Monday, April 29, 2013

Hummingbird Tongues

This weekend, I was stalking the hummingbird feeder again.  The Ruby-Throated Hummingbirds were once again replaced by the Black-Chinned Hummingbird clan.  At least, for the adult male individuals present, this was the case.  With the females or juvenile males, I am a lot less certain of my identification 

I was fortunate to get a sequence one with its tongue still sticking out after feeding:

Hummingbird tongues turn out to be pretty complicated appendages as described in this interesting video. Nothing whatsoever like I had imagined.   In addition, the lower half of their beaks are able to snap shut very fast based on a "snap-buckling" effect as described in this article, allowing them to catch insects on the fly.  I had not realized how much of their diet is not nectar.

I also imaged another individual with a big dob of pollen on its beak:

It is fascinating to contemplate the fact that reflected in the tiny hummingbird's eye is a recognizable image of the backyard.

All shots taken with Canon 60Da and Canon EF 70-200/f4L lens from approximately 5ft away at 200mm,  f/6.3, 1/1250sec, ISO-2000.

Saturday, April 27, 2013

Ruby-Throated Hummingbirds

We are right on the edge of the summer breading grounds of the Ruby-Throated Hummingbird.  I got a shot of both a female and a male.  The two males are the same individual showing how the iridescent throat coloration only shows up when illuminated appropriately.

Male Ruby-Throat with throat feathers in shadow

Male Ruby-Throat with throat feathers reflecting light

Female Ruby-Throat

Rose-Breasted Grosbeak

The Rose-Breasted Grosbeak is a migratory bird passing on its way north.  We don't see this bird in the yard very often.

Monday, April 22, 2013

Frogs in the Fountain

In our front yard we have a disappearing fountain.  I took these photos, on two subsequent days, with an iPhone of what I think may be a Cricket Frog hanging out on the fountain rocks.  The frog in the first picture was an accident as I was actually targeting the nice moss which is growing on the rocks and missed the frog altogether - they are very small!  I saw it again the second day and tried for a close-in shot.

Wednesday, April 10, 2013

Yellow-crowned Night-Heron

We saw this Yellow-crowned Night-Heron down on the San Gabriel River this evening. We often see a Great Blue Heron at the river but this species is a first.  The hill-country is not in its range.  It has year-round residence on the gulf coast and summer breading in north Texas.  I assume this one is migrating through between these two areas.  I was not able to get any closer before it flew off.  Canon 200mm f/4.0 ISO-1000.

Update 2013.05.20 - Got another shot of the heron on a different stretch of the river.  I have twice seen what might be a juvenile heron but have not gotten a photograph of it.

Monday, April 8, 2013

Black-Chinned Hummingbird

The hummingbirds have recently reappeared in our yard this Spring.  This evening, a trio of Black-Chinned Hummingbirds were fighting for territory around the feeders on our patio.  In the shots below, they are feeding on the flowers of a Texas Betony we have growing in a pot. It was late evening on a cloudy day so I had to resort to the highest ISO setting to have a chance of stopping the wing movement. Canon 60Da at  ISO-6400 with Canon EF 70-200mm/f4L at f/4.0

Sunday, April 7, 2013

Star Test of Canon 70-200mm/f4.0 L USM Lens

This post summarizes my testing of the Canon EF 70-200mm/f4 L USM lens for use in astrophotography. This lens has been consistently well reviewed on-line for its sharpness and low chromatic aberration.  At around $700, it is also very affordable for an "L" series lens.  I would very much welcome comments by other users of this lens as to whether the imperfections described are expected.

Here are the MTF curves which Canon published.  As I am using an APS-C sensor, the region of the curve beyond 13mm does not matter for me.

Imaging Tests

For this set of tests, I used a Canon 60Da camera mounted on an equatorial mount and auto-guided to remove any star-trailing considerations. I gathered images at both ends of the focal-length range, 70mm and 200mm.  For each, I tested the lens with the aperture wide open at f/4.0, reduced by a full stop at f/5.6, and reduced slightly at f/4.5.  Each of these images consisted of a 120 second exposures at ISO-800 centered on the bright star Procyon.

At each focal length, I focused the lens wide open using the electronic lens control in Astro Photography Tool, minimizing the FWHM metric.  I did not refocus for the stopped-down tests.  I captured and saved the images in Canon RAW format, debayered in MaximDL, and saved as uncompressed 16 bit TIFF files.   In Photoshop, I adjusted the black-point and applied a gamma correction, brightening the f/4.5 and f/5.6 images further to compensate for the differences in EV.  I cropped various small regions ( about 8% of full image width) along each of the diagonals and saved these as high-quality JPEG files.  A sub-set are presented below.

Full Frames

The following two images show the full APS-C frames at 200mm and 70mm.  This gives an impression of the overall field of view

Canon 70-200/f4 L USM at 200mm f/4.0 (full frame)
Canon 70-200/f4 L USM at 70mm f/4.0 (full frame)

200mm at f/4.0

The following three images show different regions of the 120sec ISO-800 frame taken at 200mm f/4.0.

Canon 70-200/f4 L USM at 200mm f/4.0 (center of frame)
Canon 70-200/f4 L USM at 200mm f/4.0 (half way from center to bottom-left corner)
Canon 70-200/f4 L USM at 200mm f/4.0 (bottom-left corner)

200mm at f/4.5

The following three images show different regions of the 120sec ISO-800 frame taken at 200mm f/4.5.  I believe there may have been a glitch in this test as the focus is appreciably worse than in either the f/4.0 for f/5.6 test.

Canon 70-200/f4 L USM at 200mm f/4.5 (center of frame)
Canon 70-200/f4 L USM at 200mm f/4.5 (half way from center to bottom-left corner)
Canon 70-200/f4 L USM at 200mm f/4.5 (bottom-left corner)

200mm at f/5.6

The following three images show different regions of the 120sec ISO-800 frame taken at 200mm f/5.6.

Canon 70-200/f4 L USM at 200mm f/5.6 (center of frame)
Canon 70-200/f4 L USM at 200mm f/5.6 (half way from center to bottom-left corner)
Canon 70-200/f4 L USM at 200mm f/5.6 (bottom-left corner)

200mm Reflection Artifact

In each of the 200mm tests, I noticed an imaging artifact near Procyon.  The image below shows the cropped central region.  The diagonal black lines cross at the center of the frame.  It is clear that the artifact is symmetrical with Procyon and might be some form of reflection artifact.

In performing the tests, I had not removed the Pro-Master 67mm Digital Protection Filter which is attached to the front of the lens.  I will need to repeat the test with this filter removed in order to see if it is the source of the artifact.

Possible reflection artifact, opposite from bright star Procyon, at 200mm

70mm at f/4.0

The following three images show different regions of the 120sec ISO-800 frame taken at 70mm f/4.0.

Canon 70-200/f4 L USM at 70mm f/4.0 (center of frame)
Canon 70-200/f4 L USM at 70mm f/4.0 (half way from center to bottom-left corner)
Canon 70-200/f4 L USM at 70mm f/4.0 (bottom-left corner)
Canon 70-200/f4 L USM at 70mm f/4.0 (bottom-right corner)

70mm at f/4.5

The following three images show different regions of the 120sec ISO-800 frame taken at 70mm f/4.5.

Canon 70-200/f4 L USM at 70mm f/4.5 (center of frame)
Canon 70-200/f4 L USM at 70mm f/4.5 (half way from center to bottom-left corner)
Canon 70-200/f4 L USM at 70mm f/4.5 (bottom-left corner)
Canon 70-200/f4 L USM at 70mm f/4.5 (bottom-right corner)

70mm at f/5.6

The following three images show different regions of the 120sec ISO-800 frame taken at 70mm f/5.6.

Canon 70-200/f4 L USM at 70mm f/5.6 (center of frame)
Canon 70-200/f4 L USM at 70mm f/5.6 (half way from center to bottom-left corner)
Canon 70-200/f4 L USM at 70mm f/5.6 (bottom-left corner)
Canon 70-200/f4 L USM at 70mm f/5.6 (bottom-right corner)


At 200mm, this lens performed well, even wide-open.  The stars are round to the corners of the frame and have consistent focus.  There is a hint of chromatic aberration in brighter stars which was more evident away from center.  Stopping down slightly to f/4.5 improves the CA but does not appreciably change the sharpness or shape of the stars.

Imaging wide open at f/4.0 has the advantage of eliminating the diffraction pattern on bright stars as the iris opening is round.  The iris blades form an octagon as the lens is stopped down leading to a well formed pattern around bright stars.  I don't always appreciate these "maltese crosses" in my images so I am glad that imaging wide open is an option with this lens.

At 70mm, the lens performance is less impressive.  This was not unexpected as edge-effects are typically worse at wider angles. Wide open at f/4.0, the chromatic aberration is much more noticeable at 70mm than at 200mm - see specifically the star above Procyon in the center image.  At 70mm, stopping down to f/4.5 has a much more pronounced effect in removing the blue halos.

Star distortions are also much more pronounced at 70mm.  The stars in the bottom left are smeared radially into ellipses, similar to what I would expect of a refractor with uncorrected field curvature. The stars in the bottom right are slightly distorted into crosses.  Stopping down the lens improves the "crosses" but not the "ellipses."

Update 2013-04-11 - Imaging Test

This image of the belt and sword region of Orion shows a more representative test, although the blog has compressed the image.  This image consists of 16 stacked exposures, each 60sec at ISO-800. These were taken with the lens at 200mm, f/4.5. Post processing in Photoshop to apply gamma stretching, gradient removal, and noise smoothing.

Wednesday, April 3, 2013

Upgrade Losmandy GM-8 Wormgear

This week, I upgraded the DEC and RA gear assemblies to Losmandy's One-Piece Worm Blocks (OPWB).  These assemblies allow the worm-gear engagement to be adjusted without disturbing the alignment of the worm-gear bearings.  In addition to getting better tracking and guiding performance,  I also want to simplify the process of adjusting the gears in the field as I seem to need to do this on every camping trip.

The new parts from Losmandy are accurately machined, as are all of their components.  Even better, they come with absolutely no instructions to curb ones engineering creativity!  ... Humm, fortunately, I was able to find instructions posted by Michael Siniscalchi for upgrading the G11 mount.  Though the kits are not identical, these instructions were of enormous help.

The first step was to remove the old worm-blocks, motors, and gears.  I think that this required every standard sized hex key from 0.05" up to 5/32" SAE.  Removing the motor from the gear box would have been much easier with a ball-ended hex key.  The only parts that are reused are the servo-motor, gear box, gear-box cover, and the original high-precision brass worm gear.

Using the new kit parts, I inserted the worm gear into the bearing housings, and mounted these back on the bracket.  I then attached the Ruland coupling to the worm-gear, leaving the 0.01" gap as suggested by Siniscalchi.  Finally, I mounted the gear box mounting plate to the end of the bracket.

The next step was to screw in the "stud screws" as shown below using the 0.05" hex key from the worm gear side until flush.

Up until this point, everything had gone without difficulty.  The next step, however, was more troublesome and where my steps deviated from those outlined by Siniscalchi.  
  • Inserting the gear-box onto the coupling took a bit of jiggling.  I suspect the issue was with the shaft of the old gear box, not the new coupling.  
  • Originally, the nylon washer shown below would have been placed between the gear box tabs and the mounting posts.  With the new mounting plate, the gear box did not sit flush on the mounting plate causing the tabs to get bent and the gear box to sit cock-eyed.   I moved the washers below the tab, raising the gearbox up off of the mounting plate.  This seemed to work better.  
  • The "centering" trick described by Siniscalchi was very important.  However, I was never satisfied with the uniform smoothness of the gear motion.  It seems that the gear box continued to wobble slightly side to side as the worm was rotated.  Short of assuming that both worm gears were slightly bent, I could not figure out where the extra wobble was coming from.  In the end, I found the best compromise placement of the gearbox and tightened down the new hex mounting posts on to the ends of the "stud screws".   
  • My kit came with two sets of mounting posts.  One set was very long, approximately 2" -  I could not figure out what these were for. The other set was shorter than the original posts. Using these, there was a large gap between the top of the posts and the surface of the gear box cover which they are meant to support. However, the provided screws were just long enough to reach down to the posts. 

After remounting the gear box cover and the servo-motor, I attached the entire assembly to the mount and ran tests to make sure the controller could slew the mount smoothly over the whole range of each axis.  The motors seemed to purr smoothly and the controller did not issue any "lag" error messages.

This process highlighted one final problem.  In an earlier post, I described how I created a DEC axis puck which raised the telescope saddle plate up 3/4".  This allowed my larger, dual-style saddle plate to clear the RA axis motor assembly.  Unfortunately, as shown in the image above, the new OPWB kit moves the servo-motor out further from the mount ... just enough that my puck is no longer tall enough ... I think it needs to be 1" tall now. While I decide whether to manufacture a new puck (uhg), I have put back on the stock Losmandy saddle.

I am looking forward to some clear skies to see how the upgrade improves tracking and guiding.  It has certainly made adjustment a breeze.