Okay, so to test (and hopefully validate) the conclusions I came up with a while back while I was a Canon guy, I decided to re-run the same test with the D700 to see if I was correct or not. This setup is not ideal, but I think it shows the point fairly well. Both of these shots are from the D700, one shot with a 50mm f/1.4 at f/1.4 with the camera in DX and the other with a 24-70/2.8 at f/2.8 to (roughly) equalize the DoF in the shot. Both are taken from the same place with the same lighting. Focusing was achieved using live view, dialing in across multiple shots and choosing the ones that seem best in focus, and closest in focus to each other. The 50mm shot is at a bit of a disadvantage because I couldn't set it to f/1.6, which would be a closer match DoF-wise to f/2.8 (it's an older MF 50mm that only has full-stops). Both images are using identical settings in Lightroom and have been resized to the same output size, with the same amount of light USM added in photoshop. The resolution differences between the FX and DX shots are obvious, but they shouldn't come into much play here - it's not a demonstration of detail per se, more a demonstration of the (obvious) optical differences between shooting at f/1.4 and f/2.8.
It's not a demonstration of DoF. It's a demonstration of the differences in optical quality between a lens shooting at f/1.4 and a lens shooting "stopped down". Unfortunately I didn't have a 75mm prime sitting around, but the differences in optical quality are still pretty obvious here.
It's regarding what you have to do to get a certain "look" on a DX camera. On the FX camera with the same focal length equivalent, you can shoot stopped down and get X amount of DoF, on DX you'd have to shoot with a wider aperture. So, while on the DX camera you would use a 50mm f/1.4 to get X amount of DoF, on the FX camera you'd use a 70mm lens stopped down to f/2.5 (roughly) to get X amount of DoF. Assuming that non-existent 70mm was also an f/1.4, you'd be closer to the lens' "sweet spot" in terms of optical quality.
According the to depth of field calculator: http://www.dofmaster.com/dofjs.html
At roughly 4 ft the DOF for DX @50mm is about 1.3 inches, while with FX @ 70mm f2.8 you get about 1.9 inches. I assume you where about 4 ft away from the guitar? So DOF is about the same.
That aside, as you state, this is not about DOF but the "look" of the photo. Photo A looks like it has more contrast to me so probably that is the FX f2.8 shot at 70mm?
With all due respect I don't get it, what are you attempting to prove with overexposed and out of focus images of that unusal guitar. "A" is a better image by the way, if I can even use that term.
Taylor Barrett wrote:
Agreed. Overexposed, washed out colors... Even I miss the point of this one.
"A" looks a little crisper.
"Even I miss the point of this one"? Thinking highly of yourself.
I think his point is showing the relative merits of shooting with FX - in some situations - and the trade off one gets with a wider aperture in DX versus the a smaller one with FX, while maintaining the same FOV and DOF. Of course "even I" could be wrong.
galenapass wrote:
I think his point is showing the relative merits of shooting with FX - in some situations - and the trade off one gets with a wider aperture in DX versus the a smaller one with FX, while maintaining the same FOV and DOF.
Yeah, that's all. Of course you'd see the opposite problem on the far side of the aperture spectrum. In another thread I had made what I thought was a fairly "no duh" statement that shooting at f/2.5 is closer to the lens' "optimal" aperture in terms of image quality - sharpness, contrast, vignetting, birefringence, etc. - than f/1.4 is. Once you get into the mid-range of apertures the differences are probably pretty negligble. But if you're shooting at the extremes of your primes capabilities for DoF reasons, you could benefit from going to FX.
This isn't to say FX is better than DX, it isn't. It's just an example of one difference between the two in a practical sense.
R. Francois wrote:
No vote just show me the results...
where is this going
I'm trying to figure out where it's starting at! I guess it's better to shoot stopped down with a DX sensor. Or is that an FX sensor? OY! I think I will just go back to film--it was all so much easier then.
PS I agree the guitar is hideous. It's even uglier than that snakeskin Nikon making the rounds a few years ago.
Sam Bennett wrote:
Yeah, that's all. Of course you'd see the opposite problem on the far side of the aperture spectrum. In another thread I had made what I thought was a fairly "no duh" statement that shooting at f/2.5 is closer to the lens' "optimal" aperture in terms of image quality - sharpness, contrast, vignetting, birefringence, etc. - than f/1.4 is. Once you get into the mid-range of apertures the differences are probably pretty negligble. But if you're shooting at the extremes of your primes capabilities for DoF reasons, you could benefit from going to FX.
This isn't to say FX is better than DX, it isn't. It's just an example of one difference between the two in a practical sense....Show more →
I appreciate the post. It might be obvious to many, but often one is attempting to get a particular FOV or DOF/FOV for the right look. Its nice to visually see the contrast implications for those who might want to shoot in available light. Particularly for those who have both formats and have a choice to make about which type of equipment to use.
Since DX mode on a D700 is actually cropped (not using the full 12MP), comparing it to an FX 12MP image isn't really a good comparison of FX vs DX. A better one would be a D300 image compared to a D700. Both would be 12MP, but then you have to take into account differences in the cameras.
crewshin wrote:
I don't get the point of this test. You are missing important variables.
Try and find someone in your area with a D300 and use the same lens on both cameras for pete's sake.
By using the same lens one would not be able to keep the FOV the same without changing distance as a variable. As for using a D300, I don't think that would alter the results of small web sized images which clearly show the expected contrast difference. We are not talking about resolution differences here but contrast differences due to smaller aperture.
In the example above FOV and DOF are virtually the same. There has been a lot of discussion here on FM about how the DOF on a FX camera looks more pleasing or at least more interesting. What Sam is pointing out is that it possible to get the same DOF and FOV with the appropriate lens selection and the appropriate f-stop on either format. When you do this FX still enjoys a contrast advantage. The one criticism is that it is difficult to use the same lens for this test (could use a zoom, or could change the distance to subject) and the lenses differ in contrast. But I still think the comparison above gives some insight, although it may not be relevant to many shooting styles...YMMV
There is indeed a lot of variables, which is why I stated this test is not ideal, but I think galenapass summed things up pretty well. I'm intentionally not showing full-resolution images or even crops of the images since that would put the DX version obviously at a very serious disadvantage - but this is not a resolution test. At some point I'll do this again with a D300 - I'd like to get one eventually.
An interesting example to do would be to use the 24-70/2.8 at 47mm and f/2.8 on the DX and 70mm f/5 on the FX - I think in that case the difference would be much less pronounced. All lenses that can open past f/2 or so have fundamental issues like birefringence that you just can't "design out", so that area will always be problematic. If you're already using high-quality zooms on your DX and FX gear, I wouldn't worry about this much. The FX will likely be a bit sharper, but not dramatically so.
