[audiobomber]

It'll be wifey lens, who did resist to upgrade to dSLR idea first, than convinced by the 18-250mm superglued to a Pentax body idea , just like her current dZLR.

From you samples I start thinking to get one for myself too, then I saw certain PP corrections in some extend they are like sharpening by high pass filter tecnique.. Is that true? Which camera did you use with this pictures I wondered, good combo.

I normally leave the 18-250 on my K100D Super and use it like a big p&s. There are a few in that file taken with the K20D, the rest with the K100DS. The photos have had some mild touchups in Picasa, including a bit of sharpening for downsizing. I find with the 18-250 photos look best with Bright Image Tone, to punch up the colours.

[Class A]

Tamron & Pentax 18-250 - different coatings?: Pentax SLR Talk Forum: Digital Photography Review

Thanks for digging that one up.
While this seems evidence that supports different coatings (notice that the poster himself isn't quite sure) it could also be that the coatings differ from copy to copy to that degree or were changed for both Tamron and Pentax versions at some point.

I don't want to cling on the "they are absolutely the same" hypothesis against evidence to the contrary, but I don't think we've seen enough of the picture to be certain either way.

Did you read the entire thread you linked, or just the title?

The entire thread. There were posters who didn't see a change (god knows what they did) but there also ones who observed effects of a correction. See the post by Greg Vaughan. The latter thought the effects weren't as strong as they thought they should have been but clearly you could see some correction being applied. So far, I haven't seen an example for correction with the Pentax version. Would be interesting to see if the degree of correction were any different.

The 18-250 wide end has more vignetting at f3.5 and 4 than any lens I've ever seen, and CA is certainly present at times.

Note that the K-7 doesn't correct vignetting.
While the in-camera correction is convenient, for ultimate results I'd do it in manual PP anyhow. From what I've seen, the K-7 corrections are quite conservative, i.e., they don't go all the way, probably to avoid overcorrection if the lens tolerances head in the wrong direction.

Distortion wouldn't vary much if any between properly performing copies, but it does vary by scene and FL. How do you correct for distortion? I don't have a program that will do it.

The (Laboratory) software that came with your camera will correct for distortion. Also other free software such as RawTherapee (works with JPGs as well) can do it.

[audiobomber]

I don't want to cling on the "they are absolutely the same" hypothesis against evidence to the contrary, but I don't think we've seen enough of the picture to be certain either way.

I'm OK with saying that the coatings don't matter, same or not.

So far, I haven't seen an example for correction with the Pentax version. Would be interesting to see if the degree of correction were any different.

The "corrections" in the Tamron 18-250 photo were insignificant. The same test with a 17-70 showed a clear difference. But there's definitely a missing piece. We don't yet know what a K-7 or K-x will do with a Pentax 18-250. Pentax does say that all DA lenses receive correction.

Note that the K-7 doesn't correct vignetting.

Thanks for pointing that out. That's disappointing, they really missed the boat there.

The (Laboratory) software that came with your camera will correct for distortion. Also other free software such as RawTherapee (works with JPGs as well) can do it.

I've tried to use the PPL software and didn't see any result. Maybe I didn't use it correctly.

[Jasvox]

I use Lightroom for processing of my favorite takes. It has a dandy little vignetting correction feature I have had to use a handful of times...but not normally a problem if you get used to the lens, knowing what it can and cant do regarding vignetting.

Regarding any distortion correction, this lens or any other, try Gimp...I believe they have the same distortion correction as CS2/3/4

At the end of the day, you may want to think more about the benefits rather than the distractions concerning this lens. A good copy will yield very nice results when used properly...many many benefits to using this lens, especially when on the road or wanting a "do it all" lens choice for certain situations. I like my copy very very much, but when I am shooting really important shot, not just in general, I use my Tamron 17-50/2.8 or a few primes....in which this lens replaces none of them.


Jason

[Class A]

The "corrections" in the Tamron 18-250 photo were insignificant.

Maybe, but there are corrections applied. Seems unlikely that the lens isn't supposed to be corrected but some small corrections take place nevertheless. If the lens isn't supported, there should be no corrections at all. It is possible that the corrections taking place are accidentally, however that seems unlikely. We really need to see a test with the Pentax version of the lens. Puzzles me a bit that no one seems to have tried that yet.

I've tried to use the PPL software and didn't see any result. Maybe I didn't use it correctly.

In the version I have (v3.51), you have to specifically activate that under "Lens aberration correction | Distortion correction". You have to manually input an "angle of view" for vignetting compensation which strikes me as being odd since the software has access to the focal length used.

[audiobomber]

Tamron 18-250 & K7 - lens correction: Pentax SLR Talk Forum: Digital Photography Review

I am convinced that the DA 18-250 benefits from lens corrections and the Tamron 18-250 does not. The camera looks like it's doing something to the Tamron, but the results show no improvement, whereas the posted DA photo shows a clear benefit.

OTOH lens correction is not the awesome feature I had hoped for. It only works on jpegs and it trades off camera processing time for computer processing time. If you shoot jpeg or raw+, that's OK, but you may miss the next shot during the second the camera needs to correct the jpeg; nice for landscapes, not for sports.

PS, why did this thread show up in my User Profile today, as though there had been a new post? My cookies have been whacky on this site for several weeks.

[Class A]

I am convinced that the DA 18-250 benefits from lens corrections and the Tamron 18-250 does not.

How come?

In the thread you provided a link to, Greg Vaughan says

I can take two pictures in a row with the K7 and the Tamron 18-250 and verify that the camera does indeed alter the picture with the lens correction on. However, it does so very subtly, and I have to superimpose the pictures to verify that anything has happened at all (obviously not nearly enough to actually correct the distortion).

Bruce Norikane states that his K-x corrects distortion of his Pentax DA 18-250 but I don't think the images he posted represent very convincing support that the correction goes beyond what Greg described as subtle changes.

When I look at them, I'd say that the very small effect is compatible with Greg's comment ("However, it does so very subtly, and I have to superimpose the pictures to verify that anything has happened at all ").

I've downloaded the large versions Bruce's images and cropped them so that they have comparable content. The comparison is still not straightforward since the camera angle changed during the shots. The difference in distortion is small. I see the upper edge of the piece of furniture is less bend in the corrected version but then it is also less near the edge of the frame.

At 18mm, the barrel distortion is quite high and a corrected image should show some pronounced "moving backwards" of the image centre when compared to the original. I don't see that happening in Bruce's "corrected" image. I think that

1. Bruce's images don't demonstrate that an appropriate amount of distortion correction is applied for the Pentax version, and
2. the amount of correction observable with a Tamron could be at the same level

So I don't think we've learned anything new and conclusive from the thread you referred to.

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Last edited by Class A; 12-17-2009 at 07:48 PM.

[cbaytan]

So I don't think we've learned anything new and conclusive from the thread you referred to.

Isn't anybody is in touch with one of the either company guys who can supply the god damn true information to us? That would be a great deal!! and a great favor!! of loyal Pentaxians isn't it?

[audiobomber]

In the thread you provided a link to, Greg Vaughan says
"I have to superimpose the pictures to verify that anything has happened at all (obviously not nearly enough to actually correct the distortion)."

We've discussed this one previously. I thought we'd agreed that the changes were insignificant, which seems to agree with the poster's view.

Bruce Norikane says:
"Kx w/Pentax DA 18-250 - no correction"

??? Bruce said "I don't have a K7, but I checked my Kx, and it corrects for distortion with the Pentax 18-250."

In fact he's the one who posted the before and after photos.

How come?

Here's why I'm convinced. I saw Tamron photos that showed no discernible improvement, and I saw in this thread a clear a reduction in distortion using a Pentax lens. The top shelf of the fireplace mantle and the leg on the left in the photo were straightened to a significant and readily noticeable degree. The other leg was not straightened, which is why I said it didn't go all the way. To which Bruce replied "It's not a great test subject. The 2x4 post on the right is curved in real life, and the white plastic shelf is slanted." So it wasn't straightened all the way because it is bent in real life. I wish he'd photographed a doorway instead. It's so bloody easy to get huge distortion from that lens.

[LeDave]

I'd get the Pentax just because it can be used on the K-7 and K-x for chromatic aberrations and distortion corrections.

[Eds]

I have the Pentax version. Considering its range, I think it takes great pictures. I keep it on my K-10 most all of the time as a quick and easy back up for my K-7. On travel, if I really need to go light, I'll put it on the K-7 and use my D-Lux 3 as a back up. Great all around lense. Can't imagine that the Tamron version is much different. Eds

[audiobomber]

I have the Pentax version. Considering its range, I think it takes great pictures. I keep it on my K-10 most all of the time as a quick and easy back up for my K-7. On travel, if I really need to go light, I'll put it on the K-7 and use my D-Lux 3 as a back up. Great all around lense. Can't imagine that the Tamron version is much different. Eds

Possibly the best superzoom ever. I think it's a clear concensus that the Tamron and Pentax 18-250's take equally great pictures because they're the same lens. But what we're debating is whether the K-7 and K-x lens correction features (CA and distortion correction) are applied to both the Pentax and Tamron versions of the 18-250mm. It would be great if you could post a photo to show that the Pentax 18-250 does benefit from corrections. Maybe someone else will come along and do the same test with a Tamron.

[audiobomber]

I'd get the Pentax just because it can be used on the K-7 and K-x for chromatic aberrations and distortion corrections.

LOL! I guess you didn't read the rest of the thread.

[Class A]

Bruce said "I don't have a K7, but I checked my Kx, and it corrects for distortion with the Pentax 18-250."

True. And I thought in his later post he said "Kx w/Pentax DA 18-250 - no correction" but the "no correction" part was just the heading for the image that followed. Sorry about that. I'll edit my post.

In fact he's the one who posted the before and after photos.

Yes, but they are not completely convincing, are they?

The top shelf of the fireplace mantle and the leg on the left in the photo were straightened to a significant and readily noticeable degree.

But as I've written because the framing is different between the two shots, the top shelf ends up nearer the edge of the image in the non-corrected version, which in itself would increase the curvature.
As I have written in my previous post, I believe a true distortion correction should be more visible and that the changes we see in Bruce's "before/after" images could well be described as "insignificant" and only noticeable if you superimpose the images by someone who does not inspect them very carefully.

Isn't anybody is in touch with one of the either company guys who can supply the god damn true information to us?

Amen.
I also wonder why there's seems to be no LBA victim who has both lenses and a K-7/x. Soon this lens will be such a classic that you'd really want both Pentax and Tamron versions.

[audiobomber]

New thread with more convincing photos. DA 18-250 mm Distortion and CA Correction w/K-7 (pics): Pentax SLR Talk Forum: Digital Photography Review

Also a statement that indicates the Tamron allows corrections to be selected, but does not correct the image. Re: DA 18-250 mm Distortion and CA Correction w/K-7 (pics): Pentax SLR Talk Forum: Digital Photography Review