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OT Safe handheld speed and DOF with digicam lenses


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Ok you or I have just bought a Leica Digilux 2 and want to know how

slow a shutter speed one can safely handhold down to.

 

Traditionally we are told it is 'safe' down to the reciprocal of the

focal length. So with a 28mm lenses we expect (with a steady hand)

to get acceptable sharpness at 1/30th handheld (for the purposes of

a normal sized print up to 10x8)

 

However the lens on a Digilux 2 has a lens with a wide focal length

of 7mm (equivalent to 28mm on a 35mm film camera) so can we safely

handhold down to 1/7th of a second or is the equivalent focal length

(1/28th) still the correct length to use in the calculation? My

experience with my own digicam suggests the 'equivalent' focal

length is the correct one to use.

 

Also I would like to get opinions on DOF.

 

I have just programmed a 'snap' mode into one of the 'custom'

settings on my digicam for the purpose of removing AF and improving

the response time when having to take quick shots. For the purposes

of calculationg DOF I had to use the 'actual' focal length (7.8mm

with my camera) and preset the manual focus, in custom mode, to

about 4 metres giving a DOF of 1.89 metres to ininity at f2.8. I

have done this and it appears to be correct in practice. I get

acceptable sharpness (at 7.8mm 'real' focal length and f2.8 when

focus is fixed at 4metres) from about 2 metres to infinity.

 

Can some 'techy' type explain why using 'actual' focal length is

good for DOF / hyperfocal calculations but it seems that

the 'equivalent 35mm' focal length must be used for calculating the

correct maximum shutter speed that will yield acceptable sharpness

when handholding?

 

Thanks.

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Hi Trevor,

 

for DOF calculations I use a smaller Circle of Confusion (COF - group of Phtographers discussing DOF) to compensate for the bigger enlargement factor. to be true, I used the Minox DOF Table for my 8.8x6.6mm Powershot :-)

 

The visibility of Camerashake seems to me more connected to subjectdistance than focal lenght. The farther away, the more is covered by even a small angle of tilting.

Oops, this is the part of the english language I haven't learnt, geometry was tought in german!

 

You and your camera are one point of a triangle the distance is the second and the subject height the third point. alpha is the angle between the horizontale distance and the tilted line to the subject height. The longer the distance, the smaller is Alpha and variations of Alpha have a bigger effect.

 

Is this understandable?

 

 

Volker

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However the lens on a Digilux 2 has a lens with a wide focal length of 7mm (equivalent to 28mm on a 35mm film camera) so can we safely handhold down to 1/7th of a second

 

 

Yes that is correct. Small-sensor digicams are therefore virtually unshakable. I love em! And I love large DOF too; things weren't meant to be unsharp. It's progress!

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Volker's partly right, but seems to forget about object size in the image: a degree of shake will create a double image with the same displacement for near objects as for far objects because the near objects are larger in the image (I know this from practice as well as theory - plenty of my pictures have some shake in them). This is one of those things that is much easier to show in a sketch (Thanks to Skully for his patience in showing me how to get a sketch into a post) so I'll add a sketch if it would help.

 

However, I agree that camera shake is more to do with the relationship between the angle of shake and the size of the resulting picture, so it is all about equivalent lens focal lengths. If you take a picture with a 50 mm equivalent lens in any format and view the picture at the same size (eg 8 x 10), the degree of visible shake will be determined by the angle the camera shakes through, not the format. I can also attest to this from practical experience.

 

A side issue: why should someone who understands the technicalities etc of photography be labeled a 'techie'? Knowing one's craft does not diminish one's aesthetic abilities at all.

 

Best, Helen

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Possibly to answer Bee's comment: I find digital cameras like the D2 to be easier to hand-hold at slow speeds because nothing moves inside them so they shake less. The same angle of shake will create the same double image regardless of the format. There is nothing magical here.

 

Best, Helen

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I have no idea what Helen and Volker are saying, so it could be we all agree or disagree or something in between. So just to reiterate: the pictures I take with a 28mm film point and shoot, at slow speeds, look more blurred than those I take with the equivalent 7mm of a digi p/s, at the same shutter speed, same object distance and same print size.
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What should think of camera shake as having a relationship with "angle of view" instead of "focal length". The "1/f" rule of thumb is really just a convenient coincidence for 35mm, if you want to adapt it to other formats (either smaller formats like digicams or larger formats like MF), it's simple enough to just use the "35mm 'equivalent' focal length" and continue to apply a 1/f rule of thumb. All that said, no two pairs of hands are equally shaky, nor is a given pair consistently shaky every day (e.g. consider your recent caffeine intake!), so do consider that one camera may be more or less shaky in your hands due to physical considerations.

 

A depth of field calculator needs to know your distance, aperture, true focal length (i.e. 7mm), enlargement factor (between sensor/film and print), and required target on-print resolution. These last two elements are typically bundled up into a "circle of confusion" parameter. As you move from one format to another, your enlargement factor changes (assuming your print size remains constant), and so you need to adapt your CoC. These changes are linear with respect to format, so with the Digilux2 you should use a CoC that's 1/4 the CoC you might use on 35mm film, as the sensor is 1/4 the width of a frame of 35mm film.

 

If you're not using a calculator or chart, but just want to relate the Digilux 2 DOF to your "experience" with 35mm film, apply a 4x factor to the aperture. For example, given comparable subject distance, and a 1/4 true focal length on the Digilux2 to provide comparable subject framing, the Digilux at f/2 will give comparable DOF as a 35mm film camera at f/8.

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1) as to "safe shake speed" - basically it is the same for equivalent focal lengths (field of view). The Digilux (or whatever) at "28mm" will be as hand-holdable as a 35mm film camera with a true 28mm mounted. I ga-rawn-tee my Digilux at "90mm" (true FL = 22.5mm) shows shake effects more like a 90 on an M6 than a 24/21.

 

2) However, non-SLR digicams a) require less force/movement to trigger the shutter, which is just an electrical contact, not a mechanical linkage, and b) don't have shutter curtains/blades thrashing around inside. Thus they may well be a bit more "hand-holdable", all other things (shutter speed, "focal length") being equal. My DL2 is certainly smoother even than an M6, which is hardly a shake-prone camera.

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