Thursday, April 2, 2020

Some Thoughts on Chromatic Aberration - 02 Apr 2020

Hooded Merganser, SOOC, 1:1 crop, Sony a7RIV, Zeiss 35/2.8, Digidapter™, Swarovski STX85@25X
I had the opportunity to digiscope a pair of Hooded Mergansers this past Monday in the ponds next to our house. With the early morning Sun shining on the pair as they swam in the dark waters I knew that exposure would be a challenge, especially with a gorgeous drake displaying a bright white hood bordered in black feathers. I made sure to expose for the white, and for the most part, did well. However, I noticed chromatic aberration (CA) creeping into some of the photos, and decided it was worth a discussion. I made sure to be selective in culling the images so that I could demonstrate some of the challenges that we digiscopers will run into when trying to capture high-contrast situations.

I was shooting with a Sony a7III and Zeiss 35mm f/2.8 pancake lens attached to a Swarovski STX85 and 25-60X Zoom eyepiece set to 25X using a Digidapter™. I had just mounted the camera to the Digidapter™that morning and thought it was properly aligned (trying to get the sharpest vignette circle at the edges of the frame and even illumination throughout the field-of-view, FOV). However, as I reviewed images in Lightroom CC I noticed some very slight CA even the center of my view, where I should not see any. The following is a series of images where the drake swam across my FOV with the first image of the duck in the center of the camera:

There is a very slight amount of CA along the edges of the white border on the hood and in the shoulder. Its not bad, but noticeable, and is easily removed during post-processing.

Now, look at the drake when its toward the edge of the frame. You'll notice more pronounced CA along the white edges with purple-fringing on one border and blue-green fringing on the opposite. Again, it can be removed in post, but it does highlight the fact that CA becomes progressively worse in all scope eyepieces as you move from center to edge

Top of the line scope manufacturers have glass and coatings that minimize CA, but cannot remove it entirely. That's why proper alignment of the camera in front of the scope eyepiece is critical to optimizing image quality and reducing CA. One of the great strengths of the Digidapter™is the ability to achieve proper alignment by being able to adjust camera position in front of the scope eyepiece. 

Luckily for me, it turned out that the locking screw on the Digidapter™ had prevented me from pushing the adapter completely in position. So, when I removed the adapter and replaced it on the scope the system operated as expected and the CA issue was greatly reduced. 

How does focusing influence CA? I found that Alignment, not Focus,  is the culprit behind the CA issue I was experiencing. I typically roll focus through the subject when I digiscope; that is, I shoot a high-speed burst while adjusting focus in front, on, and behind the subject so that I improve my chances of getting one frame as sharp as possible. I find that CA does not improve no matter how sharp the image is. That said, I also find that out of focus subjects remain CA-free when proper alignment is achieved. The images below illustrate this last point:

To expand on this, also note that zooming a scope's eyepiece will alter the critical point of focus and can magnify CA if it is a problem. There may be more detail, but typically it is at the sacrifice of image sharpness. Therefore, its a general rule of thumb that cropping an image for magnification is better than zooming an eyepiece for magnification. That said, I still tend to try my luck at zooming an eyepiece to improve magnification BUT ONLY AFTER I'VE EXHAUSTED LOW-MAG CAPTURES. 

The takeaways from this discussion?

Proper alignment of the camera in front of the scope eyepiece is key to reducing/eliminating chromatic aberration.

CA gets progressively worse toward the edges of the scope's field of view, so make sure to keep your subject in the CENTER OF YOUR FOV and CROP FOR COMPOSITION (don't frame for composition).

Digiscoping will expose any flaws that are inherent in a spotting scope or digital camera. If you are in the market for a spotting scope the first thing I recommend to potential buyers is to point the scope at a subject of high contrast, like white siding in bright sunlight to evaluate the amount of CA that you'll likely encounter. Most scopes do great in normal lighting and show no CA, so this is a great way to evaluate the quality of the optics. The same goes for testing eyepieces, whether they are zoom or fixed. And just know that adding another camera and lens in front of the scope eyepiece with magnify any flaws.

Finally,  did you notice that the first image in this post was taken with a Sony aRIV but I talked about the a7III? That's my next post.

Keep shooting, and stay well. And Stay Home!

Hooded Mergansers - 29 Mar 2020

It was a mild Sunday morning here in SE Michigan with sunny skies and temps at a balmy 60F. Forecast called for a windy afternoon, so I decided to run around the Bridgewater complex and look for ducks on the local ponds. Two pair of Bufflehead were found yesterday, so I was hoping to relocate them.

As I drove out Arsenal Rd. I spotted a single pair of Bufflehead in the pond nearest our house, but decided to drive through the rest of the complex to see if anything else had appeared overnite. The next pond over, in front of the Bridgewater entrance, a pair of Hooded Mergansers were spotted swimming by themselves. I decided to park and go after them.

Recent rains had left the ground soaked, but I didn't mind kneeling in a puddle to digiscope the birds from the edge of the grass. They were cooperative and provided some nice images with the Swarovski STX85 and Sony a7III.

By the time I had finished with these two I walked over to look for the Bufflehead, but they had flown off. Oh, well. Hopefully, these Hooded Mergansers will stick around a few days more. Stay well!

Friday, March 20, 2020

Ring-necked Duck - 20 Mar 2020

"Covid-19 Pandemic Isolation Journal - Day 1"

8 am: It is day 1 of my self-imposed isolation in light of very serious circumstances. I plan to spend the next several weeks in the house to avoid catching/spreading the virus.

9 am: I'm going birding.

Don't get me wrong. I've spent the last week and a half working late hours as part of a small group of analytics personnel supporting business-critical operations at BASF even though the company has ordered all non-essential personnel to work from home. Anxiety has been weighing on me as reports come in of the spreading infection rate, and for the most part we employees have been avoiding contact. But not everyone, and that has added to the anxiety. If we are not 100% compliant in practicing social distancing, then we are 0% compliant in avoiding the spread of the virus. I've been able to catch up enough to hopefully be able to stay away from the populace for the next several weeks.

That said, the Sun was shining this morning, and it was 66F outside at 9am. Winds were blowing, and forecasts called for a cold-front to move in this afternoon that would drop temps to the 30's overbite, and it would be cloudy and cold the rest of the weekend. I needed a bird fix, so I decided to take a drive to Pt. Mouillee HQ to look for ducks from the safety of the car. I never got farther than the Bridgewater exit.

In the pond next to Arsenal Rd., just under the Bridgewater sign, was a gorgeous drake Ring-necked Duck (Aythea collaris). I pulled over and carefully got out of the car so as not to spook it. I took some long-distance photos from behind the car as a family strolled by the walkway between me and the duck. Since it didn't mind, I was able to move closer on the grass and photograph / digiscope it from 40-70' away.

The male Ring-neck is a stunner and one of my most favorite ducks. Its species description (collaris, or ring-neck) has long been criticized since the rufous-ring collar is barely visible in even the best lighting. The bill is so striking that everyone believes it should be called Ring-billed Duck. I agree.

The Great Lake Regions gets small numbers of these ducks in the winter. Mostly seen on the Detroit River during winter months we tend to see dozens down at Pt. Mouillee as ice-out occurs and they move into the inland ponds of the State Game Area. Otherwise, they are seen only during migration. And, they tend to be very spooky and difficult to photograph. So I was thrilled that this individual was being particularly cooperative.

I took over 1000 photos trying to capture that rufous-ringed neck, but also because the winds were creating some lovely reflections off the water. Every few minutes the colors would change as waves and reflections bounced off the multi-colored bricks of the Bridgewater walls.

Taking so many photos also allows me to burn some of those identification features to my memory. The black breast, gray sides with white shoulder patches that match the bold white borders at the base of the bill and between the black bill and gray nose plate. Of course the glossy purple head appears black in almost all light except those extreme cases when sunlight hits it at just the right angle. And, we can't forget the golden-orange eyeball that forces the photographer to get focus just perfectly or the eye-color will bleed onto the head in photographs.

I would return a few hours later and find the duck gone. It may have moved to Lake Madison, but I could not confirm. Still, I was thrilled to have seen it. Too bad this Canada Goose missed the whole show.

Sunday, February 9, 2020

Monday, January 20, 2020

Snow Day Feeder Birds - 18-19 Jan 2020

A big storm hit the Midwest on Saturday and dumped anywhere from 4-9" snow, sleet and/or rain. Here at Brownton Abbey we saw 4-5" snow, just enough to send the community into a tizzy over the shoveling they didn't have to do...

The snow also brought in the birds to the feeders. Dozens of Dark-eyed Juncos, American Goldfinches, House Finches, and even flocks of American Robins and Red-winged Blackbirds! I spent a little time digiscoping some of the birds from inside the house and through the back window.

Brownton Abbey, 26340 Higgins Way
Jan 19, 2020
11:00 AM
220 Minutes
All birds reported? Yes
Comments: Feeder count during snow day.
Submitted from eBird for iOS, version 1.9.6 Build 18

4 Mourning Dove
2 Ring-billed Gull
1 Cooper's Hawk
1 Red-bellied Woodpecker
1 Downy Woodpecker
8 Blue Jay
2 Black-capped Chickadee
1 White-breasted Nuthatch
12 American Robin -- Flock in birch tree at edge of property
9 House Sparrow
36 House Finch -- Most at one counting
30 American Goldfinch -- On both feeders
36 Dark-eyed Junco -- Most at one counting
6 Red-winged Blackbird -- Suet feeder and sunflower
10 Northern Cardinal

Number of Taxa: 15