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12/13/2006 12:11:14 PM · #1 |
Pentax Telephoto SMCP-FA* 85mm f/1.4 IF Autofocus Lens
A couple questions,
1. I see it's 67mm on the front of the lens, is there any advantage to it being so large?
2. What is it called a Telephoto?
I was thinking zoom lens were telephoto lens..
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12/13/2006 12:34:33 PM · #2 |
It's probably so large because of the f/1.4
Most lenses with a low f-stop have a big thread on the front.
Telephoto because it's more than 35mm? I wouldn't even ponder the question :p
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12/13/2006 12:41:54 PM · #3 |
Just like k4rp said:
1.) It's because of the f1.4 aperature. The longer the lens, the bigger the physical aperature needed to maintain that f-stop and 1.4 is pretty big. So bigger aperature = bigger lens elements = bigger front element
2.) It's called telephoto because of the 85mm length. The zoom has nothing to do with being a telephoto or not. Is a 10-22mm lens a telephoto? No, but a 400mm prime sure is.
Hope this helps.
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12/13/2006 12:50:36 PM · #4 |
| Since a 50mm lens is considered normal, so anything longer is considered a telephoto. |
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12/13/2006 01:26:38 PM · #5 |
Ok, now I understand, thanks!
Really sounds like a dumb question now. :)
So when you see the guy's on the side lines at sporting games with these long lens that are really large at the end you know they are shooting with really fast lens, correct?
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12/13/2006 02:01:33 PM · #6 |
Originally posted by lakota:
Ok, now I understand, thanks!
Really sounds like a dumb question now. :)
So when you see the guy's on the side lines at sporting games with these long lens that are really large at the end you know they are shooting with really fast lens, correct? |
Yes, fast for the focal length. What you're usually seeing are 300/2.8, 400/2.8, or in some cases 600/4 lenses. While f/4 is not that fast, it is *very* fast for a 600mm lens.
As a side note, for telephoto lenses, the diameter of the front element needs to be slightly larger than the focal length divided by the f number. So a 600 f/4 lens needs a 150mm (6 inch) front element. |
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12/13/2006 07:39:00 PM · #7 |
Originally posted by kirbic:
Originally posted by lakota:
Ok, now I understand, thanks!
Really sounds like a dumb question now. :)
So when you see the guy's on the side lines at sporting games with these long lens that are really large at the end you know they are shooting with really fast lens, correct? |
Yes, fast for the focal length. What you're usually seeing are 300/2.8, 400/2.8, or in some cases 600/4 lenses. While f/4 is not that fast, it is *very* fast for a 600mm lens.
As a side note, for telephoto lenses, the diameter of the front element needs to be slightly larger than the focal length divided by the f number. So a 600 f/4 lens needs a 150mm (6 inch) front element. |
300/2.8 would be awesome, but just so much out of my price range. :)
What if I were to take this lens and put a 2x tele converter on it.
Would that make it equal to a 170mm f/2.8?
From the little bit I have used my 50mm f/1.8 at the basketball games I would think this 85mm f/1.4 would be awesome.
I would almost think 400mm and 600mm for sure would be over kill, but then again I don't have one to use. :) |
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12/13/2006 07:49:24 PM · #8 |
Originally posted by lakota:
300/2.8 would be awesome, but just so much out of my price range. :)
What if I were to take this lens and put a 2x tele converter on it.
Would that make it equal to a 170mm f/2.8?
From the little bit I have used my 50mm f/1.8 at the basketball games I would think this 85mm f/1.4 would be awesome. |
You lose 2 stops of light for adding a 2x teleconverter and 1 stop for adding a 1.4x teleconverter. So yes, it would become a 170mm f/2.8 lens but that depends on if the lens is compatible with teleconverters to begin with. Which I'm not sure if it is or not.
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12/13/2006 09:17:07 PM · #9 |
Originally posted by lakota:
300/2.8 would be awesome, but just so much out of my price range. :)
What if I were to take this lens and put a 2x tele converter on it.
Would that make it equal to a 170mm f/2.8?
From the little bit I have used my 50mm f/1.8 at the basketball games I would think this 85mm f/1.4 would be awesome.
I would almost think 400mm and 600mm for sure would be over kill, but then again I don't have one to use. :) |
Ummmm
That Pentax lens is more of a specialist portrait lens. A better choice for a mid tele for indoor basketball is the Pentax-FA 77mm f1.8 Limited. Its also a little cheaper and easier to find in stock.
bazz. |
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