A little question on crop factor (1 Viewer)

[Roy C]

(560mm equivalent at the long end) at 400mm (560mm) and f/5.6 up against an SX10 at "560mm" and f/5.7 and compare results.

Here's an example shot yesterday, handheld at 400mm (560mm equivalent), 1/800, f/5.6, 400 ISO. First the full image, then a 100% crop....

That Swift crop is impressive - when you say 560mm I assume you were using a 1.4tc or did you mean 640mm ?

 

[Nikon Kid]

Is there really any point in hard cropping a distance bird, the only thing I would think its good for is ID of a certain species, Now none of you would put them hard crops in your gallery would you ? I am afraid when its said these are good shots they look c**p to me.

I know I wear glasses and all that, but my eyesight is not that bad :eek!:|8)|

 

[tdodd]

That Swift crop is impressive - when you say 560mm I assume you were using a 1.4tc or did you mean 640mm ?

Oops, I mean 400mm X 1.6 for the crop factor = 640mm. Obviously 560mm is one of the figures that sticks in one's head, because of teleconverters, and I plucked it out of my memory instead of doing the maths.

So those shots were at 400m actual, 640mm AOV allowing for the crop. I shall correct my original post.

While out today I spotted this fellow, shot once again with my handheld 50D, 100-400 at 400mm (640mm equivalent!), 1/1000, f/6.3, 400 ISO and converted from raw to JPEG in Lightroom with no edits.

First is a shot from a little way away, full frame and a 50% crop. Then I moved a little closer and took another shot, which I've also included as a full frame, a 50% crop and a 100% crop....

 

[stevetb]

To John Z, if you look @ the pictures of the butterfly chart thingy, you'll see there are differences in size.

Tim, I've read this a couple of times now, and I get your points a bit more - I think when people talk about the crop factor though, they almost always talk about pixels in addition - the fact that something like the 40D is a 1.6X cropper means it has a higher pixel density than a 1dmkiii despite the same number of pixels - but people (me included) say that it has a greater reach than something like a 1dmkiii because of the crop factor - when in fact it is the higher pixel density caused by the cropped sensor, which isn't really the same thing, although still closely linked to the crop factor. Or am I talking nonsense!

 

[tdodd]

Is there really any point in hard cropping a distance bird, the only thing I would think its good for is ID of a certain species, Now none of you would put them hard crops in your gallery would you ? I am afraid when its said these are good shots they look c**p to me.

I know I wear glasses and all that, but my eyesight is not that bad :eek!:|8)|

Terry, anyone who actually wants to make use of a 100% crop as their actual photo is, in my opinion, really clutching at straws. That is no way to do photography. I put the examples up merely to illustrate what the 100% crops look like. Quite frankly, if you are having to use an image from a 50D at anything over 50% viewing magnification then you are too far away from your subject and/or your glass is too short. The problem with digital is that it makes it too easy to pixel peep, and that's when people whinge and moan about per pixel noise, and sharpness, instead of looking at the actual images produced when they perform their photography properly.

Staring at a 50D image at 100% on a screen from 12-18" away is, quite frankly, madness, but some people like to do it. A 50D image viewed at 100% is equivalent to the whole frame being blown up to around 4' across. That is an insane amount of magnification at which to judge IQ. Quite honestly it shouldn't be allowed. That is why the 50D gets a bad press. It's because of idiotic pixel peeping as a substitute for making use of the whole sensor area you paid for.

If pro quality printing requires 300 pixels per inch then a 50D might be good for prints up to 4752/300 = 16" across. That's pretty much the size of a 17" monitor, just a little more. So, to be honest you should be looking at 50D full frame images at approx "fit to screen" size to see if the are up to snuff. That's actually pretty close to viewing at 33% on my system. It may be even less on monitors with lower resolution than my 1920x1200 screen.

I think it's fair to say that for 100% crops of BIF, from a 50D and a zoom lens, those images are not bad at all. As actual useable images they are indeed poop.

All of this really reinforces my point that quality comes from bigger glass and more silicon, not cropping ever tighter onto tinier and tinier and noisier and noisier pixels.

I would recommend that people consider 35mm as a baseline for making photographic judgements and that instead of working in terms of pixels they work in terms of magnifications from that captured image. e.g. a 35mm frome is 36mmx24mm. To make a 12x8 print from a 35mm frame requires a modest magnification factor of 8X. If you take the whole image from a 1.6X cropper then to generate a 12x8 print from that you will need to magnify the captured image by almost 13X. That is a significant increase in magnification that will emphasise noise/grain, shake, blur, misfocus, diffraction etc.. If you then make heavy crops into a 1.6X sensor, or use an even smaller sensor to begin with, like a 4/3 or compact sensor then to get a 12x8 print at decent quality is asking a lot. Forget the chuffing pixels. Look at the real magnifications you are dealing with based on the actual physical size of the image you have captured vs the final product you want to create. When you expect perfect image quality from a 50X magnification of the captured image is the time you should realise you are doing something wrong. Very wrong.

p.s. A 50D image viewed at 100% on my screen is equivalent to a physical magnification of 40X. Is it any wonder that it doesn't look perfect?

p.p.s. At that sort of magnification you can also chuck your DOF calculator out the window. Your DOF will be damn near 0, for a bird photo with a long lens.

 

[tdodd]

Steve, you are spot on with that last post. Yes, there is a relationship between total number of pixels, sensor size/area and pixel density but the only value which, on its own, defines "reach" is the density. Keep the density the same and you can have any size sensor you like - the reach will be the same.

I think when people talk about the crop factor though, they almost always talk about pixels in addition

I think they almost always do not, and that is the crux of the problem. Look at the first post again. Baofeng appears to be under the illusion that "reach" comes purely from crop factor. Not a mention of pixels or pixel density anywhere. It's a perfect illustration of the confusion and misunderstanding that is perpetuated by people who keep referring to crop factor rather than pixel density affecting reach.

These people who yammer on about crop factor increasing reach need to qualify their remarks by also discussing the number of pixels involved at the same time, but they often don't. They simply say "a crop camera give more reach than a full frame camera". That's nonsense. What they need to say is that "a crop camera with the same number of pixels as a full frame camera will have more reach". Kerching! Yes. So why not just say higher pixel density gives more reach, in the first place. Why confuse things by talking about crop factor. That influences nothing on its own except angle of view.

 

[Nikon Kid]

Terry, anyone who actually wants to make use of a 100% crop as their actual photo is, in my opinion, really clutching at straws. That is no way to do photography. I put the examples up merely to illustrate what the 100% crops look like. Quite frankly, if you are having to use an image from a 50D at anything over 50% viewing magnification then you are too far away from your subject and/or your glass is too short. The problem with digital is that it makes it too easy to pixel peep, and that's when people whinge and moan about per pixel noise, and sharpness, instead of looking at the actual images produced when they perform their photography properly.

Staring at a 50D image at 100% on a screen from 12-18" away is, quite frankly, madness, but some people like to do it. A 50D image viewed at 100% is equivalent to the whole frame being blown up to around 4' across. That is an insane amount of magnification at which to judge IQ. Quite honestly it shouldn't be allowed. That is why the 50D gets a bad press. It's because of idiotic pixel peeping as a substitute for making use of the whole sensor area you paid for.

If pro quality printing requires 300 pixels per inch then a 50D might be good for prints up to 4752/300 = 16" across. That's pretty much the size of a 17" monitor, just a little more. So, to be honest you should be looking at 50D full frame images at approx "fit to screen" size to see if the are up to snuff. That's actually pretty close to viewing at 33% on my system. It may be even less on monitors with lower resolution than my 1920x1200 screen.

I think it's fair to say that for 100% crops of BIF, from a 50D and a zoom lens, those images are not bad at all. As actual useable images they are indeed poop.

All of this really reinforces my point that quality comes from bigger glass and more silicon, not cropping ever tighter onto tinier and tinier and noisier and noisier pixels.

I would recommend that people consider 35mm as a baseline for making photographic judgements and that instead of working in terms of pixels they work in terms of magnifications from that captured image. e.g. a 35mm frome is 36mmx24mm. To make a 12x8 print from a 35mm frame requires a modest magnification factor of 8X. If you take the whole image from a 1.6X cropper then to generate a 12x8 print from that you will need to magnify the captured image by almost 13X. That is a significant increase in magnification that will emphasise noise/grain, shake, blur, misfocus, diffraction etc.. If you then make heavy crops into a 1.6X sensor, or use an even smaller sensor to begin with, like a 4/3 or compact sensor then to get a 12x8 print at decent quality is asking a lot. Forget the chuffing pixels. Look at the real magnifications you are dealing with based on the actual physical size of the image you have captured vs the final product you want to create. When you expect perfect image quality from a 50X magnification of the captured image is the time you should realise you are doing something wrong. Very wrong.

p.s. A 50D image viewed at 100% on my screen is equivalent to a physical magnification of 40X. Is it any wonder that it doesn't look perfect?

p.p.s. At that sort of magnification you can also chuck your DOF calculator out the window. Your DOF will be damn near 0, for a bird photo with a long lens.

Why is it Tim you are so clever, good answer as usual :t:

 

[tdodd]

Why is it Tim you are so clever, good answer as usual :t:

It's actually because I have been giving this subject a lot of thought lately and it has become all too clear to me how absurd it is to expect faultless IQ from a 50D when viewing at 100%.

By dragging things back to 35mm film, as a baseline for applying certain rules of photography (DOF for starters, SS >= 1/FL for another, physical image magnification for a third), only then can we appreciate how unrealistic our expectations have become, compared with what has gone before

Consider that images in real life - in nature - are not digital things. Light passing through a lens has infinite detail and tonal variation. Our eyes, to all intents and purposes are analogue devices. We do not see the scenes before us represented as bundles of little dots. Our vision is one continuous, seamless representation of the light coming from the scene before us.

By digitising a scene with a camera we chop it up into tiny little bits (pixels). If you have a low resolution capture device (say a 30D) then you only approximate what each piece of the puzzle should really look like, relatively crudely. By increasing pixel density, and chopping the captured image into finer and finer pieces, such as with a 50D, we increase the precision with which we capture that image data. But there is no more "image" coming through the lens whether it is a 30D or a 50D capturing it. The photon count is the same for any given area of silicon. A 50D pixel will capture fewer photons than a 40D pixel. It should come as no surprise that a 50D pixel has more noise. But assemble all the 50D pixels back together again, to form a whole image, and the noise should be about the same as the whole image from a 40D.

The benefit of the finer granularity of detail captured by the 50D is not so that you can blow it up larger than a 30D or 40D image. It is so that with the two images compared side by side, at the same physical magnification, the 50D version will contain finer detail throughout. The 50D does not give you an excuse to magnify the image from a 50D by 1.4X larger than that from a 30D or 1.22X larger than a 40D. Magnify them equally and enjoy the superior detail from the 50D. Do not magnify the 50D image 1.4X more and then complain that you can see noise, and it is soft.

This is very much a case of the whole being greater than the sum of the parts. Do not look at the parts (pixels). Look at the whole - the image - at a reasonable level of magnificaction.

At the risk of repetition, this brings me back one again to the issue of sensor area and the focal length being the main influences on IQ. The way to really improve your IQ is to capture more photons from your subject. The way to capture more photons is to use longer glass to optically magnify the image from your subject more. Then you can use a large sensor area with which to capture that image. All this pratting about jiggling pixel densities doesn't really alter how much light you captured. It might chop it up into smaller chunks, which in itself is not necessarily a bad thing, but it won't make a step change in IQ. Is there a massive leap (or drop) in IQ from the 30D to 40D to 50D? Not really. Is the IQ from an xxD body any better than from an xxxD body? Not really. Is the IQ from a 1D3 better than from any 1.6X cropper, when coupled with glass 1.3X longer? Hell, yeah. Is the IQ from a 5D2 the best of the lot, when coupled with suitable glass? You bet you. Is IQ going to increase by buying a 4/3 body and pretending your 200mm lens is really 400mm? Not on your life.

So, does a higher pixel density really give you more reach after all? Well I'd be very careful there. Maybe, a little, but not as much as you might hope/think. You can only spread those photons so thin, and if you haven't got enough of them captured then you can't spread them very far.

 

[Roy C]

Is there really any point in hard cropping a distance bird, the only thing I would think its good for is ID of a certain species, Now none of you would put them hard crops in your gallery would you ? I am afraid when its said these are good shots they look c**p to me.

I know I wear glasses and all that, but my eyesight is not that bad :eek!:|8)|

Terry,I regularly use heavy crops for web images, attached are some 100% crops that may not be up to the standards of a lot of people but they are good enough for me for web use. Certainly not up to your standards Terry but like I have said before one man's meat is another man's poison, we all have different standards.
p.s. we have not all got managed reserves and semi tame birds to shoot at

 

[tdodd]

Roy, not a bad set there at all The clarity indicates great skill/technique on your part. The thing is, that's as far as you can go with those images - small webshots. If those are all 100% crops, they will never make it to a print to hang on the wall, or be fit for sale to the public at large. That's in no way a criticism of what you have there at all, but we do shoot for different reasons.

Personally I am not hugely interested in accumulating a whole bunch of web sized images. I want to shoot stuff I can sell, or at least enjoy full screen on my 40" 1920x1080 HDTV. Quite honestly, it is asking a lot of me and my gear to get an image of a moving subject, like a BIF, from my 50D and 100-400 that will fill a 1920x1080 screen, with a nice composition and large subject, and which looks sharp and clean at 100%. I'd far rather have 3840x2160 pixels, resized to 50%, which means I have some room to crop, but not a lot. Now, for a perched or fairly staic bird I might manage to get away with a 100% crop, but even that is not enough if my subject is too small to make a nice composition at those pixel dimensions.

Most of the bird related stuff I shoot ends up as "practice shots" because I am simply not close enough to get an image that suits my quality objectives. They might suffice for sharing on a web forum, for a bit, but many of them are not going to be keepers.

 

[Roy C]

Roy, not a bad set there at all The thing is, that's as far as you can go with those images - small webshots. If those are all 100% crops, they will never make it to a print to hang on the wall, or be fit for sale to the public at large. That's in no way a criticism of what you have there at all, but we do shoot for different reasons.

Personally I am not hugely interested in accumulating a whole bunch of web sized images. I want to shoot stuff I can sell, or at least enjoy full screen on my 40" 1920x1080 HDTV. Quite honestly, it is asking a lot of me and my gear to get an image of a moving subject, like a BIF, from my 50D and 100-400 that will fill a 1920x1080 screen, with a nice composition and large subject, and which looks sharp and clean at 100%. I'd far rather have 3840x2160 pixels, resized to 50%, which means I have some room to crop, but not a lot. Now, for a perched or fairly staic bird I might manage to get away with a 100% crop, but even that is not enough if my subject is too small to make a nice composition at those pixel dimensions.

Most of the bird related stuff I shoot ends up as "practice shots" because I am simply not close enough to get an image that suits my quality objectives. They might suffice for sharing on a web forum, for a bit, but they aren't going to be keepers.

Tim, each to their own, I am not worried about printing and at my age I am not remotely interested in selling pics (I have given away some prints to local birders but would never charge anyone). I do it purely as an hobby in my old age. I am also not interested in travelling far to get shots, I am strictly a local patch man and my only goal it to get web size shots of birds on my local patch.

The whole point of me supplying these pics is because someone suggested that nobody puts heavy crops in their gallery - my guess is that quite a lot of shots submitted to the galley are big crops.

 

[tdodd]

Fair point, Roy. I don't travel far for my birding photography either. In fact I just grab the breaks as they present themselves when I'm out walking the dog. You certainly won't catch me couped up for hours in a hide waiting for something to happen. Of course, that approach does severely limit my chances to nail award winners, but once in a while opportunity knocks.

At best I might drive 7 miles to my nearest RSPB reserve, but quite frankly that is a massive disappointment, photographically speaking. It's like someone paid no heed to the direction of the sun when laying out the boardwalks, and the opening hours give you no chance to shoot during early morning sunshine, when the light is coming in from the side and lighting the underside of the birds. With a 400mm lens, even on a 50D, it's too far to get anywhere near filling the frame with a single bird and I don't bother with flocks, birds on the ground or (with a few exceptions) in the water. Might as well leave the camera at home

What is the point in only opening from 09:30 to 17:00 in summer? The best light is between 05:00 and 07:00 and then again from 19:00 onwards. The rest of the time the sun is too high for optimum results.

 

[QuantumTiger]

I think they almost always do not, and that is the crux of the problem. Look at the first post again. Baofeng appears to be under the illusion that "reach" comes purely from crop factor. Not a mention of pixels or pixel density anywhere. It's a perfect illustration of the confusion and misunderstanding that is perpetuated by people who keep referring to crop factor rather than pixel density affecting reach.

I think there is a combination of factors here. Firstly people often use terminology (crop factor, magnification, megapixels, resolution) without being precise about what it means. Secondly there is a tendency to think in terms of single factors (eg to solve problem a I need to do b). Most situations are not single factor. Thirdly many people struggle with photography because they're not used to dealing with non-linear effects. Pretty much everything in photography revolves around square numbers (because photographs are areas) and that doesn't help. (For example doubling the number of pixels does not double resolution, it increases it by 1.4x)

For such reasons it is better to avoid talking in abstract terms and use real world examples. I've owned three eight mega-pixel cameras. A Minolta A2 (4x), an 20D (1.6x) and 1D MkII (1.3x). If I take a photo with any of these cameras at f/4 with a focal length of 50mm and print it at A4 I will have the same resolution image (in terms of pixels per inch). The Minolta image, however will look signifcantly zoomed in (equivalent to a 200mm lens). In terms of IQ printed at 6x4 there will not be much in it although the colour balance of the 1D is significantly better.

If I never actually crop my images then the argument about whether the A2 genuinely gives a higher magnifcation or not is irrelavent. To all practical purposes it gives me a closer view of the subject and for most people that is enough.

The 4x crop sensor has several advantages over the SLR. I'm dealing with a 50mm image so camera shake is less of a problem than with a 200mm lens - I can hand hold at slower shutter speeds. The depth of field also is the depth of field of a 50mm lens at f/4 not a 200mm lens at f/4 so it is not as narrow. It is also smaller, lighter and much less conspicuous. I tended to carry it more often and take more photos.

Fret not though. It also has a number of significant disadvantages over the SLR. I can't change lenses - and the lens on the camera is nowhere near as sharp as my L glass 70-200. I can start to see softness as I enlarge as well as other lens distortions. The noise characteristics are much worse too so if I crop in to get equivalent field of view to 400mm shot I can really start to see problems with the image even at 100 ISO.

On the other hand if I stick a 400mm lens on the 1D the image is much sharper, and the noise characteristics are much cleaner. I can crop my 400mm image to equivalent 800mm field of view and it is still very usable at 400 ISO.

Between the 20D and 1D there is much less difference. 1.6x to 1.3x is much less of jump than I had expected, but the larger pixels of the 1D are definately (but slightly) better quality!

The bottom line is they are all good cameras. For landscape work I miss the depth of field of the A2 and my shoulders didn't ache at the end of the day! For wildlife I would not be without my SLR. For me the decrease in crop factor from the 20D to the 1D was not biggest change. The 1D gets more shots - it's that simple. The biggest differences are autofocus accuracy, shot-to-shot speed, overall IQ and colour balance. I suppose what I'm saying is worry less about the numbers, because most modern cameras are beyond the point were detailed analysis will reveal one as much better than another. Worry instead about the things that actually help you get the shot.

Apologies for the long post!

 

[Roy C]

Fair point, Roy. I don't travel far for my birding photography either. In fact I just grab the breaks as they present themselves when I'm out walking the dog. You certainly won't catch me couped up for hours in a hide waiting for something to happen. Of course, that approach does severely limit my chances to nail award winners, but once in a while opportunity knocks.

At best I might drive 7 miles to my nearest RSPB reserve, but quite frankly that is a massive disappointment, photographically speaking. It's like someone paid no heed to the direction of the sun when laying out the boardwalks, and the opening hours give you no chance to shoot during early morning sunshine, when the light is coming in from the side and lighting the underside of the birds. With a 400mm lens, even on a 50D, it's too far to get anywhere near filling the frame with a single bird and I don't bother with flocks, birds on the ground or (with a few exceptions) in the water. Might as well leave the camera at home

What is the point in only opening from 09:30 to 17:00 in summer? The best light is between 05:00 and 07:00 and then again from 19:00 onwards. The rest of the time the sun is too high for optimum results.

I am with you on not sitting in hides Tim (not that I have an hide within 50 miles of me anyway!). Another thing I am not prepared to do is crawl around in the mud to get shots - I tend to be a walker who takes along a Camera.
Not that I am knocking anyone who puts a lot of effort into getting their shots, they get what they deserve and the best of luck to them.

 

[wilfredsdad]

Hi - having just moved from Olympus kit to Canon kit for bird photography - possibly I might offer some useful comment.
I started bird photography with an Olympus E510, Sigma 50-500mm, Zuiko 70-300mm, Olympus 1.4 tcon. One of the reasons I chose Olympus was the 2x crop factor. After a lot of effort I came to the conclusion that my high failure rate was not entirely due to my lack of skill. I found that even in reasonable light conditions with birds that weren't too far away I still ended up with a lot of poor results - the main problem being poor focus. The Zuiko was considerably better than the Sigma but then again 300m (even with the 1.4x tc) is still a bit limiting for bird photography.
I am sure that both of those lenses are perfectly good lenses for general photography, possibly sport or aircraft photography, but my experience was that they just weren't up to the demands of bird photography.
It seems to me that the question of the value of the 2x cropping factor has been well discussed above - bottom line seems to be that it offers no real advantage in practical terms. IMHO extra pixels ie pixel density does offer a bit of an advantage (basically for a given size of subject you gather more data) but it does require that noise is well controlled. From my experience with Olympus and Canon I found the 10mp sensor on the Olympus E510 to be much noisier than the 15mp sensor on my new Canon EOS 500D.
As many have said above - what really matter is the lens, and in this area Canon is a long way ahead of Olympus. There is no fixed focus 400 or 500mm lens available for the Olympus - all that is available is a 300mm f2.8 which, no doubt is a fabulous lens, but it costs over £5k. Again IMHO a fixed focus lens of minimum 400mm f5.6 (or a very high quality zoom which goes to 400m) is a basic requirement for bird photography - anything less than that is going to be a struggle.
I contacted Olympus UK to try to point out to them the need for such a lens and asked if they were going to offer one in the near future - they did not respond.
I have also noticed that whilst Canon and Nikon do have a presence at the bird and wildlife fairs, Olympus are conspicuous by the absence.
I think (for what my opinion is worth) what matters most is the lens - and Olympus don't offer what is needed for bird photography and Canon (and I think Nikon) do.
I bought my EOS 500D and a second hand (2 year old) Canon EF 400mm f5.6 USM lens for a bit less than you would have to pay for an Olympus E620 and a Sigma 50-500mm. I have found almost immediately that I get much better results (sharper and less noisy), the focus is lightening fast - even in not such brilliant conditions - and it seems to be more accurate. Further the lens is much lighter than the Sigma - and I have found that also really is a significant factor.
I don't often stick my neck out but if anybody asked me which to chose I would say Canon without doubt - hope this helps, regards Pete

 

[tjsimonsen]

The subject is the same size. The frame is smaller. That is the more accurate way to look at it. It also happens to be a physical fact.

That, Tim, is how a microscope works as well.

Thomas

EDIT: should have been electron microscope..

 

[JohnZ]

Terry, What do you think of the pics I have posted on here ? Amazingly they are all 100% crops ! This partially due to the risk of the bird flying away and probably to do with a slight touch of desperation ?
AC/DC, I have measured the pics from Keiths link and they are all the same size. 6 x 4 I believe. For whatever reason the cropped pic, using the 40D, has come out bigger than the other two ?
Tim, Large cropping is in no way a sign of clutching at straws. This is ably demonstrated by Roys pics. Perhaps you would also like to comment on the pics I have posted. Oops sorry you are not in favour of large crops are you. Please do not let your quality objectives drop for goodness sake.

 

[tdodd]

John, I have no wish to engage in a willy waving contest about people's 100% crops. If you are using a prime lens and a camera with moderate pixel density and shooting stuff that is moving about little, if at all, then you can indeed get very acceptable quality from 100% crops that will get you a decent 800x533 image or thereabouts. I don't have a prime longer than 85mm, so for me with my 100-400 zoom it is far more demanding to produce a razor sharp image from a 50D when viewing at 100%. When attempting BIF, which is my preference, it is even more difficult to get a useable image when viewed at 100%. The reason is not poor equipment, or poor photographic technique (other than being too far from the subject). It is simply that the magnification factors are pushing the boundaries to the extreme.

Back in post #25 I was talking about using 35mm film (or full frame sensors) as a baseline for extrapolating all things photographic, and proposed a 12x8 print as a yardstick for a "reasonable" level of magnification of 8X. Let's call that our "Gold Standard".

I also said that to generate a 12x8 print from a 1.6X crop body was a magnificaction of 13X. Let's call that our "Silver Standard".

Well, if we do the maths for a few cameras, when cropping to 800x533, let's see what we find. We'll need to agree on a monitor resolution density in order to convert from physical pixels to the image display size in inches. I propose 100 pixels per inch, which is close to one of many standards of 96ppi, but makes the maths a little simpler. So, if you carve out 800x533 pixels from an image, any image, it will display on that monitor at 8x5.33 inches. Let's establish that as our new "print" size. For ease goiing forward let's convert that to mm, giving a displayed image size of 203x135mm. Now let's look at what that means in terms of magnification factors when we crop at 100% from various cameras.

30D
Sensor dimensions = 22.5x15mm, 3504x2336 pixels.
A crop of 800x533 from that camera uses an area of the sensor equal to 5.14x3.42mm
The magnification factor to get from that crop to our 8x5.33" display is 39X.
That is 5X greater than our "Gold Standard".

40D
Sensor dimensions = 22.2x14.8mm, 3888x2592 pixels.
A crop of 800x533 from that camera uses an area of the sensor equal to 4.57x2.88mm
The magnification factor to get from that crop to our 8x5.33" display is 44X.
That is 5.5X greater than our "Gold Standard".

50D
Sensor dimensions = 22.3x14.9mm, 4752x3168 pixels.
A crop of 800x533 from that camera uses an area of the sensor equal to 3.75x2.50mm
The magnification factor to get from that crop to our 8x5.33" display is 54X.
That is a whopping 6.75X greater than our "Gold Standard".

1D3
Sensor dimensions = 28.7x18.7mm, 3888x2592 pixels.
A crop of 800x533 from that camera uses an area of the sensor equal to 5.91x3.85mm (That's 2.43X larger in area than an 800x533 crop from a 50D)
The magnification factor to get from that crop to our 8x5.33" display is 34X.
That is 4.25X greater than our "Gold Standard".


So, as you can see, a 100% crop from a 50D is far more punishing/ambitious/demanding than a 100% crop from a 40D, which in turn is more demanding that a 100% crop from a 30D (or 5D2), which is more demanding than a 100% crop from a 1D3. Also, even with the most lenient of those crops, you are still looking at image magnification factors that are over 4X greater than our "Gold Standard".

To put it another way, if a pro quality print requires the input pixels from our captured image to be rendered at 300ppi, and our screen only displays at a resolution of 100ppi, we should be squeezing input pixels from our captured image into our output pixels on the display at a linear reduction factor of 1/3, or 33% if you prefer. Not 100%. i.e. to produce an 8x5.33 print you would ideally want an image, after cropping, of 2400x1600 pixels, not 800x533.

So, at the end of all that, yes, you may be able to get the quality you desire when cropping to 100%, but the higher your sensor pixel density the more demanding (unrealistic?) that becomes, and your keeper rate is likely to fall. If your target is moving, like a BIF, then the challenge is even greater. Scrape by with a zoom lens with slow AF and, well, good luck.

It is for this reason that I find that for BIF I usually get just as much reach from my 1D3 as from my 50D. All that I accomplish by using the 50D is a more accurate capture of any blur/shake/misfocus, plus more pixel level noise. I rarely end up with more useable feather detail. For static subjects that is another matter altogether, but for BIF.....

p.s. - of course, for BIF, you usually want a high shutter speed, and to combat shake/blur at high magnifications you'll need a very high shutter speed, which will necessitate pushing the ISO, which in turn pushes noise. That is why I find 100% BIF crops from my 50D to be generally unsatisfactory. That is not the fault of the camera. That is my fault for having absolutely lunatic expectations for what my gear and I can deliver. Again, slow it all down for waddlers, waders, floaters and perchers and everything becomes so much easier.

To conclude, I attach an example shot yesterday with my 50D and 100-400 lens, handheld at 400mm, 1/1000, f/6.3, 400 ISO, IS on, no edits. I include the full image, a 50% crop and a 100% crop. In my opinion the 100% crop is very unsatisfactory, and really not useable. The 50% crop would be OK, just, with some tweaking, but as a print that image is only good for a 5x3 or thereabouts. I know my focus is well calibrated. I do not use a filter. I used One Shot AF and fired off several frames, in short bursts, and refocused a few times. This is representative of the batch. No absolute duffers, no clear winners. At 100% it is simply not good enough. I really do not think I could have achieved better results if I had used a tripod or continued shooting for a week. Quite simply, a 100% crop, with my gear, is pushing things too far.

EDIT : for kicks I've thrown in another image of the KF, shot a few moments earlier, this time as a full frame and 50% crop only.

 

[JohnZ]

Tim, I suspect that we are in agreement really and that it is my lack of fieldcraft that lets me down. However I also attempt BIF shots and have, to a degree, a few minor successes as I hope the shots posted demonstrate.
The Kestrel was going like a bat out of hell and should be considered very fortunate but then again none of the birds posted were exactly hanging about !
In the end it is all about what folks regard as an acceptable image ?

 

[tdodd]

A lovely set there, John. Once in a while I can get a half decent BIF when viewed at 100% but it is very rare. Perhaps it is my lack of BIF skill that is the problem, but I think I'd struggle to get even 1% of my BIF shots as sharp as that, probably nearer 0.1%. I shall continue to practice and maybe one day my "luck" will improve.

May I ask which lens you use? I imagine it is not the 1-4 zoom.