Bigging up the DA17-70

I'm liking this lens more and more and thought it was about time there was a thread in which its praises could be sung (I know I'm not the only Forum Member to rate it). Maybe it's because it's relatively new (and a lot more expensive) but it just doesn't seem to have attracted the plaudits that the DA16-45 has.

Optically it's only down side is the barrel distortion, which as Richard Day pointed out in another thread, leads to you losing more than just 1mm on the 16-45 after you've corrected. Images are detailed. Colour rendition's great. The bokeh's good. Wide performance is more than decent. And contrary to early reports I read, I've found the long performance to be excellent. See eg. link & link. Both these shots were taken wide open at 70mm and at high ISOs (800 + 400 - accidentally in the case of the first), and are minimally cropped.

It's also much better built than the 16-45 - a pleasingly solid hunk of glass.

And I'm sure mine is improving with age. The results I'm getting now seem to be better than when I first started using it earlier this year. Can this be possible? Could the climatic conditions here in Colombo have affected the alignment of optics slightly? I did quick tests on it when I got it, and it was fine - but maybe I should check again, to see if it really has improved.

The other alternative is that my ability to get the most out of it has increased. Hey, that would be nice!

I have been putting bids on a few listed on Ebay lately as I quite fancy having a look at one .. they seem to be fetching arounf £250/260 on there which is quite reasonable imo. Not managed to bag one yet though.

Given the current RRP - that would be a snip. Good luck!

I was just on Photozone.de where I also paid a quick look visit at the price comparison page. I am not interested in this lens but it certainly caught my attention being advertised at 349 DKR (40-50£). It's obviously a mistake so no chance to get it at that price. I did order 5, though

Having had a 16-45 for several years, initially on my istD, then K10D and then my current K20D, I have a real soft spot for this lens as I think that at it's current new price (which is about the same I paid for mine a few years ago! :shock it's a gem in the range. But I found the 45mm long end a limitation as I was cropping a lot of my shots taken at 45mm and that didn't help the quality that much! But overall I'm happy that I made the change to a DA 17-70.

I agree with Mhuni about the DA 17-70, if you get a good one , it's an excellent performer through it's whole range, but I have to be honest, my first one was a very poor copy and I "personally" know of quite a few that were similar and that would make me very wary of buying a s/h one unless I had the chance to test it beforehand. In fact this actually applies to any s/h lens unless I personally know its history, or the seller guarantees complete satisfaction.

At the current new pricing, I would now think twice about paying the extra £200+ for it over the 16-45, but it is a better built lens with a much more useful range and excellent bokeh.

I agree, the DA 17-70 is excellent and as you say the only downside is the barrel distortion (more than my previous Sigma 17-70).

what sets it apart for the also excellent Sigma 17-70 is colour rendition/contrast - the Pentax just produces nicer looking images

simon

Richard, I'd be interested to know how yours and your acquaintances' bad copies underperformed. From what you're saying there seem to be real QC issues with this lens. Is this right?

Also, I've been meaning to ask you - what do you do in-store to check a lens? Given that I have to buy lenses in/from countries where I'm not resident (have yet to come across a Pentax lens in Addis or Colombo), this would be a very useful skill for me to acquire!

Agree with your point about prices - is the 17-70 worth so much more than the 16-45? Probably not. I'm glad I got mine before the (double?) price rise and with the £50 cashback!

Basically they were very soft, especially at the long end, and also the AF was seriously out all over the place, i.e. back focus at one focal length, to front focus at the other and not being able to reach infinity, they were so bad you could see it quite easily even below x11 on the review screen, some were so out of alignment the AF struggled to achieve focus lock at all!

I will say that this seemed to have been the case with some early samples. I believe that later units are pretty consistent, but even so a rogue one can appear. It's usually down to transit knocks that can cause things to go out of alignment. I actually find it amazing that they can survive the transit knocks that they're subjected to before we get them!

My testing methods. They are not desperately technical, but I think they are valid and more than accurate enough for most purposes.

The following applies using a K20D or K-7, much harder to do with a body that doesn't have individual lens AF adjustment (in fact, pretty near impossible! I won't buy a DSLR now without individual lens AF adjustments).

What I do to quickly check is firstly to mount the camera on a tripod and use 2 sec delay for mirror lock up and take a shot wide open at the longest focal length on an object that would fill the screen at x11 magnification that contains considerable detail, such as a sign or a car number plate. I do all the checks using x11 magnification on the review screen (on a K20D), which equates to approx full size.

I would check for front and back focus by adjusting the lens AF adjustment from -10 to +10 to find the sharpest setting, hopefully around the center (0) setting. I don't actually like using an angled focus chart as I have found them to give inconsistent results.

I would then check again with a close object and a more distant object to check that the setting remains constant, if not, I would probably reject the lens. If it's okay, I would repeat the test at two or three other focal lengths to see if the focus adjustment stays constant. Again, if not, I would reject the lens.

I will then take a shot of a fairly flat plane object at a reasonable distance, like the front of a flat building, and examine for equal sharpness fall off across the frame, if one or two corners, or an edge, is worse than the other(s), then that indicates an alignment problem. I would recheck at medium and close distances and if there is unequal softness, I would reject the lens.

This building is a familiar sight to anyone who visits SRS!




I would do all my tests in daylight and at ISO 100.

If I do my tests at home, I sometimes use a newspaper for medium to long focus lenses that should have fairly flat field charicteristics for close tests, I do not use this for wide angle lenses, as they tend to have greater field curvature and at such close distances you're almost guaranteed to get large fall off in sharpness across the frame, but I do expect a wide angle lens to have reasonable sharpness across the frame at distances beyond 2 to 3 metres. It's vital that you ensure that your camera is perfectly aligned at right angles to avoid errors. This is a typical shot (taken at 70mm focal length).




For longer distances I use the following building in Gloucester docks. I'm sure you could find something similar.

For example at 60mm.




and at 250mm.




I hope this helps and gives you some guidelines to work with. Don't be too exacting, you can live with small inconsistencies as nothing is absolutely perfect, but usually a lens that has a serious issue in one area, will have problems elsewhere as well. It's usually quite clearly obvious when a lens is not up to the mark.

Thanks a lot for the detailed description Richard. Blimey, that sounds like a lot to do at the shop - but I guess it's worth it if you know you're going away with a decent lens.

Do you take your own tripod or does SRS provide one for you - I'm sure they'd be amenable!

The 17-70mm range of my Sigma has surprised me very positively. It has well suited for an all-round lens more than I expected (though I'd fancy a 18-105/125mm with same apertures more).

So excitement about the lens build up, but as time goes by I'm getting more and more annoyed with the poor performance of the lens. I seem to be miss focusing very often. I will do a proper statistical assessment of my pics, but this is the felling I'm getting...

I just got back from the US, took many pictures on the run, so not much checking (screen on K10D isn't great for that). I was gutted upon checking the results...

It is a pitty because when it does focus this lens is great...
Maybe I should have gone with the Pentax 17-70mm???

Actually it doesn't take that long to do a few quick tests. A poor lens usually shows up pretty quickly, it's very rare that a lens has only one weakness, faults usually manifest themselves in lots of areas.

I usually take my own kit as I try not to overstretch my welcome, or their patience!

Very interesting reading....

I have to admit, I've been thinking about buying a 17-70 for a while - a really handy range over the kit lens - one for next year certainly.

BUT....I'm still in two minds between Sigma and Pentax.

The cost difference is fairly significant, and between them they are better in different areas.

Sigma is faster wide open and at 70mm only looses out a tiny bit to the pentax - in terms of which is the fastest overall lens - that goes to Sigma; more handy for low light shooting.

Then there's the build quality - major plus point to Pentax, with (quasi) weather sealing and SDM - though the Sigma seems to focus faster.

The Sigma has a much closer minumum focus distance which does intrests me, but I've always preffered colour rendition on Pentax lenses - though a few tweaks in PP can address that.

AARRGGHH I'm still not sure which way to go. I'm not concerned about having a bad copy of the Pentax version - I think Richard is right in saying early models were a tad poorer and it seems to have been sorted now.

I think I need convincing that the Pentax version is really worth the price difference and also I know I have a really good copy of my 18-55 MKII...my heads still in a mess strying to figure out what to do I guess.

Bob

My choices, in order, with no price limitation plus some of my own observations, would be as follows.

DA 17-70, Now much too expensive, but a very nice lens overall and well made, SDM AF only and is not that fast, but very positive.

DA 16-45, The bargain in the Pentax range, great IQ wide open and the best of all at the wide end. Wobbly zoom barrel, but fast AF.

DA*16-50, Ridiculous price now, relatively weak at the wide end compared to it's stellar peformance from 24mm and above. WS, but is large and heavy and the zoom ring is very narrow (and too close to the body) in comparison to the focus ring.

Tamron 17-50, Reasonable range, very sharp, well priced and constant f2.8, no quick shift, somewhat muddy muted colours and evidence of severe field curvature at the wide end, also reports of sample variation with regard to focussing accuracy.

Sigma 17-70, For - range, price and f2.8 at the wide end that's useful if you're really stuck for light. Against - Sigma quality (?), no quick shift, warm and slightly muted colour, soft edges, reverse focusing direction to Pentax and Tamron lenses.

If I was to consider cost then it would be:

DA 16-45
DA 17-70 (just!)
Tamron 17-50
Sigma 17-70
DA*16-50

Others opinions will definitely vary!

Richard - really useful information there! I'm suprised the 16-45 comes out leaps and bounds ahead of the 16-50, (but it's a good thing!!) and considering their price at the moment...hmmmm....food for thought!!!!!

I don't think Richard is saying that the 16-50 is optically inferior to the others, though he wasn't very impressed by the wide-open performance. Above 24mm he describes it as stellar.

The 16-50's problem is the price. You have to really need the weather-sealing and large aperture to justify such a huge premium over the 16-45.

G