Spot Meter Measurment of Transmission Densities

[Sean]

APUG ORIGINAL CONTENT
New Article By: R, Eugene Smith (Dr. Bob)

(there was a url link here which no longer exists)

You can discuss the article in this thread.

 

[Sean]

I plan on getting a good spotmeter soon and will definitely try this out before investing in a densitometer.

 

[dr bob]

You should note in the article that the method is not intended to replace a densitometer. I just don't need the sophistocation of a densitometer or I would have one. Also try making the light source mask aperture as small as possible to prevent interferring glare.

In these times of changing materials, I believe this method may gain merit. And remember, practice - practice -practice.

 

[JHannon]

I have been using a spotmeter and find it accurate enough for my film tests. I use a reverse mounted 50mm lens to get the meter to focus close. I use a rear lens cap with a hole drilled in it to reduce the effects of ambient light. My light source is a small light table for viewing negatives.

Thanks, Dr Bob for a good description of the formulas and for your comparisons between the spotmeter and the densiometer. I know how much time is involved in the tests..

Is it really necessary to have the three digit accuracy of densiometers for general film testing (finding personal ASA etc).? The spotmeter seems to be accurate enough for these tests.

Regards,
John

 

[dr bob]

It is not necessary to always to use three significant figure data in normal photographic applications. It may be required in comparison of experimental results where the subject is the adjustment of mechanisms or formulae.

I must have some psycho-kinetic effect on people – Along with comments on the Spartan appearance of my darkroom, some folks seem to take issue that as an engineer, I seem to take unwarranted liberties with aperture and shutter settings (Don’t you use ¼ stops for precise exposure ?), and preparing toner baths (That lacks a ml being 100 ml, like the label says!) I guess people think all engineers are rocket scientists. Little do they realize we are often most happy to get a two-digit correlation (often even one) and we are joyful beyond belief if we get three.

All accounts of Edward Weston’s operations that I have read or heard indicate that he was totally out of the mathematical and theoretical realm. Yet he produced some of the most engaging images ever. (I wish!)

 

[Silverpixels5]

I seem to take the attitute of my college thermodynamics prof by working with the moto: '...it's close enough for government work...'

 

[LFGuy]

some folks seem to take issue that as an engineer, I seem to take unwarranted liberties with aperture and shutter settings (Don’t you use ¼ stops for precise exposure ?), and preparing toner baths (That lacks a ml being 100 ml, like the label says!) I guess people think all engineers are rocket scientists. Little do they realize we are often most happy to get a two-digit correlation (often even one) and we are joyful beyond belief if we get three.

Amen to that!

Thanks for the great article, I'll be trying this out soon.

 

[Jorge Oliveira]

Very nice article.
Very 'engineer' text.


Jorge O

 

[Flotsam]

(Don’t you use ¼ stops for precise exposure ?), and preparing toner baths (That lacks a ml being 100 ml, like the label says!)

All accounts of Edward Weston’s operations that I have read or heard indicate that he was totally out of the mathematical and theoretical realm. Yet he produced some of the most engaging images ever. (I wish!)

The most remarkable photographer that I have ever had the opportunity to learn from was a portraitist that spent his whole career from teenager to retirement at a very old, prestigious New York studio. He was a true master at posing and lighting people but as far as photography was concerned, it was 100% craft. He used a Packard bulb shutter and hand-timed his exposures by feel, in the darkroom everything was done by eye and experience. When printing he would tweak down his contrast by sprinkling unmeasured amounts of Elon into his developer tray between prints and he spotted his prints with Japanese Sumi ink. His results, in depth and tone, were consistantly superb.

Me, I use Copal shutters, an expensive exposure meter and variable contrast paper but I still spot all my B&W prints with Sumi ink, it works great.

-Neal

 

[JHannon]

It is not necessary to always to use three significant figure data in normal photographic applications. It may be required in comparison of experimental results where the subject is the adjustment of mechanisms or formulae.

I must have some psycho-kinetic effect on people – Along with comments on the Spartan appearance of my darkroom, some folks seem to take issue that as an engineer, I seem to take unwarranted liberties with aperture and shutter settings (Don’t you use ¼ stops for precise exposure ?), and preparing toner baths (That lacks a ml being 100 ml, like the label says!) I guess people think all engineers are rocket scientists. Little do they realize we are often most happy to get a two-digit correlation (often even one) and we are joyful beyond belief if we get three.

Hi Dr Bob! My question on the three digit accuracy was not meant to poke fun at anyone, you should see my photo/darkroom notebook!.. It was merely to ask if the accuracy of a dedicated densiometer is really needed for practical work, will the spotmeter do?. Looks like it will based on your measurements....

 

[middlecalf]

Other sources indicate that pyro developed negatives can't be measured properly with a densitometer. Does this method suffer similarly?

thanks,
Paul

 

[Donald Miller]

Yes it is true that pyro stained negatives cannot be measured accurately by a visual density measurement. Normally a blue channel reading on a color densitometer will be nearer for non UV light exosure sources. (I use an Xrite 310TR.) For those who use an UV exposure source then a UV reading densitometer such as the Xrite 361 T will give accurate readings.

However it I were trying to do this economically I would avail myself of the data that Bob Herbst posted on www.unblinkingeye.com. He has a correlation of a visual density to blue channel and to UV density in his article. By using the visual density of the spot meter one may be able to come to some closer silver and stain density effect then the visual reading alone would indicate. The one caveat is that if one is using Pyrocat as opposed to PMK or ABC the UV correlations may differ somewhat since the brown stain that Pyrocat imparts is more actinic to UV transmission then the other developers that I mentioned. I am not sure what developer that Mr. Herbst used. It may have been Pyrocat but I am not sure.

 

[dr bob]

Other sources indicate that pyro developed negatives can't be measured properly with a densitometer. Does this method suffer similarly?

First let it be said, this ain’t rocket science! I gave that up when I retired. This is a quick and dirty method of checking my technique especially in light of all the “new” products coming out and the demise of some of my favorite “oldies” forcing changes.

I have no data regarding staining developers. The Minolta spot meter has a pretty good response to colors excepting deep reds for example. It has no “correction” such as the Zone VI reworked Pentax but the very basic measurements I have made “around the house” indicate a rather linear response to the photographic spectrum overall.

The problem is, how can one translate readings to the final paper product? My work on this aspect is ongoing. So far, without a reflection densitometer, it has not proving easy. I make a contact print on the medium I will use for the final product and scan it with the mate’s computer equipment. Using the “dropper” tool in Paint Shop Pro, I determine the average gray scale level of the areas of interest and compare the reading(s) with the max and min density areas graphically.

So far this has not yielded a reliable match. The shapes of the curves are quite comparable but what does that mean? There are too many variables in the print system. If I can clean up the process…. Oh, the heck with it! I am only interested in the relative scale of my negatives. If the gray scale I determine in the negative correlates with my expectations I’m happy. If I have done something wrong, this method will "expose" it (puns: don’t ya hate ‘em) and indicate a "solution", e.g., pyro instead of D76.

 

[Donald Miller]

000

 

[dr bob]

“If you are wanting a means to translate transmission density readings using a spot meter to print tonalities, I wonder if a Stouffer step tablet exposure onto the paper would not be a more reliable place to begin. One could then use the spot meter to read the transmission densities of the step tablet (which are known) and then correlate those readings to actual density measurements from camera negatives.

From the contact print of the step tablet onto the paper used one could then arrive at the print tonalities as they relate to transmission densities from negatives. “

This is certainly a good method to start correlating print materials and techniques to spot meter readings. If you have access to the proper step tablet, would you consider giving it a try? The only printing aid I have is the Kodak wedge that is not calibrated in density. Even so, my attempts using it have not been to my satisfaction.

”I realize that for Zone System practitioners the normal place to begin is with film speed (EI). This is normally proposed to be .10 above film base plus fog. The next parameter is development time which is proposed as being 1.10 at Zone VIII with a diffusion light source. By my tests with a densitometer of the exposure scale of several papers these values that are commonly proposed may be close to correct but may not be accurate enough to realize the full potential of the materials used.”

Absolutely correct. That is what charms me about apug. There is always an unknown quantity and/or quality which remains just within reach but often is difficult to grasp. All the high tech and computerized gear in the world won’t help without the human factor digging in and solving problems to produce that special “artistic” creation. Any help is appreciated.

Truly, dr bob.

 

[lee]

dnmilikan said," realize that for Zone System practitioners the normal place to begin is with film speed (EI). This is normally proposed to be .10 above film base plus fog. The next parameter is development time which is proposed as being 1.10 at Zone VIII with a diffusion light source."

Don am I reading this correctly? I think the Zone VIII is around 1.30 with a diffusion light source. That has always been my target when testing film. 1.10 would be in the neighborhood of zone VII me thinks.

lee\c

 

[Donald Miller]

000

 

[Donald Miller]

000

 

[Jan Brittenson]

I just tried this myself using a Spotmeter F to read 320TXP processed in Rodinal 1+100. I sandwiched a slightly trimmed 21-step tablet in a film holder and made one exposure to find the fogging speed and toe shape, and one to produce a tonal curve up to Dmax. Pretty neat, although the meter clearly doesn't like reading low-density areas. Might work better if I add an ND filter. I cut a hole in black plastic to block out stray light and then read the patches on the light table through the mask.

So... how do I produce a curve? I don't have MS Office software, but could get OpenOffice if that helps. I can also use Linux software.

 

[Jorge Oliveira]

I'm testing OpenOffice in the laptop (and BTW it's time to upgrade it).

Use the spreadsheet function (equivalent to Excel).

Jorge O

 

[Jan Brittenson]

The spreadsheet in OpenOffice 1.1 works reasonably well, but it seems like the export functions could use a little work. If I export to PDF I get an enormous page with my sheet in the upper left corner. If I export to HTML, then it does lots of weird stuff like render text as JPEG, but tables as HTML without borders etc. The title I put in went down the page in a little box instead of across, etc. I guess I could grab the chart it output in JPEG for the HTML page and redo everything in the OO web page editor, but that's starting to become too much fiddling and work for something so simple.