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02-06-2014, 02:34 AM - 1 Like   #16
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QuoteOriginally posted by mikemike Quote
I have often read that extra mm are more important on the wide end or are more substantial than on telephoto but I don't really see why.

Attachment 205396
Simple maths. 5mm is 25% of 20mm. The same 5mm is only 5% of 100mm. Proportionately, a 5mm change of focal length will obviously have greater impact on a shorter focal length than a larger. No need to get super-scientfic about it.

02-06-2014, 05:13 AM   #17
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Actually in revisiting this the presentation would have been more interesing to show the vertical and horizontal FOV for all lenses at a fixed shooting distance, say 3 meters.

That would show the importance of each mm at the short end more,
02-06-2014, 06:20 AM   #18
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QuoteOriginally posted by Lowell Goudge Quote
Actually in revisiting this the presentation would have been more interesing to show the vertical and horizontal FOV for all lenses at a fixed shooting distance, say 3 meters.

That would show the importance of each mm at the short end more,
Especially if you show area too.
02-07-2014, 04:07 PM   #19
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I do a lot of car shows in the warm season and the difference between 15mm and 18mm is huge when cars are parked close together and there are people all around. I bought the DA 15 specificly for that purpose as 18mm wasn't enough and there wasn't room to back up. I already owned the DA 10-17 and was getting the cars well into the frame at 15 and 16 mm with the fisheye but the distortion was always present.

02-07-2014, 04:24 PM   #20
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Here you go:

https://tamron-usa.com/lenses/learning_center/tools/focal-length-comparison.php
02-07-2014, 05:07 PM   #21
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Linear relationship does not equal constant distance difference

You mentioned the relationship between focal length and the distance from subject to get 2m FOV is linear. Please see graph below, I plotted the distance from subject against focal length (in 2X steps for clarity).

Yes, it is linear, but as you double the focal length, you also double the additional distance you need to step back. So decreasing focal length doesn't really help in closing the distance from subject, but increasing focal length forces you to back away a lot more. If you have a 18 instead of a 16mm, then you will have to back away a lot more.
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02-08-2014, 06:53 AM   #22
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Well, just to stir the pot..... Math and an opinion

This discussion is extremely valuable.... Here's why...

Wide angle/ real estate, architecture aside, for birders, wildlifers, portraits and most sports, would you rather have a 24mp APSc or a 34mp FF?

On image replication, IQ, and optical engineering POVs, the ultimate solution is a very HQ FF lens on an APSc sensor. Corners cropped and 24mp in the "golden zone-APSc" is better mathematically than near a 40mp FF...

It underscores the amount of marketing hype. One must admit there is a wavelength concern on spectral compression, but it is nowhere as visibly perceivable or mathematically important due to human limitations.

Hence, a K3 with HQ glass ( F*, FA*, DA*, 50mm F1.4, etal) will be the "deadliest" (visual impact for the "target shooters) as opposed to FF where you loose on the pixel density/area, cost & speed of in-camera onboard processing, as opposed to a FF Canon, Nikon (or even K?FF when it comes out).

I have been squirreling FA*s and F*s for years waiting for FF DSLR, but my gut tells me that after owning a K?x? DSLR when it comes out and using it 6 mos in the field, I'll buy another K3x(whatever APSC) and smile all the same. I'll dump half of the FA*s, keep the important ones.. Hint... (DON'T underestimate the walk-arounds of the old 18-250DA, the 18-135WR, or the 55-300WR. and the 135-380 (or whatever) if executed well and WR, will be a game changer)...

And THE NISI LR, Bresson, Kaeseman and HD filters (eh to HD2 warranty) also help one to exploit the technologies.

Last edited by GlassJunkie; 02-08-2014 at 06:58 AM.
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