Kit 18-55 > F/16, soft?

Hi All,

Quick question - I've recently returned from holiday where I spent a lot of time shooting landscapes (sea, cliffs, rocks etc). As I wanted everything in focus I (perhaps mistakenly) set the aperture quite small (f/16 to f/20). This was in bright sunshine so shutter speed wasn't an issue. Focal lengths vary across the range 18-55. Instead of sharpness the resultant images are all very soft. I only seem to notice this issue when using the kit 18-55 SMC DAL and only when pushing it beyond f/16. Photos taken around f/11 are (mostly) all pin sharp.

My 55-300 DA (despite being at the budget end of the market) is superb and I can't fault it in any way. Likewise, I haven't noticed similar problems with my 35mm f/2.4.

I know the kit lens is supposedly better than the competitions kit lenses but - in my case, is it more likely user error or just noticing the limitations of the 18-55 compared to my other/better lenses?

I have searched but seem to see mixed opinions ... so thought it worth asking here


Steve

Quality lenses (such as macro lenses) have no problem closing after F16, but kit and 'travel zooms' have this problem. After F8-F11 the quality suffers a lot.
Most of the lenses have a sweet spot between F5.6 and F8, where they can achieve the maximum resolution.
Here is an example chart that shows that after F8 the resolution decreases.

It would really be worth posting some pictures for us to see.

MTF graphs are fine but often dont tell the whole story and the ones aren't particularly woeful. If your other lenses are performing well in the same circumstances then I suspect there may be another issue.

Thanks for the comments - I'll try to find some typical examples and upload.


Steve

Although you will get better results between about F6.3 and F11 with the kit lens, I have used mine at F16 for landscape shots where longer exposures are required and the images are sharp. It may be that your copy of the lens is not quite as good as some.

Also, are you using a tripod? The softness might be due to camera movement rather than the lens.

Regards
David

A couple of years ago I did some test on most of my lenses. Your experience at tiny apertures mirrors what I found. very soft at such settings indeed.

I know others will protest otherwise and there may be revision or sample variations in quality but I've never liked the performance of the kit lens.

But kit lens arguments aside, really you shouldn't really need to use such small apertures anyway to get everything in focus for landscapes

here's an online DOF calculator

http://www.dofmaster.com/dofjs.html

For example at f/8.0 you can get everything in focus from 4 feet to infinity with an 18mm focal length. Hyperfocal distance 6.7 feet

There may be sample variation in any lens batch, but we should expect that all the Pentax lenses will deliver good images. Our kit lenses (we have had five of these so far) have all been very consistent as it happens and have all produced pleasing results. They have been best at about f11, which is pretty much what I would expect from low cost but well made zooms.

Poorer zoom lenses will continue to improve all the way to minimum aperture, but this is as the errors in assembly get covered up by increased depth of focus at the sensor. In other words, they never reach acceptable standards.

Really good lenses should peak at just one or two stops down, and the comparitive test on CSC lenses in the new AP (out tomorrow) actually shows this very well. Sadly no Pentax lenses in that test though.

A theoretically perfect lens should peak at wide open aperture, thereafter being diffraction limited, but this never happens as there's no perfection in lens making.

Diffraction is the issue at smaller apertures. Light 'spreads' a little when it goes around an edge. The smaller the aperture the more significant this effect. Because this is an issue related to actual rather than relative aperture, it becomes more significant with smaller sensor cameras, as the absolute aperture size is considerably smaller Thus at 18mm F16 gives an aperture size of just over 1mm.

(this incidentally, is why it is so utterly pointless putting 16 MP chips in compact cameras - the actual resolving power of even the best 1/2.33 sensor cameras is around 2-3 MP)

Thanks again for the comments. Playing with the DOF calculator (suggested by Smeggypants!) I see I massively over(under?)-estimated aperture size.

I try to ensure shutter speed is adequate for focal length used and the images don't show any obvious sign of camera shake - however this may be a contributing factor (in addition to poor choice of aperture and lens softness at chosen aperture).

I can't currently upload photos as I'm away from home. However, I think I can say that whilst the lens may not be perfect, in this instance my poor results are primarily due to inexperience.

I think I'll print some DOF charts as reminders for future photography trips rather than relying on application of general rules and 'gut instinct'...

Steve

There are various smartphone apps that will do DOF calculations for any lens on any format, which can be quite useful. With static subjects I tend to be lazy these days and just "bracket" by shooting at several apertures. Generally I am a great fan of f8!

I'm a great fan of narrow DOF pics so tend to shoot at widest aperture for most things.

When I got a slr 30 years ago lenses all had distance and DOF scales. I had not used a slr for at least 10 years after it broke and last year I got a K-R with the DAL 18-55. The first or second time I used it I was shooting the America's Cup in Plymouth from the shore and I used an old Tamron AD2 80-210. I found these scales invaluable. Since then I have got a DA 55-300 and although it has distance scales - no DOF scale. Is this a thing of the past.

Mostly yes.

DOF scales were found and still are found on some prime lenses. They were also found on some zoom lenses, although this could be quite messy looking. These days zoom lenses don't move about in a linear fashion anyway, so DOF scales may not be possible.