Tips for purchasing Sigma 17-70

[joseb552]

I'm going to pick up a Sigma 17-70mm F2.8-4.5 DC MACRO tomorrow and I was wondering if there were any tips you might have to ensure it is focusing properly. I'll be bringing my XTi along with me to test on, but is there anything in particular i should be looking for?

Thanks for any advice you might have!

[evandavies]

Set to 70mm
Use Av and set to widest f/4.5
Use One Shot AF with Center Point.

Focus on a well lit sheet of paper with lots of text at an angle of roughly 45 degrees. Remember where you focused and then look at the LCD image zoomed in.
Is the point you aimed at in focus?
It is normal for the focus to be slightly behind the aim point but the aim point itself must still be in focus as well.

Good luck... ;)

[JohnJ80]

I'm going to pick up a Sigma 17-70mm F2.8-4.5 DC MACRO tomorrow and I was wondering if there were any tips you might have to ensure it is focusing properly. I'll be bringing my XTi along with me to test on, but is there anything in particular i should be looking for?

Thanks for any advice you might have!

Here's a cut and paste of why and how I test lenses.


J.

======
There are most certainly bad copies of lenses out there, but that is just like all the other reported lens issues - amplified big time on dpreview and the others. Those that have the problem report it several times typically (often loudly and vehemently) while the vast majority who are happy are out taking pictures and not saying anything. If there were anything close to the number of bad lenses reported by the posters on photography forums, the lens manufacturers would have gone bankrupt from warranty claims years ago. Your chances of getting a good lens are well above 90%.

However, there are bad copies so the proper methodology is 'trust but verify.' If you find a focus failue, then you should first examine carefully your test methodology. You should first assume an error in your testing procedure since small errors (which can be subtle) can cause bad results.

There also can be issues where the camera AF system is in spec, but off to one end of the tolerance and then a lens is mounted that is also off, but off in the opposite direction. The tolerances stack up and while both units are in spec, the resulting combination is not. I think this is the vast majority of ACTUAL reported focus problems. The solution to this, to make sure there is not a problem long term is if more than one lens has this problem, to have your camera calibrated.

There are those the report failures of a specific lens on multiple copies of the same camera. While these bodies work with other lenses, there is clearly more of an issue with the body that with a lens. What is the probability that lens after lens from a manufacturer would be bad? The potential is vanishingly small. This is a body that is probably marginal and needs to be calibrated.

That all being said, here is how I test lenses:


Read the following to understand how the AF system on your camera operates:
http://www.fredmiranda.com/forum/topic2/241524

Then download either of the following two test procedures and charts (I prefer the first)
http://md.co.za/d70/focus21.pdf
http://www.canon-dslr.com/Canon_Jan05/Canon_SLR_Focus_Test.htm


Follow the procedures and conduct the test. Do this in good light - I highly recommend that you do this in daylight since this is many times brighter than indoor lighting. Since the AF system is contrast based, the object is to test the lenses ability to work with the AF system, not the ability of the AF system to resolve low contrast shots. I recommend that you set this up to get shutter speeds of about 1/1000s at the widest aperture of the lens. You do this by getting into good light plus you can jack up the ISO as required.

To do these tests, you should use a tripod so that there is no handshake and you can be assured that you have positioned the camera properly.

Download the pictures to your computer and examine the chart on the screen to verify the focus by examining the DOF as shown by the chart.

The whole thing takes about 5 minutes after you have done it several times.

[joseb552]

Thanks guys for the great points! I want to be sure that everything is good with this new lens as I am leaving tomorrow for a 10 day trip to California / Las Vegas and need something a bit more than the kit lens as my primary.

[irish1]

Another tip---buy at a place that won't give you any replacement hassles. My first copy had horrible "zoom creep"---if you extended it to 70mm and held it upwards, the zoom would collapse on itself due to gravity. Be sure and check that as well. It probably doesn't affect the IQ, but it has a high P.I.A. factor (pain in the a**). I bought at Canoga Camera in LA and they were great about giving me a new copy, and from the time I sent it in until the time I got a new copy was less than a week (5 days?). If all is right with the lens, you'll love it!

[joseb552]

Ok, so i just got home from W01f Camera with my 17-70 DC Macro. I ran some quick tests at the store and it seemed great. Got it home and immediately took it outside for some real-life tests on the focus, here are some examples,

70mm, F4.5, 1/50, ISO 1600 (handheld)
http://farm1.static.flickr.com/144/407215040_cea63a5b99.jpg (http://farm1.static.flickr.com/144/407215040_abd9da0aee_o.jpg)

100% Crop
http://farm1.static.flickr.com/160/407215045_ef67e55d89_o.jpg

70mm, F4.5 1/60, ISO 1600 (handheld)
http://farm1.static.flickr.com/154/407215024_c60beac285.jpg (http://farm1.static.flickr.com/154/407215024_c9189b25de_o.jpg)

100% Crop
http://farm1.static.flickr.com/155/407215035_e9b45c9852_o.jpg

70mm, F4.5, 1/125, ISO 400 (handheld)
http://farm1.static.flickr.com/170/407215017_3b377cc9a8.jpg (http://farm1.static.flickr.com/170/407215017_97ffd7e5ce_o.jpg)

100% Crop
http://farm1.static.flickr.com/188/407215021_2d3ed5ba3f_o.jpg

All Crops are centered on the inteded focus target.


What do you guys think?

[T Kubik]

I'd like to see some L comparison

[grinchy]

Ok, so i just got home from W01f Camera with my 17-70 DC Macro. I ran some quick tests at the store and it seemed great. Got it home and immediately took it outside for some real-life tests on the focus, here are some examples,

70mm, F4.5, 1/50, ISO 1600 (handheld)
http://farm1.static.flickr.com/144/407215040_cea63a5b99.jpg (http://farm1.static.flickr.com/144/407215040_abd9da0aee_o.jpg)

100% Crop
http://farm1.static.flickr.com/160/407215045_ef67e55d89_o.jpg

70mm, F4.5 1/60, ISO 1600 (handheld)
http://farm1.static.flickr.com/154/407215024_c60beac285.jpg (http://farm1.static.flickr.com/154/407215024_c9189b25de_o.jpg)

100% Crop
http://farm1.static.flickr.com/155/407215035_e9b45c9852_o.jpg

70mm, F4.5, 1/125, ISO 400 (handheld)
http://farm1.static.flickr.com/170/407215017_3b377cc9a8.jpg (http://farm1.static.flickr.com/170/407215017_97ffd7e5ce_o.jpg)

100% Crop
http://farm1.static.flickr.com/188/407215021_2d3ed5ba3f_o.jpg

All Crops are centered on the inteded focus target.


What do you guys think?


Looks Great!

[grinchy]

here is 1 I took earlier today:

http://i5.pbase.com/g6/79/734079/2/75055365.CDEVXeld.jpg