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08-25-2009, 05:57 PM   #1
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K20D: Relationships among Pixel Density, Sensor, Lens

(I should maybe subtitle this question: A little knowledge can be a dangerous thing)

Coming from the world of film photography, the learning curve on the finer points of digital photography is pretty steep. So excuse me if this is a misguided question in some way.

My understanding is that, for a given sized sensor, increasing pixel density *at some point* adds little but noise. Likewise for lenses: At some point, increasing pixel density out-performs a lens.

If all this is true: Does anyone have any words of wisdom about DA lenses and the K20D? I shoot in RAW at full size (14.6 megapixels), but sometimes wonder whether I'd do just as well with smaller images.

Thanks!

08-25-2009, 06:42 PM   #2
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QuoteOriginally posted by starstuff Quote
(I should maybe subtitle this question: A little knowledge can be a dangerous thing)

Coming from the world of film photography, the learning curve on the finer points of digital photography is pretty steep. So excuse me if this is a misguided question in some way.

My understanding is that, for a given sized sensor, increasing pixel density *at some point* adds little but noise. Likewise for lenses: At some point, increasing pixel density out-performs a lens.

If all this is true: Does anyone have any words of wisdom about DA lenses and the K20D? I shoot in RAW at full size (14.6 megapixels), but sometimes wonder whether I'd do just as well with smaller images.

Thanks!
Depends on which lenses. DA 18-55mm kit or the high quality DA 14mm f/2.8 or DA LTDs.
08-25-2009, 07:41 PM   #3
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QuoteOriginally posted by starstuff Quote
(I should maybe subtitle this question: A little knowledge can be a dangerous thing)

Coming from the world of film photography, the learning curve on the finer points of digital photography is pretty steep. So excuse me if this is a misguided question in some way.

My understanding is that, for a given sized sensor, increasing pixel density *at some point* adds little but noise. Likewise for lenses: At some point, increasing pixel density out-performs a lens.

If all this is true: Does anyone have any words of wisdom about DA lenses and the K20D? I shoot in RAW at full size (14.6 megapixels), but sometimes wonder whether I'd do just as well with smaller images.

Thanks!
The K20D cannot out resolve all lenses although it can out resolve some lenses. When you shoot in RAW you only get 1 size 14.6. Shooting in RAW to get maximum resolution is not the only reason to shoot RAW and probably not the best reason to shoot RAW. What determines what resolution you need is what size you print/view the photo. If you use the max size best JPG quality you can get you will have about the same resolution as RAW but not only do you not get the control you get with RAW to make adjustments but you will probably have more resolution then you need for most printing, assuming you are not printing for max size. If you go for the smaller size JPG you will probably not out resolve most decent lenses and be good to print to somewhere around 8/10 depending on how picky you are. You do loose the RAW control but you save space and all you are doing is have the camera PP for you from RAW then throwing the RAW away. This is not changing the sensor size so you are not gaining any thing there just throwing a lot away.

I use RAW so that I have the most control later. When I PP either in camera or on my computer I can then adjust accordingly to get the resolution I want/need. If I have more noise then I want and have more resolution then I need I can trade off some resolution by using noise reduction. This is one of those things that works better with RAW. If you don’t need or want the other thing RAW can give you then just use the smaller size JPG in the camera. Just remember that this is a tattooing event. You cannot get the photo to be as good as you could get if you had used RAW.

I rarely consider the size of files regarding storage. This is one of the cheaper parts of this hobby. I do consider the size of the file for transport (i.e. E-mail) and the print/view size that it is going to be used for but I do that in PP.

DAZ
08-25-2009, 07:59 PM   #4
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Why shoot less pixels (even if you could in raw)? Storage is dirt cheap compared to ... well ... every other aspect of the hobby.

08-25-2009, 08:10 PM   #5
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QuoteOriginally posted by Alfisti Quote
Why shoot less pixels (even if you could in raw)? Storage is dirt cheap compared to ... well ... every other aspect of the hobby.
Intersting point...
Now that you've paid for the privilege of having 14.6Mp, you should take full advantage of every pixel it can give you!

Or risk being considered a waster of precious resources!
08-26-2009, 04:06 AM   #6
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QuoteOriginally posted by starstuff Quote
the learning curve on the finer points of digital photography is pretty steep.
So, let me give you something else to consider

Due to some mathematical oddity, the dynamic range (on a per pixel base) increases if you resize your image to a smaller size (an effect which of course is never considered in tests ...). But in order to really benefit from this effect, you have to capture the full available dynamic range in the first place.

The paradox consequence is this: shoot RAW (i.e. full size) if you aim for smaller image sizes!
08-26-2009, 07:13 AM   #7
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CCan you further elaborate please?
08-26-2009, 07:24 AM   #8
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"wasted" resources

QuoteOriginally posted by Ash Quote
Intersting point...
Now that you've paid for the privilege of having 14.6Mp, you should take full advantage of every pixel it can give you!

Or risk being considered a waster of precious resources!
Hmmmm.... Good point.

08-26-2009, 08:01 AM   #9
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QuoteOriginally posted by mysterick Quote
Can you further elaborate please?
DR is normally defined as the number of luminance increments between white and a gray level with 50% (or some other fixed ratio) noise.

To start with, JPG only has 256 luminance increments at all (8 Bit). Without strong shadow compensation, this will have already limited the DR to ~8 EV.

The K-7 offers optional strong shadow compensation and this may be of lesser concern when used.



Now, let's consider RAW files.

Say, a RAW file has 12 Bits or 4096 luminance increments.


The darkest gray would be 1, white 4095.

If you properly scale the image to 50% size, the darkest possible gray becomes 0.25 (from 3 black and 1 dark gray pixels). Theoretically, you get 16384 luminance increments in the smaller image. Or two full stops more DR.

However, RAW files are such that the darkest grays always are totally noisy (random) rendering the above consideration completely irrelevant

What is relevant though is this: Due to averaging, the noise of the average of 4 combined pixels is only 50% of the noise of a single pixel (Poisson law).

Therefore, you gain one full stop of DR when sizing to 50%. Therefore, a web-sized image (600x400) has three full stops more DR than the original sized image (requires 16 Bit TIFF of course).


So, even if the sensor outresolves the lens, you still shouldn't shoot smaller JPGs because this destroys dynamic range.

Last edited by falconeye; 08-26-2009 at 08:07 AM.
08-26-2009, 09:34 PM   #10
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Get the gist

Thanks, everyone ... a lot of the details in this string are over my head, but I get the general idea. Full-sized RAW it is. It's what I've been doing anyway.
08-26-2009, 09:42 PM   #11
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Falconeye....

You just melted my left lobe.

Ouch.
08-26-2009, 10:31 PM   #12
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shooting with less pixels is not the same as having a sensor with less pixel density - the physical sensors are still smaller, don't collect as much light, and have a higher noise threshold.
08-27-2009, 03:23 AM   #13
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QuoteOriginally posted by KungPOW Quote
Falconeye....
You just melted my left lobe.

Never mind, w/o your left lobe, your photography and sex will nothing but improve
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