Soft pictures when shooting distant subjects

I completely agree - as long as he's using a fast enough shutter speed to freeze any possible camera shake, DoF should be sharp at that distance.

The first thing that comes into my mind though unless I've missed it, is what sort of focusing points are you using - center, or an averaged "spread"?

ImRaptor wrote in post #7177914
Forget DoF right now.
He's talking 55mm F4.0 at 300m. Depth at this point is not really a concern. Large sensor, small sensor, doesn't matter so lets just step away from the side tracking.

DDCSD wrote in post #7177948
I think you've got this backwards. A 30D will have more "apparent" DoF than a 5D will, so a larger sensor gives you less "apparent" than you will get with a smaller sensor. Therefore, technically a D40 with a larger 1.5 crop sensor will give you slightly less DoF than a 30D with a 1.6 crop sensor. Although no human will really notice this difference.

No, he hasn't.

A 30D does have more apparent DoF than a 5D, in that you are correct, but only because you need to use a longer lens to take the shot with a 5D. It's the longer lens that changes the DoF.

Why would sensor size, in itself, change recorded DoF? If you project the exact same image onto two sensors (by using the same length lens, from the same position), you aren't going to find it coming out differently simply because one sensor only records part of it, as the part it records would be identical to that recorded by the same area in the middle of the larger sensor.

In this instance the OP shot both images at the same focal length, the larger sensor will simply record a bit more of the scene around the edges.

Oh, and one more thought to the OP. Do you have a filter on your lens? That could be causing the softness, if you do.

DDCSD wrote in post #7177948
I think you've got this backwards. A 30D will have more "apparent" DoF than a 5D will, so a larger sensor gives you less "apparent" than you will get with a smaller sensor. Therefore, technically a D40 with a larger 1.5 crop sensor will give you slightly less DoF than a 30D with a 1.6 crop sensor. Although no human will really notice this difference.

...

Every DoF is apparent; I am talking about numbers from DoF Calculator.
The rest of your post is already explained here:

sandpiper wrote in post #7177887
Actually, you aren't understanding this correctly. A larger sensor only has less DoF because (to get an identically framed image) you need to use a longer lens. It is the difference in focal length that changes the DoF, not the size of the sensor.

In fact, a larger sensor has greater DoF (when FL is unchanged) as the image needs to be enlarged less.

...

bacchanal wrote in post #7178036
Are you comparing the 18-55 to the 55-200 VR?? If so, the VR might have something to do with the difference.

OP stated, in his first post, that he is using the 55-250 IS. So, both lenses have stabilisation.

I did the tests with both systems (IS and VR) on and off. I don't have any filters on my lens. The same thing happens with my old lens (18-55) also.

The shutter speed was fast enough (it was about 1/2000 because I wanted to make sure this is not an issue).

The sharpness increased to normal when I stopped down the lens. This could be considered normal but indoors, shooting close subjects, the lens is razor sharp even wide open.

not_this_punk wrote in post #7178082
I did the tests with both systems (IS and VR) on and off. I don't have any filters on my lens. The same thing happens with my old lens (18-55) also.

The shutter speed was fast enough (it was about 1/2000 because I wanted to make sure this is not an issue).

The sharpness increased to normal when I stopped down the lens. This could be considered normal but indoors, shooting close subjects, the lens is razor sharp even wide open.

Hmm, this is an interesting detail!
It is not unheard of that the lens focuses properly at the wide end, and miss focuses at the long end.

Include both types of pictures when you shoot tomorrow!
Shoot with both cameras something close, and something far..

Yes it is pretty interesting. My lens seems to be better at the tele end. But as I see it, this happens because the apparent distance to the subject is smaller and maybe it is in the limits of the focus distances.

So where are pictures...?!?!!?

OK here are some pictures. Never mind the subjects, the pictures are purely for demonstrative purposes. All pictures were shot RAW and processed with ACR 4.4 with exactly the same settings.
This is the main image from where the crops are taken:

HTTP response: NOT FOUND | MIME changed to 'image/png'

HTTP response: NOT FOUND | MIME changed to 'image/png'

HTTP response: NOT FOUND | MIME changed to 'image/png'

HTTP response: NOT FOUND | MIME changed to 'image/png'

did you have stabilization on or off on those?

not_this_punk wrote in post #7182324
OK here are some pictures. Never mind the subjects, the pictures are purely for demonstrative purposes. All pictures were shot RAW and processed with ACR 4.4 with exactly the same settings.
This is the main image from where the crops are taken:

HTTP response: NOT FOUND | MIME changed to 'image/png'

30D+55-250 IS, 55mm at f4, 100%crop

HTTP response: NOT FOUND | MIME changed to 'image/png'

D40+55-200 VR, 55mm at f4, 100% crop

HTTP response: NOT FOUND | MIME changed to 'image/png'

Just to prove that my lens actually is sharp, here is a 100% crop from a random indoor shot:

HTTP response: NOT FOUND | MIME changed to 'image/png'

I admit that not every indoor shot is as sharp as this one, but 7/10 are, compared to 0/10 when dealing with distant subjects.

Now...Today was very cloudy. Yesterday, when the sun was shining, the differences between the pictures were even bigger. Anyway you can judge for yourselves. Just look at the indoor crop at f4 and the outdoor crop at f4. Oh and I used a tripod for the outdoor shot with self timer (10 s). I just used the flash indoors.

maybe if you went from f4 to f11 to sharpen that background as the roof in front is very sharp

sdmg9 wrote in post #7182360
maybe if you went from f4 to f11 to sharpen that background as the roof in front is very sharp

And this brings up the question as to what focus point(s) were used? I know it was asked before, but I didn't notice the answer if it was given. If all points are used, set center focus point, then try the same shot with the Canon.

Oh yeah I forgot to mention that. The center focus point was used.

The tests were repeated many times, with or without stabilization and the results are the same.

Stopping down the lens does help but I want the lens to be sharp wide open. I mean, you can see that the lens has that capability from the indoor crop. So I don't think that the lens itself is the cause. I believe that it's got something to do with the autofocus.

What focusing are you using, do you have the 30D set to use 'all-points' by any chance?

That could cause it to be picking up the foreground roof as the focusing point and not the building you want.

EDIT: too slow typing, I see that others got there first. I'm running out of theories now.

I wouldn't dismiss the lens just yet, do you have any other telephoto lenses to try this with? Are you able to rent a lens online or borrow somebody's?