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09-02-2007, 07:04 PM   #31
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QuoteOriginally posted by GaryML Quote
Many lenses, especially longer telephotos, are made with the capability of focusing beyond infinity. One reason is that changes in temperature will shift the infinity focus point as glass, metal and plastic expand and contract.

My old Pentax M* 300mm f/4 provided considerable movement past the marked infinity focus. This was by design. I recall that older versions of the Pentax lens instruction booklets mentioned this feature with the M* lens and certain A* lenses. Sometimes the infinity mark is marked on the barrel as a range. For example, my Sigma APO 100-300mm f/4 EX DG has a marked infinity range of about 5 mm (indicated with a square bracket). My DA* 50-135mm allows focus well past the marked infinity (and past the true infinity focus as far as I can tell). I think this is how the lens is designed. I seem to recall that my DA 16-45mm f/4 would also turn past infinity.
I spent most of the afternoon taking test sequences manually focused
to see what I saw. If I used an F/2.8 setting and manually focused either clear against the stop or with the 'oo' centered, it did and does make some difference in the focus. Unfortunately, I was unable to tell where the correct focus was suppose to be because of another problem.

Specifically, what I found was that the left side of the photo would be in good focus while the right side would be out of focus. My photo subject was a hedge row 50 feet or so away which I was photographing square on.

The results seemed to be slightly better on the right when backed away from the mechanical stop leading me to predict that the 'beyond infiniity' syndrome is stronger on the right than on the left---in my case the left side of the photo was deemed by me to be in focus with both settings.

For a control is took a couple of photos using an FA24-90 and it was the same both left and right.

The issue was not discernible at f/5.6, and in an apples to oranges test
because I wasn't thinking ahead---- the 16-50 seemed to have more clarity through out the photo than the FA24-90 did, but unfortunately, I used the fa24-90 at f/4.0

I'm going to do some more analysis on mine and see if I can't fence the issue in a little tighter.

I've never quite figured out what Klaus was talking about when he said on his example the focus was 'off center'. It is unclear to me whether that
is the same as what I have described or not.

A cockeyed focal plane is only an issue when the amount of it exceeds the depth of field of the lens.

09-02-2007, 07:36 PM   #32
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Revert to old firmware and do without usm for now

Hi Paul,

This is what I would do in your shoes. Someone has modified the header of an older firmware that will trick the camera into allowing you to downgrade to it. Sorry I don't have a link for you, but try Google searching DPReview.

-Matt
09-02-2007, 09:41 PM   #33
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QuoteOriginally posted by KL Matt Quote
Hi Paul,

This is what I would do in your shoes. Someone has modified the header of an older firmware that will trick the camera into allowing you to downgrade to it. Sorry I don't have a link for you, but try Google searching DPReview.

-Matt
If he is seeing what I am seeing --- apparently a cockeyed focal plane---reverting software won't help. Even manual focusing gets befuddled
with a cockeyed focal plane---because there is no right answer so it screws up.
09-03-2007, 07:00 AM   #34
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Hi again guys,

I have several other lenses that mechanically go past the middle of the oo (infinity) sign - one example is the DA21 for example. However when I focus on a subject that is say almost 1km away the AF goes right to the middle of the oo sign - even though it is physically possible to make it focus further than infinity just like the DA*. The DA* however in the same case - does indeed go past the middle of the oo sign and tries to focus past infinity and this is why all the shots come out bad (remember though it goes past what it is supposed to at all distances with my lens - not just infinity - say if I am focusing on something that's 1m away - the AF will go and stop at 1.2-1.5 meters for example ). None of my other lenses which also mechanically are able to go past infinity do so when using AF on a subject that is at infinity distance - only the DA*16-50.

09-03-2007, 07:11 AM   #35
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Don't have a polarizer on by any chance? One person reported that this can cause problems w/ a lens. Longshot though.
09-03-2007, 08:31 AM   #36
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No - didn't use a polarizer or any other filters - in the thread I linked to in one of my earlier replies on page 2 there are now 5 users of the DA*16-50 in the dpr pentax forum with this problem (inlcuding me) and 1 has just posted that they have the same problem with the DA*50-135. To me it is starting to sound like it is a QC issue that slipped through involving the AF/SDM mechanism of these DA*'s.
09-03-2007, 08:47 AM   #37
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Just was checking. Since it seems like the lens can focus (manually at least) it is more a body/compatabilty issue more so than the lens. AFAIKT it is the body that make the final AF check regardless of the "lens info". Still it is annoying and baffeling at the same time. Could be the final guesstimate is just in the wrong direction. Some logic flaw and seems to pertain to the 1.3 upgrade (or K10 in general)??? Haven't read enough about any others who either "downgraded" their software or are using a k100 ect. Would actually appreciate any tabulation of cameras/firmware ect. Ther are some who don't seem to have any issues. Not thst that helps and usually hinders
Ok so some reports show no problems w/ the old style AF:
Re: Do you have done K10D firmware upgrade to V1.30 for SDM?: Pentax SLR Talk Forum: Digital Photography Review
So it's down to the usm again. Seems it zigs when it should zag. Is it possible to MF and then half press to see if it jumps forward (or backward)? Not sure that would have any meaning but what the heck.

Last edited by jeffkrol; 09-03-2007 at 08:55 AM.
09-03-2007, 11:38 AM   #38
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Yeah it is down to SDM indeed. I am already in contact with Ned-B and am awaiting an email from him - I will let him know of the thread and the fact that people confirm it works fine with AF-screw drive but not with SDM and see what he suggests for this. I still don't think it is a body issue because if the body makes the final decision than it should get all lenses wrong no? SDM is just a means of focusing - instead of screw-drive it simply uses a motor in-lens so I do think it is something to do with the lens itself (maybe I am just trying to be optimistic here since I really don't want to send my body as-well for service along with the lens I have no backup dSLR - We'll see what Ned and Pentax will say to do ).

09-03-2007, 03:53 PM   #39
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QuoteOriginally posted by sft Quote
Yeah it is down to SDM indeed. I am already in contact with Ned-B and am awaiting an email from him - I will let him know of the thread and the fact that people confirm it works fine with AF-screw drive but not with SDM and see what he suggests for this. I still don't think it is a body issue because if the body makes the final decision than it should get all lenses wrong no? SDM is just a means of focusing - instead of screw-drive it simply uses a motor in-lens so I do think it is something to do with the lens itself (maybe I am just trying to be optimistic here since I really don't want to send my body as-well for service along with the lens I have no backup dSLR - We'll see what Ned and Pentax will say to do ).

I haven't made that confirmation (that it works with a screw drive)----but when I get a chance I will investigate---- as I have a istD body I've jumped to to many conclusions already and need to take a deep breath and do some more
investigation....
09-04-2007, 05:25 PM   #40
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I've got the DA* 16-50 as well, have used it a few times and haven't seen the problems that are being reported, but I did a few quick tests last night.

It won't focus past the centre of the infinity sign, manually or AF.

If I AF to infinity, images seem to be fine, but I haven't specifically tested for it, since I don't generally get to use my camera during the day until the weekend.

If I AF on a point, then manually move focus, and re-AF to the same point, it goes back to exactly the same focus point, and is in focus on screen.

I might borrow my girlfriends K100D and try comparing the same shot with SDM vs screw-drive, to see if I can notice any differences. Will compare it vs Tamron 28-75 f2.8 as well.

I did give the lens a difficult job last weekend, shooting a parade on a street in a country town, multiple light sources from spotlights, car headlights, streetlights overhead, with moving targets of the floats in the parade, all shot at ISO 1000-1600 at f2.8. It didn't miss focus any more than any other lens in that situation, most of the missed focus were unavoidable due to moving vehicles, lack of contrast or a light source blinding the AF. I was quite happy with the results.

Are there any other tests that would help to see if this is a bad-copy problem, or a more widespread issue?
09-14-2007, 11:38 AM   #41
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Sice you asked about tests.

seems this lens got scalded one more time. Might as well be the first bearer of bad tidings. I'm sure someone else will post it
Test Pentax DA* 16-50 mm F2.8 AL ED IF SDM - Wstęp - Optyczne.pl
Some comments:
Pentax DA* 16-50 mm F2.8 review: Pentax SLR Talk Forum: Digital Photography Review
But to add a bit of balance as well as some "pretty pictures"
1st samples of DA*16-50 f2.8 x 5img: Pentax SLR Talk Forum: Digital Photography Review
09-14-2007, 02:22 PM   #42
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Hi Jeff,

Yeah I saw those tests - in fact I responded in the thread about the review with samples of my shots to show that the lens is sharp to borders. Also saw Lance's shots - he's got a good copy it seems. My copy is optically fine too - just shame about the AF problems. I am giving the lens to relatives this Monday - they will be returning to the US in about a weeks time or so and they will send the lens to Pentax US in Colorado for me. It is a shame that there are really so many samples of this lens with either AF problems or Optical problems. Not very acceptable for a * caliber lens IMO. On the other hand the DA*50-135 seems to have very few issues compared to the DA*16-50 - I wonder what went wrong with the DA*16-50 and if they just released a whole batch of lenses that were not up to spec maybe?

When you get a good copy - its really quite good as mine is optically.
09-18-2007, 09:51 PM   #43
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Update of sorts

QuoteOriginally posted by sft Quote
Hi Jeff,

Yeah I saw those tests - in fact I responded in the thread about the review with samples of my shots to show that the lens is sharp to borders. Also saw Lance's shots - he's got a good copy it seems. My copy is optically fine too - just shame about the AF problems. I am giving the lens to relatives this Monday - they will be returning to the US in about a weeks time or so and they will send the lens to Pentax US in Colorado for me. It is a shame that there are really so many samples of this lens with either AF problems or Optical problems. Not very acceptable for a * caliber lens IMO. On the other hand the DA*50-135 seems to have very few issues compared to the DA*16-50 - I wonder what went wrong with the DA*16-50 and if they just released a whole batch of lenses that were not up to spec maybe?

When you get a good copy - its really quite good as mine is optically.
Lance did a bit more posting, seems he recovered from the original pixel peeping roast....
It is a nice lens, but I don't need it personally. That isn't saying much though
DA*16-50 f2.8 after a few days use - long post.: Pentax SLR Talk Forum: Digital Photography Review
09-19-2007, 07:08 AM   #44
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QuoteOriginally posted by sft Quote
I do find it interesting that there is quite a bit of difference at the exposures when moving from f/2.8 to a smaller aperture with the DA*. It does seem to underexpose more compared to the other lenses past f/2.8 for some reason. I read this somewhere else too regarding this lens and I can see the difference in exposure in the test shots above when comparing the f/2.8's to the f/4's.
Perhaps this is not the correct forum for the issue I am about to raise, as it might be something to have in the SLR lens review, but here goes.

After reading another thread, specifically discussing exposure variation with K mount lenses on the K10D, I have tested most of my gear to assess the exposure linearity at all f-stops. My process is simple,
- set the apature and let the camera decide the rest. but test at each lens at each apature setting, and also with the exposure set to 1/3 and 1/2 stop increments.
- Meter and shoot off a uniform exposure surface (I use either block walls, sidewalks or road surfaces as my own gray card). I do this because I want the image, regardless of focal length, to be uniform across the entire field of view.
- open the image in a photo editor, (I use PSP but any editor with gray scale histogram will do) and select a small central area of the image (I take about 10%) Note PSP can give gray scale on the selection only,
- using the histogram data, record the average gray scale value in a spread sheet. You may also want to record shutter speed
- Plot the results in a spreadsheet, with F-Stop on the x axis and exposure level on the y axis.

As users, we could develop a set of lens performance curves on different bodies, and add this to the lens review database. You could also, using a specific lens model as a "standard" provide typical exposure accuracy plots for all DSLRs.

If you want to see an impression of the resulting chart look in the SLR lens forum under a thread I started a while ago "changing lens mounts" as I did this test on a K mount lens that I converted to KA mount.

Last edited by Lowell Goudge; 09-19-2007 at 07:17 AM.
09-19-2007, 02:55 PM   #45
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QuoteOriginally posted by Lowell Goudge Quote
Perhaps this is not the correct forum for the issue I am about to raise, as it might be something to have in the SLR lens review, but here goes.

After reading another thread, specifically discussing exposure variation with K mount lenses on the K10D, I have tested most of my gear to assess the exposure linearity at all f-stops. My process is simple,
- set the apature and let the camera decide the rest. but test at each lens at each apature setting, and also with the exposure set to 1/3 and 1/2 stop increments.
- Meter and shoot off a uniform exposure surface (I use either block walls, sidewalks or road surfaces as my own gray card). I do this because I want the image, regardless of focal length, to be uniform across the entire field of view.
- open the image in a photo editor, (I use PSP but any editor with gray scale histogram will do) and select a small central area of the image (I take about 10%) Note PSP can give gray scale on the selection only,
- using the histogram data, record the average gray scale value in a spread sheet. You may also want to record shutter speed
- Plot the results in a spreadsheet, with F-Stop on the x axis and exposure level on the y axis.

As users, we could develop a set of lens performance curves on different bodies, and add this to the lens review database. You could also, using a specific lens model as a "standard" provide typical exposure accuracy plots for all DSLRs.

If you want to see an impression of the resulting chart look in the SLR lens forum under a thread I started a while ago "changing lens mounts" as I did this test on a K mount lens that I converted to KA mount.
I'm curious to see your results.....
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