[UncleVanya]

Hum if I understand this right, the DA20-40 would be naively f/2-4 or f/2.8-5.6 to keep the aspect ratio. So even variable apperture zoom do have some corrective elements or the optical formula doesn't allow f/2.

And now that we speak of the f stop displayed, it seem obvious it is just an approximation. There no point to change the actual diaphragm size when going from one focal length to another and I think the eye would suddenly see the difference in light gathering on the view finder.

So I'd really bet there isn't the "great" difference between 34mm and 35mm displayed... Well if we can speak f/3.2 to f/3.5 a great difference... That's look like 1/5 of a stop, nothing really noticable.

My guess on the f/2.8 vs f/2 is that there is some restriction inside the lens that makes 2.8 the max. Much like the DA 35 f/2.4 is not f/2 despite being a similar design to the FA 35 f/2 - there is a mask on the back of the lens that may be restricting from f/2 to f/2.4 on that particular lens.

Minor correction. f/3.2 to f/3.5 is a full 1/3 stop.

[Scorpio71GR]

It is always nice to see folks talk about lenses I don't own and have never used.

Todays lenses are so good, you can get great images from even the kit lenses. You really need to be thinking about "How will this lens fit into my lens lineup?"

I agree with Norm here. Yes the 16-50 is big and heavy. However for me the 20-40 just would not work. Many of my shots with the 16-50 are between the 16-20 range. Therefore I would lose a lot starting at 20mm. I have nothing else in this range except my 10-17 which is a completely different lens. You have to find the lens that best suits your needs. From me that is the 16-50. I rarely shoot wide open but when I do mine is still sharp. I love the idea of owning the 20-40 but I have my trusty 18-135 which rarely leaves a camera body.

Michael

[UncleVanya]

I agree with Norm here. Yes the 16-50 is big and heavy. However for me the 20-40 just would not work. Many of my shots with the 16-50 are between the 16-20 range. Therefore I would lose a lot starting at 20mm. I have nothing else in this range except my 10-17 which is a completely different lens. You have to find the lens that best suits your needs. From me that is the 16-50. I rarely shoot wide open but when I do mine is still sharp. I love the idea of owning the 20-40 but I have my trusty 18-135 which rarely leaves a camera body.

Michael

12-24 in your future?

[Scorpio71GR]

12-24 in your future?

I would love a 12-24, right now it is not in my budget. I have also considered the Tamaron 10-24. The Bigma broke my lens budget for quite awhile.

Michael

[fredralphfred]

I would love a 12-24, right now it is not in my budget. I have also considered the Tamaron 10-24. The Bigma broke my lens budget for quite awhile.

Michael

So what you're really saying is that 50-500 is not enough; you need 16-500?

[Scorpio71GR]

When I carry the 16-50 with the Bigma that is what I have, not bad for just 2 lenses. That 20-40 is a superb lens. If the DC motor focuses as fast as my 18-135 I can only imagine it must be a joy to use. If I ever get tired of carrying around the 16-50 I would definitely get one.

[Tbone51]

I had both. If you need 2.8 throughout and WR in a wide/normal zoom then keep your 16-50. There is no other f2.8 lens in a WR design that is smaller. But if you don't mind the short range and the thought of a variable lens then the 20-40 is a nice compact package. Speaking from my experience, the 20-40 does deliver prime-like images and the build quality is very similar to the DA ltds. I don't find the limited range and variable aperture ever an issue. But I can see where others would. Small lens hood okay but flare is so well controlled and for 2.50 I could get a rubber hood but I don't even think about it. AW vs. WR not sure I have an opinion and neither has been a problem for me but in super harsh weather I could see where the WR might be better. Both of these lenses are widely criticized... mostly by those who don't have them.

I also have both, and they are both great lenses. 16mm is nice for some shots (architecture, landscape), but the small size and beauty of the limited, along with its clarity, make my K5 + limited combination almost as compact as a mirrorless system (but with better photos).

[Pål Jensen]

It is a little odd. Wide aperture zoom lenses don't have the best flare characteristics. But most photographers wouldn't shoot them stopped down to f22 either. At that point, you would have considerable diffraction softening and if it makes flare worse, then it doesn't make sense. Sweet spot for the 16-50 is in the f4 to f8 range.

It is same problem at "normal" apertures. This is my car interior shot for another forum to show how light leather seats looks after half a million kilometres! Note the flare.

[mark88]

I think that is horrible. All the haze in the image are out of focus flare. Less lucky with the placement of the sun and the result would have been much worse.
Below I have stopped the lens down to F:22 to show how what the reduced contrast at "normal" aperture really is...

https://www.pentaxforums.com/forums/attachments/10-pentax-slr-lens-discussion...o-_igp0774.jpg

this is a very dirty lens or a very dirty cheap filter in front of a 16-50.
my has never done this also at f22 in full sunlight.