F2.8 Zoom how much softer than F4?

[bob_osullivan]

OK, this question developed from my previous post. It's more geneal and

hopefully more useful.

 

I just bought a canon 70-200 F2.8L. I formerly had the F4 version and a used

Sigma that I traded up from.

 

I've noticed more softness than I expected at 2.8 as compared to F4. So many

posters have said "it's just as sharp at 2.8 as it is at F4". I bought into

that.

 

I'm tempted to send it in for calibration. But first, if someone could look

at these sample shots, to compare the 2.8 vs F4 performance and let me know if

this is to be expected. I've never had a F2.8 zoom, only primes and F4 zooms

so don't know what to expect. I don't know how the file names will come out

so the there are three sets of shots. The first in each set is 2.8 the second

is F4.

 

All these are 100% crops, shot from Tripod, pretty fast shutter speeds, MLU

yada yada yada...

 

I just think the difference is too great for a $1200 lens.

 

Thanks,

[bob_osullivan]

don't know how to post multiples.<div></div>

[bob_osullivan]

Gotta be a way to do this.

[bob_osullivan]

now F4

[valo_soul]

Hi Bob,

 

I have the 70-200 f/2.8 IS version (which is supposedly slightly less sharp even than the non IS).

 

Judge for yourself.

 

This is @ f/2.8, standard JPG setting, straight from the camera.<div></div>

[valo_soul]

And now a 100% crop - Yes, that black dot on the lamppost was a spider!<div></div>

[dave chew]

Well I certainly don't by that any lens is as sharp at f/2.8 as f/4. Mine wasn't as sharp when I owned this lens.

 

If those are center crops then I'd be a little suspicious, but inconclusive. If those are edge crops then I'd say it's fine.

[mike_earussi1]

First of all, there are variations among lenses. Your's may just not be as sharp as others but still be within spects. Also the f2.8 has never been known to be as sharp as the f4 version. You buy the f2.8 because you need the extra stop not because it's sharper. Check out the Photozone tests (if you already haven't) and see for yourself.

 

http://www.photozone.de/8Reviews/lenses/canon_70200_28/index.htm

 

http://www.photozone.de/8Reviews/lenses/canon_70200_4/index.htm

[steve santikarn]

Do you mean the the photos you got from the 70-200 f2.8 lens is sharper at f4 than at f2.8 (of the same lens)? Or do you mean that the photos from the 70-200 f2.8 is not as sharp as the photo from the 70-200 f4 lens? From the same lens you'd expect the photos to be sharper as you use smaller apertures up to a certain point.

[michaelging]

I have 55, soon to be 56 yr old eyes, but to me the first photo is not focused correctly, it looks like it is back focused. My 70-200 2.8 L , lens is very sharp at 2.8 as well as F4. I have also shot with the same kind of lens that had IS and its just as sharp.

[guido_ersettigh__milan_]

what about a front or back focus instead? a larger DOF at f4 could partially hide the problem. it would be easy to fix - by a canon laboratory -

[gdanmitchell]

I'm going to agree with David who said the no lens will be as sharp at f/2.8 as it is at

smaller apertures - at least up to the point where defraction effects kick in.

 

Every lens is going to have its "best apertures," and they aren't going to be wide open.

 

Bob, if those are unsharpened 100% crops they really look fine for f/2.8, and they'll make

good prints. Shooting wide open is a trade-off. You can shoot in lower light (or at faster

shutter speeds) but you diminish DOF (could be good or bad, depending), sharpness won't

be quite as good as smaller apertures, and you are more likely to see some corner fall-off.

 

Dan

[valo_soul]

Hmmm.. nobody commented on my post. Perhaps mine is not as sharp as I thought? :P

[bob_osullivan]

Well thank you all for taking a look. James, I'll comment on your post, while the sharpness didint knock my socks off, I love the composition.

 

Anyway, I'm hearing what you are all saying. I know 2.8 won't ever by as sharp as F4, but these I think are farther off than they could be. They are center crops, and I am vey sue it's not a miss focus, or back focus issue. I've checke for that.

 

So, I am going to make some prints and see how those look, and try to get this lens a workout in some decent light outside if the sun comes back out this week. If it's still not impressing me after that, off to Canon it goes.

 

Thanks again.

[valo_soul]

Good idea Bob. I'd be interested in hearing your impressions later, and your final choice and outcome. I take interest in this sort of thing. I think I even obsess a little over my gear at this point haha. I had a few troubles earlier this year.

 

And thank you for the comment. I didn't mean to grab for attention there, hope it didn't come across that way :) I was just quite impressed that I could count the individual legs of the the spider in that frame. Quite sharp IMO for shooting wide open. It was at 105mm by the way, just FYI. I think the exif is still intact anyway.

[elliot1]

If you are not getting the results you expect, send your lens in for service. The worst case is that they will send it back without doing anything to it. I have had several high end lenses that have needed correction in the past.

[john_bellenis]

I have both these lenses - at f4 they are about the same... the conventional wisdom is that

the f2.8 stopped down to f4 should be sharper than the f4 wide open, but I don't actually see

that - they seem indistinguishable to me at f4. The f2.8 may be very slightly softer at the

edges wide open, but if those are center crops it seems like too much of a difference to me.

In actual shooting situations both are stellar lenses and your shots should not be limited by

IQ in any way. I'd get the lens calibrated ot double check your focusing (close up at f2.8 DOF

is extremely shallow).

[bob_osullivan]

Well, the prints look great at 8x10. I'm starting to think I better give this lens more of a chance to perform in the real world. I checked for front/back focus with a test chart and it seems spot on.

So, I think It's ok.

 

Thanks again for all the perspectives.

[mendel_leisk]

Take at a look at the ISO chart comparisons at The-Digital-Picture for the 2 lens. I believe his tests show the f4 a little sharper at all stops. But it's a very close race ;)

[glenn nk]

The links provided by "mike earussi" are worth reading carefully.

 

This doesn't imply that the f/2.8 isn't sharp - it's just not as sharp as the f/4. Conversely, the f/4 isn't as fast.

[valo_soul]

The Photozone tests are just that; Photozone's tests. One test for each lens. One sample (usually) against one sample. Except for a few exceptions where he had obvious poor samples. (24-70) If he were to get a bad sample of say, an 85L and an exceptional sample of some non-L zoom lens and the zoom's resolution figures surpassed the prime at equal apertures; that does not mean that the 85L is not a great lens. In fact: he only recently updated the test on the 85L, it originally showed it as being very good but not excellent, especially in the corner frame. It's now displayed as nearly excellent throughout. I believe it was the 85L anyway, or perhaps the 135 f/2. One of them was revised as being better than he had originally claimed, anyway.

 

Most tests are like this, and therefor should be taken lightly. Although they can give a decent indication of what to expect, I wouldn't purchase just on them alone. I've learned this in my purchases.

 

Your 70-200 f/2.8 should be almost indistinguishably close in sharpness at equal apertures to the f/4 version, from what I understand.

[bob_osullivan]

James, excellent point. Actually my new lens is at least as sharp if not sharper than my old F4 and current primes at F4 and smaller apertures. The original concern was the F2.8 which I had no real point of comparison. So, I shot some portraits with my 85 1.8 and this new 70-200 the other day both set at 2.8. Being wide open on the zoom and stopped down one on the prime I expectd the prime to dominate. Big surprise, IQ was indistinguishable. Guess I freaked over nothing. Pixel peeping is bad, reviewing acutal prints makes more sense. You just want to make sure you're getting the quality you paid for, and in this case I think I did now.