[Bui]

Probably it's an useless question, because it is subjective, but still I want to ask. I'm wondering whether I should send my DA 20-40 for some inspection and reparation, because it's slightly decentered, and not super sharp. I don't pixel peep and I did not buy this lens for tack tack sharp photos, but would be quite disappointing if it's lower than average standard. Last weekend when I had some free times, I did a quick comparison between it and the new kit zoom 16-50 RE, and purely sharpness speaking, I don't see any advantage from the limited, that's why the question

I attach here 3 photos from the test, please let me know your personal opinion e.g. is this acceptable for this lens?

- 23mm: 23mm | Duc Hien | Flickr
- 30mm: 30mm | Duc Hien | Flickr
- 40mm: 40mm | Duc Hien | Flickr

All photos are taken at f/5.6, my favourite aperture using this lens. Granted. this is nothing like an ideal test scenario you might say, because the scene is not flat at all. But it was the best position I could find close to my place, and also we can consider this real life photos? I used tripod with focus peaking via Live View. Focus point is on the house at the center of the scene. Problem that concerns me:

- The right border of all photos are more blurry than the left
- The 23mm is ok but 30mm is less sharp, and 40mm is much less sharp

Thank you.

[ZombieArmy]

Pictures look plenty sharp to me. Just remember this lens has severe field curvature.

[Desperado]

Backlight causes some low resolution at the top of the mountain,other than that everything seems ok to me.

[BigMackCam]

As @ZombieArmy says, the HD DA20-40 exhibits fierce field curvature... one member here described it as "runway style", and I think that's a good description. As you move further away from the centre of an image, the distance in perfect focus moves nearer to the camera at quite an alarming rate (look at the foliage on both left and right edges of your photos and the areas in best focus are closest to the camera). And this is even the case if you stop down considerably, though of course it's less of an issue then. As such, if you're not absolutely perpendicular to your subject, that can give the effect of one side being softer than the other.

Looking at your photos, I can sort of see why you think the right side is softer than the left (I see a small difference, I think), but at the sizes provided, these aren't by any means conclusive. If I were you, I would switch to Live View and move the focus point to the far left, focus on whatever is there, and see how sharp that part of the image looks. Then, move the focus point to the far right, focus, and see how sharp that part of the image looks. If left and right are similarly sharp, the lens is probably fine.

I have a love-hate relationship with the HD DA20-40 because of the field curvature. For some time - a couple of years, maybe - it sat on my shelf unused because of my early experiences with it. Recently, I've been forcing myself to use it and it's growing on me - but it depends very much on the subject matter as to how satisfied I am with the results. It's not suited to landscape shots if edge-to-edge sharpness is required... but where the subject is mostly within the centre of the frame, it can produce fantastic images. As a photographer, it's up to me to understand the lens' characteristics and get the best from them...

[superdave]

Probably it's an useless question, because it is subjective, but still I want to ask. I'm wondering whether I should send my DA 20-40 for some inspection and reparation, because it's slightly decentered, and not super sharp. I don't pixel peep and I did not buy this lens for tack tack sharp photos, but would be quite disappointing if it's lower than average standard. Last weekend when I had some free times, I did a quick comparison between it and the new kit zoom 16-50 RE, and purely sharpness speaking, I don't see any advantage from the limited, that's why the question

I attach here 3 photos from the test, please let me know your personal opinion e.g. is this acceptable for this lens?

- 23mm: 23mm | Duc Hien | Flickr
- 30mm: 30mm | Duc Hien | Flickr
- 40mm: 40mm | Duc Hien | Flickr

All photos are taken at f/5.6, my favourite aperture using this lens. Granted. this is nothing like an ideal test scenario you might say, because the scene is not flat at all. But it was the best position I could find close to my place, and also we can consider this real life photos? I used tripod with focus peaking via Live View. Focus point is on the house at the center of the scene. Problem that concerns me:

- The right border of all photos are more blurry than the left
- The 23mm is ok but 30mm is less sharp, and 40mm is much less sharp

Thank you.

I owned two copies of this lens and I was also annoyed by blurry edges, especially at 40mm. I do not have the lens anymore but something you can try is to focus somewhere between the center and the sides to see if edges become sharp, for example on one of the vertical third line. This is how I am doing with 11-18 which also have blurry sides if I focus on the center. Please tell us it this focusing trick work with 20-40 and produce sharp edges.

In regard to center sharpness, 20-40 is good but not excellent, this is normal I think. However it has a very pleasant bokeh and impressive flare resistance.

[caliscouser]

I think people already nailed it.
- Slightly low contrast due to the lighting conditions
- Non-symmetric scene making it difficult to be conclusive.
- Runway filed curvature at the long end.

I spent a lot of time experimenting at 40mm with the runway field curvature.
If you want edge to edge sharpness you have to focus further into the scene, or focus midway between the edge and the center.

In this case at 40mm I would shoot F/8. Focus on the house first, take a shot. Turn the focus manually a little towards infinity, take a shot. Repeat. Go a little bit past infinity if you want.

Then review the images. You'll see a sweet spot where there is a balance between center and edge sharpness.

Focus on the edges of the scene and you'll see this lens is capable of good edge sharpness if you can juggle the field curvature.

[richard_b]

As other has mentioned this lens has very noticeable field curvature, especially at the long end. I do like the lens for its control of flare and the contrast it delivers. My personal workaround is focus deeper in the shot than I might otherwise do with other lenses.

[Crooski]

Hello I have the 20-40 mm myself and the lens is very sharp especially in the center, At f / 5.6 and higher edges are almost as sharp as the center

With the stone wall test I have seen almost no field curvature

[BigMackCam]

Hello I have the 20-40 mm myself and the lens is very sharp especially in the center, At f / 5.6 and higher edges are almost as sharp as the center

With the stone wall test I have seen almost no field curvature

At close range, field curvature isn't an issue - hence why the test charts look good. But focus the 20-40 at long distance (using the centre focus point), and look at the left and right hand sides of your image. You'll see that distance of sharpest focus at the sides is much, much closer to the camera than the centre. It's particularly noticeable at the long end, and even stopping down won't eradicate it...

[Madaboutpix]

As other has mentioned this lens has very noticeable field curvature, especially at the long end. (...) My personal workaround is to focus deeper in the shot than I might otherwise do with other lenses.

Don't own the DA20-40, but my understanding is that at close-to-medium distances your workaround would be counterproductive, as it would cause the corners to fall out of the depth of field. To improve, at least to some extent, soft borders/edges due to field curvature, the lens would have to be focussed a little closer than you normally would for best centre sharpness. Unless it has a wavy type of field curvature, which is not as straightforward to deal with.

[BigMackCam]

Don't own the DA20-40, but my understanding is that at close-to-medium distances your workaround would be counterproductive, as it would cause the corners to fall out of the depth of field. To improve, at least to some extent, soft borders/edges due to field curvature, the lens would have to be focussed a little closer than you normally would for best centre sharpness. Unless it has a wavy type of field curvature, which is not as straightforward to deal with.

The style of field curvature on the 20-40 is rather like a rubber band tethered to each side of the lens. As the middle of the band - the centre focus point - increases in distance from the camera, the ends at each side hang on for dear life but don't want to let go As such, no matter how far away you focus, the borders are in focus at a much closer distance. At 40mm, focusing into the distance, it can be very noticeable depending on the scene and composition. In a flat field scene, for best edge to edge sharpness, you can focus on something a bit further away... which means the centre won't be optimally sharp, but the borders will be better than they otherwise would be. But, frankly, I find it best to simply accept the characteristics of the lens, use it to its strengths, and live with the limitations imposed by field curvature. In a similar way, plenty of folks get great photos with the DA18-135 at the long end, where performance away from the frame centre is lacklustre. They're just using the lens to its strengths...

[Madaboutpix]

In a flat field scene, for best edge to edge sharpness, you can focus on something a bit further away... which means the centre won't be optimally sharp, but the borders will be better than they otherwise would be.

Hm, then my error in reasoning was that I didn't account for the effect that the strength of the field curvature increases with the centre-point focussing distance, or did I just get it totally wrong?

Does the beloved but notoriously tricky DA15 behave in a similar fashion, that is, would I have to focus a little deeper into the scene to get, say, the evenest sharpness across the facade of a building squarely in front of me? And would it be a better strategy to use an out-of-centre focus point in such a case?

[Bui]

Thank you for your comments, guess I will have to perform deeper test, but I think from your first impression, looks like it's not so bad, so I might save hundreds of dollars :-)

[BigMackCam]

Hm, then my error in reasoning was that I didn't account for the effect that the strength of the field curvature increases with the centre-point focussing distance, or did I just get it totally wrong?

Correct. Or, at least, that's been my experience and perception - especially towards the long end. It's pretty unusual, and one of the reasons why I don't consider it the "stack of primes" replacement for the DA21 / 35 / 40 Limited that some folks believe it to be (not saying they're wrong... it's just that my personal opinion differs).

Does the beloved but notoriously tricky DA15 behave in a similar fashion, that is, would I have to focus a little deeper into the scene to get, say, the evenest sharpness across the facade of a building squarely in front of me? And would it be a better strategy to use an out-of-centre focus point in such a case?

I haven't shot the DA15 in enough situations to say, I'm afraid. I've heard about the field curvature on this lens, but haven't noticed it in the shots I've taken, since most of them have involved centre (or near centre) of frame subjects at quite close range. Right now, the DA15 is a shelf queen in my collection... heresy, I know, but I'll get round to shooting it more, just as with the 20-40 That said, for any lens with "runway style" field curvature, the method of focusing the centre somewhat beyond the desired distance will bring the borders into better focus. There's some trial and error necessary, of course...

[Madaboutpix]

Correct. Or, at least, that's been my experience and perception - especially towards the long end. It's pretty unusual, and one of the reasons why I don't consider it the "stack of primes" replacement for the DA21 / 35 / 40 Limited that some folks believe it to be (not saying they're wrong... it's just that my personal opinion differs).

Thanks for taking the time to answer, Mike, since I was genuinely puzzled. Also acts as some sort of confirmation that, with the DA35 Macro already in my kit, a limited budget, and a soft spot for primes, it is probably the HD21 that I want to close the moderate-wideangle gap, and not so much the HD20-40.

I haven't shot the DA15 in enough situations to say, I'm afraid. I've heard about the field curvature on this lens, but haven't noticed it in the shots I've taken, since most of them have involved centre (or near centre) of frame subjects at quite close range. Right now, the DA15 is a shelf queen in my collection... heresy, I know, but I'll get round to shooting it more, just as with the 20-40 That said, for any lens with "runway style" field curvature, the method of focusing the centre somewhat beyond the desired distance will bring the borders into better focus. There's some trial and error necessary, of course...

Don't intend to hijack this thread, but maybe some more extensive DA15 users want to chip in to share their field curvature perceptions and workarounds about this lens ...?