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Tamron 200-500mm vs. Sigma 50-500mm DG

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Old Friday 9th January 2009, 12:20   #26
carlj
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Pentax is a funny mount - since digital, it's popularity has waned, at least with 3rd party support and many lenses can be hard to source. It's why my partner sold hers and moved over to Sony/Minolta. Even there, some lenses such as the Tamron 200-500mm can still be hard to find - I was lucky with mine.

However, as Pentax can still us K/KA as well as KAF mount lenses, could be worth scouring the second user listings at ffordes and mifsuds....
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Old Thursday 15th January 2009, 03:58   #27
alan carr
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The resolving power of the Sigma 50-500 is better than the Tamron 200-500 at 500mm. The Tamron has 3% more magnification than the Sigma at 500mm.

Two 100% crops, the top one is from the Sigma, the bottom from the Tamron.
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Old Thursday 15th January 2009, 16:22   #28
geordie graham
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Originally Posted by Beth_W737 View Post
Can anyone give me advice for a lens? I have a Pentax K10D, and am going to Costa Rica in the spring (March/April), and wanted a good lens for wildlife/rain forest photos...currently have 18-55 kit lens and 50-200, but not thrilled with them...I'd been wanting a longer reach lens but am not sure whether I'd be better off getting a 400 or 500 mm lens, or a faster 2.8 lens (ie, 200 mm 2.8 or 300 mm 4). Can anyone give me some advice?

Beth
Hi Beth I have the K10D and the 50-500 Bigma.It is great in good light but can hunt a bit in not so good light it is also a a heavy lens to cart about.I have had some great pics and also been a little disillusioned with others and wonder if I should have saved up a bit more and a 300 f4 and then got a 1.4 converter.I try to keep it around 450mm if possible and then tweak with Elements 5 and have had some good results(see recent photo`s in my gallery). The real upside is because the K10D has shake reduction on the camera then it will mean all lens attached to will also benefit.Would love a 500 f4 but can`t afford one.Good luck with whatever you choose.

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Old Monday 19th January 2009, 02:05   #29
Tannin
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Oh dear, ancient thread, but there doesn't seem to be a sensible answer to the magnification question, so we had better have one.

Max magnification is simply what happens when you combine focal length and minimum focus distance. You get greater magnification if you increase the focal length (say, from 400mm to 500mm) or is you decrease the minimum focus distance. So, my 500/4 has a lower max magnification than my 100-400 because, although it's 100mm longer, it can't focus closer than 4.5m, where the shorter 100-400 can focus down to 1.8m.

As another example, consider the Canon 50mm f/1.8 and the Canon 50mm f/2.5 compact macro. Both lenses have a focal length of 50mm, but the 50/1.8 has a max magnification of 1:6.66, where the compact macro has a max of 1:2. Same focal length, but it focuses a lot closer.
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Old Monday 19th January 2009, 03:12   #30
alan carr
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Oh dear, ancient thread, but there doesn't seem to be a sensible answer to the magnification question, so we had better have one.

Max magnification is simply what happens when you combine focal length and minimum focus distance. You get greater magnification if you increase the focal length (say, from 400mm to 500mm) or is you decrease the minimum focus distance. So, my 500/4 has a lower max magnification than my 100-400 because, although it's 100mm longer, it can't focus closer than 4.5m, where the shorter 100-400 can focus down to 1.8m.

As another example, consider the Canon 50mm f/1.8 and the Canon 50mm f/2.5 compact macro. Both lenses have a focal length of 50mm, but the 50/1.8 has a max magnification of 1:6.66, where the compact macro has a max of 1:2. Same focal length, but it focuses a lot closer.
You're incorrect. In my description, the size of an object is 3% larger (measured with the caliper tool) with the Tamron than when compared to the Sigma. ie: if the Tamron was 500mm, then the Sigma is 485mm at its max end.

An object you see with your 500mm lens will be bigger than with your 100-400. It has nothing to do with the minimum focusing distance, unless you're trying to do macro work. By measuring the size of an object at the same distance from the focal plane of the camera, you can compare how much the object is magnified by one lens over the other. Hence, you can calculate the difference in focal lengths between your lenses - it's basic geometry.

Whether the difference is constant over all focusing distances, that's another matter.

Last edited by alan carr : Monday 19th January 2009 at 03:20.
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Old Monday 19th January 2009, 08:07   #31
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Sorry Alan, but the description I gave above is quite correct (though lacking some detail). I'm afraid you have got completely the wrong end of the stick here.

The difference you are observing between two different "500mm" lenses, assuming that you are measuring then both under the same conditions and focused on infinity, has nothing to do with maximum magnification, it's a simple difference in actual focal length as opposed to nominal focal length. It rather annoys me (and probably you too), but it's a fact of life that lens makers often crib a bit with their claimed focal lengths, and always (it seems) to their own advantage.

Maximum magnification, also known as "reproduction ratio" or just "magnification", is a standard performance metric used by lens designers and makers, and routinely quoted in their technical literature. Indeed, those examples I gave above were from Canon specification sheets. As examples of others from the various lens makers, you may care to look at some official Sigma specifications here and discover that the Sigma 17-70 has a maximum magnification of 1:2.3. Or go here to discover that the maximum magnification of the Nikkor 400/2.8 is 1:6.3, here to see that Pentax cite the maximum magnification of their smc FA 31/1.8 Limited as 0.16 (which you can divide into one to yield 1:6.25 if you prefer to see the number as a ratio rather than a fraction), or indeed here to discover that Tokina cite the maximum magnification of their 80-400/4.5-5.6 as 1:5.4.

Maximum magnification is measured at the minimum focus distance. Does it seem odd that the lens makers cite that figure when anyone smart enough to count change could divide the focal length by the MFD to discover it for themselves? There is a reason: focal length is always measured with the lens focused at infinity, while (obviously) maximum magnification is measured with the lens focused as close as it will go - and this changes the focal length! (Lenses are shorter when focused for close-up. You can easily see this for yourself by spending a few minutes with a macro lens and turning the manual focus ring.)

By knowing the focal length and the MFD, you can approximate the maximum magnification, but to get it exactly you then need to allow for the change in effective focal length at close focus. (I imagine that's a fairly small correction with most lenses, though I've never troubled to do the maths for myself.) In reality, there is no need to: I can see at a glance that the 100-400 has a much higher maximum magnification than the 500/4, or if in doubt I could look up the factory specs to discover that the 500/4 has a maximum magnification of 1:1.2 where the 100-400 is nearly double at 1:2.
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