I have a 70mm ltd DA f2.4 Pentax lens which I have been using for 6 months now so it is still under guarantee. I recently meticulously cleaned the front and rear glass only to find a bubble in each lens. I am not an experienced photographer so it is difficult to tell if this has had an effect on my images in any way. If there is an effect it certainly is not obvious to me in the images I have taken. Mainly Street scenes, cropped landscapes or portrait and I am happy with the results.

I first noticed the bubble in the front glass and after a bit of research I found out that a bubble wouldn't have any effect on my images so all things considered the inconvenience of going to Pentax, the replacement might be worse etc, I decided to stick with it. Now I have discovered a bubble in the rear glass also. I am a bit annoyed. This is advertised as a high quality lens made to high tolerances and yet there are faults not in one lens but two.

Should I go to Pentax and see if they will replace it or should I keep it as the lens, in my limited experience, seems to perform as it should.

Any comments on this would be much appreciated.

Kiwao

One of the reasons I thought that I was getting inconsistent focusing was because of what I read in the link below. Even though its is a different lens it could still be relevant.

link

In good conditions my 50mm lens in centre point focusing is much more consistent than this 70mm lens. My point is that when I read the Pentax bumph about how these ltd lenses are built to a higher standard with specially selected materials I do not expect the barrel to have a sloppy fit. It's poorly made and should be replaced. I took it back to Pentax and even though the technician agreed that it had too much play. They would not replace it because it is a month old. So now they have it and will try to fix it.

So while they have that lens I've reverted to using my 50mm lens which love using anyway.

Mike

Thanks for your comments. i am concerned because I have had my camera lens checked by Pentax and after backfucusing adjustments and the second time front focusing adjustments and thirdly told it's ok. The focusing is inconsistant - sometimes it's incredibly sharp and others soft and not centered. Settings the same of course. f2.4,iso 100 ,good day light, center point. Could excessive play cause this inconsistency?

Mike

I recently purchased a DA 70mm ltd lens and have noticed that there is play in the barrel ever though it only extends a short distance it is noticeable both side to side and forward and back. Much more than my 50mm lens. Is this normal. As this lens is supposed to be of a high build quality I think not. If some of you owners of this lens could tell how your lens is it would be much appreciated.

Mike

Thanks again for your comment.
I sat for hours waiting for that fish to pop up. I took a photo of a fountain and found a fish in the shot. Funny how just as your about to push the button something gets in the shot but as you say it is sharp for a distant moving object .

So I conclude that I shouldn't compensate for the cameras tendency to underexpose in post processing but should set the camera's ev value to +.5 or even +1 =less noise and posturization.

Your comments have all been useful. Thanks again.

Mike

Here are 100% crops of these images. One has been adjusted sharpening etc but no noise adjustment. No adjustment to the other except for the Lightroom default adjustments, as correctly pointed out by the previous poster, this image has noise.
[IMG]http://i266.photobucket.com/albums/ii271/kiwao/IMGP5686-1crop.jpg[/IMG]
[IMG]http://i266.photobucket.com/albums/ii271/kiwao/IMGP5695-1crop.jpg[/IMG]
Thanks again for all your comments.

Mike

Thanks again for your input. Re the above 2 images converted from raw to png, one raw to jpg. As for the pasturization theory oops posturization I think this is mainly the problem. Most of my images are under exposed and I have to adjust in processing but the problem with this theory is as I have said before these images have no processing except for the conversion from raw to png or the third one which from raw to jpg. Infact I checked the histogram for these images. The first one is under exposed and the others are 1/500 of a second bright sunny day blown highlights exposed. I will see what happens if I increase the ev value in camera.
Here are 2 more complete images. One again is unprocessed f2.4,1/2000,daylight setting. and the other is processed f6.7, 1/350,daylight setting which I found surprisingly fishy. Both taken in the same conditions.
[IMG]http://i266.photobucket.com/albums/ii271/kiwao/IMGP5695-1.jpg[/IMG]
[IMG]http://i266.photobucket.com/albums/ii271/kiwao/IMGP5686-1.jpg[/IMG]

Thanks again for all the comments

Mike

I am enjoying the comments than you very much. When I bought the da 70mm lens after I noticed that the images were out of focus which was so annoying as this lens is supposed to be pro quality according to some reviews and also for me it was expensive. So over the last month I have had my camera/lens back and forth to Pentax for front and back focusing problems. They say it is ok. So now I am inspecting every last thing in my images. May be I am seeing things that aren't there. I 'll upload complete images later and you can see for yourselves

I uploaded the images from lightroom as unprocessed images cropped at 100%. As for underexposure I thought in raw mode the camera is set so the image is underexposed to prevent blown highlights I think?. My images tend to be atleast .5 underexposed so do you think it would be ok to dial in +.5 or is it better adjust when processing.

Thanks again for your comments.

Mike

Thank for your replies. It seems that I cannot tell the difference between Bokeh and noise although the third image seems a little speckley in the background to me. Lightroom always recognises these areas as noise with its little warning triangle next to the luminous noise slider. But it does get fooled by fine details sometimes.

Anyway it is good to get the opinion of experienced photographers. Thanks again.

Mike

I am getting noise in my images shot at iso 100. These are shot with da70mm ltd lens in good daylight with k10d set in raw mode. Is this normal? Here are some cropped images.

[IMG]http://i266.photobucket.com/albums/ii271/kiwao/IMGP4536.png[/IMG]
[IMG]http://i266.photobucket.com/albums/ii271/kiwao/IMGP5854.png[/IMG]
[IMG]http://i266.photobucket.com/albums/ii271/kiwao/IMGP5852.png[/IMG]

Thanks

Mike