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  #1  
Old 19th March 2010, 03:10 PM
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Question New Flash Spot Meter

I am looking to buy a Meter to measure Flash, both incident and spot readings.

Does anyone have a working knowledge of one of these machines that they would care to share ?

I have used Incident Flash Meters in the past but would like to know where the zones of the subject will fall – hence the want for the Spot Meter function.

As far as I can tell, there are two choices, the Kenko 2100 (http://www.robertwhite.co.uk/product...1886&PT_ID=439) or the Sekonic L758D (http://www.robertwhite.co.uk/product...1139&PT_ID=179)

I went to Focus 2010 at the NEC a couple of weeks ago with the intention of finding out about wheat the devices could and could not do.
I saw the Sekonic but sadly the representative knew less about meters than I did.
It was rather hard to take anything he said seriously, particularly after making frequent mistakes about some of the things I already knew

Thanks

Martin
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Old 19th March 2010, 04:26 PM
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I've used the Sekonic, and its very good. Once you've worked your way around it its very easy and quick to use. I'm hoping to get it once I can afford it.
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  #3  
Old 19th March 2010, 04:41 PM
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I have an earlier version of the Sekonic L758 (the L558). Not much to say really - it works! The memory feature is useful for finding the SBR quickly if you are into that sort of thing (point at shadow, take reading, store, point at highlight, take reading, look on display for range).

It works well with flash, either detecting the flash itself or via synch leads and understands about flash Vs ambient if you change the shutter speed.

It's not 100% waterproof: "showerproof" I think is the term...

Had mine a few years and use it whenever I go out shooting so seems to be fairly robust, but I have yet to drop it. Cover for the spotmeter lens keeps falling off (it is tethered so you don't lose it - a minor nuisance tho).
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Old 19th March 2010, 04:55 PM
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The answer is both simpler and more complicated than you might imagine.
Incident meters don't do zones. That's it. It's as simple as that. They measure the luminosity of light falling on the subject and convert to camera setting values which will give a mid point on the film curve. What you want to know is what that mid point is in terms of a zone.

Well I can tell you it won't be zone V on a zone system going from zone 0 to zone 10. The meter manufacturers use a scale of 7 or 8 stops and place the reading in the middle of that.

A Print holds 7 stops for the sake of argument. The meter manufacturers use a scale designed to fit paper ( or thereabouts ). So looking at my chart below a 7 stop system goes from 0 to 7. Zone 7 in this 7 zone sytem is 64 units of light. The mid point of this 7 zone system is zone 4 which is 8 units of light. 8 units of light is 12.5% of 64 units of light.
It so happens that years ago I enquired of minolta what formula they used in my Minolta Spotmeter F. They told me the full formula and that their K factor was 12.5. That tells me it is calibrated to a 7 stop range.
The question is what is your prospective meter calibrated to? Well if its an older one I suspect it will be very similar to 12.5% using a 7 stop system. But if its a newer one designed for digital cameras then I'd suggest they have modified the K factor to suit the dynamic range of the top of the line digital cameras. So you better find out what the Nikons and Canons are capable of. But the meter manual may tell you.

Also note that 18% reflectance on a 10 stop range as in the zone system is around zone 3.5. But on a 5 zone system 18% is bang in the middle at zone 2.5 near as damn it.

So assuming your B+W film development has been calibrated to a 10 zone system and you use the corresponding film EI to achieve that, then if you meter something you think should be zone V with a spot meter it will give you readings to place 16 units of light on print value 5.
But if you use the same meters incident mode then it will give you a reading which places 8 units of light on a print value 5 assuming it is using a 12.5% K factor. i.e. the results will be different.
Only if you calibrate film development to a zone scale which puts the meters K factor percentage in the middle of the range will the spot meter and incident meter give the same results without modification.
Tricky isn't it.


HTML Code:
0.5        zone 0 
1          zone 1
2          zone 2
4          zone 3
8          zone 4
16         zone 5
32         zone 6
64         zone 7
128        zone 8
256        zone 9
512        zone 2
p.s. It would be nice if the modern meters allowed you to select your own K factor to suit the materials and/or camera type you are working with since these are all variables. For all I know they may but I haven't read the manuals so don't know if you can.

Last edited by Argentum; 19th March 2010 at 05:14 PM.
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Old 19th March 2010, 05:14 PM
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Martin
I have exactly the Kenko 2100 and am very happy with it. The measuring is very acurate and the all device is very easy to use. Also I like the circle of measurement, very small for little spot tight readings!
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  #6  
Old 19th March 2010, 05:38 PM
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Quote:
Originally Posted by percepts View Post
The answer is both simpler and more complicated than you might imagine.
Incident meters don't do zones. That's it. It's as simple as that. They measure the luminosity of light falling on the subject and convert to camera setting values which will give a mid point on the film curve. What you want to know is what that mid point is in terms of a zone.

Well I can tell you it won't be zone V on a zone system going from zone 0 to zone 10. The meter manufacturers use a scale of 7 or 8 stops and place the reading in the middle of that.

A Print holds 7 stops for the sake of argument. The meter manufacturers use a scale designed to fit paper ( or thereabouts ). So looking at my chart below a 7 stop system goes from 0 to 7. Zone 7 in this 7 zone sytem is 64 units of light. The mid point of this 7 zone system is zone 4 which is 8 units of light. 8 units of light is 12.5% of 64 units of light.
It so happens that years ago I enquired of minolta what formula they used in my Minolta Spotmeter F. They told me the full formula and that their K factor was 12.5. That tells me it is calibrated to a 7 stop range.
The question is what is your prospective meter calibrated to? Well if its an older one I suspect it will be very similar to 12.5% using a 7 stop system. But if its a newer one designed for digital cameras then I'd suggest they have modified the K factor to suit the dynamic range of the top of the line digital cameras. So you better find out what the Nikons and Canons are capable of. But the meter manual may tell you.

Also note that 18% reflectance on a 10 stop range as in the zone system is around zone 3.5. But on a 5 zone system 18% is bang in the middle at zone 2.5 near as damn it.

So assuming your B+W film development has been calibrated to a 10 zone system and you use the corresponding film EI to achieve that, then if you meter something you think should be zone V with a spot meter it will give you readings to place 16 units of light on print value 5.
But if you use the same meters incident mode then it will give you a reading which places 8 units of light on a print value 5 assuming it is using a 12.5% K factor. i.e. the results will be different.
Only if you calibrate film development to a zone scale which puts the meters K factor percentage in the middle of the range will the spot meter and incident meter give the same results without modification.
Tricky isn't it.


HTML Code:
0.5        zone 0 
1          zone 1
2          zone 2
4          zone 3
8          zone 4
16         zone 5
32         zone 6
64         zone 7
128        zone 8
256        zone 9
512        zone 2
p.s. It would be nice if the modern meters allowed you to select your own K factor to suit the materials and/or camera type you are working with since these are all variables. For all I know they may but I haven't read the manuals so don't know if you can.
oops error in above post...

18% is around zone 7.5 not zone 3.5 on a 10 zone system. I meant to say that on a 10 zone system, Zone V is only around 3.5% reflectance not 18% as is commonly touted.
And in the chart 512 units should say zone 10 after it but you probably guessed that one.
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  #7  
Old 19th March 2010, 08:10 PM
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I've got a Kenko 2100. Mainly use it for landscapes with spot, but it also does flash pretty well. Will display the lighting ratio between flash and ambient which is a nice touch.
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Old 19th March 2010, 09:41 PM
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I've been reading up on K factors. It seems my understanding of them is incorrect so ignore what I wrote above. However, I think the principle holds true in that if you have calibrated film dev to a 10 zone system your spot readings as per the zone system won't match your incident reading. But if you have flash spot metering then why would you be using incident too or visa versa.
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Old 20th March 2010, 07:11 AM
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Quote:
Originally Posted by percepts View Post
I've been reading up on K factors. It seems my understanding of them is incorrect so ignore what I wrote above. However, I think the principle holds true in that if you have calibrated film dev to a 10 zone system your spot readings as per the zone system won't match your incident reading. But if you have flash spot metering then why would you be using incident too or visa versa.
In that case would you like to make a modified post and I will remove the other two?
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  #10  
Old 20th March 2010, 06:43 PM
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Quote:
Originally Posted by Dave View Post
In that case would you like to make a modified post and I will remove the other two?
See http://en.wikipedia.org/wiki/Light_m...tion_constants

I am now uncertain exactly how it works since the information that minolta gave me and what is in the above link do not match. The calculations are different and I am uncertain where on the film curve the meter manufacturers readings are placing the exposure. i.e. at a mid point or higher. Therefore I can only speculate. It would be better if someone with one these meters did a test to see if the incident and spot readings are the same or different. I suspect they will be different but cannot be certain exactly why.

p.s. just delete my posts above as they are wrong.

Last edited by Argentum; 20th March 2010 at 06:53 PM.
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