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12-18-2010, 11:46 PM   #1
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hyperfocal distances

could some one help me out with hyperfocal distance for a 16-45....as it doesn't have a DOF indicator on the lens , how do you work out what the hyperfocal distance is at any given AP you have set the lens too without a DOF guide on the lens body ?

the reason I ask is that Im playing around with the movie mode. and rather than focus manually I wanted to set a small AP , then set the focus to the hyperfocal point. and then see if I can get away with the closest point that the DOF extends too....and get some half reasonable footage at say F22 without touching the lens...lazy I know. but i find it too hard to focus using the LV screen .....should wear my glasses I know....damn eyesight


Last edited by Tommot1965; 12-19-2010 at 12:42 AM.
12-19-2010, 01:29 AM   #2
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its all good, Ive found some great little dof calculators on the net...seems the best hyperfocal length for the 16-45 set at F22 will be 11 feet, that way all will be in focus from 18 inches to infinity when at 16 mm, and if zoomed in to 45 mm, from 6 feet to infinity will be in focus so that should be good if kept within those parameters

just gotta hope f22 will be enough light ...i believe the body increases ISO if a fixed AP is used in movie mode...thus helping out with the exposure until its limits are met...K5 should be better here ...anyone tried it against a K7 in this way ?

all this is good for well lit day light subjects id say
12-19-2010, 01:38 AM   #3
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You can calculate Hyperfocal distance using this formula:




Where H= the Hyperfocal distance in mm, f is the lens focal length in mm, N= the f-number, c= circle of confusion in mm. The circle of confusion is a mathematical construct-- Just use .020mm for small format Pentax sensors in this equation--do some research if you want to know why this number is used.
12-19-2010, 05:46 AM   #4
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Every hyperfocal distance has a corresponding hyperfocal scene width. When you focus on a scene at the hyperfocal distance, everything behind the scene is in focus. Similarly, there is a hyperfocal f-stop for every hyperfocal scene.

We usually want to know what f-stop we should use to make a particular scene hyperfocal.

The approximate relationship between hyperfocal f-stop, scene width, and focal length is simple for a Pentax DSLR:

Hyperfocal_f-stop ~ Focal_length_mm/Scene_width_meters

Examples:
A scene is 30' (10 meters) wide and a 50mm lens is used; the f-stop for hyperfocal conditions is:

Hyperfocal_f-stop ~ focal_length_mm/scene_width_m = 50/10 = f:5

Say a 20mm lens were used instead of a 50mm lens for the same scene:

Hyperfocal_f-stop ~ 20/10 = f:2 - you'd need to stand much closer to the subject in this case.

A scene is 15' (5m) wide and we want to use f:8, what focal length is needed for hyperfocal conditions?

8 ~ focal_length/5, or focal_length ~ 40mm

This relationship is easy to remember and easy to use. It is no different from the distance based hyperfocal equation usually used.

Dave

PS if you check this relationship with an on-line DOF calculator you'll find discrepancies of about 10-15%. That's because I rounded things off to make the equation easy to remember and use (I used c ~ .023 mm). For practical purposes it should be close enough.

01-01-2011, 03:05 PM   #5
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Easy to use HF scale

I wanted a quick hyperfocal guide for my lenses. I'd seen this calculator, but at $40 for a piece of plastic, no way!

I kept looking and found this site that has an easy to use calculator (and an easy to understand description of hyperfocal distance).

If you go to the bottom of the page you will find a "Hyperfocal Chart Calculator." Set the crop factor to 1.5, then go to the chart "Calculate Hyperfocal Distance" just below it. Fill in the top of the chart with your lenses' focal lengths.

As you can see on my chart below, the first five are my prime lenses, and at the end of the scale I put in two of the focal lengths I often use on my 55-300 zoom (ok, I don't have a 40mm yet, but I might get the Voightlander 40mm, who knows ). I next took a "screenshot" of that web page, opened it in a photo editor, cropped and made it contrasty for easy reading, and then printed it out. Folded it is about 4x4 inches and easy to pack for quick reference:



Last edited by les3547; 01-01-2011 at 05:04 PM.
01-01-2011, 03:34 PM   #6
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In a practical sense, when you don't have a distance scale (or even if you do!) focus on something at the desired distance through the view finder then consult the chart to determine the DOF produced by the aperture based on the resulting exposure setting. Use ISO to vary the aperture to get the needed DOF as required.

Or reverse the process and determine from the chart what focus distance is needed to accomplish your task and pick a target at that (estimated?) distance to set the lens. Once the lens focus is set to a known range, "focus with your feet" as you change location to maintain the DOF.

If you're going to focus on something that isn't yet in place, pre-focus on something else that IS present in the view finder at an equivalent distance and select the aperture/ISO needed to set the hyperfocal DOF. Caution: don't allow the exposure setting to track the focus point in this case.

Tape the lens at the appropriate fixed (focused) distance if necessary so you don't screw up the work you've already done. A broad, tight rubber band placed at the border of the zoom and/or focus rings may provide the necessary friction to prevent inadvertent movement.

Practice beforehand and use instant review to fine tune the results.

H2
01-01-2011, 03:58 PM   #7
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thanks for the tip Les...I did just what you suggested...but went for photo paper, and ill get it laminated and stick it in the camera bag...cheers
01-01-2011, 06:19 PM   #8
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QuoteOriginally posted by Tommot1965 Quote
thanks for the tip Les...I did just what you suggested...but went for photo paper, and ill get it laminated and stick it in the camera bag...cheers
Or even better, do as I did and download a dof calculator app for your iphone. (Dofmaster, if I remember correctly) - works a treat!

Tim

01-01-2011, 06:47 PM   #9
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Thank goodness someone brings up the topic of hyperfocal distance again. I have so much issue with this and although I have posted many questions (and receive many answers) in the past, I don't seem to get the hang of it....so I will ask again.

How do you hyperfocus something which is very far away.....eg. say a large field with nothing standing within 20m in front of you, or in a beach where the nearest mountain is like several hundred metres away....all using lenses such as DA14 and DA35 which lack the DOF markings?

I understand the usage of the software to determine the focus distance but with these kind of digital lenses, how do you do this?

sorry...silly question but i am still learning.
01-01-2011, 07:13 PM   #10
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ill try and answer that..if im wrong im sure someone will put me right


the calculator tells you at what distance the Dof will be from too infinity, if nothing is in focus before that point...at Given apertures relative to focal length


EG
the calculator that les put up shows that a 15 mm lense at 2.8 will be in focus from 12.5 feet from the focal plane, to infinity ...

.if a subject is focused on before the 12.5 feet, then DOF will extend 1/3 in front and 2/3 behind the subject....and the DOF will extend as the lens is stopped down...

EDIT

just reread your post....if your lens doesn't have a distance indicator..then you have to get the tape out Id guess, or make sure that whatever your focus point is, is within the hyper-focal DOF area

doesn't the DA 14 have a DOF indicator..and distance ?

Last edited by Tommot1965; 01-01-2011 at 07:27 PM.
01-01-2011, 07:18 PM   #11
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Elementary solution

It doesn't have to be read on the lens!!

Simply focus on something -- anything -- that appears to be at the desired hyperfocal distance.

E.g., if the chart says everything from 3.4 feet to infinity is in focus with the lens focused at 19.26 feet, lock AF or manually focus* on something -- anything -- at approximately 20 feet. The grass in front of you works fine. Then verify your results with that miraculous thing called "instant replay".

Just ensure you haven't locked exposure on a dark brick wall in shadow at 20 feet if that's not an appropriate setting for your actual subject. Then again, verify your results with that miraculous thing called "instant replay".

(* If man were meant to auto focus, Galileo would 've invented the SDM in the 16th century.)

H2

Last edited by pacerr; 01-01-2011 at 07:29 PM.
01-01-2011, 07:37 PM   #12
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Les
just looking at the chart again, are those distances at what point the Hyper-focal distance is ,

or at what point DOF will extend from/ to infinity, once hyper-focal distance is set ?

im thinking its the former..now I've reread it..and had a think about it .
01-01-2011, 08:39 PM   #13
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So if I am standing at the edge of a cliff shooting the ocean sunrise for example (citing my recent experience to Esperance, Western Australia), how and what should i focus at? there is nothing in front of me?
01-01-2011, 08:48 PM   #14
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QuoteOriginally posted by raider Quote
So if I am standing at the edge of a cliff shooting the ocean sunrise for example (citing my recent experience to Esperance, Western Australia), how and what should i focus at? there is nothing in front of me?
firstly set the Aperture that will allow Hand-held shooting..with the set ISO , then turn and focus on something along the beach that's well within the DOF of the hyper-focal length........then focus lock on that, then recompose on the sunrise

or go to manual focus and do the same...{no focus lock required}


id say at 35mm F5.6 anything about 15 or more metres away

does the camera not focus on the sunset Ok ?
01-01-2011, 09:42 PM   #15
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QuoteOriginally posted by raider Quote
How do you hyperfocus something which is very far away.....eg. say a large field with nothing standing within 20m in front of you, or in a beach where the nearest mountain is like several hundred metres away....all using lenses such as DA14 and DA35 which lack the DOF markings?

So if I am standing at the edge of a cliff shooting the ocean sunrise for example (citing my recent experience to Esperance, Western Australia), how and what should i focus at? there is nothing in front of me?
If there is nothing within 20 meters you need not concern yourself with depth of field or hyperfocal distance unless you are using a very long lens.

If you are on a cliff there is likely no foreground to be concerned about. Therefore you need not worry about depth of field.

In both instances set your lens at infinity and shoot the sunrise.

Mickey
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