First Post photos and questions about Magnification

Just bought that first macro lens? Post here to get helpful feedback and answers to any questions you might have.

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Jon B
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First Post photos and questions about Magnification

Post by Jon B »

Hello everyone,

This is my first post here, but I have been following this forum for a while now, learning a lot and finding lots of sources of inspiration.
I'm a woodworker/carpenter by trade and spend a lot of time sharpening, and experimenting with different sharpening techniques, mediums, etc. That combined with my interest in macro photography has led me to attempt taking photos of the edges of tools (primarily Japanese plane blades) during and after sharpening. It's quite common for people to use a handheld microscope to inspect the edge after sharpening but until now I have struggled to find a decent way to capture an image.

Anyhow this forum introduced me to the possibilities of using my camera (Fuji xt-20) along with a Nikon 40x 0.5ELWD 210/0 objective. I certainly have a lot to improve upon, but some initial shots using a simplistic setup to mount and capture images of the edges of some plane blades has produced decent results. A huge improvement over previous attempts to take photos through a pocket microscope using a cell phone camera :roll:

One concept that I've been tying to more thoroughly understand is in regards to magnification. After some searching here I found reference to a formula for magnification=size of sensor/field of view. After doing some basic test shots of a ruler I believe that my current setup is yielding images in the range of 40x magnification, which is inline with the objective I'm using. My camera sensor is 23.6 mm wide, and approximately 0.5 mm of a scale fully fills the frame. What confuses me is that many people in my area of work often use 100x Peak brand stand microscopes for viewing the edges of blades. That scope is equipped with a scale measuring 1 mm in 0.01 mm increments and has an overall field of view of 1.45 mm. So while my setup at approximately 40 x is capable of magnifying 0.5 mm field of view on to a 23.6 mm sensor, the peak 100x is only magnifying 1.45 mm. It seems to me that my current setup has a higher magnification than the 100x peak microscope. Visually the difference is clear.

I've searched the web as well as this forum to get a better understanding of magnification but I've yet to find any information that clarifies the difference I'm seeing between my current 40x setup and the 100x microscope. What am I missing here? I don't think the Peak scope is mis-labelled. Is there a difference in how the magnification is classified between these two setups?

Any and all advice is much appreciated,
Thanks,
Jon

P.S. The following images show a shot from a friends Peak 100 x stand microscope, with .01mm increment scale, followed by my own photos taken with Fuji xt-20, nikon bellows, and Nikon 40x 0.5ELWD 210/0 objective.
Attachments
Shot from a friends Peak 100 x stand microscope, with .01mm increment scale
Shot from a friends Peak 100 x stand microscope, with .01mm increment scale
yamamoto stropping.jpg
yamamoto 12000_2.jpg
yamamoto 8000_2.jpg

rjlittlefield
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Re: First Post photos and questions about Magnification

Post by rjlittlefield »

Jon, welcome aboard!

Your images are excellent, and your understanding seems solid.

You asked:
Is there a difference in how the magnification is classified between these two setups?
Yes, there is.

The rated magnification for microscopes with eyepieces is based on comparing how large the subject appears to be when (A) viewed through the scope, versus (B) viewed by naked eye at a distance of 10 inches. As a matter of practice, it is simply the actual magnification of the objective multiplied by the rated magnification of the eyepiece. The objective views a physical object and creates a real image, so the "actual magnification" of that stage is just a ratio of two distances: image size divided by subject size. Then the eyepiece acts as a magnifying glass, whose magnification is rated as 250 divided by focal length. Your friend's microscope, rated at 100X, is probably a 10X objective combined with a 10X eyepiece.

In your setup, the 40X objective (used as intended) will give an actual magnification of 40X onto the sensor, which is only 23.6 mm wide. This explains why your subject field is only about 0.5 mm wide: 23.6/40 = 0.59 mm. Then for presentation purposes, the image captured by the sensor will be further magnified onto screen or paper. For example on my computer screen, your images are displaying as 246 mm wide. So for me, your setup is giving an actual magnification of 246/0.59 = 417X.

If your images were printed, or displayed on a different size screen, then the actual magnification would be different. But in all cases the subject field would be the same width, 0.59 mm if the objective is set up as intended and you're showing the full image.

This sort of confusion about magnification is why the recommended "best practice" is to include a scale bar as part of the image, so that no matter how the image gets presented, even cropped, the viewer can figure out what they're looking at.

A fairly simple and very reliable way of generating those scale bars is described in the first post at viewtopic.php?t=4030 . (Be warned: that thread goes off-topic into a discussion of diffraction. That's very interesting and valuable material, but not related to scale bars.)

You are correct to be thinking in terms of the field width. Your images are much higher effective magnification than your friend's images that have a wider field. A more intuitive comparison would be to say that your system is looking through a 40X objective, and his is only looking through a 10X objective. So, your images could be accurately described as "This is what you would see through a 400X microscope."

In addition to the issue of magnification, your friend's image looks to be severely degraded by the use of a non-diffused light source. Most of what we're seeing in that image is probably just an optical effect called "speckle", which relates rather poorly to the physical structure of the metal surface. See the discussion at viewtopic.php?t=19582 for more about that.

Your images, on the other hand, appear to be done with illumination that is properly diffused to avoid speckle, while being directional enough to reveal surface texture. Nicely done!

I hope this helps. Please ask again if anything is unclear or if you have further questions.

--Rik

Chris S.
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Re: First Post photos and questions about Magnification

Post by Chris S. »

Jon, welcome to the forum! :D

I feel like I almost cut my eye on your last image. And the surface texture shown in all the images is striking.

I echo Rik's praise of your lighting. Lighting is critical for your choice of subject, and you did a great job.

Your Nikon 40x/0.5 ELWD 210/0 is a classic objective that we hear too little about. Good choice.

--Chris S.

Jon B
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Re: First Post photos and questions about Magnification

Post by Jon B »

Chris and Rik,

Thanks so much for the kind comments. And Rik your detailed explanation of magnification is incredibly helpful, thank you!
This sort of confusion about magnification is why the recommended "best practice" is to include a scale bar as part of the image, so that no matter how the image gets presented, even cropped, the viewer can figure out what they're looking at.
This make total sense, and I'm going to attempt this for my next round of photos. Thanks for sharing the link detailing your method for including the scale bars.
In addition to the issue of magnification, your friend's image looks to be severely degraded by the use of a non-diffused light source. Most of what we're seeing in that image is probably just an optical effect called "speckle", which relates rather poorly to the physical structure of the metal surface. See the discussion at viewtopic.php?t=19582 for more about that.

Your images, on the other hand, appear to be done with illumination that is properly diffused to avoid speckle, while being directional enough to reveal surface texture. Nicely done!
Lighting is something that I feel I've been lucky with thus far. I'm actually not going to any great lengths to diffuse my light, which is a simple LED light ring mounted on a small tripod. However I did find that when I set my blade parallel to the lens, I had trouble illuminating surface texture. Instead I angled the blade away for the lens, similar to your coin test from the "speckle" thread, and the results are shown in the photos previously posted. The LED light I'm using does have a white plastic cover, so perhaps that is adequately diffusing the light already. In any case I'm looking forward to playing around with the lighting some more to see how different angles affect the amount of detail captured. The down side of having to angle the blade in relation to the lens is that I have to focus stack many more photos. If I can find a way to adequately illuminate the blade parallel to the lens I could get away with taking far few images.

Your Nikon 40x/0.5 ELWD 210/0 is a classic objective that we hear too little about. Good choice.
Thanks Chris, I really owe a lot to the information I gathered here in this forum. I'm currently living in Japan, yet I have had trouble searching for and finding reasonable sources for new objectives at similar prices to what are available in the US. After some searching here I saw another member's images of butterfly scales using the Nikon 40x objective, and it seemed like a good option for my uses. I found the objective used on yahoo auctions (Japan's equivalent to ebay). It seemed reasonably priced and was in good condition so I went for it. So far I'm really pleased with the results. I'm looking forward to seeing what kind of images I can get with it on different subject matter.

Best,
Jon

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