Olympus Pen-F in HR Mode

 


Comparing High Resolution Mode at 50MP with Standard Mode


Using the same chart board and procedure as for the tests in Standard mode, I conducted a series of tests with the Pen-F and the 50mm f/2 macro lens, at 80 ISO in HR Mode, with all available aperture settings from  f/2 to f/8.  I used the out-of-camera (OOC) 50MP JPG for these tests.


For these tests I kept the camera at the same distance from the chart board as I used for the Standard mode tests, that is, with the scale line on the centre resolution chart equal to 400 pixels in Standard mode.  That enabled the IQ and detail in HR mode to be directly compared to that of Standard mode at the same camera distance.


The full set of OOC 50MP JPG images can be found here.


The ORF file for the f/5 case can be found here, and the ORI file here.

Below is the 50MP OOC HR JPG for the f/5 case (click on the image for the full size):



High Resolution Mode, 50MP, 50mm, f/5, 80 ISO



Results


In all cases, the centre and corner resolution was beyond the range of the test chart, with all rows of triplet lines being fully resolved down to and including the 1.0 pixel row.


The fine detail, colour rendition and general IQ of the images was considerably better in HR mode than in Standard mode.  Crops for the f/4 case, comparing the same parts of the chart board images in Standard and HR modes, adjusted to the same size, are shown below (click on an image for the full size):



Crop comparisons of a postage stamp from the f/4 case



Crop comparisons of feathers from the f/4 case




Tests Using the Chart Board at a Greater Distance


(1) Measuring the Resolution at 50MP


The Olympus Pen-F in HR mode produces a 50MP OOC JPG (without an associated 50MP ORF file), an 80MP ORF file, and a 20MP ORI file.  The 20MP ORI file can be renamed from ORI to ORF and processed to give a 20MP JPG.  That JPG is the first of the 8 captured 20MP images which are merged in the camera to yield the HR image.


In order to measure the resolution in HR mode it was necessary to repeat the tests using the chart board at a greater distance than normal.   I set up the camera to give a height of 400 pixels for the scale line in the 50MP JPG in HR mode, which was at 1.54 times the normal distance.


I carried out the tests across the range of available aperture settings and prepared crops of the centre chart from each of the resulting OOC 50MP JPG images.  Those image crops can be found here.


Results


Below is a comparison image showing the 1.4 and 1.3 rows of the chart at different aperture settings (click on the image for the full size view):



Comparison of Centre Chart crops at 50MP in HR Mode at Different Apertures



The calculation for resolution is LPH = 6120/reading.


The results for the different aperture settings are shown below:



The results show that the best resolution obtained by using the 50MP OOC JPG in HR mode with this lens is 4700 LPH at f/2-f/2.5.  The resolution is slightly lower at 4370 LPH for all the other aperture settings.


The maximum resolution of 4700 LPH for the 50MP OOC JPG in HR mode is higher than the maximum resolution of 2990 LPH as found for Standard mode by the factor 4700/2990 = 1.57, that is, by 57%.


The LPH resolution of a Bayer sensor is usually equal to about 1/√2 times the sensor height in pixels.  Therefore, a Bayer sensor with a resolution of 4700 LPH will have a height in pixels of about 4700 x √2 = 6630.  For such a sensor with a 4:3 aspect ratio, that would be equivalent to 6630 x 8840 = 58.6MP; and for a sensor with a 3:2 aspect ratio, it would be equivalent to 6630 x 9950 = 66MP.



(2) Measuring the Resolution at 80MP


I set up the camera to give a height of 400 pixels for the scale line in the processed 80MP ORF in HR mode, which was at twice the normal distance.


I carried out the tests over the available aperture range, and prepared crops of the centre chart from each of the processed 80MP JPG images.  For the ORF processing I used Olympus Viewer 3 (OV3) at default settings, except for sharpening set to +2.  The OV3 processor is available for download free to owners of Olympus cameras. Those image crops can be found here.


Results


Below is a comparison image showing the 1.5 and 1.4 rows of the chart at different aperture settings (click on the image for the full size view):



Comparison of Centre Chart crops at 80 MP in HR Mode at Different Apertures



The calculation for resolution is LPH = 7776/reading.


The results for resolution at different aperture settings are shown below:



The results show that the best resolution obtained in HR  mode using the processed 80MP ORF file with this lens is 5500 LPH at f/2-f/2.8.  The resolution is slightly lower at 5180 LPH for f/4- f/6.3, and then at f/7.1 diffraction reduces the resolution to 4860 LPH, and to 4450 LPH at f/8.


The maximum resolution of 5550 LPH for the 50MP OOC JPG in HR mode is higher than the maximum resolution of 4700 LPH as found for the 50MP OOC JPG by the factor 4700/4700 = 1.18, that is, higher by 18%.


Compared with standard mode, the maximum resolution of 5550 LPH for the 50MP OOC JPG in HR mode is higher by the factor 5550/2990 = 1.86, that is, higher by 86%.


The LPH resolution of a Bayer sensor is usually equal to about 1/√2 times the sensor height in pixels.  Therefore, a Bayer sensor with a resolution of 5550 LPH will have a height in pixels of about 5550 x √2 = 7770.  For such a sensor with a 4:3 aspect ratio, that would be equivalent to 10360 x 7770 = 80.5MP, which is close to the size of the 80MP file which is output by the Pen-F in HR mode.



Diffraction Cutoff Frequency


The maximum resolution of a perfect lens is limited by diffraction, which varies with f number and the wavelength of the light passing through it, and (as given here) can be expressed as:


cycles per mm = 1/(wavelength x f number)


Taking the wavelength as 550nm (0.55 µm) for the middle of the visible spectrum (green light) gives:


line pairs per mm = 1000/(0.55 x f number)


Tabulating the maximum line pairs per mm for different f numbers for a perfect lens gives:



If an image from a lens is projected onto a sensor of a particular height, the above table can be used to calculate the resolution in LPH (lines per picture height) beyond which it would not be physically possible to achieve, even with a perfect lens.


For the Pen-F, which has a sensor height of 13mm, this gives:

Maximum LPH = 2 x line pairs per mm x 13


Tabulating the maximum LPH for the Pen-F at different f numbers gives:



The above table may explain why the Pen-F has been limited to a maximum f number setting of f/8 when using HR mode.  At higher f numbers, even with a perfect lens, the maximum possible resolution falls rapidly.  At f/11 and beyond, it is likely that in HR mode with even a high quality lens will yield a resolution that is not significantly higher than would be obtainable in Standard mode.



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A Closeup Image of an Orchid taken in HR Mode with my Pen-F



Phalaenopsis orchid, Pen-F with Olympus 60mm f/2.8 macro lens, 2.5s, f/8, 80 ISO



The full sized 80MP and 50MP versions of this image can be viewed here.



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Continue to an Examination of Processing Times in HR Mode


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