Beyond 400mm

[Ray]

No, not if one is talking true focal lengths.

That's an interesting point. There's a perception that lenses designed for the smaller format will always be lighter. A good example which belies this notion is the Zuiko 300/2.8 designed for the 4/3rds format. It's actually heavier than the Canon EF 300/2.8 which is designed for full frame 35mm. (3290gms as opposed to 2550gms for the Canon).

It seems that most of the EF-S lenses which appear to be lighter than the nearest full frame equivalent are wide angle zooms with a different design to FF lenses; a design with a short back focus where the rear element is closer to the sensor. With telephoto lenses this design advantage apparently doesn't exist.

It would be interesting to see a comparison between the Olympus E-620 with the Zuiko 300/2.8, and the Canon 50D with Canon 300/2.8 IS. If we crop the 50D to the 4:3 aspect ratio of the E-620, we reduce the pixel count of the 50D to about 13.47mp. If we crop the 50D image again to the same FoV as the E-620 image, the pixel count of the 50D is further reduced to just 10.21mp. The Olympus sensor has the edge in terms of resolution, but the Canon might have the edge in terms of noise. However, if we crop the E-620's sensor to the 3:2 aspect ratio of the 50D, that edge in pixel density becomes so small as to be irrelevant.

If it's not possible to design a good quality 100-400/F4 IS lens that is no heavier than the current 100-400, then an improved 100-400/F5.6 will be very welcome. Give me a lens that is good enough to make a worthwhile difference with a 1.4x extender.

[BJL]

... There's a perception that lenses designed for the smaller format will always be lighter. ...

It seems that most of the EF-S lenses which appear to be lighter than the nearest full frame equivalent are wide angle zooms with a different design to FF lenses; a design with a short back focus where the rear element is closer to the sensor. With telephoto lenses this design advantage apparently doesn't exist.

I thought thaqt issue had been resolved years ago: the size advantage  for lenses of equal focal length and aperture when designed for a small format is essentially when the larger format lens needs to be a wide angle design while the smaller format uses a normal or telephoto design, or when both are wide but the larger format lens is even wider. In the telephoto regime, the only advantages I know of to designing specifically for a smaller format are
(1) aberration corrections can be optimized over the smaller image circle, potentially getting better IQ there at the expense of worse in the unused regions outside the smaller format's image circle but inside the larger format's image circle.
(2) lens hoods and anti-flare baffling that is tighter, blocking light coming from outside the smaller image circle but within the larger image circle.

Both could be true for the Olympus 150/2, 90-250/2.8 and 300/2.8, and for the recent Pentax DA telephoto lenses.

It would be interesting to see a comparison between the Olympus E-620 with the Zuiko 300/2.8, and the Canon 50D with Canon 300/2.8 IS. The Olympus sensor has the edge in terms of resolution, but the Canon might have the edge in terms of noise.

Of course per pixel noise comparison are of little direct practical relevance when pixel counts are different: at least the higher pixel count image is entitled to a greater degree of NR processing so that resolution after NR is equalized. (The default high ISO NR of some cameras seem effectively to do this, holding the line on noise levels so that res. declines as ISO increases. That makes sense to me so long as it is only a JPEG default, not mandatory.)

However, if we crop the E-620's sensor to the 3:2 aspect ratio of the 50D, that edge in pixel density becomes so small as to be irrelevant.

It has no effect whatsoever if the objective is equal pixel count on equal field of view. A 3:2 image from a sensor with 4.3 micron cell spacing (12MP 4/3 sensors) is still smaller than a 3:2 image from a sensor with 4.7 micron pixel spacing (50D, 500D) by a linear factor of 4.3/4.7, about 0.9, and so one gets the same framing with a focal length 10% shorter. Not huge but my main comparison was the far more clear-cut gap between 4/3 and 35mm, not the modest 10-20% linear size gap between 4/3 and EF-S.

The question of different aspect ratios is partly why I threw in the Panasonic GH1 with its wider "multi-aspect ratio" sensor that optimizes image circle usage for various shapes. 3:2 is given by cutting a wider but lower rectangle out of the same 21.5mm image circle, and 16:9 even wider and lower, all about 12MP. The options are 4000x3000 for 4:3, 4128 x 2752 for 3:2, and 4352x2448 for 16:9, so the sensor active area is 4352x3000 pixels, 13x18.9mm.

I hope for this multi-aspect ratio option in many Micro Four Thirds cameras; it will kill the debate over which aspect ratio is most useful.

[250swb]

It would be interesting to see a comparison between the Olympus E-620 with the Zuiko 300/2.8, and the Canon 50D with Canon 300/2.8 IS..............snip...... However, if we crop the E-620's sensor to the 3:2 aspect ratio of the 50D, that edge in pixel density becomes so small as to be irrelevant.

Sorry for the hefty crop from your post Ray.

But the 300 f2.8 Olympus lens is a 600mm lens in equivalency, so it is twice long as the Canon 300/2.8, and so I don't see how you can compare it unless with a Canon 600mm f2.8 lens? Is there one? Is the Olympus heavier or lighter than the Canon 600mm lens?

The other thing is the 'crop to 3:2' idea. In pretty well all periodicals I know of, it is the 3:2 ratio from FF or APS-C that is cropped down, not the other way around and 4/3thirds provides an ideal sales format. So if you take a good chunk off the ends of each 3:2 photo you start to get the true idea of how much 'resolution' is being used to fill a page.

Steve

[Vivec]

Sorry for the hefty crop from your post Ray.

But the 300 f2.8 Olympus lens is a 600mm lens in equivalency, so it is twice long as the Canon 300/2.8, and so I don't see how you can compare it unless with a Canon 600mm f2.8 lens? Is there one? Is the Olympus heavier or lighter than the Canon 600mm lens?

You really shouldn't think of it this way. 300mm is 300mm. The smaller format just crops and therefore one can make a lens that has a smaller image. The only thing that determines the "reach" is the pixel density, not the sensor format.

Take for example, the 1.5x crop Sony A700 and the full frame A900. The A700 is about 12mp and the A900 is about 24mp which gives them almost the same pixel density. When taking a shot with a 400mm lens, the A700 photo is equivalent to cropping the same photo with the A900. The A900 just captures more around it, and the A700 does not have magical extra reach or focal length.

One should only use "focal length equivalence" when buying lenses to have an idea about the FOV, but one should not use it when discussing the advantages of different formats. I think the reasoning should really be that "high-density (small) sensors are better for wildlife photography as you can use lighter lens with less focal length to get the same shot as with a low-density (larger) sensor with a heavier longer focal length".

[Ray]

But the 300 f2.8 Olympus lens is a 600mm lens in equivalency, so it is twice long as the Canon 300/2.8, and so I don't see how you can compare it unless with a Canon 600mm f2.8 lens? Is there one? Is the Olympus heavier or lighter than the Canon 600mm lens?

A 300mm lens is a 300mm lens whatever camera the lens is attached to. The equivalent focal length in full-frame 35mm terms can always be increased to almost any degree you want by simply cropping the image. Whether the image is cropped at the recording stage, as a result of the sensor being smaller than FF 35mm, or whether it's cropped later in post processing, in Photoshop, makes no difference.

A 300mm lens on a 50D results in an image with the same field of view as a 480mm lens on a FF 35mm DSLR. If I crop that 50D image in post processing to the same FoV that the Olympus 4/3rds sensor produces, using the same FL of lens, I have the same equivalent lens in 35mm terms that any 4/3rds sensor would produce, but the Olympus E-620 would have a slight advantage in terms of pixel count (12.3 as opposed to 10.2).

If I crop a 50D image from a 300mm lens to 1/4 of its original area, I get a 960mm lens equivalent on a full frame camera, but the pixel count of the resulting image is reduced to 3.75mp, so I might prefer to use a 2x extender, although a 2x extender is not necessarily going to produce a better result. The choice is really between (1) a low resolving sensor in terms of LW/PH (3.75mp) used with a high quality lens, or (2) a high resolving sensor (15.1mp) used with a low resolving lens. A 2x extender always reduces the quality of a lens by a significant degree.

The other thing is the 'crop to 3:2' idea. In pretty well all periodicals I know of, it is the 3:2 ratio from FF or APS-C that is cropped down, not the other way around and 4/3thirds provides an ideal sales format. So if you take a good chunk off the ends of each 3:2 photo you start to get the true idea of how much 'resolution' is being used to fill a page.

One should always try to use the best tool for the job. 3:2 tends to be more useful for landscapes and cropping to the 16:9 aspect ratio for HDTV. Most of my shots are landscapes. The square format would seem to most efficiently cover the image circle of the lens (without resorting to a circular sensor which is impractical).

[JamesA]

A 300mm lens is a 300mm lens whatever camera the lens is attached to. The equivalent focal length in full-frame 35mm terms can always be increased to almost any degree you want by simply cropping the image. Whether the image is cropped at the recording stage, as a result of the sensor being smaller than FF 35mm, or whether it's cropped later in post processing, in Photoshop, makes no difference.

A 300mm lens on a 50D results in an image with the same field of view as a 480mm lens on a FF 35mm DSLR. If I crop that 50D image in post processing to the same FoV that the Olympus 4/3rds sensor produces, using the same FL of lens, I have the same equivalent lens in 35mm terms that any 4/3rds sensor would produce, but the Olympus E-620 would have a slight advantage in terms of pixel count (12.3 as opposed to 10.2).

If I crop a 50D image from a 300mm lens to 1/4 of its original area, I get a 960mm lens equivalent on a full frame camera, but the pixel count of the resulting image is reduced to 3.75mp, so I might prefer to use a 2x extender, although a 2x extender is not necessarily going to produce a better result. The choice is really between (1) a low resolving sensor in terms of LW/PH (3.75mp) used with a high quality lens, or (2) a high resolving sensor (15.1mp) used with a low resolving lens. A 2x extender always reduces the quality of a lens by a significant degree.



One should always try to use the best tool for the job. 3:2 tends to be more useful for landscapes and cropping to the 16:9 aspect ratio for HDTV. Most of my shots are landscapes. The square format would seem to most efficiently cover the image circle of the lens (without resorting to a circular sensor which is impractical).

The whole idea is to place as many pixels as possible on the subject you are interested in.  Now, if you can do this with a 35mm-sized sensor camera, that's fine.  But if you can't, at some point the crop-frame sensored camera is going to put more pixels into the crop area than the 35mm camera can, thus more resolution.  Wildlife photogs in particular would benefit from a crop frame camera because they tend to crop their images because their subjects rarely occupy the entire frame.  But if you are comparing a 12 megapixel 4/3rds camera with a 12 megapixel 1.5 crop camera, the pixel on cropped subject advantage of the 4/3rds camera is so small it is practically non-existent.  However, a 4/3rd and 1.5 crop cameras, both being smaller by far than a 35mm camera may see a benefit as the subject pixel content in the 35mm camera (with the same lens) is going to be far less than with either of the smaller sensor bodies.

[BJL]

The only thing that determines the "reach" is the pixel density, not the sensor format.

Indeed. Or to use a hopelessly old-fashioned name, the sensor's resolution, measured in lines per mm.
Though to be careful, lens resolution is also a factor, and there is some tendency for this to be higher when a lens of a given focal length is designed for a smaller image circle.

[Ray]

But if you are comparing a 12 megapixel 4/3rds camera with a 12 megapixel 1.5 crop camera, the pixel on cropped subject advantage of the 4/3rds camera is so small it is practically non-existent.

Using lenses of identical quality with both formats, the differences would probably be noticeable only on large prints or at 100% view on the monitor. When the 1.6 crop 15.1mp 50D is reduced to the size and aspect ratio of the 4/3rds format, it becomes 10.21mp (according to my maths). A 12mp 1.6 cropped format, such as the 450D, would be reduced to 8mp. The 1.5 crop formats (such as the Nikons) would be reduced to less than 8mp. A 50% increase in pixel count is supposed to be worth something, on a sufficiently large print. It's the difference between a Canon 1Ds2 and an A900 or D3X.

However, when increased pixel density is combined with increased lens resolution, then one could expect a clear resolution benefit from the sensor with the greater pixel density.

I imagine a 12mp 4/3rds sensor combined with a Zuiko 300/2.8 would produce a sharper and more detailed result than either a 450D or 50D used with the Canon 300/2.8, after cropping in post processing to the same FoV as the 4/3rds sensor.

I'm assuming that the Zuiko 300/2.8 is sharper than the Canon 300/2.8. It's heavier and more expensive and, as I recall, was once considered by NASA to be the finest lens they had ever tested.

Just out of interest, I see that Photozone have retested the Canon EF-S 17-55/2.8 with the 50D. The original test was done with the 8mp 350D, so we now have a comparison showing the degree of improvement one can expect when moving from an 8mp to a 15mp DSLR, using the same lens (although it might have been a different copy of the same model for all I know).

Assuming both copies were typical, you can see from the following charts showing 'line widths per picture height' at 50% MTF, that a roughly 50% increase in pixel count seems to produce a worthwhile increase in detail when a good lens is used at its sharpest aperture. I've also included the results for the Canon 16-35 which was tested with the 350D and which appears to be a slightly less sharp lens than the EF-S 17-55. Comparing both lenses at 24mm and their sharpest aperture of F4, the 16-35 produces 2083 LW/PH on the 350D, and the EF-S 17-55 produces 2537 LW/PH on the 50D, or roughly a 25% increase in resolution.

[attachment=12692:17_55_16...PZ_tests.jpg]

[Ray]

It has no effect whatsoever if the objective is equal pixel count on equal field of view. A 3:2 image from a sensor with 4.3 micron cell spacing (12MP 4/3 sensors) is still smaller than a 3:2 image from a sensor with 4.7 micron pixel spacing (50D, 500D) by a linear factor of 4.3/4.7, about 0.9, and so one gets the same framing with a focal length 10% shorter. Not huge but my main comparison was the far more clear-cut gap between 4/3 and 35mm, not the modest 10-20% linear size gap between 4/3 and EF-S.

Yes you're right. I wasn't thinking clearly about that. If both images are cropped to the same FoV in both dimensions, the E-620 will retain its greater pixel count (and pixel density) whatever the choice of aspect ratio. However, if one crops either camera only to change to the aspect ratio of the other, the 50D retains the higher pixel count and lower noise in all circumstances. Right?  

[250swb]

A 300mm lens is a 300mm lens whatever camera the lens is attached to. The equivalent focal length in full-frame 35mm terms can always be increased to almost any degree you want by simply cropping the image. Whether the image is cropped at the recording stage, as a result of the sensor being smaller than FF 35mm, or whether it's cropped later in post processing, in Photoshop, makes no difference.

So you'd use a 300mm lens on a FF camera and crop the image to the equivalent of a 600mm lens, or you'd use a Canon '600mm' lens?  If you want to compare the weight and size of an Olympus 300mm f2.8 it has to be with a Canon 600mm f2.8, not a Canon 300mm f2.8, unless you genuinely mean you'd crop the FF image?

Steve

[Ray]

So you'd use a 300mm lens on a FF camera and crop the image to the equivalent of a 600mm lens, or you'd use a Canon '600mm' lens?

If your FF camera has sufficient pixel density, the pixel density of the latest cropped format, then yes, you could crop the image to the equivalent of a 600mm lens, and get the same effect as using that 300mm lens on the cropped format.

However, as I mentioned before, the pixel density of the FF formats lag behind those of the cropped format. The pixel density of the 1Ds3 and 5D2 is no greater than that of the old-fashioned 8mp 20D. The 50D with almost twice the pixel density of the 20D therfore still serves a purpose for those who own a 1Ds3 or 5D2.

However, a 300mm lens on the 12.3mp E-620 would likely not produce as good a result as a 600mm lens on the 5D2 because we're comparing 12.3 mp with 21mp. But we don't know for sure the extent of the difference because no-one is producing the comparisons. Very slack!  

[situgrrl]

However, a 300mm lens on the 12.3mp E-620 would likely not produce as good a result as a 600mm lens on the 5D2 because we're comparing 12.3 mp with 21mp. But we don't know for sure the extent of the difference because no-one is producing the comparisons. Very slack!  

I'm not convinced.....was outside some bank in London the other day joking with a pj with a 600mm about how I could cope with only a 35mm.  He tossed me his 1 series with 600 attached, initially I buckled under it's weight before getting it up to my eye.  For hand holding, I'm convinced I'd be better stacking 4 2x convertors on a 50mm!  I know it's got IS but all the same I doubt I could hold it at under 1/1000 and I certainly couldn't run with it.  I asked it's owner how he carried it all day, especially given the kettling that was going on.  He showed me an AP pass and pointed to a truck only 30 yards from where we stood.

All jokes aside, surely weight must become a major factor when we are talking of megaphoto lenese....and given the OPs original intentions for using the lens, I would suggest that the ability to "get the **** out quick" would tip the balance firmly in favour of the Olympus or even some hypermegaminizoom compact - many of which now hit 400mm equiv before sticking a 2x lens on them.

[Ray]

I'm not convinced.....was outside some bank in London the other day joking with a pj with a 600mm about how I could cope with only a 35mm.  He tossed me his 1 series with 600 attached, initially I buckled under it's weight before getting it up to my eye.  For hand holding, I'm convinced I'd be better stacking 4 2x convertors on a 50mm!  I know it's got IS but all the same I doubt I could hold it at under 1/1000 and I certainly couldn't run with it.  I asked it's owner how he carried it all day, especially given the kettling that was going on.  He showed me an AP pass and pointed to a truck only 30 yards from where we stood.

All jokes aside, surely weight must become a major factor when we are talking of megaphoto lenese....and given the OPs original intentions for using the lens, I would suggest that the ability to "get the **** out quick" would tip the balance firmly in favour of the Olympus or even some hypermegaminizoom compact - many of which now hit 400mm equiv before sticking a 2x lens on them.

Absolutely! Convenience counts for a lot. It's why the Canon 100-400 IS is so popular. It's not a stellar performer, but it's light, has the flexibility of a zoom and doesn't require a heavy tripod. There's no way I would buy a 400/2.8 to get a sharper result, because it's simply too heavy. I thought I might get a sharper result with the Canon 400/5.6 prime, but it didn't work out. Maybe I tested a dud.

However, the Zuiko 300/2.8 is quite heavy at 3.3Kg. I'd really prefer to have a top quality 400/5.6 which is really sharp at full aperture. I'm sure it can be done.

[fike]

one lens that hasn't been mentioned extensively is the canon 300mm f/2.8 L with a 1.4x teleconverter mounted.  Its results substantially surpass the 100-400 and while it is definitely larger than a 100-400, it isn't ridiculously so.  

There is always someone in a thread like this that objects when you use focal length equivalency to describe the effective reach of a lens when mounted on a cropped sensor.  This thread was no exception to that.  I disagree with the purists who say that the nomenclature is misleading.  I understand the technical difference, but the most effective way to describe the field of view is to equate it to a lens in 35mm terms.  You can't otherwise describe it without going into an arcane and complex explanation of the difference, that while well understood here at LL, is lost on all but the most savvy photographers. I like to say my 100-400 has a reach that is like a 160-640mm lens.  It is the least confusing way to explain my equipment setup.  

I have said many times on these and other forums that a fascinating analysis would be a 5DMkII versus a 30D but with one difference.  The lens field of view shouldn't be normalized.  What I mean by this is that you should mount and photograph a test chart with the 30D and a good lens like a 50mm f/1.4.  Then, without moving the camera/tripod fore or aft, mount the 5DMkII and reshoot the same target.  With the 5DMkII the target will not fill the image area--intentionally.  This will compare  resolving power of these two cameras with identical pixel densities.  Then use the same procedure and throw in the 50D.  More detail will be resolved by the 50D and my hypothesis is that at 100  ISO, the same detail will be resolved by the 30D and the 5DMkII.  We will then be able to isolate (without resizing) the effect of the mythical "good pixels."

[Ray]

one lens that hasn't been mentioned extensively is the canon 300mm f/2.8 L with a 1.4x teleconverter mounted.  Its results substantially surpass the 100-400 and while it is definitely larger than a 100-400, it isn't ridiculously so.

Can you show me some results? The 300/2.8 with 1.4x extender will certainly be faster than the 100-400 and will no doubt surpass it at F5.6, but will it be sharper than the 100-400 at F8, its sharpest aperture? I always prefer to use my 100-400 at F8 or F11 when the light permits. To be able to get results at F4 and F5.6 that are at least as sharp as the 100-400 produces at F8 would be worth something, but would the 300/1.4x combination produce sharper results than the best the 100-400 can do? The 300/F4 IS with extender doesn't appear to be able to surpass the 100-400, according to Photozone tests, except at F5.6 in the centre. Edge resolution at F5.6 is about the same as the 100-400. At F8 and F11, centre resolution is also about the same, but edge resolution is substantially worse with the 300/F4/1.4x.

[attachment=12714:300_F4_w...extender.jpg]

[fike]

Can you show me some results? The 300/2.8 with 1.4x extender will certainly be faster than the 100-400 and will no doubt surpass it at F5.6, but will it be sharper than the 100-400 at F8, its sharpest aperture? I always prefer to use my 100-400 at F8 or F11 when the light permits. To be able to get results at F4 and F5.6 that are at least as sharp as the 100-400 produces at F8 would be worth something, but would the 300/1.4x combination produce sharper results than the best the 100-400 can do? The 300/F4 IS with extender doesn't appear to be able to surpass the 100-400, according to Photozone tests, except at F5.6 in the centre. Edge resolution at F5.6 is about the same as the 100-400. At F8 and F11, centre resolution is also about the same, but edge resolution is substantially worse with the 300/F4/1.4x.

[attachment=12714:300_F4_w...extender.jpg]

I don't own the lens.  A friend does.  Here is a photo that is representative of the bird work he has been able to do with that lens and converter combo.  Most of the bird work at this gallery is with that lens.  Another benefit of the 300 f/2.8 is much faster and more accurate focusing than the 100-400 even with a teleconverter.

Bird Photos Using 300 f/2.8 L with 1.4X Teleconverter

[stever]

i find the 300 f4 +1.4x no better than my 100-400 at any aperture.  the 300 2.8 which i've tested (but don't own because of weight) with a 1.4x is far superior to the 100-400 at all apertures and still very good with a 2x.  I'd also say that the 400 DO at from f4 to f8 doesn't significantly change and is better than the 100-400 at f8 (although maybe not true of a really good 100-400 which seems to have significant lens-lens variation over time - current production may be better)

[Romy Ocon]

The Canon 100-400 IS is 'out-resolved' by the 50D. It needs upgrading. A good quality EF-S 100-400/f5.6 would be fine    .

Hi Ray,

Do you happen to have links to tests that show the 100-400 is outresolved by the 50D? I have this lens too and I'd be interested to see how it performs with such small pixels.

Romy

[Ray]

Hi Ray,

Do you happen to have links to tests that show the 100-400 is outresolved by the 50D? I have this lens too and I'd be interested to see how it performs with such small pixels.

Romy

I've compared the 5D with the 50D using my 100-400 at 400mm and at various apertures, and I find that the 50D will contine to record finer detail than the 5D even at F16. However, comparing the 50D with the 40D using the 100-400 seemed a waste of time. The differences are too trivial to bother with, even at F8. Looking at the test charts at photozone, I get the impression there are many lenses which are sharper at F11 than the 100-400 is at F8. One such lens is the 70-200/F4 IS. At 200mm and F11, resolution is 1952.5 LW/PH. The 100-400 at 400mm and F8 (its sharpest aperture) is just 1785 LW/PH, at the centre. (Both tests carried out using a 350D).

I don't think I kept the test results comparing the 40D with the 50D, for the 100-400. But here's a shot I found comparing the 5D with the 50D at F16. Instead of upsampling the 5D shot, I've shown it at a greater magnification. The 50D at 100%, which represents a huge print of course, shows clearly finer detail, particularly noticeable on the roof.

[attachment=12721:5D_v_50D_400mm_F16.jpg]

[Romy Ocon]

I've compared the 5D with the 50D using my 100-400 at 400mm and at various apertures, and I find that the 50D will contine to record finer detail than the 5D even at F16. However, comparing the 50D with the 40D using the 100-400 seemed a waste of time. The differences are too trivial to bother with, even at F8. Looking at the test charts at photozone, I get the impression there are many lenses which are sharper at F11 than the 100-400 is at F8. One such lens is the 70-200/F4 IS. At 200mm and F11, resolution is 1952.5 LW/PH. The 100-400 at 400mm and F8 (its sharpest aperture) is just 1785 LW/PH, at the centre. (Both tests carried out using a 350D).

I don't think I kept the test results comparing the 40D with the 50D, for the 100-400. But here's a shot I found comparing the 5D with the 50D at F16. Instead of upsampling the 5D shot, I've shown it at a greater magnification. The 50D at 100%, which represents a huge print of course, shows clearly finer detail, particularly noticeable on the roof.

[attachment=12721:5D_v_50D_400mm_F16.jpg]

Hi Ray,

Thanks for the reply and the info. I have a great copy of the 100-400 which is as sharp as my 400 5.6L at 400 mm f/5.6. My 100-400 even compares well vs. my 500 f4 IS at the center of the frame. I believe my copy of the 100-400 can harness the resolution of the 50D's sensor very well, at least in the central portion of the frame where it matters for my bird photography.  This is because I see a good improvement of captured detail on a per frame basis (as opposed to per pixel basis) when using this lens with a 1.4x TC on a 40D, which use effectively doubles the pixels/bird from the same distance.


Here are links to my user report:

1. 100-400 vs 400 5.6L - http://birdphotoph.proboards.com/index.cgi...&thread=352

2. 100-400 compared to my 500 f4 IS - http://birdphotoph.proboards.com/index.cgi...&thread=353

Romy