Comparing pixel density of FF vs. crop-sensor bodies

[normadel]

I've been wondering about all this stuff for some time, finally just reading a very excellent article comparing Full-Frame to Crop-Sensor benefits & drawbacks. that explained why, with equal megapixel counts, the crop-sensor has MUCH higher pixel density and gives MUCH higher resolution.

So I did some basic math myself to illustrate how my EOS 60D (18 MP) and 6D (20 MP) compare. MP not the same, but close.

18 MP = area  of 330 square mm. = (rounded) 54,500 pixels /square mm.

20 MP = area of 864 square mm. = (rounded) 23,000 pixels /square mm.

Thus, the 6D has LESS THAN HALF the pixel density of the 60D, and a Full-Frame sensor would have to be 47 MP to have the same density and equal resolution as the 60D.

So I said to myself, WOW!  Does this make sense? 

This leads me to wonder WHY a full-frame sensor camera costs so much more than a crop-sensor camera, with all else being substantially the same, as with a 60D and a 6D.

[rs-eos]

One major driver of cost affects not only sensors, but chipsets as well.  The larger the package, the less parts (packages) will be available per silicon wafer.  Also, if there are any imperfections in the wafer, it's easier to salvage more packages the smaller those packages are.

For chipsets, manufacturer's can get creative.  e.g. for Apple Silicon chipsets, if just a single GPU core would have a fault, Apple will turn that core off and put that chip configuration into a less expensive model (they did this with some versions of the M1 chip where some come with 7 GPU cores and others come with 8).

But for a sensor, you need all photo sites to work, so you need higher yields per wafer with no faults.

Then there are the feature sets of Full Frame vs Crop Sensor bodies.  You typically have all the higher end feature sets only in the Full Frame models which also drive up cost.  e.g. better weather sealing, higher frames per second capture, dual card slots (and cards with higher speed than SD cards), etc.

[normadel]

I've seen the 60D and 6D referred to as essentially the same camera except for sensor size. Their controls are virtually identical. Yes, there are some differences in menu-setting abilities. Not too much overall. The distinguish feature of the 6D is it's Full-frame.

That wasn't the main subject of my post.

[Tronhard]

Not sure what article you are referring to (having published one here myself) but, as Ricky said, there are many more reasons why a FF camera costs more to produce than a crop-sensor camera.  Crop-sensor units are rare in the higher end of the camera market. Canon make only the 7D series in the DSLR line for prosumers for example. Furthermore, production volumes have a major impact.  Canon have produced literally millions of crop-sensor bodies but nowhere near as many FF bodies - in part because of the resultant cost of bodies and lenses (in particular) puts them outside the pockets of many casual and consumer users.  As Stalin said "quantity has a quality all its own".

A major influencer of sales is that a lot of people don't need the FoV benefits delivered by a FF camera at the wide angle end, but will enjoy those benefits at the telephoto end for general-purpose shooting of kids, sports events or whatever.  Throughout the range, as the price goes up, the features and robustness does too.  Again, a lot of consumers will not need the levels of build quality that a pro or prosumer will want - for them it's a tool to do a job and they will use it until it no longer works or fits their needs. So, they don't cycle through bodies as fast as consumers do.  I still shoot with the EOS 5DMkIII which is 10 years old and it does a great job. 

The optics are the big factor in cost, again as Ricky mentioned.  While the quality of the optics does not necessarily deteriorate in EF-S lenses - there are more cheaper kit lenses, but there are some truly excellent APS-C optics designed for crop bodies.  However, the most expensive units, and with premium optics and construction, are in the L series  and they are all for FF bodies. 

[normadel]

Trevor:

The article I speak of is titled "Focal Length, Field of View, Shutter Speed, Sensor Size & Equivalence" and was provided (a web link) by a contributor on this forum after creating it for students in his photography course. Sound like you? I saved it as a PDF file. It's wonderful. Taught me everything that has been puzzling me for years.

[Tronhard]

Yes that was the title of my article!  The file name on my computer was called Equivalence.PDF.  It should have my name on the bottom, although the first iteration did not - HERE  is the link to an updated version. I am glad and gratified that it was helpful. 🙂

[normadel]

So, what do you think of my math, logic and conclusion comparing 60D and 6D in pixel density and resolution? 

[Tronhard]

Well, as far as it goes, your logic is sound.  However, it's not all about pixel density.  Larger pixels should each collect more light, thus they should be less liable to suffer noise.  There is a perception that MP count is everything, but as always, it is a playoff between factors.   We have already established pixel density for crop sensors is usually greater than a remotely comparative FF sensor.  But now we come to noise and light gathering...

So, on a pixel level, when comparing two sensors of the same MP but different sizes, the pixels of the FF sensor will be bigger and gather more light on an individual basis.  But another perspective is on the overall light gathering / noise relationship of a sensor incorporating those larger pixels.  That should be greater for less pixel dense sensors on the basis that each sensor is more efficient.

So it's a balance between resolution, dynamic range and noise and, like the holy trinity of exposure (aperture, ss and ISO), where the emphasis falls produces different outcomes.  How those are used is very much up to the performance of the individual elements (including lenses), the environment within which one operates, and what one wants to produce

This is why, for example, a lot of cameras of significantly smaller sensors have relatively modest MP counts.  An example is the Olympus TG series of tough cameras.   These are designed to work underwater, down to a depth of 10m and use one of the smallest sensors around, so they are dealing with dark environments and small sensor areas.  At one point, Olympus actually reduced the pixel count of their sensor as an upgrade in order to improve the low light capability. 

For a while I used some of the PowerShot SX## Bridge Camera units - from the 40 to the 60 series.  They had tiny 1- 2/3 sensors of between 12MP and 20MP, combined with a super-zoom lens of 21 up to 1365mm.  They gave amazing results - in good light, but when that dropped they were subject to a lot of noise.  So, for a Bridge camera I went for a larger sensor - a 1" sensor with almost 5x the area for the same pixel count.  I chose the Sony Rx-10MkIV, which has a BSI/Stacked 20MP sensor of truly excellent performance, and is far, far less subject to noise.  It has a 24-600mm Equivalent zoom that can be boosted to go up to 1200mm Equivalent without significant deterioration by some computational photography.

Looking at the R-series bodies...  The R5 FF sensor at 45MP has about 1EV less dynamic range that the R6 FF sensor of 20MP - so I use both for their different strengths.

Then we come to other issues...  The more dense and larger the sensor, the bigger the file size.  While large, detailed sensors like the R5 will be great for cropping and landscape work, the files they generate are large and can be unwieldy.  So, for sports pro's who are shooting and sending images of games in real time to their publications, large unwieldy files transmitted to the web is not helpful.  That is why the sports-oriented R3 has the relatively modest 23MP sensor, but has brilliant tracking, great DR, and top-end connectivity to the web.

Finally, we come to the R7, mooted as the new replacement to what was the flagship 7DII, crop-sensor DSLR. The R7 has a 32MP sensor, about the same as the 90D (for which I think it is a true replacement).  Now that has a pixel density equivalent to an 83MP FF sensor, and results so far from in-field use indicate that it develops noticeable noise at about 3200 ISO - remembering that to overcome the lower overall sensor light-gathering capacity of the crop sensor, it will likely have to boost ISO to get a decent shutter speed for wildlife, or sports - which seems to be its intended main use.

[normadel]

Once upon a time it was simple. Frame size a constant, shutter speed-aperture and ISO were all you needed to know.  Higher ISO film = more grain.  It's all passed my ability to understand it all.

Guess I just have to keep taking pictures and enjoy what I get.

Thanks for sharing your knowledge.

[Tronhard]

In the end, photography is all about what we get out of it.  I have gone through a lot of stress lately: between losing my wife, having a couple of strokes, and then COVID came along: resulting in long periods of lockdown and isolation.  So for me, being able to go out and take even one photo is a tonic. 🙂
We each enjoy photography in a different way... some do street, others portrait, wildlife... the possibilities are endless, but I think photography offers several universal benefits:

1. It has technical and artistic aspects: using our left/ right brain. The former is understanding how to control the camera and the latter is the creative use of it to create images that we love to keep, share or sell.
2. It makes us actively aware: without doubt photographers learn to see more of their surroundings as a discipline in seeking and capturing images and that is a gift in itself.
3. It encourages us to be physically active: one can't take photos sitting on the couch all day, so it encourages us to get up, go out and seek those images, which is important for our physical and mental health.  I use a lot of heavy, large super telephoto lenses, and I do weights frequently to handle those in the field, and that pays dividends for my own physical and mental health.

We engage in those elements in different ways and with different balances, but in the end it's a wonderful occupation and to be enjoyed for itself.  I hope you will continue to enjoy it within your own context for a long time to come!