hey Ash, Chris, anyone? ND markings on 20X lens equal...? at DVinfo.net

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Old August 10th, 2006, 03:49 AM   #1
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hey Ash, Chris, anyone? ND markings on 20X lens equal...?

when you purchase ND filters (4x4, or threaded) they usually have an f-stop equivalent... example:

ND Filter ---- f-stop reduction
.1 ------ 1/3
.2 ------ 2/3
.3 ------ 1
.5 ------ 1 2/3
.6 ------ 2
.9 ------ 3

but our 20X lens marks the barrel with ND markings: 1/6 & 1/32... anybody know what these are equivalent to or ever measure how much it's stopping down... i'd like to purchase a complimentary set of additional ND's and don't want to get duplicates... (and they're not the obvious fractions, cause 1/32 is less than 1/6, however 1/32 stops it down more (less light))... are they the log equivalent...
somebody has to know...

(and yes i reposted while rephrasing - there were 30 views and no posts on my last thread - so i figured it wasn't you usual helpfuls not being helpful but instead, me not articulating too clearly)

thanks,
Lonnie
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Old August 10th, 2006, 08:56 AM   #2
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I believe the 1/6 is equivalent to a 0.8 and the 1/32 is equivalent to a 1.5. I am going off memory so that could be off...




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Old August 10th, 2006, 01:39 PM   #3
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I remember the reading that regarding the 16x manual lens (I know you're talking about the 20x, but I'm assuming the methodology is the same), those fractions represent how much of the light you're left with after applying the filter. So 1/8 (on the 16x manual) means it cuts out 7/8 of your light, and 1/32 means it cuts out 31/32 of your light.

1/8 cuts out 3 stops, then, and 1/32 should be 5 stops. I THINK. Could be talking out of my ###. Maybe someone can back me up. Or not.
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Old August 10th, 2006, 02:14 PM   #4
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thanks ash,

and as for josh,
with all due respect - cutting out 31/32 of light - that's not an ND filter, that's called a lens cap...
thanks for responding though,
Lonnie
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Old August 10th, 2006, 03:21 PM   #5
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Well then what do the fractions mean? Let me rephrase, then. . .you're left with 1/8 and 1/32, respectively, of the light coming in before applying the filter.

The stronger filter cuts out an awful lot of light. . .

5 stops =

original light level/2 =
1/2 (/2)=
1/4 (/2) =
1/8 (/2) =
1/16 (/2) =
1/32
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Old August 10th, 2006, 03:41 PM   #6
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I'm also a little unwilling to believe that the 1/32 setting leaves you with only 1/32 of the light coming through the lens. An ND filter that opaque would only be useful on the surface of the sun. :)

That said, I admit that I have no idea what the fractions mean either--I just don't think that's it.
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Old August 10th, 2006, 03:47 PM   #7
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I dunno guys, check it out.


You're outside on a blinding sunny day.

Your lens is open all the way. This should be 1.6.

Cutting out 5 stops is the equivalent of stopping down to f8, not at all unreasonable for a sunny day.


1.6 (open)
2 (approximately half the light)
2.8 (1/4)
4. (1/8)
5.6 (1/16)
8 (1/32)
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Old August 10th, 2006, 04:14 PM   #8
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Actually Josh is quite right.

This is Basic Photography 101.

Each full f/stop lets in one-half the amount of light of the previous f/stop.

If you shoot at f/4, that is 25% of the light you're letting in at f/2. And so on.

You can do the math from there. And yes 1/32 means you're blocking 31/32 of the total light coming in.

If you could stop down to f/22 (like some still cameras lenses), that's about 1/2000th of the light at f/1.4.
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Old August 10th, 2006, 04:31 PM   #9
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Old August 11th, 2006, 09:57 AM   #10
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Quite right. Remember your shutter speed is 1/48, or 1/60 and the camera has an effective ISO, of about 400-640. On a bright sunny day, you need a LOT of ND.
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Old August 12th, 2006, 03:12 PM   #11
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Mark, forgive me if I misunderstand your intention, but shutter speed has nothing to do with f/stops. A fraction of time is very different from a fraction of light.

I concede "defeat" in that I saw on Canon's XL-H1 page that using its 1/32 ND filter is the functional equivalent of stopping down 5 stops, which would indeed mean that 1/32 of the light is getting through the lens. It just doesn't look like 5 stops to me. Guess my eye is a little off.

Anyway, it's good to know what the fractions on the lens mean. It seems like fractions of transparency is an odd way of marking the filters though. Stops would be a more useful measurement. I know that "f/stop" technically only truly refers to aperture opening, but plain old "stops" would just make more sense. At the very least, it seems like the decimal measurements used on all other ND filters would be less confusing to work with.
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Old August 12th, 2006, 06:36 PM   #12
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Quote:
Originally Posted by Jarrod Whaley
Mark, forgive me if I misunderstand your intention, but shutter speed has nothing to do with f/stops. A fraction of time is very different from a fraction of light.
His intention as I read it was to give a scenario using standard shutter speeds. And with an ISO rating that high, you are going to have to kill a lot of light coming through the lens on a sunny day to hold your exposure which serves to illustrate just how strong a 1/32 ND is.

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Old August 12th, 2006, 07:15 PM   #13
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Old August 12th, 2006, 08:29 PM   #14
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Thanks, Greg. That's exactly my point.

Jarrod, shutter speed has everything to do with f stops. Changing one affects the other. Remember your Photo 101. Closing the aperture down one stop, halves the amount of light reaching the CCD chip. Conversely, opening the aperture one stop, doubles the amount of light reaching the CCD. If the light is constant, then changing one requires changing the other.

If you are shooting 24P video, or film, then your shutter speed will be 1/48th of a second. If you are shooting 60i-regular video, then your shutter speed is 1/60th of a second. With film and video, your shutter speed is pretty much fixed to these times. Therefore, you can only change the amount of light reaching the chip by closing, or opening the aperture. Imagine shooting a 400 speed film on a bright sunny day. At 1/48th of a second, your aperture is going to be somewhere around f/16. So, you need a lot of ND, to bring down the exposure to f/4, or f/2.8 at 1/48th of a second.
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Old August 13th, 2006, 12:06 AM   #15
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Mark is absolutlely correct!! Shutter speed and aperature go hand in hand.

Most have a history with 35mm photography where if you were to be shooting a sunny day with 100 asa film a standard ballpark exposure would be 125 @ f16. In general if you upped your shutter two speeds you would have to open up your aperature two stops.
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