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02-19-2007, 09:16 PM   #1
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K100D Macro mode confusion

I have a K100D, and for this question am using a DA 18-55 lens. With the camera in the green AUTO PICT mode, and shooting a closeup (can be any small object) the camera will automatically select MACRO mode, displaying the flower icon in the viewfinder display. The shutter speed may be 1/60 with an aperture of F5.6. If I turn the mode dial to the dedicated MACRO mode, the shutter speed will remain the same but the aperture stops down to F13. I certainly understand the difference in depth of field the two different apertures will yield, but I donít understand why the camera is setting two different apertures. Why doesnít the aperture stop down to F13 when the AUTO PICT mode decides to select MACRO mode? MACRO, as selected by AUTO PICT, does not yield the same exposure as dedicated MACRO, though the manual implies they should be the same. Has anyone else experienced this, and do you have any explanation?

02-20-2007, 02:38 AM   #2
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Have you actually taken a photo on the two modes? The exposure difference witht eh same shutter speed from f5.6 to f13 is huge, more than 2 stops! I don't own a K100D and haven't noticed this on my DS, sorry.
02-20-2007, 06:05 AM   #3
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Yes, I have taken photos. Results when the AUTO PICT mode selects MACRO, and setting the camera in dedicated MACRO mode are considerably different, as you would expect with such a variation in apertures.

BobG
02-20-2007, 06:50 AM   #4
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Maybe you've discovered a glitch. You say the photos are different; which, in your opinion is correctly exposed.

02-20-2007, 07:30 AM   #5
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I was test shooting some closeups last night of a figurine and other small objects under tungsten light, using the built in flash with white balance and ISO set to auto. With the camera in AUTO PICT mode, it selected MACRO (displaying the flower icon in the viewfinder), and set the aperture to F5.6. Resulting photo had shallow depth of field with a yellow cast from the ambient light. With the mode dial set on dedicated MACRO, the camera set an aperture of F13. The resulting photo had great depth of field and the color was excellent. Obviously the camera upped the flash output to compensate for the stopped down aperture. I prefered the second exposure, especially since the DA 18-55 is much better stopped down. I don't understand why, with the distance to object and all other parameters remainging the same, why the exposure setting in AUTO PICT - MACRO and dedicated MACRO are not the same. I know how to shoot manually, but I'm experimenting with all of the settings on this camera to see how they function.

BobG
02-20-2007, 07:55 AM   #6
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your camera has several setting that all appear to do the same things.. the dedicated macro is more correct.. the small aperture is selected for obvious reasons..

auto pic is just popping up the flower to tell u your subject is close.. so in other words its not real macro mode..

u are better selecting your own aperture then letting the camera do the rest.. P mode and either AV or TV make a lot more sense..

the other thing to note is the ev button works by adjusting the flash power when the flash is being used..

the k100 has that many silly options and modes they all interact with each other in strange unexpected ways.. its better to learn not to use them.. i never do..

i dont use them because i dont know what they do.. or how exactly they do it.. he he

trog
02-20-2007, 08:21 AM   #7
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Hi Bob,

I'm going to dissect your message. It's not to start an argument but to point in specific directions to information already collected. What follows is part reasoned fact and personal opinion.

QuoteOriginally posted by BobG Quote
I was test shooting some closeups last night of a figurine and other small objects under tungsten light, using the built in flash with white balance and ISO set to auto.
Pentax WB is particularly weak in the tungsten light color temperature range. For any 'real' shooting, a custom WB would be much preferred in tungsten light, especially at low light levels. Several forum threads bear this out.

QuoteOriginally posted by BobG Quote
With the camera in AUTO PICT mode, it selected MACRO (displaying the flower icon in the viewfinder), and set the aperture to F5.6. Resulting photo had shallow depth of field with a yellow cast from the ambient light.
Later, I'll elaborate some on program lines; I believe here the camera is doing a simply pattern search for any acceptable shutter speed/aperture combination for the observed/metered exposure value.

QuoteOriginally posted by BobG Quote
With the mode dial set on dedicated MACRO, the camera set an aperture of F13. The resulting photo had great depth of field and the color was excellent. Obviously the camera upped the flash output to compensate for the stopped down aperture.
Again, the program line thing. The macro program line is probably depth of field biased.

QuoteOriginally posted by BobG Quote
I preferred the second exposure, especially since the DA 18-55 is much better stopped down
Any move away from the aperture's range ends should be a move toward the lens sweet-spot.

QuoteOriginally posted by BobG Quote
I don't understand why, with the distance to object and all other parameters remaining the same, why the exposure setting in AUTO PICT - MACRO and dedicated MACRO are not the same.
Program lines. Pentax employs four basic variations: Normal-the first it finds by a pattern search, Depth-biased toward small apertures (f/16, f/22). Speed- biased toward fast shutter speeds (1/500, 1/1000, etc) and MTF-biased toward the lens sweet-spot.

Normal:
If you google 'exposure value' one of the hits will be on a site with a chart of exposure vales plotted as a function of shutter speed and aperture. If you pick the EV where the camera starts (as in just powered on or remaining from the previous shot), and move up one line, right one number, down one, down one again, left one, left one, up one, up one, up one... You get a square clockwise pattern search across the table. Note that there are diagonal lines of equivalent EV that give a range of shutter speeds and apertures-all for the same EV. Now with a new exposure there is a second point in the table, a new EV. As soon as the pattern search reaches any point along the EV line corresponding to the new EV value, it has a shutter speed/aperture combo that is proper and the search stops. Not a perfect system, but easy to program and fast!

MTF:
Modulation Transfer Function. Ultimately A measure of where the lens system transmits a typical packet of light containing many frequencies in the best manner possible. Newer lenses have this programmed into the lens circuitry and the camera reads this data and biases both shutter and aperture selection appropriately.


QuoteOriginally posted by BobG Quote
I know how to shoot manually, but I'm experimenting with all of the settings on this camera to see how they function.
A much recommended procedure; I take some personal gratification and admire your spirit. In short, you have found a shortcoming-the pattern search. It's normal operating procedure.
02-20-2007, 10:28 AM   #8
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John,

Thanks for the info. While the results of both exposures are accurate for each of the apertures selected by the camera, your explanation helps me better understand why different apertures are selected when the camera is working in the AUTO PICT - MACRO mode or the dedicated MACRO mode. Perhaps I should not take the manual so literally for some automatic operations?

BobG

02-20-2007, 12:11 PM   #9
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"Program lines. Pentax employs four basic variations: Normal-the first it finds by a pattern search, Depth-biased toward small apertures (f/16, f/22). Speed- biased toward fast shutter speeds (1/500, 1/1000, etc) and MTF-biased toward the lens sweet-spot."

which when it bottoms down to it can all be done with a small amount of knowledge and far easier useing the P mode and the av or tv mode..

macro.. small aperture bias for greater depth of field..

sport.. fast shutter bias to freeze action..

portrait.. large aperture bias for shallow depth of field..

landscape.. smaller aperture bias for lens sweet post and maximum image detail..

normal.. no bias.. kind of in the middle average where no extremes of anything are required..

snow.. one f-stop over normal exposure bias to compensate for too much white in the image fooling the camera into under exposing..

put the camera in P mode.. learn where it goes wrong and add the appropriate bias via the av or tv options.. plus the ev button where needed.. let the camera teach u..

mosly in P mode it wont go far wrong.. u need to know when it needs some help.. when it does give some..

trying to work out the wierd ways its various auto modes get applied is hard work and not very productive..

trog
02-21-2007, 05:48 AM   #10
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For anyone interested, I have found that the wide difference in apertures (where I started this thread) that the camera selects in AUTO PICT Ė MACRO or dedicated MACRO mode only occur when the built in flash is on. With the flash turned off (in manual) or when not needed, the apertures the camera selects when in AUTO PICT Ė MACRO and dedicated MACRO modes are the same. The AUTO PICT mode works as advertised. When it decides to select macro, it yields the same exposure as if I turned the mode dial to the dedicated MACRO setting. Iím continuing to learn how the camera thinks. I know a lot of you abhor the AUTO PICT mode, but there are times when I want to use it and need to know that itís doing itís thing properly. When sightseeing and moving quickly, I sometimes want to be able to just frame and shoot. If I see an exposure setting in the viewfinder thatís not right for the scene, then Iíll make an adjustment. Iím really pleased with my K100D.

BobG
02-21-2007, 08:01 AM   #11
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one day i will take the trouble to frame some identcal shots.. one in P mode.. and one in auto pic mode.. just to see what bias the camera feeds in..

i find that for the vast majority of my shots the camera makes a good job simply left in P mode.. in over 4000 shots i have never used autopic or the scene modes..

its not because i dislike auto.. i love it.. but so far P mode seems auto enough.. the green dial just another setting to fiddle with..

trog
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