critical focus and the color evf and zebra bars at DVinfo.net

Josh Bass · May 20th, 2002, 02:32 AM

I remember reading that although achieving and accurate critical focus was difficult using the XL1s's color EVF, it could be done by using the zebra bars, as they "snap into focus", I believe it was. Can someone clarify? I tried it out, and all I noticed was that the area around the zebra bars (I think it was purple, and no, I'm not smoking anything) got smaller as the focus got more . . .um. . .focused.

Bill Ravens · May 20th, 2002, 07:11 AM

zebra is electronically superimposed on the image.....there is nothing to focus, so what you heard was urban legend

Mike Avery · May 20th, 2002, 07:43 AM

No, it's not an urban legend. However, the comment I made about "snapping into focus" was in reference to the 16x manual lens.

I find when using that lens the change in appearance of the zebras is a good way to know when you've hit focus.

I don't remember the change being so obvious with the auto lens, but it's been a long time since I've used one.

Mike Avery

Josh Bass · May 20th, 2002, 01:05 PM

Ah. Okay. Well, I'm planning on getting that manual lens. . .so I guess it'll make sense then. Thanks.

Bill Ravens · May 20th, 2002, 01:16 PM

The zebra is not designed to facilitate focusing and won't work for this purpose.

Chris Hurd · May 20th, 2002, 01:41 PM

Bill, here's the deal with that... we all know that zebra bars are used for exposure control, and we know that the zebra bars not designed to facilitate focusing. As you state, they most definitely are not intended for that purpose. *However* the tip is that the zebra bars themselves change in appearance slightly when an image snaps into focus. It's unintentional and not by design, and if Mike Avery sees it using the 16x manual lens then I'm inclined to believe him.

As for myself, this is how I know my viewfinder diopter is in perfect focus. Sometimes it's hard to tell if the EVF has proper focus because of the low resolution of the LCD screen. So I'll purposefully overexpose the image to show the zebra pattern, and focus the viewfinder diopter using these bars. Hey that's not what they're for, but it works!

Josh Bass · May 20th, 2002, 01:43 PM

I feel I have started some sort of conflict. Now gentlemen, let's please not come to blows. I'll not have the two or three of you hitting each other with Canon XL1ses. . .they're just too expensive. Use an SVHS cam.

Bill Ravens · May 20th, 2002, 01:46 PM

Well, it seems I may owe everyone an apology. I've been reading "focus" as in lens focus....not, diopter focusing of the viewfinder. For this error on my part, you have my deepest apologies. Chris, thanx for clearing my clouded perception. Sorry for giving the impression that "we're coming to blows". It isn't that, at all.

In fact, I can see how using the zebra stripes for diopter focusing may work quite well.

Josh Bass · May 20th, 2002, 02:08 PM

Wait. Now I'm confused. We're talking about the "diopter" is it . . .the actual viewfinder glass? I thought we meant the lens of the camera. Nevermind then. Guess it's another 1500 for the b&w viewfinder for me! Boy Howdy!

Don Palomaki · May 20th, 2002, 03:34 PM

How is this for a rationalization.

Note that auto focus is judged by contrast. Contrast is highest at best focus. But contrast being higest means whites are whiter (like with good laundry detergent) and blacks are blacker.

Now whiter whites can mean pushing narrow white portions of the image into zebra, causing zebr to appear if the white level is at the threshold of zebra.

In summary, do not count on it work at all (or evenmost) times and places.

Mike Avery · May 20th, 2002, 05:39 PM

I am talking about focusing the lens by using zebras. Yes, I understand it might not make sense to an opto-mechanical engineer, but to my eye it works.

I can definately see a change in the zebra pattern when I hit focus, and at least one other conributor to this forum has noticed the same thing.

It's not the only tool I use to focus, but it helps.

Mike Avery

Josh Bass · May 20th, 2002, 07:19 PM

So you were talking about the lens focus earlier, then?

You said that was not your only method of focusing. What else do you use? Still talking about the color viewfinder, just for clarification.

Bill Ravens · May 20th, 2002, 08:16 PM

There is a great deal of mis-information floating around this internet. I would just like to make sure that an innocent newbie reading this thread sees the diffrerence between opinion and a phenomenon based on a known principle of optics.

Chris Hurd · May 20th, 2002, 08:35 PM

Thread closed.

Let's just say that the zebra bars are first and foremost a measure of exposure and leave it at that. Thanks,

May 20th, 2002, 02:32 AM	#1
Josh Bass Slash Rules! Join Date: Apr 2002 Location: Houston, Texas Posts: 5,472	critical focus and the color evf and zebra bars I remember reading that although achieving and accurate critical focus was difficult using the XL1s's color EVF, it could be done by using the zebra bars, as they "snap into focus", I believe it was. Can someone clarify? I tried it out, and all I noticed was that the area around the zebra bars (I think it was purple, and no, I'm not smoking anything) got smaller as the focus got more . . .um. . .focused. __________________ The Bass' camerawork The Bass on IMDB

May 20th, 2002, 01:05 PM	#4
Josh Bass Slash Rules! Join Date: Apr 2002 Location: Houston, Texas Posts: 5,472	Ah. Okay. Well, I'm planning on getting that manual lens. . .so I guess it'll make sense then. Thanks. __________________ The Bass' camerawork The Bass on IMDB

May 20th, 2002, 01:16 PM	#5
Bill Ravens Join Date: Nov 2001 Location: santa fe, nm Posts: 3,264 Images: 10	The zebra is not designed to facilitate focusing and won't work for this purpose. Last edited by Chris Hurd; May 20th, 2002 at 08:36 PM.

May 20th, 2002, 01:41 PM	#6
Chris Hurd Obstreperous Rex Join Date: Jan 2001 Location: San Marcos, TX Posts: 27,368 Images: 513	Bill, here's the deal with that... we all know that zebra bars are used for exposure control, and we know that the zebra bars not designed to facilitate focusing. As you state, they most definitely are not intended for that purpose. However the tip is that the zebra bars themselves change in appearance slightly when an image snaps into focus. It's unintentional and not by design, and if Mike Avery sees it using the 16x manual lens then I'm inclined to believe him. As for myself, this is how I know my viewfinder diopter is in perfect focus. Sometimes it's hard to tell if the EVF has proper focus because of the low resolution of the LCD screen. So I'll purposefully overexpose the image to show the zebra pattern, and focus the viewfinder diopter using these bars. Hey that's not what they're for, but it works! __________________ CH Search DV Info Net \| 20 years of DVi \| ...Tuesday is Soylent Green Day!

May 20th, 2002, 01:43 PM	#7
Josh Bass Slash Rules! Join Date: Apr 2002 Location: Houston, Texas Posts: 5,472	I feel I have started some sort of conflict. Now gentlemen, let's please not come to blows. I'll not have the two or three of you hitting each other with Canon XL1ses. . .they're just too expensive. Use an SVHS cam. __________________ The Bass' camerawork The Bass on IMDB

May 20th, 2002, 07:11 AM	#2
Bill Ravens Join Date: Nov 2001 Location: santa fe, nm Posts: 3,264 Images: 10	zebra is electronically superimposed on the image.....there is nothing to focus, so what you heard was urban legend

May 20th, 2002, 07:43 AM	#3
Mike Avery Regular Crew Join Date: Dec 2001 Location: Michigan Posts: 87	No, it's not an urban legend. However, the comment I made about "snapping into focus" was in reference to the 16x manual lens. I find when using that lens the change in appearance of the zebras is a good way to know when you've hit focus. I don't remember the change being so obvious with the auto lens, but it's been a long time since I've used one. Mike Avery

May 20th, 2002, 01:46 PM	#8
Bill Ravens Join Date: Nov 2001 Location: santa fe, nm Posts: 3,264 Images: 10	Well, it seems I may owe everyone an apology. I've been reading "focus" as in lens focus....not, diopter focusing of the viewfinder. For this error on my part, you have my deepest apologies. Chris, thanx for clearing my clouded perception. Sorry for giving the impression that "we're coming to blows". It isn't that, at all. In fact, I can see how using the zebra stripes for diopter focusing may work quite well.

May 20th, 2002, 02:08 PM	#9
Josh Bass Slash Rules! Join Date: Apr 2002 Location: Houston, Texas Posts: 5,472	Wait. Now I'm confused. We're talking about the "diopter" is it . . .the actual viewfinder glass? I thought we meant the lens of the camera. Nevermind then. Guess it's another 1500 for the b&w viewfinder for me! Boy Howdy! __________________ The Bass' camerawork The Bass on IMDB

May 20th, 2002, 03:34 PM	#10
Don Palomaki Wrangler Join Date: Sep 2001 Location: Northern VA Posts: 4,487	How is this for a rationalization. Note that auto focus is judged by contrast. Contrast is highest at best focus. But contrast being higest means whites are whiter (like with good laundry detergent) and blacks are blacker. Now whiter whites can mean pushing narrow white portions of the image into zebra, causing zebr to appear if the white level is at the threshold of zebra. In summary, do not count on it work at all (or evenmost) times and places.

May 20th, 2002, 05:39 PM	#11
Mike Avery Regular Crew Join Date: Dec 2001 Location: Michigan Posts: 87	I am talking about focusing the lens by using zebras. Yes, I understand it might not make sense to an opto-mechanical engineer, but to my eye it works. I can definately see a change in the zebra pattern when I hit focus, and at least one other conributor to this forum has noticed the same thing. It's not the only tool I use to focus, but it helps. Mike Avery Last edited by Chris Hurd; May 20th, 2002 at 08:37 PM.

May 20th, 2002, 07:19 PM	#12
Josh Bass Slash Rules! Join Date: Apr 2002 Location: Houston, Texas Posts: 5,472	So you were talking about the lens focus earlier, then? You said that was not your only method of focusing. What else do you use? Still talking about the color viewfinder, just for clarification. __________________ The Bass' camerawork The Bass on IMDB

May 20th, 2002, 08:16 PM	#13
Bill Ravens Join Date: Nov 2001 Location: santa fe, nm Posts: 3,264 Images: 10	There is a great deal of mis-information floating around this internet. I would just like to make sure that an innocent newbie reading this thread sees the diffrerence between opinion and a phenomenon based on a known principle of optics. Last edited by Chris Hurd; May 20th, 2002 at 08:37 PM.

May 20th, 2002, 08:35 PM	#14
Chris Hurd Obstreperous Rex Join Date: Jan 2001 Location: San Marcos, TX Posts: 27,368 Images: 513	Thread closed. Let's just say that the zebra bars are first and foremost a measure of exposure and leave it at that. Thanks, __________________ CH Search DV Info Net \| 20 years of DVi \| ...Tuesday is Soylent Green Day!