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Ann Bens
Zooming and focussing
on Jan 24, 2014 at 10:50:49 pm

When using a zoom lens for video does one zoom in on the subject, focus and zoom out for good focus.
Just like with a videocamera?
Or are there different rules for dslr.

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Steve Crow
Re: Zooming and focussing
on Jan 25, 2014 at 12:35:05 am

The rules are different for a DSLR because most DSLR lens are not guaranteed to hold focus once you zoom out so set your framing, adjust your focus and then, if you want, hit the optical magnification option (usually 5x and 10x) to digitally zoom in so that you can fine tune your focus.

Some people use external monitors specifically to help them focus better - not only is the screen usually larger than the LCD on the back of the DSLR but they often have focus assist features built into them.

Not sure off hand if Magic Lantern firmware for Canon currently supports anything like focus peaking to do this directly on your camera's LCD screen.

Steve Crow
Crow Digital Media
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Steve Crow
Re: Zooming and focussing
on Jan 25, 2014 at 12:38:28 am
Last Edited By Steve Crow on Jan 25, 2014 at 12:41:58 am

Oh it looks like ML does indeed support focus peaking, here's a video demonstrating this feature on a Canon T2i

http://magiclantern.wikia.com/wiki/File:Magic_Lantern_Focus_Assist_Feature_...

ML Version 2.3 apparently also offers the following focus assist capabilities: "focus peaking, zoom while recording, trap focus, rack_focus, follow_focus, stack_focus."


Steve Crow
Crow Digital Media
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Joseph W. Bourke
Re: Zooming and focussing
on Jan 25, 2014 at 3:57:10 am

Steve -

The ML focus peaking works like a charm! I was just using it today to experiment with some rack focus shots. Some of the other features you listed (rack focus, follow focus) I think would be at their best with the new STM lenses. In my experiments with the ML rack and follow, the increments seemed a bit chunky, not the smooth movement you can get with a hand pulled focus.

Joe Bourke
Owner/Creative Director
Bourke Media
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Steve Crow
Re: Zooming and focussing
on Jan 25, 2014 at 9:51:20 pm

Joe - that's cool to know, I'm thinking of trying ML again. I have installed it a few times but each time ended up removing it simply because I didn't like the way it cluttered my LCD screen and changed button functions - I guess there probably is a way to control the screenlayout of ML functions - I assume if you turned them off completely that would work but maybe there's a middle ground.

Steve Crow
Crow Digital Media
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Steven L. Gotz
Re: Zooming and focussing
on Jan 25, 2014 at 8:09:49 am

As Steve points out the rules are different. I only wish they were the same.

What my camera does is it allows me to set it so that when I am set for manual focus, I get a magnified image in my viewfinder when I turn the focus ring. I believe a real DSLR may call that "Live View"?? Mine is a mirrorless so it is all live view all the time.

I can't afford a zoom lens that keeps the same aperture through its range. Therefore, with the aperture changing, you can imagine that the focus might change a bit.

Steven


http://www.stevengotz.com



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Bill Bruner
Re: Zooming and focussing
on Jan 25, 2014 at 8:55:20 am

Ann - it's not the type of camera - it's the lens.

A "parfocal" lens holds focus throughout the zoom range and allows you to zoom in, set your focus and zoom out.

A "varifocal" lens does not.

Those of us who come from motion picture film or video are accustomed to parfocal lenses.

Most still camera lenses are varifocal, however.

I shoot with Panasonic GH cameras, and the Panasonic 12-35 and 35-100 hold focus throughout the zoom range, as seen here at several focal lengths with the 12-35 on the Panasonic AF100 camcorder:



With these cameras, you can also adapt parfocal video (or cinema lenses), as seen in this test from GanEdenVideo (a little shaky, but you get the idea):



Here's a smoother example (with star filter):



B4 adapters and parfocal video lenses are not that expensive. Here's a Fujinon 14x constant f1.7 parfocal zoom for $599 with a B4 to micro 4/3 ada... (and a 2X extender to avoid vignetting).

Hope this is helpful,

Bill
Hybrid Camera Revolution


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Ann Bens
Re: Zooming and focussing
on Jan 25, 2014 at 7:52:02 pm
Last Edited By Ann Bens on Jan 25, 2014 at 7:53:01 pm

I have the Nikon 7100 with a 18-200 lens (3.5-5.6). This is my travel lens, cause I don't want to change lenses all the time.
I usually film with my Canon XF100 but there are some situations (countries) where a semi-prof filmcamera is not allowed. Hence the use of the dslr.
Hence the question for fast/accurate focussing.

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Steve Crow
Re: Zooming and focussing
on Jan 25, 2014 at 9:57:43 pm

Yeah Ann the other problem with your current zoom lens is that it doesn't maintain the same aperture as you change zoom so when you zoom in your image will darken and you will have to adjust ISO or shutter speed (although I keep my shutter speed as 2x the frame rate pretty religiously which for me means 1/50 of a second most of the time)

A constant aperture zoom lens is not cheap - maybe look for a good used one if budget is an issue. Something in the 24mm-70mm range zoom lens is a very popular choice

Steve Crow
Crow Digital Media
http://www.CrowDigitalMedia.com


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Bill Bruner
Re: Zooming and focussing
on Jan 25, 2014 at 11:29:40 pm

Understand - thanks for the clarification. If you want a parfocal lens for your D7100, you might want to look at the new Sigma 18-35 constant f1.8 for Nikon ($799 on backorder from Adorama, marked up a few dollars, but in stock at Amazon).

Here is what it can do (shot by Erik Naso on his Canon C300 - please watch at 1080p):







Note that focus and exposure stay constant throughout the zoom range.

Again, hope this is helpful!

Bill
Hybrid Camera Revolution


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Ann Bens
Re: Zooming and focussing
on Jan 26, 2014 at 12:02:33 pm
Last Edited By Ann Bens on Jan 26, 2014 at 12:22:50 pm

That looks beautiful.
I have a look at the lens.
Thanks for your input.

Some of Nikons lenzes are a bit beyond my budget.
Is there much difference between Sigma, Tamron, Samyang and Tokina.

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Steve Crow
Re: Zooming and focussing
on Jan 25, 2014 at 9:52:32 pm

A great explanation Bill!

Steve Crow
Crow Digital Media
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Brian Cheng
Re: Zooming and focussing
on Apr 15, 2014 at 6:11:52 am

Hmm.... I'm very unexperienced here....
How do I tell if my lens is a par-focal or a vari-focal lens?
When I open the lens' user's manual, it just said "Canon EF-S18-55mm f/3.5-5.6 IS STM lens is a high-performance standard zoom lens equipped wIth an IS, and has been developed for EOS cameras compatible with EF-S lenses".

Help~~~

$$


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Steve Crow
Re: Zooming and focussing
on Apr 15, 2014 at 6:42:25 am

Brian,

I can't tell you absolutely for sure but here's what I strongly suspect - since this lens isn't even a fixed aperture and is not one of the super high end models I very much doubt it is safe to use the zoom in, focus and zoom out method.

Steve Crow


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