Can anyone answer this question, on a lens, for a friend of mine?

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A friend at work just bought a used 18-200 off eBay. He already has a 55-200. Both are DX, being used on a DX body. He also has an 18-105 DX lens.

So.. all that being said.

He shot a picture of a lamp at 18, using the used 18-200 and his 18-105. The pictures were pretty identical, in the size of the lamp in the photo. No question on that.


He shot at 200 with the 55-200 and got this:

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He took his newly acquired eBay 18-200, shot it at 200 and got this:

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He then took his older 55-200, set it to 125 and got this:

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His question is.. Why does the 18-200 shot at 200, not look the same as the 55-200 shot at 200. They were all shot from the exact same distance on the same body. Why is 200 on one lens not 200 on another? Is his eBay lens bad? He says it feels 'funny' when it is zoomed.

So opinions wanted. I think the lens is bad. Thanks to all who answer to help him out.

Don
 
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It's normal for that lens. With the 18-200 set at 200mm and focused at that distance the field of view is not the same as 200mm when focused at a greater distance. The term for this phenomenon is 'focus breathing'. At that physical distance the 18-200 has approximately the same field of view as the 55-200 does at 130mm. However, when both the 18-200 and the 55-200 are focused on an object an infinity you'll see they both offer about the same FOV.

In order to achieve the 18-200mm focal length range the focus breathing became more pronounced than with some other lenses where it's not as noticeable. In other words, it was a design compromise in order to offer that focal range.
 
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I Googled that:
http://m43photo.blogspot.com/2010/10/focal-length-and-focus-distance.html

You learn something new every day! Thanks!


It's normal for that lens. With the 18-200 set at 200mm and focused at that distance the field of view is not the same as 200mm when focused at a greater distance. The term for this phenomenon is 'focus breathing'. At that physical distance the 18-200 has approximately the same field of view as the 55-200 does at 130mm. However, when both the 18-200 and the 55-200 are focused on an object an infinity you'll see they both offer about the same FOV.
 
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'focus breathing' could make a lens at 200mm appear to have the same field of view as another at 130mm? That seems like a huge difference, considering both were focused from the same distance. Maybe repeat the test with an object farther away. But if a lens can lose 70mm just due to focus variation that does not sound right.

Also, if you have info on field of view and focal lengths, please contribute in this thread:
https://www.nikoncafe.com/vforums/showthread.php?t=301934
 
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Have you run the test yourself? I have heard of Focus Breathing before but I didnt think the effect was 70mm...

I would ask him to bring it round so you can try for yourself. Maybe its not fully extending properly when zooming
 
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focus breathing' could make a lens at 200mm appear to have the same field of view as another at 130mm?
With the lens in question, yes. Even the 70-200 VR II suffers from focus breathing. When at 200mm and close focus its FOV is equivalent to 134mm.

I have heard of Focus Breathing before but I didnt think the effect was 70mm...
Focus breathing is very pronounced with the 18-200. And the 130mm (vs 125mm) equivalent is not a typo. And as you can see with the 70-200 VR II, 70mm is not unusual.


"The 18-200mm is a notorious heavy breather: it is so significantly short of 200mm at its closest focus distance that even casual users notice this." - Thom Hogan
 
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It's normal for that lens. With the 18-200 set at 200mm and focused at that distance the field of view is not the same as 200mm when focused at a greater distance. The term for this phenomenon is 'focus breathing'. At that physical distance the 18-200 has approximately the same field of view as the 55-200 does at 130mm. However, when both the 18-200 and the 55-200 are focused on an object an infinity you'll see they both offer about the same FOV.

In order to achieve the 18-200mm focal length range the focus breathing became more pronounced than with some other lenses where it's not as noticeable. In other words, it was a design compromise in order to offer that focal range.
that's a very good description of a complex piece of information. well put mate. i actually understand it now.

this strikes me as yet another reason never to go down the 'super-zoom' route.

18-200 is an ~11x zoom pull. that's ridiculous imho.

80-200 is only 2.5x, 35-70 is 2x and 20-35 is a 1.75x zoom pull. my D series versions of these zooms are all sharp.

i had the misfortune to have to use a <third party> 28-300 on a Canon 5D a couple of years ago. that lens is woeful and has put me right off super-zooms ever since.

it just strikes me that too many compromises have had to be made to get that range. i'd rather haul a couple of shorter zooms around than compromise overall image quality.

super-zooms are attractive for people to buy, especially people on a budget. lets face it, camera gear is expensive for the new swish stuff and the promise of one, light piece of glass that allegedly covers a huge range is very tempting.


while judging pictures for my local show society, i've seen numerous examples of otherwise stunning, once in a lifetime shots that are just ruined by a super-zoom's foibles.
 
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AH! Explains what I've seen in my macro shots, focusing a few inches makes a difference in "size" of other things in view. Makes me go looking for a focus rail (again).
 
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Or even the Nikkor 70-200 f2.8 VR II as it's just as bad :eek::confused:.

Phil.
Keep in mind, this issue is noticeable only near the lens' close focus limit. If you're using a lens at 200mm, it is reasonably presumed you aren't shooting something at 3ft. The "focus breathing" phenomena is more pronounced with my 70-200vrii than it was with my 80-200afs, but for my shooting it has never been an issue and certainly would have no affect on my interest in a 200-400/4!
 

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