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Blurred on Wide Angle


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#1 Herbert Camilleri

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Posted 12 December 2006 - 03:12 AM

Dear ALL,

I have got an XL2 and when I have a wide angle shot I see that there is no detail in my shots but when I am close the picture is sharp. I use A as a mode, do you think I should use the Tv mode or I have something to do with gain or the lens itself? thanks in advance and it seems that I have dropped in the right place for questions like these.
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#2 Bob Hayes

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Posted 12 December 2006 - 08:34 AM

It might be a back focus problem. Put the focus in Manual. Zoom out about half way. Focus on something with good crisp edges. Zoom in, if the image is way out of focus you may have a back focus problem.
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#3 Herbert Camilleri

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Posted 12 December 2006 - 08:54 AM

I try to make the test next Friday because the camera isn't with me , by the way if it is the back focus problem what might be wrong with the camera, is it the lens or it needs to be calibrated or so? thanks for you help , you put my mind to rest ....I 'll check it and let you know
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#4 Jon Mello

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Posted 12 December 2006 - 10:26 AM

Herbert,

[A] mode is a full automatic mode. I would suggest [M] (full manual) when it comes to critical focusing. Also, I have experience using a Century Wide Angle adapter with XL's and have found that the range of crisp focus is limited to about 40% of the zoom range. In addition, I'm not aware of a backfocus adjustment on the 20x flourite, if in fact that is the lens you are using. Hope this is of some help!

Best of luck!


~Jon Mello - RI USA
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#5 Jon Mello

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Posted 12 December 2006 - 01:01 PM

Herbert,

... a Century Wide Angle adapter with XL's and have found that the range of crisp focus is limited to about 40% of the zoom range....


Herbert,

Correction. After re-reading your post, I realize you may not be using a Wide Angle Adapter, but instead have a wide shot.

The XL image can get a little soft on very wide shots due to to pixel averaging. This is not a technical issue with the lens however, but an issue with available resolution.



~Jon
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#6 Herbert Camilleri

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Posted 12 December 2006 - 01:03 PM

Thanks Jon, it feels great here, I love this forum, you people are great.....I finally found a live forum with good people, thanks for everything....I'll try the test and see...I 'll keep you posted. And by the way..HAPPY CHRISTMAS TO ALL
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#7 Herbert Camilleri

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Posted 18 December 2006 - 03:18 PM

Hi Guys , I made the test and it is ok, I guess I had the gain almost full on, thanks for your help , wish I could help you in anything.
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#8 Herbert Camilleri

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Posted 24 December 2006 - 06:31 AM

Hi People, I guess I was wrong about the test because I did the same but both my cameras failed the test, I have put the camera 3 meters away from a focus chart , put camera to M mode then zoomed to half way, manually fcoused and the zoomed to full and I got a blurred image.....Am I doing it right? or I have to do it in a different way?, any suggestions will be very welcome. Thanks again
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#9 chuck colburn

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Posted 24 December 2006 - 02:06 PM

Hi People, I guess I was wrong about the test because I did the same but both my cameras failed the test, I have put the camera 3 meters away from a focus chart , put camera to M mode then zoomed to half way, manually fcoused and the zoomed to full and I got a blurred image.....Am I doing it right? or I have to do it in a different way?, any suggestions will be very welcome. Thanks again



Hello Herbert,

With zooms, set the lens on the LONGEST focal length and focus on your test target (if you have one) or use the front page of a news paper, zoom to the shortest focal length. If the image is soft then adjust the back focus setting if your video lens has one or have your cine lens collimated to the proper flange focal depth. Anyhow repeat the process again to see if you need to readjust the back focus slightly. All things being equal the lens should now hold focus (as good as the particular lens will allow) thru the zoom range.

Merry Xmas.
Chuck Colburn
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#10 Bob Hayes

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Posted 24 December 2006 - 03:25 PM

Hi People, I guess I was wrong about the test because I did the same but both my cameras failed the test, I have put the camera 3 meters away from a focus chart , put camera to M mode then zoomed to half way, manually fcoused and the zoomed to full and I got a blurred image.....Am I doing it right? or I have to do it in a different way?, any suggestions will be very welcome. Thanks again


What you have done is the opposite of what I am recommending.

HOW TO REALLY ADJUST BACK FOCUS
1. Set camera to wide open. You need a proper exposure so do it with lighting and or camera adjustment.
2. Put camera in manual focus. Zoom all the way in and focus manually.
3. Zoom all the way out and see if it is sharp. On a wide lens this isn?t very easy. At this point you adjust the back focus until the image is sharp. I don?t think your camera has back focus so if it is off you need to take it in.

WHAT I AM RECOMMENDING YOU TRY.
1. Although the above is the correct and recommended way to check back focus and I religiously do it. I find it is tough to see whether the wide shot is as sharp as it can be so I have developed two other easy field tests.
2. I zoom out halfway and try to ?eyeball? focus. Then I zoom into what I have tried to focus on. If the camera is back focused OK you should be close but not perfectly in focus. If the Back Focus is off when you zoom in you may be very out of focus. I do this check occasionally while I am shooting with the camera on my shoulder as a quick back focus check.
3. Another technique I use is to zoom in on a feature on a horizontal plane. The most accurate method is to use a metal tape measure pointing away from you on a table top. I focus on part of the tape measure like 7?. Then I slowly zoom out. If the back focus is on you will see the depth of field get wider but the original number will still be sharp. If the focus is off you will see the depth of field expand but in extreme situations it will move away from the original focus. So 7? might be soft but 4? to 6? is sharp.
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#11 chuck colburn

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Posted 24 December 2006 - 06:23 PM

What you have done is the opposite of what I am recommending.

HOW TO REALLY ADJUST BACK FOCUS
1. Set camera to wide open. You need a proper exposure so do it with lighting and or camera adjustment.
2. Put camera in manual focus. Zoom all the way in and focus manually.
3. Zoom all the way out and see if it is sharp. On a wide lens this isn?t very easy. At this point you adjust the back focus until the image is sharp. I don?t think your camera has back focus so if it is off you need to take it in.

WHAT I AM RECOMMENDING YOU TRY.
1. Although the above is the correct and recommended way to check back focus and I religiously do it. I find it is tough to see whether the wide shot is as sharp as it can be so I have developed two other easy field tests.
2. I zoom out halfway and try to ?eyeball? focus. Then I zoom into what I have tried to focus on. If the camera is back focused OK you should be close but not perfectly in focus. If the Back Focus is off when you zoom in you may be very out of focus. I do this check occasionally while I am shooting with the camera on my shoulder as a quick back focus check.
3. Another technique I use is to zoom in on a feature on a horizontal plane. The most accurate method is to use a metal tape measure pointing away from you on a table top. I focus on part of the tape measure like 7?. Then I slowly zoom out. If the back focus is on you will see the depth of field get wider but the original number will still be sharp. If the focus is off you will see the depth of field expand but in extreme situations it will move away from the original focus. So 7? might be soft but 4? to 6? is sharp.


Hi Bob,

A zoom lens inhertently has only three positions in it's focal length range where it can be in absolute proper focus at the film plane. This is it's longest and shortest zoom positions and a position somewhere between these two. This is due to the fact that all zooms suffer from what's called the "S" curve, that is as you zoom from the longest to the shortest focal length the focus moves away from optimum focus one way from the film plane untill you reach that position where it begins to move out of focus to the towards the opppisite side of the film plane. By not starting at the longest focal length you are not going to be able to set up optimum back focus be it either with a moveable back focus adjustment like on some video lenses or by shimming the lens mount in or out as on cine lens or a video lens which does not have a back focus adjustment incorperated in the lens. If there is a problem with the movement of the internal moving groups of optics ( the variator and the compensator ) then no matter what you do to set up back focus ( shimming or setting the back focus adjuster you are not going to have a very functional lens. These types of adjustments need to be done in an optical repair shop that has an optical collimator and/or a thru the lens projector.

Anywhow heres to happy holidays and peace, love and understanding for the new year.

Chuck Colburn
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#12 chuck colburn

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Posted 25 December 2006 - 08:59 AM

Dear ALL,

I have got an XL2 and when I have a wide angle shot I see that there is no detail in my shots but when I am close the picture is sharp. I use A as a mode, do you think I should use the Tv mode or I have something to do with gain or the lens itself? thanks in advance and it seems that I have dropped in the right place for questions like these.


Merry Christmas Herbert,

If you don't already have a test target and you have a printer with your computer print one or more of these, (five is good, one for each corner and one in the center) and mount them on a piece of poster board and side light it from both sides at a 45 degree angle (like on a copy stand). These are called siemens stars and work well with video or cine lenses as it is easy to see the image snap in and out focus. Glossy paper seems to work better but is not mandantory.

http://www.sinepatte...Sector Star.gif

Chuck
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#13 Hal Smith

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Posted 25 December 2006 - 10:36 AM

a test target and you have a printer with your computer print one or more of these................

There's also a nice Siemans Star at:

http://www.chatercam.....ocus star.pdf

I printed it off on an HP Laser and it looks pretty good.

MERRY CHRISTMAS AND A PROSPEROUS NEW YEAR TO ALL THE CINEMATOGRAPHY. COM GANG FROM THE HEARTLAND!!!!!!!!!!!
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#14 chuck colburn

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Posted 25 December 2006 - 12:10 PM

There's also a nice Siemans Star at:

http://www.chatercam.....ocus star.pdf

I printed it off on an HP Laser and it looks pretty good.

MERRY CHRISTMAS AND A PROSPEROUS NEW YEAR TO ALL THE CINEMATOGRAPHY. COM GANG FROM THE HEARTLAND!!!!!!!!!!!


An the same to you and yours Hal,

Your target link is actually what the original siemens star target looked like. I just called the one I found that because I couldn't remember, and probally still can't, how to spell sinusodial. The one advantaged to the one I put up is since the divisions are finer they showup astigmatism and certain other video artifacts easier. But for just focus checks your link would be easier to work with. Plus I like the four little targets around the star. A grouping of these on a board would be good for showing curveture of field also.
Here is the link to where I found the target. They have many types for quantifying different aspects of video imaging.

http://www.sinepatte...om/i_Stdrds.htm

Chuck Colburn
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