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Measuring bugs

Hello all,
I have written a brief article on a procedure for accurately measuring bugs in macro photographs. I would appreciate any and all comments or criticism.
Measuring bugs
Thank you in advance,
Bruce Marlin

Super helpful! Hope some of the editors use this link to help new members.

Thread count
When I'm black lighting, I hang a white sheet with a thread count coarse enough to resolve, and use that to measure the moth, such as here:

In cases where a lateral view is more informative, such as here:

the perspective can make that difficult. You have to follow-up with a dorsal image in that case.

Autofocus, Photoshop, and Money
Bruce - Thanks for writing the article. I was thinking of doing something similar. I only shoot in the field and I use a similar method to what you describe, shoot the insect and then shoot a ruler.

Autofocus: Using custom functions, Canon and Nikon DSLR camera bodies allow the photographer to switch the autofocus control from the shutter button to an AF-On button on the upper right corner of the back side of the camera body. So to autofocus, I hit that button with my thumb. It does the same thing as depressing the shutter button half way. I actually prefer this arrangement for all wildlife photography as there are a number of advantages. For starters, see explanations here and here. When I conduct in the field nature photography programs, it's my first recommendation. The learning curve is fast. I find most people are used it in less than an hour.

After I autofocus a series of shots, I then shoot the ruler manually by moving the ruler to the point where it's in focus as you describe. Because I haven't touched the autofocus button, the focus has not changed from the last insect shot, provided I release the autofocus button as soon as that last insect shot was taken or better yet, the instant just before that last shot. If I see that I'm off, I'll manually focus by moving in or out. If the shot is bad, I try again if possible.

Photoshop: In Photoshop I draw a path or box, whichever is easier, around the insect and hit copy and then paste it to the ruler image. I turn down the transparency of the insect layer to 50% and then move and rotate as needed to line the subject up with the ruler. Neither the subject nor the ruler needs to be oriented when shooting.

I know these two tips sound complicated but once done, I think getting the hang of both is easy and quick. Shooting and post processing are both faster. You can keep autofocus. It can be more accurate because you can precisely place the image where it needs to be with respect to the ruler.

Money: Plastic, paper or coin, it doesn't matter. If you don't have the ruler with you, shoot money. You can always measure it with a ruler later. If nothing else, you'll have Andy Warhol smiling from above.

If you like the method(s), you might want to add it to your page. Feel free to email me any questions if any of this is unclear.

Grid paper
An alternative to using a ruler for stationary bugs is grid paper. Examples:

your article
And to address your article more directly:

Your point about photographing a ruler is good, and for some photographers, the method would be very useful. Also, I think articles on technical methods--especially inexpensive ones--are great.
In fact, I often use the exact method you describe or a close variant.

I shoot almost exclusively hand-held shots of insects in their environment. When I say hand-held, I mean really hand held. I usually have my camera in one hand and make extensive use of the fully-articulated LCD. I'm often kneeling on sharp scree or clinging to a steep slope with my left hand.
For my kind of photography, it'd be extremely clumsy to turn off autofocus and zoom and get a shot of a ruler for each shot. I always shoot in bursts (7 fps using my current Lumix FZ 1000) and the camera is focussing between each shot. Each burst is 5 or more photos. And I almost never stop then. I reframe, rezoom and shoot another burst until the insect leaves or I'm satisfied. I often end up with 20-30 shots of the same insect.
When I've tried shooting the ruler separately in the same environment, it's often proved to be difficult to measure using Photoshop. Measuring individual stationary objects in the same scene is more successful, though often the insect isn't really in the same plane as the stationary object. (This works better for spiders or insects feeding on flowers.)
In fact, I find it pretty difficult to get a hand-held ruler in the same plane as the insect.

Well, there's a method that is very precise, but... requires that you shoot the insect and the photo separately, and don't refocus in between.

1. Take a photo of the bug, and make sure you don't change the focus after the shot.

2. Make sure you switch to manual focus if you were on auto focus.

3. Take a picture of a ruler by moving he distance between the ruler and the camera until you have a sharp focus, and take a photo.

Because of the shallow depth of field, the magnification will be the same for the ruler, and the bug, so you can use the photographed ruler to measure the photographed bug. I didn't invent the idea, I read about it here on bugguide. It works well for me.

Just to add to this discussion:
Some bugguide editors don't want to see photos with rulers in them. A size estimate may not aid identification, I've been told.

I bought some Staedtler 562 04FL-12 flexible plastic rulers. I cut a 10 cm piece off the metric edge, smooth the cut edges and carry that in the field. The gray plastic is quite close to neutral.

For images I take with my Nikon dissecting microscope and a Nikon Coolpix 995, I made some 10 mm clear rulers by creating an image in Photoshop, sizing and printing on clear laser printer stock. These "rulers" are 1 cm long, divided into ten millimeters and half-millimeter marks. You can cut out one at a time from a piece of the sheet. You need a big black mark at the end of each ruler, because they're very hard to see.
Of course, these aren't great, but they do the job, are disposable, are nearly free and can be manipulated right up next to whatever you're photographing.
Here are a couple of examples.

Occasionally I've tried to use one photo with a ruler and a separate photo--taken at nearly the same time--without a ruler. That's really difficult.

Some editors
like myself don't mind or prefer to have a ruler in the image, size is important for ID's on lots of things, especially the small stuff!

Rulers present/absent in images
We've just had another round of correspondence with an editor who was/is frassing anything with a ruler in it.

I photograph moths frequently and in *many cases* size matters a lot, especially in the absence of any other context in a photo. Is that moth forewing 5 mm long? 8 mm? 15 mm? 3 cm? The aid to identification can be more subtle than that: Is the FW 5-6 mm, or 6-8 mm? A millimeter rule can often resolve that. Having a documented image of an insect right next to that ruler is hard evidence.

I and many others here are getting into the "dual image" habit of first documenting a moth (e.g. on a sheet at a blacklight) with good crisp macro images, *then* trying to get a follow-up image with a ruler in the same frame as the moth. See my discussion on this iNaturalist blog:

Nothwithstanding the comments that measurements of this nature are not suited for sub-millimeter range, this is a simple, (somewhat) convenient, and sometimes critical way of getting a "calibrated" measurement of an insect in the real world. Perhaps including the image with the ruler is superfluous when filling in the "Size" field on BG, but how are we to gage how someone measured an insect for that information?? (I absolutely disagree that this field could be filled out by extracting some measure from a field guide or other reference; that's NOT the point of that field.)

One suggestion
Make the ruler as unobtrusive as possible. Here are a few examples:

Others may not be as good as these examples but are still acceptable. If the picture is dominated by the ruler and the bug looks completely secondary, such image does not belong in the guide.

Another suggestion
The rulers could be cropped out of all those sample photos after the photographer records the bug's size.

Maybe missing the point
Cropping out the ruler illustrates the disparity of opinion on this admittedly controversial "rule" or suggestion for BG images. It seems that the urge to eliminate rulers from images arrises principally out of a sense of aesthetics for the subject images at the expense of offering up the hard evidence of an insect's size. In the absence of a ruler in at least one image (not all), who can verify an insect's size, whether asserted in the "Size" field or not?

And size matters. Folks who assert that size isn't important in identifying insects either haven't tried to work in tough insect groups or are so thoroughtly *into* identifying their specialties that they have presumptive knowledge for identification that escapes less knowledgeable viewers. In either of these cases, a measurable image will be instructive for the rest of us.

Trouble is, there are contrary points!
"In the absence of a ruler in at least one image (not all), who can verify an insect's size, whether asserted in the "Size" field or not?"

If a photo of mine includes a number in the Size field with no indication that it's approximate, I got that number from a photo, later discarded, of the bug with a ruler. (There are exceptions. If I couldn't pose the ruler next to the bug, I might get a size from a photo of the bug with an object I can measure later, as when a bug walks onto my wristwatch.) I do this because I understand the rule as "No rulers in submitted photos." Now it seems that not all who have a stake in BG endorse that rule.

Who can verify an insect's size? Just the photographer. That goes for the location and date, too. We don't usually hold up a bug next to a road sign to prove where we were.

Points well taken...

Back to the picture of the ruler used to measure...
I should have mentioned if you prefer, you can use the widest aperture of the lens for the ruler shot. This narrows the depth of field making focusing at the right distance a little easier.

I like the method a lot, but it comes down to familiarity with Photoshop. I actually move the ruler directly over the bug at 50% transparency. Often I will a copy for reference. Usually I delete the ruler for the photo I submit. Occasionally I just move it off of the bug. On disadvantage of not including the ruler has been mentioned. You have no way of knowing if I am estimating of measuring.

This thing about aesthetics leads me to just keep a reference in case someone really wants an exact measurement. I resize the rule photo usually to save space, and rename it so it is first in the sequence. That makes it easy to see when I have a folder with actual measured sizes.

Information is good. If you have it preserve it. Whether it is important or not, it is better to have it than not to. Good call.

I carry half of a 6-inch/15-cm transparent plastic ruler. It fits easily in a pocket, and I've never met a bug as long as 7 cm.

Your website has some impressive images!

Size Matters
It's handy to have a ruler longer than you need because then you have a handle that can stay out of the frame. A lot of my shots with a ruler would be impossible if I had to lay the ruler down. I probably only use the first couple of centimeters.

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