Equipment/Basic Question - please advise!

[futureal33]

Hi,

Ive posted quite a bit on here recently, all my questions relate to the same general theme, lenses.

I am in the market for a new lens, but after reading lots and lots of reviews, and buying 2 lenses which I owned for less than a week, I am back to square one... please let me explain..

I have a 40D with the kit lens (18-55 IS) and I am looking to replace this lens with something better. I tried both the Tamron 28-75mm 2.8 and also the Sigma 18-50mm 2.8 Macro - both of which had nice IQ, but I found the Tamron was horrendous at autofocussing in low-light, and the Sigma also had an auto focus issue where even when tripod mounted it wouldnt focus on a specific location - I know I could have got this fixed but it put me off the lens, and now Im back to square one... here comes my question (and the complicated part!)

I want to buy the Canon 17-55mm 2.8 IS lens.. However I have read quite a few reviews which say it is soft at f2.8 - and it gets really good by around f4-5.6 - this sets alarm bells ringing in my head because the only reason I want this lens over my kit lens (f3.5-5.6) is because of its f2.8 potential - but if f2.8 is unusable due to it being overly soft and you are forced to step down to f4... then what is the benefit?!

I appreciate IQ (distortion, colours, USM focusing etc) may all be better on the 17-55.... but in terms of aperture performance only, if the 17-55 has to be stopped down to narrower apertures to be considered "sharp" then I cant see how it is better than the 18-55 kit lens which, both to me and on reviews, is considered sharp from f3.5 upwards!

Now both the kit lens and the 17-55 have IS (infact the kit lenses IS is rated at 4 stops where the 17-55 is only rated at 3... but thats debatable nodoubt!) so there's nothing between them in terms of IS.
Obviously there is the extra 1mm at the wide end to consider, but again that is negligable IMO.

So if the kit lens can be used at any aperture without worrying if it is going to be soft, whereas the 17-55 CAN take pictures at 2.8 at the tradeoff of it being soft, is there any benefit?!

Or should I be considering something along the lines of the Sigma 17-70mm OS f2.8-4 or the Canon 15-85mm f4-5.6 IS

Or should I just keep the kit lens, and buy a good quality 24mm prime (as thats the range I shoot at most!)?

Questions, questions, questions.. I know - but the 17-55 is a £750 investment so I want to be sure Im doing the right thing and from what ive read about its aperture performance I am now wondering if its worth it?

Thnx for any help

 

[mgdaviso]

I think the question you have to start with is..... what sort of pictures do you want to shoot? Only then can you start deciding what sort of lens you need.

 

[petersmart]

If you go here:

http://www.the-digital-picture.com/...CameraComp=0&SampleComp=0&FLIComp=0&APIComp=0

you can compare a lot of lenses.

In fact if you compare the cheapest Canon lens around - the 50mm f1.8 you'll find it has incredible sharpness from f2.8 onwards and is perfectly usable from f2.0.

The only problem with using any lens wide open is the very small DOF which means that focussing has to be spot on.

.

 

[tdodd]

40D + 17-55 @ 35mm, f/2.8, 1/100, 1600 ISO, 100% crop, no edits. This was shot from the hip as a candid and so the prospects for focus being in the right place were a bit hit and miss. I'm happy with it....

Please click the resize bar to see the image properly.

Another example with similar settings....

Please click the resize bar to see the image properly.

Of course, people say the 40D is a soft camera, due to the strong AA filter, so perhaps a little work on sharpening might be in order, and at 1600 ISO in these examples perhaps it is not the fairest test of the lens.

Here's one on my 30D at 100 ISO, again no sharpening adjustments....

Please click the resize bar to see the image properly.

 

[TCR4x4]

No lens is going to be ultra sharp at its widest aperture.
I really wouldn't fret using the 17-55 at f/2.8 and stopping down to f/4 is no big deal either really. With the IS you'll get your shot most of the time.

This is a crop, from an image I took on a 50D, handheld at 1/80

Exposure 0.013 sec (1/80)
Aperture f/4.5
Focal Length 50 mm
ISO Speed 400

At f/2.8 the DOF probably wouldn't have been deep enough to get the fly and berry in focus, so stopping down a bit made all the difference, but still has a nice OOF background.

flyberry by TCR4x4, on Flickr​

 

[HoppyUK]

17-55 is the sharpest thing out there. Superb lens. Buy with total confidence.

I don't know what you have been reading, but that lens in particular always gets rave reviews. Rightly so. I had one a 40D and would get one again if I ever went back that way. It is sharper at f/2.8 than many 'good' lenses at f/5.6.

Beware of that particular test on TheDigitalPicture linked above. Read and believe the text, but ignore the lens chart images which don't show the lens at its best due to the quirks of their test procedure. This is explained in the small print, hidden in their 'Help' section with specific reference to that lens.

Or save yourself a lot of bother and worry and just buy it