Archive for the ‘education’ Category

“Winter Meadowhawk” dragonflies

December 8, 2017

The season called “winter” is defined two ways: atmospheric scientists, including meteorologists and climatologists, define winter as the three-month period from December to February; astronomers define winter as the time period that begins on the December Solstice (12/21) and ends on the March Equinox (03/21), although the actual dates for these events may vary slightly.

Several Autumn Meadowhawk dragonflies (Sympetrum vicinum) were spotted on the first day of climatological winter at Occoquan Bay National Wildlife Refuge, Prince William County, Virginia USA. Therefore I think it is appropriate to call them “Winter Meadowhawks.”

The last two photos show the same male, perching on different surfaces. My guess is he was looking for a good source of thermal energy on a cool, windy day.

The Sun is always low in the sky during winter, even at its maximum altitude. Indirect incoming solar radiation (insolation) is less intense than direct insolation. The last photo shows the male dragonfly perched on a south-facing wooden board that is perpendicular to the surface of the Earth, therefore the solar energy received by the board is more intense than the energy received by the ground. This probably explains why the male moved from the ground to the board.

Enrichment

The last photo was taken on 01 December 2017 at 11:33:50 a.m. EST, as shown by the EXIF information for the image. The altitude of the Sun was 28.9° at 11:30 a.m., meaning a ray of sunlight formed an angle of 28.9° with horizontal surfaces such as the ground. At the same time, a ray of sunlight formed an angle of 61.1° with vertical surfaces such as the wooden board shown in the first and last photos. That’s the beauty of mathematics — some simple geometry shows clearly which surface received more intense insolation. Smart dragonflies!

Related Resource: Sun or Moon Altitude/Azimuth Table, U.S. Naval Observatory.

Copyright © 2017 Walter Sanford. All rights reserved.

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Thermal energy vampire!

November 24, 2017

The following photographs show an Autumn Meadowhawk dragonfly (Sympetrum vicinum) perching on Walter Sanford (hey, that’s me!) at Occoquan Bay National Wildlife Refuge, Prince William County, Virginia USA. This individual is a male, as indicated by his terminal appendages.

All three photos were taken by Lisa Young during a photowalk with me along Easy Road.

Most dragonflies are skittish. Some species of dragonflies are “friendly,” such as Blue Corporal dragonflies (Ladona deplanata) and Autumn Meadowhawk dragonflies (Sympetrum vicinum). It’s probably not a coincidence that both types of dragonflies are early- and late-season species, when the ambient air temperature is cooler.

Some odonate experts speculate dragonflies perch on people in order to absorb thermal energy radiated by the relatively warm human body. Or in this case, a black backpack — a good spot since darker-colored objects absorb and re-radiate thermal energy more quickly than lighter-colored objects.

Related Resource: Five Guys, a blog post by Walter Sanford featuring photos of male Autumn Meadowhawk dragonflies taken before the meet-up with Liza Young.

Copyright © 2017 Walter Sanford. All rights reserved.

Eastern Gartersnake

November 18, 2017

An Eastern Gartersnake (Thamnophis sirtalis sirtalis) was spotted during a photowalk along Easy Road at Occoquan Bay National Wildlife Refuge, Prince William County, Virginia USA.

After taking a closer shot of the snake’s head (above), I backed away for a wider view that shows the snake is a little more than two (2) feet in length (below).

Eastern Gartersnakes can be differentiated from Common Ribbonsnakes (Thamnophis sauritus sauritus) by the presence of “dark vertical lines on the supralabial scales.” This key characteristic is shown clearly in the following photo.

Copyright © 2017 Walter Sanford. All rights reserved.

Unambiguously Sympetrum ambiguum

November 10, 2017

Two Blue-faced Meadowhawk dragonflies (Sympetrum ambiguum) were spotted during a photowalk along Charlie Road at Occoquan Bay National Wildlife Refuge, Prince William County, Virginia USA. Although Blue-faced Meadowhawk is on the species list of dragonflies and damselflies at Occoquan Bay NWR, this is the first time I have seen Sympetrum ambiguum at the refuge.

Male

This first individual is a male, as indicated by his terminal appendages.

19 OCT 2017 | OBNWR | Blue-faced Meadowhawk (male)

This guy was skittish. I was able to take one photo before he flew toward the tree canopy. The preceding photograph is what my good friend Mike Boatwright calls a “record shot,” that is, a photograph that records (verifies) my sighting of the male Sympetrum ambiguum. The photo was cropped slightly for improved composition.

Female

The last individual is a female heteromorph, as indicated by her tan coloration and terminal appendages.

The preceding photograph is my “record shot” of the female. I worked the shot…

…until I found the best viewpoint, shown below.

The first and last photos of the female were cropped slightly for improved composition; the second photo is uncropped.

Copyright © 2017 Walter Sanford. All rights reserved.

Autumn Meadowhawk dragonflies (mating pairs)

November 4, 2017

This blog post features more photos taken using my Fujifilm X-T1 digital camera, Fujinon XF55-200mm zoom lens, and a Fujifilm MCEX-11 extension tube. The camera was set for manual focus in order to use focus peaking; back-button focusing was used to focus automatically.

In wheel

ISO 640 | 200mm (~300mm, 35mm equivalent) | f/11 | 1/500s | 0.33 ev

Two of many mating pairs of Autumn Meadowhawk dragonflies (Sympetrum vicinum) were photographed on 27 October 2017 at Hidden Pond, Meadowood Recreation Area, Fairfax County, Virginia USA. Both pairs are “in wheel“: the male is on top; the female is on the bottom.

ISO 800 | 200mm (~300mm, 35mm equivalent) | f/18 | 1/500s | 0 ev

In tandem

The last mating pair is “in tandem“: the male is on the upper-right; the female is on the lower-left.

ISO 800 | 200mm (~300mm, 35mm equivalent) | f/16 | 1/500s | 0 ev

After copulation, Autumn Meadowhawks engage in a form of guarding behavior known as “contact guarding,” in which the male and female fly “in tandem” to egg-laying sites. Contact guarding is used by some species of odonates to prevent aggressive males from hijacking the female.

Related Resource: Adding an 11mm extension tube, a blog post by Walter Sanford.

Copyright © 2017 Walter Sanford. All rights reserved.

Adding an 11mm extension tube

November 2, 2017

Optics theory

The net effect of adding an extension tube between a lens and camera body is the “working distance” is decreased, that is, the distance from the front of the lens barrel to the subject is decreased. A smaller working distance means the same lens will focus closer to the subject, thereby increasing magnification.

The effect is greater at shorter focal lengths, as shown by the following annotated table of magnification for the two extension tubes sold by Fujifilm USA.

Table courtesy Fujifilm USA.

Theory into practice

On 27 October 2017 several Autumn Meadowhawk dragonflies (Sympetrum vicinum) were spotted perching on the small dock at Hidden Pond, Meadowood Recreation Area, Fairfax County, Virginia USA. All individuals featured in this photo gallery are male, as indicated by their terminal appendages.

All photos in this set were taken using my Fujifilm X-T1 digital camera, Fujinon XF55-200mm zoom lens, and a Fujifilm MCEX-11 extension tube. The camera was set for manual focus in order to use focus peaking; back-button focusing was used to focus automatically.

At 200mm, the working distance of the lens is 905 mm (90.5 cm, ~35.63 in), or approximately three (3) feet. With an 11mm extension tube mounted between the lens and camera body, the working distance is reduced to 665 mm (66.5 cm, ~26.2 in), or a little more than two (2) feet. At a focal length of 55mm, adding the extension tube would result in photos that look more like “macro” photos; at 200mm, adding the extension tube resulted in photos that look like a lens with a longer focal length was used to take the shots.

All of the following photos were slightly cropped for improved composition. The 11mm extension tube is the difference-maker that enables me to take close-up shots using a mid-range telephoto zoom lens such as the Fujinon 55-200mm.

ISO 640 | 200mm (~300mm, 35mm equivalent) | f/11 | 1/500s | -1 ev

ISO 640 | 200mm (~300mm, 35mm equivalent) | f/11 | 1/500s | -1 ev

When I changed the aperture from f/11 to f/16 (larger to smaller opening) for more depth-of-field, notice the ISO increased from 640 to 800. ISO was set for “Auto” with a limit of 800.

ISO 800 | 200mm (~300mm, 35mm equivalent) | f/16 | 1/500s | 0 ev

ISO 800 | 200mm (~300mm, 35mm equivalent) | f/16 | 1/500s | 0 ev

ISO 800 | 200mm (~300mm, 35mm equivalent) | f/16 | 1/500s | 0 ev

ISO 800 | 200mm (~300mm, 35mm equivalent) | f/16 | 1/500s | 0 ev

More tech tips

Focus peaking can be activated when the camera is set for manual mode. Using back-button focus (AF-L button) in manual mode enables one to retain full control of the exposure triangle, focus quickly, and see what’s in focus before shooting a photograph. Fuji Back Button Focus (4:06), a YouTube video by Ashraf Jandali, provides a clear demonstration of how to use back-button focus on the Fujifilm X-T1.

In order to reduce “camera shake,” I almost always shoot in shutter priority mode using the reciprocal rule. Remember, it’s the 35mm equivalent that matters: since my lens is ~300mm, the shutter speed should be set for at least 1/300s; in this case, it was set for 1/500s. In manual mode, I set the shutter speed and aperture; ISO was set for “Auto” with a limit of 800. An inexpensive Sunpak 6700M aluminum monopod was used for added stability.

Editor’s notes

Did you notice I didn’t use an external flash unit to shoot the preceding photos? The afternoon Sun is lower in the sky in late-October than it would be at the same time during mid-summer. I wanted to faithfully capture the shadows cast by the dragonflies in order to convey the feeling that the Sun is setting on these dragonflies, literally for the day as well as figuratively for the current odonate season.

Copyright © 2017 Walter Sanford. All rights reserved.

Quick and dirty macro photos (Part 2)

October 29, 2017

A mating pair of Autumn Meadowhawk dragonflies (Sympetrum vicinum) was spotted on 25 October 2017 during a photowalk along the boardwalk in the central wetland area at Huntley Meadows Park, Fairfax County, Virginia USA. This pair is “in wheel.” The female is the primary subject; the tip of the male’s red abdomen is the secondary subject.

The first photo is my favorite in the set.

ISO 100 | 56mm (~300mm, 35mm equivalent) | f/4.1 | 1/800s | -1 ev

All odonates (dragonflies and damselflies) have a 10-segmented abdomen, numbered from front to back. Notice the small black “rivets” around the joint between segments seven and eight (S7, S8) of the male’s abdomen. Does anyone know the function of these structures?

ISO 100 | 56mm (~300mm, 35mm equivalent) | f/4.1 | 1/800s | -1 ev

Each compound eye has approximately 30,000 ommatidia!

ISO 100 | 56mm (~300mm, 35mm equivalent) | f/4.1 | 1/800s | -1 ev

Tech Tips

The photographs in this gallery were taken using my Panasonic Lumix DMC-FZ150 superzoom digital camera set for ~12x zoom, Raynox DCR-250 close-up filter, and Canon 580EX Speedlite external flash (manual mode). The close-up filter screws onto the front of the camera lens using a 52-43mm step-down ring.

I estimate the “working distance” between the camera and subject was approximately three-to-six inches (~3-6″). I attempted to photograph several mating pairs of Autumn Meadowhawks; this is the only pair that allowed me to get close enough to shoot some macro photos.

Related Resource: Quick and dirty macro photos (Part 1), a blog post by Walter Sanford featuring photos of male Autumn Meadowhawk dragonflies.

Copyright © 2017 Walter Sanford. All rights reserved.

Quick and dirty macro photos (Part 1)

October 27, 2017

Several Autumn Meadowhawk dragonflies (Sympetrum vicinum) were spotted on 25 October 2017 during a photowalk along the boardwalk in the central wetland area at Huntley Meadows Park, Fairfax County, Virginia USA. All of these individuals are male.

The photographs in this gallery were taken using my Panasonic Lumix DMC-FZ150 superzoom digital camera set for ~12x zoom, Raynox DCR-250 close-up filter, and Canon 580EX Speedlite external flash (manual mode). I estimate the “working distance” between the camera and subject was approximately three-to-six inches (~3-6″). Now that’s what I call cooperative models!

ISO 100 | 56mm (~300mm, 35mm equivalent) | f/4.1 | 1/800s | -1 ev

The following photo is my favorite in the set.

ISO 100 | 56mm (~300mm, 35mm equivalent) | f/4.1 | 1/800s | -1 ev

Each compound eye has approximately 30,000 ommatidia!

ISO 100 | 56mm (~300mm, 35mm equivalent) | f/4.1 | 1/800s | -1 ev

The Raynox DCR-250 close-up filter is a relatively inexpensive solution that enables my Panasonic superzoom digital camera to be used for macro photography. Set-up is quick and easy — the filter simply screws onto the front of the camera lens using a 52-43mm step-down ring.

As you can see, depth-of-field is very shallow, caused in part by shooting in Shutter Priority mode rather than Aperture Priority. A cooperative subject, good light, and a lot of patience are essential for success.

Related Resource: Quick and dirty macro photos (Part 2), a blog post by Walter Sanford featuring photos of a mating pair of Autumn Meadowhawk dragonflies (in wheel).

Copyright © 2017 Walter Sanford. All rights reserved.

Polymorphism or old age?

October 25, 2017

Some species of female odonates are polymorphic, meaning females can be one of two or more colors. In contrast, some species of female odonates become discolored with age.

The thorax and abdomen of female Autumn Meadowhawk dragonflies (Sympetrum vicinum) can be either tan or red. The difference in color is the result of either polymorphism or age-related discoloration. More research is required to establish cause and effect.

Several tan and red female Autumn Meadowhawks were spotted during a recent photowalk at Occoquan Bay National Wildlife Refuge, Prince William County, Virginia USA.

Tan

This individual is a tan female, as indicated by her terminal appendages and noticeably thicker abdomen than males of the same species.

Red

The following individuals are red females.

Copyright © 2017 Walter Sanford. All rights reserved.

Great Spreadwing (practice oviposition)

October 15, 2017

This gallery — named “practice oviposition” (egg-laying) — features a six-photo time series of a female Great Spreadwing damselfly (Archilestes grandis).

Female Great Spreadwing damselflies, like all female odonates, have two cerci (sing. cercus), superior appendages that have little or no function. Also notice two styli (sing. stylus), structures that serve as sensors (like “curb feelers“) in egg positioning during oviposition.

(See a full-size version of the original photo, without annotation.)

The female uses her styli to guide the ovipositor into position, as shown in the next two photos.

In this case, I saw no evidence that the ovipositor actually penetrated the tree twig. I think this was a practice run in preparation for the real thing, as the title of this blog post says.

Copyright © 2017 Walter Sanford. All rights reserved.


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