Nikon lens not what it purports to be

[DouglasMorley]

I've had my Nikkor 18-70mm zoom for some years now and am happy with it. It isn't perfect but no lens is.

A recent copy of N-Photo's sister mag Digital Camera World magazine included a lens test chart which I used yesterday with both my D200 and D7000 cameras evaluating 50mm, 35mm, 18-55mm lenses plus the 18-70.

Apart from the quality of each lens, which I wont go into here (though the lowly 50mm f1.8D came out tops), what surprised me most was that the supposed 18mm on the 18-70 read to the eye as much closer to 16 or 17mm, and the 70mm virtually identical to the 50mm on the other lenses.

I later checked the 70mm against the 70mm setting on my 55-200 lens and found that the magnification was greater on the 55-200.

What I wonder now is my 18-70 a one off or has anyone else discovered this 'problem'?

We all, or at least I do assume that what's on the tin accurately describes the contents. Now I have my doubts.

[greenwing]

I don't know if it applies to the 18-70, but I know that some zoom lenses lose focal length when at their closest focus. I think this applies to the 18-200 and 70-200 which are both more like 150mm than 200mm when focussed at their nearest. Could this be what's happening in your case? Do the 70mm settings match more closely at infinity focus?

Chris

[DouglasMorley]

Interesting possibility though not in my case. I photographed an object in a scene some 25feet away using both the 18-70 and my 55-200 both set at 70mm on the same camera. The image from the 55-200 showed considerable enlargement over that of the 18-70.

At the 18mm end of the lens images compared to that of my 18-55 lens show more of the scene equating in my estimate to a 16 or 17mm focal length.

I hasten to add that I have no complaints about the quality of these images which implies there is no technical fault, just a false impression that the lens is not what it is supposed to be.

I have a wide angle zoom so shall see if I can verify my wide angle observations.

[DouglasMorley]

In case anybody is the slightest bit interested I did check the 18-70 Nikkor against my Tamron 10-24mm and it does approximate to 17mm at its supposed 18mm focal length.

Would you Adam and Eve it?! Well I do. Even if, as I suspect from the lack of response to my thread, nobody gives a monkey.

[JonnyM]

Just because nobody replies doesn't mean they're not interested.

[DouglasMorley]

Thank you JonnyM for your comment.

Maybe I'm a one off myself but if I'm interested in a topic, especially if that topic might affect me, then I would respond, maybe to ask a question, maybe to comment. I do enjoy dialogue.

Still the 18-70 optic is old news.

On a broader issue about communication in general I am dismayed especially regarding comment over photographer's images. As a photographer and viewer of other's images I have in the past enjoyed commenting on images that have impressed me or even when I thought comment was warranted endeavouring to say something positive and constructive or helpful. Now I mostly don't bother as it is indeed rare for my comments to be acknowledged and I am so often the only commenter anyway.

The response to my thread here only cements my belief that I only produce hot air in the wind.

[StephenBatey]

In theory, the marked focal length should be accurate to about 1%. Yours clearly isn't within this limit.

There are a number of factors that could cause a change in focal length when no change should occur, and as pointed out, focusing is one of them.

I haven't bothered to check, but from memory infinity for a camera lens is usually taken to mean about 1000 times the focal length; in the case of a 70mm lens if I've used the Windows calculator correctly that would be around 83 yards.

For what it's worth, I'm not a regular here and only just saw your post.

[DouglasMorley]

Thank you Stephen for your comments. My forum post was in part an endeavour to see if any others with this lens would have sufficient interest to check if theirs was the specified focal length or if mine was a rogue.

As so far no one has I can only conclude that I'm alone or that there's no interest. Which must be my point to JonnyM.

I wonder if second hand photo dealers are swamped with the 18-70 lens, or if it is dust gathering at the back of cupboards such being the rapid turnover in kit lenses. It has been superseded by at least three 18-55s if I remember correctly.

[greenwing]

I don't have the 18-70, and never did. As well as the 3 18-55s, there have been the 18-135 and 18-105 VR. Lots of people think the 18-70 was better than any of these, citing the metal mount as evidence.

What does the exif data tell you about focal lengths on the 18-70? It's not likely to be any different than the barrel markings, but then the lens is not likely (surely!) to behave more like a 16-50.

Chris

[DouglasMorley]

Greenwing,

The EXIF data tells me, and always has told me that the lens's extremes were 18mm and 70mm. On that basis alone I have never had any reason to doubt them as I have never directly compared this lens to similar optics. I feel pretty sure that very few owners and users have either - and that might well include lens testers from publications as well.

As Stephen Batey rightly points out a 1mm difference is hardly worth anyone's concern so 17mm or 18mm probably would not get noticed. However 50mm against 70mm is somewhat more extreme. Either all 18-70 Nikkors are in fact 17-50mm and everybody's been duped, or I have a rogue.

Without input from a 18-70mm lens owner, I'll never know.