I have a 750D with the 18-55 mm kit lens. I find the sharpness rather disappointing and am considering buying the 17-55 mm which, according to reviews, is much better in that respect, although over three times the weight and expensive. My camera body is classed as entry level, though top end; taking account of focusing ability and in-body processing would I see that improvement in my images or would that only be the case when used with a top end body.
Hi Mike, so I have a few thoughts to unpack regarding your question. 1. Your body will do nothing for how sharp the images from the lens can be, a better Autofocus system can help make sure you get the shot sharp, but technique is just as important (Understanding the AF system). You do not need to rely on the AF system to decide what to do with focus. I have shot with a single focus point placed on top of what I want to capture with maximum sharpness 90% of the time, in all my DSLRs all the way back to my 20d i got in 2004. And of those 90% usually it is the center point which is the most accurate, and I hold the shutter button half way to adjust composition while keeping focus locked, and then complete the button press to take the photo. 2. Upgrading lenses will as a general rule improve issues you have with a cheaper lens. However there is more to consider here, sharpness, chromatic aberration, vignetting are all issues that plague zooms more than prime lenses. Take sharpness, generally a lens is sharpest stopped down a few stops, maybe 5.6 for example. As a general rule zooms are not consistently sharp through the zoom range, and also lenses will get softer towards the edges of the image, the degree to which this happens is dependent on the lens. I am not sure which 18-55 you have, the non-IS i believe is a bit soft at 18 and 55 ends. The IS version I thought was reasonably sharp from 18-35mm, so performance varies between models as well. So if you have the IS lens you may not see a huge difference as I expect it will perform similarly to the 17-55 in regards to sharpness, the 17-55 is also an older lens design from the mid-2000's so it may not be as snappy with AF as some newer lenses. The big up side of the 17-55 is that it is faster and will shoot as wide as 2.8. Also consistent aperture lenses tend to have better performance than ones with a variable aperture so you will read better things about a 2.8 or 4.0 zoom over something that is 4.0-5.6 for example. Another thing to consider when buying lenses is will you stay in a crop body forever? The 17-55 like the others is only usable on a crop sensor camera. You can purchase standard EF lenses and use them on crop cameras and full frame, future proofing your investment. Maybe it is worth saving up for a 17-40 or a 16-35, both are L lenses and a zoom you will not need to replace.
Thank you, that is very helpful. I have looked at the reviews again and realise that at f5.6 & f8.0 the sharpness is similar to the 17-55 except at the long end, and for depth of field reasons I probably would not use the large apertures much, where the 17-55 seems to excel, so for the time being I will stick to the 18-55 IS STM
