All Lenses Are Not Made Equal

Wanting to reduce the number of lenses I owned prompted me to consider one zoom that covered the focal length range of a couple of lenses. By gettng an 18-70mm, I could get rid of my old 35-70mm and the 18-55 VR kit lens. So I bought a used Nikkor 18-70mm 3.5/4.5 G ED. The only thing I would give up was the VR.

I didn't want to wait to get home to do test comparisons so as soon as I received the 18-70, I went and borrowed my co-worker's 18-200 and made test shots at 18mm, 55mm and 70mm. I was completely baffled by the results. I thought they would pretty much be the same. It appeared that the 18-70 had a wider angle of view at the same focal length as the 18-200.

1) At 18mm Focal Length:

 

 Nikkor 18-70mm

Nikkor 18-200mm VR

2) At 55mm Focal Length:

 

 Nikkor 18-70mm



Nikkor 18-200mm VR

3) At 70mm Focal Length:

 

 Nikkor 18-70mm



Nikkor 18-200mm VR

My first thought was that it may be that the two lenses had different minimum and maximum focusing distances that affects the magnification but I really didn't know enough., OR the 18-70 was broken. It was used afterall.

So I sent a troubleshooting question to Nikon USA to find out whether or not I was comparing apples to oranges.

Here's the email I sent them:

Quick question. Do different sized DX lenses take in the same angle of view at similar focal lengths? Example: @18mm will the dimensions be the same between 18-55, 18-70 and 18-200?

I just purchased a used AF-S 18-70mm 3.3-4.5 ED lens for my D80. The seller said it works great but when I compared it at similar focal lengths with an 18-200 VR, the results were varied. The 18-70 seemed wider to the point where the:

18-70@70mm is almost equal to 18-200@55mm.

I attached comparison shots for your reference.

Is this a fair comparison? or is the 18-70 inherently wider? or is the 18-70 defective? I need to know so I can decide whether to return the 18-70. Thanks for your input.

Nikon USA techies are great because they are responsive and there are no stupid questions. It turns out I wasn't comparing apples to oranges. I was in fact comparing apples to apples but the thing is... there are different kinds of apples.

Here's their reply:

Sorry for the delayed response. To answer your question quickly, not necessarily, no.. 
Different lenses with similar focal length ranges do not necessarily display the same picture angle. Each lens, particularly zoom lenses are designed and constructed differently with differing amounts of elements and groups of elements.. While the focal lengths may be the same, the angles of view may be different. As a result, an 18-200 with not be the same as an 18-70 @ 50mm. I would not say there is anything wrong with your 18-70mm based on a different picture angle than your other lens at 18mm.

Thank you,

Dave

So if you own some lenses with overlapping focal lengths and wondered why they turn out different, you have your answer.