Megapixels or Focal Length?
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Hey folks,
I heard this question this past week and thought it was worth addressing because it could be confusing.
The question nets out to this. If I am going to shoot a distant subject, such as a critter, am I better served with a higher megapixel sensor and a shorter focal length lens, or a lower megapixel sensor and a longer focal length lens.
When we shot film, there was no question, always go with the longer lens so each element of the desired image takes up more space on the emulsion, that we see as grain.
The person asking the question was curious if digital changes things. He was looking at a Canon R6, a fine camera rated at 21.4 megapixels and a Canon R5, another fine camera rated at 45 megapixels. He was wondering if he used a shorter focal length lens (wider angle of view) and then cropped in shooting with the R5 vs a longer focal length lens (narrower angle of view) with no crop, which would deliver a higher quality image.
As you can imagine, the answer is at a high level, it depends.
The R6 delivers 21.4 megapixels across a 36x24mm surface area measuring 5496x3670 pixels
The R5 delivers 45 megapixels across a 36x24mm surface area measuring 8216x5477 pixels
What Does This Tell Us
In order to have a higher megapixel count, the R5 uses smaller surface area pixels. While more pixels should mean more detail, it also means less efficiency and more power required overall.
It also tells us that in the same surface area, the R6 has 67% of the pixel count of the R5 taking into account the length and width of the sensor. Therefore if I shoot the R5 and crop in 30% or about ⅓, I end up with approximately the same pixel density but over a much smaller surface area. I am effectively throwing away about 50% of the RAW data that the sensor has captured.
Follow the math. This is a two dimensional construct. A crop of 30% of the vertical axis leaves 70%. A crop of 30% of the horizontal access leaves 70%. Since we are operating in two dimensions to get the effective data reduction we multiply the effective remainder in each axis by it’s counterpart. 0.7 x 0.7 is 0.49 or about 50% so even with a small crop you have given away a lot of the pixels that you paid for up front, and while the pixel count looks similar to the less megapixel camera, you are also working with smaller pixels so there is greater potential for loss.
Which leads us to the answer we thought was correct in the beginning. When considering lens focal length vs sensor megapixels, for the optimum image quality go for the longer focal length lens.
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I'm Ross Chevalier, thanks for reading, watching and listening and until next time, peace.
