VX2100 > F2.4 +3db > how is this possible? at DVinfo.net

Go Back   DV Info Net > Sony XAVC / XDCAM / NXCAM / AVCHD / HDV / DV Camera Systems > Sony HDV and DV Camera Systems > Sony VX2100 / PD170 / PDX10 Companion

Sony VX2100 / PD170 / PDX10 Companion
Topics also include Sony's TRV950, VX2000, PD150 & DSR250 family.


Reply
 
Thread Tools Search this Thread
Old January 9th, 2005, 11:53 AM   #1
Major Player
 
Join Date: Sep 2002
Location: US & THEM
Posts: 827
VX2100 > F2.4 +3db > how is this possible?

Filming with the VX2100 last night, and to my surprise the display read F2.4 +3db when I turned it on.

thumbing the wheel for smaller iris kept the +3db however when I opened up the iris to 'open' it reset to 0db and then everything was as usual.


question is how did that happen? I would like to know because that could be useful, perhaps there is some button sequence that does it which I stumbled across?
__________________
John Jay

Beware ***PLUGGER-BYTES***
John Jay is offline   Reply With Quote
Old January 10th, 2005, 01:00 PM   #2
Major Player
 
Join Date: Mar 2003
Location: Somerville, MA
Posts: 360
If the vx 2100 is like the PD 170, I'm thinking that you had gain and speed in auto. When you opened the iris, the camera compensated with less gain.
Bob Harotunian is offline   Reply With Quote
Old January 10th, 2005, 03:21 PM   #3
Major Player
 
Join Date: Sep 2002
Location: US & THEM
Posts: 827
yes

the 170 has independent gain control, but the VX does not and the only way to see a gain increase in the LCD with the VX is after passing through 'open'

AEA exposure mode does not show the gain/speed being applied for a fixed iris setting


Its almost like theres a PD170 under the hood of my VX which is bursting to get out !!

Maybe it will evolve into a PD170 through natural selection

Perhaps I should kept it in a dark cupboard when I am not using it and who knows :)
__________________
John Jay

Beware ***PLUGGER-BYTES***
John Jay is offline   Reply With Quote
Old January 10th, 2005, 07:09 PM   #4
Wrangler
 
Join Date: Dec 2002
Location: Mays Landing, NJ
Posts: 11,543
John: I hate to burst your bubble, but your VX-2100 has not morphed into a PD-170 ;-) I just tried on my VX-2000 and it can also do this (or add any other amount of gain desired at f2.4).

How? Simple: the maximum f stop varies from f1.6 to f2.4 as you zoom from wide to telephoto. That's why the finder simply displays "OPEN" when you reach the max. Zoom your camera all the way to telephoto then turn the exposure wheel. As you open the iris it will eventually get to f2.8, then to OPEN. At full telephoto OPEN = F2.4 (look at the specs in the back of your manual). Therefore as you turn the exposure wheel you will start adding gain.

Now here's where it gets interesting. Zoom out slowly - as you get about halfway out the display changes from OPEN 3dB to F2.4 3dB. Now zoom all the way wide and turn the exposure wheel - it changes to F2.4 0dB, turn it again and you get F2.0 0dB, etc.

For another experiment, zoom in and turn the gain way up, something like OPEN 12dB for example. Zoom full wide and you get F2.4 12dB. Turn the wheel one click and it changes to OPEN 9dB. This is interesting... it jumps to OPEN 9dB, which is the equivalent of F1.6 9dB!
Boyd Ostroff is offline   Reply With Quote
Old January 11th, 2005, 10:41 AM   #5
Major Player
 
Join Date: Sep 2002
Location: US & THEM
Posts: 827
Hey Boyd,

Thats it! Excellent detective work!!

Turning on the cam I remember it was part zoomed so your explanation is right on target, it just threw me to see the cam display that after power up
__________________
John Jay

Beware ***PLUGGER-BYTES***
John Jay is offline   Reply With Quote
Old January 12th, 2005, 03:24 AM   #6
Inner Circle
 
Join Date: Mar 2003
Location: Billericay, England UK
Posts: 4,711
Yes, that's just the way my 2000 works as well. It's not been talked out here though, as most people seem happily unaware that the lens loses a stop as you zoom from one end to the other.
Tom Hardwick is offline   Reply With Quote
Old January 29th, 2005, 01:55 AM   #7
Trustee
 
Join Date: Aug 2003
Posts: 1,483
So in low light, if you use a tele lens, you
can avoid having the cam go to smaller f-stops,
because you're not zooming as much?
Dave Largent is offline   Reply With Quote
Old January 29th, 2005, 07:00 AM   #8
Regular Crew
 
Join Date: Jul 2004
Location: Baxley, Georgia
Posts: 103
Just Math

It's simple math. The f-stop is simply a measure of the focal length divided by the lens opening.

F-stop = focal length / lens opening

So when you zoom in your f-stop will increase and when you zoom out it will decrease. The diameter of the aperture is remaining constant.

If you are familliar with the inverse square law you will understand how this can happen. Light intensity diminishes as the square of the distance from the source. I don't know if this law applies exactly to the focused light from the lens but it helps to understand what is going on. When you zoom in on a subject with a constant aperture setting the amount of light hitting a given surface area (ccd) at a given distance from the lens is reduced. Your lens is allowing a given amount of light "i" through at all focal lengths based on a given aperture setting. Lets say at full wide all of this light, the entire image from the lens, is focused on the ccd's. However, when you zoom in the image that is cast at the ccd gets larger but the ccd is still the same size and can only see the middle portion of that image. The same amount of light "i" is getting through the lens to make up the entire image but because the entire image is much larger than the ccd you are only getting a fraction of that light "i" that is hitting the ccd. What the ccd sees is a smaller portion of the same image seen at wide. This is what makes the objects in the image look bigger and darker for a given aperture. This is my analysis of what is happening anyway.

Edit:
I did a Google search and found a much more thorough explanation for anyone who may be interested.
http://www.faqs.org/faqs/rec-photo/lenses/tutorial/


__________________
Lamar
Lamar Lamb is offline   Reply With Quote
Old January 29th, 2005, 07:23 AM   #9
Inner Circle
 
Join Date: Mar 2003
Location: Billericay, England UK
Posts: 4,711
Look at it this way Dave. If you're filming in a dimly lit room using maximum wide-angle and maximum aperture (f 1.6) then as soon as you start to zoom the camera will start to apply gain-up. By half way (36 mm focal length) the gain-up will be +3 dB and by maximum telephoto (72 mm) the camera will be at +6 dB.

If you wanted to film at zero gain up, you'd have to double the amount of light in the room to film at full telephoto.

Why? because the Sony lens designers wanted to keep the size, weight and cost of the zoom down, and they do this by making the maximum aperture at full tele one whole stop smaller than at wide-angle. It doesn't have to be so, but this is what the Sony design team settled on. Some cameras (the Canon MVX3i for instance) lose less than half a stop, whereas others lose nearly two stops.

tom.
Tom Hardwick is offline   Reply With Quote
Old January 29th, 2005, 07:34 AM   #10
Regular Crew
 
Join Date: Jul 2004
Location: Baxley, Georgia
Posts: 103
Sorry Tom. I didn't mean to throw that edit above in on top of you you.
__________________
Lamar
Lamar Lamb is offline   Reply
Reply

DV Info Net refers all where-to-buy and where-to-rent questions exclusively to these trusted full line dealers and rental houses...

Professional Video
(800) 833-4801
Portland, OR

B&H Photo Video
(866) 521-7381
New York, NY

Z.G.C.
(973) 335-4460
Mountain Lakes, NJ

Abel Cine Tech
(888) 700-4416
N.Y. NY & L.A. CA

Precision Camera
(800) 677-1023
Austin, TX

DV Info Net also encourages you to support local businesses and buy from an authorized dealer in your neighborhood.
  You are here: DV Info Net > Sony XAVC / XDCAM / NXCAM / AVCHD / HDV / DV Camera Systems > Sony HDV and DV Camera Systems > Sony VX2100 / PD170 / PDX10 Companion

Thread Tools Search this Thread
Search this Thread:

Advanced Search

 



Google
 

All times are GMT -6. The time now is 01:13 AM.


DV Info Net -- Real Names, Real People, Real Info!
1998-2017 The Digital Video Information Network