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Lens "Harp Test"


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#1 Graham Murphy

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Posted 07 April 2007 - 02:40 PM

Hi All,

I was wondering if anyone could tell me what the proper procedure is in which to perform a "harp test" for lenses? I've looked up the archives and couldn't really find much. Thanks in advance.

Cheers,


Graham
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#2 Nick Mulder

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Posted 07 April 2007 - 06:17 PM

Source yourself some chewable morphine (the cherry flavor gummy-bear version in my opinion is the most effective :wub:) ... then pretty much follow the instructions here

Just like time-lapse really...
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#3 Mike Panczenko

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Posted 07 April 2007 - 09:08 PM

What is a harp test- I can't find much on google.
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#4 Chris Keth

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Posted 09 April 2007 - 02:53 PM

What is a harp test- I can't find much on google.


I have never done it but read some stuff about it. I get the idea that it's a more elaborate version of shooting a ruler at various stops to have a good visual sense of your depth of field.

It involves something in the realm of a bunch of resolution targets at difference distances shot at different f/stops.
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#5 David Negrin

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Posted 18 August 2007 - 03:35 PM

Hi All,

I was wondering if anyone could tell me what the proper procedure is in which to perform a "harp test" for lenses? I've looked up the archives and couldn't really find much. Thanks in advance.

Cheers,
Graham


I've never heard it called a harp test before, but, a card test yes.
Take a 1x3 board 24'' long, cut slices every inch not going all the
way through the board. Grab the board with a c-stand and set it
horizontally, Place your rig with the center slot @ 5' to the film/ chip
plane. Put the ace in the center slot ( hold cards in place with tape shims)
Place red or black cards going away from camera and the opposite
color coming towards camera. fan them out so all you see is the # and
suit in the corner. find out at what stop your lenses were calibrated, most
camera houses go at t-2.8 . When you see the set up you will see how the
focus falls off on the lens, The numbers going back from the ace might be
soft @ the 3, while the cards coming towards the lens might fall off @ the 2.
giving you the results on the focus carrying 2/3rds back, and then you can
play your depth ( if you need to) more effectively. I have to admit I haven't
heard of anyone doing one in over 10 years.
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#6 christian hennermann

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Posted 23 August 2007 - 05:57 PM

I've never heard it called a harp test before, but, a card test yes.
Take a 1x3 board 24'' long, cut slices every inch not going all the
way through the board. Grab the board with a c-stand and set it
horizontally, Place your rig with the center slot @ 5' to the film/ chip
plane. Put the ace in the center slot ( hold cards in place with tape shims)
Place red or black cards going away from camera and the opposite
color coming towards camera. fan them out so all you see is the # and
suit in the corner. find out at what stop your lenses were calibrated, most
camera houses go at t-2.8 . When you see the set up you will see how the
focus falls off on the lens, The numbers going back from the ace might be
soft @ the 3, while the cards coming towards the lens might fall off @ the 2.
giving you the results on the focus carrying 2/3rds back, and then you can
play your depth ( if you need to) more effectively. I have to admit I haven't
heard of anyone doing one in over 10 years.




oh, yes, they do it in cape town my bru!
it's part of every propper camera/lesns test. even though i must admit it's realy a bit too much.
the meaning of the harp test is to make sure that ur eyefocus is correct. calibrating the eyepiece is nbot enough.
u perform a lens test in order to make sure the focal length from the lens/camera mount to the film gate is correct.
the harp test makes sure the focal length from the camera mount to the eyepiece is fine aswell.
it should be 52mm(for ARRI) just like the focal length of the filgate.
if it is incorrect u'll get into toubles when u rely on eyefocus instead on ur measuretape.

we taek a test chart that consist of thin lines (about one every 1cm). if u twist it it looks like a harp. place it in front of the camera, close focus, take a long lens e.g. 85mm, open the stop to create a small depth of field. now focus one of the lines and mark it with a arrow or colored dot or whatever. the lines running away from the camera and the closer ones should be slighty out of focus and completly soft. shoot it and looking at the test the result needs to look just like what u've seen through the eyepiece. if not- if any other line is more in focus than the one u've marked withe the arrow/dot- u need to fix the focal length from camera mount to eyepiece.

but i've honestly nerver heared of anyone who had to adjust it....
cheers
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Metropolis Post

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Media Blackout - Custom Cables and AKS

CineLab

Gamma Ray Digital Inc

Glidecam

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