Posts Tagged ‘Brook Snaketail dragonfly’

Ophiogomphus aspersus exuvia

March 20, 2018

A Brook Snaketail dragonfly (Ophiogomphus aspersusnymph was collected by Bob Perkins on either 10 SEP 2017 or 03 OCT 2017 (the date is uncertain) along the New River in southwestern Virginia. The nymph was reared in captivity until it emerged on 31 OCT 2017 and metamorphosed into an adult female. The following specimen is the exuvia from the nymph. Brook Snaketail is a member of the Family Gomphidae (Clubtails).

A two-step process was used to verify the identity of the exuvia.

  1. Determine the family.
  2. Determine the genus and species.

Step 1. Family

First, determine the family of the specimen. For reference, watch the excellent Vimeo video Identifying dragonfly larva to family (8:06). Here’s the decision tree used to identify the exuvia as a member of the Family Gomphidae (Clubtails).

  • The specimen has a flat labium that doesn’t cover the face (not mask-like), as shown in Photo No. 1, 4, and 5.
  • Antennae are club-like (not thin and thread-like, as in  Aeshnidae larvae), as shown in Photo No. 1.

No. 1 | Ophiogomphus aspersus | exuvia (face-head)

Step 2. Genus and species

The dichotomous key for Ophiogomphus that appears on p. 262 in Dragonflies of North America, Third Edition by Needham et al. was used to verify the genus and species of the exuvia. The eleventh couplet [11, 11′] is as follows.

11(10). Lateral margins of prementum slightly convergent in distal 1/2 (Fig. 320c); lateral abdominal spines about 1/8 length of lateral margin of corresponding segment; in dorsal view, cerci about 2-1/2 times as long as basal width; dorsal hooks on abdominal segments 3-6 erect (Fig. 322d). [aspersus]

11’. Lateral margins of prementum parallel or slightly divergent in distal 1/2 (Fig. 320K); lateral abdominal spines each about 1/5 length of lateral margin of corresponding segment; in dorsal view, cerci each about twice as long as basal width; dorsal hooks on abdominal segments 3-6 appressed (Fig. 322d). [rupinsulensis]

No. 2 | Ophiogomphus aspersus | exuvia (dorsal)

The word “process,” as in “dorsal abdominal process,” is defined as follows.

An upstanding prominence, usually narrow and rod-like or spine-like. Source Credit: Glossary, Dragonflies of North America.

The dorsal hooks, a.k.a., dorsal abdominal processes, on abdominal segments three through six (S3-S6) are erect. Hey, call them whatever you like, including “erect” — there are raised bumps along most of the mid-dorsal abdomen, some of which are raised more noticeably than others, as shown in Photo No. 3.

No. 3 | Ophiogomphus aspersus | exuvia (dorsal-lateral)

The next two annotated images show ventral views of the exuvia.

No. 4 | Ophiogomphus aspersus | exuvia (ventral)

The flat labium doesn’t cover the face and the lateral margins of the prementum are slightly convergent in the distal half, as shown in Photo No. 5.

No. 5 | Ophiogomphus aspersus | exuvia (prementum)

Lateral spines are present on abdominal segments seven through nine (S7-S9) only. Did I measure the length of the lateral abdominal spines to see whether they are about one-eighth (1/8) the length of the lateral margin of the corresponding segment? In a word, no — the length looks about right to my unaided eye.

The cerci are about two-and-a-half (2-1/2) times as long as their basal width. Again, the length looks about right to my unaided eye.

No. 6 | Ophiogomphus aspersus | exuvia (anal pyramid)

The rudimentary ovipositor shown in Photo No. 4 and 7 indicates this individual is a female.

No. 7 | Ophiogomphus aspersus | exuvia (rudimentary ovipositor)

After emergence

The next photograph shows the Brook Snaketail dragonfly after emergence from one of Bob Perkins‘ holding tanks. Ophiogomphus aspersus is 44-49 mm in total length (Paulson, 2011).

Image used with permission from Bob Perkins.

This individual is a female, as indicated by its rounded hind wings and terminal appendages.

Image used with permission from Bob Perkins.

The last close-up photo shows a ventral view of the subgenital plate.

Image used with permission from Bob Perkins.

Tech Tips

The following equipment was used to shoot Photo No. 2-4: Canon EOS 5D Mark II digital camera, in manual mode; Kenko 20mm macro automatic extension tubeCanon EF100mm f/2.8L Macro lens (set for manual focus); Canon MT-26EX-RT Macro Twin Lite set for “Master” mode, and Canon 580 EX- and Canon 580EX II Speedlites set for “Slave” mode. Photo No. 1 and 5-7: Canon MP-E 65mm Macro lens (manual focus only, set for 2x magnification) plus the multiple-flash setup.

Adobe Photoshop CC 2017 was used to annotate selected images.

Bob Perkins’ photos were shot using a Canon EOS Rebel T3i camera body and Canon EF-S 60mm macro lens.

Copyright © 2018 Walter Sanford. All rights reserved.

Composite image

March 16, 2018

Among many useful tips for better macro photographs shared by Lester Lefkowitz in Close-Up and Macro Photography, by B&H Photo (1:54:02), Lester emphasized trying to keep the focal plane parallel to the subject. Good idea. The problem is many subjects, such as odonate exuvia, aren’t flat and macro lenses are well-known for extremely shallow depth of field.

Focus stacking can be used to increase depth of field. Adobe Photoshop CC 2017 was used to create a composite image of two photos: one photo focused on the prementum; another photo focused on the anal pyramid. The two photos were shot at f/22, so the head and tail were acceptably in focus in both images. In contrast, the following composite image is perfectly in focus from head-to-tail.

100mm | ISO 100 | f/22 | 1/500s | 0 ev

The simple two-image focus stack worked better than some composite images that I have created using many more layers. I routinely shoot macro photos of the same specimen that are focused on different key field marks for identification. Encouraged by success, I think I’ll take a second-look at my photo library to see whether there are more candidates for creating simple composite images.

The Backstory

A Brook Snaketail dragonfly (Ophiogomphus aspersusnymph was collected by Bob Perkins on either 10 SEP 2017 or 03 OCT 2017 (the date is uncertain) along the New River in southwestern Virginia. The nymph was reared in captivity until it emerged on 31 OCT 2017 and metamorphosed into an adult female. The preceding specimen is the exuvia from the nymph.

Tech Tips

The following equipment was used to shoot both photos in the composite image: Canon EOS 5D Mark II digital camera, in manual mode; Kenko 20mm macro automatic extension tubeCanon EF100mm f/2.8L Macro lens (set for manual focus); Canon MT-26EX-RT Macro Twin Lite set for “Master” mode; and Canon 580 EX- and Canon 580EX II Speedlites in “Slave” mode.

Adobe Photoshop CC 2017 was used to create the composite image by “round-tripping” with Apple Aperture.

  1. Open the photos as layers in Photoshop. (Two, in this case.)
  2. Edit/Auto-Align Layers…
  3. Edit/Auto-Blend Layers…
  4. Layer/Flatten Image
  5. Save

Copyright © 2018 Walter Sanford. All rights reserved.

High-speed sync flash photography

March 14, 2018

Background information

DSLRs and many, if not most mirrorless cameras require a mechanical shutter in order to properly expose larger digital image sensors. The default flash sync speed of my Canon EOS 5D Mark II DSLR is 1/200s: external flash units work with the camera at shutter speeds of 1/200s or slower; a black bar will appear on images at shutter speeds greater than 1/200s.

That’s a problem, especially if you prefer to shoot at faster shutter speeds. What’s the solution? High-speed sync. Rather than a single burst of light, high-speed sync uses imperceptible rapid pulses of light that enables your camera to work properly at shutter speeds greater than its default sync speed. Sounds great, right? Not so fast. As it turns out, the power output of external flash units is reduced by using high-speed sync.

Among other reasons that I bought the new Canon MT-26EX-RT Macro Twin Lite recently is because it supports high-speed sync (HSS), unlike the older model it replaced. I experimented with HSS so I could use a faster shutter speed in order to diminish/eliminate camera shake/vibration, a big problem in high-magnification macro phototography. Problem is, the Guide Number of the macro flash isn’t powerful enough to shoot HSS indoors. (Outdoors should be fine.) Again I ask, what’s the solution? More power! (Grunt, grunt.)

I  used wireless multiple flash photography by setting the macro flash in “Master” mode and two Canon Speedlites (580EX and 580EX II) in “Slave” mode: one of the macro twin lites is Group A, the other macro twin lite is Group B, and the other two flashes are Group C. All flashes fire at the same settings automatically, as configured currently. If the master flash is set for HSS, then the slave flashes also fire using HSS. The system works in either ETTL- or Manual modes. (I prefer Manual mode for macro photography.)

Test shots

Photo No. 1 is a test shot of the lens cap for a Canon EF 100mm Macro lens using high-speed sync flash photography. Notice the shutter speed is faster than the default sync speed of 1/200s.

No. 1 | 100mm | ISO 100 | f/18 | 1/320s | 0 ev

Photo No. 2 shows a Brook Snaketail dragonfly (Ophiogomphus aspersus) nymph that was collected by Bob Perkins on either 10 SEP 2017 or 03 OCT 2017 (the date is uncertain) along the New River in southwestern Virginia. The nymph was reared in captivity until it emerged on 31 OCT 2017 and metamorphosed into an adult female. The following specimen is the exuvia from the nymph.

No. 2 | 100mm | ISO 100 | f/22 | 1/500s | 0 ev

Notice the f/stop is smaller and the shutter speed is faster than the first test shot. As you might guess, that means I increased the power output of the master- and slave flashes until the image was exposed properly.

Tech Tips

The following equipment was used to shoot Photo No. 1 and 2: Canon EOS 5D Mark II digital camera, in manual mode; Kenko 20mm macro automatic extension tubeCanon EF100mm f/2.8L Macro lens (set for manual focus); Canon MT-26EX-RT Macro Twin Lite set for “Master” mode; and Canon 580 EX- and Canon 580EX II Speedlites in “Slave” mode.

Copyright © 2018 Walter Sanford. All rights reserved.


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