Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
02-06-2013, 12:29 AM   #1
Junior Member
sarahparish91's Avatar

Join Date: Jul 2012
Location: Orange, NSW
Photos: Albums
Posts: 34
sigma 50mm 1.4, very soft wider then 2.5

Hi, I have a Sigma 50mm 1.4, and a pentax k5, I usually stick to 2.5 or smaller as anything wider then that starts to get really soft, even if it's in focus, it looks like everything has glowing edges. Is this normal of the sigma lens, or is there something wrong with it? thanks,

02-06-2013, 12:47 AM   #2
Veteran Member




Join Date: Oct 2011
Posts: 818
Just interested to know, when you mean the photo is in focus, are you meaning by using autofocus or manual focus?

Coz if you are using autofocus, it might just mean FF/BF issues. This would help the guys here out in troubleshooting your issues.
02-06-2013, 12:54 AM   #3
Junior Member
sarahparish91's Avatar

Join Date: Jul 2012
Location: Orange, NSW
Photos: Albums
Posts: 34
Original Poster
I usually use auto focus, but even when I use manual focus, the image will still have glowing edges regardless of whether or not it is in focus. If that makes sense, I will upload some sample images at different apertures in a minute
02-06-2013, 12:58 AM   #4
Veteran Member




Join Date: Oct 2011
Posts: 818
Ouh..... Wait, don't upload just because i was asking..
I'm no expert when it comes to such detailed troubleshooting. Guess it's best to wait for those who are more experienced than me.
If it isn't FF/BF due to autofocus issues, i'm not too sure.

02-06-2013, 01:14 AM   #5
Senior Member




Join Date: Aug 2011
Location: Sydney
Photos: Albums
Posts: 232
The Sigma 50 is prompt to flare without the hood.

Did you use the lens hood?
02-06-2013, 01:34 AM   #6
arv
Site Supporter




Join Date: Aug 2010
Photos: Albums
Posts: 374
IMO you should better upload few examples. Sigma 50mm is famous as being sharp even wide open, and Sigma lenses are also famous for inconsistent autofocus, focus shift and being decentered.

A.
02-06-2013, 01:57 AM   #7
Junior Member
sarahparish91's Avatar

Join Date: Jul 2012
Location: Orange, NSW
Photos: Albums
Posts: 34
Original Poster
Here is a link to the photo on flickr, I've labeled the apertures below the photo. I cropped at 100% and tried to keep enough foreground and background in so you can see the focus is on the middle of the paperclip. I do use the lenshood, and these photos were taken on my back verandah, in the shade with the sun on the other side of the house. This fuzziness has always been there, I had read online that sometimes the photos are soft at a wider aperture, so I assumed it was that, but it's really bugging me I can't open it up further, so I thought I would check if it was normal or not.

Untitled | Flickr - Photo Sharing!
02-06-2013, 02:44 AM   #8
Pentaxian




Join Date: Sep 2009
Location: Southern California
Photos: Gallery | Albums
Posts: 3,181
This is consistent with my experience with other (non-macro) Sigma lenses - they tend to be soft and/or have other significant image degradation within the first stop of wide-open.

It appears that the focus moves toward the front of the paper clip throughout this first stop, but it also appears that the focus point (wherever it is!) is still soft. A quick check of the images on Sigma 50mm F1.4 EX DG HSM Lens Sample Photos and Specifications also look to me like it can't deliver great images within the first 1-1.5 stops or so, similar to your observation.


Perhaps you do have a poorer copy - maybe some other Sigma owners can help you decide this. But I believe Sigma lenses generally cost less because they cost less to make, so I would expect you to encounter something similar again. However, as I said, those who own this specific lens can probably help you more.


However, to be fair, none of the Pentax 50s (except for the K or A 50/1.2) can deliver great images faster than f/2 either (I've owned all but one of the AF models, and a few MF ones). In fact, the DA*55 is the only 50ish AF K-mount lens I know of that can perform well near wide-open in the f/1.4 to f/1.8 range.


Last edited by DSims; 02-06-2013 at 02:58 AM.
02-06-2013, 02:44 AM   #9
Site Supporter
kiwi_jono's Avatar

Join Date: Dec 2009
Location: Christchurch, New Zealand
Photos: Gallery | Albums
Posts: 1,038
Looks like a classic case of Front Focus to me. You can see the area in front of the clip that is actually in focus.

To prove it, focus on the same scene (f1.4) with Live View (contrast focus setting) - I think you find it is then in focus.
I think you will need to tweak this in focus adjustment menu to fix it with phase focus.
02-06-2013, 03:04 AM   #10
Junior Member
sarahparish91's Avatar

Join Date: Jul 2012
Location: Orange, NSW
Photos: Albums
Posts: 34
Original Poster
What about the green glow on the out of focus areas of the paper clip at a wider aperture? I might try the same test in the am with a ruler, that might make it easier to see the focus point (should have thought of that earlier).
02-06-2013, 03:14 AM   #11
sTi
Forum Member




Join Date: Feb 2011
Posts: 98
QuoteOriginally posted by kiwi_jono Quote
Looks like a classic case of Front Focus to me. You can see the area in front of the clip that is actually in focus.

To prove it, focus on the same scene (f1.4) with Live View (contrast focus setting) - I think you find it is then in focus.
I think you will need to tweak this in focus adjustment menu to fix it with phase focus.
The problem with the Sigma 50/1.4 seems to be that it (or at least several copies I've read about) show a pronounced focus shift (see here for explanation: What is Focus Shift? ) when stopping down. So whereas the focus will be in front at 1.4 (like in your sample IMO), it will be spot on by around 2.5 (after that the focus shift issue is normally no longer a problem, it usually occurs at the first one or two stops for fast lenses). So using an AF correction to get the focus right at 1.4 would mean that you will get back focus at smaller apertures. Not very useful IMO. Normally the LensROM inside the lens is supposed to correct the focus shift by telling the camera to use a different AF correction depending on the used f-stop. I don't know if Sigma uses this feature to communicate with the camera at all and thus whether it would be possible to correct this problem by sending it to Sigma for calibration.
My DA*55/1.4 does not show this behaviour at all, so it seems to be possible to avoid this focus shift issue with fast lenses.
02-06-2013, 03:17 AM   #12
sTi
Forum Member




Join Date: Feb 2011
Posts: 98
QuoteOriginally posted by sarahparish91 Quote
What about the green glow on the out of focus areas of the paper clip at a wider aperture? I might try the same test in the am with a ruler, that might make it easier to see the focus point (should have thought of that earlier).
This is called "bokeh fringing", see e.g. at the bottom of this page for an explanation and examples: Canon EF 100mm f/2.8 USM L IS macro (APS-C) - Review / Lab Test Report - Analysis
02-06-2013, 03:19 AM   #13
Senior Member




Join Date: Jan 2007
Location: Tampere, Finland
Posts: 191
QuoteOriginally posted by sarahparish91 Quote
Hi, I have a Sigma 50mm 1.4, and a pentax k5, I usually stick to 2.5 or smaller as anything wider then that starts to get really soft, even if it's in focus, it looks like everything has glowing edges. Is this normal of the sigma lens, or is there something wrong with it? thanks,
I am no expert with this lens as I have not shot enough with it, but IMO the sharpness degrades towards the minimum focusing distance quite a lot, especially with the most wider apertures (seen best in the last picture; others were taken somewhere 1-3m from the subject). This is no macro lens after all. Here are few examples with the widest aperture. By clicking the thumbnail you should see the full size image. Those are without any particular post processing, just exported from Lightroom 4 with default settings. First two are with K-7, last one with K-5. Also these are not maybe the best examples for your style of shooting but examples nonetheless And very beautiful photos btw in your flickr account! I can see you can use this lens as it should be used (I have lot to learn)!





02-06-2013, 03:31 AM   #14
Junior Member
sarahparish91's Avatar

Join Date: Jul 2012
Location: Orange, NSW
Photos: Albums
Posts: 34
Original Poster
sTi, thankyou for that!

jpyykonen, I cannot click on your thumbnails it comes up with a blank screen saying 'no access' ... And thankyou for your compliment, I am just in the process of uploading a bunch more photos
02-06-2013, 03:31 AM   #15
Pentaxian
VisualDarkness's Avatar

Join Date: Nov 2011
Location: Uppsala, Sweden
Photos: Gallery
Posts: 4,439
Sigma AF 50mm f/1.4 EX DG HSM (Canon) - APS-C Review / Test Report
QuoteQuote:
"The HSM ("Hyper-Sonic-Motor") AF is very fast and virtually silent. AF accuracy is a difficult topic for the Sigma. It seems to suffer from pronounced focus shifts when stopping down ("Residual spherical aberrations") which is probably the reason why many users report back- or front-focusing issues."
Yep, the focus is perfect at smaller apertures in your shots but quite front focused in the wide open one. Maybe calibrate it for wide open as it affects smaller apertures less?

It should be a really sharp lens and many recommends it over Pentax/Nikon/Canon 50/1.4 offerings due to being sharp straight from F1.4.
Reply

Bookmarks
  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Tags - Make this thread easier to find by adding keywords to it!
50mm, k-mount, pentax lens, sigma, sigma 50mm, slr lens
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
For Sale - Sold: Pentax FA 50mm 1.4 , Sigma DC 17-70mm 2.8-4.5 macro noquarter15 Sold Items 5 07-30-2012 08:14 PM
pentax 35 mm 2.4 very soft ? snoop21 Pentax SLR Lens Discussion 27 05-22-2011 09:37 AM
For Sale - Sold: Tamron Adaptall SP 70-150 Tele Macro Soft; Pentax 135mm 3.5, 135mm 2.5, 50mm 1 stillnk Sold Items 3 04-24-2011 10:11 PM
looking for recommendations for something wider then the 50mm 1.7. boosted03gti Pentax SLR Lens Discussion 4 06-04-2010 12:34 PM



All times are GMT -7. The time now is 06:10 PM. | See also: NikonForums.com, part of our network of photo forums!
  • Red (Default)
  • Green
  • Gray
  • Dark
  • Dark Yellow
  • Dark Blue
  • Old Red
  • Old Green
  • Old Gray
  • Dial-Up Style
Hello! It's great to see you back on the forum! Have you considered joining the community?
register
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]
Top