Sigma 18-125 pincushioning

[bloomer]

This week I became the proud owner of a Pentax DS2... who knows, maybe the only one in Australia! Anyway, I have a Sigma 18-125 for it. Today I was doing the first real tests of it, and I am really horrified at the pincushioning... almost throughout its range.

Coming from my film SLR, I'm used to the Pentax-A 28-80mm/3.5-4.5. That is by no means a great lens, but the minimal distortion in comparison to the Sigma is striking (I just have to look through the viewfinder, not even check the pictures!).

Do I have a particularly bad copy of the Sigma, or do people just ignore the pincushioning (there are considerably more reasonably positive reviews than negative reviews)?

[coldrain]

People know this lens is a cheap, big zoom range lens. It is a compromise for zoom range, not for distortionless optics. That is why you do not see many complain about it, it is a given. Same with the 18-200 from Sigma, 18-200 VR from Nikon and the 18-200 from Tamron.

If you want less distortion, you need to go for better lenses, wich probably will not offer such a convenient zoom range.

http://www.photozone.de/8Reviews/lenses/sigma_18125_3556/index.htm

[jeisner]

Do I have a particularly bad copy of the Sigma, or do people just ignore the pincushioning (there are considerably more reasonably positive reviews than negative reviews)?

This lens has bad distortion end of story.. It is pretty amazingly good in other respects though, considering the price and range it covers...

My advice is to live with it or use the free tool 'ptlens', which has settings in it specifically for this lens (among others) to remove the distortion, works well if the distortion is damaging the photo.. Be carefull though as you will see how bad the distortion is ;-)

If you want to be free of distortion, suppliment the 18-125 with the Pentax 16-45/4 ;-) I ended up selling the 18-125, but honestly for the price and range it is a very good performer..

[bloomer]

People know this lens is a cheap, big zoom range lens. It is a compromise for zoom range, not for distortionless optics.
I was prepared for some distortion, without a doubt, and I had read the photozone review, amongst others. But i really wonder if the pincushioning evident in the attached picture is acceptable for so many people, or if I've got a lemon.

Picture taken on DS2 from same distance (approx 90cm) for each lens. Please ignore the lack of technical quality -- just rustled them up now for illustrative purposes.:D
http://web.aanet.com.au/dunques/lensdifferences.JPG

[Clyde]

...I really wonder if the pincushioning evident in the attached picture is acceptable for so many people, or if I've got a lemon.


Picture taken on DS2 from same distance (approx 90cm) for each lens. Please ignore the lack of technical quality -- just rustled them up now for illustrative purposes.:D
http://web.aanet.com.au/dunques/lensdifferences.JPG

Yeah you got distortion there, but at least at this resolution the sigma looks pretty sharp!

Just trying to make lemonade...

Clyde

[Shosta]

Ptlens could be a good tool for you.
http://epaperpress.com/ptlens/

[coldrain]

Lets just conclude that that Sigma is not designed to make screen shots with. It is more a convenient walk around lens for outdoors... and then most of the time the distortion will not be as obvious.

[George Riehm]

This week I became the proud owner of a Pentax DS2... who knows, maybe the only one in Australia! Anyway, I have a Sigma 18-125 for it. Today I was doing the first real tests of it, and I am really horrified at the pincushioning... almost throughout its range.

Coming from my film SLR, I'm used to the Pentax-A 28-80mm/3.5-4.5. That is by no means a great lens, but the minimal distortion in comparison to the Sigma is striking (I just have to look through the viewfinder, not even check the pictures!).

Do I have a particularly bad copy of the Sigma, or do people just ignore the pincushioning (there are considerably more reasonably positive reviews than negative reviews)?

If your goal was to have a lens for screen shots the 18-125 is not it. If you wanted a good, sharp, walk-around lens then you have chosen wisely.

The final comment from photozone.de makes the same sort of statement, and adds focus problems, which appear unique to Canon dSLR's, so they don't apply to your Pentax (or my Nikon).

I have had great results with the 18-125, but have to admit I haven't used it for screen shots, and apparently neither should you.;)

Maybe you should try one of the other wide 7X lenses out there from... uh... OK make that a 5X starting at 24mm.

[bloomer]

C'mon folks, the screenshot was just a quick and simple illustration. I don't give a damn about photographs of monitors. I do care about the bending of straight lines falling within the outer 25% of the lens image, whether I'm photographing a piece of cake or a stand of bamboo or someone's balcony. I agree that much of the distortion is not immediately apparent in visually busy images with few straight lines at the periphery.

I wonder if this is a film vs digital thing -- as an image can be retouched using ptlens or other software, the quality of the original image is seen as mattering less than if one were working with a film camera? I've never before used a lens with such clear distortion throughout its range, hence the shock.

[George Riehm]

C'mon folks, the screenshot was just a quick and simple illustration. I don't give a damn about photographs of monitors. I do care about the bending of straight lines falling within the outer 25% of the lens image, whether I'm photographing a piece of cake or a stand of bamboo or someone's balcony. I agree that much of the distortion is not immediately apparent in visually busy images with few straight lines at the periphery.

I wonder if this is a film vs digital thing -- as an image can be retouched using ptlens or other software, the quality of the original image is seen as mattering less than if one were working with a film camera? I've never before used a lens with such clear distortion throughout its range, hence the shock.

I guess it depends on your definition of quality. For many it is a sharp, relatively contrasty, high ratio zoom lens good for everyday shooting.

If you want a higher quality lens in the ultra wide (18mm) 7X range, for under $300 it doesn't exist. Kudos to Sigma for compromising in the right direction.

[Turo]

I guess it depends on your definition of quality. For many it is a sharp, relatively contrasty, high ratio zoom lens good for everyday shooting.

If you want a higher quality lens in the ultra wide (18mm) 7X range, for under $300 it doesn't exist. Kudos to Sigma for compromising in the right direction.

I agree, I was recommended the Sigma for my Nikon by a few people and I am extremely happy with it. For the price, its hard to beat. The pincushioning can be a bit of a problem (although my pictures don't seem to have it as bad as the example you posted above), but that is something that is easily fixed with a little PP.

[Esoterra]

I am likely cheering on my own team when I say that I like the pincushioning of the 18-200 when I am photographing landscapes with objects of interest in the close foreground. I don't see it all the time, but for the right picture its really great!