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Telephoto Lenses with focal lengths longer than 60mm.

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Old 17th September 2011
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Just about the maximum

Alerted to a Sabine's Gull yesterday, a rare pelagic vagrant (even rarer inland) from Greenland, I hot-footed it to my local tip to get a glimpse. Spotted it OK but it was around 150 metres away and I had to take the shot through a wire-mesh fence. Used the 300mm f2.8 + EC14 but the results using a monopod were poor. I tried IS on and off but the results were the same. Today I went back with a heavy duty tripod and switched the IS off and managed to get a few record shots that I was happy with, but realised that for this combo this was about the maximum usable distance. Now I know!

Sabine's Gull, juvenile:



E5, ISO 100 to get the best out of it.

David
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Old 18th September 2011
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Re: Just about the maximum

Yes,

300mm times 1.4 will render an angle of view of approximately 3 degrees and, at 150 meter distance, that transforms into full frame capture of an object about 2.8 meters large.

Considering the bird is 30 cm meaning you are utilizing perhaps 1/10 of the sensor width (1/100 of the pixels) to render the subject, I believe the result is very good for being a "record shot", its is definitely sharp. Given the light conditions you should be happy.

If you are intested I could share some pictures showing what a 1200 mm digiscoping setup is capable of at long distance (100 m or more).

/Tord
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Old 18th September 2011
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Re: Just about the maximum

Looking back at my original image and taking into account your calculations it would appear that I substantially underestimated the distance to the bird. This is the whole image, converted to jpeg and it would appear to me that the actual field of view is more like 4 metres, strangely the Exif shows a focus distance of 29m!



So what distance would this equate to?

Yes thanks, I would like to see some digiscoped birds to compare. One of the guys who was observing the bird next to me digiscoped it with a Kowa 883 and Lumix LX5 and got superior results on the first day, although some others (using Swarovski scopes) had much inferior images. On the second day which had high winds (30km/hr) no-one digiscoping had usable results as far as I am aware.

Thank you for your interest and information.

David
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Old 18th September 2011
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Re: Just about the maximum

Hi David,

According to Olympus specifications the angle of view is 4.2 degrees.

Add the EC14 and you will get 3 degrees approximately (for long focal lengths you can approximate angle of view proportional to the inverse of the focal length, this its not true for wide angles).

Looking at the whole picture: The bird occupies 42 pixels in X-axis, and seems to be angled about 30 degrees, so the corrected length should be 49 pixels. 49 out of 800 pixels is 1/16,5.

A Sabine's gull is 27-33 cm long, say 30 cm. The width of the picture is 16,5 times that, about 5 m

1/tangent (3 degrees) is about 19

5 times 19 is 95 meters - that is the distance to subject I would estimate, given the data about the lens and bid size.

+/- 10% depending if the bird is a large or small specimen.
+/- few% depending on the correct estimation of the bird's angle

I'd say the distance is between 83-106 meters.

My experience is that you often overestimate distances. (I did above calculations on some of my pictures, comparing assessed distance and calculated).

Let me know if failed in explaining the reasoning.


Below are some long digiscoping shots for reference (using a Nikon ED82A scope, most with the Canon S95 camera). For some of the shots I did push the camera zoom beyond the sweet spot (usually 1.5-2X), which explains the softness. It's a total different game, though...


/Tord


#1: Fox, 300+ meters

#2: Fallow Deer, 200 meters

#3: Common Shellduck, 75 meters

#4: Common teal et el, 100 meters

#5: Common Kestrel, 75 meters

#6: Common Kestrel, hovering, 150 meters

#7: Common Buzzard, 150 meters

#8: Garganey, 60 meters
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Old 18th September 2011
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Re: Just about the maximum

In a situation like that I'd have stacked a 2x behind the 1.4 rather than crop.

In my film shooting days I sometimes stacked 2 OM 2x-A TC's behind my 350mm to give me a 1,400mm f11.
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Old 18th September 2011
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Re: Just about the maximum

Thank you Tord for all your calculations, my head is still spinning but it shows what I thought - that I always tend to overestimate distances.

--------------------------------------------------------------------------------
Quote:
In a situation like that I'd have stacked a 2x behind the 1.4 rather than crop.

In my film shooting days I sometimes stacked 2 OM 2x-A TC's behind my 350mm to give me a 1,400mm f11.
I was never happy with the 300 plus EC20 so I am not sure how it would work with a EC14 as well, does anyone else have experience of this combo?

David
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