22 replies to this topic

[nfoto]

I routinely shoot a few attempts of UV with any new lens, mainly relying on the implicit rear filtration of the built-in Baader U in my modified Nikon D3200 (filter courtesy Vivek Iyer).

On most occasions, there is little to see and even less to report, as modern lenses tend to be quite impermeable to the passage of UV. My newly acquired LAOWA 100 mm f/2.8 *Ultra-Macro CA-Dreamer 2X' lens (the blurb is the maker's labelling) gave some serious food for thought, though.

I quickly found it responded around -3EV re one of my UV-Nikkor 105/4.5 work horses, which is pretty similar to many other lenses which let in a sliver of UV-A. However, once the NEF was pulled up in Photo Ninja, i was in for a real surprise as there was plenty of chromacity left to play with. A most unusual situation. Even more surprising was the total lack of focus shift visible-UV, and a degree of image sharpness that even UV specialist lenses will struggle to match.



I noted this lens is a welcome addition to the arsenal of optics suitable for 'artistic' UV. True, the contamination of IR rears its ugly head as the lens itself probably transmits just a modicum of UV, but the pleasantness of the outcome cannot be denied. And the sharpness -- my oh my. Factor in its fairly low asking price and this is a no-brainer acquisition.

Caveat: it does hot spot in IR. So one cannot have the complete cake and eat it. Just to warn you.

[colinbm]

If you could keep those trees still it would be a corker....

[nfoto]

I do happen to enjoy movement in an image .... Of course movement was to be expected when shooting at base ISO 100 on a heavy overcast, windy day !!

The ISO performance of my D3200 discloses its age as a digital recording system. I can do up to ISO 400 for close-ups without much loss of qulity, however from there abouts the increase in graininess commences to be troublesome. Still, having had a modified D200 as UV work horse for a long time, ISO 400 is fantastic anyway.

(the Z6 easily delivers at ISO 1600, but there is the striping issue to consider)

[Stefano]

Hi Birna, how did you process the image? I notice it doesn't have the usual UV false colors (blu/violet and greenish yellow), and you said this lens is good for artistic purposes, so I guess you just played with the colors. Did you swap channels or something similar? Is the red in the foliage an IR leak or is it due to its UV absorption curve? (foliage can appear reddish after channel swapping).

[StephanN]

Stefano, on 01 October 2020 - 15:53, said:

Hi Birna, how did you process the image? I notice it doesn't have the usual UV false colors (blu/violet and greenish yellow), and you said this lens is good for artistic purposes, so I guess you just played with the colors. Did you swap channels or something similar? Is the red in the foliage an IR leak or is it due to its UV absorption curve? (foliage can appear reddish after channel swapping).

I second that, would be very interesting to know

[Andy Perrin]

If I'm reading the original post correctly, the red is simply the IR leak.

[StephanN]

Andy Perrin, on 01 October 2020 - 16:30, said:

If I'm reading the original post correctly, the red is simply the IR leak.

Doesn't it say the photo was taken with the Baader U filter? On the other hand, if the colours are from the original photo and no photoshop-paint, then it has to be IR, right?

[UlfW]

-3EV is quite a lot of attenuation in the UV band. Then the remaining OD4 IR leakage of a Baader U likely becomes significant

[StephanN]

I see, still getting my bearings with all these leaks. And the IR-hotspot is the reason for the blurred trees in the centre

[nfoto]

Nah. Blurring is wind-induced. Decidious trees are more easily impacted than conifers. So simple biological explanation will suffice.

I like vegetation red instead of pale green-tinged, so just did a slight colour adjustment. Compared to the traditional UV "palette" the colours were pretty muted anyway. The IR leak was, as indicated by Ulf above, quite significant. I felt like a throwback to my first period with digital UV (D1, D1X) when vegetation typically turned red.

The are few flowers around this late in the season and most of the few are UV dark all over, like the tansy Tanacetum vulgare. I did pick a Malva this afternoon and will do a direct UV flower comparison wih that subject -- if the closed corolla unfurls!!

Ulf, -3 EV is the overall response through the Baader U compared to the UV-Nikkor. So not indicating the UV region alone is -3EV down and the IR unimpacted.

[Cadmium]

Birna, A very beautiful image, truly!
However, a UV image? Hmm.
I would want to start with an unprocessed image, you have that, of course, and your process is divine, but I can't make any judgement from that.
I would want to see the raw UV shot, no processing, except a usual standard optimized white balance, that would help a lot.

Pertaining to the lens, I keep hearing people talk about a 'grease' issue. I don't know if that is rare, but it doesn't seem to be that rare, and it would concern me.
https://www.shutterb...apo-lens-review

Edited by Cadmium, 01 October 2020 - 22:04.

[nfoto]

OK, the Malva moschata flower later this afternoon decided to open its corolla, thus allowing me to snap a few UV frames. NB: the frames were taken about 1 hour apart.

This is UV-Nikkor 105mm f/4.5 @f/8, ISO 100 and -2EV output on my Broncolor studio flash (uncoated xenon tube, distance to subject approx 80 cm). Nikon D3200 with built-in Baader U. NEFs run through Photo Ninja with standard settings.



The photo was taken at 1:2 scale. Thanks to the very long focusing travel on the UV-Nikkor, getting pin-point placed focus on the anthers was a breeze.

Now, the LAOWA, again set to f/8. As it responds less to UV, I had to increase flash output to 0EV and ISO to 200, i.e. effectively bumping the exposure 3EV re the UV-Nikkor. Getting perfect focus was very difficult even with a tripod-mounted camera due to the excessively short focus travel. The smallish finder of the D3200 wasn't exactly helpful either in this case.

The LAOW clearly is transmitting much less deep into UV-A, so the rendition was less detailed and had less contrast. However, the major floral pattern was evident enough.



For focus stacking using a motorised rail, the issue of getting perfect focus with the LAOWA would effectively disappear.

[dabateman]

Birna,
That reminds me of the Nikon AF-d 105mm f2.8 lens in UV. If you have one might be fun to compare.
Mine is good for UV photography, which surprised me. I don't have a converted Nikon camera though, so I loose the AF with my m43rds cameras.

[Cadmium]

Birna, This are very nice. Thanks! I especially like the blue one.

Edited by Cadmium, 02 October 2020 - 01:30.

[UlfW]

nfoto, on 01 October 2020 - 20:41, said:

Ulf, -3 EV is the overall response through the Baader U compared to the UV-Nikkor. So not indicating the UV region alone is -3EV down and the IR unimpacted.

That is exactly what I meant.
This leads to a really bad UV-IR ratio from the lens + filter.
That makes even a smaller IR leakage quite pronounced.

Edited by UlfW, 02 October 2020 - 04:55.

[nfoto]

Exactly as I made clear from the beginning. That is why one gets 'red' vegetation. However, as the Malva shot demonstrated, still one gets the UV signature of the flower -- even with a powerful studio flash quite close. Thus a sliver of real UV has to get through. The anthers are UV dark as they should.

I concluded this is a lens for "artistic" purposes. For UV documentary use, I have Coastal 60 and UV-Nikkors.

[nfoto]

To round up the Malva study, here is the UVIF record of it. Anthers glow brightly as do the basal bracts. The pollen grains themselves glow in pale green hues. However, in order to appreciate the latter, one would need far higher magnification.

I'm off to a transgender conference for the weekend, however on my return I'll try using another Laowa lens, the 24mm f/2.8 Ultra-Macro 2.5-5X for a quick assessment of the fluorescent pollen itself. That is, if the Malva hasn't perished while I'm away.



Nikon Df, Laowa 100mm f/2.8 @f8, "NEMO" UV-torch (thanks, Ulf!!).

[Cadmium]

UlfW, on 02 October 2020 - 04:52, said:

That is exactly what I meant.
This leads to a really bad UV-IR ratio from the lens + filter.
That makes even a smaller IR leakage quite pronounced.

I understand the ratio situation, except, the IR that would be 'forced' through a Baader U (given a bad ratio because the lens may be suppressing most of the UV) would be in the higher IR range,
a range that would be more monochromatic,
so the usual black UV areas might look gray, but not colored red, brown, warm, or the like, just gray...
If the UV-pass was a stack, using any number of U-type filters, stacked inadequately enough, then you would have a lower Red/IR range leak in the +/- 700nm range, and that would render the red, brown, warm.
So, I am not understanding any out of band color coming from a Baader U.

I know, old example, but I think this illustrates my point about the 'color' of the leak between a Baader U higher leak and a stack having a 700nm range leak.
Of course, these leaks are both 'forced' in the sense that their UV is entirely removed by the 610nm longpass filter,
and that the exposure time is much longer than the optimized UV photos at the left that are not stacked with the longpass.
You see how the Baader U out of band leak is white/gray, and the UG11 stack is brown/warm.
I just don't think any color would be forced through a Baader U, it should be entirely gray/white monochrome.

Edited by Cadmium, 03 October 2020 - 04:38.

[Stefano]

Steve, I agree that's the case in a RAW image, without a WB applied to it (or anything else). Birna's image is more artistic than "accurate" or "scientific", she did apply a WB (judging from the gray wall, etc.) and liked the trees red, and so she intentionally made them red (instead of "pale green-tinged").

I'm simply saying that when you apply a WB, areas that were "natively" gray change color, and so do leaks. If you ever noticed, when you overexpose in UV and IR under WB, you don't get white, but a blueish/yellowish color (in my case, I have yellow in UV and blue in IR, under sunlight).

[UlfW]

Cadmium, on 03 October 2020 - 04:22, said:

I understand the ratio situation, except, the IR that would be 'forced' through a Baader U (given a bad ratio because the lens may be suppressing most of the UV) would be in the higher IR range,
a range that would be more monochromatic,
so the usual black UV areas might look gray, but not colored red, brown, warm, or the like, just gray...

I do not think that is correct. The peaks of leakage in Baader U coincides with the UG11 peak around 700nm.
There it is different sensitivities due to the Bayer matrix filter.
In NIR this area is the most sensitive due to the behaviour of the semiconductor material in the sensor.

In this case the colours in the image are also shifted due to white balance.
Compare how different the foliage colours get for different RG-type filters when the image is properly white balanced against pure gray.

In Birnas image above you have weak light from the very top end of the UV-A range competing with the IR leakage around 700nm.
A white balanced image could get very interesting colour combinations depending on sensor sensitivities and UV-IR ratios.
You cannot expect the colours to always be close to the normal surrounding colours. Light close to red might turn out as red, but could also be very different.

Edited by UlfW, 03 October 2020 - 11:59.