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01-05-2011, 12:25 AM   #1
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Do I need a new lens

I am a bit puzzled about my lens. I have a sigma 28-80 which I took the image 'Stephanie' with. Which was f8 1/250 and it is just not sharp. In fact unless I was in their face, none of the shots were very sharp with this lens. On the other hand I have a Pentax wide angle lens which I shot the 'Grass tree' with, on f13@2secs. I find it to be very sharp. Should I be thinking of a dedicated Pentax lens to replace the Sigma, or do I need to always choose a higher f stop? I have another image which was taken on f8 1/250 with the sigma (wedding)in which I would have thought the people behind would be sharp but as you might see they are not; in fact the couple in front are not too sharp either (well IQ wise I'm sure they are!)

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01-05-2011, 12:34 AM   #2
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Hi Trishy.
The 28-80 is not the best lens, but at f/8 it would be expected to be reasonably sharp in the centre in the areas where focus is placed. What you may also be experiencing with shooting up close and personal is the blurriness of pretty ordinary bokeh from this lens in the out of focus subjects. You may well have needed to stop down further to render all the people in the shot sharply, but you will end up running into other limitations like diffraction and a slower shutter speed, causing camera shake.

If you're looking for a replacement for the 28-80, I'd suggest a Tamron 28-75, a Sigma 17-70 or even a Pentax DA 17-70. These are considerably better in IQ than your current Sigma.
01-05-2011, 12:51 AM   #3
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Thanks Ash I have written those down and will have a browse. I have another wedding in April and want better shots. though as there was a 23 knot wind at the above wedding they were pleased with their shots. (Does your IQ here mean same as mine; intelligence quotient)
I do swear that lens worked fine on my 1stD??
01-05-2011, 01:06 AM   #4
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Yeah, looks like you have a soft copy of the sigma. You would be much better off with a few good primes IMHO.

01-05-2011, 02:19 AM   #5
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does the shot look focused in the VF, have you a body that will allow AF fine adjustment with FF/BF.

try and focus the lens Manually and see if you can get a sharp result..if you can Id say you need to calibrate the body with that lens..

what was the FL of the lens for your images...also the rough distance you were away from the subject

for example , if you were at 80mm f8 and your subject was 5 metres from the focal plane the DOF would only extend for 1.25 metres and that would be 550mm in front of the subject and 700mm behind [ thank god for DOF master on the iphone} ..so the people to the rear of the last image would be outside the DOF in this instance....

Last edited by Tommot1965; 01-05-2011 at 02:48 AM.
01-05-2011, 02:43 AM   #6
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Take a look at the items for sale here. On top of the suggested lens, you may want to look into the Sigma 24-60 or 24-70 f2.8. Those should give you better results... unless you have a back-front focus issue as explained Tommot1965, on the body itself.

Just in case:
IQ - image quality, as far as I know
01-05-2011, 03:06 AM   #7
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QuoteOriginally posted by Ash Quote
Hi Trishy.
The 28-80 is not the best lens, but at f/8 it would be expected to be reasonably sharp in the centre in the areas where focus is placed. What you may also be experiencing with shooting up close and personal is the blurriness of pretty ordinary bokeh from this lens in the out of focus subjects. You may well have needed to stop down further to render all the people in the shot sharply, but you will end up running into other limitations like diffraction and a slower shutter speed, causing camera shake.

If you're looking for a replacement for the 28-80, I'd suggest a Tamron 28-75, a Sigma 17-70 or even a Pentax DA 17-70. These are considerably better in IQ than your current Sigma.
One could add to Ash's good advices that if you are looking for a used Pentax lens with the same focal range, one hidden gem is the SMC Pentax-FA 28-70 constand f4. It does not go for much but is a very good lens. Of course the more modern alternatives on Ash list gives you more wide angle on an APS-C camera. You might also want too look at prime alternatives. If 2-3 new primes are out of your budget (say the 21, 40 and 70 ltds) a pair of used manual focus 28 and 50mm lenses could surprise you with what results you can achieve with them.
01-05-2011, 03:40 AM   #8
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Trish, you don't say what body you are using now but it's likely the extra resolution is exposing the shortcomings of your lens.

I've done wedding photography for round 25 years. When I first moved to digital I used a Sigma 18-125 for weddings on my *ist D and the images were fine. When I upgraded to the K10D the images all looked very soft. I bought the DA* 16-50 and haven't looked back. Wedding photos taken with the K5 look great.

As a rule of thumb be prepared to spend at least as much on your lenses as the camera body. I'd be buying something new if I was you. I would recommend going for a DA 17-70. You will find the extra width really handy for your shots indoors.

01-05-2011, 08:19 AM   #9
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Thanks for all this. I am writing down all these suggestions to follow up. Interesting about the 'what body are you using'. (wish it were a younger one!) I am actually using the Kx and wondering if that is the problem? As mentioned I'm sure all was sharp with the 1stD. I need now to sift through all the abreviations in your notes. I had a look at the review of a sigma 17-70 and it mentions it as a macro?
What is APS-C?
I do have a manual lens which is good, but just don't trust my eyesight!

Last edited by trishytee; 01-05-2011 at 08:33 AM. Reason: Left out some text
01-05-2011, 08:26 AM   #10
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im not familiar with a KX..does that have FF/BF adjust ?

have you tried a test on the lens in question to see if its focusing at the AF point..
01-05-2011, 06:16 PM   #11
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The K-x is a brilliant little camera, don't you worry about that Trishy.
Its resolution is excellent and handles noise reasonably well if you need to shoot at high ISO.
As for IQ, I assumed you knew it meant image quality from your first post.

If you want a single lens to do the job for you, I'd suggest the Tamron 28-75 if 28mm is wide enough for you. Excellent IQ and f/2.8 maximum throughout the focal range. Also very good value.
01-05-2011, 06:20 PM   #12
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You are on a camera forum asking if you need a new lens.
Of course you need a new lens.
You can never have too many lenses.
01-05-2011, 07:14 PM   #13
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QuoteOriginally posted by Tommot1965 Quote
im not familiar with a KX..does that have FF/BF adjust ?

have you tried a test on the lens in question to see if its focusing at the AF point..
The K-x does not have focus correction adjustment. But checking adjustment might be the ticket.

QuoteOriginally posted by Ash Quote
The K-x is a brilliant little camera, don't you worry about that Trishy.
Its resolution is excellent and handles noise reasonably well if you need to shoot at high ISO.
As for IQ, I assumed you knew it meant image quality from your first post.

If you want a single lens to do the job for you, I'd suggest the Tamron 28-75 if 28mm is wide enough for you. Excellent IQ and f/2.8 maximum throughout the focal range. Also very good value.
+1 to any of these, or Douglas' suggestion is also a good one. I had the Sigma EX 28-70 for a while and it also worked well for me (heavy though).

QuoteOriginally posted by Wheatfield Quote
You are on a camera forum asking if you need a new lens.
Of course you need a new lens.
You can never have too many lenses.
yesss....

Other stuff.
I'm not sure if you are shooting RAW or JPG, but if JPG, and you bought a Pentax branded lens, you are going to gain corrections for distortion and chromic aberration (the dreaded purple fringe) automatically. If you use lightroom to process, then you probably have equally good choices in Sigma or Tamron.

That first shot - what flash are you using? is it the onboard one?
01-05-2011, 08:52 PM   #14
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PHew! Well there is a Tamron for sale second hand which I might look at, unless of course I would be better off with the Pentax which I can always put on a Pay it off scheme. Now clarkey, the first shot was with the Pentax off camera flash and I was bouncing off a reflector as I didn't want them to have a washed out look as my reading was from the sky. (don't have light room)Tommot: having probs with the abreviations, and not sure what focusing at the AF point means (auto focus?) or how to check adjustment. I have noticed on auto a hell of a lot of whirring seems to occur?Oh, and I do shoot in raw. Sorry Ash I was being funny when I talked about IQ above I was playing with words. (Sharp? Stupid?) Keep it coming. Let me know thoughts on Tamron 28-75 Ooops jsut remembered the ad said for a: Tamron AF 28-75mm F/2.8 XR Di LD Aspherical (IF) Macro Lens with NIKON mount. Is that only for Nikon or will it go on a pentax. Yes, my IQ is not to high either.
01-05-2011, 09:08 PM   #15
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Trish

FF is front focus...BF is back focus..

Af point is the red square in the View finder..{ I always select center AF point }

to check to see if you lens/body combo is FF or BF.....you need to shoot a test chart and check the results.

there are many on the web that you can print out...

lay the test chart on table...mount you camera to a tripod...set the largest F stop you can..then shoot the target point of the chart...if its in the middle of the depth of Field {DOF}..then all is well...if its at the far edge of the DOF the lens is seen to be FF..if the target is at the near edge of DOF.. the lens is said to be BF

google FF/BF tests..plenty online for this

if your body lens combo is either FF or BF....you will need to send it in for calibration....

the K7/5 can do it with AF fine adjust within the menu.


could you please post the EXIF for the last picture with the four people in it..Im intrested to know if DOF would extend to the woman and child, given the settings that you had

hope this helps
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