DA* 50-135 comparison

I know received wisdom says that a lens with an enormous zoom range is often not optically marvellous, but what are you basing this assertion on, John?

What I see in the images in front of me.

What I perceive as a slightly lower degree of quality that would be magnified somewhat by the time it became an A3 print, which would be my requirement for a lens.

What do you see?

Well looking at the crops of the bottles, say for the 18-200 and the 18-55, I'm not seeing a significant difference in sharpness.

And going back to the bunnies at F5.6, I don't think it's at all obvious that one is sharper than the other (once they've been made much more nearly equal in saturation and contrast).

So I'm not clear exactly what you mean by "degree of quality".

It's not conclusive because the resolution of our screens is not sufficient and also our monitors probably differ anyway.

"Quality" is also a subjective term, but I mean it as a summing up of sharpness, resolution, bokeh, contrast and all the other optical properties into a summation that is pleasing to the eye.

There is a difference though in the images, and it is marked at wide open aperture or near to wide open aperture but becomes more difficult to spot at smaller apertures.

When I did similar tests I used maps to photograph - lots of fine detail - and I made my conclusions from A3 prints. The results were interesting but they did fall into line with expectation. But stopped down, the differnce between the 18-55mm and 16-45mm lenses was not appreciated by many viewers, and they certainly would not have paid the extra for the better lens. Had they bought it after taking quite correct advice they would have been very disappointed that nothing miraculous happened to their photography.

Lens testing like this is just intersting vut not conclusive, but the real test os whether or not our lenses produce images that fulfill our expectations.

I was afraid you'd say this. With all the differences in equipment and perception from one person to another, it becomes very hard for the less experienced such as myself to tune into to what it is that the more experienced are actually talking about.

Let me press you a little, if I may.

Which of these pictures do you this was made with the better lens, in terms of the characteristics you mentioned above, and why? Please don't look at the EXIF, nor at the earlier pictures on the thread - nor at the filenames !!





Edit: sorry, I've rephrased the question slightly.

OK, not the easisest of tasks, but I'll have a go.

There's a problem with the point of focus because I'm not convinced that it's in the same place for the two shots, but have a look at the "hairs" top right against the blue background. Also look at the reproduction of the catchlight in the eye. Look at the sharpness of the detail just beyond the eye.

Although neither lens shows any more information than the other, the right hand picture reproduces it with slightly more crispness. I am assuming that this is not because the contrast has been tweaked, but just taking it at face value that both images are unretouched.

Rather you than me!

Dan

Well.

The first of these is based on Amoringello's IGP6624.jpg - the Pentax 18-55 at F5.6.

The second of the two, the one you say is crisper, is his IGP6620.jpg, the Sigma 18-200 at F5.6, unchanged by me.

In the originals he showed us, the picture from the Pentax lens (ie the first one here) was extremely dark in comparison, making it very difficult to compare the two.

So I tweaked the brightness, contrast and saturation, only of the Pentax shot, until it looked as nearly the same as I could make it without spending hours on the task. I didn't apply any sharpening to either, of course.

As you say, I think the focus points are different, which makes it very difficult to compare, and hence a test of only limited usefulness.

Personally, I think the only thing that can be concluded from the test shots is that it's not at all obvious that the Pentax is the better lens.

Thanks for doing the comparison!

Not a problem, but please remember that we know that the Pentax 18-55mm wide open is fairly soft and that the picture changes dramatically by f8.

If you really wanted to see what the comparison is between lenses then I do have prints, but I'm not sure where you are located, so offering to meet and discuss may not be an option.

I'm tempted to suggest that we have a lens meeting at the ADAPS clubroom in Atherton, Manchester. There were no takers when we tried a PU event with model and presentations all day, but I could do an evening meeting with perhaps and hour presentation followed by discussion.

We would have to put something into the club funds to cover use of the rooms, but my time would be the right price - free.

Does anybody think this would be a good idea?

One thing I have to say is I'm surprised my photography hasn't improved!
I spent all this money on the lens and I haven't had one offer to buy my stuff. Argh! Fuzzy bunnies and oil&vinegar are very popular photos, are they not?

Anyway...
I do find the DA* lens fantastic to work with, as far as silent focusing and water resistance are concerned. And when stopped down a stop or so, its results are much better than wide open at f/2.8.

Here are two more images to consider. Again aperture is all the way open at f/2.8. The vignetting is MUCH better at F/4.0, but I have not been able to go back to re-take the reflections photo at another f-stop.
I'll have to try to reproduce here and see what effect there is.

I don't know how this might compare to other lenses, I just happen to be out shooting during my lunch hour and noticed the effects when I got home.

Vignette, f/2.8 1/1000 sec, 135mm



Reflections, f/2.8, 1/5 sec, 50mm
Note the reflections of the lamp posts

Maybe the focusing is silent because it isn't doing any....

I am very surprised that there is so much vignetting wide open.

Q: Did you have the lens hood on, and is it any better with it off?

This is a DA* lens after all. Makes me wonder whether I actually want one. Chris (SRS) says his are on their way from Belgium and I've pre-ordered one, but . . . I'm not sure I like this. What's the point of owning an expensive lens if its not good wide open?

Q: What focal length was this image taken at?

If it's there at f2.8, it'll still be there at smaller apertures, but to a lesser extent.

Vignetting was taken at 135mm. It is much less at 50mm (that seems backwards to me), or if you stop down a bit. Hood makes no difference.

This is what we should expect. Wide angle (relatively) lenses that take their light from a wider field need larger front elements to gather that light evenly. That's a sort of botched explabnation, but think how much the relatively long barrel of the lens will shade that light compared to at the telephoto end where there is a straight view right gown the lens barrel. So to speak.

There's much more to a lens than the figures will tell you, and pictures of dark streets and teddy bears won't tell you much more.

I'd prefer to judge a lens on the basis of portraits (skin tones) and outdoor pictures in sunshine.

G