Back in February, I was preparing a talk on digiscoping for a local camera club and decided to tackle the same question a different way. I went to the Rothschild's Mere hide at Woodwalton Fen and spent a couple of hours taking pictures of the same subjects with various digiscoping setups and also with my Canon 300mm F4 prime lens which I could then use as a standard for comparison.
Here are some Cormorants sat on the tern raft in front of the hide taken using the Canon 60D with the 300mm F4 lens.
|Scaled down image from full frame: 300mm, F8, 1/1000s, 400 ISO|
|100% crop showing the measurement I made from the beak tip to the back of the head on a line projected through the point of the yellow triangle on the face|
Whilst viewing the image at 100%, I measured the width of the head of the adult Cormorant on the right, from the tip of the bill to the back of its head along a line projected through the point of the yellow triangle below its eye. This line was 263 pixels long in this case.
To check that this worked reasonably well, I put my 1.4x converter on the lens and took, as near as possible the same shot (bearing in mind that this all takes time and birds move!).
|Scaled down image from full frame: 300mm with 1.4x converter, F8, 1/1000s, 800 ISO|
|100% crop. Same measurement - 374 pixels|
Here is a digiscoped picture of the same bird with my telescope's eyepiece on its minimum magnification of 20x.
|Scaled down image from full frame: Digiscoped image, Kowa 823 with 20-60x eyepiece on minimum, Canon 60D with an Olympus 50mm F1.4 lens wide open at 1/320s, 800 ISO mounted on the eyepiece.|
|100% crop, Same measurement: 925 pixels|
With the telescope's eyepiece bumped up to its maximum magnification of 60x here is what I got.
|Scaled down image from full frame: Digiscope at 60x, 1/60s, 800 ISO|
|100% crop, same measurement 3052 pixels|