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02-27-2008, 08:43 PM   #1
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Lens indecision... plus images!

I really have to bite the bullet and get a lens. I find the kit zoom too slow, and sometimes too distorted. I do take pictures of walls and architecture, far more than I take pix of people, animals or flora, so this distortion stuff matters. Correcting in an image editor is time wasted. I also need something fast enough for indoor art events: dance, performance etc.

The 43mm limited is top of my heap, since I think I'll like the focal length. But I also am very fond of the wide end, as my previous post on 28mm as the "perfect normal" would attest. While I'd like to justify a 70 or 77mm, I just don't think I'd need it often.

So, as an experiment I went through the useful shots I took today. Here's one now, Speaker God:


And another with a totally different feel, Lost Childhood:


Then I compiled the focal lengths in order, just for the shots I ended up using: 55, 28, 43, 30, 18, 40, 40, 33, 24, 18, 18, 33, 28, 28.

Grouping them looks something like this:
3x 18
1x 24
3x 28
3x 30-33
3x 40-43
1x 55

This is telling me to get the 43mm, a 28mm and an 18mm. Of course there is no 18 or 28 currently available, and the 21mm is perhaps too slow. So instead I'm being pushed into the 31mm limited I cannot afford. And that still leaves the wide end unanswered.

OK, assuming I go for an older 28mm instead of a 31mm, I can group the focal lengths this way:
3x 18
7x 24-33
4x 40-55

To be complete I'd have to say there were two or three shots I needed something much longer for.

Ignoring my limited lust for a moment, I have to ask myself if I would ever want to be switching lenses that often. I'd have to do so eight times for the sequence I'm analyzing here. Maybe what I need instead is just a better version of the kit, in other words the 16-50mm zoom. That would be an easy decision if it didn't cost as much as two limiteds and weigh as much as three! (Besides, I do not see distortion figures for it anywhere.)

Apparently I am not reaching any conclusions. But at least I got to share a thought process and a couple of photos. Maybe others will find this useful and/or enlightening.

02-27-2008, 10:04 PM   #2
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That's a good approach to figuring out the right primes to buy. I've done it the hard (not to mention slow and expensive) way: buying a lens, trying it out, and selling it again if I thought something else would be better. That's why my 2nd DA21 (I sold one a while back and have been regretting it) is presently on its way from Adorama.

That gives me the combo of DA21 - FA31 - FA77, which I think ought to do it for a while. Maybe until student loans come in and I can pick up a DA14, anyway...

BTW, the 31 is such an amazing lens to use, it could easily take the place of several lenses at the focal lengths you won't be using anymore. How's that for desperate rationalization?
02-27-2008, 10:11 PM   #3
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To be honest, if distortion is your only concern, and resolution is secondary, then nothing will beat the old Zeiss Flektogon 20/4 or 20/2.8. Resolution wise, it's not that far behind from the DA21 (for a good copy that's). This lens is known for its architectural purpose. The "zebra" version of the 20/4 is somewhat better than the 20/2.8 at distortion control while the latter is better at flare control.
02-28-2008, 08:06 AM   #4
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QuoteOriginally posted by aegisphan Quote
To be honest, if distortion is your only concern, and resolution is secondary, then nothing will beat the old Zeiss Flektogon 20/4 or 20/2.8.
I wouldn't say distortion is my only concern, but it is more a concern for me than (apparently) other people. Maybe I just need to get better at correcting it in software.

Isn't the Zeiss Flektogon 20/4 a screw-mount lens? While I might be able to get better at manual focusing, it is difficult with my poor eyes. And with the relatively poor viewfinder on the K100D, which is nothing like what I was used to in film days. But the big inconvenience would be stop-down metering. I have never done that in my life.

To see how I'd like manual focusing I bought an old Auto 28mm. I can simply never get it in focus, but my conclusion is that it is too soft for me. So, resolution is certainly important as well. I can name two things that aren't, so much: flare control and CA.

QuoteOriginally posted by Finn Quote
That's a good approach to figuring out the right primes to buy. I've done it the hard (not to mention slow and expensive) way: buying a lens, trying it out, and selling it again if I thought something else would be better.
That must be fun, but it's not practical in Ireland when everything has to come with extra shipping charges and there is not one store on the whole island that sells Pentax. I keep thinking I should have chosen Canon, there's so much of their gear floating around. But still...ugh!

QuoteOriginally posted by Finn Quote
That gives me the combo of DA21 - FA31 - FA77, which I think ought to do it for a while.
What's it like changing lenses all the time? I have no experience with that, but I'd live in mortal fear of dust. Actually, I had to retouch dust off the images above, and now need to learn how to clean the camera. The built in Shake thingie doesn't seem to do much.

02-28-2008, 10:17 AM   #5
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A plug for DxO

If you want to eliminate the distortion, and your camera body is a K10D, DxO has a plug in for the kit lens. I have just received my update to DxO and am running up a set of sample shots for people to look at.

I should be able to upload some distortion correction shots tomorrow. I think the $100 it cost me was really well worth it.

I don't have either kit lens, but I have the DA* 16-50 and 50-135 lenses. The 16-50 has CA quite badly, and as do all short zooms, has distortion problems. DxO with a check box before processing, simply eliminates the lens flaws.
02-28-2008, 11:07 AM   #6
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QuoteOriginally posted by Canada_Rockies Quote
If you want to eliminate the distortion, and your camera body is a K10D, DxO has a plug in for the kit lens.
I just downloaded and tried PTLens. So far I am liking it a lot. Will try some other images but this looks like a sure thing. Lots easier than making corrections manually. And way more accurate since it has lens data built-in. Also cheap.

OK, maybe now I don't care so much about distortion!
02-28-2008, 11:08 AM   #7
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As I said, the Flektogon resolution is pretty close the DA 21 without the distortion weakness.

I don't have the K100D, but on my K10D, here's how i use my manual lenses. I use wide open to focus until i hear/see the peep/AF confirmation/my prism in line. Then I stop down the lens, press the green button, and fire away. Review the histogram to see any underexposure/overexposure problem to adjust the shutter accordingly. Admittedly, it's not a very fast way to do it, but since architecture is still, so I suggest my method. Though with practice, you can nail it pretty quick also.

Other than that, you might want to try out that DxO alternative since I don't think any other wide end for Pentax platform would have little distortion or good res/distortion performance.

QuoteOriginally posted by rparmar Quote
I wouldn't say distortion is my only concern, but it is more a concern for me than (apparently) other people. Maybe I just need to get better at correcting it in software.

Isn't the Zeiss Flektogon 20/4 a screw-mount lens? While I might be able to get better at manual focusing, it is difficult with my poor eyes. And with the relatively poor viewfinder on the K100D, which is nothing like what I was used to in film days. But the big inconvenience would be stop-down metering. I have never done that in my life.

To see how I'd like manual focusing I bought an old Auto 28mm. I can simply never get it in focus, but my conclusion is that it is too soft for me. So, resolution is certainly important as well. I can name two things that aren't, so much: flare control and CA.



That must be fun, but it's not practical in Ireland when everything has to come with extra shipping charges and there is not one store on the whole island that sells Pentax. I keep thinking I should have chosen Canon, there's so much of their gear floating around. But still...ugh!



What's it like changing lenses all the time? I have no experience with that, but I'd live in mortal fear of dust. Actually, I had to retouch dust off the images above, and now need to learn how to clean the camera. The built in Shake thingie doesn't seem to do much.
02-28-2008, 12:04 PM   #8
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You can fill the wide end with a Sigma 10-20. Rectilinear corrected looks good for this kind of images, as long as you don't use 10mm too often.

02-28-2008, 03:37 PM   #9
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The focal length listing seems like a good way to proceed. I went through three other sessions and tallied those with the one I posted above, so I have a better statistical sample. Here's what I got:

13x 18
3x 20
1x 21
3x 24
8x 28
1x 30
1x 31
2x 33
3x 35
3x 38
3x 40
3x 43
3x 50
3x 55

How to analyze this? The best way may be to see which shots could most likely have been covered by which primes, and then assign a score for how many shots would have been landed.

There were an awful lot of shots at the wide end of the zoom, but I do not remember thinking I was missing too much else. I am sure going down to 16mm would be nice sometimes. I cannot justify the 14mm though, since 18mm is relatively a lot different. So I won't give that a score and won't be able to find a home for half the wide shots. A 20mm might meet my needs for the wide end, but I am really thinking compromising 2mm here might be too much. As suggested, the Sigma 10-20 would open up lots of creative possibilities, but for now I need something faster.

Let's be generous and say a 20 or 21mm is good for half the 18's. Give these lenses a score of 10. A 28mm should be able to handle the 24-33mm region: 15. Let's score the 31mm for 28-35: 15. For the 35mm I'll include the 30-40 range: 13.

The 40mm will include 35-43: 9. For the 43mm I'll score the shots in 38-50mm. It might even have been good for some of the 55mm, but I won't include them. Score: 12. A 50mm would maybe get me 43-50 but only one of the 55s, for a score of 7. Finally, I needed a telephoto for 2 shots. But this is misleading since I am only tallying my best shots... those that required a telephoto would have gotten away!

A summary looks like this, despite the fact there is no current 28mm or 18mm prime:
18mm: 7
20-21mm: 10
28mm: 15
31mm: 15
35mm: 13
40mm: 9
43mm: 12
50mm: 7
telephoto: 2+

For hanging in there with me I give you another image, this my most extreme pseudo-HDR, just because the building called for it.

02-28-2008, 04:00 PM   #10
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Ever considered the Pentax DA 16-45mm f/4? It does cover pretty wide compared to the kit lens. It's cheap, it's sharp and the colour rendition is very nice.

DA 16-45 at 16mm straight from the camera.
02-28-2008, 04:36 PM   #11
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Another one you might want to consider is the Tamron 17-50/2.8. It will be released sometime in March in the Pentax mount for the first time and if the pricing is the same as it is for other mounts, you can pick one up at Beach Camera for $409.

If you don't want to wait for the Tamron, Sigma has the 18-50/2.8 Macro and the 17-70/2.8-4 (not as fast as the constant aperture lenses, but still faster than the kit) lenses available now.

Another wider angle lens that Tamron is supposed to be coming out with is the 10-24/3.5-4.5; I don't know when they're planning on releasing it, but if you need wider than the 16-18mm range, that might be one worth waiting for.

I know you were concerned how slow the 21 is, but if you don't mind carrying around a larger lens, then there's the Sigma 20/1.8 if you need something really fast and AF.

HTH,
Heather
02-28-2008, 08:43 PM   #12
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Thanks for the suggestions. I have researched all these zoom lenses, paying particular note to Photozone. The main thing I don't like about the kit lens (amazing deal for the money, IMO) is that it's not fast enough. I was also wanting to reduce distortion but the software I just tried seems to work miracles in that regard, so that's now not a huge priority. (Still better to not have to correct.)

There are five zoom lenses that compete as upgrades to the kit.

Pentax DA 16-45mm f/4: I like this range and from all reports it is amazingly sharp. But it's not gaining me any speed at the wide end. It's 50% heavier again than the kit, which makes it the lightest of the alternatives. It costs £310, which seems good for the quality. If I lived in Arizona and not Ireland I'd get this in a heartbeat.

The Pentax DA* 16-50mm f/2.8 is not only faster but weather sealed and silent. Countering that it's the biggest of the bunch and the most expensive (£530). Worse yet are the build quality issues, so much so that Photozone refused to review it. Buying via mail, I cannot risk that.

Giving up a little on the wide end yields the Tamron 17-50mm f/2.8 SP AF XR Di-II LD, in the middle of the pack at £260. It is sharp but has higher distortion. The Sigma 17-70mm f/2.8-4.5 seems a bad choice. At the wide end it has worse border resolution than the kit and isn't even constant aperture like the Tamron. The final choice is the Sigma 18-50mm f/2.8 which is a faster plug-in replacement for the kit, with very low distortion and great resolution.

If I'm willing to give up on speed I could extend the choice out further to real all-rounders like the Sigma 18-200mm f/3.5-6.3 DC. It's no heavier and no more expensive. People don't seem to complain about the IQ but I cannot imagine one gets an extra 150mm for nothing. But the glowing reviews of the similar Tamron 18-250mm seem to imply you do!

Conclusions:
* If I want to go fast and gain 1mm: Tamron 17-50mm.
* If I want to extend kit reach with similar quality: Sigma 18-200mm.
* If I want to go as wide as possible with the highest IQ but can stand being one stop slower: Pentax DA 16-45mm.

Seem like reasonable conclusions?
02-28-2008, 11:28 PM   #13
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QuoteOriginally posted by rparmar Quote
Giving up a little on the wide end yields the Tamron 17-50mm f/2.8 SP AF XR Di-II LD, in the middle of the pack at £260. It is sharp but has higher distortion. The Sigma 17-70mm f/2.8-4.5 seems a bad choice. At the wide end it has worse border resolution than the kit and isn't even constant aperture like the Tamron. The final choice is the Sigma 18-50mm f/2.8 which is a faster plug-in replacement for the kit, with very low distortion and great resolution.


Conclusions:
* If I want to go fast and gain 1mm: Tamron 17-50mm.
* If I want to extend kit reach with similar quality: Sigma 18-200mm.
* If I want to go as wide as possible with the highest IQ but can stand being one stop slower: Pentax DA 16-45mm.

Seem like reasonable conclusions?
The Sigma 17-70mm is as sharp or sharper than the 16-45mm, and at f4 it's already better than the Pentax wide open. It also has similar color to the kit 18-55 (as in "very good"), althought it varies with the subject.

I haven't heard very good reports about the 18-50mm. Distortion is the same as the 17-70, and it still has significant vignetting at f8. It is supposed to be sharper (Nikon tests on photozone) but I haven't heard that from any Pentax shooter. Border resolutions is almost the same for both, but the 17-70 handles CA better.

Sigma AF 17-70mm f/2.8-4.5 DC (Nikon) - Review / Lab Test Report
Sigma AF 18-50mm f/2.8 DC EX macro - Review / Lab Test Report

I'm getting so good at defending my own equipment
02-29-2008, 06:22 AM   #14
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Sigma vs. Sigma vs. 16-45mm

QuoteOriginally posted by ricardobeat Quote
I'm getting so good at defending my own equipment
I am glad you posted links to tests for the same system, though they are unfortunately not for Pentax. As Photozone goes to pains to point out in each and every review, you cannot compare lenses across mounts, especially in resolution. I must say though that this site makes it very difficult to cross-compare lenses, even for the same camera. One of the mistakes they make is in changing the scale on the graphs. As I read these tests there is not much to choose between the lenses. The 18-50mm has less resolution at 35mm, more CA and less distortion, but it's not so different that it might matter.

QuoteOriginally posted by ricardobeat Quote
I haven't heard very good reports about the 18-50mm.
To defend this lens (which I do not have), Pop Photo called it "a stellar performer", FredMiranda has an overall rating of 8.2 and Photodo said "highly recommended".

In comparison the 17-70mm got 9.0 at FredMiranda and "good" from Photodo. Though I have not found the same raves for this lens, I agree I should not have dismissed it so quickly. I suppose I'd rather have a constant low aperture than the slightly greater reach, especially considering the similar performance.

QuoteOriginally posted by ricardobeat Quote
The Sigma 17-70mm is as sharp or sharper than the 16-45mm, and at f4 it's already better than the Pentax wide open. It also has similar color to the kit 18-55 (as in "very good"), althought it varies with the subject.
Now on this point I'll have to differ. Comparing the Sigma 17-70 to the Pentax 16-45 it is clear the Sigma has the advantage of larger aperture on the low end, but better resolution? At 16mm the Pentax ranges from 1750-2300 LW/PH from the centre to the extreme borders of the frame. The Sigma has poor performance at the edges in comparison, down to 1100, and nowhere beats the Pentax. Unfortunately the remaining focal lengths compared are not similar, but from 35 up both lenses float in the very good range. What is apparent is how consistent the Pentax is, with better figures wide open.

The Sigma colour may be as good as the Pentax kit, but that's moving the target. Would anyone say it is as good as the Pentax 16-45?

I must say that before this thread I had not payed close enough attention to that lens, turned off by the extra stop. Now I am reconsidering, though there are always confusing dissenting opinions. What's up with dpreview when they say "One clear issue with our sample was extreme softness at the edge of the frame when shooting at wide angle and in portrait format, especially with the lens angled sharply upwards"? Did they just get a bad unit?
02-29-2008, 06:27 AM   #15
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My comments on the DA 16-45 & Sigma 17-70 here:
https://www.pentaxforums.com/forums/186179-post10.html
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