Aperture problem in Nikkor 55-200 f/4-5.6 VR?

[Felisek]

I have just bought a Nikkor 55-200 f4-5.6 VR lens for my D7100 camera. I noticed that pictures taken with aperture fully open look quite underexposed. In a series of photos taken outdoors with the same exposure level but aperture varying from f4 to f11, those with f4, 4.5 and 5 were underexposed. The effect is most pronounced at f4.

Then I took a series of pictures indoors with constant artificial light and looked at them in ViewNX2. The histograms for f greater than f5 are very similar, but f4 was underexposed again. just to make sure that this wasn't a problem with camera metering I took another series in manual mode with full-stop increments: f4, 5.6, 8, 11 and 16, doubling the shutter speed every time. Again, the f4 was underexposed, while f5.6, 8 11 and 16 were quite similar. In order to correct the f4 histograms to those from f5 and higher, I had to apply exposure compensation of about 0.8-0.9.

This means than my lens is underexposing at f4 by almost a full stop. According to DXOmark test, the lens is behind the manufacturer's f by only about 0.3-0.4 stop and this doesn't change much with the aperture.

It seems to me that the aperture in the lens doesn't fully open below f5. I'm about to send it back for a replacement, but wanted to ask here if anyone else experienced a similar problem. I hope this is a not a "feature" of this cheap lens.

My other lens is Sigma 17-50 f2.8. It doesn't show any issues with exposure of focus, so I don't think the problem is in the camera.

 

[Marcel]

I would guess you were using the camera in manual mode? But did you notice the markings on your lens? It says 4.5-5.6, which means that when you use the longer focal length (probably from 100-200, the lens will not go below f 5.6. So, if you take a reading with the lens at 55mm, put it on manual and then zoom to 5.6 without changing your shutter speed, you will underexpose your shots.

It's kind of hard to diagnose without further knowledge of your methodology...

 

[pedroj]

F4 at 55mm and F5.6 at 200mm...Was your focal length the same in all your tests...

 

[Felisek]

Thanks guys, but yes, my lens was at the same focal length for each test. Here is an example:

https://plus.google.com/photos/1152...s/6000924955863298433?authkey=CKKVo_n-74XVvgE

The apertures and shutter speeds are as follows

f4 1/30 s
f5.6 1/15 s
f8 1/8 s
f11 1/4 s
f16 1/2 s
f22 1 s

So, theoretically, each picture has the same exposure. And indeed, most of them are very similar, f4 being the exception. It needs compensating by about 0.8 EV to get a similar exposure. See what I mean?

 

[Marcel]

Thanks guys, but yes, my lens was at the same focal length for each test. Here is an example:

https://plus.google.com/photos/1152...s/6000924955863298433?authkey=CKKVo_n-74XVvgE

The apertures and shutter speeds are as follows

f4 1/30 s
f5.6 1/15 s
f8 1/8 s
f11 1/4 s
f16 1/2 s
f22 1 s

So, theoretically, each picture has the same exposure. And indeed, most of them are very similar, f4 being the exception. It needs compensating by about 0.8 EV to get a similar exposure. See what I mean?

OK, they were taken at the same focal length, but what focal length was it? I can't see the exif of the shots you've posted. And, if you were above 100mm, then it would explain the difference. Even if your camera says it's f-4, it could be slightly different in the real world. When using manual exposure, and taking a reading at f8 and then changing shutter speed and aperture manually to get the same exposure, you will run into this below f 5.6 because your lens looses speed at longer focal length. Now if you were to use Aperture priority and meter the shots, your camera would compensate for the lens f-stop variation by giving you a slightly longer exposure.

If you don't understand my point, then maybe you could send Nikon your shots and ask them if they think the lens is problematic. I, for one, would appreciate to find out what they would say about it.

 

[Felisek]

Marcel,

You can see some Exif data if you click "Photo details" on the right-hand side. These pictures were taken at 55 mm, so f4 should be available.

Also, these particular pictures were actually done in aperture priority mode and I used matrix metering. However, the camera set shutter speeds exactly as expected, each twice the length of the previous one. Then I repeated this experiment in manual mode setting aperture and shutter speed to the values specified in my previous post and the results were identical.

BTW: at 200 mm you can't set f=4, the camera will not accept it. You can only set 5.6 or higher.

 

[Marcel]

Marcel,

You can see some Exif data if you click "Photo details" on the right-hand side. These pictures were taken at 55 mm, so f4 should be available.

Also, these particular pictures were actually done in aperture priority mode and I used matrix metering. However, the camera set shutter speeds exactly as expected, each twice the length of the previous one. Then I repeated this experiment in manual mode setting aperture and shutter speed to the values specified in my previous post and the results were identical.

BTW: at 200 mm you can't set f=4, the camera will not accept it. You can only set 5.6 or higher.

Thanks for the info. This leaves me without an answer. I don't know what to think of it except that there might be either a lens or a shutter speed problem. But I'm not a camera technician so I would say you should send your results to Nikon and ask them. We are just a bunch of Nikon users and as far as I know, we don't have any authority to diagnose camera problems. We sure like to help finding solutions to problems, but when it comes to measuring shutter speed and light transmission to a lens... then I give up.

There is one thing though that I just thought of. What light was used to take this shot. The only reason I ask is because I've had situations where the light flickering gave me some exposure and color temperature problem. Since the shutter speed is faster at f4, maybe the shot was taken while the light was half way on... Just a thought.

 

[Felisek]

Thanks for the info. This leaves me without an answer. I don't know what to think of it except that there might be either a lens or a shutter speed problem. But I'm not a camera technician so I would say you should send your results to Nikon and ask them. We are just a bunch of Nikon users and as far as I know, we don't have any authority to diagnose camera problems. We sure like to help finding solutions to problems, but when it comes to measuring shutter speed and light transmission to a lens... then I give up.

Yes, I know. I just wanted to check that this is not a known "feature" of the lens with which I have to live with. It really looks like a genuine fault, though I'm not sure if this is from the lens or the camera. I'm going to borrow the same lens from a friend tonight and check if it shows the same problem.

Sending these results to Nikon might be a good idea. Do you know who I should contact about this?

There is one thing though that I just thought of. What light was used to take this shot. The only reason I ask is because I've had situations where the light flickering gave me some exposure and color temperature problem. Since the shutter speed is faster at f4, maybe the shot was taken while the light was half way on... Just a thought.

Good point. But the effect is reproducible indoors and outdoors, in different conditions, so it does not come from light.

 

[Felisek]

Found a technical support on Nikon web site, will send them a message. When (and if) they reply, I'll post it here.