FMF - Friends of Minerals Forum, discussion and message board

[Jordi Fabre]

Christian Rewitzer, kindly, wrote a text explaining their "tricks" to do photographs of micro specimens.

As if someone does not know him, Christian is German, he is exhibitor in Munich Show and in other German Fairs, and have an enormous reputation for the quality of his photographs micro. You can see a gallery with their images in Mindat: https://www.mindat.org/gallery-5825.html.

Thanks Christian to be so kind to share with us your knowledge!

Equipment

Microscope

I use a Carl Zeiss Discovery.V20 microscope with a motor-driven focus and zoom adjustment that can be remote-controlled by a personal computer. This is a real advantage by taking z-stack photos, as I will explain later.

With several objectives on a revolver one can vary the field of view additionally to the zoom. However, my preferred “dark field” illumination cannot be combined with all objectives at the same time for geometric reasons.

Therefore I prefer the PlanApo 1,5 objective which allows a FOV of app 1,5 mm as a minimum. All smaller objects cannot be further resolved with optical equipment, because physics have their limitations there.

More informations: https://www.zeiss.de/mikro

Illumination

Very important for a good picture is a good illumination. Lots of light from all sides have two main disadvantages: You get infinite annoying reflexes and no 3D effect. For getting a 3D effect, you need shadow. Light coming nearly horizontal achieves best 3D-effects, what a view outside an aircraft during sunrise or sunset always shows very impressively. At microphotographics You can combine the necessary with the useful measure.

Lamps generate not only light, but also heat. Heat is not so recommendable especially for samples with embedded crystal water. They might be destroyed by that quickly. The solution is a cold light source. A halogen bulb generates light, which is transported via glass fiber optics to the objekt. Heat and light are dislocated by that.

I use a light source MC 1500 from Schott.
https://www.polytec.com/ger/_files/VisiLEDs_Uebersicht.pdf

Camera

A primary requirement when choosing a camera is the compatibilty with a photo tubus adaption. Manufacturers of scopes serve a certain number of available cameras on the market. SLR cameras have a bigger imager and more pixels. However the preview of the final picture is only available at consumer cameras. Aditionnally some consumer cameras offer a display to swing out with tilt and swivel ability, which is a big ergonomic advantage in sitting position.

Using compact-cameras with a zoom, a full scale picture should be feasible in the range of the optical zoom. If You must shift into the digital zoom for having a vignetting free picture you loose a lot of resolution.

The maximum resolution of an objective calculates as follows:

d: distance between two points
λ: wavelength of light
A: numeric aperture of the objective

The wavelength of visible light is in the range of 400-700 nm. Green light has app. 500 nm. The numeric aperture of best objectives with a reasonable free working distance of app 30 mm are in the area of 0,25. Thus the minimum distance between two points, which can be resolved is app. 1 µm.

A FOV of 1 mm, achieved with a 5 Mpixel camera, has a pixel distance of app 1/2500 mm or 0,4 µm. This shows, that a further increase of the number of pixels above 5 Mpixels doesn’t achieve higher resolution in the highest magnification area.

Actually I´m using a Canon Power shot A620 but for many other cameras are adapters available.

Digital postprocessing

The most important improvement since i do my photos digitally came for me with the z-stack technology. The depth of field is defined by the Abbe-formula. Even if one takes best optical equipment available it doesn’t change the fact, that for displaying minerals the depth of field is by far not sufficient. At a FOV of 3 mm my scope has a depth of field of 0,08 mm. That means I need at least 12 layers to display a cube of 1 mm side length sharply from bottom to top. This is the reason, why most of all microphotographs are not really sharp in wide areas.

A remedy offers only the z-stack technology. The focus of one frame is changed incrementally in z-axis. The increment depends on the size of the frame, I choose normally the half depth of view, see table xy. There is the digital display of the z-axis and the ability of controlling that remote very helpful. Depending on the topology of the probe I need between ten and thirty layers. Those are merged afterwards by special software.

Beside the own software of the big scope manufacturers there are several third-party-solutions on the market. I actually work with helicon focus.

Next is (moderate!) sharpening. A single optimization of each picture is necessary. It is amazing what an improvement from sharpening results.

I continue with the colour correction. Although the white balance is done correctly and colour temperature of the light source was kept constantly the colours of the picture and the colours of the original normally are not equivalent. With my camera I get a little bit too much red, so yellow probes appear to be orange. This is a systematic fault and can be compensated generally.

The whole workflow until I get the final result for one picture takes app half an hour.

[Jordi Fabre]

Christian told to me that if anybody needs help or wants to discuss with him topics related with micro photographs, he can contact with him via eMail: C.Rewitzer(at)web.de

Also, next days he will send to me some unpublished photos. As soon as I get them I will publish them here.

Really kind Christian, thanks a lot!

Jordi

[MaryFender]

Beautiful work. I look forward to seeing more of his photographs.

[Jordi Fabre]

First batch of unpublished photos from Christian Rewitzer. Most Spanish minerals.
Again, thanks Christian!

[ikram]

thank you very much Jordi and Christian,
for publishing theses nice lovable photos here.relay amazing strange photography.
ikram

[Jordi Fabre]

Second batch of unpublished photos from Christian Rewitzer. The photo of the Cetineite is terrific...

Enjoy!

[MaryFender]

Just wonderful!!! We look forward to a book.

[ikram]

Very beautiful nice photos, congratulation Christian ,
ikram

[Jordi Fabre]

The third set of photos from Christian.

I don't know if the visitors of this Forum are enjoying the photos of Christian as I enjoy, because if so, we are the happiest forum in the world ;-)

[Jordi Fabre]

The last set, I have no more photos of Christian. I think I'm going to ask him for more, I have enjoyed so much publishing them, that now I can't pass without doing so. ;-)

[Jordi Fabre]

A Christmas gift from Christian Rewitzer: seven Spanish micro-wonders.

[MaryFender]

What a gift. Thank you Christian and Jordi. Merry Christmas to you too.

[ikram]

very nice Spanish micro-wonders , really mind blowing , regarding Christian Rewitzer a very nice popular personality, he really like to hear from others.
thank you very much and congratulation Christian Rewitzer.
Happy new year and Christmas.
ikram

[John S. White]

The only thing lacking with regard to these extraordinary photos is a better means of indicating size. Magnification is very hard to relate to, most of us can't easily translate that to crystal size or field of view size. The photos are lovely, the best I have seen.

[parfaitelumiere]

really good shots,a wonderfull travel into the micro world!