Sharpness issues

[russell2pi]

I am looking for some help ironing out some blur issues I am having with a borrowed camera (Pentax K10D with Sigma 18-50/3.5). I am hoping it's just me and not the gear, but would like to know how to fix it.

Here is a sample image. They are not all this bad but all have a noticeable lack of sharpness.

76560

Yeah, a boring scene with bad lighting - I have no choice over the viewpoint or field of view as I'm duplicating historical photographs. This one is north-facing and I chose late afternoon to try to at least get some sunlight on one face of the war monument.

Shot in RAW+JPEG, P mode 50 mm 1/125 f/8, hand-held with stabilisation on, and tweaked in Adobe Camera Raw to remove chromatic aberration, sharpening plus tweaks to tone/exposure to bring up foreground and tone down the sky.

I still think I need to re-think the lighting (maybe light the street well and bring up the monument in photoshop?) but what really has me stumped is the lack of sharpness. Have a look at this 100% crop:

76561

OK, the haloes on backlit chimneys etc are probably an unavoidable consequence of severe backlighting? But what about the blurriness in the signs, which are in the shade? The in-camera JPEG looks similar here so it's not just my ACR fiddling doing it.

So, what's the problem? Is this the best I can expect from this lens? Did I not hold it steady enough? Should I turn off IS? Is AF hit and miss - should I shoot a few times in the hope that one's not blurry??

[ricktas]

at 1/125 of s second there is a chance this could still be caused by camera movement. Try taking some shots with your camera on a tripod

[jjphoto]

I can't comment on that camera/lens combo but sharpness needs technique too.

1. Always use a good tripod. The best tripod is the biggest one you can carry. Don't hand hold. Forget IS. Even 1/125 may not be a high enough shutter speed for a 50mm focal length. IS is OK when handholding as it ceratinly does help but it does have it's limitations and I avoid it if I don't actually have to use it.
2. Never forget rule No. 1
3. Use mirror lockup if you have it, or use a delayed shutter release if you don't. In any case try to minimise your contact with the camera during the exposure itself so ideally use a self timer with a mirror lockup.
4. Use Live View or similar to focus if you have that option. Don't rely on AF or AF assist. Don't even rely on the viewfinder which may not be properly calibrated, I've seen plenty of examples that were not. Remember that only one point in the image will ever be perfectly focused, even when the lens is stopped down for greater dpeth of field, so make sure that point is where you need it to be for best effect.
5. Don't underexpose. If anything blowout the highlights you don't need, maybe the sky in some cases, to get a better exposure in the details that you do need. Bracket your exposures.
6. Use your lenses sweet spot if you can. Most lenses are least sharp wide open and stopped down. They tend to (there are exceptions) have a sweet spot about 2-3 aperture stops down from wide open.

I think, but I don't know for sure, that your problem may be the lens as I don't really think you are doing anything particularly wrong.

JJ

[arthurking83]

I'd say it's 99% lens(the other 1% could be operator error).

In most situations f/8 would be stopped down enough to achieve a decent level of sharpness at the very edge of the frame, but this lens probably doesn't provide enough quality for this purpose.

Cheap kit type lenses are notorious for quality control issues. How new is the lens, have you ever got super duper sharp images from it.. if it's not brand new, has it ever been banged about a bit.. not even directly! Small knocks and bumps whilst in the safety of the padded camera bag can be enough to knock out lens alignments.
Have you checked the rest of the image for sharpness detail. Is the centre section of the image more sharp? Similarly sharp? Less sharp? What about the right hand side?

For 100% safety of mind.. always shoot on a tripod, lens hood in the correct orientation, mirror lockup if available or exposure delay, etc.
This way your head won't spin around as much trying to chase an issue that's simply not there.
To reduce the possibility of operator errors(eg, camera blur), a quick succession of frames always helps. Even if you don't get a sharp shot in a series of 6 successive rapid shots, the blur detail in all 6 is bound to be slightly different, which then points to the operator as the weakest link!

Is it possible to loan another lens too?

[russell2pi]

Thanks for the replies- looking through some other images, there are some good sharp ones that tend to be closer to the middle of the zoom range. Here's an example at 23 mm, f/8, 1/350, 100% crop also near far left of frame.

I have also borrowed a 28-90 Sigma so maybe I should give that a go. Many of these photos have to be taken from the middle of the highway so I'm not that keen on mucking around with tripods, changing lenses etc!

Maybe I should try some systematic tests of the lens at different zooms and apertures, on a tripod with self timer just to iron out what's going on?

[Lance B]

I don't think it is the lens as the lens isn't all that bad, I am thinking it might be a focus error issue, possibly back focus or front focus. I would like to see some test shots of something like a paling fence shot at a 45 deg angle and a mark on the fence that your focus point has focused on. Use the 50mm end and the widest aperture of f5.6 (to get the narrowest depth of field) and then focus on the mark on the fence with the central focus indicator. Stand, or better still use a tripod, about 3 feet away and take the photo. If you stand, make sure you have a decent shutter speed of at least 1/125sec to avoid camera shake. Look at the result and see if the mark you have focused on is sharp. Try it a few times to make sure you have done it correctly.

Now, if the mark on the fence is not sharp, but a point in front of the mark (front focus issue) or a point behind the mark (back focus issue) then you have a focus issue with the camera. Some of the K10D has been known to have a few focus issues and hence why the subsequent upper level Pentax cameras (and indeed Canons and Nikons) like the K20D, K-7 and K-5 have focus adjustment feature which allows for the fine tune of the focus point for various lenses. It is not necesarily an issue with the camera as such, but that lenses and cameras are built within a range of acceptability for QC purposes. The problem arises when the camera may have been manufactured at one end of the acceptable QC range and the lens at the other end and therefore the two never reallt match up and the focus is off a tad. When I had a K10D it had a focus issue with 3 of my 16 lenses and I needed to manually focus them for critical focusing. No big deal, as I was aware of it and I could adjcut for it.

As I wrote this first part above, you have abviously posted another post above. The issue with zooms sometimes is that they can be sharp at one focal length and have no BF (back focus) or FF (front focus) issue, but at the other end of the zoom range they can have a BF or FF issue. This may be what you are experiencing with your lens.

Also, at the wide end, and at distant subject matter where there is little contrast, the camera may have difficulty focusing on something and therefore misfocus, especially on "slower" type lenses. By slower, I mean their maximum aperture is not large like an f2.8 or f1.4 lens. Your Sigma is and f3.5 at the wide end and this is not consuidered a fast lens and may have difficulty focusing on distant low contrast scenes. Contrast is needed to assist the auto focus system to lock onto a target correctly and if it doesn't you may get misfocus.

When using a longer focal length like the 50mm end, you are generally enlarging the subject matter and therefore mau have a better target to AF onto.

Were you using single AF point or multiple auto AF points?

I am not saying that this is what is wrong with your camera/lens combo, just that you need to test it to see if that is what you are experiencing. I hope this helps and that you get to the bottom of your problem. If you wre in Sydney, I would be more than happy to assist you in finding out what the problem is, but alas you're in Seymour, Victoria. :(