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Comment by jebarker | Hacker News Reader

> But copepods typically range from about 0.2 to 1.7 millimeters in length, just large enough to magnify using conventional lenses and equipment

Does that mean conventional macro camera lenses or a microscope?

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If we're talking simple math on magnification:

It's very easy to find macro lenses that have 5:1 magnification, meaning that an object is projected onto the sensor 5x it's size. Taking 1.7 mm and projecting that onto a Canon R5 45 MP sensor with 5x magnification gives us something that would be around 1934 pixels in length (just under 1/4th the width of the sensor that is 8192 effective pixels wide).

I think you can convert 5x into 10x or 15x pretty easily without much loss in image quality.

That's not the problem, the problem is getting enough light (without boiling your specimen, which they briefly mention) and nailing the focus. At such magnification, both problems are challenging.

> It's very easy to find macro lenses that have 5:1 magnification

That is bit of an exaggregation. Afaik there is for example exactly one 5:1 macro available on the Canon R series RF mount, and in general they are pretty rare.

There's a few 5:1 dedicated macro lenses. Around 2:1 and above though, handholding becomes near impossible and you almost always need focus stacking due to the very shallow depth of field. Not to mention powerful lights.

So even this "conventional" option that you can readily buy is quite the niche.

For a 0.2mm subject, 5:1 is not enough. Luckily, one can use a microscope objective on a camera, like this:

https://c7.staticflickr.com/1/411/31944206126_fee397795a_b.j...

It doesn't have to be a bellow, they can also be a fixed tube, but the idea here is that the camera's sensor is at a specific distance to the back opening of the microscope objective. It would be the same distance where normally the eye piece of the microscope goes.

This way, you can do 10:1, 20:1, 50:1, 100:1. You'll have ever greater problems though the more you magnify (vibration, light, composition).

The device in the bottom is an automated focus rail, a WeMacro in this case. You set a start point and end point, and it takes all photos in between. It can move by as little as 1 micron and is quite cheap.

I think conventional camera gear will do it.

If you enjoy this view into microworlds, here's one of my favourite macro photographers. This is a collection of garnets (sand grains) that are 0.2 to 0.3 mm across. That's basically dust IMO!

https://www.flickr.com/photos/194954457@N05/sets/72177720296...

He talks about his gear here. His technique and patience is extraordinary. His gear is fairly modest: Olympus OM-D EM-1 Mark II camera, MC-20 Teleconverter, Olympus 60mm macro lens, Kenko 16mm extension tube, & Raynox 505 close-up lens. That's an older model of Micro Four Thirds camera (the format has magnification and depth of field advantages over fullframe) so you could probably acquire such a setup in the range of $1K used. And then spend a lifetime refining your art... :-)

https://www.dpreview.com/forums/thread/4690261

For that size I would use a 1X or 4X microscope objective attached to a camera (this is in fact how my DIY automated microscope at home for looking at tardigrades does it).

I don't understand the part about needing high light intensity- at such low magnification, I have to attenuate my LEDs significantly and take extremely short exposures (like, running a 1A LED at 10mA and 1-10us exposures). But I can't fault his results.

For the light intensity, it's likely that he's using a much smaller aperture to increase depth-of-field than you are, and that will crank up the light requirements.

It's not inconceivable that a conventional camera could work here, although it is borderline. Quick napkin math: Sony A7RV produces 9504x6336 pixel images from 35.7x23.8mm sensor, resulting roughly 266 pixels/mm. With a 2x macro lens (Laowa has some), it would mean that 0.2mm subject would be 266x0.2x2=106 pixels across. Not exactly HD, but possibly still usable.

This line puzzled me. Surely, if each drop of seawater was filled with 1mm length creatures you'd notice?

Not every creature is 1mm.

Macro photography most likely. Microscope images tend not to have bokehs like the ones in the article. You can use flourescent microscopy to make those glow in the dark images but the field of view is about 2 or 3 orders of magnitude too small for this.

at such low magnification, the depth of field (not field of view) is pretty big, you can usually see significant out-of-focus detail. But normally people just put the sample in a well and cover it with a coverslip, which makes a thin section.

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