Crop sensor - extra reach?

[Martyn D]

Cheers Richard and Phil for explaining

 

[HoppyUK]

Richard can you explain this for me please? I don't understand the less enlargement bit, are you talking output here?

When comparing full frame vs crop format - and in this case shooting the same subject from the same position framed the same - with a D700 (FF 12mp) and a 300mm lens, against a D300 (crop 12mp) and 200mm lens, the change in sharpness happens immediately at the imaging stage on the sensor, when the picture is taken. In other words, it's the lens.

Both cameras have the same number of pixels, but the D300's sensor has less than half the area of FF. It's pixels are half the size so the resolution demands on the lens are twice as high.

Therefore, the image recorded by the smaller sensor has the same resolution, but less contrast and lower perceived sharpness.

 

[Major Eazy]

Thanks for the replies all.

I thought I understood this, but am now a bit confused.

Was hoping someone could help with a practical example. Say I want to take a telephoto picture of a bird a distance away. I have one 200mm lens that works on both my D300 and D700, both of which have same pixel count

By using it on the D300 I get extra reach so the bird fills the frame and no cropping is needed. By using the D700 I have to crop PS to get the bird to fill the frame.

Put these 2 pictures side by side and is one better than the other or are they the same?

The D300 use a crop sensor, namely the DX-format, which gives a 1.5x crop factor.

The D700 use a full frame, namely the FX-format, which do not any crop factor.

So...

A 200mm lens on a D300 means 200 x 1.5 = 300 therefore in effect the crop factor acts like turning a 200mm lens into a 300mm lens, that is why the subject looked closer.

A 200mm lens on a D700 will still be the same as a 200mm on a film camera. Because full frame sensors were made to be about the same size as a full 35mm frame. Result in you having to crop unwanted background to get closer to the subject.

But if you put a 300mm lens on the D700, you would get roughly the same closer view as the 200mm on the D300, so you wouldn't need editiing to crop in closer on the photo taken by the 300mm on the D700 same as you don't need editing to crop in closer on the photo taken by the 200mm on the D300 because the D300's 1.5x crop factor turned the 200mm into a 300mm.

Think of the crop sensors as if they were acting like a 1.5x teleconverter.

 

[Major Eazy]

Thanks for the replies all.


Put these 2 pictures side by side and is one better than the other or are they the same?

Although of course, one photo may be little better than the other, but what different do it make to a human? Not everybody have the same good eyesight. Of course you can display both photos side by side and let an expert look at them and he/she willl tell you "This one is better than the other." but pick someone at random, and let that Joe Q Public look at the photos, he/she will say: "Oh, that's a good wildlife photo!". They would not notice the tiny difference as long as you frame the photo good either using the extra reach on a crop sensor camera or using a computer to crop in after using a full frame camera.

 

[sk66]

for a given pixel density all that changes is the bit of the image that is recorded. Every thing else is the same.

Paul, this is untrue and it's unhelpful to claim otherwise.

Take say a Nikon D300 and D700, same pixel count and same generation technology, but different formats,

If we pretend that the pixel count is the same, and the lenses are of equal quality, the ff image will be better because its being enlarged less for the final output size.

At the very basics, I agree with Paul....if pixel density (not count) is the same the image is the same other than FOV.

And if the pixel count is the same (not density) they will print exactly the same size for a given ppi/dpi.

My D800 behaves VERY MUCh like the D7000 did (does) in all aspects (iso noise etc etc) and my D4 behaves much more like the D3s. Fewer pixels of larger size are better in low light. More pixels on subject are better in good light *assuming the lens is delivering adequate detail.*

And this is important to understand...a longer lens actually increases the magnification of detail delivered to the sensor.... a crop sensor only "enlarges" the detail after it's been captured. A 200mm lens on DX is NOT the same as a 300mm lens of FX.

 

[HoppyUK]

At the very basics, I agree with Paul....if pixel density (not count) is the same the image is the same other than FOV.

And if the pixel count is the same (not density) they will print exactly the same size for a given ppi/dpi.

My D800 behaves VERY MUCh like the D7000 did (does) in all aspects (iso noise etc etc) and my D4 behaves much more like the D3s. Fewer pixels of larger size are better in low light. More pixels on subject are better in good light *assuming the lens is delivering adequate detail.*

And this is important to understand...a longer lens actually increases the magnification of detail delivered to the sensor.... a crop sensor only "enlarges" the detail after it's been captured. A 200mm lens on DX is NOT the same as a 300mm lens of FX.

Of the four posts quoted above, including your own, only one is wholly correct.

When comparing formats, sharpness has very little to do with pixels, and everything to do with lens MTF performance.

Noise is another question, but that is most closely related to sensor area (photon collection) and sensor/processing engine than anything else.

 

[SoDoSoPa]

Theres always a blazing debate every time this question is asked, All things aside your right with your original post, Its only the FoV that changes so theres no need to go into the technical details of how cameras and lenses work differently.

 

[HoppyUK]

Theres always a blazing debate every time this question is asked, All things aside your right with your original post, Its only the FoV that changes so theres no need to go into the technical details of how cameras and lenses work differently.

Hardly surprising given the amount of misinformation on this topic, of which this thread is a prime example. Comments like 'only the field of view changes' are miles off the mark.

 

[PaulButler]

When comparing full frame vs crop format - and in this case shooting the same subject from the same position framed the same - with a D700 (FF 12mp) and a 300mm lens, against a D300 (crop 12mp) and 200mm lens, the change in sharpness happens immediately at the imaging stage on the sensor, when the picture is taken. In other words, it's the lens.

Both cameras have the same number of pixels, but the D300's sensor has less than half the area of FF. It's pixels are half the size so the resolution demands on the lens are twice as high.

Therefore, the image recorded by the smaller sensor has the same resolution, but less contrast and lower perceived sharpness.

Thanks for the additional explanation (most of which I already know) - what was throwing me was the phrase "image requires less enlargement to make the same print/output size," I was having a mini thick attack (happens often sadly). Having thought about it I believe you were referring to enlargement in respect of the sensor size specifically.

 

[SoDoSoPa]

Hardly surprising given the amount of misinformation on this topic, of which this thread is a prime example. Comments like 'only the field of view changes' are miles off the mark.

I think i know what i'm talking about matey.

A 200mm lens gives through a full frame camera give more field of view than a 1.5 cropped sensor where it is mistaken for people thinking that suddenly thier lens becomes a 300mm. It is still 200mm but there is less field of view.

BTW i didnt join this discusion for an argument like how you have implied i dont know anything about this topic, It is unfriendly and i though against TP rules!!!

 

[HoppyUK]

I think i know what i'm talking about matey.

A 200mm lens gives through a full frame camera give more field of view than a 1.5 cropped sensor where it is mistaken for people thinking that suddenly thier lens becomes a 300mm. It is still 200mm but there is less field of view.

BTW i didnt join this discusion for an argument like how you have implied i dont know anything about this topic, It is unfriendly and i though against TP rules!!!

I don't want an argument either, and I absolutely didn't say that cropping an image (by whatever means) changes focal length. But to say that "only the field of view changes" with different sensor formats is a serious error of omission.

Sharpness also changes, and that's central to the OP, depth of field changes too amongst other things.

The only point I'm trying to get over is this: as resolution goes up, image contrast goes down and the image is less sharp. Crop format DSLRs demand much more resolution from the lens than full frame, and that's why FF sharpness is better. These are facts, not up for debate TBH.

Explanation of lens MTF and how sharpness is measured here http://www.luminous-landscape.com/tutorials/understanding-series/understanding-mtf.shtml

 

[HoppyUK]

Thanks for the additional explanation (most of which I already know) - what was throwing me was the phrase "image requires less enlargement to make the same print/output size," I was having a mini thick attack (happens often sadly). Having thought about it I believe you were referring to enlargement in respect of the sensor size specifically.

Maybe my meaning was a bit ambiguous, sorry for any confusion.

A digital image doesn't have any physical size to be 'enlarged' at output, it only has pixel dimensions*. The sharpness difference between formats happens before that, at the (analogue) moment of capture when the image hits the sensor. That's when lens MFT performance impacts sharpness.

*Edit: eg 6000x4000 pixels would just be a 24mp image, regardless of sensor format.

 

[sk66]

I don't want an argument either, and I absolutely didn't say that cropping an image (by whatever means) changes focal length. But to say that "only the field of view changes" with different sensor formats is a serious error of omission.

I think there is a "compilation" of factors being mixed in with "crop factor."

Sharpness also changes, and that's central to the OP, depth of field changes too amongst other things.

Assuming the same pixel density/size (i.e. D800 and D7000) sharpness doesn't change due to sensor size. The diffraction limit remains the same as well.
And the DOF difference is due to using a wider lens for the same FOV...it's not really a sensor characteristic. You *could* take a picture of the same scene, with the same lens, from the same distance, and the DOF would be the same....but you would have to crop the DX image for the same composition. (this is disregarding COC based upon print size/viewing distance)

as resolution goes up, image contrast goes down and the image is less sharp. Crop format DSLRs demand much more resolution from the lens than full frame, and that's why FF sharpness is better. These are facts, not up for debate TBH.

I have never seen any explanation that higher resolution reduces contrast. It *can* if the lens is not up to the task. But again, this is due to pixel density/size and not sensor size in of itself. The D800 and D7000 require the same level of IQ from a lens.

I think the "problem" is that at one time it was safe to assume a larger sensor was going to have lower pixel density/ larger sensor sites, but that's not necessarily the case anymore.

Having owned and used both the D800 and the D7000 I would say the raw images are virtually interchangeable between them in every aspect. If the D800 has any advantage it's in the "processing" after the sensor, and I don''t really see it. The only significant difference is the FOV captured (if using the same lens/settings from the same distance).

There is (can be) a huge difference between the D800 and the D4. In some situations, with the right lens, the D800 will do better and deliver a sharper image with more detail. In many other situations the D4 will do better and deliver better images. Again, this is due to pixel size/density and not the sensor size.

 

[HoppyUK]

I think there is a "compilation" of factors being mixed in with "crop factor."


Assuming the same pixel density/size (i.e. D800 and D7000) sharpness doesn't change due to sensor size. The diffraction limit remains the same as well.
And the DOF difference is due to using a wider lens for the same FOV...it's not really a sensor characteristic. You *could* take a picture of the same scene, with the same lens, from the same distance, and the DOF would be the same....but you would have to crop the DX image for the same composition. (this is disregarding COC based upon print size/viewing distance)


I have never seen any explanation that higher resolution reduces contrast. It *can* if the lens is not up to the task. But again, this is due to pixel density/size and not sensor size in of itself. The D800 and D7000 require the same level of IQ from a lens.

I think the "problem" is that at one time it was safe to assume a larger sensor was going to have lower pixel density/ larger sensor sites, but that's not necessarily the case anymore.

Having owned and used both the D800 and the D7000 I would say the raw images are virtually interchangeable between them in every aspect. If the D800 has any advantage it's in the "processing" after the sensor, and I don''t really see it. The only significant difference is the FOV captured (if using the same lens/settings from the same distance).

There is (can be) a huge difference between the D800 and the D4. In some situations, with the right lens, the D800 will do better and deliver a sharper image with more detail. In many other situations the D4 will do better and deliver better images. Again, this is due to pixel size/density and not the sensor size.

"I have never seen any explanation that higher resolution reduces contrast." I just explained it in this thread.

TBH, lens MTF charcteristics are rarely discussed and get drowned out with the general hype around pixels. However, there is plenty of debate if you look around.

Just look at any set of MTF graphs, from Canon or Nikon, or Leica has some particularly good ones showing MTF at several levels of resolution. They all clearly show contrast dropping as resolution increases. There's some good reading on MTF from Zeiss here, if you want the full technical explanation http://www.zeiss.com/C12567A8003B8B6F/EmbedTitelIntern/CLN_30_MTF_en/$File/CLN_MTF_Kurven_EN.pdf

A rather easier read is the link to Luminous Landscape I gave earlier, this one http://www.luminous-landscape.com/tutorials/understanding-series/understanding-mtf.shtml Here's a quote from the introduction: "...the word sharpness is vague and can mean different things at different times to different people. MTF on the other hand is the terminology that lens designers use, and which you need to come to terms with if you really want to understand how to describe the complex interaction between resolution and contrast.
"For the optical designer contrast and resolution are in conflict. Increase one and you reduce the other..."

 

[Nod]

Thanks for the replies all.

I thought I understood this, but am now a bit confused.

Was hoping someone could help with a practical example. Say I want to take a telephoto picture of a bird a distance away. I have one 200mm lens that works on both my D300 and D700, both of which have same pixel count

By using it on the D300 I get extra reach so the bird fills the frame and no cropping is needed. By using the D700 I have to crop PS to get the bird to fill the frame.

Put these 2 pictures side by side and is one better than the other or are they the same?

Chop 'em both in against a D800!

For me, the biggest draw of FF is the wide angles it allows me. I use my 12-24 Sigma all the way wide a fair bit and also use an 8mm fisheye (also a Sigma). On crop bodies, the FoV is severely restricted, being the same as an 18-36 on FF and having the top and bottom croipped off the circular image the fisheye gives me.

I've upgraded from a D700 to an 800 for the extra MP which will allow me to crop into FF images and still (if I want to) print up to A3 - the D700's "mere" 5MP Dx crop images simply don't allow that.

While MTF graphs and other statistics can be useful, there tend to be sample variations between individual examples so if the lens tested was a particularly good one (and, if a manufacturer knows a sample is going to be tested, they would very likely pick a good 'un), the one an end user gets could well be less good - hopefully it wouldn't be too poor but possible less stellar than the one sampled. (Equally, a randomly obtained lens bought off the shelf could be a poor example and a buyer could get a better performer - that's the chance we take as end users!)