DAs Versus Kit

Nathan - thank you for that link it has helped me understand why I love my 35mm f2 so much.

Mike

It helped me not loosing hope on my 50 f1.4, and 31 f1.8, and 100mm macro that all need some minimal adjustment, and I can look forward to buying the K7 that (like the K20) should have lens focus adjustment....

Can't wait!!

That's the only feature of the K20 that would make me change from my K10 and as things aren't too bad anyway I'll not change anytime soon (I and my bank balance and wife hope)

Mike

I am beginning to lose the will to live here!

I am satisfied that the focus is not out. Both the kit lens at 35mm and the DA at 35mm were on auto-focus for these shots. If one is out, would the other not be? The phase detection focus unit is in the body, after all, not in the lens.

I have shot the pix again and taken great care over the focus settings. Also some real world shots at 100%. My personal feeling is that there is nothing wrong with the 15mm, this being wide open. And look at the distortion free drawing. The 35DA is wide open at f2.8 to show it at its worst. This looks like a good lens to me.

I note doing these tests, how different the same picture taken on different occasions can look due, I suppose to light,contrast and colour temperature variations.

Results here are (in order)
Ruler, auto focus centred at 2 inches mark, DA35, f2.8. I have not posted the manual focus result as it is absolutely identical.
Centre at 100% da15 f4
Centre at 100% da35 f4
Real world pic of neighbour's house, da 15 f4 at 100% near centre
Real world pic of neighbour's house, da 35 2.8 at 100% near centre
These pix are without sharpening, dng straight to jpg, minimum compression.

I think what is upsetting people here is not that the DAs are bad but how good the kit lens is!

For the little it's worth I think Nathan's article quite probably covers your experiences. Regarding the kit lens - every lens I have bought has been substantially better than the kit lens I had.

Mike

[quote:3496ace15f="lemmy"]I am beginning to lose the will to live here!

I am satisfied that the focus is not out. Both the kit lens at 35mm and the DA at 35mm were on auto-focus for these shots. If one is out, would the other not be? The phase detection focus unit is in the body, after all, not in the lens. ""

OH MY GOD ARE YOU KIDDING ME?

And you are the one that's beginning to loose the will to live???

So you're saying that if 1 lens focuses correctly on your body (which you still haven't said what body it is) then ANY OTHER LENS MUST BE FOCUSSING CORRECTLY AS WELL???????

Seriously now, you do understand that every lens is different, has completely different design, number of elements, distance from one component to the other, and distance from the focussing screen and sensor. How can you even think that each lens will behave in the same way???

and NO i'm sorry, but as good as the kit lens might be, it is NOT better than ANY prime lens in the pentax range - IF - you have a correct focus of the lens on your body. THe pictures from the 15mm are horrible, and the lack of distorsion is nothing special at all, considering that many zooms are just as good.

Forcefully put but I think I agree with Nathan.

Mike

passionately i would say.

I am italian, and I apologise for the "loudness" of my post.

I'll chip in and and say I agree with Nathan, it looks to me that your camera's focus is off on the Primes, the 15mm being worst..... sorry

the camera in question is a gx10,

The kit (18-55mm) lens is highly variable and some have had dire ones, some rather good ones. I am lucky that my Mk 1 kit lens seems to be in the latter category.

Having said that, your primes should be much sweeter than the photographs you have posted.

Kris

Are you sure? I suppose it depends on the size of sample you take, but we've had four Mk I and two Mk II and they have all been good, pretty much indistinguishable in performance. The Mk II versions are slightly better, but we expect that.

"Real world pic of neighbour's house, da 15 f4 at 100% near centre"

This one looks really poor..... It must improve quite a bit on stopping down?

I can't see there being a focus problem with these due to the depth of field on 15mm and 35mm lenses.

When testing lenses like this it's essential to repeat each shot 4-6 times re-focusing for each shot and then pick the best out of the group. Usually at least one will have severe camera shake/ focus problems.

If I get a bad result I go back and re-test to try and better the poor result. If I can't I know there weren't any errors in the test and the lens is at fault.

Very often superior lenses don't actually show any improvement in the actual photograph. This used to be the case with film where up to about 140 LPM could be recorded, but only about 90 LPM was possible on a B&W print. Superior lenses have much better control over aberrations.

shim

I'm sorry to upset you Nathan. I'll take the pictures down if you wish, no problem.

Shim, the picture was taken on a tripod, mirror up dekayed action at 1/1500th or so and fired with the Pentax remote.

So Greytop, what you're saying is that my camera focusses correctly with the kit lens but not the primes? And Nathan says that even if one lens focusses correctly on my camera body, another will not necessarily?

When I focus on the 2 inch mark on the ruler (see pic above, made with 35mm) with any lens, if it is sharp on screen, surely it should be on the sensor? If, as Nathan says, each lens will be focussed differently because they are constructed differently, that would mean each lens focussed on screen at the 2 inch ruler mark, might show sharpness at different points, some at 1.8 inches, some at 2.2 inches or whatever in the picture.

As far as I know, DA lenses have no focus calibration so it can only be done on the camera body. Which lens then would I adjust the body to focus with? If they are all different, I suppose it must be calibrated for each lens. Is this possible? Is it reasonable to expect a photographer to do this?

I think that if I see a sharp image on the screen I should expect a sharp image on the picture. If it's out, calibrate it. But it should then focus accurately with all lenses, not just some.

My results, by the way, with the 15mm accord with dpreview's test Here

Lemmy, I am not upset by your pictures, I am upset by your mis-understanding of what i've been trying to explain to you.

FIrst of all, cameras like the K20 have INDIVIDUAL FOCUS ADJUSTMENT FOR EACH LENS. And therefore, yes, as you say, "it is reasonable to expect a photographer to do this"!!!

I did not say that "each lens will be focussed differently because they are constructed differently" I said that EVERY LENS IS DIFFERENT, AND MIGHT BE FOCUSSING DIFFERENTLY. (Please read the article I linked previously)

THe distance between the last element of a lens and the sensor is probably different in every lens you own. Just look at them!! My 100mm Macro's last element is a whole inch inside the body of the lens!

I really wished you understood the physical difference between lenses as REALITY - And then preoccupy yourself with assessing, if your lenses actually have an individual back-focus/front-focus issue, or not. (The answer is YES btw!)