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Which focal length can I expect most minimum focus distance?


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#1 Ira Ratner

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Posted 31 August 2008 - 10:24 AM

I have the stock 17-69 zoom on my K3, which indicates a minimum focusing distance of 6 feet.

For my holograms, since I'll be shooting on a semi-circular track, that means I would need a minimum 6' radius track. And when you add the larger outside track, that takes up a lot of space that I just don't have in my living room and I don't have a garage. (Poverty sucks.)

I also have both fixed Asahi 55mm and 28mm, so as far as focal lengths go, will either of these allow me to get in there a lot closer, so I can get away with a smaller track? The maximum I'll be filming is from the top of someone's head to their waist.

I know there are big issues like final quality, possible linear distortion from using a wide angle, etc., but since this is for holograms, I don't think the basic rules of filmmaking apply.

Thank you all for putting up with my stupid questions, and may everyone near Hurricane Gustav stay safe.

Edited by Ira Ratner, 31 August 2008 - 10:27 AM.

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#2 Jason Debus

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Posted 31 August 2008 - 02:55 PM

Hi Ira,

I don't know the minimum focus of the Asahi lenses but I've used a close-up lens kit to get around the minimum focusing of the stock k3 lens. A x3 close-up filter is essentially a magnifying glass/filter which allowed me to get within 1 foot of the subject with the stock k3 lens.

As far as which focal length has the 'best' minimum focus, I wouldn't use focal length to determine that, it all depends on the lens.

Hope this helps!

Jason
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#3 Adrian Sierkowski

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Posted 31 August 2008 - 03:19 PM

To echo Jason, it does depend on the lens, though you must also remember, the wider the lens, generally given the same subject distance and same stop the deeper the DoF.
For example, my 9.8mm lens will have more in focus @ F4 and 10 ft than my 25mm lens will. Of course, the Field of View won't match at all.
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#4 Ira Ratner

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Posted 31 August 2008 - 04:06 PM

Thanks, guys.

I probably didn't (as always) express my end game well enough.

At a 77mm diameter for filters for a stock K-3 lens , we're talking Cokin here for a closeup filter, correct? But if I'm shooting with a 55mm prime, and just shooting waist to top of head, even less, do I get a better--meaning to say a SHORTER--minimum focusing distance than I would with a zoom, based on the very nature of primes versus zooms?

I ask because I just bought a 3-filter (+1, 2, 3) Tiffen closeup set at 49mm diameter which will work on my 28 and 55, but which is totally useless on the K-3's zoom because of its 77mm filter size.
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#5 David Auner aac

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Posted 31 August 2008 - 04:48 PM

At a 77mm diameter for filters for a stock K-3 lens , we're talking Cokin here for a closeup filter, correct? But if I'm shooting with a 55mm prime, and just shooting waist to top of head, even less, do I get a better--meaning to say a SHORTER--minimum focusing distance than I would with a zoom, based on the very nature of primes versus zooms?


Yes. Normally, primes will focus closer than zooms. The rule also says that shorter focal lengths will generally focus closer than longer lenses. Of course, the exception is macro lenses which tend to be longish but also focus very close (I have a 55/3.5 Nikkor that focuses down to some 10-15cm/4-6" IIRC).

Cheers, Dave
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#6 John Brawley

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Posted 31 August 2008 - 04:50 PM

I have the stock 17-69 zoom on my K3, which indicates a minimum focusing distance of 6 feet.

For my holograms, since I'll be shooting on a semi-circular track, that means I would need a minimum 6' radius track.


Sorry to distract from the topic, but how do you make holograms with a K3 ?

jb
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#7 Ira Ratner

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Posted 01 September 2008 - 07:11 AM

Sorry to distract from the topic, but how do you make holograms with a K3 ?

jb


I shoot 180 frames of the subject in a semi-circle (one for each degree of a semi-circle), and the film gets Tele-cined to digital stills for delivery to the hologram supplier. (They have a magic machine there.)

If I can rig a filmholder, I might even take a crack at scanning the frames myself, but I know that's wrought with danger and would probably be too labor intensive.

I know there's a totally digital solution for me to shoot these, but I'm getting into 16mm anyway (just a beginner), so I figure this will be good practice working with the camera, lighting and metering, tracks, etc. Also, if this economy ever picks up, I'd like to do this as a sideline. I'm hoping to one day shoot a bunch of people (those with big egos) on a 100' reel, because you can fit a lot of sequences at 180 frames each. Once processed, I can then review on my editor, pull my best 180 for each, and either scan or send the spliced bunch on a reel to the Telecine house.
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#8 darrin p nim

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Posted 02 September 2008 - 04:09 PM

I apologize in advance if this is not what your are requesting but lens diopters will help increase close focus for your K3 zoom lens.

Partially discussed in: http://www.cinematog...showtopic=33034
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#9 Ira Ratner

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Posted 02 September 2008 - 07:53 PM

Thanks for the input, Darrin.

The thing is, those correctors really mess with quality. They're a last choice kind of thing, and if you have the lens to do the job without them, it's like apples and oranges:

You stay away from them.

Edited by Ira Ratner, 02 September 2008 - 07:54 PM.

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