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Comment by Algernon posted on Difference between Pentax f/1.4 and f/1.7 at 06/02/2011 - 13:53
This was a test of two lenses wide open f/1.4 -v- f/1.7 taken
from the centre of the frame only. Best of 4 shots in each
case.
100% crops.
The f/1.7 was a clear winner
from the centre of the frame only. Best of 4 shots in each
case.
100% crops.
The f/1.7 was a clear winner
Comment by Algernon posted on Difference between Pentax f/1.4 and f/1.7 at 06/02/2011 - 12:16
Smeggypants wrote:
I've just run the following quick test which clearly shows no change from f/1.4 to f/1.8 using an Expodisc pointed at the grey sky. Lens focused on infinity.Algernon wrote:
.... digital sensors can't see f/1.4 they can only see it as f/1.7
This is clearly untrue. Sensors can see the difference between 1.2 and 1.4, never mind 1.4 and 1.7.... digital sensors can't see f/1.4 they can only see it as f/1.7
Exposure Test Constant shutter speed of 1/800th sec.
50mm A f/1.4 Lens 100ISO
Apertures decrease by 1/3 stop between each frame (set in K20D)
Shot RGB Centre Aperture
1 111 f/1.4
2 116 f/1.6
3 111 f/1.8
=========================First Change in Density
4 99 f/2.0
5 82 f/2.2
6 72 f/2.5
7 57 f/2.8
The first sign of the shots getting darker was between f/1.8 and f/2.0
So basically using a constant shutter speed of say 1/800th sec you can use any aperture in manual from f/1.2 to f/1.8 and the shots will all have the same exposure
The lens vignettes below f/2.8. At f/2.8 the exposure is almost constant across the frame.
Comment by Algernon posted on Difference between Pentax f/1.4 and f/1.7 at 06/02/2011 - 12:03
I'm surprised they got 23kg past Health and Safety Procedures?
Even the building industry has a 20kg limit for manual handling,
other industries are lower.
Seems a bit silly letting passengers put packages overhead that
staff can't remove because of H&S
Even the building industry has a 20kg limit for manual handling,
other industries are lower.
Seems a bit silly letting passengers put packages overhead that
staff can't remove because of H&S
Comment by Algernon posted on hand luggage on planes now extra headroom at 06/02/2011 - 10:45
Excellent lens. The colours are really good and the bokeh on the shot of the two girls is better than I expected from this lens. (Note: bokeh is a photographic term not a description of someones rear )
I've got this lens and the very similar M 80-200mm f/4.5 version, very similar performance but the M is a bit smaller and lighter, superb build quality and a real bargain on ebay. Both lenses are very underestimated.
I've got this lens and the very similar M 80-200mm f/4.5 version, very similar performance but the M is a bit smaller and lighter, superb build quality and a real bargain on ebay. Both lenses are very underestimated.
Comment by Algernon posted on SMC Pentax A Zoom 70-210 f/4 at 06/02/2011 - 10:26
Isn't the output format just Motion Jpeg?
Comment by Algernon posted on Pentax k-5, am i doing something wrong or have they made a false statment? at 05/02/2011 - 19:49
Could do with a diagram
Comment by Algernon posted on Pentax k-5, am i doing something wrong or have they made a false statment? at 05/02/2011 - 18:58
gillbod wrote:
i disagree. the contention made in the LL article is that the light coming from the edge of the exit pupil is coming from too sharp an angle for the sensor to pick it up, so the manufacturers sneakily up the iso to balance the exposure.
BUT, if you see a change in the depth of field, then this light from the edge is being picked up. even though the depth of field it's an optical property, it remains for the sensor to detect it.
Once the light has passed through the lens, within reason it can't be changed and if the lens is set at f/1.2 that will be the property of the light. You could blank off half the sensor and you wouldn't really alter it apart from only having half the photo i disagree. the contention made in the LL article is that the light coming from the edge of the exit pupil is coming from too sharp an angle for the sensor to pick it up, so the manufacturers sneakily up the iso to balance the exposure.
BUT, if you see a change in the depth of field, then this light from the edge is being picked up. even though the depth of field it's an optical property, it remains for the sensor to detect it.
gillbod wrote:
the LL article even says this in the open letter they wrote:
[quote="Mark Dubovoy"] In fact, is not even clear that large aperture lenses will deliver a shallower depth of field as intended. The DxO measurements to date prove that the marginal light rays just don’t hit the sensor. The point regarding depth of field is that these rays are also responsible for a larger blur spot when out of focus. If they are lost, they not only don’t contribute to the light intensity at the sensor, but they also don’t blur the out of focus planes as much as you would expect at wide apertures.
[/quote]He needs to explain this better. Possibly he hasn't got all the test results and they may even involve film tests for comparison. The DOF is set by the lens aperture which is f/1.2? If it is seen as only f/1.7 from an exposure point of view, information/detail of OOF areas can't be re-constructed. So possibly the OOF areas we see on the digital negative is just a bit of a mish mash of what light the sensor has managed to pick up from what it can actually see.the LL article even says this in the open letter they wrote:
[quote="Mark Dubovoy"] In fact, is not even clear that large aperture lenses will deliver a shallower depth of field as intended. The DxO measurements to date prove that the marginal light rays just don’t hit the sensor. The point regarding depth of field is that these rays are also responsible for a larger blur spot when out of focus. If they are lost, they not only don’t contribute to the light intensity at the sensor, but they also don’t blur the out of focus planes as much as you would expect at wide apertures.
It's probably better to forget DOF and just look at the exposure, which I previously found to be in line with the DxO. My results shown below.
Quick test on a K20D indicates that Pentax haven't adjusted
anything and the 'A' 50mm f/1.4 lens underexposes at f/1.4 by
about 2/3 stop. Seems OK at f/2.0 This is using Av program.
Quite a simple test in the end. Just set Av take shot.
Adjust aperture by 1/3rd stop. Take another until you
get to f/4
Look at the pics on a lightable type viewer. Do screen capture and
import into editor read off values. You can see it anyway.
My RGB values were from f1.4 (topline)
117 = f/1.4 Underexposed
124
130
138 = f/2.0
140
135
133 = f/2.8
130
129
128 = f/4
I used Expodisc and it was within 0.1 stops according to the LV's in
the Exif data for matrix metering.
Comment by Algernon posted on Difference between Pentax f/1.4 and f/1.7 at 04/02/2011 - 17:16
It's better to use just Jpegs for these tests. RAW might get altered even when it's not intended.
The Exif Data is recording the same exposure time for 3 shots though?
What is the reason for that?
At least the Canon hasn't been messing around with the ISO. I thought
they all looked the same from the noise point of view
The Exif Data is recording the same exposure time for 3 shots though?
What is the reason for that?
At least the Canon hasn't been messing around with the ISO. I thought
they all looked the same from the noise point of view
Comment by Algernon posted on Difference between Pentax f/1.4 and f/1.7 at 04/02/2011 - 14:56
The test using the "grey sky" as the light source is unfortunately not very scientific as you are not using a stable light source. Were you using a tripod so you were at least using exactly the same area of sky?
The Exposure was taken at f/1.4 by pressing the Green Button. AWB was used. The value from the center of the frame from Corel Photopaint was 111R 111G 111B. From the K20D Service Manual Pentax calibrate their screens to 110R 110G 110B and the Expodisk can vary the reading by 1R 1G 1B so at f/1.4 my camera is spot on exposure wise.