Image sensor size, pixels, resolution - laymen's terms needed please

[EmPea]

Hello everyone,

I'm extremely new to SLRs (I was basically used to the point-n-shoot-n-hope the pic comes out method prior to this) and trying to learn as much as I can about them before making any silly moves on a purchase I may come to regret later on.

Anyways, would someone be able to explain in laymen's terms what image sensor size is and how it relates to megapixels and resolution? I've been reading around and understand that a full frame sensor will capture a larger portion of a view compared with a smaller sensor, all else held constant, but what does this mean about the pixels and resolution?

Also, I have read that generally I am better off having a larger image sensor using fewer megapixels than a smaller image sensor with more megapixels -- is this correct, and if so, why is that?

Thanks in advance.

[Photo-John]

Welcome to the site, EmPea. I do believe we can help. Or at least confuse you more...

Pixel size is the key. The bigger the pixel, the better the image quality should be. A digital camera sensor contains millions of pixels, hence the term, "megapixel." The more pixels on a given sensor size, the smaller those pixels will have to be and the more image quality will be compromised.

The reason a "full frame" sensor usually provides better image quality is that it allows for larger individual pixels. But the actual pixel size - measured in microns - is still the critical spec. A good example are the two new pro DSLRs from Nikon and Canon. The Nikon D3S has a 12-megapixel full frame sensor and the Canon EOS-1D Mark IV has a 16-megapixel APS-H (1.3x crop factor) sensor. The Nikon's pixels are much larger than the Canon's and it's reasonable to expect that the Nikon will have much lower noise. Not that the Canon will have poor image quality. I expect it to have excellent image quality - except at higher ISO settings, where the Nikon's larger pixels will start to make a difference.

It's not quite as simple as just pixel size. In-camera noise reduction via software and sensor cooling are also important to a camera's final image quality. But pixel size is always the first thing to look at.

I want to caution against worrying too much about image quality, though. While it's true that a particular camera might have better image quality than another, you have to ask yourself if it will really make a difference for you. The camera with the best image quality might cost more than you can afford. Or it could be too heavy or too slow. You need to put aside the marketing and hype and carefully consider your real needs. If you're moving from a compact camera to a digital SLR for the first time, any camera you buy is going to blow away your old camera. So it might be best not to worry about sensor size right now. My usual recommendation is to buy the least expensive digital SLR and invest your money in lenses. I've had a whole bunch of digital SLRs since I bought my first. But I'm still using lenses I bought when I was shooting film. Lenses are really your most important investment.

Does that help? Let us know if you have more questions

[Anbesol]

I agree with what John said. Particularly in being dismissive about splitting hairs with image quality when picking a camera. Any DSLR will do much better than what you are used to, and the variety and niche differences in the cameras may be more important to your shooting style than what little difference there may be in image quality. Full frame for example will always be heavier and bulkier than an APS equivalent, and probably more importantly: cost thousands more.

The image quality produced at even the bottom rung of DSLR can still be used in most professional situations, if that tells you anything about image quality.

Some features worth considering:
Video Recording - note that most video capable DSLR do not have the ability to autofocus while recording.
Live View
Dual control dials, more on the fly switches and tactile interface.
Viewfinder brightness.
LCD brightness and resolution. This makes a bigger difference than most would think.
Image Stabilizer options: In camera or in lens.
Build quality/Weather sealing.

Now don't go off and buy a DSLR only to pair it with a junky lens, thats like building a nice fancy hot rod then putting a Honda Civic motor in it.

[Photo-John]

Now don't go off and buy a DSLR only to pair it with a junky lens, thats like building a nice fancy hot rod then putting a Honda Civic motor in it.

Nice analogy

[readingr]

Nice analogy

I'm not sure that it is a good analogy - we race the civic engine in the UK but then we have few hotrods

But I agree with everything said so far.

I always look at the photography I want to do, chose the lenses I need and then look at the body to do the job. Mexapixels don't really matter as was shown by a program in the UK where pro's and I mean well known pro's were given various camera's including phones to take pics with and they loved the compact and phones because of their portability and did not consider the mexapixel issue that relevant.

The odd thing was they all complained about the weight of the hasselblad which had a meager 49MP but did take excellent photo's.

Always handle the camera's because what you'll find is that one camera will suit you more than the rest and any of today's DSLR's will do an excellent job.

Roger R.

[Franglais]

Hello everyone,

I'm extremely new to SLRs (I was basically used to the point-n-shoot-n-hope the pic comes out method prior to this) and trying to learn as much as I can about them before making any silly moves on a purchase I may come to regret later on.

Anyways, would someone be able to explain in laymen's terms what image sensor size is and how it relates to megapixels and resolution? I've been reading around and understand that a full frame sensor will capture a larger portion of a view compared with a smaller sensor, all else held constant, but what does this mean about the pixels and resolution?

Also, I have read that generally I am better off having a larger image sensor using fewer megapixels than a smaller image sensor with more megapixels -- is this correct, and if so, why is that?

Thanks in advance.

I'm going to do a few basic definitions. Let's examine the architecture of a DSLR. Your have, from front to rear:

1. The lens, which is interchangable. The lens has built into it a diaphragm to limit the amount of light coming through the lens (expressed as an f stop). It also has a focussing mechanism, which moves the internals back and forth to make the image on the sensor sharp at a given distance. And if it's a zoom lens then it has a zoom mechanism the moves the internal components around to change the focal length, which changes the view cast on the sensor
2. An instant-return mirror. This reflects the image from the lens upwards into the viewfinder so you can see it (and also allows the autofocus detection mechanism to work)
3. The shutter, which hides the sensor up until the moment when you press the shutter. Then the mirror swings out of the way and the shutter opens to expose the sensor to the image for precisely the right amount of time to give a perfect exposure (you hope)
4. The sensor. This is a flat electronic circuit with millions of photosensitive elements laid out in a regular pattern. Each element is filtered to respond to either magenta (reddish) or cyan (bluish) or yellow light
5. The image processing circuitry. This takes the signal coming from the photosensitive elements, amplifies it, corrects it and combines adacent elements (one magenta, one yellow and two cyans) to make - a pixel - which can contain all possible colours and white and black.

The number of megapixels is the number of pixels vertically time the number of pixels horizontally. My D70 had about 2000 pixels vertically x 3000 pixels horizontally = 6 million pixels.

The bigger the photosensitive element the more light it can collect so the signal has to be amplified less and the number of errors (noise) is lower. A 24x36cm sensor (full frame) is about twice as big as an APS-C sensor (used in most DSLR's). If you put the same number of pixels on both then the ones on the 24x36 sensor are twice as big and - surprise - you can push the ISO (sensitivity to light) to about double what you can on the APS-C. However apart from that a 12Mpix image is a 12Mpix image, no matter what camera it came from.

"Resolution" means "making it look sharp" and there are lots of places where you could use this term:

- the lens must have high resolution because it has to draw an image which is sharp on the miniscule photosensitive elements in the sensor
- the more pixels you have the bigger you can make the final image. However it depends on what you are using to view it:

>> My computer monitor is set to display 1280x1024 pixels = 1.3 Megapixels. If I use ACDSee to view on screen a 6MPix image and a 24Mpix image then it's going to downsize both to 1.3 Megapixels for display and I'm going to see no difference
>> If you do a print on an inkjet printer then the rule of thumb is to have not less than 200-250 pixels per inch of print (300 pixels per inch for industrial printing). If you have less it won't look super sharp. If you have more it won't look any better because the inkjet can't print any finer. In other words a 6Mpix image can do a perfect 8x10 inch print and even a 10x16 comes out well

Is that helpful?

[Mark Woodworth]

John really nailed a lot of the key aspects in regards to sensor size and image quality. It is also probably safe to say that today's 12 megapixel camera using the same resolution and same sensor size from 5-6 years ago, probably produce better image quality.

With that said, knowing the things I know now, that I didn't know when I entered the DSLR market a few years ago, I might have done things a little different. Basically what I'm saying is that I would have worried less about the body that I was using, and more about the lenses and the type of photography that I was producing.

What I mean by that is, I wouldn't go out and buy a camera just for it's high ISO, low noise capacity if I didn't already have fast glass to go with it. IE primes or f/2.8 lenses.

You will benefit more from learning how to use the camera correctly in manual or "semi-manual" modes, and see your biggest improvement in photographic quality from doing just that, then going out and spending what some people spend on their cars, for camera equipment.

The conclusion, you will be making a huge upgrade over a point and shoot in terms of image quality and probably your confidence your ability to get the shot you want. Which will be exactly what you need to determine how much time/money you want to spend between full frame and APS-C sensor cameras!

[readingr]

>> My computer monitor is set to display 1280x1024 pixels = 1.3 Megapixels. If I use ACDSee to view on screen a 6MPix image and a 24Mpix image then it's going to downsize both to 1.3 Megapixels for display and I'm going to see no difference
>> If you do a print on an inkjet printer then the rule of thumb is to have not less than 200-250 pixels per inch of print (300 pixels per inch for industrial printing). If you have less it won't look super sharp. If you have more it won't look any better because the inkjet can't print any finer. In other words a 6Mpix image can do a perfect 8x10 inch print and even a 10x16 comes out well

Is that helpful?

Ahhh! don't forget that the bigger the picture the less pixels are required because you stand further back from the print - so A2 or bigger needs less pixels than a 10x8 because you stand back further so the pixels in the A2 print will be bigger.

A 12MP camera can therefore print up to the size of a 3 storey building because the pixels on paper need to bigger to compensate for the distance you need to be from the print to be able to see the complete picture. So up to A3 the MP required stays resonably constant because of the distance from picture to the eye to make sense of the picture.

Hope that makes sense.

Look at large posters closely and you'll see big dots per pixel.

Roger R.

[Loupey]

...Also, I have read that generally I am better off having a larger image sensor using fewer megapixels than a smaller image sensor with more megapixels...

This statement is overly simplified. Larger sensors mean bigger, heavier, costlier cameras. In addition, larger sensors require more expensive lenses.

Food for thought: I could show you 8"x12" prints taken from a 4 year old 6mp dSLR along with 8"x12" prints taken with a 1 year old 15mp dSLR and you probably wouldn't know which camera was used. But, I could show you two 8"x12" prints taken with the same 6mp camera with two different professional grade lenses but yet you would be able to see a difference.

I think any dSLR currently on the market will be able to produce images of sufficient image quality for you. Just make sure the system that you buy into will have the lenses and accessories that will allow you to grow.

[EmPea]

Wow! Thank you all so much for all the feedback -- this is a lot to digest: I will have to read it a couple times over before the questions begin to flow, but I feel like you all really shed a lot of light about some technical questions I had -- particulary about the MPs -- I just wasn't getting how let's say a 6MP SLR was better than a 12MP point and shoot (now I do, THANKS ALL!).

The SLR will actually be a bday/xmas gift for my brother (killing two birds with one stone here) -- and in the mean time I'm hopin he'll let me make use of it sometimes as well
He doesn't have experience with SLRs but knows far more than I do about all these technical aspects that I am just learning about these days, and I don't want to make any impulsive and expensive purchases and come to regret them later (trying to be an informed consumer here).

So if I should use more of the investment in a good lens, what type of lens should I be looking at? I know he'll want to use this for photos of his cars, as well as landscapes and scenery. The max I'm willing to spend is $1200, so anything over that is really pushing it.

I was originally looking at the Nikon D90 or the Canon 50D, but now I'm even questioning that -- what I'm thinking now is if I buy a really expensive SLR, there won't be anything left over for a lens. Can anyone offer suggestions for a camera/lens?

Thanks again for all your help!

[Franglais]

..
So if I should use more of the investment in a good lens, what type of lens should I be looking at? I know he'll want to use this for photos of his cars, as well as landscapes and scenery. The max I'm willing to spend is $1200, so anything over that is really pushing it.

I was originally looking at the Nikon D90 or the Canon 50D, but now I'm even questioning that -- what I'm thinking now is if I buy a really expensive SLR, there won't be anything left over for a lens. Can anyone offer suggestions for a camera/lens?

Thanks again for all your help!

The D90 + 18-105VR kit lens is about $1199,95, which sounds just right.

The 18-105mm kit lens is well-matched to the camera (according to the tests - I don't have one). The resolution is very high and it's specifically designed for an APS-C DSLR. It gives you a range of views from wide-angle to medium telephoto so it would be fine for landscapes, portraits and static pictures of cars. If you wanted to shoot racing cars in action you would probably need something longer.

The 18-105 is excellent value but it's not very durable (mostly plastic construction, like almost all kit lenses). This is fine for the average shooter but for someone who uses the camera every day I would go for metal construction (example: a 16-85VR and a 70-300VR).

In your place - I think I would go with the D90 + 18-105 and see how he likes it. If after a while he starts complaining about the lens then you think about a replacement for next Christmas.

BTW I would avoid the Canon 50D + 28-135mm kit. The lens is an old designed-for-24x36-film model and it can't do wide-angle on the 50D.