UV macro with the Coastal 60/4 APO

[nfoto]

Raining heavily today, so staying indoors the C-19 way was not difficult. I collected some dandelion heads yesterday and decided to give them a make-over with proper UV macro treatment. In this case, the Coastal 60mm f/4 APO reversed on extension to give m=2.52X. Camera D600 full-spectrum, filter Baader U, focus stacking N=59 frames in Zerene.

 

The CO 60 did make a slight hot spot in this configuration thus I have designed a better hood for it to mitigate the potential flare issue. However, sharpness and detail rendition are both excellent. The lens hood used this time just simply wasn't narrow enough.

 

 

This is a small 100% crop of the frame. Dandelion pollination biology is entertaining stuff on several levels. The plants simply don't need any pollinators at all, yet provide lots of goodies for all the pollinating insects eagerly attracted to these flower heads. The style is designed like a chimney sweeper's brush and push through the tube of fused anthers on their way, thus getting a good dusting of pollen grains. Afterwards, the style front splits into two revealing the receptive stigmatic areas inside, which are purely superfluous as the flower already is [apomictically] self-fertilised. A true unrequited love affair.

 

I'll experiment further tomorrow with the "new" lens hood and hopefully, improved results. I might increase magnification too. 4X should be feasible.

[bvf]

That's stunning - far better than I can get with non-UV-specialised lenses.

 

I've just this minute posted elsewhere that your earlier comment about using a lens hood to avoid UV hotspots has solved that problem for me. As a hood I used an M42 extension tube screwed into the front of the filter.

[nfoto]

Thanks -- not dissatisfied myself. However, I should drop ISO further to max 100 as the stacking algorithm (Pmax) exacerbates the noise appearance of the final outcome. Getting enough UV illumination is not a problem as I used a single 1600 Ws studio flash spaced about 0.7 m away and reduced its output by approx. 2 EV. The flower head was in a water bath bolted to a large heat sink for maximum dissipation of flash energy.

 

I have redone the lens hood for the next time using a narrow C-mount spacer. Hopefully this will end any hot spot tendency.

[colinbm]

Fantastic Birna, lovely fine details

[dabateman]

Excellent crop.

Reminds me to get back into macro. Have to look into the worlds within our flowers.

 

[JMC]

Lovely image Birna. Stacking images makes such a huge difference.

[nfoto]

A true understatement ....

 

Yes, getting anything sensible out of the 3-D chaos inside a dandelion head would be near impossible without resorting to focus stacking. At least when magnifications exceed 1X.

 

As I run the camera on A/C mains power and the files are directly transferred to a spacious network storage device, the stack length itself could be extended many times over. However, we are dealing with biological specimens that eventually start to respond to all the UV we are pounding them with. Heat build-up can be mitigated by heat sink(s), but the flower response to UV itself cannot. Thus much more than 100-120 flashes over the span of a few minutes tend to make the flower move out of alignment.

[nfoto]

As usual in this business, the cause of the flare (tendency to hot spot) was not from where I thought, viz. from an inadequate rear lens hood. Rather, it was caused by leakage around the (makeshift) holder for the Baader U upstream of the lens itself. I wrapped the filter section in aluminium foil and now apparently the flare is gone.