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UltravioletPhotography

Making Stereo Images


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Updated 2nd April 2020 - Notes on Positioning image forwards/backwards - see end of post.

 

This post accompanies my recent one on focus stacking, and addresses creating 3D/stereo images – especially of close-up and macro images.

 

I generally use focus stacking when creating a stereo image. Whereas differential focussing on a normal image can add something positive to the result by making the important part of the subject stand out from the rest, I find that in stereo photographs it is better to have everything in focus and let the eye wander round and pick on whatever grabs its attention.

 

The principle of stereo photography is simple – take two images separated by the distance between the human eyes, then overlay them so that the left-hand image is visible only to the left eye, and the right-hand image only to the right eye. The simplest way to do the separation of the left and right images is to make anaglyphs: the left image contains only its red channel, and the right image contains only its blue and green channels. The superimposed images (which always have some red and cyan fringeing) are then viewed through a pair of spectacles consisting of a red filter for the left eye and a cyan (minus red) filter for the right.

 

These spectacles are the only special equipment you need to buy. There are lots available on ebay. I have tried a dozen or so different types. The best ones I have come across cost a couple of dollars and have black card frames, and some of them are branded Sony. The others all leak light through the filters to some extent, resulting in ghost images when viewing the photograph. Price is not an indicator of how well they will work.

 

When working close up, the principle of separating the two images by the distance between the eyes breaks down. As you get closer to the subject, the distance between the two exposures needs to be reduced. The problem is that when you get really close, you can't get the same bit of the subject to appear in both the left and right images. So a different approach is needed.

The method that works for me is to swing the camera between the two exposures. I always take the right image first, then swing the camera clockwise (when viewed from above) through 5 degrees, and then move the camera sideways to the left to bring the subject back into frame for the left-hand image.

 

To effect the swing through 5 degrees, I use a tripod panoramic head like this:

https://www.ebay.co....igAAOSwpdpVXu-2

 

I also have a Benro geared tripod head that should be able to do this, but it's more difficult to read 5 degrees off the scale.

 

To move the camera sideways to the left I use a slider. You can use the Velbon Super Mag Slider that I mentioned in the post on focus stacking as this allows both forward/backward and left/right movement. But the amount of left-right movement may be too restricted for some shots. So you can also use some of the lower cost slider rails – although they are not so well engineered and not so good for fine forward movement for focus stacking, they are quite adequate for coarse left-right movements. I often use one of these (with the forward/backward slider removed):

https://www.ebay.co....kMAAOSwWxldF4iy

 

Another approach that I have read about, but not tried, is to have the camera fixed between the right and left exposures and to have the subject on a turntable which is rotated by 5 degrees between the two exposures.

 

If you read texts about stereo photography they will almost certainly say that you must not use a toe-in technique like I have described above. This may have been true in the days of film because the perspective would be different between the two images making it impossible to get a good overlay. But in the digital world, modern software seems quite capable of handling this.

 

For close-up and macro work, each of the right and left images is a focus stack to get the whole of the subject in focus – so it could involve 200 separate exposures to create a single stereo pair.

 

Once you have got your two images, you need to overlay and colour them. You can do this manually using software like GIMP, but it's far easier to use specialist stereo software – I use the excellent and free Stereo Photo Maker (https://stereo.jpn.org/eng/stphmkr/). This has loads of options for overlaying the images, so make sure you select the anaglyph options. The software handles the overlaying of images, cropping them, rotating them and correcting perspective. Just make sure that is has correctly chosen which image is left and which is right.

 

Stereo Photo Maker always gives an acceptable image. However, you may want to experiment with various options and effects. In particular, you can slide the left and right images sideways with respect to each other to make the image recede or appear to come through the screen towards you: this can give dramatic effects as you can see in these examples – the first image is as created by default by Stereo Photo Maker, and the second has been adjusted so that the flower appears to be coming through the screen towards you.

 

post-245-0-67785000-1585494322.jpg

 

post-245-0-02060900-1585494336.jpg

 

But you need to avoid violating the rule that says parts of the image near the edge of the frame do not appear to be crashing through the window frame. In this example, the central flower is coming though the screen at you, but left and top edges of the image are uncomfortable to view.

 

post-245-0-30539300-1585494346.jpg

 

A couple of tips when viewing the stereo images. Firstly, you can often magnify the image on the screen to some extent so that you zoom into the image, and then you can scroll around the image. This gives the feeling of being within the flower and flying around it.

 

Secondly, you may get a better viewing experience (especially if you have zoomed into the image) by moving yourself a bit further away from the screen.

 

Update 2nd April 2020 - Positioning the image

 

After writing the post I realised that I should add some comments about how to make the image appear to be further forward or backward. I referred to this above but didn't provide a good explanation. Ths is important when manipulating the stereo image to get the right effect, and is quite easy to get your head around. So hopefully these notes will be useful to those who want to give stereo a try.

 

When you overlay the left and right images, they can only be made to overlap perfectly (i.e. with no colour fringeing on the anaglyph) at one point (actually a plane) which corresponds to a certain distance into the 3D image. By moving the images left or right relative to one another the plane of perfect overlap moves forwards or backwards. So you can choose at what depth in the image the plane of perfect overlap is set. Now this plane of perfect overlap is highly significant: it appears to the eye (or, more correctly, to the brain) to be at the same level as the "window" - i.e. the frame around the image, which is of course on the screen you are viewing. So if the plane of overlap is brought forward (by moving the left/right images sideways relative to one another), the image appears to recede behind the screen, and if the plane of overlap is moved back then the image appears to be coming through the screen towards you.

 

So you can use this to get dramatic effects of having part of the image coming through the screen towards you, simply by moving one of the left/right images to the left or to the right. But if you overdo it, you could make the image unpleasant to view as the brain tries to interpret what you are throwing at it.

 

Now, there is a rule which must not be violated. If you look at the parts of the image that are touching the edges of the window, they must be at or behind the level of the window - i.e. the plane of perfect overlap must be in front of the parts of the image that touch the edges of the window.

 

To try to illustrate this. let's say you were taking a picture of someone outdoors pointing at you and you wanted their pointing arm to appear to come through the screen towards you. That's easily achievable. But you must not increase the effect to the extent that things like the horizon or buildings or trees or other parts of the subject's body that are touching the edge of the window appear to be coming through the window: the brain cannot interpret this as it cannot understand a horizon coming through the window, and you will get an unpleasant viewing experience near the edge of the image.

 

So anything that touches the edge of the window must be at or behind the window. Anything inside the frame which does not touch the edge of the window can be made to poke through the window towards you without causing any problem. If you're photographing flowers, you can have the flower coming though the window at you, but you must ensure that leaves etc. in the background stay the other side of the window.

 

If you are using Stereo Photo Maker (and I strongly recommend that you do) and use the Auto facility to align images (which I always do), then the software ensures that this rule is not violated. However, you can then adjust the relative position of the left/right images by using the left- and right-arrow keys on your keyboard. So you can make part of the subject come through the screen (or, if you wanted, recede away from you). This may cause a rule violation, but:

  • you might get away with it if the image near the edge is indistinct (dark or out of focus)
  • you may be intending to crop the image to cut out the surrounding parts which are causing the rule violation.

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I tested a Loreo 3D macro lens and doesn't transmit any UV.

The now super expensive Panasonic 12.5 mm f12 3D lens does work for UV. But you need to modify it to hold filters and add at least 0.8mm washer for macro extension.

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Thanks for the comprehensive and understandable explanation :) I guess there is no way -- now -- escaping from looking up anaglyph gear on eBay,
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HI Bernard,

This technique has been around for ages, so I always have a few pairs of 3D specs, just in case. I enjoyed them all, but the second one seems to pop out of screen the most. I see what you mean by the top edges, in the last one.

 

Unfortunately, I've found that some people simply can't see 3D, due to astigmatism. Trying to describe the 3D effect to someone who can't see it, is akin to describing a color to a blind person.

 

The 3D effect that fascinates me the most is holography, as it can be viewed by anyone, without special equipment. I think you'd need a specialized laser for UV imaging, but UVIFL would be possible.

 

I digress, but here's site that produces some interesting holo kits. The cost rapidly increases for full color, but surprised this can done with instant film processing.

www.litiholo.com/

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I remember reading about laser holography when I was a kid, but had no idea there are consumer kits to produce them.

 

Just need "someone" to try them out and see what you can do with them. But as you say, it's not going to work for reflected UV.

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It seems to me that the turntable method is the simplest, and would automatically provide any toe-in needed. It also strikes me that matching the focus-stacking exposures accurately, left-to-right, could be quite difficult.

 

A UV hologram could only be viewed under UV light--a bit of a problem, that. Were there some way of enlarging it. it could be directly viewed with longer-wavelength visible light. Otherwise, one could make a secondary video of it as the viewing angle changed, using a UV-sensitive camera.

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Thanks for the comprehensive and understandable explanation :) I guess there is no way -- now -- escaping from looking up anaglyph gear on eBay,

 

Actually Birna you may have everything you need depending on which stackshot kit you have. If you have the rotation base you would be all set. Just program in the rail to focus stack one set or take a single image. Then if you have their rotation base, set that up with your subject. So that after your first stack or image is done. Just program in a rotation of 5 degrees or different amounts on your subject and shoot an other stack.

That is a deam system of mine. Setup a program to run a stack, have an automatic filter wheel, to change filters for following stacks, then rotate the subject and shoot the whole thing again automatically while I sleep.

Then hope the subject didn't fall over while I was away. I would also like to setup timmers on different light sources to also be triggered. But then the whole thing would just be too robotic.

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I've also viewed stereo images using color filters held up to each eye. :lol:
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