Originally posted by Jewelltrail Edgar, since you are not clear about why I make certain points, I’ll try again. However, this time I’ll try a different route, so please do not take me as being curt--okay?
In a nutshell, you can not compare a wide-to-normal lens to a near-normal-to-short-telephoto lens and call that apples to apples--IT IS THAT SIMPLE!
Compromises go into wide angle design--compromises which affect performance in other areas, particularly vignetting. Let me give you a concrete example of why your illustration is not apples to apples. What are the vignetting numbers for the 28-75mm @ 17, 18, 19, 20 and so on MMs? There are none, because the 28-75mm is not apples to apples to 17-50mm--right? However, ironically for our discussion, there is a way to provide apples to apples for these 2 lenses because they each provide almost exactly the same focal range on their designed format--right? In other words,
on their designed formats, each lens is a wide to normal lens--in other words, on their respective formats, the lenses are apples to apples. ta----daaaaaaaa.
Natural vignetting is unduly affected by wide angle lenses.
Again, Natural vignetting is unduly affected by wide angle lenses. Conversely, Natural vignetting is not unduly affected by normal lenses. Is this helping?
If you want apples to apples, place each lens on their intended mounts and look at the vignetting numbers. The reason I did not provide vignetting numbers for the 28-75 on APS-c is because those numbers have no place in this discussion. Now, once again, the reason I got into this discussion is because you wrote something which is not accurate. Here it is again:
Am I more clear in this post? The vignette performance of the 17-50 is not a weakness; rather, it is an inherent result of designing a lens from wide to normal--. Also, and again, this is NOT, as you say, “typical for lenses designed for APS-C as opposed to lenses designed for full frame (such as the 28-75mm).” In fact, vignetting is much more typical of lenses designed for full frame. PERIOD!!!!!
Okay, sure, you have a purpose in this thread. You wish to explain the awesome nature of the 28-75. I too bought a 28-75mm Tamron, because I knew it was great value. I too wish to relay its awesome nature here in this thread--
but I will not make unfounded claims for its performance---this is our point of departure. You started the thread, this does not license you to censor or dogmatize its content. Okay, I am finished--will not return to this thread now because I have done all time will allow me to do. Best of luck to you.
No, just the Tamron 28-75 is best than 17-50 on APS-C camera, compared in the same focal range (28mm to 50mm). In APS-C żok?
Pentax have only APS-C sensor, and If in future have an FF, then the 17-50 do it worse than 28-75
If I need a lens for that range of focal, (28-50) Tamron 28-75 is best than Tamron 17-50, Just that.
If I need more wide or more tele, that is other point to analyze in the moment of decision.
Very sorry for my terrific English