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 p.2 #6 · Best versatile portrait lens for APS-C: Canon RF 24mm f/1.8 or RF 35mm f/1.8 | |
johnctharp wrote:
I'm glad you found it helpful - there is a lot of information out there from people at various stages of the process of learning 'photography' from the technical perspective - and of course the art perspective will never be fully 'learned'!
The thing with 'bokeh' is that it's the quality of the out of focus areas, not the 'amount'. But further, that is complicated by things like aperture diameter and subject distance - that's what determines how deep or shallow your plane of focus is, which determines how much of your subject can be in focus.
But more on aperture diameter - that's not the f/number, but the number that it comes from. So if you have a 50mm f/2 lens, then the aperture diameter is 50mm/2, or 25mm. Between that number and how far your subject is away, you can compare depth of field between lenses and sensor sizes and whatever else in general.
So the thing with 'crop' lenses is that the world largely communicates about photography in 35mm full-frame, also known as 135-format, with a 36mm x 24mm sensor. 'Crop' then means something smaller than that, so we apply a 'crop factor', which for Canon APS-C is 1.6x. Other APS-C is 1.5x (there's some history there), Micro Four-Thirds (MFT) is 2x, and so on. For sensors that are larger than 'full frame', we'd apply something like a 0.8x crop factor.
Crop factor lets you figure out, primarily, field of view. Because a 50mm lens is always a 50mm lens optically speaking, how big the sensor behind it is tells you how wide that lens is. So on MFT, it's a telephoto lens. On a medium-format camera, it's a mild wide-angle lens. On a large format camera (when you start measuring the film in inches!), it's a wide-angle lens.
But you really only need to know two things to understand most of the discourse on photography: what a lens is in full-frame terms, and what the crop factor is for whatever format you're shooting.
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Things get trickier when it comes to aperture and noise.
Noise is somewhat easier to explain, in that ISO is signal amplification - anything other than the base ISO (say 100 usually for Canon) is then being amplified, along with whatever noise was captured. Same as turning up the radio, if the signal is weak, you get more signal and more noise!
The main thing to know here is that, like having a smaller antenna, having a smaller sensor means that the amount of signal you can capture is limited, which means that there are situations where you will be beyond getting a shot due to too much noise versus what a camera with a larger sensor would. This is dynamic range.
But, and it's a big but, you don't actually need all of the dynamic range available in modern cameras. No doubt you've seen or taken great pictures with a phone camera - if there's good lighting, even that tiny sensor can pull off professional-looking photography! Full-frame helps here by being larger than APS-C, but only so much.
The bigger difference is that full-frame sensors and APS-C sensors are not built to the same level of technology. This is a business decision on the part of sensor makers (and camera makers in the case of Sony and Canon). So typically the best full-frame sensors will be better than the best APS-C sensors by more than the crop factor would suggest, and older full-frame sensors hold up really well!
Still, as above, any modern APS-C sensor will give you more than you need as long as you have enough good light.
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For aperture, the reason I mentioned aperture diameter above and set it opposite to subject distance, is that due to the smaller sensor in APS-C and thus narrower field of view at similar focal lengths (again, crop factor), for the same focal length to get the same framing on APS-C, you have to take a step back. This is why you see APS-C lenses on the wider side, where a 24-70 would be a standard zoom for full-frame, we get the ~18-55 lenses on crop.
The challenge is as in the part you quoted me of above, that the fastest lenses for APS-C aren't any faster than full-frame lenses in terms of f/stops, so even if you have a 35/1.2 or a 50/1.0 or whatever for APS-C, those aren't going to wind up providing shallower depth of field than their full-frame equivalents (at best, they'll match). You'll also find that there are simply no equivalents for the level of detail you can get on full-frame when using APS-C; the best lenses for APS-C are still going to be the professional full-frame lenses barring exceptions that can be counted on one hand. Good crop lenses are that rare!
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But on the other other hand, you'll notice I also mentioned that this might not all matter - because, if you want to go shoot tight portraits with say a 50/1.2 lens, you can... but you're going to have to be okay with getting one iris of the subject in focus, and everything else out of focus including the eyelashes in front of that one iris. The other eye will be out of focus too unless the subject was facing the camera perfectly. And the nose or the ears? Just blur.
So fast lenses can be useful, however, shooting fast lenses wide open all the time isn't likely to get the images you actually want. And that's why having a smaller sensor and / or slower lenses is totally fine!...Show more →
This is very useful well thought out advice, but let me isolate one sentence:
"the best lenses for APS-C are still going to be the professional full-frame lenses barring exceptions that can be counted on one hand. Good crop lenses are that rare!"
I agree that the best lenses are going to be professional FF lenses, but the OP would probably benefit from knowing there is a pretty full set of sharp and generally well corrected f/1.4 APS-C lenses for Canon RF mount made by Sigma. These lenses include 12mm, 16mm, 23mm, 30mm, and 56mm lenses. They also make 2 RF mount f/2.8 zooms (10-18mm and 18-50mm) and even a 17-40mm f/1.8 zoom. Tamron makes a quite nice 11-20mm f/2.8 zoom as well. All of these lenses are quite competent and good options that extend the capabilities of APS-C sensors for the RF mount. It is more than you can count on just one hand and for many shooters it is more than enough. They all come a pretty reasonable prices as well. So, if you are ok with f/2ish prime lenses on FF and f/4ish zoom lenses on FF you can get similar capabilities on APS-C with good reasonably priced lenses for wide angle to short telephoto focal lengths. Beyond that you would need to use FF lenses for Canon RF mount, but other mounts have good APS-C telephoto primes and zooms so there is reason to hope that Canon will have such lenses in time as well.
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