't require very much camera movement. Maybe 10 metres or something like that.
* Shoot at f/5.6 or f/8 so you have plenty of depth of field and any apparent softness isn't actually something that's out of focus.
* Focus on the target in the centre of the frame, recompose without refocusing so that the target is in one corner, and shoot.
* Repeat three times to put the target in the three other corners. Make sure you refocus each time you put the target in the centre.
* Compare the 4 images at high magnification.

You're not looking for absolute sharpness, because it's difficult to know exactly what to expect and it depends on what camera you have. But you are looking to see whether the 4 images are comparably sharp. If the lens is decentred, it will be obvious.

Why not post (crops from) the 4 images here?
 
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I use a variation on Stewart's method that gives two indications of any decentring that may have occurred.

Shoot an overhead power line or telephone line from the perpendicular......one shot with the cable across the top of the frame and one across the bottom. If there is a problem then it'll manifest itself as both softness and a relatively high level of CA......modern lenses have aspherical or achromatic elements whose calculated profiles will induce rather than correct CA when they're mispositioned.

Bob
 
Looking at the 2048 sample on Flickr on my 40" Samsung TV used as a monitor nothing wrong with it at all!

Can even see tiny clods of earth sticking on the tyre treads so doubt if you could get it much sharper.

Refused permission to view the 2nd pic.
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I can't see anything obvious but then again I'm viewing from a phone. I would consider having it serviced at N P S, you'll have the peace of mind then that it's back to full spec
 
thanks, what im finding is a lot of out of focus riders helmets with the rest of the rider sharp. I take around 2000+ mx pictures everyweek and not had this issue before its a new issue the last week. I normally tend to be focused pretty central on the rider. The bottom picture taken a few weeks ago prior to the problem is fine the whole rider is sharp but the top picture taken the other day the chest upwards is soft and the helmet is very soft but chest down is sharp, its not a one off as had lots like that and all shot at f2.8 where as normally i just wouldnt have this problem.

all the rest of my images on flickr are spot on but there not from the last week other than the top one which i just uploaded so i could put it on here, maybe its my eyes lol

by the way the body is a D4

ill try the test you suggest
 
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Given that your EXIF shows 85k actuations on this camera, I would not be surprised at the lens going off kilter if it lives a hard life. Not necessarily a knock, could be some dust/grit upsetting the focussing mech or something but as it is a work tool, I would get it off to Nikon to check it out and hire one whilst its away if you have nothing to cover for it.
 
yeah the lens has had a hard life the last 18 months thats for sure. Only thing that makes me think its damage rather than wear is that it just suddenly lost its mojo. Having said that i was working yesterday and it took some superb shots so think its a random issue, or perhaps it its just me !

ive been thinking of getting a new lens the VR2 version so think ill do that and have this serviced and keep as a back up
 
If it is the VRI then it is older than the camera then? So the camera EXIF only tells part of the story.

I still have one going strong, but the VRII certainly has less vignetting and unlike the VR1 is designed for FF, which the VR1 wasn't !

If the issue is random, then I am again drawn to the grit/sand/dust explanation, as this will change over time and use.
 
thanks bought the lens around 18 months ago from a local tog and it was basicly new, the D4 ive had about 4 months as got it from a friend and ive put about 30k on it. id estimate the lens has done about 100k but still looks and feels in good condition. The grit and sand is quite possibly the answer though as plenty of it around me and as you say would explain the randomness of the problem. so far ive only noticed the problem at f2.8-f3.5. Think ill try shooting for a day keeping the aperture around f6-f8 and see if it shows its self....
 
suggs said:
Think ill try shooting for a day keeping the aperture around f6-f8 and see if it shows its self....
Click to expand...
I don't think that's necessarily a good idea. You risk just masking any problems by having a greater depth of field. Heck, why not just shoot at f/64 and have everything in focus? Saves wear and tear on the AF motor too...
 
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