[Jdurock]

Good evening Pentaxians,

I am considering the purchase of a used copy of the subject lens, but after comparing images to my Tamron 17-50 f2.8 at similar apertures I am at a bit of a loss. The resulting images that I was getting from the Pentax seemed all over the place (soft in the center and sharp on the edge then vice versa) and this may have been a result of the focus, but I am not sure.

The following images (100% Crop) were both taken from the same spot at 1/60 sec, f4 - ISO 100. Hand held with K3. There may have been a slight adjustment in focus as the results seem quite different.

Image 1 Center

Image 1 Edge


Image 2 Center

Image 2 Edge


The details in the foreground car tire are very good in image 2, but the edge of image 2 is fairly soft. Vice versa for image 1 as the details in the tire are less but the edges are fairly sharp for the lens being wide open. I also found the images of the Tamron to be over all sharper, but of course its not quite as wide and its bigger and heaver and is not quite as elegant!

Because of these results I am not sure if its worth while to purchase the limited lens or just stick with the Tamron for use as my main landscape lens. It seems that this lens is praised by so many, but I really couldn't take it out of the store in order to test it better, so I am not sure what to do.

Can anyone help me decide please!

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Last edited by Jdurock; 01-17-2017 at 08:25 PM.

[MadMathMind]

You can't expect much of a 15mm lens wide open. UWAs that are sharp corner to corner are extremely expensive and large. The DA15 is neither. You really need to stop it down to f/8 for it to start to be ok on the corners. f/11 and f/16 are really where it's good. This is the nature of UWAs. They are at their best when stopped down a lot. Then they do really cool things.

But it looks like you've got the sharpening WAAAY too high in any case. Those are some pretty wild artifacts you're seeing. Definitely looks like extreme over sharpening to me rather than anything else.

[Jdurock]

Here is F8 (1/50, ISO 200) at the edge, so as you can see from image 1, it actually looks better at f4.

[COLOR="Silver"]

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---------- Post added 01-17-2017 at 10:17 PM ----------

To the left of the Boston Pizza, right at the edge of the frame there is a Starbucks and in the F8 image I can barley make out the Starbucks sign (kinda like a long blob), but in my F4 and F5.6 image they are significantly clearer.

[rrstuff]

What you are seeing is a field curvature. DA15 has a strong field curvature, and this is actually quite useful for a 'grand landscape' style shots. The field curvature allows things that are both near, and far to be in focus in a specific, and very popular style of a shot. Take a look at one of my shots with DA15 that takes advantage of this effect: Death Valley, Badwater basin by Jerzy Szablowski - Photo 173892023 / 500px
This is F6.3, but it's pretty sharp throughout, because the scene roughly matches the curvature of the focal plane. I think these kinds of shots is what Da15 excels at.

What DA15 is not well suited for are pictures of flat things at a distance, when you expect sharp corners, for example a shot of the city from top of the skyscraper, or a nightscape of a city skyline. It is possible, but you will have to focus at a hyperfocal, not infinity, and stop down the lens.


I think you will find this helpful:
Tim Ashley Photography | Field Curvature - a Layman's Guide (or How to Focus a 'Tricky' Lens)

[Jdurock]

I will definitely have to look at Tim Ashley's site, thank you for the reference. I figured there was some field curvature, but I just wasn't sure.

[Lowell Goudge]

In looking at the posts I would question how focus was achieved, there could be an issue of inconsistent focusing depending upon selection of focus points and what the subject actually was that you are using for the focus target. Note that focus sensors are not infinitely small, and may not always interpret the scene and on jet to focus on the same way you do

I also note that 1/60 is not perhaps fast enough depending upon the enlargement ratio.

You need to remember that the rule of thumb of 1/fl for shutter speed is by taking a full frame image printing it on an 8 X 10 sheet. A zoom in at an extreme magnification ratio exposes flaws, because the definition of acceptably sharp was based upon a point being no bigger than 1/100 of an inch on the 8x10 with our ability to pixel peep we enlarge much more than that today, and need to consider the rules again.

[DeadJohn]

Your samples show a focus difference. #1 looks focused for the edge while #2 for the center. I can't tell whether the lens has a problem or not from those samples.

The DA15 is a special Pentax lens. It has great contrast and colors, plus legendary flare resistance. Sharpness is not it's strong point; photos are acceptably sharp but not when you start pixel peeping at 1:1 resolution.

Focusing can be tricky because any 15mm lens gives a lot of depth of field. The photo might look in focus, then you turn the focusing ring and it still looks in focus.

To the left of the Boston Pizza, right at the edge of the frame there is a Starbucks and in the F8 image I can barley make out the Starbucks sign (kinda like a long blob), but in my F4 and F5.6 image they are significantly clearer.

How did you focus? At f8, if the lens is focused at infinity things as close as 5 feet away should look in focus.

[Jdurock]

The focus was on the center of the frame, but I was not sure if it was focused to infinity for the f8 shot or not. Since the car in the center of the frame was more than 5ft away I would assume it was at infinity but I am not sure.

I also had one other quick question I wanted to ask. When manually focusing form close to infinity with the copy of the lens I was testing there seemed to be a slight resistance (almost as if something was resisting the focus action). When focusing from infinity to close the focus felt smoother but not so much in the other direction. Is this normal? I thought that it might be the quick shift focusing system, but as this is my first limited I wasn't sure and the sales man couldn't confirm this was an issue or not.

I really appreciate all your feedback!

[rrstuff]

The focus was on the center of the frame, but I was not sure if it was focused to infinity for the f8 shot or not. Since the car in the center of the frame was more than 5ft away I would assume it was at infinity but I am not sure.

I also had one other quick question I wanted to ask. When manually focusing form close to infinity with the copy of the lens I was testing there seemed to be a slight resistance (almost as if something was resisting the focus action). When focusing from infinity to close the focus felt smoother but not so much in the other direction. Is this normal? I thought that it might be the quick shift focusing system, but as this is my first limited I wasn't sure and the sales man couldn't confirm this was an issue or not.

I really appreciate all your feedback!

As in it 'catches' a little at one end? But only sometimes?
That's exactly how it is with mine and it's been fine for the past 1.5 years of (extensive) use.

[Jdurock]

by 'catches' do you mean it feels a bit rough in one direction sometimes?

[rrstuff]

by 'catches' do you mean it feels a bit rough in one direction sometimes?

Over a short distance towards the end of the scale, there is a slightly higher amount of force required to move it, and it feels rougher over that short distance.

[Jdurock]

Interesting!

[pakinjapan]

I think you will find this helpful:
Tim Ashley Photography | Field Curvature - a Layman's Guide (or How to Focus a 'Tricky' Lens)

I just switch to K-3 and notice this when using DA15 as well. While most people say what cause this but very few offer a possible way to fix it. The article on you link is the only one (as of what I have found) give me a very good possible way to fix it. Thank you a lot.

One thing I accidentally find out is; for cityscape shooting, if I stop down to around f11, live-view zoom to 100% at about 1/4 portion of the lower left corner of the image and make sure that part is in focus, the overall final image will look good.
But for the same setting, if I make sure center part of the image is sharp / in focus (which is what I usually do on my old K5- and have no problem with the end result.), corner sharpness on K-3 will be terrible.

The article said; try it the other way around, focus wide open first then stop down and shoot.
The question is, Stop down to what f number will offer the best result for DA15?
I will find it out hopefully this weekend.

[rrstuff]

I just switch to K-3 and notice this when using DA15 as well. While most people say what cause this but very few offer a way to fix it. The article on you link is the only one (as of what I have found) give me a direction of a possible fix. Thank you a lot.

One thing I accidentally find out is; for cityscape shooting, if I stop down to around f11, live-view zoom to 100% at about 1/4 portion of the lower left corner of the image and make sure that part is in focus, the overall final image will look good.
But for the same setting, if I make sure center part of the image is sharp / in focus (which is what I usually do on my old K5- and have no problem with the end result.), corner sharpness on K-3 will be terrible.

The article said; try it the other way around, focus wide open first then stop down.
The question is, Stop down to what f number can give the best result for DA15?
I will find it out hopefully this weekend.

What I tend to do is to choose a corner focus point and it generally looks good for the landscape shots. I typically do between F6.3 in low light to F11 in good light.

F11: Against some odds - Death Valley by Jerzy Szablowski - Photo 173864937 / 500px
F9: Diagonal, Badwater Basin by Jerzy Szablowski - Photo 174200343 / 500px
F7.1: Malibu Creek by Jerzy Szablowski - Photo 192206947 / 500px

All done using a corner AF point. A shot at F6.3 is in the message above.

[pakinjapan]

What I tend to do is to choose a corner focus point and it generally looks good for the landscape shots. I typically do between F6.3 in low light to F11 in good light.

F11: Against some odds - Death Valley by Jerzy Szablowski - Photo 173864937 / 500px
F9: Diagonal, Badwater Basin by Jerzy Szablowski - Photo 174200343 / 500px
F7.1: Malibu Creek by Jerzy Szablowski - Photo 192206947 / 500px

All done using a corner AF point. A shot at F6.3 is in the message above.

@rrstuff , thank for the tips