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Old April 7th, 2008, 05:42 AM   #1
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Letus won't focus on gg

I'm in a panic here. I have an important interview this morning and sometime between last night and this morning, my Letus has lost the ability to focus on the ground glass. It gets close, but the image is soft. I can't figure it out at all. Has anyone else run into a problem like this? Thanks.
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Old April 7th, 2008, 07:03 AM   #2
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We need bob Hart to be online - he's the expert.

I'm a bit confused though - are you talking about the focus of the lens on the front of the Letus or the focus of your camera on the letus?

Let's get some facts out of the way

what model letus?

which camera?

which lens?
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Old April 7th, 2008, 07:44 AM   #3
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Letus Extreme w/ the EX1. Nikon lens. I was focusing on the Letus' ground glass. I've managed to correct it (I think) by taking off the Letus and putting it back on again. I had performed a back focus recently on the EX1 and that may have contributed to the problem- although it worked fine yesterday. I'll see how the interview goes as is. I'm a little nervous the focus is going to shift. Running late - thanks.
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Old April 7th, 2008, 08:01 AM   #4
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if you're worried about the focus - do you really need the LEX for the interview? - is the look going to be significantly better that the EX itself?
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Old April 7th, 2008, 08:39 AM   #5
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Yeah - it makes a big difference. The shallow dof just looks that much better and I don't have to zoom as much. I think I'm OK now (cross my fingers).
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Old April 7th, 2008, 11:30 AM   #6
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Bill.


The EX1/Letus Extreme guru is one Philip Bloom. Therefore treat anything I say with a pinch of salt and a jaundiced eye.

To be on the safe side, when you shoot your interviews, try to avoid opening your camcorder aperture wider beyond about f5.6. Use the camcorder ND filter to control light levels or even better put some ND in front of the Nikon lens if that option is available to you.

If the lighting conditions are dull and will require you to open everything up wide including the camcorder iris, you may find things going soft and furry again.

Try to find an alternative environment which will permit you to keep the f5.6 aperture or add some artificial light unless you find it working okay anyway.

As for why it would not focus, I can't offer an answer just a few guesses.

If you are using an autofocus function for initial focus on the groundglass, point the Letus and Nikon lens at a plain surface, not a textured or detailed area, especially not one which has bright highlights in it.

When following the recommended method of focussing on the groundglass, the Nikon lens is set to a narrower iris to deliberately make the groundglass texture apparent.

With textured backgrounds and bright highlights, the Nikon lens at narrow aperture will pass an image which will be fairly sharp all over.

The autofocus may try to focus right through the groundglass onto the aerial image which will be apparently sharper to the camcorder than the groundglas image and it will leave the groundglass texture in a blur.

My recollection of the EX1 is unclear. I did not have it long enough to read up and learn to use it properly.

I think it had a manual Fujinon lens but an autofocus function may have been there??? It was friendly enough like the Z1 that a lot of what I did with it was instinctual and I was concentrating on the memory card system which is a whole new high science for a slow-learner like me.

Back on the subject -- I have been tricked by aerial image when using an outdoors garden environment to set the focus on the groundglass manually with the Z1 and I suspect that if you were setting manually, you may have encountered the same problem.

If you had moved the camcorder lens focus very far in the opposite direction to that which seemed so elusively to be approaching but never getting to sharp focus, then you may have found the groundglass texture focussing sharply and the projected image re-appearing again with it.

Purists will shoot holes in this comment with suggestion that sharp aerial image and sharp groundglass image are co-incident. My reponse to that is that it is not always so and I do not know why except that the combination of camcorder iris and achromat can change the rules.


Good luck with it.

Last edited by Bob Hart; April 7th, 2008 at 11:51 AM. Reason: errors
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Old April 7th, 2008, 02:43 PM   #7
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Bob. Thanks for your response. I wound up getting the right focus using the expanded focus on the GG. I was alarmed because the peaking didn't kick in at all and it usually does (not during expanded focus). The interview went perfectly in any case.

I used a 105mm 2.5 Nikon lens. Not all that fast, but I find even with my 1.4 85mm lens, I have to be almost completely wide-open with both the Nikon and the EX1. I use a 600w softbox at about six feet which is about as close as I like to go. How can you get your iris to 5.6? I suppose I could bring the softbox in a few feet, but my clients are older usually and don't like that!
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Old April 7th, 2008, 07:30 PM   #8
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Nothing is writ in stone for iris setting. If it works, it is all that matters.

The end-results give their own testimony.
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Old April 7th, 2008, 11:27 PM   #9
 
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what it is,
good words, Bob
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