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Old February 9th, 2007, 05:38 PM   #16
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Quote:
Originally Posted by Steve Oakley
no. I think the stock lens looks ok wide. I think its just a matter of it being very temperature sensitive. in any event, I've simply gotten into the habit of checking the B.F. everytime I load a new tape.


Steve Oakley
But it seems like I am not even able to backfocus on it wide, because I can't tell if the BF is in percise focus when I go wide. And focusing the lens does not seem to be able to resolve my subject from far way (about 10 feet).

In setting my BF, when I have the chart 3 meters away and go wde, it seems like I am only able estimate its focus, as any little movement on BF ring takes the chart way in/and out of focus.
Are there any ways that you recommend to dial in the wide end, should I move my chart closer in?
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Old February 9th, 2007, 06:03 PM   #17
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Quote:
Originally Posted by Ben Garvey
But it seems like I am not even able to backfocus on it wide, because I can't tell if the BF is in percise focus when I go wide. And focusing the lens does not seem to be able to resolve my subject from far way (about 10 feet).

In setting my BF, when I have the chart 3 meters away and go wde, it seems like I am only able estimate its focus, as any little movement on BF ring takes the chart way in/and out of focus.
Are there any ways that you recommend to dial in the wide end, should I move my chart closer in?
Bring the chart a bit closer, no closer than 2 meters should be fine with a standard type zoom lens. You have to be careful, because it is a fine adjustment and the backfocus pops in and out of focus very quickly. Having a good monitor helps.
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Old February 9th, 2007, 06:25 PM   #18
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Originally Posted by Brian Drysdale
Bring the chart a bit closer, no closer than 2 meters should be fine with a standard type zoom lens. You have to be careful, because it is a fine adjustment and the backfocus pops in and out of focus very quickly. Having a good monitor helps.
Thanks, I was trying to adjust through the Viewfinder, so maybe that is the problem.
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Old February 9th, 2007, 06:58 PM   #19
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Quote:
Originally Posted by Ben Garvey
But it seems like I am not even able to backfocus on it wide, because I can't tell if the BF is in percise focus when I go wide. And focusing the lens does not seem to be able to resolve my subject from far way (about 10 feet).

In setting my BF, when I have the chart 3 meters away and go wde, it seems like I am only able estimate its focus, as any little movement on BF ring takes the chart way in/and out of focus.
Are there any ways that you recommend to dial in the wide end, should I move my chart closer in?
This is what I experienced also.

I don't see how it possible to adjust back focus without an HD monitor.
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Old February 9th, 2007, 10:12 PM   #20
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use focus assist and the LCD. its far from ideal but it works once you get the hang of it. usually I bring a 13" sony broadcast CRT as backup. I do plan to change to a LCD soon once I find something for a few hundred that has what I need.

Steve O
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Old February 21st, 2007, 11:40 AM   #21
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I think my focus is swaying a little everytime I take the camera out.
I'm currently recording 25p SD at the moment (HDV is next), the focus assist is lit up like a christmas tree but when I view the footage back home there's a definite softness/blurryness to it.
Should you expect progressive footage to be less sharp than interlaced (25p vs 50i for example?)
I've used the chart, but was advised around 30 foot away - I'm going to do this again tomorrow but at around 2-3 metres.
I have to rely on the camera's LCD and viewfinder and don't have the luxury of a quality monitor (either field of HD monitor at home). It's often difficult to even see what's coming off the camera in bright sunlight.

It's somewhat frustrating viewing such footage on a camera capable of so much...yes, I'd like to borrow guys like Tim Dashwoods head for just one day!

I'll attempt the chart again in the meantime and see if the footage improves.
Cheers.
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Old February 21st, 2007, 02:55 PM   #22
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I just read this whole thread and didn't notice a mention to open the aperture all the way when backfocusing.

On the stock lens open all the way up to F1.4 to get the shortest DOF possible. If you are outside turn on the ND filters and increase the shutter speed if necessary. I've seen people try to backfocus at F4 and F5.6 and it is totally useless at those smaller aperture settings.

The procedure is:
  1. Warm up the camera in the shooting environment.
  2. Open the aperture as much as possible (F1.4) and control exposure with ND or shutter.
  3. Set your Siemens Star at around 3 meters (10 feet) from the camera.
  4. Zoom in all the way, set the focus (NOT the back focus) on the Siemens Star.
  5. Zoom out all the way, set BACK FOCUS adjustment for a sharp Siemens Star.
  6. Zoom back in and confirm focus. (If necessary, adjust lens focus and repeat.)

This should be performed before every shoot or change in environment. Temperature changes will cause the mount to expand or contract and throw off the back focus.

Backfocus is a huge issue with all HD production because of the relatively short focal plane of the CCDs combined with very high resolution. Bad focus is instantly noticable on the big screen, and proper back focus should be a priority.
The backfocus problem was so bad with the Sony F900 being used in film productions, that Clairmont created their own lens mount out of "space age" materials. More info here.
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Old February 22nd, 2007, 04:53 AM   #23
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Quote:
Originally Posted by Tim Dashwood
I just read this whole thread and didn't notice a mention to open the aperture all the way when backfocusing.
Excellent post Tim. I had my suspicion about the back focus on this camera as I always seem to be adjusting it. At least I know it's not my eyes that are going.

They should print your post in the manual, just below where it says, "It is only necessary to perform this when the lens is attached for the first time". Muppets.
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Old February 22nd, 2007, 05:08 AM   #24
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Yes, great advice. It can get a bit lonely out there where you're convinced it's either your equipment (new at that) failing or you're going mad. Good to know these gremlins appear for other people too.
I might try and laminate a star chard and keep this in the bag for all shoots now...don't suppose the laminate 'gloss' would effect the focus? Is it possible to pick up a plastic backed star chart (as per warm/grey cards etc)?
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Old February 22nd, 2007, 11:03 AM   #25
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Originally Posted by David Scattergood
Yes, great advice. It can get a bit lonely out there where you're convinced it's either your equipment (new at that) failing or you're going mad. Good to know these gremlins appear for other people too.
I might try and laminate a star chard and keep this in the bag for all shoots now...don't suppose the laminate 'gloss' would effect the focus? Is it possible to pick up a plastic backed star chart (as per warm/grey cards etc)?
You can buy a made up star chart from Panavision UK at the Panastore.

http://www.panavision.co.uk/

Although, it would be cheaper to print out one and get it laminated. However, one of the Panavision charts does have an Annular Focus Target as well as the star. This uses the V/F peaking to help set the backfocus - it works extremely well on the high end HD cameras, however, I couldn't say how well it would work with the JVC's focus assist.

It could be worthwhile putting this thread up as a sticky, because I gave the method of setting the backfocus on a previous thread and I expect it will be a re-occurring question.
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Old February 22nd, 2007, 11:27 AM   #26
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Thanks Brian - I'll take a look and yes there are a few recent threads with priceless advice which could do with being stickies perhaps?
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