Tuesday, November 8, 2011

[UV, VIS, IR] Canon f3.5 / 25mm - Topogon clone

Also took a few shots today on a dull+gray day using another famous and quite rare rangefinder lens, a Canon f3.5 / 25mm Topogon clone designed by Mukai Jirō in 1956 with Leica thread mount (LTM 39mm x 26tpi) with a diagonal angle of view of 82° (on full format). My friend Marco Cavina has a very good article about those lenses based on the TOPOGON design HERE .

These Topogon clone lenses are all successors of the famous HYPERGON lens designed by Emil von Hoegh around 1900.

Shots were done @f8 and ISO640 on my UV sensitive camera.

[click on image to see a larger one]

Left VIS, right UV (bw) 100% center crop:

Left VIS, right IR (bw) 100% center crop:

Now color differentials (full format) to make focus shift visible:




As you see, there is some small focus shift (UV and especially IR image show slight back focus), but nothing dramatical (focus was not touched, the shift could be calibrated of course). Interestingly enough, there is only a very small shift between UV and IR (a 695LP filter was used), but overall the IR shift is much larger than the nearly neglectable one for UV (Baader-U filter was used).

In terms of exposure, the one for UV was -7.7EV as compared to the VIS shot, whereas the one for IR was the same as for VIS. All shots (VIS, UV, IR) needed identical exposure correction (+2/3 stop) for a proper exposure using A mode.

Here now closeups using one of my last Rudbeckias. Distance between lens and flower was about 100mm (using a thin helicoid for closer focusing, as with most rangefinder lenses, the closest focusing distance is one meter):




Not that bad actually also that lens ;)

That Canon 3.5/25mm transmits UV to about 350nm, but the UV shot above was taken using the calibration of a flat transmitting quartz fluorite lens, to show the effect also in the resulting color. A color calibration could have been done also for that lens.

Stay tuned, more will follow on that fascinating subject...

More info on this very interesting field may be found on my site http://www.pbase.com/kds315/uv_photos