18-200 not exactly 200? Comparison to 55-200

[elyone]

I received my 18-200 that I will be using with my D90. (I intend to sell my 55-200 VR together with the D40 and

18-55. I know all the arguments of superzoom vs. not, etc, thats not what this is about.)

 

 

Anyway, I took some comparison shots while I still have all three lens.

 

 

It seems to me that the 200 end of the 18-200 does not reach as far as the 200 end of the 55-200. This NOT about

distortion etc, simply the reach. It does not even seem close. i.e. the 55-200 magnifies more than the 18-200

when I compare the 200 end, on each. I stood in exactly the same place, only switching lens. (Pardon the

unimaginative shots).

 

The 18 end of the 18-200 seems a bit wider than the 18 of the 18-55.

 

Am I missing anything here? I did not use a tripod, true, but I did this a bunch of time, and the result is

clear, the 18-200 does not 'zoom in' as much as the 55-200.

 

Should they not be? Even though they are both labeled 200?<div></div>

[elyone]

oops need to add the other images. I will upload and link to them:

in this folder:

http://www.photo.net/photodb/folder?folder_id=869374

[Hector Javkin]

Test it at a longer distance. Internal focusing lenses often change their focal length drastically when focused on near objects. Your two lenses presumably suffer this effec to different degrees.

[elyone]

Ah, OK. Will try that. Thanks.

[ronald_moravec1]

Recheck at infinity. Nikkor zooms at close distances shorten focal length.

 

There are also tolerences to exact focal length. They may not match at infinity either or they both might be 200, 195, or 190 or one

195, the other 190.

[at]

yup, as others have stated, you must focus at infinity. I just learned this myself from a fellow

photo.net'er.

[User_276104]

Even though close focus may play a part, nothing is constant. One day while messing around with lenses, I found

that an 80-400mm VR @ 80mm produced a tighter crop than an 85mm f/1.8D.

 

And my 80-200mm f/2.8D produced slightly different crops between D2x and D40 bodies.

[dave wyman]

I think you'll find, if you retake your two original photographs, at the same focal lengths, that you will be able to focus closer with the 18-200mm lens than you can with the 55-200mm lens, which will make up for the difference you see.

[richard_driscoll]

Hi Avi,

 

If you search the Net you'll find many references to the effect you've noticed.

 

Many zoom lenses achieve close focusing, at least in part, by reducing the focal length and on the 18-200 this

effect is pretty extreme. If you repeat the experiment at infinity focus you should see much less difference.

 

As a matter of interest the internal focusing system also reduces focal length to prevent having to rack the lens

out a long way. Also, when you add a close-up lens to a prime lens to focus closer the focal length is also

reduced and this is why the working distance is reduced compared to what it would be with extension tubes.

[ShunCheung]

If you can check the archives, we have had the exact same discussion a few times before, and I have seen the same question coming up in DPReview forums.

 

Keep in mind that focal length is measured at infinity. Therefore, you should compare focal lengths only at infinity, as some of the above follow ups point out.

[elyone]

Thanks all. I hate it when I feel dumb.

Anyway, if this thread is deemed superfluous, a moderator is welcome to delete it.

[ShunCheung]

Avi, this is a very reasonable question. It is merely that plenty of people are not aware that only the effective focal length at infinity counts.

[tri-x1]

I wasn't aware of the effect. Now I am. Thanks

[mendel_leisk]

I've got a Canon 24-70 and a Canon 24-105. Both profess to 24mm wide end, but the 24-105 is markedly wider, more like 22mm, comparing to the 24-70. This shift seems to countinue throughout the zoom range. Bottom line: qouted zoom ranges are not exact. It's simlar to a car engine that's quoted as being 2 liter displacement, when in fact it's 1995, or 2150. It's close, but might be rounded a bit.