APSC and FF sensors, and TDP's ISO 12233 chart comaprison...

[Eccentric M]

Hello, I am a huge fan of TDP's ISO 12233 chart comparison tool (and the whole website in general), but there's something that intrigues me...

I've compared lenses on both the 1Ds3 and 60D and there seems to be a noticeable difference in the IQ. I am sure the anti-aliasing filter and the sensor play a role, amongst other things, but I didn't know it mattered that much.

I have a canon EOS 7D and I am thinking of replacing my 70-300 IS lens (the black one) with another telephoto lens. I have a few in mind, such as 70-300L and 400 5.6L, but I am not that pleased with the image quality of the lenses on the EOS 60D from the ISO 12233 crops on the site. Especially when the new EF-S 55-250 IS STM has comparable or better IQ than the L lenses on the 60D...

Am I thinking about it too much?

[PatrickH]

I was wondering if someone was going to bring this up. I was also pleasantly surprised when I saw the ISO chart for the new 55-250 STM. Aside from some additional vignetting, IQ seems to compare favorably. I am very interested in checking out the full review. This plus the new Sigma could make for a nice/versatile kit at a good value.

That said I don’t regret my L tele lens purchase. Sharpness aside, I get the following with my 70-200.

Fixed, 2.8 aperture at all focal lengths (and the subject separation and low light benefits that come with it)
Weather sealing
Very fast focusing
A front element that does not rotate
Compatibility with extenders
Full frame compatibility
Great overall construction and handling

For the most part you can’t find these features on a dedicated APS-C lens, and they matter enough to me to justify the premium.

[neuroanatomist]

Full frame sensors yield sharper images in standardized tests like the ISO 12233 crops and Imatest SFR tests. The reason is the bigger sensor - with the framing matched, the APS-C image must be enlarged more for a given output size, meaning a softer result. The increased sharpness with FF is evident in real-world shooting, too.

In focal length-limited situations, where you could fill the APS-C frame but need to crop the FF image (can't get closer or use a longer lens), the APS-C sensor would *theoretically* deliver higher resolution. However, ISO noise plays a role in perceived sharpness. I've found that in practice when comparing current/recent sensors, an image from a FF sensor cropped to match the APS-C FoV has equivalent IQ at up to around ISO 800, and the cropped FF image has progressively better IQ as the ISO goes up from there.

[Eccentric M]

Thanks for the replies!

How could an L lens be so bad that a 55-250 would beat it in the image quality test on APS-C sensors like 60D? I read neuroanatomist's reply but idk. I'd like to get a 70-300L or something in that caliber in the future but I am unsure if I should drop the extra cash since the 55-250 IS is on par IQ wise...

I'm confused, sort of.

[9VIII]

Similar to how sensor cost goes up exponentially with size, lens cost goes up in the same way.
A small lens is relatively easy to polish and if a fatal mistake is made the cost incurred is low.
A lens with double the surface area not only has twice the chance of flaws, but all of the costs associated with producing that lens will be that much greater as well (and remember that time=money, if one large lens takes the same time to produce as ten smaller ones, that will have a significant impact on end cost).
In other words, they can make smaller lenses with a much higher degree of precision because everything involved in making them is so much less expensive.

Surprisingly, the two lenses in question here (55-250 IS STM and 70-300L) aren't actually all that different in front element diameter (44mm vs. 54mm. Note that I'm just using the F numbers for that figure). It is not insignificant, but it's not on the same scale you get with big whites and such.

I'm reminded of two articles I read recently.

http://www.lensrentals.com/blog/2013...o-perfect-lens

http://www.imaging-resource.com/news...-from-the-insi


Notice how in the "no perfect lens" article, lens sharpness is more of a fluid thing than a "it's sharp or it's not" type of deal. I'm just now realizing how it would be easier to get everything lined up right on a crop sensor. You could potentially take the exact same lens and come out with a much different result if tuned just for a crop sensor. On full frame, again, problems increase exponentially with size. With that much more space to balance out you're going to have to make more compromises.
Finally it makes a little more sense why crop lenses would be cheaper to produce.
Also consider that the 55-250 IS STM is going to be made with cheap labour and with cheap components. Where the 70-300L is made in Japan with an aluminum body (read the factory tour for some perspective on that), USM, probably superior IS, etc.

(Sadly no fluorite elements in that lens. I'm starting to wonder if Canon has a very limited supply of those, and whether or not their reasoning for not updating the 400f5.6 is that it would suck up their entire supply of fluorite and they don't want starve the supply of sports and journalistic lenses just to make lenses for a bunch of birders .)

[Kayaker72]

Thanks for the replies!

How could an L lens be so bad that a 55-250 would beat it in the image quality test on APS-C sensors like 60D? I read neuroanatomist's reply but idk. I'd like to get a 70-300L or something in that caliber in the future but I am unsure if I should drop the extra cash since the 55-250 IS is on par IQ wise...

I'm confused, sort of.

Eccentric M,

First, there are several factors that go into image quality. You can see things like sharpness and contrast in the ISO 12233 test as well as some evidence of distortion. All important, but image quality includes color rendition, bokeh, etc. It is entirely possible that the EFS 55-250 STM is exceptionally well calibrated to the APS-C sensor and deliveries excellent IQ. Perhaps it is better than something like the 70-300L. Several lenses, EFS 17-55 and EFS 15-85, are considered on par with the "L" glass IQ. I haven't heard enough about the EFS 55-250 to have an opinion but it is very possible and not unprecedented for an EFS lens to rival the IQ of "L" glass. And the charts certainly look good.

But just keep in mind that the "L" stands for "Luxury." You are buying hopefully the best IQ, but also build quality and various high end features (such as AF speed). To an extent, this is like saying that a Honda drives as well as an Acura. It may be true, but the Acura is more luxurious. I have an old EF 75-300 that I used on my film camera. I've taken some pictures I love with that lens but I still bought a 100-400L. I've tested them side by side, and there is an improvement in IQ, no doubt. But it certainly isn't equivalent to the price difference, and it may not be "that" noticeable until you crop. But, the 100-400L is rock solid. The 75-300 wobbles when extended. I think the AF is faster and more accurate on the 100-400L. In short, I have no regrets. But I certainly do not hold any disdain for the 75-300 or non "L" glass. Most of them are very capable and sufficient for most photographers.

A slight tangent, but I spent a long weekend at a hotel in Northern New Hampshire over Labor Day. We were sitting in a front porch area and this couple asked me to take their picture. They had a rebel. We got to talking and they were very pleased to have a dSLR, but they only had the kit lens. The husband had gone online and was researching telephoto lenses because he wanted to take shots of his kids at outdoor sporting events. He ended up not buying anything because the websites he went too, in his opinion, kept bashing anything that wasn't "L" glass and he couldn't afford it. I don't fault him, I've seen people bash everything, even the 5DIII or 1DX....or, of course, the whole nikon vs canon thing. But, because of spending so much time on internet websites and forums he ended up not getting a lens that sounded like it would absolutely meet his needs. I think I may have talked him into the 55-250 or a 75-300.

If you do not specifically want the features of an "L" lens such as the 70-300L, then by all means buy the EFS 55-250 STM. The charts look good, it may be an excellent lens. Brian tends to be very fair, in my opinion. You may want to wait for his review, or at least email him to ask when one is coming. If he does a review, it'll highlight the pros and cons.

Good luck in selecting the best lens for you. It can be a challenge.

Brant