Reality check on aperture, DOF, and Telephoto lenses

Djarum

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So, over on the other forum there is complaint that the new 40-150 should be faster, say starting at f2.8 or something like that. Looking at the specs, the lens seems really small for what it is. At any rate, the complaint was associated with DOF and the slow aperture. For a telephoto lens, I would agree that we could all use more light, but shallower DOF?

Some numbers with subject 10 feet away:

150mm @ f5.6 gives me .22 feet of acceptable focus on :43:
25mm at @ f2.0 gives me 2.9 feet on :43:

150mm @ f2.8 gives me 1.32 inches on :43:.

APSC
200mm at f5.6 is .15 feet
FF at
300mm at f5.6 is less than an inch.

At less than an inch with a subject, like a bird, 10ft away, would be difficult to shoot, IMHO. Do we really need shallower DOF when using a telephoto lens?
 

photoSmart42

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At less than an inch with a subject, like a bird, 10ft away, would be difficult to shoot, IMHO. Do we really need shallower DOF when using a telephoto lens?
Who's going to shoot a bird at 10 ft away with a long tele anyway? The larger apertures are very useful when shooting objects far away which is what most tele lenses are used for anyway, in which case your DOF is pretty much irrelevant because it's very deep. So a larger aperture in that situation helps with low-light/fast action situations where you want a higher shutter speed without having to crank up the ISO too much into the noise.

Having faster tele lenses is a valid point.
 

Djarum

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Who's going to shoot a bird at 10 ft away with a long tele anyway? The larger apertures are very useful when shooting objects far away which is what most tele lenses are used for anyway, in which case your DOF is pretty much irrelevant because it's very deep. So a larger aperture in that situation helps with low-light/fast action situations where you want a higher shutter speed without having to crank up the ISO too much into the noise.

Having faster tele lenses is a valid point.
Not saying it isn't, but I wouldn't consider the DOF decrease in the case of m4/3 an issue.

And I shoot birds at 10 - 15 ft away all the time with my 40-150. Someone in the apartment complex put up bird feeders last year.
 

JoepLX3

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Someone in the apartment complex put up bird feeders last year.
With a new mouse every hour?

My application of fast tele lenses would still be people, but a little further away than in case of a 20 mm F1.7...
 
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