JD07
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 Re: For Travel: Sony E 70-350 f4.5-6.3 -or- FE 100-400 f4.5-5.6 + 1.4TC? | |
chiron wrote:
JD07 wrote:
chiron wrote:
JD07 wrote:
If I am carrying a full-frame, I would never be quick to put a crop lens on it. Once you factor in the effective maximum aperture as well as focal length, often you can find comparable or better full-frame options.
For example, in the OP it is noted that the aps-c E 70-350 f4.5-6.3 will give an effective field of view of 105-525mm on a full-frame sensor (which, of course, is also the effective field of view if used on an APS-C camera). However, it is also worth noting the aperture will be the equivalent of f/6.75-9.45.
For comparison, I believe the Tamron 50-300mm f/4.5-6.3 is only about 40g heavier and 8mm longer than the E 70-350, and the Tamron would give you 50-300mm f/4.5-6.3 with your full-frame sensor, and the option to crop from there. And if you crop to APS-C size (either by shooting in APS-C crop or cropping in post-processing), you would have the equivalent of 75-450mm f/6.75-9.45. So, if you are willing to switch from full frame to APS-C crop, effectively you would end up with 50-450mm f/4.5-9.45 (versus the E 70-350 giving you effectively 105-525mm f/6.75-9.45). My choice would be the Tamron over the E 70-350. YMMV of course.
I am not sure that I understand clearly the issue of aperture on a crop camera and what people say about this. I am more concerned with the issue of light reaching the pixel sites than I am with dof.
My own understanding, which may be wrong, is that the total light over the entire sensor is greater for a full-frame lens, with its larger image circle, because the total area of the sensor receiving light from the lens is the entire area of the sensor; and that the total light over the whole sensor from an aps-c lens is less because the lens, with its smaller image circle, is illuminating only part of the sensor. And that the difference is proportional to the crop.
However, in my understanding, the amount of light reaching each pixel site within the respective image circle of each lens is exactly the same, resulting in each lens needing the same exposure settings for a correct exposure.
Is that not correct?
If you are using the same lens and aperture setting, you are correct that the light intensity (light per unit area) is the same whether you are using a full-frame sensor or APS-C sensor. And if the sensors use the same technology, things like noise at the pixel level will be the same. However, you are also correct in saying that the larger sensor gathers more light in total. And it is the total light which is relevant to things like noise at the image level.
If you want to get into the details, I highly recommend this website:
http://www.josephjamesphotography.com/equivalence/
Perhaps the simplest way to think about it though is this. I am sure you will have experienced looking at an image on a small screen (eg the back of your camera or a phone) and thinking it looked nice and sharp, but then seeing the image on a larger screen and seeing it is not sharp at all. Obviously, it was only when the image was enlarged that your eyes detected the lack of sharpness. In the case of an APS-C image versus a full-frame image, the APS-C image as taken is smaller, so it has to be enlarged more than the full-frame image to reach the same output size (your computer screen, a print of a particular size, or whatever). The extra enlargement required magnifies things like noise in the image, making it more apparent at the image level.
So far as depth of field goes (which I realise you said is not a priority for you), if you use the same focal length and aperture, shooting with an APS-C sensor (including a full-frame sensor operating in APS-C crop mode) means you have to be further away from your subject compared with using the same focal length on a full-frame sensor to get a similar image. So, the lens/aperture doesn't change physically, but the distance to subject is greater. And depth of field increases (so you get less blurring of the out of focus area) as distance to subject increases, so the APS-C image has greater depth of field.
To be clear, I am not trying to suggest that APS-C images are no good and no one should ever be happy with them. That is absolutely not the case. My point is just that if I am carrying a full-frame camera, I am not going to be quick to put an APS-C lens on it.
Thank you for a very clear and graceful explanation, and for the link. All that you say makes perfect sense to me. But I don't understand why people would say you are losing aperture when you use a crop camera or crop in camera. That seems inaccurate to me. It seems more accurate to say that one is losing sensor size, or losing image size, or gaining potential noise, acquiring a magnification loss, or creating increased relative dof. But the aperture is not changing; the size of the image on the sensor is changing, which actually has nothing at all to do with the aperture.
I agree! As you say, the aperture does not actually change. I guess you could say something like "you are losing the effect of aperture." Even that is not correct though, as it depends on which particular effect you are talking about. Perhaps saying something like "you are losing the effect of aperture as relevant in the context of equivalence between shots taken with cameras with different sensor sizes" would be getting closer, although it would be quite a mouthful! I like your idea of losing image size. That would be simple and clear, I think.
Anyway, I can only put "you are losing aperture" down to one of those situations in which photographers do not say what they really mean, such as when someone says their aperture for a shot was (say) 2.8 or f/2.8 (which, of course, means the relative aperture or f-stop was set to f/2.8; the actual aperture being the focal length of the lens divided by 2.8), or says they should have used a faster shutter speed (meaning they should have used a shorter shutter open time; generally speaking the speed at which the shutter opens or closes will not change, and the difference is in the length of time the shutter is open and the sensor is exposed - which, presumably, is why Canon cameras use Tv (time value) as the abbreviation for shutter priority mode).
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