6 Essential Camera Skills | Infinity Focus | Sensor Sizes | Depth of Field & More 

Thanks very much.

Welcome to our content Mark. New show out this Sunday at 4pm UK time!

Glad it was helpful!

Hi. Thanks for your question. Where the confusion is happening is between “compressions” and “magnification”. The former is influenced only by altering your distance to subject. The latter is influenced by both distance to subject and focal length (or indeed, sensor size). If you only have a single subject (no foreground and no background - for example a wall) then you can’t change the compression of the scene because there is nothing to compress (it’s already flat). However, you can still make it larger or smaller by either changing focal length or distance to subject. If you have two (or more) subjects at different distances then by moving the camera closer or further from the closest subject (in fact all of them) will change the perspective (compression). If you simply stand in one place (distance to subject is fixed) then by changing the focal length all you will do is alter the magnification of all subjects equally. So for example, if I had stood 4m from my daughter and used a 50mm lens, but then changed to a 100mm lens without moving, both my daughter and the church will double in size (so the perspective stays exactly the same). However, if I now double my distance to my daughter to 8m and still use the 100mm lens, she becomes half the size (because I’ve doubled my distance to her but kept the same magnification), so she’s now the same size as when I was using a 50mm lens from only 4m. Because I haven’t doubled my distance to the church (let’s say my daughter is 100m from it - I have changed my distance from 104m to 108m, so hardly any change) this hasn’t been affected to the same degree as my daughter has, but the change in focal length has affected them equally. So by doubling the distance and the focal length to my daughter, she remains the same size, but because I haven’t doubled my distance to the church but have doubled the focal length. It effectively becomes twice the size. Does this help?

​@@PhotographyOnline Hi Marcus, thanks for the amazingly speedy reply. I did not expect that, especially at that time of night! Ahhh right, now I see the cause of my ignorance. It would appear that we agree on most that I said. The only difference I can see is how we use the terminology. Maybe I should start using the term compression instead of magnification when talking about a subject, ("relative" to some background in the distance), staying the same size in frame at any given focal length because I have to change my distance too the subject to allow for the FL. So it seems to me that FL and distance to subject are two sides of the same coin, so to speak. You can't have one without the other if you want to keep your subject the same size in frame. As you rightly say, if you double the distance to the subject you have to double the FL to keep the subject the same size which in turn makes the background twice the size in frame. It makes a lot more sense now. Thank you for taking the time out to reply. Just one more thing. When you was talking about dof and being able to get the same focus front to back by using a large aperture, Matt Granger showed the same thing about 9 years ago. It still falls on deaf ears, lol.

Thanks for watching!

Hi Rohann. Thanks for your comments but you are mistaken about your depth of field theory. Depth of field increases by a factor of 2 (ie - it doubles twice) if you double the distance to the subject. If you then double the focal length, depth of field reduces by a factor of 2. So the two changes cancel each other out. Also, what part about the FL vs distance isn’t “technically” true? Thanks for watching and we look forward to hearing your theory. All the best and happy new year.

@@PhotographyOnline Oh I wouldn't call it a theory at this point, that's a bit generous. Let's go with "loose hypothesis". I was mostly observing that the extreme crop of your 12mm shot seemed to be at "infinity" in terms of focal point, but with the 200mm comparative shot there was an obviously much-shorter DoF. Perhaps this only applies when one is comparing vs infinite focus? Or was it more because the focus was slightly past the subject in the 12mm shot (obviously nearly impossible to nail it from that far away at 12mm)? I have yet to experiment and compare, and am reluctant to argue against physics, just trying to wrap my head around it. And I meant it the opposite way around -- the idea that FL compresses the background is "practically" true but not technically true (as you folks elegantly demonstrated), in that using a longer focal length to get a similarly framed photo does result in background compression, but because of distance and not FL. There are also some wider shots that are practically impossible with longer FL's due to positioning. Fantastic segment though, I'm honestly not sure why I hadn't encountered this previously! Cheers, and thanks for continuing to output these fantastic episodes!

Hi Kenneth. Thanks for the comment. We use a Canon R6 and just shoot in standard 4K (not log). We still process the output but only to tweak it. We usually use the RF35mm f/1.8 for most things but also sometimes use a vintage Minolta Rokkor 58mm f/1.2 lens which is stunning. Although we record in 4K, we output in standard 1080p, so it’s good to know you are impressed with the quality, as it’s really nothing special. I hope this helps. Marcus

Hi. You just need to use the actual focal length as this is what determines where infinity starts. The size of the sensor simply crops the image - it doesn’t change anything else (such as depth of field or magnification - which many people think it does). Hope this helps

@@PhotographyOnline Thank you. I thought as much, but wanted to be sure.

No. For IR you would focus slightly closer, not further away.

You still capture 4 times the light on the full frame camera - thus the individual pixel may be of similar quality, in terms of the full image captured you will have less noise visible at whatever size you show your image.

@@karlgunterwunsch1950 You would have to show this mathematically. I suspect that with equivalent lenses, each sensor site would receive precisely the same number of photons under identical shooting conditions. I mean, if you took equivalent lenses, one 35mm format, and one four-thirds format, and glued them to a light meter at the same aperture settings, the light meter would not show four times the exposure from the 35mm format lens. The light would register at the same value.

@@yukonchris There is simple maths involved - on constant area size the amount of light photons captured will be equal (pixel peeping) but the area of the 35mm sensor is 4 times as large as the 4/3rds sensor - thus the absolute amount of photons will be 4 times as large. When you look at the individual pixels of the 4/3rds sensor you still will be looking at a group of 4 pixels from the FF sensor if you captured the same subject.

@@karlgunterwunsch1950 In a practical sense, however, if the sensors are roughly equal in terms of wiring efficiency, then it's the electrical resolution of each pixel site that, cumulatively, results in the quality of the image. As per the original poster, the pixel pitch will be the same in the case he has suggested so the resolution of each site will be identical. Each pixel will receive exactly the same amount of light, and have exactly the same ability to collect photons with exactly the same maximum capacity. So far so good. The only place where this differs, and where your extra light is going, is to additional pixels on the 35mm sensor which fall outside the four-thirds imaging area. So in absolute terms, there is indeed four times the light falling on the 35mm format sensor, but it is completely irrelevant to the imaging ability of each individual pixel. It only comes into play when you consider the enlargement of the image for display, and that is calculated geometrically by the outside dimensions of the finished piece. Will you see a difference? It would depend on how far you want to push the enlargement, and there would be diminishing returns because compared to an 11"x17" print, both sensor sizes are tiny. So, in most cases, the answer is no. If you are doing massive enlargements, perhaps, but then you might want to shoot 8"x10" negatives to start with. For, the sorts of prints you're going to frame and mount on the walls of a home, there is probably no discernable difference between those two small sensors. This comes from personal experience by the way. I maintain both a 35mm format system (30 MP Canon EOS R), and a m43rds system (16 MP E-M1) I occasionally print at 8x10, 11x14, 17x20. It's just about impossible to see quality differences. Finally, while in total terms, you are receiving more light on the 35mm sensor, the cost you will pay come in the form of larger glass elements to cover that area. Making larger elements is more difficult and more expensive. Unless you are willing to fork out a lot of cash, you may see a small drop in optical efficiency, and image quality overall. So, the argument becomes really academic. There are always tradeoffs. The question is whether they result in real world discernable and significant differences. As raw processing algorithms improve, I'd argue that even tiny sensors on phones, which are just a fraction of the area of either of the formats we've discussed, may be able to produce results that are indistinguishable from what we're doing with our current sensors. Ultimately, if you can make images you like, it doesn't matter.

Hi Thom. Yes you would get a very similar result in terms of noise (assuming all other aspects such as sensor type and processors are identical) but you would end up with more noise in the final print due to having to enlarge the MFT image to a greater degree. As I mentioned in the feature, the only real advantage to having a smaller sensor is to be able to reduce the bulk and weight (and therefore - price). For some people, this is a priority, but if image quality is your priority, then the larger the sensor, the better the output (assuming all aspects are equal). Hope this helps. (Marcus)

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We’re just happy that we’ve helped to prove beyond all doubt that the world is in fact flat. Thank god the truth is now out there!