Full Frame vs Crop Frame DSLR Thoughts - My 5D II 17-40L Experience
Above is an example of the size difference between a full frame sensor and a typical 1.6 crop sensor. Full frame sensors are found in the more expensive DSLR's. The 1.6x crop sensors are found in the Canon digital rebel series as well as the 10D-60D series and also the 7D. A lens will project a view larger than the full frame view, obviously it has to. The crop sensor images a smaller area more in the middle of the lens compared to the full frame sensors. This can act as "more reach" or "less wide angle". If you stick a 14mm lens on a full frame you get a 14mm wide view. On the 1.6x crop you'd have to times that by 1.6x and end up with a 22mm view which isn't as wide. This is because you aren't imaging as wide of an area as the full frame is with x lens on. So crops can either suck in that sense or they can be "good" at the telephoto side, since a 400mm lens acts more like a 640mm on a crop sensor.
All this isn't the point of this topic, but it is worth considering anyway. The main point is going to deal with the fact lenses have weaknesses away from their centers. I knew this but didn't give it as much credit as I should have when I went from a crop sensor, Canon XSi, to a full frame Canon 5D II this year, 2010. I'm also doing this because some are asking why I sold my 5D II. This will explain why I did. Money 50% of the reason and having to spend MORE money to get a quality lens for it was the other 50%. It's a good thing the "need" aspect worked out just fine anyway, as I never needed a full frame. So all was well, minus whatever I lost in buying and selling lol...which was pretty darn bad, but oh well.
Also this isn't a crack on the 5D II or any other full frame camera. The 5D II was/is a great camera.
The first thing that jumped out at me when I got the 5D II and was using my Canon 17-40L(this is where the problem is.....the lenses....but the lenses on full frames)...was the horrible vignetting/darkening in the corners. Yes you can remove this stuff in the RAW converter but that's rather besides the point. If you are shooting higher dynamic range scenes to begin with, well your already darker shadows/foreground/etc will be that much darker thanks to vignetting. The more you have to open/fix things in a RAW conveter the more noise you'll see anyway. I tested the 17-40L at various degrees of stopping the lens down and found there was no improvement past F7.1. F7.1 really did make things a lot better compared to wide open at F4. So I started to just shoot at F7.1 and nothing less. This got old while chasing storms and kept requiring me to bump the ISO up(so much for the much greater noise levels by going full frame....if I need to ISO up because I'm stopping down to get rid of vignetting).
Here is a link to a vignetting comparison at the great site, the-digital-picture.com, showing how bad 17-40 vignettes on a full frame and the difference an even more expensive lens would make. CLICK HERE If you cursor over the image you can see the comparison between the 17-40L at F4 and the 16-35L II also at F4. Essentially a stop and a half darker than the 16-35L II at any given location. Upwards of 4 stops vignetting! Also on that image is a smaller square. That smaller square is the same crop view as I have above here. So you can see on a crop sensor even the bad 17-40L vignetting is not an issue at all. So there are two things to see there. 17-40L fine on a crop sensor. Get a full frame it's highly likely the 17-40L will bug the crap out of you then. The 17-40L is not a cheap lens. It is an L after all and is around $750. Unless you can stop down all the time, it's just not up to par for full frame. You'll find yourself wanting to dump even more money to get the 16-35L II so you can get rid of that nasty aspect. Again, unless you happen to be able to use it stopped down all the time. I wish I had kept some F4 storm shot examples.
But there's more to this, that stopping down doesn't help quite as much. Not only will vignetting be worse on full frame, but so will corner sharpness. Because again, full frame is seeing further out on lenses where more problems are going to occur. Go full frame, it is simple....plan on spending even more money on lenses to make the jump worthwhile. The 16-35L II is double the price of the 17-40L.
The above was taken with the canon 5D II and 17-40L stopped down at F9. I have the square on there again to show the area that would have been imaged on a crop sensor. In short the 17-40L looks great on the crop sensors when it comes to vignetting and sharpness, but sucks on full frame.
100% crop from near dead center. Unsharpened RAW looks plenty sharp.
Now this is a 100% crop from the upper left corner. It's flat out pathetic. This is a F9 stopped down shot too! Do this wide open at F4 on the full frame and well it sure isn't going to be better. It is useless bad is what it is. Unless you always have clouds or sky or something without detail in your corners. This was the stuff that had me dying to have my XSi and 10-22 EF-s back. Pretty annoying when you drop that much more money and wish you had what you sold to get it back. The sharp center of frame example shows it wasn't out of focus. The corners just suck.
100% crop dead center on the left side. Still not good. This is an L quality lens on a full frame.
One more, also F9 17-40L on a full frame 5D II.
100% unsharpened center.
100% unsharpened upper right corner. Again, this is F9 on a Canon L 17-40.
17-40L on my crop sensor rebels always looked great! Stick the same exact lens on a full frame and it just looks horrible. All because the full frame camera images further out on the lens. Between the extreme soft corners stopped down out of center and the extreme vignetting, I couldn't help but keep thinking the same thing over and over and over after making this jump to the full frame 5D II. I thought...."I can get better images from a rebel XSi and my 10-22 EF-s!" But oh yeah, I already sold them to go to the 5D II!!! I had two choices, either dump my 5D II and go back to the crop sensors.....or I dump even more money into photo gear and get a better ultrawide...a $1600 16-35L II. Or worse yet a $2200 14L. I wanted a resolution bump from the XSi was the only reason I upgraded to the 5D II, since a T1i 15mp wasn't much of a jump and the 18mp T2i wasn't announced yet. They announced that 1 week after I went with the 5D II for an upgrade.
The choice was simple for me. Sell the 5D II. Crop sensors are for me. Now happily have a T2i and replaced the 10-22 EF-s I sold with a new one. And again, there's zero cracking on the 5D II here. One just better have some disposable income to buy the lenses full frame demands. Otherwise those sad corners kinda kill any reason on having a full frame to begin with. Because again, trying to fix lesser lenses by stopping down more only makes you have to ISO up more anyway in many cases(handheld)....squashing the benefit of better noise levels on a full frame. And the noise aspect is pretty negligible.
I'm all about wide angle shots of storms and the weather. I just won't need any crazy dof control nor any beefed up focusing system like on the 7D, 1D, etc. The tool for the job for me is simply the rebel series. Always has been. Like right now I can think of one easy question. $800/T2i + $750/10-22 EF-s image......or $2600/5D II + $1600/16-35L. Honestly the image quality difference is going to be negligible. Most certainly not worth an increased $2500 pricetag. As I understand it even the 16-35L II isn't perfect on a full frame anyway. My 100-400L will also feel more telephoto with a crop too.
So anyway, there truly are some good benefits to staying crop sensor. If one doesn't have much expendable income, then they don't have much to worry about. If one does, eh it's probably worth thinking on anyway and what one needs for the job they do. One thing is clear, if you go full frame it's pointless to then not have lenses that are up to the task. Makes more sense to have lesser lenses and a crop sensor imaging their better inner areas....than full frame and a lense displaying soft and vignetting corners. If someone else paid for my gear with the restriction I had to use the setup, I'd still prefer a T2i + 10-22 EF-s than a 5D II with a 17-40L. By a long shot sadly enough. Now if one swapped the 17-40L for a 16-35L II on the 5D II....then yeah of course that would be another story.
Other lenses will for sure show the same weaknesses on a full frame. The cheap 50mm 1.8 prime, which is a good sharp lens, is a lot different on a full frame compared to crop. Wide open at F1.8 you have about 1 stop fall off in the corners on a crop sensor. You are around 3.5 stops fall off on a full frame when used wide open. Based off the vignetting examples on the-digital-picture.com. I remember seeing how bad it was when using it too.
And one more time, cause I know how gear fans are, the 5D II is a great camera. The 17-40L is a good lens too, at least when on crop sensors. Just some stuff for some to consider if they hadn't already. If they didn't come out with the 10-22 EF-s then I'd actually need a full frame camera to get as wide. Given the 10-22 EF-s exists and how good it is, I just have no full frame needs. Course it is F3.5 and a 16-35L or 14mm are both F2.8! LOL It would still be a good chunk of change for that small increase in lens speed. The only thing I think I'd actually need full frame for would be Milky Way shots. There the higher ISO ability and faster lens options could be truly useful. Otherwise what I shoot I don't have enough need.