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Mineral PhotographyHigh-power, high CRI LED lightning

15th Jan 2017 17:05 UTCJyrki Autio Expert

Is LED lightning a viable option for mineral macro photography now when manufacturers claim color rendering index of 85-90 for white 4000-5000K SMD LED chips?

I see an advantage of getting lot of light on budget and possibility to get the light source close to the sample.

Any experiences on LED-lightning?

15th Jan 2017 19:37 UTCTony Peterson Expert

Seems unlikely but we're all interested. Try to find an emission spectrum and give us the link. I doubt very much that it even approaches the continuous spectrum needed for accurate colour photography. If manufacturers could make a light that emits at the same rgb wavelengths that cameras measure, though, that would do the trick.

15th Jan 2017 19:48 UTCJyrki Autio Expert

Here is one sellers site

http://www.yujiintl.com/high-cri-led-lighting

15th Jan 2017 19:50 UTCReiner Mielke Expert

I have been using LED lights for years and have had no issues with it. I used to use halogen lights but the heat was a big problem, the LEDs solved that one nicely.

16th Jan 2017 16:24 UTCJyrki Autio Expert

04803570016031827599337.png
Here are couple of emission spectra Tony asked. I did not search very hard.


Yuji
00270550015660010514752.png


Cree
01997440015660010512630.png


Nichia Ra 90

16th Jan 2017 17:24 UTCRonald J. Pellar Expert

That dip in the blue-green part of the spectrum will cause problems with color rendering of certain mineral specimens, e.g., dioptase. In general, for photography, CRI should be better than 90.

16th Jan 2017 17:50 UTCJeff Weissman Expert

08691000016031827594865.jpg
Something like this will be very useful in resolving these issues, and is only about $10.00, depending on supplier - similar color checker cards are available in many different sizes and some with a greater number of colors. This one is from http://www.dgkcolortools.com/



17th Jan 2017 17:17 UTCJyrki Autio Expert

01120440016031827605996.jpg
Here are three pictures of dioptase. One is fluorescent light and two not especially high CRI LED illuminated. Camera white balance adjusted with gray card and no post processing. Does any of these look like real dioptase?

02900270015660010517987.jpg

04341730015660010517080.jpg

17th Jan 2017 18:40 UTCRonald J. Pellar Expert

Try the same photo with tungsten or tungsten-halogen.

17th Jan 2017 19:14 UTCJyrki Autio Expert

03750700016031827609410.jpg
Here is one with Redhead 800W DXX R7 halogen bulb. Tomorrow I check if there is tungsten halogen in house.

17th Jan 2017 23:28 UTCRonald J. Pellar Expert

Definitely more blue. Fluorescents and LEDs have that dip in the blue-green whereas tungsten is full spectrum.

18th Jan 2017 03:58 UTCTony Peterson Expert

In my opinion NO light source will allow correct color for dioptase because it is extremely birefringent and strongly pleochroic - any hint of polarization in the detector (film has it because emulsion crystals are aligned; semiconductors that are not cubic will also have a directional response) will result in a color imbalance relative to our non-polarizing eyes. None of the above examples looks like dioptase to my eyes and the blue under halogen is quite typical. It is frustrating that one of the most beautiful minerals we know is so hard to capture!!

18th Jan 2017 12:40 UTCRonnie Van Dommelen 🌟 Manager

Isn't the RGB representation of digital images as much a problem than the source (although understandably, we don't have control over that like we do the source)? The green and blue-green colors are always the farthest from the RGB gamut.


Diagram of the problem:
http://cdn.digital-photo-secrets.com/images/color-space-cmyk-compare.jpg

18th Jan 2017 14:15 UTCVolker Betz 🌟 Expert

Hi all,

I was a bit absent from internet for a few days. So my late comments. I switched from halogen lights to LED-lights a few years ago.


At present my experience is, that LED ( I use now mostly 5500 K versions) and control colour in life view with colour calibrated monitors works fine.


The colour of crystals is not as simple as that from "normal" pigments as luminescense (the alexandrite effect) can vary colour, also plechroism is present.


My experineces with LED are fine, but the secret is the post processing. Pictures from dioptase can be set to any hue you want, if not to many other colours are present. The tools color-balance, saturation an spectral sensitivity are very powerful. I mostly do that with helicon filter.


I wrote a paper about the subject in two parts. The first was was printed in Lapis 12/2016 and the second will be in Lapis 2/2017.

Sorry, it´´s in German.


And by the way: Ronnie hit the most important point: if the crystals show colours outside the colour space then only a fifth colour additional to cmyk can help (in printing).


Volker

18th Jan 2017 14:57 UTCLarry Eicher

I'm uninitiated. What is wrong with using a Canon 580 ex slave?


Regards,

Larry

18th Jan 2017 15:13 UTCRonnie Van Dommelen 🌟 Manager

Larry,


It's hard to know what the lighting will be like on a specimen with flashes. You want to reflect light off crystals to highlight shape, striations, transparency, etc and thus you need either many lights or a few lights and reflectors. I've seen professionals use very high end flashes that output a low level constant light that is used during lighting composition (i.e. flash and reflector placement), but without that you are in-the-dark so-to-speak.

18th Jan 2017 15:30 UTCJyrki Autio Expert

>Volker Betz wrote: Pictures from dioptase can be set to any hue you want, if not to many other colours are present.


If we take above diopside as an example: It is mixed with calcite which should be white. Any odd color in calcite would be discernible. There are no clear areas of diopside and calcite because they are randomly mixed.

How difficult it is post process this?

18th Jan 2017 20:25 UTCRonald J. Pellar Expert

Ronnie, Volker a few comments on the chromaticity diagram:


1) Colors outside the RGB and/or CMYK locus are referred to as "out-of-gamut" colors.

2) The out-of-gamut colors cannot be reproduced exactly in staturation and/or brightness.

3) Out-of-gamut colors can be matched exactly in hue.

4) White balance affects hue only.

5) The dioptase problem is minimized by proper hue rendition.

5) "Alexandrite" effect is related to the color temperature and spectral content of the light source as well as the spectral content of the minerals spectral reflectance characteristics.

6) Full spectrum light sources and proper white balance are two way to remove some of the color rendition problems. LEDs, with their large gap in the blue-green are a real problem for some mineral rendition. There are some new LEDs that use a UV LED and a better assortment of phosphors and should provide better CRI numbers, e.g., 95 or above, and offer more hope for the photographer. Until these are more readily available I would recommend tungsten or tungsten-halogen.

7) Selective hue adjustment in photos can be done with masking techniques to affect the mineral that needs hue adjustment without affecting the other minerals on the specimen. Very diverse specimens are a real problem (pain) to create the masks, but who said mineral photography was easy? :-D

19th Jan 2017 14:11 UTCRonnie Van Dommelen 🌟 Manager

Ronald,


Thanks for that clear explanation! Especially #1-4; I didn't know that. So, in other words, we can match the hue exactly, just not the saturation of the green? So a specimen in the hand will look richer (more saturated) in color than a photo of the specimen.

19th Jan 2017 15:58 UTCJyrki Autio Expert

Color gamuts were a real eye-opener. I have looked at those before but this was a good practical example of human vision vs. different technologies.

In my pictures there has always been something wrong with color of almandine-pyrope garnets (red-violet). That color seems not to be that far out of gamut so the explanation might be something else than with color of dioptase.

19th Jan 2017 17:48 UTCRonald J. Pellar Expert

Ronnie, your interpretation is correct.


Jyrki, the two biggest contributors to color problems are, in order, white balance and spectral quality of the light source. They can impact a mineral specimens in different ways, but hue errors seems to be the cause of most complaints. Fortunately hue can be corrected to match a given specimen, but you must be very careful to match "apples" with "apple", i.e., make sure that the color temperature of the light source used to look at the specimen is the same as the color temperature of the monitor image that you are trying to match and that extraneous light sources are not present to affect your eye's adaptation. The biggest problem in hue matching is keeping the other parts of the specimen from changing hue in a bad way while getting the main mineral correct.

19th Jan 2017 18:51 UTCJyrki Autio Expert

05626070016031827606444.jpg
Ronald: Thank you for your answer and sorry if I keep on inquiring, but I am very interested in this.

Here is one example:

When I found this garnet on a sunny spring afternoon I thought this must be the bluest garnet I have ever seen. It is from a metamorphic garnet and cordierite rich rock and most probably Mg-rich almandine.


However when photographed it turns out dull reddish purple, not vivid blueish purple seen in low sunlight. This is second or third take of this mineral I uploaded in Mindat but not a good one still.

So this difference in real life and picture is about both the spectral quality of light and eye adaptation to ambient light?

19th Jan 2017 19:06 UTCVolker Betz 🌟 Expert

Dear Friends,


as I use ( only LED) I find the benefits of new light architecture are supreior against some hue trouble with some problematic species like dioptase.. I may be a bit old fashioned but thre are two different goals. The one is the sceen picture in the rgb colour space and the other the CMYK + extra colour for printed pictures.


At present LED perfome well for mineral photography if all the "tricks" are used.

I used halogen light for alsmost 40 years and I also never made better pictures as now with LED.

Despite some arguments with lacks in spectral continuity.


So my hint: ist not the instrument, ist the skill and experience of the photorgrapher.


Volker

20th Jan 2017 13:07 UTCLarry Eicher

Ronnie,


I thought that was part of learning to be a photographer. I suppose it is like the old film days when you had to intuit the exposure. I have been finding that I need reflectors. I want to highlight the crystal faces but not over expose them. I find that I need to lean toward underexposure and improve exposure in post processing. I have been trying a scrim between the subject and the flash which seems to help.


I am thinking of looking into LEDs on goose necks. WUSIWUG. I have a long way to go.


Regards,

Larry

20th Jan 2017 15:20 UTCJyrki Autio Expert

I have read this whole thread as cautious yes for LEDs.They have their problems if you are after highest color qualities. Otherwise not so bad.

20th Jan 2017 16:45 UTCScott Rider

I must thank all who contributed to this topic. I attempted to take pictures of some New Jersey prehnite the other day and those images are coming out a yellowish hue, with ZERO green.. Then I came accross this topic, and boy have I learned many things, especially on how I am doing things incorrectly....


. So, I have looked into ordering some high CRI LED lighting, as I don't want to mess with tungsten (heat issues with my setup). I bought some LED bulbs with a CRI of >95. They weren't too expensive, but not too cheap either...


If I can remember, I'll post to this site whether those LEDs I ordered will be any good in the blue-green spectrum. I currently was using cheap fluorescent lighting (I am a newby in terms of photography and the box said daylight so I was suckered into that...) and was satisified with most my images of my specimens, less all the blue and green ones. They always come out more yellow on my current lighting setup...


I think I'll try to do both the prehnite, and Cavansite, another mineral I cannot reproduce on camera.... Cavansite is one of my favorite minerals and I cannot reproduce the colors unless I am outside, and it gets close there... But not with my controlled lighting setup... Its quite frustrating... But thanks to you all, I think these new bulbs will be great. I should get them hopefully by the end of this week.


THe CRI is supposidly 95 on the bulbs I bought... Looking into the research, those should cover the blue spectrum...

20th Jan 2017 18:30 UTCVolker Betz 🌟 Expert

Dear Jyrki,

I experimented with your almandine photo. I could get it more blue but only limited. Due to the white luster on the almandine crystal the possibilities to alter the hue are limited. I would recommend to use non reflecting spots from the side or a back light with 5500 K.

Then you see more the transmitted light than reflected light and the bluish hue is better visidible and can better adjusted.


Volker

20th Jan 2017 19:38 UTCJyrki Autio Expert

Dear Volker,


I'm glad you took time to think about my question. I will try again as suggested and compare it against natural lighting conditions after couple of months, when we have good light here up north. ;-)


Jyrki
 
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