Sigma 18-200 or 18-170?

[GovtLawyer]

After reading some threads that the 18-200 measures out to only 170, and not being able to find one poster who could point me to an actual test, I performed my own test. I am neither a scientist or a mechanical engineer, so my test would not stand up to the requirements of either. My test was simple. I took a number of photos at 144 or 150 (so said the data file) and then took the same photo all the way out. The data file said 200. If it was a real 200, I would expect the lens to have brought me approximately 1/3 closer to the subject than it did at 150. Results: NO WAY THIS IS A 200!

Time after time the difference between the 150 and all the way out, was at most 10 or 15% more. Not very dramatic at all. Could I measure this? Perhaps, but I simply used my eye.

If this has been noticed before, does anyone know if Sigma has commented on this? Would you imagine this is a poorly calibrated lens, which should be returned or exchanged, or is it the entire lens line? If it is the line, I'm a bit more than angry. It sounds like a fraud or other consumer scam.

[ron chappel]

This is completely normal for zooms- all manuafacturers do it sadly.
Especially with consumer zooms...and more so with lenses that focus internally.
The usual focal length tollerance is about 10-15% i've heard, but some do go a little under even that.
Internal focus lenses need to be measured at infinity because they change focal length when focused closer

[MrChad]

You may want to also double check what 200mm lens you are comparing this too.

I'm not doubting your 200mm may come up short, but in tests with a 28-300mm Tamron vs. a Canon 75-300mm EF, you need to be careful. The Tamron may be short, but the Canon 300mm zoom sometimes, do to it's front rotating lens, can actually focus past 300mm in some cases.

I'm not saying this is the case in your comparison, but it's best to have several sources of 200mm focal, a prime would be the best measure for you of a true 200mm.

That said I'm not sure the difference between 150mm and 200mm is all that great on any of my tele's. I would need some primes to compare reach personally. But many hyper sooms like the 28-300mm or the 18-200mm may likely be a tad short on the long end.

[GovtLawyer]

You may want to also double check what 200mm lens you are comparing this too.

I'm not doubting your 200mm may come up short, but in tests with a 28-300mm Tamron vs. a Canon 75-300mm EF, you need to be careful. The Tamron may be short, but the Canon 300mm zoom sometimes, do to it's front rotating lens, can actually focus past 300mm in some cases.

I'm not saying this is the case in your comparison, but it's best to have several sources of 200mm focal, a prime would be the best measure for you of a true 200mm.

That said I'm not sure the difference between 150mm and 200mm is all that great on any of my tele's. I would need some primes to compare reach personally. But many hyper sooms like the 28-300mm or the 18-200mm may likely be a tad short on the long end.

I haven't compared it to anything. I simply looked at the reach of a photo which the datafile says was shot at 144 or 150 and compare it to the photo it says was shot at 200. Common sense tells me that it should bring me in approximately 1/3 closer (another 50MM is 1/3rd of 150).

I just came back from doing a test in the street. I shot at lowest compression and size, so I ought to be able to post the entire shoot on the web, without cropping. Again, at infinite focus, manual focus, infinite manual, whatever, the tele end does not appear to be much longer than than the 150.

[MrChad]

I have a Sigma 18-125mm DC, these are really having your cake and eating it too kind of lenses. You won't find a Canon with this kind of reach, that said coming up a few (mm) short in FOV isn't unthinkable.

I find that with zooms, you really need to compare them to primes or a handful of other zooms, even then because of focusing required for the lens you may find a slight change in FOV between lenses.

Case in point, you may find reviews online for the Canon 75-300 IS vs. 70-300 IS DO, both don't always have the same FOV at 300mm, this is do to the differences in focusing methods. I have yet to doubt my 125mm end of my Sigma is 125mm, but if you told me it looked more like 115mm, I wouldn't be surprised or upset, after all who else makes these kinds of super (hyper) zooms?

I'm not sure what standards are used to rate the lens focal lenght, but at infinity maybe these hyper zooms appear short on the long end, but maybe focusing at a distance of 5ft they have the same FOV as a prime of the same focal length? I would assume we would need to know the standard for focal length, is it theoritical distance of the optics (lens elements) from the focal plane (sensor-film) or is it equivilant FOV? I haven't looked into this or given it much thought at this point since, I can likely crop in any extra reach I need on the Drebel much easier then I could with film in the past.

[GovtLawyer]

I have a Sigma 18-125mm DC, these are really having your cake and eating it too kind of lenses. You won't find a Canon with this kind of reach, that said coming up a few (mm) short in FOV isn't unthinkable.

I find that with zooms, you really need to compare them to primes or a handful of other zooms, even then because of focusing required for the lens you may find a slight change in FOV between lenses.

Case in point, you may find reviews online for the Canon 75-300 IS vs. 70-300 IS DO, both don't always have the same FOV at 300mm, this is do to the differences in focusing methods. I have yet to doubt my 125mm end of my Sigma is 125mm, but if you told me it looked more like 115mm, I wouldn't be surprised or upset, after all who else makes these kinds of super (hyper) zooms?

I'm not sure what standards are used to rate the lens focal lenght, but at infinity maybe these hyper zooms appear short on the long end, but maybe focusing at a distance of 5ft they have the same FOV as a prime of the same focal length? I would assume we would need to know the standard for focal length, is it theoritical distance of the optics (lens elements) from the focal plane (sensor-film) or is it equivilant FOV? I haven't looked into this or given it much thought at this point since, I can likely crop in any extra reach I need on the Drebel much easier then I could with film in the past.

I think the bottom line is that all agree the 200 end is probably not a 200. While there are varying reasons given for this, and various means given to test it, the conclusion is inescapable. Now, am I bent out of shape over this? NO! However, I am a bit miffed. I think the lens should be sold as a 28 to 185 or whatever. I think rounding off to the nearest high number is an advertising ploy, which this consumer doe not appreciate. Yes, I like the lens, and yes, it is a great walkaround. I'm just a guy who believes in truth in advertising, and in this case it doesn't appear Sigma is being particuarly honest.

Now, is there a chance that Sigma didn't know the true reach of the lens? NO WAY!

[sharrowm]

If I read your first post right your test went something like this:

1. You took a picture at ~150mm (according to the data file)

2. You then took a picture of the same subject at 200mm (confirmed by the data file)

3. You compared the 2 pictures and discovered that the subject in the second picture was not 33% bigger than the first, thus your conclusion is that it must not truly be a 200mm lens.

Question: Why would you assume that the datafile is correct for the first picture but incorrect for the second picture?

Your conclusions may be correct, but I bring up this point just to show that your test (as you said) is not very scientific. You have too many variables to draw any conclusions.

[MrChad]

My point was to actually state the lens may very well be a 200mm lens but it may appear to have a different FOV when focusing at different length from the position of the focal plan. I could very well be wrong but until you know the industry standard for focal length it would be in accurate to state the lens is short per say. Especially with out a direct comparison.

You may infact be right, I was just trying to point out what may be a technicality, I don't think Sigma would lie about the marketing of it's lenses, at least I would hope not.

There also may be a % tolerance for what constitutes focal length for zooms that works in the industry. Maybe Sigma is being generous with it's tolerance too.

[GovtLawyer]

If I read your first post right your test went something like this:

1. You took a picture at ~150mm (according to the data file)

2. You then took a picture of the same subject at 200mm (confirmed by the data file)

3. You compared the 2 pictures and discovered that the subject in the second picture was not 33% bigger than the first, thus your conclusion is that it must not truly be a 200mm lens.

Question: Why would you assume that the datafile is correct for the first picture but incorrect for the second picture?

Your conclusions may be correct, but I bring up this point just to show that your test (as you said) is not very scientific. You have too many variables to draw any conclusions.

A very good point, and I thought of it as well. The photos were taken from 18 all the way to 200. While it is not scientific, the 18 appeared to me to be what I have been used to seeing from a film 28 MM. I am fairly confident that the point of view is as wide as it should be. As I continued through the zoom length, using the barrel markings and comparing them to the data file, it seemed as if each step was correct, approximately, in relation to the step before. Except, the last jump from 150 to 200. I am also aware of the other anecdotal evidence (on these boards) referring to the same problem. I have never heard anyone complain that the focal length is inaccurate on the wide end. So, my test, coupled with what I have heard, indicates to me that the telephoto end is not accurately stated by SIGMA.

I'd love to see another test, done more scientifically than mine, with more precise measurements. In any event, the lens is a keeper for me; although, I do believe SIGMA has not been consumer friendly in its description of the lens.

[Paul Carpentier]

Is the Sigma a true 18-200? The answer is "yes, but...". Check it out for yourself:

http://www.pixagogo.com/9247155371

Paul

[MrChad]

Is the Sigma a true 18-200? The answer is "yes, but...". Check it out for yourself:

http://www.pixagogo.com/9247155371

Paul

I think this may be what I was trying to say?, the lens may only be 200mm at some focused lengths, just as my Canon 75-300mm may be a tad longer (320mm-ish) at some focused lengths. Mind you this is still all speculation on my part I have not done any "testing" per say. The 75-300 IS does this becuase the front element rotates out to focus, I'm not an optical engineer and as such don't spend much time contemplating lens optics, I actually hated engineering Physics II and III so I'll leave that to someone that really cares about optical elements. Does the rear element move on the Sigma during focusing does it move and change the over all lens optical length, I don't know.