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06-06-2011, 05:24 AM   #46
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QuoteOriginally posted by geekette Quote
I mean the silly camera does through the lens metering when stopped down. Why then when we snap it, is the exposure off. When we snap it, it should stop down to the same amount no?
Fastest manual lenses I had were all f2 (M85, Helios, Jupiter) - none had problem with stopdown metering.

06-06-2011, 06:51 AM   #47
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Just measured on a grey/white garage door in the shade with an ist ds, iso 200, spot meter on the grey.
{Aperture}, <shutter millisec as reciprocal of speed> , [Gimp Level@ peak hist as parts of of 255]
A_Lens Pentax-A 1:2 50 mm in Av mode
{16, 8, 4, 2} ,<50, 11, 2.8, 0.6> [150, 159, 168, 151]

M lens Rikenon XR 1:1.4:50mm M mode,pressing the meter button to let the camera set the shutter at each aperture
{16, 8, 4, 2, 1.4} , <50, 11, 2.8, 0.6, 0.5> [176,178,178,178,188]

Much less than the variations shown in Lowells graph, unless I miss understand his method.
And not too bad, I think considering hand held and the rounding of the shutter speeds.
06-06-2011, 06:15 PM   #48
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QuoteOriginally posted by wombat2go Quote
Just measured on a grey/white garage door in the shade with an ist ds, iso 200, spot meter on the grey.
{Aperture}, <shutter millisec as reciprocal of speed> , [Gimp Level@ peak hist as parts of of 255]
A_Lens Pentax-A 1:2 50 mm in Av mode
{16, 8, 4, 2} ,<50, 11, 2.8, 0.6> [150, 159, 168, 151]

M lens Rikenon XR 1:1.4:50mm M mode,pressing the meter button to let the camera set the shutter at each aperture
{16, 8, 4, 2, 1.4} , <50, 11, 2.8, 0.6, 0.5> [176,178,178,178,188]

Much less than the variations shown in Lowells graph, unless I miss understand his method.
And not too bad, I think considering hand held and the rounding of the shutter speeds.
A couple of fine points,

first, your exposure seems high. Normal exposure should be 110-125. a high exposure will reduce the impact of non linearity because the grey scale of the histogram compresses as you move off nominal.

Second, I measured the central 10% of the frame, not the whole histogram, because I can do so, and this eliminates things like vignetting on the lens fromt he histogram.

Third, where is your contrast setting? contrast can have a 20% impact on the variance in greyscale

Also the changes can be high ly pronounced, and more apertures should be tested.

but these should not impact the results to the extent they are different from mine, although as I have always maintained the *istD series cameras were the best metering with manual lenses.

However, the basic method is what I used.
06-06-2011, 07:56 PM   #49
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Hi, Lowell, the image was 2 white garage doors separated by grey siding in the centre.
I spot metered on the grey siding. Camera was in default settings, AWB, and "bright" jpg tone
Last post , I put only the results of the average histo for whole image, which is dominantly of the white doors, hence high brightness.
So here are the levels of the grey area that I spot metered on, from a rectangle in Gimp, the histo is almost an impulse in the grey area,
lower down on the gamma curve than the white doors.
{Aperture}, <shutter millisec as reciprocal of speed> , [Gimp Level@ peak hist as parts of of 255]
M lens Rikenon XR 1:1.4:50mm M mode,pressing the meter button to let the camera set the shutter at each aperture
{16, 8, 4, 2, 1.4} , <50, 11, 2.8, 0.6, 0.5> grey spot area:[133, 133, 127, 127, 143] . whole image: [176,178,178,178,188]

This is showing constant metering for the ist ds in range 1/20 ~ 1/1500 and at 1/2000 it over exposes by 12%.
Next time I will do the intermediate stops as you mention, and I will do it at higher iso in low light on a grey card
Incidentally, I am starting to use the ist and the MX together, and they track generally.

06-06-2011, 08:19 PM   #50
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QuoteOriginally posted by wombat2go Quote
Hi, Lowell, the image was 2 white garage doors separated by grey siding in the centre.
I spot metered on the grey siding. Camera was in default settings, AWB, and "bright" jpg tone
Last post , I put only the results of the average histo for whole image, which is dominantly of the white doors, hence high brightness.
So here are the levels of the grey area that I spot metered on, from a rectangle in Gimp, the histo is almost an impulse in the grey area,
lower down on the gamma curve than the white doors.
{Aperture}, <shutter millisec as reciprocal of speed> , [Gimp Level@ peak hist as parts of of 255]
M lens Rikenon XR 1:1.4:50mm M mode,pressing the meter button to let the camera set the shutter at each aperture
{16, 8, 4, 2, 1.4} , <50, 11, 2.8, 0.6, 0.5> grey spot area:[133, 133, 127, 127, 143] . whole image: [176,178,178,178,188]

This is showing constant metering for the ist ds in range 1/20 ~ 1/1500 and at 1/2000 it over exposes by 12%.
Next time I will do the intermediate stops as you mention, and I will do it at higher iso in low light on a grey card
Incidentally, I am starting to use the ist and the MX together, and they track generally.
the over exposure at high shutter speed could be the camera.

When I do the tests< i do them with the max shutter a little lower usually because I can always remember when photo magazines used to publish shutter accuracy, the top end used to be a little "sketchy"
06-08-2011, 08:08 PM   #51
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QuoteOriginally posted by wombat2go Quote
Just measured on a grey/white garage door in the shade with an ist ds, iso 200, spot meter on the grey.
{Aperture}, <shutter millisec as reciprocal of speed> , [Gimp Level@ peak hist as parts of of 255]
A_Lens Pentax-A 1:2 50 mm in Av mode
{16, 8, 4, 2} ,<50, 11, 2.8, 0.6> [150, 159, 168, 151]

M lens Rikenon XR 1:1.4:50mm M mode,pressing the meter button to let the camera set the shutter at each aperture
{16, 8, 4, 2, 1.4} , <50, 11, 2.8, 0.6, 0.5> [176,178,178,178,188]

Much less than the variations shown in Lowells graph, unless I miss understand his method.
And not too bad, I think considering hand held and the rounding of the shutter speeds.
The *istD does not suffer from the stop-down exposure issue.


Steve
06-08-2011, 10:39 PM   #52
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QuoteOriginally posted by dlacouture Quote
As I said before, all these problems disappear when using a Canon EE-S screen...
The stop-down metering response is flawed by the brightness optimization done by Pentax on their screens. They are optimized to boost perceived brightness for apertures between f/1.4 and f/5.6, using their Fresnel lens (located on the underside, and the same culprit as for the limited DoF preview).

From my tests, I've not seen any indication that Pentax uses some internal tweaking between A-position and a given aperture, except for the fact that Matrix metering cannot work out of A-position. Using CW give me similar results between A and the widest aperture in stop-down.

What they should do is simply offer one linear focus screen for us legacy lenses users... But as Canon already does, why bother?
I suppose the OP and other participants know that if they have third party split focusing screens installed, it messes up the spot metering, at least on the K10 and K20 in my experience. Other metering modes are not as significantly affected per KatzEye. I didn't install one of the K5.
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