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Canon 5d Focus


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#1 Jeremy Hunt

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Posted 07 December 2009 - 06:06 AM

Hi

I recently did some focus pulling on the 5d, when i mesured the distance with the tape (from the subject, to the sensor) it said the distance was about 15 feet, but on the lens it said it was about 10. Does anyone have an explination for this? We were using nikon primes which need an adaptor and we were shooting at f2/8 for that shallow effect.

Any advice is greatly appreciated
-Jeremy Hunt
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#2 Ram Shani

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Posted 07 December 2009 - 06:20 AM

it can happen because of the adapter

maybe the back of the lens is a little to far from the sensor
so the marks are not in the right place
i had the same thing when i used my letus35 with canon lenses(on video camera)
try to check with normal canon lens

Edited by Ram Shani, 07 December 2009 - 06:25 AM.

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#3 Kristian Schumacher

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Posted 07 December 2009 - 01:40 PM

I agree. It is probably in the adapter. When I use Canon lenses the focus is always spot on. With Nikons it varies a little depending on which adaptor I use, but it can be quite a bit off mark.

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#4 K Borowski

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Posted 07 December 2009 - 02:12 PM

Sorry, am not really up on stills cameras, but is there an "extension factor" because you are using a smaller sensor than a 35mm 8-perf. equivalent?

If so the focal length increases. Therefore, the focusing will also likely shift in the same direction.


People find optical conversion formulae intimidating, but they honestly are very simple to use. Give me the conversion factor and I'd be happy to post some for you. Keep in mind WWII combat cinematographers, who'd often not even finished high school, were using them constantly with only prime lenses to work with!

Edited by Karl Borowski, 07 December 2009 - 02:13 PM.

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#5 Kristian Schumacher

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Posted 07 December 2009 - 05:06 PM

Sorry, am not really up on stills cameras, but is there an "extension factor" because you are using a smaller sensor than a 35mm 8-perf. equivalent?

If so the focal length increases. Therefore, the focusing will also likely shift in the same direction.


People find optical conversion formulae intimidating, but they honestly are very simple to use. Give me the conversion factor and I'd be happy to post some for you. Keep in mind WWII combat cinematographers, who'd often not even finished high school, were using them constantly with only prime lenses to work with!



The Nikon-to-Canon adapter is supposed to have the right dimensions to compensate for the difference in ffd between the two standards, but mine (and I believe quite a few others) are not accurate. Some too thin, some too thick, giving a focus that can be either side of what is correct. I have also heard from people that say theirs are spot on. A matter of luck, I guess. I am personally not bothered too much about it. Normally, I focus through the finder, but I have also used Nikon lenses that I have had to "calibrate" and mark with tape on the lens barrel for accurate focus by tape. The expanded focus function is OK for setting the focus mark right.
Sorry Karl, but the focus does not change with the sensor/film size, nor the focal length. Only the crop of the image will change, so the angle of view will be narrower the smaller the frame ;-)


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#6 Dan Salzmann

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Posted 07 December 2009 - 06:47 PM

Since stills lenses unlike film lenses are designed for photographers that focus by eye (if not using autofocus, these days) the focus markings do not have to be that accurate because, well hardly anyone is really "supposed" to use them other than as a rough guide for focusing using the hyperfocal distance instead of using optical focus. Those marks are just a tweak more accurate on higher-end older non-AF lenses.
Best to set focus marks by eye on the 5D with or without adaptor. The built-in focus assist feature which magnifies the image on the LCD screen is often quite handy as well.
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#7 Satsuki Murashige

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Posted 09 December 2009 - 02:40 AM

Since stills lenses unlike film lenses are designed for photographers that focus by eye (if not using autofocus, these days) the focus markings do not have to be that accurate because, well hardly anyone is really "supposed" to use them other than as a rough guide for focusing using the hyperfocal distance instead of using optical focus.

+1. I don't know how anyone can trust the "marks" on a still lens, whether or not you are using an adapter. They don't even have witness marks (hash marks next to the corresponding footage number). You've got to get eye marks with the focus assist and transfer them to the barrel or follow focus, and God help you if you're using a AF servo lens. That, or pull off of an onboard HD monitor.
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#8 Jeremy Hunt

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Posted 12 January 2010 - 12:05 PM

+1. I don't know how anyone can trust the "marks" on a still lens, whether or not you are using an adapter. They don't even have witness marks (hash marks next to the corresponding footage number). You've got to get eye marks with the focus assist and transfer them to the barrel or follow focus, and God help you if you're using a AF servo lens. That, or pull off of an onboard HD monitor.


The marks were pretty useless interems of the actual numbers.

Lol

It was on a skate dolly on a table, i made few marks on the table itself, and we did an ultra fast move with no follow focus. It was fun! I havnt seen the footage yet, but the monitor said it was in focus.

@ Karl, unfortunatley the camera isnt mine, but if i remeber corretly i think we were using nikons, but i cant be sure. Sorry for the late reply, i completley forgot about this post, i would love to have those conersion charts if you have still got them.


View on Vimeo

this is something different, if anyone is intrested.

(this is not my footage, i only did the focus on it)

Edited by Jeremy Hunt, 12 January 2010 - 12:08 PM.

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#9 Stephen Williams

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Posted 12 January 2010 - 01:11 PM

Sorry, am not really up on stills cameras, but is there an "extension factor" because you are using a smaller sensor than a 35mm 8-perf. equivalent?

If so the focal length increases. Therefore, the focusing will also likely shift in the same direction.


Hi Karl,

I never expected you to ask such a question! A 50mm lens is always a 50mm lens, the focal length will NEVER change whatever you attach it to.

Stephen
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