Sharper images on 30D vs 7D

[PhotoPaul]

Hey all. I've recently been using my 30D on the beach as I'm too paranoid about sand in the 7D. Interestingly enough I'm finding I have been getting sharper images from the 30D than the 7D.

I want to start a process of elimination to see what it might be and was after some pointers. This is the way I was thinking of going:

Use the same subject (input on what to shoot for the tests would be greatly appreciated) and same lens at same settings on both bodies, take photos through the f/stop range. Repeat for all lenses. Compare results.

Would that be the best way to go?

The reason I'm asking is I was told by Dennis Cale a while back that 18mp+ on a crop sensor may cause a type of distortion at the edge of the pixels which results in loss of sharpness. This was when he was discussing my 30D saying that 8mp on a crop sensor will probably be sharper.

I'm just wondering if there's any truth to that or if it's just that I haven't got my head around the new camera just yet.

Cheers all. I appreciate any and all input.

-Paul

[MarkChap]

It could be something as simple as micro adjusting the focus on the 7D/Lens combo, may need to be done for all lenses.

All bodies and lenses are made within a certain tolerance level, so if your 7D marginally back focuses for instance as does your lens, then all your images will be slightly out,
However your 30D might front focus marginally, so with the same lens, that back focuses just a tad, then your images will be spot on.

Search "focus Micro Adjust" on google and you will have a plethora of tutorials to choose from

[PhotoPaul]

Thanks Mark. I will check that out.

[William W]

I assume that you mean shooting raw and then converting and sharpening.
I suspect that you will need a different sharpening routine for the 7D than what you use for the 30D: this might mean some trial and error.
If you are picking nits, then I also suspect that the 7D will require more careful exposure and will be more sensitive processing and also to the RAW conversion software which you use, so maybe try a few and see which suits your particular taste.

If, on the other hand, you are discussing JPEG SOOC: the Canon Picture Styles hold NO equivalence between models.

WW

[ameerat42]

Well, try a couple of in-respective-camera jpegs, too.
Am.

[arthurking83]

......

The reason I'm asking is I was told by Dennis Cale a while back that 18mp+ on a crop sensor may cause a type of distortion at the edge of the pixels which results in loss of sharpness. This was when he was discussing my 30D saying that 8mp on a crop sensor will probably be sharper.

.....

There's not really anything that a sensor will actively do to create image aberrations in this way.

The sensor is just a receiving unit for the lenses transmission(of light).

What can happen tho, is that a sensor has such high acquity(or the ability to resolve detail) .. that if your lens distorts the image, for example at the periphery of the frame, that instead of seeing a lower resolution of something that looks like what you expect to see .. you see a higher resolution of the finer detail which is distorted in some way ..... usually, but not limited too blurring.

So if you take an exposure of a specific scene, keeping this scene exactly the same for two shots, one with the 7D and the other with the 30D, using the same lens and the same variables such as aperture, lighting quality, etc ... and then downsample both images to the same output(eg. 1024, or 1600 pixels wide) .. do you still see that the 30D still looks sharper?

Also note that because of the higher pixel density, the 7D will also be affected more so by diffraction, at a wider aperture value compared to the 30D.

So for example if the 30D was diffraction limited with your preferred lens at say an aperture value of f/8, and the 7D is diffraction limited with this same lens at f/5.6 .. then if you shoot at f/11 or f/16, you may notice a slight blurring of the 7D image at the pixel level when compared to the image by the 30D which is less affected by diffraction.
Mind you this is hard to see at the best of times, and the detail has to be extremely fine to be obvious to the eye.

Other possibilities can be simple camera shake!
Funny as it sounds, it's as true as many folks make it out to be. Your handholding technique needs to be so much more rigorous using a camera with a higher pixel density.
Optical stabilisation can help, but is not the definitive cure for this situation .. it just helps.
Found this out the hard way myself .. D300(12Mp) to D800(36Mp) D800 is a bit harder to shoot with in marginal conditions and then pixel peep the resulting images.

[PhotoPaul]

Thank you authurking, that was very informative. Just the kind of explanation I was seeking. It's possible that is what Denis was implying and I misunderstood.

William W, I always shoot RAW and thanks for the tip.

Am, I'll try that out too.

Thanks all for the advice, I've plenty to go on now.

[swifty]

How are you viewing your images to judge sharpness?
If you're looking at both at 100% on screen and the 30D appears sharper, it could be as simple as the fact that with both images viewed at eg. 100%, you're at a higher magnification on the 7D.
Resize both to the same viewing size on screen or in print, is the 30D image still sharper?

[Dug]

Another factor could be the the 7D is putting any deficiency in your lens under greater scrutiny than the 30D.

To take this out of the equation as much as possible, use your best lens for your comparison, probably a prime if you have one.

Check at DxOMark to see if your lenses are here in the Canon test section : http://www.dxomark.com/index.php/Len...Database/Canon

They also give a "Best at" aperture and focal length, so use that also in your comparison.

[Arg]

Are they sharper when viewed fit-to-screen, or viewed 1:1?

1:1 is not apples to apples, because the 7D pixels are smaller.

Fit-to-screen is more appropriate, although you still have to account for the way your PC and monitor handle the different pixel counts. They could be causing it.