Sensor size, megapixels and image quality questions

[amymnc]

Originally Posted by Mr Guy

They even point out on another of their pages that 6mp images tend to do just fine for their big ol' wall clings:

I had a 10x20 landscape print done at Mpix a couple weeks ago and it's gorgeous if I do say so myself. Shot on a bottom of the totem pole D40 with the 18-55 kit lens (which I rarely use, the 55-200 VR is my fav). If it was blown up to poster size I might have had some problems...but this one looked exactly as it did on screen. No grain and no noise that I could find.

[vandergus]

Originally Posted by Mr Guy

I know, for me personally, my camera may not actually out resolve all of my lenses, but it certainly out resolves my skill level.

Haha. So what's the diffraction limit of your skill level? Is that two beers or three?

[Mr Guy]

Originally Posted by vandergus

Haha. So what's the diffraction limit of your skill level? Is the two beers or three?

I'm not sure, but I do know that red wine only takes a couple glasses before it overcomes the fstop advantage from shooting wide angle primes with in body Pentax image stabilization.

[OsmosisStudios]

Originally Posted by Tyler

Interesting points. I've never thought about downsizing an image to get better image quality. So, the less you try to cram into a sensor the better your image quality depending on the situation...am I reading that right? It seems like it has a lot to do with what you're shooting and for me that could be a number of things.

Digital sensors are kinda like film in a sense. With film, the faster the ISO you used, the larger the grains were. This is because larger grains absorb more light. Its also why at higher ISO you got more grain. DIgital is slightly different, in that the grains dont change from ISO to ISO: the sensor uses a bunch of "well" or "buckets" to collect light. The less of them that are on a sensor, the more light (the larger) each one can be, thus more light. As you crank up the ISO on a dSLR, you're increasing the signal that each pixel gives to the processor, thus creating digital noise which is a byproduct of the electrical analog/digital conversion. Its not quite the same thing, but its similar.

As you increase the resolution (megapixels), you're getting more "wells", but they become smaller. This means you get more pixels to play with but you cant adjust the ISO as much before the noise becomes objectionable. By downsampling an image, youre essentially grouping "wells" together to create one. Noise is less visible and images appear sharper. Having more pixels means you can get more in each inch of print, too. a 600DPI print will look smoother and nicer than a 300DPI print, and considerably better than a 150DPI print. You'd have to have them side-by-side, though.

It's sorta like how if you look at a mosaic with a bunch of big tiles, you have to stand really far back, but if you have a mosaic with a bunch of tiny tiles, you can stand closer and still see a pattern.

Originally Posted by Tyler

Again...very good points (I really appreciate your insight). I don't think I'll be able to play around with each of the cameras to see what I like best. But, this has given me a lot to think about. I am leaning towards a full-frame camera since I used to shoot a ton with an old Nikon N70 and I'd love to have a file that's comparable with old slides and negatives.

Sensor size has nothing to do with the output of film. Theyre totally dependent. Most people judge a low-iso frame of film (or a slide) to be anywhere between 15 and 25 megapixels: You can get that in a T1i, which is a crop-body. The only way the sensor size affects images is with noise levels (pixel density) and with the focal length of lenses (no crop factor with full-frame sensors).

To be honest, I think youre a little confused about the ways in which dSLRs and film SLRs are similar or different. You can compare the two, but there are so many differences in the core elements that its very hard to do with something like this. Just accept that digital is different and then go from there.

[Tyler]

Originally Posted by OsmosisStudios

Sensor size has nothing to do with the output of film. Theyre totally dependent. Most people judge a low-iso frame of film (or a slide) to be anywhere between 15 and 25 megapixels: You can get that in a T1i, which is a crop-body. The only way the sensor size affects images is with noise levels (pixel density) and with the focal length of lenses (no crop factor with full-frame sensors).

To be honest, I think youre a little confused about the ways in which dSLRs and film SLRs are similar or different. You can compare the two, but there are so many differences in the core elements that its very hard to do with something like this. Just accept that digital is different and then go from there.

That's the first I've heard that a 15mp camera is equivalent to a good slide film (Velvia for example) If that's the case then I'm not going to beat myself up over the differences between 15-25mp. I've read in a few places (I can't find the links now) that until you get into the ~25 mp range then your image quality isn't close to that of film...I guess that's where my main question comes from.

I don't think I'm confused - I certainly know that there are differences between film and digital and I've accepted those differences. I was mainly wondering why Nikon would make a full frame camera that wasn't 25 mp (assuming, at least in my mind, that it needed to be 25 mp to match film) - that's all.

[OsmosisStudios]

Originally Posted by Tyler

That's the first I've heard that a 15mp camera is equivalent to a good slide film (Velvia for example) If that's the case then I'm not going to beat myself up over the differences between 15-25mp. I've read in a few places (I can't find the links now) that until you get into the ~25 mp range then your image quality isn't close to that of film...I guess that's where my main question comes from.

I don't think I'm confused - I certainly know that there are differences between film and digital and I've accepted those differences. I was mainly wondering why Nikon would make a full frame camera that wasn't 25 mp (assuming, at least in my mind, that it needed to be 25 mp to match film) - that's all.

As I said, its 15-25mp, depending on the quality of film. I never claimed 15mp would equal good velvia. That being said, its still not a huge amount of difference as long as your image itself is well exposed and is made using good quality lenses and with proper technique. It really does depend on how the image was taken.

NIkon makes a full-frame camera that is less than 25mp because its not necessary. 25mp in digital terms is so high that its almost counter-productive. The other reason is that until recently, 25mp on a digital camera was only really available on the Medium Format bodies. Canon has had it's 21mp sensor for only a little while, and the D3x was only released earlier this year.

[Tyler]

Originally Posted by OsmosisStudios

As I said, its 15-25mp, depending on the quality of film. I never claimed 15mp would equal good velvia. That being said, its still not a huge amount of difference as long as your image itself is well exposed and is made using good quality lenses and with proper technique. It really does depend on how the image was taken.

NIkon makes a full-frame camera that is less than 25mp because its not necessary. 25mp in digital terms is so high that its almost counter-productive. The other reason is that until recently, 25mp on a digital camera was only really available on the Medium Format bodies. Canon has had it's 21mp sensor for only a little while, and the D3x was only released earlier this year.

Thanks for all your input Os - it has been very helpful and eye-opening at the same time. I was too stuck on wanting to get a full frame 25mp camera but our discussion has really helped and I feel more confident going into a crop-sensor camera.

[wulf]

Don't forget the question of whether your computer is up to processing the resulting image. If you get a new camera and find it takes a minute to open an image or perform an operation on it, you might end up with better results from a more limited camera. Of course, you can buy the power to cope with larger images but both that and suitable backup costs are factors to figure into your budget.

Wulf

[Tyler]

Originally Posted by wulf

Don't forget the question of whether your computer is up to processing the resulting image. If you get a new camera and find it takes a minute to open an image or perform an operation on it, you might end up with better results from a more limited camera. Of course, you can buy the power to cope with larger images but both that and suitable backup costs are factors to figure into your budget.

Wulf

Great points Wulf. I have a new HP DV6 with plenty of power but with all my pictures/videos and music the hard drive is already half full. Yikes