Fast Stacker (Arduino based automated focus stacking rail)

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rjlittlefield
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Post by rjlittlefield »

pulsar123 wrote:Dmap never worked for me - even when contrast is set to zero I get a tone of artifacts, would take forever to retouch it.
Quite possibly a higher setting would work better for you. It turns out that for many stacks, setting the contrast threshold to zero is a very bad thing to do because it makes the depth determination too dependent on image noise.

There's a tutorial, How To Use DMap, linked from the Tutorials index page, that discusses this issue and some ways of dealing with it.

--Rik

pulsar123
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Post by pulsar123 »

rjlittlefield wrote:
pulsar123 wrote:Dmap never worked for me - even when contrast is set to zero I get a tone of artifacts, would take forever to retouch it.
Quite possibly a higher setting would work better for you. It turns out that for many stacks, setting the contrast threshold to zero is a very bad thing to do because it makes the depth determination too dependent on image noise.

There's a tutorial, How To Use DMap, linked from the Tutorials index page, that discusses this issue and some ways of dealing with it.

--Rik
Thanks, I'll check that tutorial.

pulsar123
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Post by pulsar123 »

BTW, here is my setup:

ImageIMG_7673 by First Last, on Flickr
ImageIMG_7672 by First Last, on Flickr
ImageIMG_7674 by First Last, on Flickr
ImageIMG_7675 by First Last, on Flickr

What is currently missing is a convenient way to adjust the height of the target. I will get a lab jack from ebay in a couple of weeks, which should do that job nicely.

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Post by Pau »

What is currently missing is a convenient way to adjust the height of the target. I will get a lab jack from ebay in a couple of weeks, which should do that job nicely.
Sure, but the plastic pail toy is so nice...
Pau

ChrisR
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Post by ChrisR »

I'm thinking ..
you could do without the diffuser/beam widener on the flash which is for a 24mm(?) wide angle. You really only need the beam width the same as the head for this. Would gain some light?
A piece of white tissue paper over the middle of the funnel would tame the hotspot at the top,
and you can use bits of aluminum foil as a fill reflector - it tends to stay where it's put :)

Image
Chris R

pulsar123
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Post by pulsar123 »

ChrisR: Thanks for the suggestions. I actually think hiding the flash's built-in diffuser would make the hot spot on top even hotter (because wider beam sends more rays outside the hot spot, many of them being reflected back to the target by the piece of white paper under the cone), but I could give it a try. I don't need more light at this magnification - 1/16 power at ISO 200 gives a perfect exposure. (And from the data I've seen ISO 100 is not less noisy on Canon 50D, and in fact has less dynamic range than ISO 200; the native sensitivity of the sensor is around 160).

I was thinking myself of placing some extra diffusing material on the top of the cone, to soften the hot spot. Also perhaps I could cover the wider part of the top of the cone with black material, to reduce the rim-brightening, and make the illumination more front-lighting? That of course would reduce the amount of light the target gets.

Not sure about placing foil inside the cone - the whole purpose of this design is to reduce specular reflections, and I suspect the foil will make it worse.

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Post by wayupnorth »

I have been contemplating one of these for flower work, Maplin also sell a USB version. Would be great to position the object remotely. No idea if it is stable enough for "real" macro work.

Image

ChrisR
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Post by ChrisR »

I actually think hiding the flash's built-in diffuser would make the hot spot on top even hotter (because wider beam sends more rays outside the hot spot, many of them being reflected back to the target by the piece of white paper under the cone)
Don't forget the inverse square thing;
by the time your "wider" rays have done the distance and lost power at the reflector, and come back, they'll be a few stops down.
I've not found they contribute very much.
I don't need more light at this magnification
If your funnel material is as I think it might be it'll be allowing a lot of straight-through light, which is giving you the hot spot. When you diffuse it you will lose a lot.
I could cover the wider part of the top of the cone with black material, to reduce the rim-brightening, and make the illumination more front-lighting?
Again, it has to get reflected/diffused in from the sides so you may find it's not very strong. I wouldn't at this stage do anything to reduce the angle the light comes from. One change at a time is easier to work with, too.
I suspect the foil will make (specular reflections) worse
Again it wasn't a random suggestion - I've found that if you use well crinkled foil to bounce back light from a wide angle, which was well diffused already, it doesn't cause specular reflections. It will if you don't get rid of the hot spot.

YMMV, of course.
Chris R

pulsar123
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Post by pulsar123 »

Thanks - many good points! I'll give foil a try. But I'll also try to attach a small circular white reflector (parallel to the ground) to the pin, right under the insect - this should crate a much better bottom reflector (and perfectly diffuse, unlike foil) than what I currently have.

The light is only following inverse square law only when the light source size is much smaller than the distance to the subject. In my case it is not exactly the case, so illumination will change slower than 1/R^2 (it's like sitting in front of a giant softbox). But I got your point.

pulsar123
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Post by pulsar123 »

UPDATE [03/03/2016]: New version (s1.14) of my focusing rail software was released. The important new feature is the support for Full Resolution Silent Picture (electronic shutter; only Canon cameras), with or without an external flash. Also some bug fixes. The rail was tested at magnification 10:1 (5 um steps), and it works very well.

Full details:

http://pulsar124.wikia.com/wiki/Whats_new

pulsar123
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Post by pulsar123 »

ChrisR: I did some semi-scientific testing of modifications to my diffuser. I discovered that a ball in a ball pen is a perfect subject to test light diffusion: it is like a 180 degrees fisheye lens showing the whole diffuser; it is small enough (0.5mm) to fit into your FOV even at 20:1; you don't need to stack to see the whole diffuser sharp; and it is already conveniently attached to a holder (the pen).

I measured two numbers for each setup: the exposure loss in the brightest spot (using my original lighting as a point of reference), and the light contrast (brightness in the bottom half divided by the brightness in the top half).

Here is my original lighting setup: flash with a built-in diffuser + a bottom diffuser (a large sheet of paper). The exposure loss is 0EV; the contrast is 0.53 (so bottom is ~2x darker than the top - not great):

ImageFlash diffuser + bottom diffuser by First Last, on Flickr

Then I removed the bottom diffuser; the exposure was 0EV, the contrast got noticeable worse (0.40) - so inverse square or not, the bottom diffuser is really important:

ImageFlash diffuser by First Last, on Flickr

Then I did what I hoped would be the only fix I need - I added a small piece of white paper right on top of the cone (a top diffuser), and put back the bottom diffuser. I lost quite a bit of light at the top (-1.5EV), but the contrast became a very reasonable 0.74. Actually my goal is not to get to 100% flat light - I still want some shadows, so placing a small diffuser on the top indeed seems to be the only fix I needed:

ImageFlash diffuser + bottom diffuser + top diffuser by First Last, on Flickr

Finally, I tried your other suggestion - removed the flash' built-in diffuser (the bottom and top diffusers stayed). I gained some light at the top (now the loss is only -0.75EV), but at the expense of worse contrast (down to 0.69):

ImageBottom diffuser + top diffuser by First Last, on Flickr

So I think I converged to a good compromise - a combination of flash diffuser, large bottom diffuser, and a small paper diffuser placed on the top of the cone results in nice diffuse light, and hopefully sufficient illumination at 1/16 flash power and ISO 200 (to be tested).

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Post by ChrisR »

What I was suggesting relied on a reflector inside the funnel, of course its hopeless to leave out altogether, the reflector underneath ....... whatever, if it works, then fine.
Good idea using a ballpoint pen. I've tried a black glass pin head and one painted grey. The latter is better for showing relief. They work but are quite large. Didn't think of a ball-pen!
Last edited by ChrisR on Sat Mar 05, 2016 4:47 pm, edited 1 time in total.
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pulsar123
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Post by pulsar123 »

First stacked shot with improved lighting - a fragment of a peppercorn at 10:1. 250 shots with 7.5um step, using electronic shutter (FRSP).

ImageAlien peppercorn by SyamAstro (500,000 views - thank you!), on Flickr

nsomnius
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Post by nsomnius »

Pulsar, you had mentioned previously that moving the camera stage by hand could generate enough electricity to damage the motor driver. Have you considered adding a Schottky diode to prevent the back current possibility? Personally, I would like the ability to be able to safely move the carriage around during shot setup, for example. Maybe in practice that isn't necessary but it would at the very least eliminate that possibility from being a concern. I know others do this but I'm asking you primarily for your input on how it might affect the fast stacking ability, if there's any interaction there.

pulsar123
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Post by pulsar123 »

nsomnius wrote:Pulsar, you had mentioned previously that moving the camera stage by hand could generate enough electricity to damage the motor driver. Have you considered adding a Schottky diode to prevent the back current possibility? Personally, I would like the ability to be able to safely move the carriage around during shot setup, for example. Maybe in practice that isn't necessary but it would at the very least eliminate that possibility from being a concern. I know others do this but I'm asking you primarily for your input on how it might affect the fast stacking ability, if there's any interaction there.
My software completely eliminated the need to move things by hand. (And moving by hand is bad not just because of the back current, but because it breaks the rail calibration.) Simply choose the appropriate acceleration factor - command *A, and then use rewind/fast forward keys "1"/"A" to precisely position the rail. Another important reason for using that versus moving the rail manually is that the proper way always does fully backlash compensated moves, which is critical at magnifications 3:1 and higher.

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