Second attempt at diffuse lighting - 2 coins

[specious_reasons]

When I posted the silverfish scales last week, I had taped 2 pieces of paper used to separate microscope slides into a circle and used that as a diffuser. This time I went to the store and bought a pack of ping pong balls. Having discarded the silverfish, I opted to fish into my pocket for coins.

I'm pretty sure I'm doing several things wrong. I'm looking for opinions on improvements.

1) I'm not sure I picked good angles - my 2 light sources were at about 90 degrees from each other, at equal angles from the top of the coin.

2) Focus - I really need to fix it such that the camera is focused exactly the same as the eyepiece. At the relatively low light of this setup, I can't use the "live view" function to get better focus results. I was also disappointed at my depth of field. This is my 4X objective, and I thought I got better DOF. Is it common to stack images like this?

3) I didn't read the thread Litonotus started. I think I should have - I'd have more exposures than the one I chose.

I did "auto" color adjustments in Photoshop RAW on these images.

FDR's eye:


Lincoln's eye


(I initially thought this was Eisenhower, but this is FDR.)

[specious_reasons]

Here's another picture of the dime.

[rjlittlefield]

1) I'm not sure I picked good angles - my 2 light sources were at about 90 degrees from each other, at equal angles from the top of the coin.

I'm unclear on how the pingpong balls are being used. The bright slopes in this image are brighter than I would have expected for a pingpong ball serving as a light tent, wrapped all around the subject. Can you show us a snapshot of your illumination setup?

Is it common to stack images like this?

Yes. The DOF of a 4X NA 0.10 objective is less than 0.1 mm. Step sizes of 0.050 mm or even 0.025 mm are common.

--Rik

[specious_reasons]

I had to tear it down already, so I'm setting it up approximately like I had it:



The 1/2 ping pong ball is over the subject, and that's about where I had the lights - give or take an inch or two. The only light I was using were the 2 LED lamps, although at some point in time I'll probably add a flash.

The exposure time was ~2 secs, ISO 400.

[Litonotus]

It seems you have the same problem I have - highlights become just a white spot with no details. Some very interesting suggestions how to solve that problem are here: http://www.photomacrography.net/forum/v ... hp?t=19560

[rjlittlefield]

Thanks for the setup picture. It explains a lot.

Three suggestions:

1. Cut another pingpong ball with a smaller hole in the top. The hole should be just large enough for the objective to look through. This will allow light to shine down onto the subject, instead of all coming from the sides.

2. Move the lights farther from the pingpong ball, so they illuminate the ball more evenly instead of shining brightly on two small areas. Also raise them higher, so they illuminate more of the top of the pingpong ball that you will leave in suggestion 1. Again the point is to get more light shining down onto the subject instead of coming from the sides.

3. Read the thread suggested by Litonotus. If you cannot get rid of the too-bright reflections by adjusting the illumination, then you must do it with multiple exposures and postprocessing (masks or HDR).

--Rik

[specious_reasons]

Thanks for the setup picture. It explains a lot.

Three suggestions:

1. Cut another pingpong ball with a smaller hole in the top. The hole should be just large enough for the objective to look through. This will allow light to shine down onto the subject, instead of all coming from the sides.

2. Move the lights farther from the pingpong ball, so they illuminate the ball more evenly instead of shining brightly on two small areas. Also raise them higher, so they illuminate more of the top of the pingpong ball that you will leave in suggestion 1. Again the point is to get more light shining down onto the subject instead of coming from the sides.

3. Read the thread suggested by Litonotus. If you cannot get rid of the too-bright reflections by adjusting the illumination, then you must do it with multiple exposures and postprocessing (masks or HDR).

--Rik

That's why I bought a whole pack of balls. Thanks for the advice.

The hole I cut was sized approximately so I could fit the 10X objective inside of it. While not exact, it's a decent fit. I'll try some new shots later in the week.

[specious_reasons]

So, I got the opportunity to try out a few things.

This is the setup of the latest attempt:


And this is a sample from that (complete with lint from my pocket):


(I actually have 3 exposures of Jefferson's eye, this is the middle exposure, and I let Photoshop raw run auto correction.)

It's not shown in the picture, but I've been using a glass side to support the coins. Should I cover the glass?

[rjlittlefield]

This looks good to me. The image retains detail in both bright and dark areas.

There remain some areas that are almost pure black. Those will be mirror surfaces facing directly toward the objective. The black areas are essentially the camera sensor looking at its own reflection. We call this "the black hole" and there's no way to get rid of it except by viewing the subject through a partially reflecting mirror so that illumination light either is coming out of the lens or appears to be. There is an example at http://www.photomacrography.net/forum/v ... hp?t=15820 using a piece of thin but plain glass as the reflector.

In a microscope setup this is called "brightfield episcopic". It is usually done by placing the beamsplitter above the objective. Placed below the objective there are difficulties with working distance and with too much image degradation from looking through the mirror. At low magnification and small NA (say 4X NA 0.10), it can be done using a coverslip as the mirror, analogous to the glass at the above link.

Do you see other aspects of your current setup that you would like to improve?

--Rik

[specious_reasons]

This looks good to me. The image retains detail in both bright and dark areas.

There remain some areas that are almost pure black. Those will be mirror surfaces facing directly toward the objective. The black areas are essentially the camera sensor looking at its own reflection. We call this "the black hole" and there's no way to get rid of it except by viewing the subject through a partially reflecting mirror so that illumination light either is coming out of the lens or appears to be. There is an example at http://www.photomacrography.net/forum/v ... hp?t=15820 using a piece of thin but plain glass as the reflector.

In a microscope setup this is called "brightfield episcopic". It is usually done by placing the beamsplitter above the objective. Placed below the objective there are difficulties with working distance and with too much image degradation from looking through the mirror. At low magnification and small NA (say 4X NA 0.10), it can be done using a coverslip as the mirror, analogous to the glass at the above link.

Do you see other aspects of your current setup that you would like to improve?

--Rik

Yes but I think I need more time and practice (and skill and talent and new hardware ) before I should ask for more help.

I'll experiment with a coverslip on top. Thanks for the wealth of information.

I'm curious to know how to make a clean round cut in a ping pong ball. I halved the ball fairly cleanly, but the hole on top is rough and uneven. I used a craft knife to cut it in half, but used a drill bit for the top hole and the hole wound up being more of a large roundish tear.

[ChrisR]

Ball - A pair of dividers, the type with two needles. With a little care one point stays still while the other scratches a circle until you're through, or nearly though, then a scalpel can cut the rest.

[rjlittlefield]

If your kit includes a Dremel rotary tool, try that. Some people like it, some don't.

--Rik