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05-31-2009, 04:58 AM   #1
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OK i have to be doing something wrong!

Hi Guys

Im looking for your help please.. im sure its me.. not the camera

i mentioned a while ago that my 2 sigma's seem to be over exposing after putting the jinfinance split prism screen in. the issue seems to be intermittent having had some nice shots and some lousy shots too.. i havent replaced the split screen with the original yet.. but that is my next step..

today it was black cloud and sunshine out on the estuary and i thought i would fire a few shots off while pootling around on the boat.. well once again some over exposed and some partially over exposed.. joy!

anyway linked are some pics i took (real crappy blurred and out of focus ones as the boat was rocking a bit) but are just an example..

am i expecting too much from the camera (i hope not as my old p&s would deal with these conditions) or can you give me hints on why its just not playing right..

i have in the pics a combo of spot metering and multi segment as i was trying to eliminate it...

thanks for any hints i'll appreciate them lots

Steve

Camera: PENTAX
Model: PENTAX K20D
ISO: 100
Exposure: 1/30 sec
Aperture: 6.7
Focal Length: 300mm
metering multi segment

image linky http://picasaweb.google.com.au/lh/photo/ANAbdWwvcCC5BKrPPcc6ig?authkey=Gv1sR...eat=directlink



Camera: PENTAX
Model: PENTAX K20D
ISO: 100
Exposure: 1/250 sec
Aperture: 6.7
Focal Length: 70mm
Metering Spot

image linky http://picasaweb.google.com.au/lh/photo/1Ev1jwNGycl64GUlFO1aeg?authkey=Gv1sR...eat=directlink



Camera: PENTAX
Model: PENTAX K20D
ISO: 100
Exposure: 1/125 sec
Aperture: 5.6
Focal Length: 300mm
Flash Used: No
Metering Spot
image linky http://picasaweb.google.com.au/lh/photo/aq6GK8_gPp9iD-NDaLaahw?authkey=Gv1sR...eat=directlink



Camera: PENTAX
Model: PENTAX K20D
ISO: 100
Exposure: 1/90 sec
Aperture: 5.6
Focal Length: 300mm
Flash Used: No
metering multi segment

image linky http://picasaweb.google.com.au/lh/photo/jZJmtYqbfMDhwdVgekd_6g?authkey=Gv1sR...eat=directlink




Last edited by 5teve; 05-31-2009 at 06:18 AM.
05-31-2009, 06:01 AM   #2
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Which Sigma lenses are you using? And just to verify - Did you check to make sure the Aperture ring on the lenses was set to A?

The first picture - ISO: 100 Exposure: 1/30 sec Aperture: 6.7 - was it that dark? If it's as bright as I think it looks in there, there's no reason for you to use such low shutter speeds. That would account for the over-exposure.

Same with the last picture - you should decrease your exposure time (I would think at least 1/125-1/250) and the aperture as needed.

Could you post a few of the images with the EXIF data intact? The explanation might just be in that data
05-31-2009, 06:15 AM   #3
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Apologies i was in a rush...

These were all done using a sigma 70-300 f4-5.6 non APO and i was using aperture priority... shutter was being set automatically..

i will add links shortly to the above post.. should have intact exif..

no the light wasnt that bad.. which is why im struggling.. if i was setting everything manually i could understand... but the camera is deciding..

this is why im wondering if the split prism, with it darkening at 300ish mm as it goes to f5.6 is effecting the metering enough to throw the exposure out..

hope this explains a bit more

thanks for looking

Steve
05-31-2009, 06:19 AM   #4
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Doesn't Katz Eye say not to use spot metering with their split prism screens, because of metering errors?

05-31-2009, 06:33 AM   #5
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I believe it becomes an issue on smaller apertures yes, however i was using it after taking an equally poor shot with multi segment to see if it calmed things down a bit.. i think it only becomes an issue at f8 and above.. but i see darkening at f4 onwards of the donut prism..

Thanks

Steve
05-31-2009, 07:05 AM   #6
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QuoteQuote:
Duck Dodgers Doesn't Katz Eye say not to use spot metering with their split prism screens, because of metering errors?
Below, from the Katy Eye website, is precisely what Katz Eye says:


Metering Information
"Because of the presence of the prisms, the Katz Eye™ focusing screen for the Pentax K10D/K20D will have some effect on the camera’s light metering. Test results for each of the three metering modes are as follows:

Center Weighted Average (CWA) Metering Mode: Our testing showed CWA metering mode to be accurate for all AF lenses having a maximum aperture of f5.6 or larger (lower f number).
Evaluative Metering Mode: Our testing showed evaluative metering mode to be accurate for all AF lenses having a maximum aperture of f5.6 or larger (lower f number).
Spot Metering Mode: Our testing showed spot metering mode to be within factory tolerance for all AF lenses having a maximum aperture of f2.0 or larger (lower f number). Lenses having a maximum aperture smaller than f2.0 (lager f number) will show a significant shift toward increased exposure, with the shift increasing for lenses with smaller maximum apertures. Spot metering mode is NOT RECOMMENDED when using a split prism focusing screen with lenses slower than f2.0. However, if spot mode must be used, it is strongly advised to first take a test shot, check the histogram, and adjust exposure compensation as required.
Please note that Katz Eye testing was performed on the K10D and while it is expected that the K20D results will be similar, K20D users are strongly advised to confirm metering results with a test photo prior to beginning critical work."
05-31-2009, 07:21 AM   #7
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If I may complicate this a little more, the K20D book states on page 98 that CWA will be selected by the camera regardless of what setting is made by the user if the lens is not DA, FA, J...or A lens (in other words Pentax is how I read this). So Sigma lens default to CWA regardless of your spot or multi-segment setting. If I read this correctly, you can take your metering method out of the equation and just pretend they are all CWA, because they are.

Now that I have stated this I need to go mount the Sigma and do some testing to see if results match the exif.....
05-31-2009, 07:52 AM   #8
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It is similar to that, but a little different.
Camera would see Sigma something as a A or F lens i believe, if not even more (since it can relay focal length to the camera).
And if you've ever used any manual lens (no communication to the camera, M, K, m42 etc), you'd see that CWA metering icon shows up in top LCD, but it doesn't with any of my 30/1.4 or 30-700 Sigma's (Non Pentax lenses respectively). Unless the aperture isn't set to anything other than A (F-- and CWA can be seen on top LCD).

I had similar behaviour with split screen. It is because of focal length and current open (metering) aperture. You just have to learn what EV compensation is needed at each setting.
It is because at different focal lenghts light falls upon the focusing screen at different angles.

If the screen were plain ground glass it would diffuse the light in all directions no matter what the focal length is. Because of the optical features included in focusing screens (microlenses in original, prism and doughnut in split) the light reaching metering sensor may be directed differently at different falling angles. Camera has information to compensate those light changes for original screen. Changing the screen introduces some error.

If you try to find it, there was a graph showing this error somewhere on this forum.

05-31-2009, 10:32 AM   #9
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Make sure one of the e-dials is not set for EV comp. If it is set to EV comp, and you don't touch the e-dial at start up, the first pictures will be correctly exposed, but as soon as you turn the e-dial, your exposures will go to hell. To check for that on the K20D, go to "menu", then "C", then lines 20 to 25. I think that might be where your problem is.
05-31-2009, 11:18 AM   #10
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I have the tamron verison of this lens, I used last weekend, at sunny day, i set to f8 and up, pictures came up very sharp. Also, did u change the EV+_ on the camera. but try to use higher aperature, if too slow, u can set iso to 400.
05-31-2009, 12:24 PM   #11
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If you want to know what the camera's meter saw, open the original photos with PhotoME. In the Manufacturer Notes section, look for the AE Metering Segments line (try ctrl+F and "ae meter") and click the <Graphic> link. Compare the numbers you see there between the good and bad shots.
05-31-2009, 06:19 PM   #12
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QuoteOriginally posted by Jewelltrail Quote
Below, from the Katy Eye website, is precisely what Katz Eye says:


Metering Information
"Because of the presence of the prisms, the Katz Eye™ focusing screen for the Pentax K10D/K20D will have some effect on the camera’s light metering. Test results for each of the three metering modes are as follows:

Center Weighted Average (CWA) Metering Mode: Our testing showed CWA metering mode to be accurate for all AF lenses having a maximum aperture of f5.6 or larger (lower f number).
Evaluative Metering Mode: Our testing showed evaluative metering mode to be accurate for all AF lenses having a maximum aperture of f5.6 or larger (lower f number).
Spot Metering Mode: Our testing showed spot metering mode to be within factory tolerance for all AF lenses having a maximum aperture of f2.0 or larger (lower f number). Lenses having a maximum aperture smaller than f2.0 (lager f number) will show a significant shift toward increased exposure, with the shift increasing for lenses with smaller maximum apertures. Spot metering mode is NOT RECOMMENDED when using a split prism focusing screen with lenses slower than f2.0. However, if spot mode must be used, it is strongly advised to first take a test shot, check the histogram, and adjust exposure compensation as required.
Please note that Katz Eye testing was performed on the K10D and while it is expected that the K20D results will be similar, K20D users are strongly advised to confirm metering results with a test photo prior to beginning critical work."

JewellTrail

Thanks for the information there.. im assuming the katzeye is a similar split prism with the donut shape around the split?
basically what they are saying is that the lens has to be f5.6 or higher (smaller number) to be guaranteed to work. so my 70-300 is right on the limit.. and when i run the aperture at >f5.6 thats when i'm hitting issues..

do you run any AF lens's that you maybe could test this theory too? (as you are a great advocate of the jinfinance split prism your reviews and passion led me to buy one.. which i dont regret as its a great tool for manual lenses... shame the k20 doesnt meter well tho but i may have to look at swapping it out for AF lens use.. )

i will be able also to try this when my sigma 28-70 ex f2.8 arrives..


QuoteOriginally posted by imtheguy Quote
If I may complicate this a little more, the K20D book states on page 98 that CWA will be selected by the camera regardless of what setting is made by the user if the lens is not DA, FA, J...or A lens (in other words Pentax is how I read this). So Sigma lens default to CWA regardless of your spot or multi-segment setting. If I read this correctly, you can take your metering method out of the equation and just pretend they are all CWA, because they are.

Now that I have stated this I need to go mount the Sigma and do some testing to see if results match the exif.....
im the guy..

when i first bough the camera i read the manual from cover to cover and spotted this.. which worried me so i posted the question.... i was reassured this wasnt the case... and the icons on the info screen show it isnt.. the sigma's are seem as pentax lens's would be.

QuoteOriginally posted by ytterbium Quote
It is similar to that, but a little different.
Camera would see Sigma something as a A or F lens i believe, if not even more (since it can relay focal length to the camera).
And if you've ever used any manual lens (no communication to the camera, M, K, m42 etc), you'd see that CWA metering icon shows up in top LCD, but it doesn't with any of my 30/1.4 or 30-700 Sigma's (Non Pentax lenses respectively). Unless the aperture isn't set to anything other than A (F-- and CWA can be seen on top LCD).

I had similar behaviour with split screen. It is because of focal length and current open (metering) aperture. You just have to learn what EV compensation is needed at each setting.
It is because at different focal lenghts light falls upon the focusing screen at different angles.

If the screen were plain ground glass it would diffuse the light in all directions no matter what the focal length is. Because of the optical features included in focusing screens (microlenses in original, prism and doughnut in split) the light reaching metering sensor may be directed differently at different falling angles. Camera has information to compensate those light changes for original screen. Changing the screen introduces some error.

If you try to find it, there was a graph showing this error somewhere on this forum.
ok so i am not the only one... and it takes some learning so i'm happy with that to some extent! it makes sense that the metering is affected due to the darkening.. the main issue i have is that i am so new to DSLR photography (or just plain old SLR for that matter) that to get any shots im having to think real hard about everything im doing.. and losing shots because of it! i'll get there i just havent got the years of experience that you very valuable guys have!

are you still using the split screen?

QuoteOriginally posted by flyer Quote
Make sure one of the e-dials is not set for EV comp. If it is set to EV comp, and you don't touch the e-dial at start up, the first pictures will be correctly exposed, but as soon as you turn the e-dial, your exposures will go to hell. To check for that on the K20D, go to "menu", then "C", then lines 20 to 25. I think that might be where your problem is.
edials are all set up to standard settings.. i havent messed with them as i was learning from scratch.. so to get +/- ev i would have to have pressed the ev button plus rotated the front dial in AV mode.. i definitly have not done this.. thanks for the thoughts tho, it would also be consistent across all shots! i think the exif shows also 0ev added.

QuoteOriginally posted by winglik Quote
I have the tamron verison of this lens, I used last weekend, at sunny day, i set to f8 and up, pictures came up very sharp. Also, did u change the EV+_ on the camera. but try to use higher aperature, if too slow, u can set iso to 400.
thanks also... are you using a split prism? if so i would be interested to see if it happens at all on your camera.. and what split prism you have! as i mentioned above i didnt set the ev at all.. (its not something i currently think about!)

from what i can see the higher aperture is what is causing the issue (anything above 5.6) but to confuse matters i have just checked my past 3 outings.. and there are pictures @ f8 that are fine, pictures at f5.6 that are overexposed and it seems quite random (hence i think it is still me!)

Thanks

Steve
05-31-2009, 06:21 PM   #13
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QuoteOriginally posted by Quension Quote
If you want to know what the camera's meter saw, open the original photos with PhotoME. In the Manufacturer Notes section, look for the AE Metering Segments line (try ctrl+F and "ae meter") and click the <Graphic> link. Compare the numbers you see there between the good and bad shots.
Thanks for the link... nice software!

the first shot of the boat shows the following...

AE Metering Segment 1: 9.8*LV (center)
AE Metering Segment 2: 9.9*LV (center edge)
AE Metering Segment 3: 9.6*LV (upper, mid-right)
AE Metering Segment 4: 9.5*LV (upper, mid-left)
AE Metering Segment 5: 9*LV (upper, right)
AE Metering Segment 6: 8.9*LV (upper, left)
AE Metering Segment 7: 9.9*LV (mid-right)
AE Metering Segment 8: 9.8*LV (mid-left)
AE Metering Segment 9: 9.8*LV (right)
AE Metering Segment 10: 10*LV (left)
AE Metering Segment 11: 12.1*LV (lower, mid-right)
AE Metering Segment 12: 12*LV (lower, mid-left)
AE Metering Segment 13: 12*LV (lower, right)
AE Metering Segment 14: 11.8*LV (lower, left)
AE Metering Segment 15: 9.1*LV (top)
AE Metering Segment 16: 13.1*LV (bottom)

how does this look in your opinion?

Thanks

Steve
05-31-2009, 09:55 PM   #14
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I don't see any reason to expect reasonable exposure from the spot-metered shots. Unless you point directly at an 18% gray card or have a very good sense that what you are metering off is the same value, you should not use spot metering, ever.

So the only question is why the multi-segment shots were off. I'm guessing you had exposure compensation or bracketing turned on.
06-01-2009, 12:39 AM   #15
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spot metering i understand... except that using that it does work... sometimes!

the multi segment.. well as i have said previously... i will guarantee that there is no exposure compensation or bracketing turned on... i have double checked on the exif, but until it was mentioned on this thread i hadn't even thought of using it! (let alone know how to do it!) the shots were taken while driving the boat so i had to be fairly quick.. not enough time to mess around with the camera...

i have been out today with the original screen.. and played some more.. the camera seems to be playing much more nicely now.. from what i can see on camera screen.. whether or not it is the same on the PC i will find out shortly!

Thanks

Steve
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