Focusing by the Book...?

S

SadMax

Well-known member
Most of my shooting has been done in 16mm, so I am new to the wonderfulness that is the DVX100A...

Are there tables available to allow focusing this camera the way I'd focus a 16mm unit...measure distance from desired plane-of-focus to the film plane, read a chart, set the lens and that's it...?

A lot of people seem to note the trickyness of getting good focus even with the monochrome viewfinder mode. Can we do it by the numbers...?
 
Re: Focusing by the Book...?

I couldn't find he original table, but one of our users (Stas) posted this on another board (from the original table).

Measured from the accessory shoe / light mount.

50% 3’10"
51% 3’11"
52% 4’
53% 4’1"
54% 4’2.5"
55% 4’4"
56% 4’5"
57% 4’6.5"
58% 4’8"
59% 4’10"
60% 4’11.5"
61% 5’
62% 5’2"
63% 5’4"
64% 5’6"
65% 5’9.5 ‘
66% 6’
67% 6’3"
68% 6’6"
69% 6’9"
70% 7’
71% 7’4"
72% 7’8"
73% 8’
74% 8’6"
75% 8’12"
76% 9’6"
77% 10’
78% 10’8"
79% 11’6"
80% 12’4"
81% 13’4"
82% 14’7"
83% 16’
84% 17’9"
85% 19’11"
86% 22’9"
87% 26’6"
88% 31’10"
89% 39’9"
90% 52’11"
91% 79’5"
92% 160’8"
93% Infinity

Personally, I love Ron Dexter's focus chart--it really pops, even with the DVX100.

http://www.rondexter.com/professional/equipment/focus_pattern.htm
 
Re: Focusing by the Book...?

Barry, I though there was a difference between the DVX100 and the 100a. Is that your understanding?
 
Re: Focusing by the Book...?

Well, yeah, the close-focus distance. The 100 stops focusing at 50 (i.e., 50 is the smallest MF number you can get in full telephoto mode). The 100A goes down to 37, allowing for focusing at about half the distance (20 inches) versus the 100's minimum object distance of about 39 inches.

But all the other numbers stay the same, the only difference in the chart is from 37 to 49.
 
Re: Focusing by the Book...?

The original focus chart for DVX100 was on www.flickerfactory.com, but it's no longer there... bummer.

I KNEW I should have pirated it! :)

The russian site seems to have an exact replica, though.
 
Re: Focusing by the Book...?

/me stretches brain muscle.

This chart will be accurate for all zoom factors because zoom is either coupled to the focus length or it is not relevant?

Also, Barry you mention that the DVX-100A will go down to MF 37-49 in addition to 50+... but at 50 we're already down to 3' or so... what do the additional numbers gain? Down to 5 inches?

Tying in a related subject, using a chart to translate Zoom factor to focal length in mm will essentially give you an equivalent to screwing on a new lens with the given focal length, yes?
 
Re: Focusing by the Book...?

The chart is accurate for all zoom settings (assuming your backfocus is set accurately, of course).

The additional numbers get down to about 20 inches (one of the improvements in the 100A is that they lowered the minimum focus distance from 39 inches on the 100 down to 20 inches on the 100A).

And I'm not sure I understand the last question: the book includes a zoom to focal length mm equivalency chart, and that chart is also available on the site here somewhere. So if you were to want to emulate attaching a certain focal length lens to your camera, you could look up the focal length in the chart and use the equivalent zoom setting (Z00-Z99). Is that what you meant?
 
Re: Focusing by the Book...?

[quote author=Barry_Green link=board=news;num=1102624976;start=0#7 date=12/20/04 at 12:38:23]The chart is accurate for all zoom settings (assuming your backfocus is set accurately, of course).[/quote]

Backfocus? That's a new term for me. Do you mean that the focus should be correct for the furthest "in" zoom to be used?

[quote author=Barry_Green link=board=news;num=1102624976;start=0#7 date=12/20/04 at 12:38:23]The additional numbers get down to about 20 inches (one of the improvements in the 100A is that they lowered the minimum focus distance from 39 inches on the 100 down to 20 inches on the 100A).[/quote]

Ah, okay. Does anyone have these numbers perchance?

[quote author=Barry_Green link=board=news;num=1102624976;start=0#7 date=12/20/04 at 12:38:23]So if you were to want to emulate attaching a certain focal length lens to your camera, you could look up the focal length in the chart and use the equivalent zoom setting (Z00-Z99).  Is that what you meant?[/quote]

Yes, that's exactly what I meant. Okay, with this in mind, why do people buy lots of lenses? Why not simply use a zoom lens? Sorry to sound naive, but I am trying to understand the production values represented!

Thanks for your help.
 
Re: Focusing by the Book...?

[quote author=Bischofftep link=board=news;num=1102624976;start=0#8 date=12/21/04 at 05:11:29]Backfocus? That's a new term for me. Do you mean that the focus should be correct for the furthest "in" zoom to be used?[/quote]
On a lens with properly-adjusted backfocus, the lens will "hold" focus regardless of what zoom setting you're at. You can zoom in to full telephoto, set focus, then pull back to full wide angle and still be at 100% sharp focus. That's the way it's supposed to work. If the backfocus is not properly adjusted, the lens may lose focus as you zoom out. This *should* never happen with a non-adjustable lens such as the DVX's, but some people have complained about it, so I guess it may somehow be possible.

Ah, okay. Does anyone have these numbers perchance?
Click to expand...
I published the updated chart in the book, and I think it's been posted on the forum here as well, try searching for like six to 12 months ago.

Yes, that's exactly what I meant. Okay, with this in mind, why do people buy lots of lenses? Why not simply use a zoom lens? Sorry to sound naive, but I am trying to understand the production values represented!
Click to expand...
"Prime" lenses are sharper, clearer, faster, and just generally look better than zoom lenses. Zooms are much more complex designs, with many more glass elements, etc... which results in less light transmission and more opportunity for internal reflections, flares, etc. It's a lot easier to design a super-sharp prime lens than it is to design a zoom that can compete in sharpness and aperture etc.

But there's no comparing convenience -- a zoom is infinitely more convenient to use than a series of primes, where you actually have to get up and move the camera to adjust framing (vs. a slight zoom-in or zoom-out). On video cameras prime lenses are a rare exception, something like the Zeiss DigiPrimes might be used on a film destined for theatrical blow-up but probably 99.99999% of video is shot with zoom lenses. In film/motion picture work, there's a much higher usage of primes, zooms are much less common.
 
Re: Focusing by the Book...?

I have your excellent DVX book and somehow missed the focus chart, apologies!

Thank you for the education re: Prime lenses! This makes great sense.

Learn something new everyday... and around here usually more than ONE something!
 
Re: Focusing by the Book...?

[quote author=Barry_Green link=board=news;num=1102624976;start=0#9 date=12/21/04 at 11:36:06]
On a lens with properly-adjusted backfocus, the lens will "hold" focus regardless of what zoom setting you're at.  You can zoom in to full telephoto, set focus, then pull back to full wide angle and still be at 100% sharp focus.  That's the way it's supposed to work.  If the backfocus is not properly adjusted, the lens may lose focus as you zoom out.  This *should* never happen with a non-adjustable lens such as the DVX's, but some people have complained about it, so I guess it may somehow be possible..[/quote]


Hi!

I am one such person having prob with back focus... I suppose there's nothing I can do about it myself but to send it for servicing?
 
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