UV focus stacking

[Thomas Males]

I have been wanting to try focus stacking for a while and today was my first try with a motorized slider.

 

I have only taken pictures of two flowers, so far, an orchid: Phalaenopsis ssp. moth orchid family. (and a rose, not posted)

 

I have a Canon EOS R modified for ultraviolet by LifePixel, EF 40mm f2,8STM, flash, and focus rails,

 

This picture is one of the better ones, but not sharp all over, and maybe a bit dark.

 

Speed 1/100, f 6,3, iso 50 raw file, CR3, eleven pictures, processed in digital photo professional 4, and then Helicon Focus.

 

I did not find any tread on focus stacking, thats why I started one.

 

Have you tried focus stacking in UV ? and if so, any thoughts?

[nfoto]

Nice try. The peculiarities of the Moth Orchid stand out.

 

I've done some UV stacking, but mainly in the true "macro" range, i.e. 2 to 10(-15) X magnification. One does need a lot of UV illumination to get proper exposure at such high magnifications. I typically use 2, sometimes 3, Broncolor studio strobes with uncoated Xenon tubes.

 

With a proper automated system, such as a Stackshot or similar rail, one can do detailed studies of flowers or other stationary subjects. However, flowers have a propensity to start wilting after a number of UV blasts from the flash(es).

[nfoto]

This is an example, the flower of Glechoma hederacea at m=3.

 

 

Taken with my Nikon D3200 (internal Baader U) and JML 50mm f/3.5 at f/16, 1/200 sec., 42 frames in Zerene Stacker.

[Thomas Males]

Thanks for input, stackshot is the one I use, I plan to try on lichen outside soon, no wild flowers this time of year, (that I know of).

[Andrea B.]

I’ve made a few simple stacks. Mostly by hand. (Example: For a 5-petaled flower, I would make 5 shots, each focused on a different petal. And then make 3-5 shots of stamens and stigma.)

 

Changes in the flower position due to direct response to UV stimulation can sometimes happen. It’s fascinating to see the flower begin to turn towards the UV light source in a short interval - minute or two. But that does tend to wreck a stack.

 

I’ve had a couple of flowers whose anthers “jumped” when the UV flash fired. And of course if you are working close, a UV flash or torch can sometimes fry the flower. Freshly cut flowers wilt and droop even when immediately placed in water, but eventually stabilize if given a few hours.

 

But UV floral stacking certainly can be done with a bit of patience. I’d suggest initial stacking trials with a robust flower type like a sunflower, florist rose (strong stiff stem, beautiful petal texture in UV), or chrysanthemum. And your idea to stack-shoot lichens is a very good one. Lichens don’t move much.

 

******

 

Thomas, I’m going to move this topic to the technical section. This board is for Rules about forum membership and post content.

[enricosavazzi]

One thing to remember is that loss of resolution due to diffraction is wavelength-dependent, so in the NUV you can stop down between roughly half a stop and one stop (depending on NUV wavelength) with respect to VIS to get the same diffraction-limited CoC as in VIS on the subject side. This in turn translates to fewer and "thicker" images needed in an NUV stack of the same total thickness.

 

This of course assumes that the lens you are using has a variable aperture and its resolution is diffraction-limited.

[bvf]

I've done a lot of photo-stacking of flowers, both UV and vis. A lot of this with macro. Like Andrea, I've had a lot of problems with flowers twitching, drooping, and stamens waggling about in the time taken to make the stack.

 

I don't have the luxury of a motorised slider, so the movement is done manually. Seems to work well, but must be slower than having a mechanised slider.

 

I'va also done a lot of stereo photo stacks, which of course doubles the time needed.

[nfoto]

Sometimes one can circumvent the wilting issue by putting flowers onto a heat sink. For example, drill a hole into a slab of aluminium, fill it with water and put the flower there. The high end version is with a CPU-type cooling fan bolted onto the heat sink itself.

 

I have used the above approaches for doing UV photomacrography of Lemna (duckweed) -- these tiny plants have thin, delicate fronds and reduced flowers that dry up almost immediately.

[dabateman]

The reason why I bought the Canon 40mm f2.8 STM lens is I have become lazy with the Olympus internal focus stacking mode. With the firmware hack you can focus stack automatically the Canon 40mm with either of the Metabones adapters. The speed booster or the pass through BT2 adapter. The penalty of the Speed booster isn't too bad, the aperture shifts from F2.8 to f2, but you loose 1/3 stop of 370nm UV light.

Biggest problem is the Em1mk1 has a minimum shutter speed of 1/8 seconds. So I have to either blasted the lights or use flashes. Fortunately, Olympus is the only one smart enough to allow for a delay in the auto focus stacking mode. So you can use flashes.

My Em5mk2 doesn't have the 1/8 seconds limit. But I don't have it full spectrum converted.

I also got an Olympus Em14 adapter (1.4x), which has a 2 and 1/3 stop loss of UV at 370nm. However in using it I discovered that the 2x internal tele extension mode works with automatic focus stacking. So that is better.

I should post something about this. I typically get into a cycle of taking images and then not sharing them.