Thanks Daniel. That's all news to me. [:P][H]
If crop bodies have that kind of effect on aperture, why on earth would anyone buy a crop body? And moreover, why would anyone spend extra cash for fast lenses if their bodies counteract the light gathering ability? Is everyone oblivious or am I missing something?
*phews* this is complicated [:P]
brendan
Because of pixel density (resolution). If you take a 5D Mark II and crop it so that the FoV is similar to the 7D you will have a similar amount of noise but much less resolution. Larger format sensors are only fully uitilized when you don't crop.Originally Posted by bburns223
Mark nailed it. It's because of cost and pixel size. You can get most of the features of the 5D2 in the 500D, but for a quarter of the cost. The smaller pixel size is an advantage in lens-limited situations, because longer, slower lenses are sometimes more expensive. For example, 800mm f/5.6 on the 5D2 gives you about the same capability as 500mm f/4 on the 7D, but the latter is much cheaper. Similarly, even if Canon did make a 480mm f/6.3 IS, they would probably sell it for a much higher price than your 300mm f/4 -- so you would be better served by sticking with APS-C.
I think most photographers are indeed oblivous to the ways in which f-number scales with format size.
Well, there are a lot of considerations that go into the purchase of a lens and/or body. If light gathering ability was the main factor, then it would indeed be better to buy full frame instead of a bunch of f/1.4 L primes on APS-C. But for many cases, the choice is more nuanced.
Only rarely does the focal length and features of a lens match up very closely between APS-C and FF. One example of a close match is the 135mm f/2 on FF compared to the 85mm f/1.2 on APS-C. In that situation, the cheaper 135mm is superior. But other lenses don't have similar equivalents. For example, if you want to get the 50mm f/1.2 on APS-C for its smooth bokeh, you could get the 85mm f/1.8 on FF, but the bokeh will not be quite as smooth: it does not have the characteristic undercorrected spherical aberration of the 50mm f/1.2.
They cost less
There are other reasons, too, that stem from the limited choices of cameras Canon offers. If you want a high frame rate, you can't have full frame. If you want a better autofocus than the 5D has and want to spend less than 6K, you can't have full frame. If you want the highest possible pixel density, a crop body makes sense.
Personally, I wouldn't buy an expensive, fast lens (85mm f/1.2, 200mm f/2) for a crop body. But one might if one was limited by other constraints to a crop body, and needed the fastest lens possible on that body.
Possibly. But the expensive, ficticoius 480mm f/6.3 would no doubt have far superior image quality to the real, less expensive 300mm f/4 after cropping.
I bet you're right.
There was a thread a while back that talked about how DOF changes with a crop body, along with focal length, and I understood that, but you're now saying that it affects shutter speeds and total exposures also? I use a crop XS and a 50/1.8. Common exposure settings in my house (in the winter) are 1/80, f2.0, ISO 400, and 1/80, f2.8, ISO 800. Those are equal exposures obviously. Now since 1/80 is perfect for stopping camera shake and my son's motion, that is usually what I aim for in an exposure. Are you saying that if I put my 50/1.8 on a 5D body, and kept the ISO at 400 or 800 andthe shutter speed at 1/80, the aperature would change?
I haven't figured out how to quote two people in one post, but brendan didn't you ask why anyone would buy a crop body? Full frame starts at $2500! Outta my league... for the meantime...
Lewis
No, that's not what I meant. I was responding to this question from bburns223: "would I have to use a slower shutter speed on a crop body to attain the same results as on a FF body?". Normally, when APS-C and FF have the same exposure, FF will have 1.3 stops more total light (and less noise). But bburns223 was asking if it's possible to give the APS-C more exposure (such as by slowing down the shutter speed) to get the same noise level as FF. The post you quoted was in response to that -- explaining that it is possible, and showing exactly what exposure duration would be needed to do so. Of course, comparing different exposure durations does not usually make sense in the real world. After all, APS-C and FF will have the exact same amount of camera shake when used at the same angle of view.
I don't mean to get too far off topic, but I would like to point out that those are actually different exposures. The brightness is the same, though. Exposure is the total amount of light falling on the sensor. It is a product of light intensity and duration. Brightness is affected by gain from the ISO setting, which makes the weaker exposure similar in brightness to the strong exposure. I hope that wasn't too much of an aside. If you'd like to talk about it further, I'd be happy to start a thread on it.
No, that's not what I meant. If you asked me "if I use longer exposure durations on my XS, could I get the same low-noise level of a full frame camera that uses shorter durations?", then I would say yes, just as for bburns223. But as you know, that means your XS shots would have more motion blur from camera shake and subject motion (assuming the same angle of view).
Thanks Daniel, that clears a lot up. I thought I read all of the posts leading up to mine pretty thoroughly, but I guess I missed that you guys were talking about noise.
No, that's ok. I know what you mean, I was just being general. Thanks again for the explanations.
I have narrowed it to sticking with my xsi getting a 5d mk.I or a 40d
I shoot real estate for my job so I'm leaning tword the full frame but I would still like to hear what you all think the pros and cons are of getting ether one
Price is not relevant for the pros and cons thought. Thanks
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