Finally at 40mm the difference in quality between the centre of the image and towards the edges of the image becomes greater, although the issue with sudden softness in the very far corners appears to have vanished. Peak quality across the frame is now at f/11 where the centre is very good, and the quality towards the edges not too far behind. Then he took his staff in his hand; and he chose for himself five smooth stones from the brook, and put them in a shepherd’s bag, in a pouch which he had, and his sling was in his hand. And he drew near to the Philistine.

As with any other general purpose/ultra wide angle lens, this lens has far more uses than I am going to think of. Now some of might say that this comaprism is not really fair, because the Canon 10-18mm is optmized for APS-C sensors, while the 17-40 is a fullformat lens. In addition there are differences in the maximum aparture and of course the price tag. Just grab the ring at any time, no need to move any switches. If you don't want AF, set the AF / MF switch to MF. Apochromatic lenses have special lens elements (aspheric, extra-low dispersion etc) to minimize the problem, hence they usually cost more.

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Of course if I look for problems instead of taking pictures I can always find them. The weak point for sharpness for any wide zoom is the corners at the widest setting, wide open. Canon's own MTF curves confirm this. Here's a full image: As I'd normally expect for an ultra-wide lens, distortion at 17mm is quite pronounced. Here Imatest recorded 7.46% barrel distortion, which is quite high, but not uncharacteristic for a lens of this type. Unfortunately the curvature increases towards the corners in a non-uniform fashion, which may make it difficult to completely correct the effect in image editing software afterwards. At 40mm very mild pincushion distortion is present. Here Imatest recorded a level of 0.303%, which will be barely noticeable in most cases. The rubberised zoom and focus rings are quite narrow compared to a lot of newer lens designs, but they are still easy to operate. The zoom control has little resistance and doesn't suffer from zoom creep either, which will please tripod shooters. The focus ring is nicely damped, and as the focus motor's an Ultrasonic one, manual adjustments can be made at any time.

Gary Wolstenholme takes a look at this popular lightweight ultra-wide angle zoom lens, which has a constant aperture of f/4, an Ultrasonic focusing motor and sealing against the elements. Then he took his staff in his hand, and chose five smooth stones from the wadi, and put them in his shepherd’s bag, in the pouch; his sling was in his hand, and he drew near to the Philistine. Falloff of illumination towards the corners is quite pronounced at f/4 and 17mm. Here the corners are 2.57stops darker than the image centre. The lens needs to be stopped down as far as f/8 results to achieve visually uniform illumination here. The level of vignetting is reduced at 40mm with the corners only being 1.37stops darker than the image centre at f/4 and visually uniform by f/5.6. I know it has high levels of distortion and corner performance isn't great, but for landscapes stopped down to say f8/11 would it be good enough? Shakir: What! has then your Lord preferred to give you sons, and (for Himself) taken daughters from among the angels? Most surely you utter a grievous saying.then the 16-35 L II is a better choice (you need at least f/2.8 - or image stabilization for motionless subjects). This lens does not extend with a very small exception - the objective end lens elements move in/out slightly inside the lens barrel during focusing.

Seeking the best printer for your business? Hit your productivity targets with inkjet and laser printers that are a perfect fit for any workspace – including home offices. L lenses have a Je ne sais quoi about them. Maybe it's contrast, microcontrast, clarity, or whatever you want to call it.If you have a 1.6x camera ( 30D, 20D, Rebel), then Canon's cheapest lens, the 18-55mm, gets much closer. Diffraction is usually the sharpness-limiting factor for all lenses, especially on digital SLRs, at about f/11 and above. See How Sharpness Varies with Aperture. And he took his staff in his hand, and chose him five smooth stones out of the brook, and put them in the shepherd's bag which he had, even in his scrip; and his sling was in his hand; and he drew near to the Philistine. If anyone is worried that he might not be acting honorably toward the virgin he is engaged to, and if his passions are too strong [ a] and he feels he ought to marry, he should do as he wants. He is not sinning. ( T) They should get married. 37 But the man who has settled the matter in his own mind, who is under no compulsion but has control over his own will, and who has made up his mind not to marry the virgin—this man also does the right thing. 38 So then, he who marries the virgin does right, ( U) but he who does not marry her does better. [ b] CA (Chromatic Aberration) is very well controlled, though some can be expected in the corners below 24mm.