Re: Step Wedge

From: Sandy King ^lt;>
Date: 11/11/04-08:07:13 PM Z
Message-id: <a06020438bdb9cab45a67@[]>


You are correct in that the density values are total transmittance.
But since you are using the step tablet in the camera in front of the
film the density of the substrate must be taken into account in
giving the exposure, just as if you you were to place the material in
front of the lens as with a filter. Hope this makes sense.


>Hey Sandy,
>Thanks for the responses to the group- I hadn't even considered
>flare factor before I brought the topic up.
>My step wedge is hand calibrated by stouffer- at least it looks like
>it is. They wrote in ballpoint pen on the
>sleeve the actual densities of each wedge- I'm assuming someone must
>have actually measured it personally.
>If that is the case, I am guessing the density values must be total
>transmittance, including the substrate,
>but I might be wrong about that.
>Sandy King wrote:
>>For some reason I had it in mind that you wanted to compare of
>>different film, or perhaps of different developers. For what you
>>have in mind I think the method you suggest is certainly valid.
>>On a practical note, remember to take into account the B+F density
>>of the step wedge. This should be about log 0.05, or about 1/3 of a
>>stop, so you should probably increase your metered exposure by
>>about this much.
>>>I wasn't really planning on doing any hard core film comparisons with the
>>>test- just basically wanted to see if my shutter and lens and lightmeter
>>>are giving me close to the density that I am hoping to achieve when I make
>>>an exposure. Also, I was hoping to plot the curves using a few different
>>>development times to visualize the effects of plus and minus times.
>>>Since my negs are destined to be scanned, and corrected, and ultimately
>>>digitallly printed on film for contact printing, if my results are a 1/10
>>>stop off here or there, I could probably still sleep!
>>>On Thu, Nov 11, 2004 at 03:36:39PM -0500, Sandy King wrote:
>>>> Etienne wrote:
>>>> >
>>>> >As an abstract exercise (especially for someone who, like me,
>>>> >whips up his or her own negative emulsion for fun), it's interesting to
>>>> >know what the film does, on its own. But when I load my
>>>>holders, I'm after
>>>> >the most direct understanding of what my negatives are going to look like
>>>> >when they come out of the Jobo, and rolling all of the relevant practical
>>>> >factors into the material characterization gives me this.
>>>> >
>>>> But my point is not that practical testing in the camera is not
>>>> relevant, but simply that it is invalid as a means of comparing EFS
>>>> of different films. For that you need a system with a common light
>>>> source and some control that permits repeatable exposures to an
>>>> accuracy of about 1/10 of a stop.
>>>> Sandy
Received on Thu Nov 11 21:00:48 2004

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