Lens evaluation: what am I missing here?

NorthernFocus

I've been evaluating several different telephoto/zoom lenses recently, trying to decide on a purchase. This is the first time I've seriously considered upgrading to a pricey (for me) piece of glass like a Nikon 200-400VR or a 300 2.8. For the obvious cost advantages I'm also looking at a Sigma 300 2.8, a 120-300 2.8 (I already own the Sigma 1.4x and 2x TCs) or the Bigma 50-500. Considering the difference in cost between Nikon and Sigma lenses, I started looking for objective information to justify the additional cost. Which led me to seriously studying and comparing MTF charts for the first time.....:scratch

OK, to get to the point... On a typical MTF chart, contrast and sharpness drop off the further you go to the right (i.e. further from the center of the film/sensor plane). Most of them really drop off out beyond 15mm from center. Which brings me to my point. I shoot a D200 with a DX sensor which is roughly 16x24mm. So how the lens performs beyond the 12mm point on the chart is irrelevant isn't it? Obviously if one were to decide to go to a full format camera in the future it may be an issue, but let's just assume I'm living for the here and now :huh

I'd appreciate others' perspectives especially if someone can tell me what I'm missing here.

pathfinder

Lenses designed for a full frame sensor, do even better on a smaller APS sensor precisely because the smaller sensor does not capture the less sharp corner areas.

That is exactly what the MTF charts are telling you.

The Sigma 120-300 f2.8 is a nice lens - very sharp, but the absence of IS is noticed at time - It is better used on a a tripod.

What is your budget?

ziggy53

articblooms wrote:

I've been evaluating several different telephoto/zoom lenses recently, trying to decide on a purchase. This is the first time I've seriously considered upgrading to a pricey (for me) piece of glass like a Nikon 200-400VR or a 300 2.8. For the obvious cost advantages I'm also looking at a Sigma 300 2.8, a 120-300 2.8 (I already own the Sigma 1.4x and 2x TCs) or the Bigma 50-500. Considering the difference in cost between Nikon and Sigma lenses, I started looking for objective information to justify the additional cost. Which led me to seriously studying and comparing MTF charts for the first time.....

OK, to get to the point... On a typical MTF chart, contrast and sharpness drop off the further you go to the right (i.e. further from the center of the film/sensor plane). Most of them really drop off out beyond 15mm from center. Which brings me to my point. I shoot a D200 with a DX sensor which is roughly 16x24mm. So how the lens performs beyond the 12mm point on the chart is irrelevant isn't it? Obviously if one were to decide to go to a full format camera in the future it may be an issue, but let's just assume I'm living for the here and now

I'd appreciate others' perspectives especially if someone can tell me what I'm missing here.

I'm not a big fan of MTF charts. Canon, for instance, uses "calculated" MTF as opposed to the "measured" MTF that almost everyone else uses. Everyone seems to have their own methodology as well, so comparisons between manufacturers is not reliable.

If you want to use the "measured" resolution charts posted at sites like "http://photozone.de/" that's fine as long as you realize that they generally use single lens samples and it's only fair to compare in a single camera manufacturer, and the site points that out.

claudermilk

That's why you look at multiple sources. I usually try to look at photozone's data, manufacturer MTFs and photodo's MTFs where available at minimum. I also look at sample images as much as possible.

NorthernFocus

Thanks for the feedback, everyone. One of the best and worst aspects of the web is the availability of information. Looking for multiple sources of information an a given topic is definately a wise thing to do . Regarding the use of MTF charts, it is not meaningful to compare charts of a given lens produced by different sources. However, it is meaningful to compare charts of different lenses produced by the same source . For instance using Nikon's charts to compare a 300 2.8 against their 200-400 VR is useful.

Thanks again,