DSLR advice needed

[kalniel]

Originally Posted by BUFF

diffraction limiting will also occur slightly earlier on a 15Mp sensor than on a 12Mp one of the same size.

Depends what you mean by earlier - earlier in the sense of the range of the camera, but it'll kick in in terms of MP at exactly the same level as on a 12MP camera.

IE if an APS-C sensor can only resolve 13MP of yellow-green light at f/8 then the 12MP camera will not be diffraction limited but the 15MP will, however the 15MP is still recording 13MP of useful information vs the 12MP camera's 12MP

But then you look at it on screen at 3MP and print at 6MP, so you don't need the extra in most cases

[BUFF]

I meant that diffraction limiting may be observed at a larger aperture than on a smaller Mp sensor of equivalent size e.g 10Mp diffraction limit is ~f16 whereas on 15MP it may be ~f13.

as you say though if printing it's more likely that the print specs. may be the ultimate limiting factor.

[GSte]

So one more thing....

Would it be worth getting a second hand 40D over the other Canons, or would I not notice much difference?

[kalniel]

Originally Posted by BUFF

I meant that diffraction limiting may be observed at a larger aperture than on a smaller Mp sensor of equivalent size e.g 10Mp diffraction limit is ~f16 whereas on 15MP it may be ~f13.

That's the same thing as what I said - but the point is the diffraction is only limiting you to less than your total MP, which still might be more than the 10MP camera is capable of. You can't be diffraction limited to less MP than the other camera is, assuming it has the same sensor size.

In your example the 15MP camera might need f13 to get it's full 15MP (actually, it's about f/10), but while diffraction is limited it at f/16, it's still able to resolve say 11MP (actually 3, same with the 10MP camera ).

http://www.luminous-landscape.com/tu...solution.shtml

What happens when you're limited to less resolution than the camera is capable off? Nothing, when you're comparing the same size pictures. But if you blow them up to 100% magnification you'll see increasing softness as the same light information is spread over neighbouring pixels. Back to needing to blow up pictures more than you could with the lower MP camera to be able to see the difference.

[kalniel]

Originally Posted by GSte

So one more thing....

Would it be worth getting a second hand 40D over the other Canons, or would I not notice much difference?

You'd notice the difference in size, weight, viewfinder, burst speed etc. But the pictures taken would be very similar.

I really liked how the 40D felt in my hands, and couldn't stand the 450D/500D.

[BUFF]

Originally Posted by kalniel

In your example the 15MP camera might need f13 to get it's full 15MP (actually, it's about f/10), but while diffraction is limited it at f/16, it's still able to resolve say 11MP.

No, you still get a 15 MP or 12MP image irrespective of aperture just that resolution no longer improves once you hit the diffraction limit & indeed may well fall away.

(actually, it's about f/10)

Bear in mind that there are 2 different APS-C sizes (Canon & everyone else ), different sensor construction (micro lenses etc.) & of course different attached lens quality so there is no 1 absolute value.

& then of course we have to consider the output medium (printer, monitor etc.) & whether it has the ability to demonstrate any difference ...

complex subject with lots of variables

[kalniel]

Originally Posted by BUFF

No, you still get a 15 MP or 12MP image irrespective of aperture just that resolution no longer improves once you hit the diffraction limit & indeed may well fall away.

I'm not really talking anything about the size of the image, just the resolution of it. Yes the 15MP image is larger, but that's all normalised as soon as you resize or print.

Bear in mind that there are 2 different APS-C sizes (Canon & everyone else ), different sensor construction (micro lenses etc.) & of course different attached lens quality so there is no 1 absolute value.

Sensor construction doesn't affect diffraction limits on resolution. Anything infront of the sensor can only reduce the resolution, like AA filter, lens etc. but when you're comparing the 450D with the 500D you can assume most things are the same. The improved sensor design of the 500D affects the S/N ratio, which more or less counteracts the effect of smaller photo-sites.

& then of course we have to consider the output medium (printer, monitoe etc.) & whether it has the ability to demonstarate any difference ...

Indeed.

[BUFF]

Originally Posted by kalniel

Sensor construction doesn't affect diffraction limits on resolution.

of course it does - more photosites on same size die means that they are smaller>worse diffraction - an analogy would be that it's a bit like looking through a fence with smaller mesh.

Anything infront of the sensor can only reduce the resolution, like AA filter, lens etc. but when you're comparing the 450D with the 500D you can assume most things are the same. The improved sensor design of the 500D affects the S/N ratio, which more or less counteracts the effect of smaller photo-sites.

if you were comparing a 500D & 50D you could assume similarity but between the 450D & 500D sensor I think not.
& unless I'm reading this wrongly your end statement kind of goes against your earlier statement that smaller photosites has no effect on diffraction ...

[kalniel]

Originally Posted by BUFF

of course it does - more photosites on same size die means that they are smaller>worse diffraction - an analogy would be that it's a bit like looking through a fence with smaller mesh.

The mesh in your analogy is the lens aperture, nothing to do with the sensor.

The limit on an APS-C sized sensor with an f/8 aperture is 13MP equivalent resolution for green light. That's fixed, nothing to do with how many photosites are actually on the sensor. If you have less than 13MP then there's theoretically room for more at f/8. If you have more then you're not taking advantage of them at f/8. The diffraction limit is the same though.

if you were comparing a 500D & 50D you could assume similarity but between the 450D & 500D sensor I think not.
& unless I'm reading this wrongly your end statement kind of goes against your earlier statement that smaller photosites has no effect on diffraction ...

Smaller photosites have no effect on diffraction limit. S/N is nothing to do with diffraction limit either. But smaller photosites do have an effect on S/N, which can be offset by technology or micro/gapless lenses etc.

[Bobster]

Originally Posted by GSte

So one more thing....

Would it be worth getting a second hand 40D over the other Canons, or would I not notice much difference?

for your use, not really only thing thr 500 doesn't have over the 40 is shooting speed.. 40 is 6fps (though you can get 6.5 if you shoot over 1/500 if i remember right) and the size is bigger, the consumer bodies are smaller than the prosumer/pro bodies

and the 40 doesn't have a movie mode..

ive got shots taken @ f/18 and i cant see the diffraction (photo has been blown up to 30x20in)

[kalniel]

Originally Posted by Bobster

ive got shots taken @ f/18 and i cant see the diffraction (photo has been blown up to 30x20in)

Exactly, which is why all this talk of megapixels is silly - diffraction will have limited you to 3-6MP worth of information or so on APS-C, but spread that out in a sensible way, add in some tricks like micro-contrast and as long as you're not peering at it from a few cms away it's still good enough.

[GSte]

Went for a 500D with kit 18-55mm lens in the end, it just arrived today and the step-up in image quality over my super-zoom bridge is staggering!

Thanks for all the help chaps.

[kalniel]

Nice! Want to see pics!

[GSte]

Actually finding it hard to take any good ones! I've had some outdoor portraits that have turned out nicely, sharp focus, etc, but the majority of the pics I've taken look mediocre at best, and generally worse than those I've taken with my point and shoot!!!!! I dunno if it's just the stock lens or the settings I'm using (mainly the basic auto modes..... auto, landscape and portrait, all using AF) but most images seem very soft and lacking any decent sharpness!?!?! I don't think it could be the light levels, as they were taken in daylight and it wasn't particularly overcast...... will I need to learn how to use full manual setting to get my pictures to look even vaguely good, or should I just get some better lenses? The inbuilt flash is really annoying me too....

[Blastuk]

Post some decent sized samples so we can see what you're seeing..

[Bobster]

Originally Posted by GSte

Actually finding it hard to take any good ones!

change the camera to M set the focal point to center and then adjust aperture, exposure, focus, compose and shoot..

also DSLR's aren't the same as digital P+S, you will get a slightly softer looking shot out of the camera as they don't have the same aggressive sharpening in camera as the P+S do, as you are generally throught to know what you are doing by owning one