Friday, November 25, 2011

[UV,VIS,IR] Staeble Lineogon f3.5 / 35mm wide angle lens for reflected UV

Here some test results using the Staeble Lineogon 3.5/35mm lens for reflected UV photography, as well as for IR after having done some successful transmittance tests as shown here on my BLOG

VIS:


UV:


VIS-UV differential:


IR:


VIS-IR differential:


UV-IR differential:


[please ignore the shadow image in the last three images caused by ND+IR stacked filters, this is unrelated to the lens performance]

In summary one could say that the lens performs quite well; there is some focus shift, but rather small. No wonder actually, since Stable was the subcontractor of Novoflex, so the Noflexar 3.5/35mm and the Lineogon 3.5/35mm share the same optics based on my research. The mechanics are different though, as the Lineogon has a quite smaller barrel and also lacks the close-up focusing mechanism teh Noflexar is so famous for. It also has a M39 thread mount, but not a Leica register, as it once was made for the Braun PAXETTE camera, having a 44.0mm register.


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

[UV] Tested transmittance of eight 35mm wide angle lenses for reflected UV

I conducted a test today to measure the UV transmittance of some older manual focus lenses I had sitting around, all f = 35mm and all having either M39mm or M42mm thread mount, so may easily be adapted onto modern DSLR's, if their back focal length fits the camera register.

Be reminded that this is only a test of the suitable UV transmittance, not of other important parameters for UV photography (sharpness, contrast, freedom of flare or hotspots etc.)



Of course the well known Novoflex Noflexar 35mm stands out as a very well transmitting lens and it is actually not a surprise that the Staeble Lineogon does about equally well - it is the same optics inside as Novoflex subcontracted to the German company Staeble to design their optics, which my own research concluded. Be reminded that the Lineogon was made for the PAXETTE camera with M39 thread mount, but for a 44mm register (so is NOT Leica compatible, but helps to adapt as it allows for 15mm more space).


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

Friday, November 18, 2011

[UV] Baader-U versus Andrea-U filter

I noticed that I haven't published a test of the 2" Andrea-U filter I had bought beginning of May 2011, so here it is. It is sold under the moniker "Andrea-U filter", like Baader sells his as "Venus-Filter".

A first comparison of the uncoated 2.05mm thick Andrea-U filter with the Baader-U2 filter (2", new type) brought the following results:

I) Transmittance

A spectral scan results in the following transmittance graph (@ zero and 45 degrees angle of light):


The results of the Baader-U2 filter is also shown, to be able to compare both filters. Andrea-U has some leakage into the violet/deep blue to about 410nm, but there is no sign of IR-leakage (up to 850nm).


II) Reflected UV Photography Test
(using UV sensitive camera, Cerco 94mm lens; Rudbeckia hirta as a target, Xenon flash; identical settings for aperture, flash energy, exposure)



- leftmost: using Baader-U2 filter, using my standardized "standard false UV color palette"
- rightmost: using Andrea-U filter, using my standardized "standard false UV color palette"
- middle: using Andrea-U filter, using a "special false UV color palette" (developed to match the results when using the Baader-U2 filter)

The resulting Andrea-U image has an exposure which is about 1/4 stop less that that of the Baader-U2. There is no sign of IR-leakage (up to 850nm); the somewhat warmer tone of the middle image was caused by the special palette used. All images were processed identically otherwise.


III) Summary

The Andrea-U filter is mechanically well made (the description is printed on foil and taped on the rim, which might eventually come off after long use - I would have preferred it printed or engraved of the metal, but that would certainly have increased cost).

Personally I would rate it a quite useful filter for the 375nm range, especially if used with older "normal" UV transmitting lenses since in the 375-400nm range it has a higher transmittance as the Baader-U2 filter (25% higher = 0.5EV at 390nm).


IV) Incorrect maker statements

The maker of the Andrea-U filter states that "The leading Venus filter (i.e. the Baader-U filter) is a dichroic filter" which is not correct. It is further stated that "This sensitivity to the angle of incidence (AOI) of the light results in some ultraviolet light being rejected that should have passed to the sensor... in other words, a false representation of the object being photographed in the ultraviolet is created." Also that statement is not correct and I will in the following course prove why:

The Baader U filter is an ionic colored filter that defines its properties mainly and it has a two sided dichroic overcoating that only has to block unwanted VIS and NIR leakage. I measured the Baader-U filter at 0-degrees and 45-degrees and my findings were 1) a decrease in transmission of about 0.2 stops (that effect also any pure ionic colored filter has (I show UG11 as an example and also show that under I) above for the Andrea-U filter), as the transmitting light has to pass simply a thicker glass passage - although the Andrea-U filter also shows that effect, it is not mentioned on the maker's site) and 2) a widening of the FWHM of about 12nm.

Both results are irrelevant for practical photographic work based on my experience.

Baader-U (ionic colored filter, with dichroitic overcoating to block NIR leakage):


UG11 (ionic colored filter, that has NIR leakage):


I don't understand why these possibly misleading stetements were made by the maker, as his Andrea-U filter is a good one and certainly finds a use for reflected UV photography. But I leave any interpretation of that to the interested reader...


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



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:

VIS-UV:


VIS-IR:


IR-UV:


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):

VIS:


UV:


IR:


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

[UV, VIS, IR] Orion-15 f6 / 28mm - Topogon clone

Took a few shots today on a dull+gray day using a very small and lightweight russian rangefinder lens, an Orion-15 f6/28mm Topogon clone with Leica thread mount (LTM 39mm x 26tpi) with a diagonal angle of view of 75° (on full format). My friend Marco Cavina has a very good article about that lens HERE including quite surprising photographic comparisons with much more expensive Leica lenses.

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:

VIS-UV:


VIS-IR:


IR-UV:


As you see, there is some focus shift (UV + 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 larger than that for UV (Baader-U filter was used).

In terms of exposure, the one for UV was -7.3EV 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 150mm (using a thin helicoid for closer focusing, as with most rangefinder lenses, the closest focusing distance is one meter):

VIS:


UV:


IR:


Not that bad actually ;)

That Orion-15 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.

A downside should be mentioned: that lens has a 40.5mm deep set front filter thread that does not allow step rings to be mounted, so some clever idea how to attach filters is called for...


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