Lens Test – can you help?

I recently bought a Sigma 18-250mm F3.5-6.3 DC HSM Optical Stabilised Lens for my Canon 600D Digital SLR Camera. Some of the reviews on Amazon made it clear that, with such a long zoom range, there would be some compromise on image quality; but overall the lens got a good rating. 

I’ve had the lens for a few months now. While I like the flexibility of the zoom range (I’m not serious enough to want to carry around additional lenses), I’m not so happy with the image quality. But I can’t tell if this is due to the fact that the lens is a compromise or that I’ve been been sent a faulty model.

Below are three photos that show the nature of the problem — generally a halo or soft-focus effect around sharp edges. Admittedly it’s mostly apparent when displaying the images at their maximum size in flickr, but I’d like to know if this is typical. If you have any idea, I’d appreciate a comment. 


London Eye 4

London Eye – vislible ‘glow’ around the struts.(Large size)


Seagull – chromatic aberration around the top of the bird’s head? (Large size)


Roof Repairs

Roof repairs – again, an unintended soft-focus effect? (Large size)



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2 responses to “Lens Test – can you help?

  1. Jim

    Hi,This kind of chromatic aberration is to be expected, and will also vary depending on the particular camera (i.e. sensor) you’re using too. I wouldn’t worry too much about it as at a practical level, many of these aren’t visible unless you are looking at the high-res version, and if you’re concerned about them being visible when printing, try a test print to see – you may be worrying needlessly. If you do want to try and reduce the problem, two ways you might remedy this include: shooting in RAW, and using the a RAW editor, such as Adobe PS RAW editor (part of the CS package) or Lightroom, to correct for chromatic, vignetting and other barrel distortions. Alternatively, if you have a clear visible chromatic fringing, using photoshop you can also desaturate for that isolated colour on an adjustment layer, and then carefully paint over the fringing – this is a quick hack as it just renders the fringing into grayscale, but so long as it’s only a small fringe, it is invisible when printed or viewed at screen resolution.

  2. Anonymous

    Many thanks Jim – very helpful. It’s good to know there are post-processing options though I’m a bit lazy on that front. I can see from your website that you’re prepared to work hard at your art ?????just by glancing I can see you have some fabulous shots there!

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