[S0l]

Hi all,

i'm having doubts lately about my K7 + sigma 17-70mm, i'm not sure it is properly focused. Been very disappointed by CA, fringing and general (lack of) sharpness of the images the last two times I relied on it (music fest & mountain trek)

So i get out the tripod and my trusty sigma 30mm/1.4 , of which i'm very fond and satisfied quality-wise, in order to shoot some comparison shots.

Doing so has been a big mistake because my doubts have decoupled ; i now have doubts about the 30 too, and i'm afraid i'm catching pixelpeeping fever...


Here goes :

INSIDE :




Vs




OUTSIDE 1 :




Vs




OUTSIDE 2 :




Vs







I would like to have your opinion concerning the sharpness of each lens at 100% zoom ; I don't have much references to judge myself since i've never been a peeper up to now, that's why i'm asking you guys : what do you think? I have also uploaded all the raw jpegs there :

Lens Tests - Raw jpegs pictures by s0lspot - Photobucket

I'd really appreciate it if anyone could enlighten me...those kind of doubts are really bothersome since they affect trust in the lenses you use and restrain your photography in general...


Thanks a lot!


PS: Admins please move the thread if i posted it in the wrong section.

[icywindow]

In the indoor shot, I notice flare from the overhead light - are you using the lens hood for both lenses?

[hcc]

Let me ask a question. On tripod, did you switch off the SR?

I ask because SR must be off when using the camera on tripod.

[JinDesu]

Let me ask a question. On tripod, did you switch off the SR?

I ask because SR must be off when using the camera on tripod.

Timer mode should disable the SR automatically. Can you do 100% crops or provide the original jpegs? Or are these 100% crops?

[calsan]

There's a LOT of haze in the outside shots. So they're not going to be sharp due to the light being diffracted in the air.
You would need to use a circular polarizer to see better results.

[SpecialK]

At the size posted I see no significant difference.

[arv]

IMO focus plane is different at inside pics. Zoom focused more on background, so pics are not comparable.

A.

[bdery]

first of all, you live in a beautiful place!

Second, I see no problems with the pics you posted. They might be too low-res to see the "problems" (if any). But pixel-peeping is a BAD thing to do, it prevents you from enjoying photography. If your lenses worry you, you could try adjusting the AF (if your body allows it), and if really youthink there is a problem, send then to Sigma.

[S0l]

Hi,

a big thanks to all of you for your replies, here come the answers.


icywindow : no i didnt use the hoods, the overhead bright spot was a sun ray shining off cd's onto the wall.

hcc & jin: good question, i did not disable the SR nor did i know you had to switch it off when you use a tripod : why is that? The cropped images are only crops, no resize so if you maximize them you'll have 100% zoom. I've also uped the original jpegs on photobucket as mentioned in the original post.

calsan : totally agree, the problem is the light/air has been this way for at least 10 days, today it is even worst...i guess it's the heatwave going on through Spain causing a lot of land/moisture evaporation. Seeing as i dont have a polarizer i can't do anything about it.

Special & arv : thanks for input, concerning the focus plane the 17 70 is hard to adjust in order to get to exactly 30mm as the value isnt printed on the lens barrel : only 24 and 35, in between it's all a guess, the K7 isn't precise enough to give me the exact focal lenght : either 28 or 31mm...

bdery : thanks, it really is beautiful & magic here in Granada...great cheap friendly beautiful place to chill out for a few months...a good get away from the big cities...beaches & ski slopes both only 45 minutes away... shared flats starting at 120-140€/month for a room... Thanks for your feedback, i definately do not want to start peeping, i know exactly what you mean.


Anyway in order to be sure I just took 2 more inside pics with each lens, scene about 2,5m away, the first one in AF and second in MF (used the camera's focus confirmation viewfinder flash & sound beep in MF). All are shot using A mode, no hood, SR off (jin is right, 2s timer switches it off automatically) ; . I've uped the four pics there, look at the file name for description :

Lens Tests - Raw jpegs pictures by s0lspot - Photobucket

Aperture was 5.6, Auto speed : 1/6 for the 30mm and 1/8 for the 17-70mm (don't know why the camera chose to slow it down for the brighter 1.4 30mm?) and 200 iso.

Please check those out, let me know your gut feeling and that will be it with these questionings...

Thanks a lot in advance to all the community!

[JinDesu]

From what I read on another thread, using the same aperture on different lenses doesn't necessarily mean you are getting the same aperture. So that can be the reason why one is metering 1/6 and one is metering 1/8.

The reason why people suggest turning off SR (which timer and remote shutter does automatically) is because the manual says so - well actually it's because while the SR is active, it shakes the sensor, so if you don't actually have camera motion, it can introduce the smallest blurs into the image.

I actually cannot determine a difference in those shots.

[arv]

First four indoor pics seems fine and I can see no difference. However in the last couple pics there is a different focus plane again (not FOV, check difference between edge of table in the center and lattice at lower right corner or green bottle with yellow label). IMO lenses are fine, at least for this pics size.

A.

P.S. Once I was in Granada at Fiesta del Dia de la Cruz... and phrase "wine pours freely" gained real meaning... . One day I'll have to get back there.

[Parallax]

When I first looked at the inside pics, it looked more like motion than OOF. I think the problem there was SR being on while a tripod was used.
That doesn't necessarily mean there isn't a focus issue, but to know for certain you'll need to repeat the tests with SR off. As mentioned earlier, use of the self timer will disable it and will also eliminate any chance of blur induced by movement from pushing the shutter release button.

[S0l]

JinDesu, thanks a lot for clearing that up, clearly in these tests this is a non-issue seeing the timer was used in all pictures. Thanks for your opinion!

Arv : yeah there seems to be some distortion, is that fixable in-cam or do I have to post-process them? Anyhow you join Jin in your opinion about the lenses : i can keep them!

Parallax : thanks for jumping in, as you can see in my previous reply i upped 4 more inside pics without SR : what do you think about the lenses? Keeper?

I'm beggining to think the original doubt about the 17-70 may have been caused by the CPL filter I used, a Starblitz one, now that I think of it when I removed it to shoot those test pics I went through a great deal of effort twisting it off and now i'm suspecting it wasn't properly screwed in : I think one section of the filter got onto the wrong lens thread resulting in the filter not being parallel to the front glass. Could this misalignement cause gross image aberrations such as CA, fringing and blur?

Thanks again guys & gals!

[Parallax]

the wrong lens thread resulting in the filter not being parallel to the front glass. Could this misalignement cause gross image aberrations such as CA, fringing and blur?

No, that wouldn't matter. A crappy quality filter will, though. If your pics are sharp without the filter, and dull with it; throw it away. There's a reason that a B&W 72mm circular costs from $90 - $200+, depending on model, and the starblitz is, I'm guessing, about $20.

[JinDesu]

If you can get a Pentax remote, that pretty much guarantees there is no shaking from pressing the shutter button (on lighter tripods, you can observe the camera strap moving a little even after the 2s timer). I use the remote all the time because I'm afraid that my heavy hand introduce too much vibration - and I'm also clumsy so sometimes I bump the stupid tripod while moving away.