Which densitometer for B&W?

<p>Hi,<br>

I've been developing the rolls of b&w film I shoot for two years. To determine my EI of several films and define my dev times I've been using the densitometer function included in Vuescan, but, as I'm not sure if this function is accurated, I've decided to buy a densitometer in e-bay.</p>

<p>I mostly develop with PMK so I need a densitometer capable to read color.</p>

<p>What are your recomendations.<br>

Are X-Rite 880<a href="http://cgi.ebay.es/X-RITE-880-COLOR-PROCESS-CONTROL-DENSITOMETER_W0QQitemZ200348431048QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item2ea5b272c8&_trksid=p3286.c0.m14&_trkparms=65%3A12%7C66%3A2%7C39%3A1%7C72%3A1315%7C240%3A1318%7C301%3A1%7C293%3A1%7C294%3A50"> </a> and 890 good for my purposes?</p>

<p>Do I need some kind of card to calibrate the densitometer?</p>

<p>thanks</p>

<p>You need a step wedge to calibrate any densitometer. Available from Stouffer.</p>

<p>You may want to also look into a site called LabX. It is an auction site for used scientific equipment. There is a photo section. I have never used this site, except to look around, so I don't know how smoothly things will go, but there was a great variety of equipment when I visited last. A link to the Lab Equipment > Photography page: http://www.labx.com/v2/newad.cfm?catID=104</p>

<p>There's usually a densitometer in there somewhere.</p>

<p >The densitometers you mentioned are strip reading instruments. They are designed to handle pre-exposed and frozen test materials made and sold by all major film makers. These strips are pre-cut to a specific size and pre-exposed in locations that form a specific pattern. It will be difficult for you to use these instruments on films that you have exposed. The size and placement of the points you wish to read will not correspond to locations on the pre-exposed test strip. You need a unit that will allow you to place the probe at locations of your choosing. </p>

<p > </p>

<p >As to black-and-white and color densitometers. For black-and-white work you want an instrument that reads what is called “visual”. Years ago densitometers were non-electronic; the operator turned a dial while peering through the instrument. The view was two fields superimposed, the operator turned a calibrated dial and when the two fields matches as to density, the value was read. Today’s densitometers for black-and-white use a sensor and filter that delivers the same values. This is called a “visual” calibration and the Wratten 106 filter is used. </p>

<p > </p>

<p >Densitometers for color films use a strong red – green – blue filter. Red is Wratten 92 Green Wratten 93 and Blue is Wratten 94. For critical work densitometer makers fit “status” filters. These are laboratory grade and there are separate sets for color negative film, color papers and slide films. </p>

<p > </p>

<p >It is unlikely you will be able to purchase a black-and-white only instrument. Modern instruments will read red – green – blue and visual. You do not need “status” filters for your application. I think the visual mode will serve your needs. </p>

<p > </p>

<p >To calibrate any transmission densitometer you need a calibrated step tablet. A strip of film with 21 steps of density and a data sheet that states the density of each step. The densitometer you purchase will include such a strip. You can buy a Step Tablet # 2 from Kodak. The steps are 0.15 density units apart. </p>