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p.1 #15 · p.1 #15 · No significant advantage to use 1.6x vs 1.3x crop DSLR with super-tele lens | |
Gonemad wrote:
So, in preparation for my birding in the next month or so, I've been doing some math to figure out if there's any significant advantage to pair a 1.6x crop or 1.3x crop DSLR with the 400mm. As it turns out, it is quite significant when the focal length is between 100mm to 200mm, but not significant enough beyond that. The calculation basically converts focal length in mm to the equivalent power in binocular.
mm 1.3x crop 1.6x crop delta
100 38.5 yds 31.3 yds 7.25 yds
200 19.1 yds 15.6 yds 3.5 yds
400 9.6 yds 7.8 yds 1.8 yds
600 6.4 yds 5.2 yds 1.2 yds
800 4.8 yds 3.9 yds 0.9 yds
How to read the results. Using a 100mm lens on a 1.3x DSLR, an object at 100 yds would appear to be 38.5 yds away. Likewise, the same 100mm lens on a 1.6x DSLR would make the object appear at 31.3 yds, which is a significant gain of 7.25 yds difference. But, using a 400mm lens, the difference is only 1.8 yds. That's quite astonishing! Does this even sound reasonable or is my math way off?
EDIT: I removed references to 7D and 1D4, because the specific sensor type was derailing my point which is limited to only the magnification power. Each sensor type will further affect the quality of the image, but that's an exercise and discussion for another time....Show more →
two problems:
1. when you are distance limited the only thing that actually matters (for the most part, actually if you had the same pixel pitch a wider FOV would be nicer since you could get the same reach but have an easier time spotting and tracking; OTOH a smaller FOV would mean less wasted storage space) is pixel density, for the final result it really doesn't matter whether you crop off a little bit of edges or a ton of edges
2. even if you wanted to just go by what you are doing it doesn't make sense to compare the way you are comparing, you need to compare the delta's percentage of the cropped appearance distance difference and you'll notice that the 7.25/31.3 = 1.8/7.8
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