Lens test: Sigma 18-50mm F2.8 Vs kit lens

fingerz

fingerz

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My Sigma 18-50mm F2.8 EX DC arrived today and what better way to break it in than by pitching it in a head-to-head battle with the kit lens. I had intended to set the tripod up near a window and shoot stuff outside but it was windy and rainy so I decided to shoot indoor stuff instead. Not ideal but hopefully I'll be able to do an outdoor test at some point.

This is the whole frame I used. The two little squares denote the sections used for the 100% crops in the two comparison images (middle and edge).

lenstest_sigvkit_wholeframe.jpg



Method - camera
This test was done at 50mm. I haven't tested the 18mm end of the scale yet but I'll probably do that when I get a chance to do an outdoor test. My method was as follows. I set the camera up level on the tripod and locked it off. I used the Sigma lens first because I knew that its full zoom was exactly 50mm. Sadly the kit lens doesn't have a marking on the barrel to denote 50mm so I had to guess it as best I could. In the end (according to the Exif data) I think it was about 47mm. I set the white balance to indoor so all shots would have the same colour cast. I autofocused on the same point for both lenses (the adidas symbol at the top of the 'middle' box in the pic above). I shot in manual mode and noted down the shutter speeds for each aperture. I then used the same set of aperture/shutter settings on the kit lens, even though (oddly) the camera thought those settings were exactly one stop brighter than it did with the Sigma lens. The shots all came out looking exactly as bright as each other so I'm not sure why it thought the settings were too bright for the kit lens. It's worth mentioning that I didn't use the Sigma's lens hood as I didn't have one for the kit lens and I didn't use any UV filters, just so it was as fair as possible.

Method - processing
Once I had the shots I did nothing to them at all in RawShooter apart from convert them all to Tiff files. In photoshop I just took the 100% crops I needed and applied the same small amount of unsharp mask uniformly to all the images. I applied the sharpening because when I did the comparison between the 16-35L and the kit lens it was much easier to see the differences after sharpening was added.

Results
You can see the results here. I'm using text links because the final comparison images are pretty big. They're about half a meg each:

Middle of the frame:
http://www.jameyhoward.com/filebucket/lenstest_sigvkit_middle.jpg

Edge of the frame:
http://www.jameyhoward.com/filebucket/lenstest_sigvkit_edge.jpg

Conclusion
My conclusions are that the Sigma is either sharper or at least as sharp as the kit lens at all apertures where they compete. However, when the Sigma gets to f/3.5 and wider it starts to get quite noticably soft at the edges of the frame. Whether this is due to shallow depth of field I'm not experienced enough to say. The middle of the frame in the f/2.8 shots doesn't look too bad to me. The shadow contrast looks about equal between the two lenses. The Sigma's sweet spot seems to be a bit wider, at around f/5.6 compared to around f/8 on the kit lens. Although the edge of frame results for the Sigma look slightly sharper at f/8.

Overall I'm quite happy with my purchase. I think it will fill the gap nicely until I get a job/eye that requires something with an 'L' on the end. One slightly annoying thing is that the Sigma's lens hood doesn't allow you to get your fingers far enough in to remove/replace the lens cap (or turn a polariser). So you've either got to remove the hood to fiddle with your filter and take off the lens cover or just walk around all day with the lens cap off (which I tend to do anyway) and the polariser set how you want it.

Edit - reading this back it sounds like I've made my mind up and I'm just posting this for information, which isn't the case. I'd value feedback from you lot on what you think of the comparisons etc. Cheers. Sorry. Cheers.
 
Just went to try the Hoya 67mm circular polarising filter I got at the same time. Screwing it onto the front of the lens. Little metal ring pops out of the filter, followed by the polarising glass.

Lovely bit of craftsmanship there. I've managed to get it all back in and given it a quick shake to make sure. Not the best start though.
 
fingerz said:
Just went to try the Hoya 67mm circular polarising filter I got at the same time. Screwing it onto the front of the lens. Little metal ring pops out of the filter, followed by the polarising glass.

Lovely bit of craftsmanship there. I've managed to get it all back in and given it a quick shake to make sure. Not the best start though.
Click to expand...

..not just me then! that happened on both my Hoya Skylight 1B and Circular Polariser, in fact they were both like that out of the case from new, one edge of the metal ring having popped out of the filter housing :annoyed:
 
Nice write up Jamey..so F5.6 through to and incl F16 all look better on the Sigma from your pics of the centre of the frame and at the edge all the way through to F22. It also shows how bad the Canon kit lens is at the edge in general, although you have to say that for a low value starter lens it does produce reasonable results that most would never question.
 
It may only be one step up in your opinion but you are also gaining a faster lens which I would guess is essential for the type of photography that you are most interested in.
 
I guess I could do the same thing with my Tamron 28-75.

I do have a problem though....

Where am I going to find that many shoe boxes :ponders:



Your test confirms what I always thought about the kit lens - it is not as bad as people make out. I bought the Tamron as much for the constant f2.8 as any other reason.
 
Steve said:
It may only be one step up in your opinion but you are also gaining a faster lens which I would guess is essential for the type of photography that you are most interested in.
Click to expand...

Sorry Steve what do you mean by faster ??

Thanks
 
RobertP said:
I guess I could do the same thing with my Tamron 28-75.

I bought the Tamron as much for the constant f2.8 as any other reason.
Click to expand...

I also own the Tamron and like many Sigmas if you get a good one its bloody great. The constant F2.8 is also very nice, especially for throwing out backgrounds at 75mm.
 
Mr THX said:
Sorry Steve what do you mean by faster ??

Thanks
Click to expand...

Sorry...by faster I mean a lower F stop..which in turns means that the lens will let in more light allowing the camera to use faster shutter speeds at the same ISO settings. Good for action or low light shooting. The sigma is capable of using lower F stops than the Canon kit lens and so is said to be "faster"

Hope that helps. :)
 
Well I typed this while Steve was posting so here my :beer: assisted effort.

The F stop number tells you how big the 'Aperture' is. A 50mm f1.0 lens would have an objective lens 50mm diameter so the ratio of focal length/aperture diameter is 1.

A lens which can only do f5.6 at 50mm focal length would have a hole for the light 50/5.6 = 8.9mm diameter.

So faster = bigger diameter... lower f stop figure
 
so the 2 of you with the Tamron, im in for one of these, worth the money?
 
RobertP - yeah I agree about the kit lens. I never thought it was that bad tbh. Certainly not for the price, anyway. And the constant f/2.8 was also one of my main concerns. Although having a non-rotating front end is very nice. Pity it's nearly impossible to use the CPF and the lens hood at the same time but I guess it's always going to be fiddly, at best.
 
EosD said:
so the 2 of you with the Tamron, im in for one of these, worth the money?
Click to expand...

I'd say so. It is on my camera most of the time and I feel pretty confident of the results I get using it. Feels solid.

You can leave the hood on and easily fit/remove the lens cap due to the novel design of the latches. no problem with filters either.

For dropping the camera back in the Crumpler bag (lift flap drop it in type - easy access) the hood takes only a second to rotate off turn over and refit reversed.

If do ever get round to testing it, it may be softer wide open but I don't notice it and would not hesitate to use it at f2.8

Minuses -

You certainly know you are carrying it! Way heavier than the kit lens.
If you don't use the zoom latch it will drop to full zoom under gravity if you point it down. (does no harm)
Some say the AF motor is noisy - you can hear it but not a prob to me.


Just occaisionally I could do with a bit more width. The range of the Sigma may be more flexible.
I intend to keep the Tamron and maybe get a Tokina 12-24 for scenery etc.
 
thats a good write up too Fingerz, wanna do a review?
 
Thanks Robert, i know Steve is happy with his, some top shots hes got from it, i think i will try and find one locally to play with then make a purchase!
 
Steve / Robert

Thanks for that, understood the lower F stop - it was the 'faster' remark that caught me out - I'll catch up with all this lingo before long.

Again thanks :D
 
'faster' shutter speeds for the same shot with a large aperture....
 
The canon hoods seem less tolerant when you do that - the Tamron you can just spin it off and slap it back on without thinking...canon ones seem to need a bit more lining up or they bind a bit.
 
EosD said:
so the 2 of you with the Tamron, im in for one of these, worth the money?
Click to expand...

I'll add my voice to that... definately worth the money.

I find it quite light, especially compaired to the Canon and Sigma models. The new Sigma 24-70 EX apparently comes close to it for picture quality + has a bit better build quality and an extra 4mm at the wide end (but you lose 5mm at the long end).

As Robert has said, it is a bit noisey when focusing but not excessively so, and if you like your landscapes then you'll probably be looking to add a wider lens to the collection aswell sometime in the future (or just use you kit lens)... but as a walkabout lens it's hard to beat, very sharp, good contrast, thumbs up :thumb:
 
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