|
Forum: Pentax SLR Lens Discussion
04-11-2010, 12:07 AM
|
| |
Again thanks a lot for this useful information.
As I am obviously dealing with experimented people, could you recommend lenses for such camera with minimum 300mm focal and f4 aperture ?
|
|
Forum: Pentax SLR Lens Discussion
04-10-2010, 01:12 PM
|
| |
| |
|
Forum: Pentax SLR Lens Discussion
04-10-2010, 11:18 AM
|
| |
Hello,
I would like to buy a second hand 300mm f2.8lens for my K20D and got a proposal for the above item.
Will the autofocus and aperture control work with this lens or will I loose some features ?
Many thanks for your help.
|
|
Forum: Pentax DSLR Discussion
06-21-2008, 02:39 AM
|
| |
@Ben_Edict: Thank you very much for your precise review of each picture. Many people just gave general comments on pictures without reference to any particular picture. I agree with most of your explanations, if I stick to the rule about the 18% grey or so.
Having used the K20D for some time know, I would not recommend this camera for "quick shooting", especially for outdoor use.
*) Hardly readable viewfinder indications in highlights
*) No indication of the set light measure method in the viewfinder nor on the LCD screen. When one considers the implication of forgetting to reset it to multi-seg mode...
*) Too many AUTOMATIC modes
*) Useless Liveview mode
*) Multi-seg AUTO mode far from satisfactory (I would expect an AUTO mode to work without applying correction, would I not ?)
*) SPOT meter not convenient to use, setting exposure on the main subject based on 18% gray subject is not enough to get a proper exposure in most situations.
*) With the K20D one needs to apply corrections (or use manual mode) for nearly any single shot. Better not be in a hurry to take a picture.
Sorry for the Pentaxists, but it is not because I own a K20D that I will post only "oh Pentax is the best". This is like I am.
Finally I thanks all of you who spend their time on this instructive thread, that I consider now closed for myself.
Best regards
|
|
Forum: Pentax DSLR Discussion
06-20-2008, 02:06 AM
|
| |
This is the Pentax comment regarding this subject (in French):
Les photos sont certes un peu sous exposées, mais cela reste la consequence de photos qui sont faites dans des conditions extremes en terme de contraste. Les conditions d'eclairage que voud utilisez pour faire ces tests sont tres difficiles pour un capteur ou pour une pellicule. Il faudrait utiliser plutot le bouton memoire d'exposition en association avec la mesure spot. La mesure pondéré peut etre aussi tenté, mais le manuel reste sans doute la meilleur solution.
Il ne faut pas oublier, que la photo necessite aussi du Post traitement, et dans ces conditions extremes, il est presque obligatoire de passer par des logiciels de traitements photographiques, pour obtenir les plus beaux resultats, comme au temps de l'argentiques ou apres le photographe intervenait le devellopeur-retoucheur.
What I understand is that a K20D is not able to properly shoot (in automatic) these kind of "extreme scenes"...
|
|
Forum: Pentax DSLR Discussion
06-04-2008, 05:16 AM
|
| |
Thanks for this very very interesting document. It helps to understand the meter calibration rules. I have put it on my bed-side table !
So I made two other samples of a white sheet of paper shot @ f16 Av mode.
Lunasix indicates 1/500 (17 EV)
1144.jpg: multi-seg, viewfinder indicates 1/250. PhotoMe reports EffectiveLV = 16.3 EV
1145.jpg: spot, viewfinder indicates 1/500. PhotoMe reports EffectiveLV = 17.1 EV
 
In both cases all AEMeteringSegments (PhotoMe) are around 16 EL. I would have expected them to be all around 17, this would be consistent with Lunasix, EffectiveLV (photoMe) for spot measure.
Therefore this shows that multi-seg measure is interpreted by the firmware and the final decision in this case is to over-expose one small EV (this is explained in the PDF documentation referenced). Let us forget the multi-seg measure (EffectiveLV) which is software decision based on undocumented PENTAX logic (or secret) and which is too much scene dependant.
To which calibration corresponds 1145.jpg ? The RGB histogram shows an average around 100/255 in the centre (Gimp). To which reflectance does it correspond ?
As a subsidiary question why are the AEMeteringSegments showing 1 EV less than the actual values ?
I am sure falconeye can answer !
jeffkrol nearly answered my first question above, but which formula to use to convert RGB gray -> % luminance ?
|
|
Forum: Pentax DSLR Discussion
06-02-2008, 08:59 AM
|
| |
@Zewrak: thanks for your review.
I admit that some of the pictures were mistakenly taken in spot mode (the K20D does not remind you in viewfinder, nor on the LCD the meter mode) on a white part of the subject and therefore can explain the underexposure (up to -2 EV).
But 1008.jpg has been shot with multi-seg, not spot meter...
On white sheet of paper, I carried out some tests with K20D @ f4, 100 ISO compared to an OM4 SLR and a Lusanix F light meter
K20D multi seg: 1/500, spot 1/750 (some times 1/500)
OM4 centred weighted: 1/250, spot: 1/250 (spot + highlight compensation 1/60)
Lunasix: 1/500
I know in advance what many of you will say.
According to LV formula the above K20D / Lunasix measure should give around 13 EV
I checked the EXIF data taken with PhotoME that shows a range 12-12.3 EV on each segment, with centre segment 12 EV, but Effective LV is 13.1 EV (shot in multi-seg mode). Effective LV, is consistent with Lunasix measure, but not individual segments values.
@falconeye Is PhotoMe trusted ?
Could some body kindly send me a link to a picture shot on a white sheet of paper, because what I get seems really dark to me (IMGP1143.jpg) ?
 |
|
Forum: Pentax DSLR Discussion
06-01-2008, 11:22 PM
|
| |
@falconeye: thanks for all your very interesting posts, they are very instructive. It will take me some time to review and understand them ! I'll post my comments afterwards.
You are saying that the spot measure would give a different value than the mult-seg on a same uniform frame. If it is so, this spot meter measure is pretty awkward. One will use spot meter to adjust the exposure of his/her subject on a given interest and does not expect to have to compensate, unless this zone of interest is abnormally dark or very bright.
On Olympus (SLR) camera (0M2 spot, OM4), brand which has pioneered the multi-spot measure, this was working perfectly (that is the picture was exposed accordingly to the spot zone). The documentation was complete on the subject (an not 2 tiny pages out of the 280 pages user manual). To cover the above two extremes cases (dark, or bright subjects) there were 2 buttons highlights / shadows that one would presses after taking the spot measure which over / under expose accordingly.
Furthermore the K20D does not indicates anything in the viewfinder (hardly readable in sunlight), nor on the LCD display about which measure mode is set ! That is why I forgot to reset the spot mode to multi-seg mode after use. This makes me say that Pentax has not designed this feature to be used in the field (may be in a lab with a piece of 30% grey cardboard handy...), especially if on top of that, one has to systematically add 1,5 LV on a average subject... Very disappointing !
To my taste K20D comes with too many modes (green mode, Sv, TAv), functions that are good on paper but unusable in the field (Liveview, spot-measure), confusing menu / Fn with again too many functions (especially photo-lab like functions) , too many buttons (AF is even duplicated).
So why did I buy this camera ? I was attracted by: 3/2 format, old PENTAX lens still usable, wireless flash system, spot measure, shake reduction on the sensor itself, sensor dust detection, immediate start-up time.
My next input on this thread will be to investigate whether my camera is faulty or not. Fortunately this forum exists, and again I thank all you, because for the time being PENTAX support has still not replied to my initial query (the guy was absent, then busy, be sure you'll get soon an answer) ...
|
|
Forum: Pentax DSLR Discussion
05-31-2008, 05:26 AM
|
| |
Please let us talk on precise facts, rather than general considerations. In that case please explain why 1109 is more exposed than 1110. The white wall should, as you say, fool the camera in multi-seg measure, but I end up with a less exposed picture using the spot measure on the face ! I have been using a spot meter camera (with a tiny central spot) for a while and never got that abnormal behaviour.
If this is normal for a K20D, I wonder who uses the spot meter !
|
|
Forum: Pentax DSLR Discussion
05-31-2008, 05:15 AM
|
| |
Disagree. Please check 1110 vs. 1109: it shows the spot measure is doing the opposite of what it should do !
|
|
Forum: Pentax DSLR Discussion
05-30-2008, 10:14 AM
|
| |
Thanks for spending your time analyzing my pictures.
I followed your advice and installed the photoMe utility. It is amazing to see the amount of information stored within the picture (thanks my VISA # was not there).
I am not very clear with the Effective LV and Segment LV. I guess that the Effective LV is the value the firmware will choose for setting the physical parameters (aperture, ISO, speed), based on the segments LV and some Pentax magic ? If so why in spot measure the Effective LV is not the centre segment LV ?
Where do you read this information ?
|
|
Forum: Pentax DSLR Discussion
05-30-2008, 07:51 AM
|
| |
Well, your point confirms that the Kx0D series are not very good at light measuring.
I will not trust the K20D light meter anymore, and I start wondering whether I made the good choice with this camera...
If I was to re-program the firmware, I would increase exposure at least +0.5 IL on multi-seg and +1 IL on spot measures.
I have 2 friends who use respectively Nikon and Leica digital cameras who do not complain of exposure problem in auto mode (both of them have taken shots in the same environment, viz. desert scenes). Again I hope that my camera has got a malfunction, because I cannot accept the results I published along this thread. I do not wish to use Photo Laboratory to correct any single picture I have shot. Sorry if again I touch most of Pentax users on this site.
|
|
Forum: Pentax DSLR Discussion
05-30-2008, 12:06 AM
|
| |
This is a very interesting comment. I will disable that mode to see the difference.
However I was more or less considering picture 905 OK. Please have a look at 906 taken with spot meter on the same subject which is darker.
You will notice that most of the other pictures are taken with EDR = off. So it cannot explain all.
For instance 1109 / 1110 were taken with EDR = off and again it shows an underexposure in spot meter measure vs. multi-seg measure.
Thanks a lot.
P.S. I still have not got feed-back from Pentax support regarding this problem.
|
|
Forum: Pentax DSLR Discussion
05-23-2008, 03:43 AM
|
| |
Thanks falconeye for your judicious remarks. It is true that I wear glasses. I just walked outside to do some testing (for a change there is a good mid-day sun light today !). If I move away from the camera there is 1.5 IL biais in the measure (with the view finder in the sun light). But with the glasses in contact with it, I have not managed to biais the measure.
Also what is your opinion about the 2 couples of pictures 905/906 and 1109/1110 ? For my opinion I should have got opposite results (higher exposure with the spot measure).
Many thanks
|
|
Forum: Pentax DSLR Discussion
05-23-2008, 01:54 AM
|
| |
| |
|
Forum: Pentax DSLR Discussion
05-23-2008, 01:11 AM
|
| |
Thanks for your comment.
This is exactly what I did, please compare 906 with 905 (same scene) 906 has been shot with spot mesure and is worse than 905 !!!
|
|
Forum: Pentax DSLR Discussion
05-21-2008, 11:09 PM
|
| |
I am happy that you spend some time downloading and checking my pictures.
Please note that I have beeen using SLR for 20 year and especially models with spot meter (introduced with Olympus OM2-spot) so the problem of understanding what is backlight shooting, etc. is not mine.
What I learn from the above is the (Pentax ?) 18% exposure. I take note.
Please take a bit more time to compare set of pictures I uploaded that are to me inconsistant:
905.pef to be compared to 906.pef
1109.jpg to be compared to 1110.jpg
Whatever factory % the light meter is set , you will agree that it should be the same % whatever mode one uses (spot versus multi-seg), right ?
So how can one expect that the same frame, with a major white and bright background and a smaller darker subject is exposed more with a multi-seg mesure than with a spot mesure on the darker subject ?
Thanks again
Merci flyer pour l'explication !
|
|
Forum: Pentax DSLR Discussion
05-21-2008, 01:05 PM
|
| |
Thanks for your feedback.
Please could you mention the picture name your are talking about, it would help the understanding. I have not much understood the % given.
Pictures 353, 356, 368 and 387 were shot with spot mesure. I could understand the explanation for 387 wich has a white and bright center. But this is not the case of 368.
Also I posted some 2 (small) jpeg files in /jpg directory (same ftp site):
1109 is multi-zone mesured
1110 is spot mesured (on the face)
I would expect 1110 to be better exposed (considering my subject is on a bright white background).
Aloso the 905.pef and 906.pef is interesting: 905 is multizone wheras 906.pef is spot measured on the signpost. 906 is worse than 905.
I (or my K20D centre zone) is confused !
Pentax Browser is 3.50
Thanks again
Marc
|
|
Forum: Pentax DSLR Discussion
05-21-2008, 01:23 AM
|
| |
| |
|
Forum: Pentax DSLR Discussion
05-20-2008, 11:37 PM
|
| |
Hello,
Thanks for all your feedback.
Yes it is true that I am complaining fast. But this is in line with the poor exposure I get.
Yesterday I contacted the Pentax hot-line to complain about the issue. I uploaded some offending PEF files on a private ftp site for their investigation.
Most (if not all) my picture were taken in P-mode. Sometime I use the central light measure rather than averaged one, but it does not change much the problem.
Nothing really advanced...
Note that this problem does not affect all the pictures, but many of them.
Regards
Marc
|
|
Forum: Pentax DSLR Discussion
05-20-2008, 06:20 AM
|
| |
Hello to all,
I recently purchased a K20D with the starter kit (18-55 + 50-200).
I am back from a 4WD trek in Morocco with a load of pictures.
I am amazed to realize that most of the pictures are underexposed. Actually for most of the picture I must use the Photo laboratory software to increase the light (and not slightly !)
Even some pictures taken in low contrast conditions are underexposed. My son's cheap camera does far better than my K20D !
I am terribly disapointed with this camera.
I cannot imagine somenone is satisfied with the K20D light measuring.
I hope Pentax releases a new firmware to correct this problem very soon.
Regards
Marc
|
