P900 at and near 2000mm

 


P900 at 1800mm and 2000mm EFL


In their review of the Nikon P900, Imaging Resource concluded:  “Perhaps most important to us in the "not-so-good department" is that the lens is not overly sharp at its full optical 2000mm equivalent reach. Backing off to around 1800mm and less improves sharpness significantly, and that's still a farther reach than any other fixed lens camera currently offers, but it's important to know for anyone wanting critically sharp images and expecting them at full optical telephoto reach”.


The perceived sharpness of an image can depend on a number of factors, including resolution and acutance, as discussed on the Cambridge in Colour website here.


I have previously measured the resolution of the P900 at several different focal lengths as described here, but I did not test at 1800mm EFL.  I found that the resolution at 1500mm EFL was 1960 LPH and 1870 LPH at 2000mm. Assuming that the resolution at 1800mm equals 1960 LPH (it is likely to be somewhat lower than that) then 1960 lines will be resolved in the height of the 1800mm image. 


Although a resolution of 1960 LPH at 1800mm will be slightly higher than the 1870 LPH at 2000mm, the magnification factor will be correspondingly lower, as it covers a wider field of view.  That is, an object in the 1800mm image will be smaller linearly by a factor of 1800/2000 = 0.9 compared with the image at 2000mm.  Therefore the 1800mm image will only resolve 1960 x 0.9 lines = 1764 lines, when compared at the same size as the 2000mm image.  Since the 2000mm image resolves 1870 lines, this calculation predicts that the 2000mm image will provide more detail than the image taken at 1800mm.


To test this, I used a tripod set at 12m from chart board, at the centre of which I attached a photo of a boar’s head cut from a magazine.  The printing on the magazine at a macro level consisted of a circular looking pattern of ink spots when I enlarged a closeup of the photo using my Panasonic ZS40, as shown in the crop below (click on the image for the full sized view):



Crop from Closeup Image of Magazine  Photo


I took several shots of the board from 12m at 1800mm and 2000mm EFL and compared the SOOC JPGs in different ways.  I viewed each side-by-side at 200%; I compared crops covering the same central area; and I made crops of the platypus stamp and compared them at the same size.  These images are shown below (click on an image for the full sized view):



Above: Chart Board at 12m, 1800mm EFL, f/6.3



Above: Centre Crop from the Previous Image



Above: Chart Board at 12m, 2000mm EFL, f/6.5



Above: Centre Crop from the Previous Image



Above: Stamps Compared: !800mm at Left, 2000mm at Right


I compared several pairs of replicate images to ensure that what I was seeing was consistent.  To my eyes, in each case the 2000mm images showed slightly more central detail than the 1800mm images. 

In the case of the boar photo, I could see more of the circular ink spots around the eye area.  For the platypus stamp, I could see more vertical lines in the background shadow area across the top and down the LH side; and more continuous white horizontal lines in the water areas.


Conclusion

From the tests I concluded that somewhat greater detail can be captured with the P900 of an object in an image taken at 2000mm EFL than in an 1800mm EFL image taken from the same distance.


I then examined depth of field (DOF) with the P900, as described on the following page.






Continue to DOF with the P900


Return to P900 Testing


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