More megapixels vs sensor size

[Soocom1]

Go to Flickr or such and do a search on something familiar like the pyramids or Eiffle tower. Then shake the results down by camera type including film. Then observe how much detail can be resolved in each image based on camera type and format size.

Yes, an image taken at the same distance of something with an iPhone 13 will have super image presentation. But then blow that image up say 5 to 20 times and watch.

Compare it to a similar MF or FF image and youll see.

There is also a factor of image compression that takes place but thats another discussion.

 

[Soocom1]

In fact I might just do that. Set up a shoot with equal light. Equiv focal distance/ lens and format size.

 

[greybeard]

Simply put,

The larger the sensor, the less you must enlarge it to any viewing size.
A 2x crop sensor image must be enlarged twice as much as a full frame sensor image just to view it.
Enlarging 2x more reduces the visual resolution to half.
But in the general case, either likely are still acceptable, except the extreme cases.

The effective focal length being 2x is simply a result of the greater viewing enlargement required. Using any image, simply zooming in 2x more in the photo editor produces exactly the same cropped enlargement effect. It might be more detail seen, but that is NOT more detail created, the 2x enlargement has the loss of resolution (pixels are spaced 2x further apart,, half the dpi). A sample of this editor zooming is shown at Crop Factor and Equivalent Lens Focal Length Explained

The more megapixels, the more detail can be resolved in the lens image.
The more of that is more that survives the viewing enlargement.

The longer the actual real focal length, the more it is enlarged by analog enlargement instead of digital resampling.

The maximum resolution is more sensor size, and more pixels, and a longer lens.

I can offer of what I think is an example at Have our cameras hit a megapixel resolution limit?
with full frame, 36 megapixels, and a mild telephoto lens.

You are thinking analog film and not digital. The more pixels a sensor has determines how big its' images can be enlarged and not necessarily the sensor size. However, a 24mp FF sensor will have better low light performance than a 24mp apc sensor because of the larger pixels light gathering abilities. I have worked quite a bit with a 24mp D750 and a 20+mp apc Z50. D750 is FF and the Z50 is a crop. The images from the 2 cameras are almost identical from ISO 100 to around 1600. From there on up however, the Z50 gets noisier by about 1 stop meaning the D750 is about as noisy at ISO 3400 as the Z50 is at 1600. The larger sensor has a lower noise floor than the crop sensor. Every generation of cameras gets better and better high ISO performance.

 

[WayneF]

You are thinking analog film and not digital. The more pixels a sensor has determines how big its' images can be enlarged and not necessarily the sensor size.

Oh my. I very strongly disagree, in the extreme degree. You must not do any printing?

Both sensor size and pixels are all important to the degree of digital enlargement. That is kinda the point of crop factor.

If it is a D850, 35.9x23.9 mm and 8256 x 5504 pixels, and we print it to be 10 inches long dimension, that prints as 8256 pixels / 10 inches = 827 dp on paper (which is of course seriously and pointlessly overdone, and we ought to be ashamed about our procedure (a copy does need to be resampled smaller), but that is the math. 10x25.4 / 35.9 is about 7x enlargement of sensor size.

But print it 30 inches which is 8256 / 30 = 275 dpi on paper. 30x25.4 / 35.9 is about 21x enlargement. We will like that one.

Or print it 50 inches which is 8256 / 50 = 165 dpi on paper. 50x25.4 / 35.9 is about 35x enlargement. It will need to be viewed from a distance.

Or print it 100 inches which is 8256 / 100 = 83 dpi on paper. 100x25.4 / 35.9 is about 71x enlargement. It will need to be viewed from even more distance.

And you actually think that if handheld to view, all of these will be the same pristine quality and indistinguishable? Possibly if viewed on your monitor screen (if pixels are enough, but video normally resamples smaller to fit the screeen), but you really ought to look into printing sometime.

I imagine you are saying, "but if we had enough pixels". I am saying that is of course Not an option from any one sensor we might own.

Digitizing a lens image on a sensor, or if scanning film, or if printing enlarged on paper, these result in a resulting image dpi resolution depending on image enlargement size of the final destination sensor. But resolution is about pixels per inch, and yes, enlarged printing is the same issue with film.


EDIT: I am realizing now that an example with about our largest DSLR sensor (47 megapixels) was not the most clearly dramatic example. I should have used like a tiny 1/2.6" cell phone sensor, 5.5 x 4.1 mm sensor, 6.3x crop factor, which requires a lot of enlargement to view it at any size. Then to print even 10 inches is 10x25.4 / 5.5 = 46x enlargement, and 1/46 of the original sensor dpi resolution.

 

[greybeard]

Oh my. I very strongly disagree, in the extreme degree. You must not do any printing?

Both sensor size and pixels are all important to the degree of digital enlargement. That is kinda the point of crop factor.

If it is a D850, 35.9x23.9 mm and 8256 x 5504 pixels, and we print it to be 10 inches long dimension, that prints as 8256 pixels / 10 inches = 827 dp on paper (which is of course seriously and pointlessly overdone, and we ought to be ashamed about our procedure (a copy does need to be resampled smaller), but that is the math. 10x25.4 / 35.9 is about 7x enlargement of sensor size.

But print it 30 inches which is 8256 / 30 = 275 dpi on paper. 30x25.4 / 35.9 is about 21x enlargement. We will like that one.

Or print it 50 inches which is 8256 / 50 = 165 dpi on paper. 50x25.4 / 35.9 is about 35x enlargement. It will need to be viewed from a distance.

Or print it 100 inches which is 8256 / 100 = 83 dpi on paper. 100x25.4 / 35.9 is about 71x enlargement. It will need to be viewed from even more distance.

And you actually think that if handheld to view, all of these will be the same pristine quality and indistinguishable? Possibly if viewed on your monitor screen (if pixels are enough, but video normally resamples smaller to fit the screeen), but you really ought to look into printing sometime.

I imagine you are saying, "but if we had enough pixels". I am saying that is of course Not an option from any one sensor we might own.

Digitizing a lens image on a sensor, or if scanning film, or if printing enlarged on paper, these result in a resulting image dpi resolution depending on image enlargement size of the final destination sensor. But resolution is about pixels per inch, and yes, enlarged printing is the same issue with film.


EDIT: I am realizing now that an example with about our largest DSLR sensor (47 megapixels) was not the most clearly dramatic example. I should have used like a tiny 1/2.6" cell phone sensor, 5.5 x 4.1 mm sensor, 6.3x crop factor, which requires a lot of enlargement to view it at any size. Then to print even 10 inches is 10x25.4 / 5.5 = 46x enlargement, and 1/46 of the original sensor dpi resolution.

I print all the time, usually 16x20. Your original statement read that larger sensor sizes need less enlargement than smaller sensors to achieve the same size print. This is entirely true with film as I have worked with everything from 4x5 to 110. However, a 24mp full frame and a 24mp crop sensor at iso 100 will enlarge pretty much the same assuming they are both using a high quality lens. The differences usually shows up when the ISO gets above 800. That is when noise start creeping into the crop sensor image. (jmho) By the way, people are making some giant prints from iPhones these days and their sensors are really tiny.

 

[WayneF]

However, a 24mp full frame and a 24mp crop sensor at iso 100 will enlarge pretty much the same assuming they are both using a high quality lens.

I of course still strongly disagree simply because the basic math and theory disagrees. You aren't aware of that? I think you are only speaking of casual monitor viewing.

You are just saying that you think a 1.5x crop factor is not largely different than a 1x crop factor. That's somewhat true enough, they are fairly close, but still, there is a difference, certainly in any more extreme cases. Crop factor says one is only 2/3 size and requires 1.5x greater enlargement to be the same size. Greater enlargement reduces printing resolution.

Assuming the same pixel dimensions, when you are printing the larger one at 300 dpi, the smaller one only has 200 dpi to give there, and that is an absolute difference. Perhaps not a generally a huge difference yet, as printing at 200 dpi is generally often nearly OK, but it certainly is a definite difference if you have high detail to show. One is not the equal of the other. One is only 2/3 size.

 

[greybeard]

I of course still strongly disagree simply because the basic math and theory disagrees. You aren't aware of that? I think you are only speaking of casual monitor viewing.

You are just saying that you think a 1.5x crop factor is not largely different than a 1x crop factor. That's somewhat true enough, they are fairly close, but still, there is a difference, certainly in any more extreme cases. Crop factor says one is only 2/3 size and requires 1.5x greater enlargement to be the same size. Greater enlargement reduces printing resolution.

Assuming the same pixel dimensions, when you are printing the larger one at 300 dpi, the smaller one only has 200 dpi to give there, and that is an absolute difference. Perhaps not a generally a huge difference yet, as printing at 200 dpi is generally often nearly OK, but it certainly is a definite difference if you have high detail to show. One is not the equal of the other. One is only 2/3 size.

Then, why is a 24mp crop frame file and a 24mp FF file the same size?

 

[WayneF]

Then, why is a 24mp crop frame file and a 24mp FF file the same size?

What do you mean by "same size"?

If you mean sensor size in mm, then of course, they are Not the same size. A 1.5x crop factor is 2/3 the size of a full frame 1x sensor, which image on it must be enlarged 1.5x more to view at the same size. That is the same as film, because both are the enlargement of the image detail, becoming spaced over more inches, i.e., less resolution. All the pixels do is to simply try to reproduce the original image detail.

If you mean like the same 6000x4000 pixels size, then that's just how the two sizes constructed their pixels (smaller sensor with smaller pixels), but the smaller sensor is still only 2/3 the size of the larger. Any image detail still has to be enlarged 1.5x greater to view at the same size.

Instead of concentrating on a mildly different 1.5x crop (which still seems easy enough to me), try thinking of a 2x or 6x crop factor. Then very clear difference, no mystery.

 

[RacePhoto]

Then, why is a 24mp crop frame file and a 24mp FF file the same size?

Because the image they produce is the same size.

I don't want to get into the whole, which is better, because an older full frame that's X# MP vs a newer crop camera that's also X# MP the newer will be better. So just saying crop vs full, doesn't work.

And just for the bottom line on the debate. There is no free zoom. You have a cropped image, and the focal length is identical because the distance to the sensor is identical or the lenses wouldn't work. Some might argue the crop is better with a full frame lens, but...

Pixel Pitch of the one camera vs the other. How many and how large are they. That's the answer.

Just like film. A 2 1/4 square with the identical film will produce a better image, than a 35mm. Grain is grain. Pixels Are pixels, if they are all equal. Pixel Pitch is the roughly the digital version of grain fineness.

 

[WayneF]

Because the image they produce is the same size.

Same size in pixels as you say, but (assuming crop means 1.5x which sensor is 2/3 dimensions), the image that you view has to be enlarged half again more to view the same size. That reduces viewing resolution to 2/3. Not the same result. Casual viewing of smaller enlarged images may not notice the difference, but critical viewing will know. The larger you enlarge both (to be same viewing size again), the more noticeable it is.

You have a cropped image, and the focal length is identical because the distance to the sensor is identical or the lenses wouldn't work. Some might argue the crop is better with a full frame lens, but...

Not true, so there is a big but. A sensor 2/3 the size must use a focal length 2/3 shorter (for a wider view) if it is going the produce the same full frame image frame (for identical appearing images). Because, the meaning of "crop" is the image field is cropped smaller, less field of view is included, so is Not the same image as full frame. But if you have the shorter lens for the crop sensor (to see all of the wider field), then that is no problem getting the same appearing image.

Just like film. A 2 1/4 square with the identical film will produce a better image, than a 35mm.

Yes, enlargement wise, it is the same idea as film. Pixels are better than grain to be able to reproduce the image, however either way, enlarging an image more (to view a smaller image at the same size as the larger image) costs a proportional reduction in resolution. (pixels spaced further apart is obviously less pixels per inch of resolution).

 

[Soocom1]

If you seriously want to see the results, go take an iPhone12,13,14,200 or whatever, an APS C, M43, Full Frame or MF, EVEN a 4x5 LF and shoot EXACTLY the same object from EXACTLY the same distance, one after another.
then review the images at phone screen size, Mac screen size, and wide screen TV sized screen and look altho hem yourself.


Stop trying to rationalize and just put it all to practice.

Then make your choice.

 

[RacePhoto]

Same size in pixels as you say, but (assuming crop means 1.5x which sensor is 2/3 dimensions), the image that you view has to be enlarged half again more to view the same size. That reduces viewing resolution to 2/3. Not the same result. Casual viewing of smaller enlarged images may not notice the difference, but critical viewing will know. The larger you enlarge both (to be same viewing size again), the more noticeable it is.



Not true, so there is a big but. A sensor 2/3 the size must use a focal length 2/3 shorter (for a wider view) if it is going the produce the same full frame image frame (for identical appearing images). Because, the meaning of "crop" is the image field is cropped smaller, less field of view is included, so is Not the same image as full frame. But if you have the shorter lens for the crop sensor (to see all of the wider field), then that is no problem getting the same appearing image.



Yes, enlargement wise, it is the same idea as film. Pixels are better than grain to be able to reproduce the image, however either way, enlarging an image more (to view a smaller image at the same size as the larger image) costs a proportional reduction in resolution. (pixels spaced further apart is obviously less pixels per inch of resolution).

Maybe I didn't state that right, but if the lenses are to work on two different cameras, the distance to the focal plane must be identical. The image is identical with the same lens, the only part that changes is the sensor size. Thus "crop sensor" and since the projection is identical, the image is identical.

What's different is the image on a crop sensor is much larger than the sensor, so only part is recorded. The identical image on a full frame sensor, is identical, but the sensor is larger, so it sees all of the image.

I'm not trying to produce the same view, I'm saying why the lens creates the identical image, in both cameras. Only the crop sensor doesn't record the entire image, because the sensor is smaller. Also that gives a different field of view and the impression that there's some kind of zoom. It's not free telephoto, it's just cropped.

Except for the fact that sensors vary in quality and pixel pitch, if an identical (see hypothetical) full frame sensor in one camera as an identical spec. crop sensor in another camera, take the identical image, with the identical lens, the only difference is that = One Is Cropped.

Of course in reality crop sensors are not identical in quality or specifications. I could throw a wrench in all of this and compare a newer crop sensor to an older full frame sensor, and now the cropped FF image wouldn't be as good as the crop camera image?

Two main points. You only get an image as good at the sensor, no matter if it's crop of full. There is no free zoom, just because you have a different size sensor.

Let be throw another wrench into this. If the crop sensor is only using the center 2/3rds of the projection, any edge flaws, distortion, or color aberrations that are near the edges, will be less noticeable, because it's the center part of the image.

This is all about optics and has nothing to do with print size or image size. Just what the sensor sees from the lens. It's identical.

 

[WayneF]

This is all about optics and has nothing to do with print size or image size. Just what the sensor sees from the lens. It's identical.

Not correct when you realize the whole concept. Yes, if assuming use of the same lens or same focal length on a cropped sensor and on a full size sensor, then the lens does of course project the same image, but the crop sensor crops it smaller (which is also a smaller field of view reproduced). It is simply a smaller image (in terms of magnifying the image detail). But we have not viewed the image yet.

And what use is any image if we do not view it? And to view it, we must enlarge it to viewing size. Since the cropped image is smaller, it must be enlarged more to be the same viewing size, and more enlargement reduces the resolution in that image. If printing both at same size, then like instead of printing at maybe 300 dpi, same size is only 200 dpi (assuming 1.5x crop). If that enlargement is carried too far, it becomes a pretty sorry image. Size is very important. Dpi is about inches.

But one sentence I was very pleased to see is:

>>There is no free zoom, just because you have a different size sensor.

That is absolutely correct, yet it is confused by so many. Yes, cropping (any cropping) does add an apparent illusion of a zoom effect, simply because we must enlarge the smaller image more to be the same viewing size again. It is a smaller image, and the only effect is simply the greater enlargement. You can reproduce this exact same zoom effect by simply zooming any existing image in your photo editor (which is a cropping to a smaller image).

But again, more enlargement costs resolution. Even if the cropped sensor might provide the same pixel dimension (they don't today) , the image (meaning the captured lens detail) still must be enlarged more to be the same viewing size.

 

[Don Fischer]

I guess this is what's wrong with digital. You have to have a master's degree in something to figure out what your camera will actually do. I have a D7000 and the way I figure out how big I can print a photo is to print one and see what happens, all that math to figure it out lose's me. I'm getting a roll of paper to try 10x30 and maybe even a 13x38. Then I'll know what I can do and the only math needed is to subtract the cost of paper from my check book. I'm terrible at math! Why does it seem everything about digital needs to be turned into a science project?

 

[WayneF]

I guess this is what's wrong with digital. You have to have a master's degree in something to figure out what your camera will actually do. I have a D7000 and the way I figure out how big I can print a photo is to print one and see what happens, all that math to figure it out lose's me. I'm getting a roll of paper to try 10x30 and maybe even a 13x38. Then I'll know what I can do and the only math needed is to subtract the cost of paper from my check book. I'm terrible at math! Why does it seem everything about digital needs to be turned into a science project?

There are some numbers, but planning is a really big help. It's really just simple arithmetic, as easy as the check book. I think the D7000 images are 4928x3262 pixels, and the dpi number spaces those pixels over the inches. Dpi is just that many pixels per inch. For a round number example,
3000 pixels spaced 300 per inch will cover 10 inches.
3000 pixels covering 10 inches are spaced 300 pixels per inch.

Specifically, to print 8x10 inches at 300 dpi needs
(8x300) x (10x300) = 2400x3000 pixels, so your camera has pixels to spare (for cropping, etc).

Learning that simple relationship should be a big help with printing all of your life. It's worth paying a little attention. Same as a carpenter measuring before sawing. If ordering the 8x10 from the one hour printing place, then be sure to plan to send them enough pixels.

Many of the better photo editors provide a tool for cropping to an aspect ratio (image length / its width, in either pixels or inches or mm). A 6x4 print aspect is 6/4, simplified to 3:2 (also seen as 1.5:1). This Aspect Ratio is a shape (and is as important as size), and it is wise to be sure the image to be printed is the same shape as the paper size to be used.

The DSLR images are aspect ratio 3:2, and compacts and phones are 4:3. A 6x4 print is 3x2, but a 8x10 print is 4:5 (a different shape). So all image edges may not fit on the print paper, so to prevent surprises (like heads cut off, etc), it's very wise to crop to fit first.

This is not highly technical digital stuff, it's simply about the shape of the image and of the paper.

IMO, the best procedure is to first crop to the viewing aspect ratio (final choice of cropping selected by eye for the most pleasant viewing, like omitting some of the wasted blank surrounding space, etc.). And then resample smaller (only smaller) to the reasonable pixel dimensions to print it as desired.
Be sure to keep the original image file too, because you may have different plans next time.

If I understand your paper numbers correctly, then
to print 30 inches is 4928 / 30 = 164 dpi, and
and to print 38 inches is 4928 / 38 = 130 dpi.

Which is not 300 dpi (and 250 to 300 dpi is best for hand-held viewing), but a 3 foot print will be on the wall, viewed out at least at a few feet, and it should work fine for that. It is just if viewed at only one foot or so that you may see the difference. Two feet or more should be OK.