[Alex-Nelson]

The swedish website Objektivtest.se (www.objektivtest.se) has begun their review of the HD PENTAX-D FA 150-450mm F4.5-5.6 ED DC AW. And even if the review is far from finished, they have allready published MTF charts for both full frame and ASP-C.

TEST: Pentax HD D FA 150-450 mm F4,5-5,6 ED DC AW

It's a swedish site so for most of you guys who are not swedes the text needs translation. For instance with the aid of google translate. But the MTF is straight forward. The lens holds up really well all the way up to 450mm with full frame. It will seemingly perform quite well on a K-1.

Also check out their review of six full frame Pentax FA lenses here: TEST: Six full frame prime lenses for Pentax K-1

Lots of interesting reading!

---

Last edited by Alex-Nelson; 04-02-2016 at 02:50 PM.

[Ari]

An interesting read! I plan on repurchasing the 31, 43 and 77 after I finish paying for the the k-1, grip and 15-30 that I'm (impatiently) waiting for.

[nomadkng]

ok, maybe someone far wiser than me can explain why the FF MTF was done at 20 lp/mm and the APS-C was done at 30 lp/mm?

from other sites, such as Sigma, Tamron and even Pentax, usually it's 10 and 30.

but if I compare the 30's, I've seen a lot better results, with Sagittal "scores" in the 75ish-80 from several sites.

the charts on this site put them in the 50's.

that would scare the bejeebers out of me if I were thinking about plunking down 1700 for this lens.

attached is the sigma 50-500 mtf which is a lens known as decent but not stellar. when comparing the green sag (solid) (30 lp/mm) with the blue Sag (solid) (30 lp/mm) from the Swedish results, it seems the Sigma is 20-30% better at resolving than the Pentax. I find that very hard to believe.

so while you're at it, explain to me what happened in this comparison. I'm actually asking so I can have a better understanding of lens comparisons. I know there can be several variables to MTF charts, but they shouldn't have THIS much discrepancy, surely.

[Alex-Nelson]

ok, maybe someone far wiser than me can explain why the FF MTF was done at 20 lp/mm and the APS-C was done at 30 lp/mm?

from other sites, such as Sigma, Tamron and even Pentax, usually it's 10 and 30.

but if I compare the 30's, I've seen a lot better results, with Sagittal "scores" in the 75ish-80 from several sites.

the charts on this site put them in the 50's.

that would scare the bejeebers out of me if I were thinking about plunking down 1700 for this lens.

attached is the sigma 50-500 mtf which is a lens known as decent but not stellar. when comparing the green sag (solid) (30 lp/mm) with the blue Sag (solid) (30 lp/mm) from the Swedish results, it seems the Sigma is 20-30% better at resolving than the Pentax. I find that very hard to believe.

so while you're at it, explain to me what happened in this comparison. I'm actually asking so I can have a better understanding of lens comparisons. I know there can be several variables to MTF charts, but they shouldn't have THIS much discrepancy, surely.

The Sigma MTF charts are theoretical, better than in reality. And the one's at Objektivtest.se are actual measurements. The Sigma 50-500 mm is in fact nowhere near the performance in that chart. Also note that the 30 lp/mm at Objektivtest.se show performance just for APS-C, so they stop at a radius of 15 mm, whereas Sigmas show full frame.

I think the reason why they measure full frame at 20 lp/mm is becasuse it's a frequency that represents both contrast and resolution. 10 lp/mm is mostly about contrast. 30 lp/mm is probably chosen for APS-C because it's a smaller format that requires exactly 1.5x higher resolving power to compare to full frame. 1.5x20 = 30.

[stevebrot]

ok, maybe someone far wiser than me can explain why the FF MTF was done at 20 lp/mm and the APS-C was done at 30 lp/mm?

Calculation is relative to image height, IIRC.


Steve

[monochrome]

This has the capacity to become, similar to the DxO 'score', a case where readers who only look at the charts without understanding the methodology and theory can be misled.

[HopelessTogger]

I'm too thick to understand charts. Is this lens good or bad or average or what?

I ask because it looks to be a good focal length for airshows et.al.

[Digitalis]

Please bear in mind this is based only on one sample of the lens, bear in mind In some cases there can be wide variation in lens performance - especially with multi-element telephoto zoom lenses with focal length ratios greater than 1:3.

Unfortunately there was an excellent tutorial on reading MTF charts on Luminous landscape - which is now, for reasons that I can only assume is to diminish public knowledge of photography, is now behind a paywall.

[BrianR]

Unfortunately there was an excellent tutorial on reading MTF charts on Luminous landscape - which is now, for reasons that I can only assume is to diminish public knowledge of photography, is now behind a paywall.

This one- https://luminous-landscape.com/mtf/?

The full article is on the Internet Archive (a minor problem with a retroactive paywall).

[osv]

Lens MTF Test Results

[nomadkng]

Please bear in mind this is based only on one sample of the lens, bear in mind In some cases there can be wide variation in lens performance - especially with multi-element telephoto zoom lenses with focal length ratios greater than 1:3.

Unfortunately there was an excellent tutorial on reading MTF charts on Luminous landscape - which is now, for reasons that I can only assume is to diminish public knowledge of photography, is now behind a paywall.

I've read that article before. In fact, I think that is the article that helped me start to figure things out when translating MTF charts. I understand it's only one lens and is subject to sample variation. But is it safe to conclude that the lens tested was an underperforming lens based on the produced MTF results?

If so, it might be a good idea to add that caveat when discussing this article.

[Alex-Nelson]

I've read that article before. In fact, I think that is the article that helped me start to figure things out when translating MTF charts. I understand it's only one lens and is subject to sample variation. But is it safe to conclude that the lens tested was an underperforming lens based on the produced MTF results?

If so, it might be a good idea to add that caveat when discussing this article.

Why would be safe to assume the lens was underperforming? The MTF charts look good. You can compare with the Nikon AF-S 80-400mm G ED VR lens which they also have tested and gave the rating "Toppklass" (Outstanding). The Pentax 150-450mm doesn't really seem worse.
TEST: Nikon AF-S 80-400 mm f/4,5-5,6 G ED VR

Again, don't compare theoretical MTF found on the lens producers websites with MTF made by actual measurements. If you do, you will allways be disappointed with the latter.