Lens Quality Question

[gonzo_entertainment]

I try to stay at 5.6 (just as I would for a still) unless desire for shallower DOF, or lighting I can't control drive me lower than that.
That area, 4 to 8, is the sweet spot on most lenses. That's usually one of the things you use to evaluate a lens, how "crisp" does it look at lower F stop numbers. My primary lens (probably 60% of my shots) is the Takumar 50mm 1.4 which was always a respected lens because it's tack sharp at 2.8.

[c3hammer]

It depends on whether you are measuring contrast or resolution...

I'll concure that what I'm calling sharpness is partly due to more contrast (acutance) with better lenses. I have also found that with faster glass you can generally use a lower ISO setting which also lends to a sharper image. I've found that for poorly lit documetary work, the combination of resolving power, acutance and speed of a lens allow for what I would call a radically "crispier" image. While a GH2 might be a great camera for controlled lighting it's horrible for blown highlights and the high contrast associated with mid day sun. The Canon's do a much better job with the type of work I do. Adding great glass to a Canon APS-C cam doubles down the range it will perform well in. Not in pure resolution, but in where you can tell your story in nearly the highest quality available.

Cheers,
Pete

[mail4joeg]

Basic lens fundamentals. If you want sharpness, you shouldn't be shooting f1.anything. Aperture of f4-8 is the sweet spot of most lenses, if I'm not mistaken. David Mullen shoots most scenes between f4 and 5.6, I believe. Unless you're obsessed iwth blurry backgrounds, or it's completely dark...

PS -- He beat me to it, above.

Test your lenses at various apertures.

[M1CEtro]

Hello All, thanks for your comments on this.

Reading through all of these posts has brought up a concept I never considered before. Shooting with my 7D for video, (with the exception of daytime shooting) I'm so used to using the lowest F stop possible on every lens so I can keep the ISO as low as possible and have minimum noise. But from what I'm reading, it seems like some of you are saying that a lens may produce a "sharper" image at an F-Stop other than the lowest stop? That there is a sweet spot for sharpness on a lens? I was under the assumption, that with non optimal lighting, the lowest F Stop (most of the time at 1.8) will produce the best image, is this not the case? My workhorse is a 28mm 1.8 prime. How would you suggest that I test to find the sweet spot of my lens for video?

[deltoidjohn]

M1CEtro, do not confuse best with sharpest. For portraits, or even IV's, you don't always need maximum sharpness, so using lower F-stops makes sense. If you're trying to show a close up a jewelery, you'd want it as sharp as possible to show the detail, so you'd want to use the lens around f/4 or 5.6 to get maximum sharpness.

It's all a matter of balancing your needs in each situation, and it may well be that in sub-par lighting you will still get the best overall image by shooting wide open, as per your assumption. Sharpness is no good if it's too dark to see the image!

As for finding the sweet spot of your lens, the easiest way is probably to scan through some reviews of your lens. Most professional reviews will test the lens at each F-stop and note the sharpest aperture.

[unadog]

If you really want a "sharp" image, don't forget to apply some fairly aggressive sharpening to counteract the strong anti aliasing filter in the Canon.

When Canon released the 1DsII (pre video days), Chuck Westphal recommended in a white paper that you use an unsharp mask in Photoshop at (300, .1, 1) as a standard "capture sharpening" step (as opposed to later sharpening for creative or output purposes.)

Those of you who are familiar with Photoshop will realize that is a pretty aggressive sharpening setting - higher than I would have tried without having someone recommend it. The current 18 MP crop sensors have a smaller pitch, but they are fairly similar to that 16MP sensor in the 1DsII. There is a lot of information in the image that can be brought back. (I sharpened a still image last night at (300, .9, 1) for text legibility.)

Now it all really depends on the final destination for the image, content, aesthetic, etc. I used to mask the face on portraits, or apply blur to the face to lose sharpness and detail for fashion images. But the strong AA filter in the Canon **can** be counteracted by appropriate software techniques.

Actually if you look at the Nikon D800E, people say it has "no AA filter." That is actually not true - it has two filters, one AA filter, and a second filter that immediately "undoes" the AA effect - reverses the effect. (Most people assume that was to keep the same image path intact from the D800 to the D800E.)

That is the same concept of capture sharpening in software with PS. It really is quite effective in regaining detail where you want it back.

Pretty similar in concept to using flat, low saturation, Adobe RGB images out of the camera to render a final look. Beginners always used to complain that Canon images were flat, didn't have that "pop" - which is really a good thing. They weren't high saturation, sharperned, sRGB images for teh web. Don't take that initial image as a given.

On lenses - "L"'s for most zooms are almost as good as non-L primes (in general). L primes are usually better than non-L, with some exceptions (on the non-L's being pretty decent, not the L's really being poor.)

Canon is updating most of their line - 24, 28, 24-70, etc. But the new lenses are not cheap. The one I lust after is the 24-70 II. I use my 24-70 I about 70% of the time (then the 70-200 next, then 24, 50, 85.) If I had only one lens the 24-70 L II would be it. But at $2,300 you can buy a whole raft of non-L primes. (Canon lenses retain their value pretty well though, so I don't mind spending more for some. The true cost is purchase price - sale price.)

Good luck!
Michael

[Barry_Green]

Lenses are typically sharpest in the middle of their f-stop range, so usually at least 1 stop down from wide-open, and at least 1 stop up from fully-closed; for many lenses, it's better to go 2 stops down or 2 stops up.

So on an f/1.8 lens (let's call it f/2) the sharpest range is usually going to start at about f/4. Lenses used wide-open will usually be softer, have more vignetting, and be prone to more flare.

The problem with getting the sharpenst lens on a 7D is that the sharper the lens, the more you'll see aliasing. A softer lens can actually deliver all the resolution that the 7D can handle, and sometimes softens the image enough that it helps minimize the aliasing.