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woelen
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[*] posted on 17-4-2009 at 14:19
Chemistry-related photography


I recently had questions from quite a few people about making pictures of chemicals, chemical reactions and so on. I decided to write a web page about the subject, so that others can read about it, and if people have comments on it, then I would like to receive them.

http://woelen.homescience.net/science/chem/misc/photography....




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[*] posted on 17-4-2009 at 14:51


Very nice explanation!

I am seriously considering buying the same camera as you, as mine just cannot zoom in well enough. You have seen quite few foto's from me and they are a LOT worse than yours.

Another problem is the lighting condition in my lab. In my fume hood I have a TL-light, wich emits yellowish light. Therefore when I make a picture, the colors appears to be different in the picture than in real. But also for my eye. I had a pinkish powder, and it appeared pink in the hood, and purple outside of the hood.

I really like your pictures very much I must say. Is that your dog by the way? Looks like a nice dog ;)
I love dogs.
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[*] posted on 17-4-2009 at 16:13


Thank you woelen for this very nice lesson in photography! And yes, I like your dog too. It reminds me of our family dog Heidi, a black labrador, now deceased :(

Your first picture shows a lamp. Is this an alcohol lamp? What is the fuel? I am having trouble getting a nice flame like yours on my alcohol lamp. I should post a picture to show you how bad it is.
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[*] posted on 18-4-2009 at 07:48


it`s worth a mention, that in the DOF section (Depth Of Field) that using a smaller aperture will also increase this, but you`ll have to compensate with a little extra exposure time.




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[*] posted on 18-4-2009 at 10:31


No, the dog is not ours, it is just someone's dog ;)

YT, you made a good remark about the aperture size. I added a section about this. However, keep in mind that there are limits in decreasing aperture size, due to technical issues in lens construction (introduction of abberation)




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[*] posted on 19-4-2009 at 01:36


Quote:

However, keep in mind that there are limits in decreasing aperture size, due to technical issues in lens construction (introduction of abberation)


I have to disagree on this one. Lens performance usually gets better with smaller aperture, because you are using the central part of the optics, which show less faults. However, digital cameras show diffraction limits, which depend on the size and pixel density of the sensor.

The fisheye effect you mention is only an issue in case the lens is a wide-angle and has extreme field curvature. This is a common issue with cheap, uncorrected optics, but not with a decent lens.

Quote:

Another problem is the lighting condition in my lab. In my fume hood I have a TL-light, wich emits yellowish light. Therefore when I make a picture, the colors appears to be different in the picture than in real. But also for my eye. I had a pinkish powder, and it appeared pink in the hood, and purple outside of the hood.


This is a white balance problem. See if your camera has an option to adjust white balance and do so using a piece of paper.




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[*] posted on 20-4-2009 at 04:05


Quote:
I have to disagree on this one. Lens performance usually gets better with smaller aperture, because you are using the central part of the optics, which show less faults. However, digital cameras show diffraction limits, which depend on the size and pixel density of the sensor.

My personal experience is that a very small aperture size leads to so-called 'fringing' on sharp edges. This of course depends on camera quality, but even expensive cameras suffer from this effect and this becomes more notable when the aperture size is very small. So, there is some optimum. You probably are right that this is not due to lens defects but to defects/limitations in the CCD array. I'll look into that and check out what is the exact cause of this fringing. But fact remains (from a practical point of view) that there is a certain optimum in image quality over the full range of possible aperture sizes.

Quote:
The fisheye effect you mention is only an issue in case the lens is a wide-angle and has extreme field curvature. This is a common issue with cheap, uncorrected optics, but not with a decent lens.

Well, theoretically you may be right, but in practice it IS a problem, even for cameras in the EUR 500 range. I am speaking out of experience, and if you can find a camera, which has the same image coverage, but at a larger distance from the lens, then you certainly will have less perspective distortion. I really want to urge people, who buy a new camera for chemistry-photography to pay a lot of attention to this issue.

My Pentax Optio S (simpy handheld pocket camera, EUR 200) outperforms my Panasonic FZ50 (semi SLR, EUR 500) when it comes to nice undistorted macro photography. For most other things of course this more expensive camera (such as night-time exposures) outperforms the small Optio S. Point is, that the mainstream market for cameras is geared towards what most photographers want to do. Scientific photography is a niche market and the large camera brands do not focus on that. So, if a camera performs well in that field, then it generally is not by intent, but by good luck.
I'm quite sure that you can find cameras especially designed for this purpose, but probably the price tag also will be the one, we all know from 'scientific' equipment.


As vulture suggested, white balance correction is an option and if the yellow effect is not too strong, then you can use that. For not too bad coloration, this leads to good results.
For very strong coloration, white balance correction is not the best way to go anymore. The sensors are designed to work for a certain spectral distribution and with a strongly differing spectral distribution, part of the gamut (space of possible representation for colors) is not used and this leads to lower color resolution. For that purpose, special filters are available, which correct for color of the light source. I myself have a blue filter for yellow color and a pale orange filter for correction of pictures under a deep blue sky. I use these in preference to electronic balancing of the color (which can be done in the camera, but also afterwards on a PC).




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[*] posted on 20-4-2009 at 08:18


Quote: Originally posted by woelen  
Quote:
I have to disagree on this one. Lens performance usually gets better with smaller aperture, because you are using the central part of the optics, which show less faults. However, digital cameras show diffraction limits, which depend on the size and pixel density of the sensor.

My personal experience is that a very small aperture size leads to so-called 'fringing' on sharp edges. This of course depends on camera quality, but even expensive cameras suffer from this effect and this becomes more notable when the aperture size is very small. So, there is some optimum. You probably are right that this is not due to lens defects but to defects/limitations in the CCD array. I'll look into that and check out what is the exact cause of this fringing. But fact remains (from a practical point of view) that there is a certain optimum in image quality over the full range of possible aperture sizes.


Thanks Woelen for an interesting discussion. I quite agree that quality drops at small aperatures. There are two parts to this

1) the lens performance that Vuture was talking about - whether this actually improves with smaller aperatures is a arguable, while deviations from parabolic introduce aberations and should increase with lens size, statistical fluctuations in the lens surface and material charactersitics contribute more as you are averaging over less of the lens surface

2) The lack of sharpness with very small aperatures you mentioned is actually a physical principle, which is why expensive cameras cant solve it. At very small aperatures you can effectively neglect the lens and what you have is a pinhole camera. Light can not resolve separations less than its wavelength so passing thru a pinhole the size of a micron one gets an interferrogram. The effect gets progressively smaller at larger slit sizes. It can be estimated. If we have a sharp source directly behind a slit size 2a the phases at the slit edges are equal. A deviation x in the perpendicular plane a distance L away from the slit on the other side from the source makes the phases unequal by

sqrt(L^2 + (a+x)^2) - sqrt(L^2 + (a-x)^2) ~ 2ax/L

setting this to half wavelength (lam/2) we get the distance of the first minimum, and the characteristic deviation for a fade to black

2ax/L = lam/2

so angular fuzziness (in radians) ~ x/L = lam/4a

Clearly the smaller the a the greater the angular fuziness. When slit size 2a approaches lam/2, the whole thing is fuzzy in accord with the qualitative considerations above. If slit size = 1mm we have an angular fuziness of about 10^-3 rad.

[Edited on 20-4-2009 by len1]




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[*] posted on 20-4-2009 at 09:45


Quote:

Light can not resolve separations less than its wavelength so passing thru a pinhole the size of a micron one gets an interferrogram.


I'm well aware of this, however, this is not an issue with most, if not all commonly used lens and aperture combinations, because they never reach these dimensions.

Most lenses don't go smaller than f/22, if we're talking about a lens with a front element of, say, 30mm (which is already very small), this amounts to a physical aperture of 1.3mm. An APS-C DSLR @ 10MP is diffraction limited at f/16, so you reach that before you start getting into trouble lens wise.


Quote:

I myself have a blue filter for yellow color and a pale orange filter for correction of pictures under a deep blue sky. I use these in preference to electronic balancing of the color (which can be done in the camera, but also afterwards on a PC).


I don't understand why you'd do that. White balance is perfectly able to correct for the situations you mention. The real problem with digital sensors is the rendition of purple, which is usually off.


Quote:

My Pentax Optio S (simpy handheld pocket camera, EUR 200) outperforms my Panasonic FZ50 (semi SLR, EUR 500)


Price is not the issue here. The FZ50 likely has worse macro capability because its megazoom shows significant field curvature in the wide angle area. This is a typical compromise for megazooms from which the optio doesn't suffer with its smaller zoom range.


If you can, get yourself a camera which allows RAW shooting. This will make white balance issues moot and allows for easy correction of lens distortion and chromatic abberation (in fact most RAW convertors correct CA automatically).

A good website to look for tests of photography gear is:
http://www.dpreview.com/


[Edited on 20-4-2009 by vulture]




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[*] posted on 23-4-2009 at 04:24


Quote: Originally posted by vulture  
Quote:

Light can not resolve separations less than its wavelength so passing thru a pinhole the size of a micron one gets an interferrogram.


I'm well aware of this, however, this is not an issue with most, if not all commonly used lens and aperture combinations, because they never reach these dimensions.


Yes, but the point of what I posted above is that this effect has a remnant at aperatures much larger than a micron as expressed by the formula

angular resolution = x/L ~ lam/2a where a is the apperature

- the smaller the aperature the more blurred sharp edges become.



[Edited on 23-4-2009 by len1]
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[*] posted on 23-4-2009 at 10:11


Good to see the posts back again (good work Polverone!)

Vulture, as I said, I only use the filters in more extreme conditions. Most situations can be corrected by the camera or by PC software afterwards, but sometimes it is better to use that kind of filters (otherwise they would not exist).

Anyway, when someone purchases a new camera, aimed at chemistry-photography, then one has to put emphasize on other properties as usual. I know the dpreview site (it indeed is quite good), but the kind of things which I encountered are not mentioned on that site. For supermacro photography, the 3D properties are not covered, only flat objects like details of a playing card are covered or parts of a watch's hour plate.





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[*] posted on 23-4-2009 at 12:58


Quote:

the smaller the aperature the more blurred sharp edges become.


Ofcourse, but like I said, this is not an issue with common lenses because the increase of depth of field is noticed, while the loss of sharp edges is undetectable by the human eye. It's all good and true in theory, but for standard photography it's a non-issue.


Quote:

Vulture, as I said, I only use the filters in more extreme conditions. Most situations can be corrected by the camera or by PC software afterwards, but sometimes it is better to use that kind of filters (otherwise they would not exist).


Filters that have real use are polarizing filters, ND (grad) or filters that block visible light and allow IR or UV to pass. All the rest is just there to make money. Camera shops get a higher profit margin from selling filters than selling cameras. The general public is usually not aware they can create the same effect using in camera or PC software.


Quote:

For supermacro photography, the 3D properties are not covered, only flat objects like details of a playing card are covered or parts of a watch's hour plate.


It's a good indication, significant deformation by the lens will manifest itself as warped edges of perfectly flat objects for example.


[Edited on 23-4-2009 by vulture]

[Edited on 23-4-2009 by vulture]




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[*] posted on 23-4-2009 at 13:46


A good macro (60mm micro-nikkor) will stop down to f/57 to increase DOF at extreme close-up so pin-sharp images are obtainable at very small apertures. . .
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[*] posted on 23-4-2009 at 19:45


Quote:


Ofcourse, but like I said, this is not an issue with common lenses because the increase of depth of field is noticed, while the loss of sharp edges is undetectable by the human eye. It's all good and true in theory, but for standard photography it's a non-issue.


The reason I posted this is that the theory predicts precisely what woelen noted - bluring on sharp edges on small aperatures.
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[*] posted on 23-4-2009 at 23:24


The fringing woelen notices might be CA (which is a lens "defect") or because he reached the diffraction limit for the sensor, which lies appreciably low for digital compacts with high pixel density.

I have never noticed loss of edge sharpness with my DSLR when using small apertures and these pictures are scrutinized at 100%.

Anyway, the point I'm trying to make is that you are shying people away from using smaller apertures which are absolutely necessary with macro photography to get any decent depth of field and thus a usable image. A camera that shows fringing at f/16 should be dumped with the garbage, no offense. Sharp macro photography would be impossible if this effect was truly relevant, because people easily go to f/32 and beyond in that area of photography.

If you look up lens test at photozone.de you'll see that resolving power increases with decreasing aperture and CA decreases. Only when the diffraction limit of the used sensor is reached, the resolution starts to drop again, but CA remains less than before.




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[*] posted on 23-4-2009 at 23:46


Quote:
The fringing woelen notices might be CA (which is a lens "defect") or because he reached the diffraction limit for the sensor, which lies appreciably low for digital compacts with high pixel density.



The diffraction limit is precisely what I have calculated, although you attribute it to the sensor - the limitations of the latter are normally called its resolution. The diffraction limit is associated with the physical dimensions of the lens and position of the focal plane

If you dont believe me its (right) in wiki

Quote:


Even if a lens is designed to minimize or eliminate the aberrations described above, the image quality is still limited by the diffraction of light passing through the lens' finite aperture. A diffraction-limited lens is one in which aberrations have been reduced to the point where the image quality is primarily limited by diffraction under the design conditions.




[Edited on 24-4-2009 by len1]

[Edited on 24-4-2009 by len1]
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[*] posted on 24-4-2009 at 09:42


@Hissingnoise: The lens you are referring to indeed is a nice piece of apparatus. Unfortunately it also has a high price tag, which makes it too expensive for most amateurs (just this single lens has a price in the 500...700 euro range). You also need other equipment and then the total cost goes well beyond EUR 1000.



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[*] posted on 25-4-2009 at 04:40


Indeed woelen, it's a pro-lens but I mentioned it to illustrate the fact that very small apertures can be used without any compromise in image quality.
An aperture of f/57 looks little more than a pinhole. . .
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[*] posted on 25-4-2009 at 09:07


I wish I had such a lens and suitable body. It would open up great possibilities. You even can use a small flash unit with such a small aperture, leave the lens open and go around the subject, giving miniature flashes from many different directions. With some experimenting this could lead to fantastic macro pictures having a mix of soft light (due to all the little flashes from different directions) and direct light with glitters and sparkles on crystalline matter. Of course this does not work in non-static subjects, such as bubbling liquids.

I'll bring in some nuances in the webpage in the section on aperture size. I am convinced that the remark about too little aperture size is too strong. With pro-lenses and ditto body one can use very small aperture size. But I still would like to advice people to experiment first when they have less than pro equipment (as most of us have).

[Edited on 25-4-09 by woelen]




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[*] posted on 25-4-2009 at 09:34


I don't have such gear either, woelen, but a photographer friend does---the notable thing about his stuff being the sheer weight.
Just lugging the laden camera-bag is a feat in itself. . .

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[*] posted on 26-4-2009 at 07:00


Quote:

Even if a lens is designed to minimize or eliminate the aberrations described above, the image quality is still limited by the diffraction of light passing through the lens' finite aperture. A diffraction-limited lens is one in which aberrations have been reduced to the point where the image quality is primarily limited by diffraction under the design conditions.


This merely says that once all other lens defects have been mitigated, the only thing that can limit quality is diffraction by the lens aperture. It does not say this will happen or is a significant effect in normal photography.

http://www.cambridgeincolour.com/tutorials/diffraction-photo...

http://www.sankey.ws/diffraction.html


Quote:

I wish I had such a lens and suitable body. It would open up great possibilities. You even can use a small flash unit with such a small aperture, leave the lens open and go around the subject, giving miniature flashes from many different directions. With some experimenting this could lead to fantastic macro pictures having a mix of soft light (due to all the little flashes from different directions) and direct light with glitters and sparkles on crystalline matter. Of course this does not work in non-static subjects, such as bubbling liquids.



I have a D200 and a Nikkor 105mm macro lense. Taking pictures with multiple flash bursts is a PITA when it comes to nailing the exposure. It's far easier to create a soft lightsource. Ever wondered why there are no shadows on an overcast day? Because the lightsource is extremely large, light is coming evenly from all directions.

There's a simple and cheap solution to this problem:
http://strobist.blogspot.com/2006/07/how-to-diy-10-macro-pho...

I did this myself and it really works. If you don't have an external flash unit you can simply use another lightsource.

[Edited on 26-4-2009 by vulture]




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[*] posted on 27-4-2009 at 15:09


Quote:


This merely says that once all other lens defects have been mitigated, the only thing that can limit quality is diffraction by the lens aperture. It does not say this will happen or is a significant effect in normal photography.


In the previous post you referred to diffraction, now you say it irrelevant. If you follow the formula I gave you can see to what degree it is relevant.

aperature/wavelength ~ 1:1000 for 1mm aperature.

This means if you look with a 1mm aperature at an object 1m away, detail to the level of 1mm will be blured - even with a perfect lens.

So using macros at this level will not help
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[*] posted on 28-4-2009 at 11:04


Quote:

This means if you look with a 1mm aperature at an object 1m away, detail to the level of 1mm will be blured - even with a perfect lens.


This demonstrates why this is not a relevant problem in macro photography.

For the 105mm Macro lens I mentioned, for example, the smallest aperture you'll reach is 62/57 = 1,08mm for a focusing distance of 0.31m. Once you increase subject distance the aperture minimum is limited to f/32 (macro lenses have smaller apertures with shorter focusing distances). So you never reach this limit.




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[*] posted on 29-4-2009 at 11:30


Could anybody in England reccomend a decent easy to use camera?
I plan on taking photos and posting in prepublication the results of my newly re-done Contact process plant.
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[*] posted on 17-7-2009 at 20:46


I thought I would add a little bit of something that I find very helpful. Using a basic digital camera(5mpx) its damn near impossible to take macro type photos of crystals and see any detail at all. Normaly all my crystal photos turn out to be blurs and nothing more yet today I decided to try placing a lens from an old telescope infront of the camera lens. The results made me extreamly happy.

Here is a photo of a couple grams of recrystalized piperine taken from about 1 ft away

I left the photo the size it is so everyone can get an idea of the detail that you normaly can not get on these types of cameras. If anyone wishes that I resize it I will do so. This area is only about 2in*2in at the very most yet it was able to produce an image with this much detail. You can also see if you look real close that the camera is no longer limited by its focal length but instead the amount of mega pixels it has obvious by the grainyness along the edges of some of the crystals.

I have been attempting to photograph crystals with this thing for sometime so to have success with it has me happier then a necropheliac in a morgue.

Cheers:D.
~Sedit

[Edited on 18-7-2009 by Sedit]





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