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09-30-2014, 07:20 AM   #1
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cropping advice

I have posted this in general as the answers I have no doubt I will get, might,be of use to beginners.

I have a enormous problem understanding the relationships between sensor size, mp , resolution, photsite sizes and so on.

I understand the size relationships between the physical measurements of Full Frame; APS-C ; 2/3rds; micro 2 thirds and so on and crop factors but thats about it.

Example:

If I take a image of a wine bottle standing on a table. with a k5IIs and a K3 both with the same 50mm lens and fill the frame with the bottle would I be the same distance away? answer is yes I think?

if the answer is yes then once downloaded if I zoom in to the label and fill the computer screen will they both be equally sharp and well defined? or will one be more pixalated?

Now if I take the same image with a FF and a 50mm lens and again ensure to fill the frame with the bottle and again then later zoom in to fill the screen with the label only will the ff image be of a better quality ?

See this what I don't understand , what is the benefit of using say a Sony A7 or a A7R or a Nikon 810 over a K3 ?

There are sensor size differences between them all and the simple answer I am looking for is,

if in the scenario given above every image was correctly exposed and absolutely in focus , which camera would give the best rendition of the cropped in label image if it was then printed to A3+?

this link gives the sensor specs if that helps? Sony A7 versus Sony A7R versus Pentax K-3 - Side by side camera comparison - DxOMark

09-30-2014, 07:48 AM   #2
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So, from what it sounds like, you are not understanding the relationship between a physical object relative to the size of the camera's sensor?

Well, if you take a K5iis and a K3, set up the same shot, same distance away, same lense, etc, you will end up with an image of two different sizes.
A Pentax K5iis has an image resolution of 4928 x 3264 pixels at its full 16.1 MP.
A Pentax K3 has an image resolution of 6016 x 4000 pixels at its full 24.1 MP.

The sensor is the same size (K3 = APS-c (23.5 x 15.6 mm)) (K5iis = 23.7 x 15.7 mm)) the only difference is the resolution, so assuming you have a display that can display an image with that many pixels, the photo will be made smaller for your display, so you should end up with an image approx. the same size, aside from actual pixels in the image.

Now, say you have a FF camera, its a whole new ballpark, because you're talking a sensor 36 x 36mm which is considerably larger, but they do have a higher resolution. I have never compared images from a FF camera to a APS-c camera, however on the display they should all be the same size. To tell you the truth, a FF camera would give you the best end result for cropping, but it depends on your distance relative to the focal length of the lense. Are you two feet away, or ten feet away? Depending on the distance, you will need more, or less cropping. The Sony A7R has a 36mp sensor, with a resolution of 7392 x 4920 pixels. So, that means you will get the best results with that particular camera, and the reason for this is because on a computer display, for example, I use a Dell UltraSharp U2410. It is 24 inches corner to corner, with a resolution of 1920 x 1200 pixels (Yes, the image is much larger than that). It has a pixel density of 94.34 pixels per inch. So, now say I am displaying the same image, one captured from each of the three cameras you mentioned, the one with the highest resolution is going to look the best, the reason for this is because, there are more pixels in that image, meaning they are placed closer together, the closer together they are, the less distortion there will be when you zoom in/ crop the image, however, there comes a point when blowing up images where the relative size of the sensor/ MP quality don't matter. Using the K5, which has a resolution of 4,928 x 3,264 pixels. I can effectively make prints as large as 40 inches by 60 inches, with little to no distortion. FF technically is better, but there comes a point where you are paying for a lot of tech, but not a lot of real world difference in quality. There is more quality in bigger sensors or sensors with a higher resolution, but you honestly won't see it as drastically as you might expect.


Hope this helps!
09-30-2014, 07:54 AM   #3
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It's easier for you to think of pixel density.

k-5/Nikon D7000 - APS-C sensor - 16MP
Nikon D800 - Full Frame sensor - 36MP

They have the same pixel density, given pixels per square mm/cm. So the larger sensor on the D800 can be cropped to the same dimensions of the k-5/Nikon D7000, and you'll get basically the same result. The advantage of the D800 is that the larger full frame sensor allows it to have the same ISO performance as the k-5/D7000 while giving it much more pixels to work with in a given subject image. And with the larger quantity of pixels, when scaled to the same sizes - it will have better performance overall compared to the k-5/D7000.

And the reason why it matters when the k-3 has more pixels is that the k-3's higher pixel density reduces its high ISO performance in comparison to the k-5 (not a lot, because of the different sensor technologies, but it is there). So the D800 will still outperform the k-3.

That is what a FF sensor affords over an APS-C sensor.
09-30-2014, 08:50 AM - 1 Like   #4
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QuoteOriginally posted by adwb Quote
If I take a image of a wine bottle standing on a table. with a k5IIs and a K3 both with the same 50mm lens and fill the frame with the bottle would I be the same distance away? answer is yes I think?
Yes.

QuoteOriginally posted by adwb Quote
if the answer is yes then once downloaded if I zoom in to the label and fill the computer screen will they both be equally sharp and well defined? or will one be more pixalated?
The k-3 will hold up better to this level of magnification due to it's higher pixel density resulting in the label being more pixels across compared to the k-5 image, though the difference probably won't be earth shattering. You can do a practical test comparing your k-5 with your k10d in this way.

QuoteOriginally posted by adwb Quote
Now if I take the same image with a FF and a 50mm lens and again ensure to fill the frame with the bottle and again then later zoom in to fill the screen with the label only will the ff image be of a better quality ?
All other things equal (sensors using the same/similar technology), then yes. Though again, probably not earth shattering.

QuoteOriginally posted by adwb Quote
See this what I don't understand , what is the benefit of using say a Sony A7 or a A7R or a Nikon 810 over a K3 ?

There are sensor size differences between them all and the simple answer I am looking for is,

if in the scenario given above every image was correctly exposed and absolutely in focus , which camera would give the best rendition of the cropped in label image if it was then printed to A3+?
The big advantage of FF over APS-C is the size of the captured image on the 'negative', it's just bigger. It's maybe easier to imagine you were using film of these sizes, so you actually have two negatives showing the same framing but of different sizes. The label on the FF negative is physically larger than the label on the APS-C negative. When you go to enlarge them to print at A3+, you're enlarging the APS-C negative more than the FF negative. Any flaws end up being more magnified, degrading image quality more.

Again, this difference is not enormous between APS-C and FF. Compare something really tiny like a P&S camera with a large format film camera and the differences in magnification to get to A3+ becomes massive and much more noticeable.

My experience with different sensor sizes is tiny digital P&S, APS-C both digital and (ugh) film, some film 35mm, along with some pinhole photography using 5x7" photo paper as the negative. The pinhole experience was very illuminating on how a large sensor can handle incredibly poor optics ('optics' is probably the wrong term as there's no glass, just literally a hole made with a pin). With this huge 'sensor', nothing needs to be magnified to get a 5x7" output, what's captured is already visible to the human eye. Not that it's mind bogglingly sharp or anything, but it's pretty amazing given the little hole you're using. Compare that with the magnification needed to go from the sensor of a P&S to even a 5x7" print, you needed to start with something much sharper per unit area of your sensor/film to stand up to this magnification.

In general, bigger is better assuming you can get the same framing (not always the case for the long-lens crowd). Things do get iffy when comparing sensors from different generations, i.e. the Canon 5d may have been a clear winner over APS-C sensors of it's day, but it won't hold up quite as well to modern day APS-C. Also things start to not matter so much when the sensor sizes get close or your print size is not taxing on even the smaller format you're considering, and it's best left as an exercise for the individual user to determine how much of a difference is important to them.

05-23-2015, 08:30 AM   #5
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See this what I don't understand , what is the benefit of using say a Sony A7 or a A7R or a Nikon 810 over a K3 ?

The benefits are not really in the image quality on screen but in printing, as explained by others. But most of all, depth of field and low light performance.

Anyway, the reality is that the difference is minimum, despite how hard they try out there to make such s big deal of difference.
If you really need professional quality, then even ff is ridiculous. You think that fashion pro photographers shoot with ff? Think again. They don't work for Armani or dior. Professional formats are from 6x6 and above. Stuff for billboards on the walls of new York.
I have been there, shooting with mamyia 6x7.

You can make good money even with cropped sensors but you won't ever work for those names for important campaigns. For all the rest, crop sensor is more then fine and top lenses are what really matters if you want to be published by good editors.
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