Camera crop factor (1 Viewer)

Photovisions · Sep 23, 2007

I’ve been on this forum for a few months now and have also browsed several other wildlife and bird forums. My main interest is in photography of birds rather than birds per se, although I have always (since childhood) had a soft spot for them

I am fairly knowledgeable about digital camera’s and have been involved with CCD’s for the last 15 years.

Whilst perusing different sites, something has struck me. Several people seem to prefer the smaller chips of cameras because it gives them longer reach or equivalent longer focal length. For example, I have a full frame Canon 5D and a 500mm F4 lens that I mostly use for bird photography, then I hear some preferring a 20D/30D with the same lens because of the 1.6 crop factor. They believe they are using a 1.6 x 500 = 800mm focal length, so much better than my system.

Is this a common belief here or does every one realise this is not the case?
Here is a quick question: Which is better for achieving more resolution, 400D or 1DMkIII assuming same lens and same shot conditions?
Adrian

Roy C · Sep 23, 2007

Photovisions said:
I’ve been on this forum for a few months now and have also browsed several other wildlife and bird forums. My main interest is in photography of birds rather than birds per se, although I have always (since childhood) had a soft spot for them

I am fairly knowledgeable about digital camera’s and have been involved with CCD’s for the last 15 years.

Whilst perusing different sites, something has struck me. Several people seem to prefer the smaller chips of cameras because it gives them longer reach or equivalent longer focal length. For example, I have a full frame Canon 5D and a 500mm F4 lens that I mostly use for bird photography, then I hear some preferring a 20D/30D with the same lens because of the 1.6 crop factor. They believe they are using a 1.6 x 500 = 800mm focal length, so much better than my system.

Is this a common belief here or does every one realise this is not the case?
Here is a quick question: Which is better for achieving more resolution, 400D or 1DMkIII assuming same lens and same shot conditions?
Adrian

Hi Adrian, I think that most people know that the 1.6 crop factor just gives you a different FOV (field of view) as opposed to a different focal length (a 500mm lens will always be 500mm regardless of the camera).
But there are some advantages in this for bird photography IMO - to crop a full frame camera shot, from say the 5D, to the same FOV as a 1.6 crop factor you will be left with less than 5MP, this in turn gives you less cropability.

gordon g · Sep 23, 2007

I agree with Roy that most people realise you are simply changing the field of view, giving an apparent increase in focal length.
I use a fullframe camera, and regularly crop in quite heavily. Yes this does reduce the megapixel count, but it really depends on what you are outputting - for web and 6X4 prints, 5Mp is more than adequate, for A3+ prints, clearly not.

Photovisions · Sep 23, 2007

Hi Roy

The cropability and comparing camera's depends on the pixel density for each camera. For example the 400D has a huge number of pixels for its size of chip with each pixel about 5.7 microns. The 5D has larger pixels (about 8.2u) and of course a larger chip. So, as far as pixel density goes, the 400D is the better camera when the object of interest does not cover the whole chip. In fact the density is 8.2/5.7 or 1.4x better. Another way to look at this, is that to achieve the same resolution, the 400D needs a 360mm lens and the 5D a 500mm lens (approx!).

This is where, I think the new 40D excels, it also has pixels of 5.7u, the same as the 400D.

For birds that very rarely fill the field of view (we always need more reach don't we), then pixel density is important.

Roy, you may well know all this and apologies if you do, but, from my general reading, there seem to be a lot out there that dont.

Adrian

Roy C said:
Hi Adrian, I think that most people know that the 1.6 crop factor just gives you a different FOV (field of view) as opposed to a different focal length (a 500mm lens will always be 500mm regardless of the camera).
But there are some advantages in this for bird photography IMO - to crop a full frame camera shot, from say the 5D, to the same FOV as a 1.6 crop factor you will be left with less than 5MP, this in turn gives you less cropability.

Photovisions · Sep 23, 2007

Hi Gordon

Agreed. In fact it would be interesting to know how much photographers are cropping prior to posting here. Sometimes you can get an idea, but other times it is hard to tell. Of course the best shots are those that fill the frame after the photographer has got pretty close to a bird. My recent Cormorant flight shot was presented at full frame, but I could have been 200 yards away with a heavy crop and would people notice?

I find this conversation interesting:eek!:
Adrian

Keith Reeder · Sep 23, 2007

Actually,

I think that many folk really do believe that they're getting a real optical increase in focal length from the crop factor - you only have to see how people refer to it to get that impression.

Pretty much on a daily basis you see posts which clearly indicate that the user is of the belief that by using a 300mm lens (say) on a 1.6 crop camera they've got a 480mm lens.

Roy C · Sep 23, 2007

Photovisions said:
In fact it would be interesting to know how much photographers are cropping prior to posting here.
Adrian

This is something I have been harping on about before Adrian - when people try to judge different lenses from small web images for instance it has always been my contention that it is hard to judge because you never quite know how heavily the image has been cropped.

Roy C · Sep 23, 2007

Keith Reeder said:
Actually,

I think that many folk really do believe that they're getting a real optical increase in focal length from the crop factor - you only have to see how people refer to it to get that impression.

Pretty much on a daily basis you see posts which clearly indicate that the user is of the belief that by using a 300mm lens (say) on a 1.6 crop camera they've got a 480mm lens.

I think there were lots of people that thought this,say a year ago Keith, But I have seen hundreds of posts where they have been put right and I reckon most have now got the message. Having said that there are still novices that obviously get mixed up between crop factor and focal length.

GYRob · Sep 23, 2007

the 1dsmk3 would be a nice camera to take a 1.6crop from as there would be more pixsels than say a 40d .
i think people Know it doesent make the lens longer but dont understand that its FOV .
to be honest i dont know what they DO think happends lol
i was there once too .
FF is good on the 5d if you can fill the frame or only crop a little Then its about the best value going -as the next up costs far more.
Rob

Photovisions · Sep 23, 2007

Keith and Roy - sounds like we are shooting from the same barrell
Roy - The truth will only come out with looking at an A3 print, something an internet forum cannot offer.

Rob - The 1Ds has slightly larger pixels than the 40D and 400D at 6.4u, but an enormous FOV. This will be a great camera and am thinking myself of selling my 5D to upgrade.

BTW cropping a 5D image makes no difference to the resolution achieved of a bird. If the bird is small in the FOV, then you cannot improve the resolution of that bird in a web image or print by cropping. Sometimes a severe crop that is blown up to an A4 or A3 print will look awful.

mjmw · Sep 23, 2007

Roy C said:
I think there were lots of people that thought this,say a year ago Keith, But I have seen hundreds of posts where they have been put right and I reckon most have now got the message. Having said that there are still novices that obviously get mixed up between crop factor and focal length.

Looking at just users of Birdforum or dedicated photography forums, I think you are right. However, I would guess that if you look at all the owners of digital cameras, the majority would not have a clue about crop-factors, pixel densities and resolution.

Cropping for presenting images on the web...who really cares? I look at some beautiful images here, knowing that they have been cropped to give maximum impact for this presentation medium. The fact that they can't be printed bigger than 6x4 is meaningless in this context.

Having said that, I am trying to get better at posting how much I crop and have pretty much always mentioned if I cropped a lot (leaving 50% or less of the frame).

Keith Reeder · Sep 23, 2007

Roy C said:
I reckon most have now got the message.

I dunno, Roy - for everyone that finally gets this, you can be sure that someone else will step up to take his place.

Even respected websites like Luminous Landscape mislead: they call it the "DSLR Magnification Factor", and although the article here does say:

OK, firstly, when you put a 300mm lens on a D60 you do NOT get a 480mm lens – it is still a 300mm lens

it goes on to say things like:

it behaves in similar, but not identical, fashion to a longer focal length lens

This is great for nature and sports photographers as the net result is more real pull than before with no trade off of maximum F Stop loss

and

For a given print size the subject will appear bigger in the frame. Thus it appears magnified compared to a 35mm camera.

We know the implications of these statements, but it seems to me that they can easily be read as suggesting that you get something for nothing, focal-length wise, from a crop sensor.

mjmw · Sep 23, 2007

From a traditional photographic point of view the effect of the crop-factor is very similar to extra focal length - it gives a larger subject size in the frame and decreased DOF at a given distance and aperture.

Neither of these things relate to the maximum possible quality of the digital image itself or the cropability (love that word Roy - makes me think of the old British Gas adverts...).

For example, yesterday my wife and I were laying side-by-side on the beach photographing waders. She was using a 20D (1.6x CF) and bare 400mm lens, I was using a 1D2N (1.3x CF) and bare 500mm. We both got images of a Sanderling at the same time. Both sets of images are pretty much the same with regrard to subject size, DOF and number of pixels.

So, for the average camera user, does it really matter?

Photovisions · Sep 23, 2007

Mark, from a practical point of view, you are right, there would be little difference from your cited example, but not as a result of the crop factor. The pixel size for your1D2N is 8.2u and your wife's 20D is 6.4u, so the 20D will have 8.2/6.4 better resolution by a factor of 1.28x. So to have the same image scale viewed at 100% on a computer monitor, your 1D2n will need to have a lens of 512mm focal length to match your wife's 400mm lens. Notice this has nothing to do with the FOV.

Taking another example, I have a 5D and 500mm F4 lens. The pixel size on the 5D is 8.2u. If I upgrade to a 1DsMkIII (pixel size 6.4u), although the FOV is the same at 35mm, the image scale is better on the 1DsMkIII by a factor of 8.2/6.4 = 1.28. This means that to achieve the image scale for the new camera the 5D would need a lens of 640mm focal length. Therefore the smaller pixels of the 1DsMkIII are offering better resolution despite the same crop factor. Amazingly, at no expense of increased noise too.

Adrian

Photovisions · Sep 23, 2007

Keith

"This is great for nature and sports photographers as the net result is more real pull than before with no trade off of maximum F Stop loss"

That is very naughty!!
Adrian

Photovisions · Sep 23, 2007

Mark, one more point

"From a traditional photographic point of view the effect of the crop-factor is very similar to extra focal length - it gives a larger subject size in the frame and decreased DOF at a given distance and aperture"

I could do exactly the same for you in photoshop, just interpolate pixels to increase the size of the object and crop the total image. In terms of resolution, this would give exactly the same result as you describe above.
Adrian

mjmw · Sep 23, 2007

Photovisions said:
Mark, from a practical point of view, you are right, there would be little difference from your cited example, but not as a result of the crop factor. The pixel size for your1D2N is 8.2u and your wife's 20D is 6.4u, so the 20D will have 8.2/6.4 better resolution by a factor of 1.28x. So to have the same image scale viewed at 100% on a computer monitor, your 1D2n will need to have a lens of 512mm focal length to match your wife's 400mm lens. Notice this has nothing to do with the FOV.

Errrmmm...aren't you just explaining why there is a difference in field of view?

Putting it simply, both cameras have the same number of pixels, but the 20D's are 'smaller', leading to a smaller sensor and smaller coverage of the image circle from the lens. Therefore a smaller field of view.

If you used the same focal length lens on the 20D and 1D2N then more pixels would cover the bird with the 20D, so the subject has better resolution...but the overall image resolution is the same. This means it has better potential cropability.

But in my example, because the subject size is roughly the same due to different focal lengths, roughly the same number of pixels are covering the bird...so the resolution is roughly the same...

...or am I completely missing your point?

Keith Reeder · Sep 23, 2007

Hi Mark,

ultimately a lot of this is just semantics, but for me a thing is what it is - no more, no less.

So - rightly or wrongly - as far as I'm concerned anything which implies that the effect of (for example) a 1.5x crop sensor and a 1.5x TC is the same - and that is essentially what is being implied in these circumstances - is a misleading misrepresentation of what's really going on.

Photovisions · Sep 23, 2007

Mark..

"Errrmmm...aren't you just explaining why there is a difference in field of view?"

That would be another way of looking at it, but I wanted to avoid that statement to get a better understanding of resolution.

You raised an interesting point regarding subject resolution and overall image resolution. What is important, is it not, is subject resolution? The overall resolution is meaningless to me, but I appreciate that others believe a 50MP resolution camera must be the bees knees. What would happen if the pixel size was 20u or 0.1u? Not practical I know, just trying to make a point.
Adrian

mjmw · Sep 23, 2007

Photovisions said:
You raised an interesting point regarding subject resolution and overall image resolution. What is important, is it not, is subject resolution? The overall resolution is meaningless to me, but I appreciate that others believe a 50MP resolution camera must be the bees knees. What would happen if the pixel size was 20u or 0.1u? Not practical I know, just trying to make a point.

I guess it all depends on how you work with your camera - I compose my images in camera and work to get the main subject the size I want in the frame at the start. So I don't think about it in terms of overall and subject resolution. I am also more concerned about how the individual sensor pixels behave rather than a larger density to allow me to crop more.

To put that in context of the different sensor sizes. If I am using the 20D I know that I don't have to get as close as when I am using the 1D2N or I only use a 1.4x instead of a 2x TC.

Camera crop factor (1 Viewer)

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