Re: Tamron 50-400mm f/4.5-6.3 Di III VC VXD Image Thread
If you shoot with the 50-400 at minimum focus distances (MFD), the following might be of interest to you.
I did some additional measurements, and here are the key observations.
1) Tamron 50-400 lens magnification ratio drops from 0.5 at 70 mm FL and 27 cm MFD to 0.25 at 167 mm FL at 76 cm from the target to camera sensor (at 167 mm FL the lens cannot focus when the distance is shorter that 76 cm).
2) Lens magnification ratio drops further to 0.21 at 195 mm FL when MFD is 1 m (100 cm)
3) Lens magnification ration is close to 0.27 at 400 mm FL when MFD is 146 cm.
These results are illustrated by the following uploads where we are looking at a $1 bill. Interestingly, the printed part of the bill (excluding the borders) is 147 mm, in a 4.08 to 1 ratio to the sensor width of 36 mm. Thus, when the lens magnification is 0.25, we expect to see the $1 billl occupy the space almost exactly from edge to edge of the picture (and sensor) frame.
Upload 1 illustrates this point. This image was taken at 167 mm when the lens magnification is very close to 0.25
Upload 2 is an image at 195 mm when the magnification dropped to 0.21
Upload 3 is an image at 400 mm, when the magnification ratio is close to 0.27
Upload 4 is a compilation of the central crops from uploads 1 - 3, for a closer inspection. I don't see any significant differences. When pixel-peeping, I see a slight loss of contrast at 400 mm, compared to the image at 167 mm, but this difference is not visible without pixel-peeping. Also, I have observed a systematic improvement of the image contrast on closing from f/6.3 (lens is wide-open) to f/8, but once again, I doubt this should be visible without pixel-peeping, especially at ISO higher than 100.
The bottom line: to achieve a magnification greater than 0.25 - 0.27, the FL should be in the 70 to 160 mm range, with the corresponding distances to the subject in the 27 to 70 cm range. Considering that the length of the camera system is 20 cm from the sensor to the front element of the lens (without the hood), this means that the front side of the lens is going to be at about 7 to 50 cm to the subject.
When shooting this close is impossible for some practical reason, perhaps it would make sense to zoom in all the way to 400 mm and shoot from the MFD of 146 cm (roughly 1.5 m).
There seems to be no benefit in shooting at the MFD from 170 mm to < 400 mm FL.
Nov 15, 2023 at 11:25 PM
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