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I have just started learning photography.I am trying to understand lenses. my question is "Will I get the same result if I use 18-55mm lens at 55mm (full zoom) and 55-200mm lens at 55mm (no zoom), if not, then why?" I only own 18-55mm kit lens, so can't experiment.

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In general, yes, since 55mm focal length is 55mm focal length.

In particular, no, since no two lens designs are exactly the same.

Can you tell me what difference will I get?

It depends on the specific designs of the two lenses in question. What are their maximum apertures? How many aperture blades? How much light fall-off is there between the center and the edges/corners? How much and what type of geometric distortion is there at 55mm on each lens? How well is the lens corrected for chromatic aberration? Etc.

Would there be a slight fish-eye effect in one vs. the other?

There likely could be. It all depends on the specifics of the two lenses in question. Generally zoom lenses show barrel distortion at the short end of their range and pincushion distortion at the long end of their range. But that is a generalization. Not all lenses follow such generalizations.

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    It depends on the specific designs of the two lenses in question. What are their maximum apertures? How many aperture blades? How much light fall-off is there between the center and the edges/corners? How much geometric distortion is there at 55mm on each lens? How well is the lens corrected for chromatic aberration? Etc. – Michael C Nov 10 '16 at 8:52
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    And how close to exactly the nominal focal length each lens actually is at the zoom extreme. – mattdm Nov 10 '16 at 10:24
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    This would be a bit more (technically) accurate if you replace "general" with "theory" and "particular" with "practice." – Carl Witthoft Nov 10 '16 at 12:15
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    @CarlWitthoft As the saying goes, in theory there's no difference between theory and practice. In practice, however... – anaximander Nov 10 '16 at 13:08
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    @CarlWitthoft: I independently made that same edit, but the poster reverted it... which is unfortunate because the phrases he chose make no sense here. – BlueRaja - Danny Pflughoeft Nov 11 '16 at 7:54
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They will be very similar, as the focal length are the same. However because of lens design the image quality might be massively different, as distortion, chromatic aberration and the available maximum aperture might mean you get better results using one lens over the other.

Generally for cheaper kit lenses it is usual that they do not have a constant maximum aperture range. For example it is common to have f3.5-5.6 18-55 and f4-5.6 55-200 lenses. (f3.5-5.6 18-55 means the lens' maximum aperture is f3.5 at 18mm and f5.6 and 55mm, and some intermediate values between them) In this case for example the first lens will only get you to f5.6 at 55mm, while the other will get you down to f4 on 55mm. And obviously a larger aperture (smaller f number) means a smaller depth of field and a better low light performance, both which are important in a lot of photography scenarios. On the other hand most cheaper zoom lenses might have more vignetting and distortion issues on their smaller focal lengths, meaning you might still get a worse performance from a telephoto zoom at the 55mm setting.

But while it is possible to compare the two, most likely neither of them will produce a better image than a (usually similarly cheap) f1.8 prime lens in the 50mm range (I know that while 50mm and 55mm are not the same they are quite close in this regard, and 55mm prime lenses are usually more expensive)

The notes above are mainly valid for the cheaper zoom lenses, as more expensive zoom ones usually have a constant maximum aperture range (for example they can do f4 at both the 55mm and the 200mm position) and they usually have a more constant performance over their zoom range, and also somewhat between each other. This means you might get similar (but not the same) optical quality by choosing any of them at the same focal point.

However they will usually still be outperformed (especially on the maximum aperture setting) by fixed focal length prime lenses, sometimes even by very cheap ones.

If you do not have access to the lenses you might want to check some lens reviews on the internet, they usually tell you about the performance of the lens and you can usually check some sample pictures to decide yourselves. Some of the sites also try to shoot the exact same thing with the different lenses so you can actually compare the results on your own.

For example I checked two completely different (different manufacturer, quality, mount type, etc.) lenses on photography blog.

This is a picture made with a Canon EF-M 18-55mm at 55mm:

Canon 18-55 at 55

And this is a picture made with a Fujifilm XF 55-200 at 55mm:

Fujifilm 55-200 at 55

While it's obvious they were taken from slightly different angles at different times, and also with different cameras (with slightly different crop factors which also affect the picture) they still look fairly similar.

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    Depending on the lenses, focus breathing might also affect the field of view when focussing on something much closer than infinity. – Peter Taylor Nov 10 '16 at 17:55
  • The top picture is much better (more interesting) than the one below. I would probably attribute this to lighting though and not the equipment used. – Octopus Nov 10 '16 at 21:37
  • @Octopus The top image is much better composed with framing and leading lines that are minimized or excluded from the lower image. – Michael C Nov 11 '16 at 3:51
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Although your composition will likely be the same, there may be differences in falloff (vignetting), barrel distortion and chromatic aberration. You may also reach limits of the lenses' apertures.

In both cases, you're operating the zoom at an extreme, and you can't expect the results to be as good as, say, a 24-105 at 55m, and certainly not as good as a 55mm prime lens. (Assuming that low values of distortion, falloff and aberration are "good" for you - if not, you want a cheap plastic camera!).

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    Not all zoom lenses perform best in the middle of their range. There are some notable exceptions that do better at both the wide end and the long end than they do in the middle. They are the notable exceptions, however. – Michael C Nov 11 '16 at 0:05
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The answer has a few dependencies. First, which brand? Nikon has been hitting it out of the park lately for sharpness in the low end kit lenses, which Canon does not have the same reputation for their 18-55 to my knowledge.

So let's assume the Nikon kit lenses. Both of these have a great reputation for sharpness, however the 55-200 is a better lens than the 18-55, despite the 55-200's slightly wider range of 3.6x versus the 18-55'2 3.0x. Now, I say that based on one site's measurements (photozone.de) on 10mp cameras, but I think it is born out by other sites as well.

The key here is that almost all zooms fade somewhat at the long end, so the 18-55 is at its weakest at 66 while the 55-200 is at its strongest. This makes a significant difference in the final image quality, especially as the megapixel count climbs. There is also the fact that kit zoom lenses have variable apertures and are at their slowest at the long end, so the 18-55 is at 5.6 wide open, while the 55-200 is a full stop faster at 55, which is f/4. That too is a big difference.

So, the 18-55 shows wide open sharpness (line widths per picture height) as 1935 at the center and 1856 at the border. By contrast, the 55-200 shows center sharpness at 2203 at f/4 and 2205 at f/5.6. The border drops drastically, though to 1666 and 1789 respectively. That is a visibly sharper lens in the center, while being a bit softer at the borders. For portraiture, the 55-200 beats the 18-55 hands down. For landscape or architecture, it's a close match, but I would personally still choose to shoot the 55-200 given the center sharpness.

Now, there is an area where the 18-55 beats the 55-200 at the common focal length. The chromatic aberration (fringing) is better controlled on the 18-55. But both are well under 1px in width and so will not be all that visible. I would not differentiate on this score.

The 18-55 loses on distortion, which might be expected when you consider that it starts out pretty wide. The 55-200 is better controlled at 55mm.

Vignetting shows a small difference wide open at 55mm, with the 55-200 being slightly better.

So to me it looks like a handy win for the 55-200 at 55mm. And of course, you get to zoom in and step back to compress the background for better and better portraits as a bonus.

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