Higher MP = Longer Focal Length?

Zillah

Just a thought. If I have a much higher pixel count that some other guy, does that mean that my functional focal length can be longer because I can crop the image while keeping the image quality he has?

mathias

Not necessarily , high pixel count for the same size sensor can cause problems with noise on some models , so cropping the picture to match a lower pixel count can reduce quality.

Sensor size and effective focal length are related , not pixel count , so if you have a bigger sensor along with the bigger pixel count , then it would be true in a way.

Zillah

Well, lets say two shots both taken at 100ISO, so there's no noise to speak of.

You and I both shoot something at 100mm. Your images come out at 4 MP, mine come out at 12MP. All else is equal. I can crop my image down to your 4MP and the net result is as if I had a 150mm lens (fairly arbitrary estimate).

No?

elven

Sensor size.... unless you have a sensor that is 3x bigger, so the pixels aren't squished in more, you won't be getting an equivalent result. (My maths may be questionable but the logic is right)

I would imagine also that if you were actually shooting on the above mentioned larger sensor with the same lens, you wouldn't be getting the same (appearance of) sharpness that you would get shooting with a 150mm lens if you were enlarging it, because it isn't just down to the sensor...

Then you have to start considering the actual perspective effects that you get between wide/tele lenses, your final image would usually be (imperceptibly, but still) distorted either concave or convex a certain amount depending on the length of lens, the DoF is also affected by the focal length, and purely cutting off the edges of the frame wouldn't simulate those effects as well.

In a very very basic way what you say is logical but if you look into it with any kind of detail it falls apart...

Oriel

I will depend hugely on the qualilty of the lens too.

mathias

This is a quote from the website linked below ,

So what's the take-home message?

Well, if you're shopping for an ordinary digicam, bear in mind that money spent on higher resolution may actually be buying you less than nothing. A lower resolution camera can actually be a better product in every respect.

http://www.dansdata.com/gz059.htm

And this is a more technical explanation ,

http://photo.net/equipment/digital/sensorsize/

So the answer in short , is no , you gain nothing from a higher megapixel count with the same sized sensor in most compact cameras when the resolution in question is greater than say 4MP.

In actual fact , given a smaller MP count for a given sensor size , the lower res camera can produce better pictures because of the larger individual light gathering elements!!

A higher megapixel count gives better results only if the sensor size is significantly larger , such as the new Canon mark III with a 1.3 multiplier or the 5D with a full 35mm sensor.

This is unavoidably linked in to apparent Focal length also as using high MP counts to compensate for shorter lengths is going to significantly affect quality.

Roen

I would have thought that pixel density would have the largest role in this.

magicbastarder

mathias wrote:

A higher megapixel count gives better results only if the sensor size is significantly larger

by that reckoning, an early (say 1MP) full frame sensor would outperform a modern 8MP sensor, 60% the size.

mathias

by that reckoning, an early (say 1MP) full frame sensor would outperform a modern 8MP sensor, 60% the size.

Missing the point ,
Dont forget the part

when the resolution in question is greater than say 4MP

Thats important , the megapixel race is over and has been since they reached this level ( approx 4-5MP) ,below this there was indeed noticeable improvements , however now , squeezing more MP into these same sized sensors is no benefit and can actually take away from performance in other areas , most noticeably noise , but other areas too.

So for instance , the Sony DSC -P100 , performs the same if not slight better , than the DSC -P200 , which has 2 megapixels more , thats because the sensor is the same size , and the extra pixels in the 7.1 MP are no real benefit.

After reaching a certain MP count in a certain sensor size , you start trading off High MP counts for light gathering element size and this reduces picture quality , but the general public are still hooked on MP count and manufactures go with this ,

Not so on the high end , where Nikon and Canon are happy to stick with 6-8 MP on a certain sensor size as this is optimum and concentrate on improving other areas !!