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Orb weaver: partial eclipse of a brick

 
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rjlittlefield
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Joined: 01 Aug 2006
Posts: 18239
Location: Richland, Washington State, USA

PostPosted: Wed Sep 06, 2017 10:39 pm    Post subject: Orb weaver: partial eclipse of a brick Reply with quote

Somehow the visual appearance of this image reminded me of the recent solar eclipse, hence the title.



The above is whole frame. Here is a closer crop:



The shooting situation was quite unusual for me -- a "long distance closeup". Normally my strategy is to get close to my small subjects, but in this case the subject was sitting in quite an inaccessible location -- behind a shrub, to which the web was attached. Any attempt to approach the subject resulted in wiggling the shrub, which caused huge movements of the web. So I ended up shooting from 5 feet away.



This required reaching into my quite limited supply of long lenses and sundry other parts, eventually assembling this combination:
  • An ancient manual focus Vivitar 200 mm f/3.5 lens, M42 Pentax screw mount. This is no doubt a bargain-basement telephoto, $26 from eBay a few years ago. I bought it for use at f/18-20 as a tube lens behind microscope objectives. But no matter, it works here too.
  • 14 mm M42 extension tube, to allow the 200 mm to focus down to about 4 feet.
  • An even more ancient Vivitar 1.4X teleconverter in M42 mount. This is left over from when I was in high school, late 1960's.
  • M42-to-Canon adapter.
  • Kenko Pro 300 1.4X DGX teleconverter in Canon mount.
  • Canon T1i camera (APS-C sensor).



Because the air was calm and the spider was not inclined to move, I could take my time with framing, focusing, and exposure. This was shot at ISO 400, 1/8 second with EFSC, nominal f/5.6 (effective f/11 including the teleconverters). Manfrotto 410 geared head on a substantial tripod made framing straightforward. Focus was troublesome, even with Live View, because touching anything moved the camera to make the zoomed-in Live View vibrate like an earthquake.

These optics are pretty soft and have substantial chromatic aberration, both radial and longitudinal, so I shot raw and converted carefully so as to cancel the CA and bring out detail without introducing excessive noise.

I'm pleased with how this came out. Hope you find it interesting!

--Rik
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tpe



Joined: 26 Aug 2007
Posts: 467
Location: Copenhagen Denmark

PostPosted: Thu Sep 07, 2017 4:24 am    Post subject: Reply with quote

The lack of noise is impressive as that you managed to take a close up at the distance you did. Must be a good camera Wink.

Tim
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rjlittlefield
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Joined: 01 Aug 2006
Posts: 18239
Location: Richland, Washington State, USA

PostPosted: Thu Sep 07, 2017 4:00 pm    Post subject: Reply with quote

tpe wrote:
The lack of noise is impressive as that you managed to take a close up at the distance you did. Must be a good camera Wink.

Not particularly, though obviously good enough to keep me from upgrading. The Canon T1i is an old model. I just now checked my records; it turns out that I bought this camera in September 2009, now eight years ago. It is APS-C format, 4,752 x 3,168 pixels, so about 4.7 microns pixel size. I normally shoot at ISO 100, the lowest setting. On this camera ISO 400 is as high as I like to go for normal photography. At ISO 400, pixel noise is becoming annoyingly obvious when viewed at actual pixels.

To make the images shown here, I used a process of progressively downsampling with averaging, to reduce both resolution and noise, followed by aggressively sharpening with a narrow USM filter, applied at the display resolution.

The higher magnification crop is taken from an image that is only 1/3 the width and height of the camera image, hence about 3X less noise, then sharpened by a whopping 200% at 0.7 pixels to make the version that is posted. In principle, essentially that same image could be constructed by applying the corresponding USM of 200% at 2.1 pixels directly to the camera resolution image, and then downsizing. But I don't like that route because Photoshop does not accurately preview what the image will look like after downsizing, so I find it very difficult to select appropriate settings for the USM.

Similarly the lower magnification whole frame is produced by starting with the 1/3-size image and downsampling by 2X to make an image that is 1/6 the original dimensions, followed by another USM 100% at 0.7 pixels.

I did not apply a conventional "noise reduction" filter at any stage.

--Rik
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