Wednesday, August 3, 2011

Light Meter

The light meter I use is a Sekonic Studio Delux. It can measure light as reflected or as incident. Reflected light bounces off the subject, while incident light falls onto a subject. I had been using reflected light for a long time and never really figured out what the ISO of emulsions was. Now I use incident light readings exclusively and get better results. The light source is independent of the subject and is not dependent on what is being photographed.

A white plastic dome is placed over the sensor in order to measure incident light. Readings are taken from the subject with the meter facing the camera. If it is bright outside a screen is placed in front of the sensor to block some of the light. In that case the dial must be read a special way. Usually, as in low light conditions, black numbers are used. There are red numbers which are used when the "high slide", as it is called, is inserted. Those numbers are to the left; the dial is rotated clockwise and they are revealed.

On a bright sunny day the amount of light is usually 320 give or take a block with the high slide in front of the sensor under the white plastic dome. When you aim the light meter at the camera from the subject and depress the center button the red needle will move up to 320 or 320+1 more block; let go and the needle is fixed in place.

The large dial is in two parts. It looks black but there is a white part under it. That moves a red pointer. The red triangular pointer is aligned with the needle. It serves to remind you of the reading so more can be taken. The black dial moves a scale of numbers. The numbers are the same as the needle numbers and are to be aligned with one or the other triangles in the white scale inside the dial. The red scale is used with the high slide and the black scale is used without it. 320 is put over the red H.

A little white square shows the ISO setting. The lowest setting is one click below 6. ISO of Liquid Light is below that. One full stop will raise or lower the number 6 by twice or half. Above 6 is 12, below it and not shown is 3. 320 by the red H is moved over so that 160 is on the red H making ISO to be 3 when the ISO is on 6 (one click up from the maximum). Then move it again so that 80 is aligned with the red H and ISO is 1 1/2. Move it again and you get 40 on H and 3/4.

There are two dots between the 6 and 12. ISO decends from 6, 5, 4,3, 2 1/2, 2, 1 1/2, 1 1/4, 1, 3/4.

That is how I have been thinking. The dial, however, shows different numbers; ISO is indicated above the f16 number as 1, 2, 4, 8. Not 6. I suppose the lowest number on the dial is actually 6, one click lower than the number and not aligned with it, but since it does not align I don't use it that way.

At the bottom of the dial on the light meter a red 1 will align with white 16. ISO is 1. Bright sun is f 16 at 1 second. That is -3 stops or three more stops of light from 6, when foot candles are 320, my way.

Monday, August 1, 2011

The Scientific Method

The High School Chemistry book begins with a teaching about the scientific method. Simply stated, that is to 1) State the problem. 2) Gather observations. 3) Form a hypothesis. 4) Conduct experiments. 5) Evaluate the results.

1) State the Problem. Now I have a problem with two plates made so far. One of the plates is the Liquid Light bracket test and the other is the better work photo of the Field House that followed. The problem is that both have the same exposure, part of the bracket test has the same exposure as the Field House. The biggest part of the problem is that when I developed the bracket test I could not see any image form in the area that has the same exposure as the Field House, but when I developed the Field House photo it was observable.

Without the present study of the scientific method I would not pursue it. I went right past it and onto making large format images.

2) Gather Observations. I take a lot of notes when working. The notes are written again into a word processor document. I now have a format for all good photographs and some of the bad ones. A photograph fills the width of the page at the top. Under it, in bold, the title. The first paragraph under that lists the size, date, emulsion, camera, lens, and exposure, including the Foot Candle reading in incident light. The next paragraph is how the image was developed and fixed. A brief comment follows and the final paragraph tells something of how the plate was made.
Everything fits onto one side of one page. All photographs have the same format and information. It helps me figure out what is going on.

023 Frick field Wedge Test ...This plate was scraped twice, one end was thicker than the other.
025 Field house ...The emulsion must be very thin because it cleared so fast.

When I developed the Wedge Test, the part that was good didn't develop; it stayed white and I thought there wasn't an image there.

3) Form a Hypothesis. Thick emulsion may have a higher ISO than thin emulsion.

4) Conduct experiments. Make two plates, one thin and one thick with emulsion. Expose them both the same, develop them both the same, developing the thin one first by observation.

5) Evaluate. When I had developed 023, no image showed until it was cleared after 20 minuets in fixer, then the image showed to be the better part. I may have been overdeveloping thick plates! 025 cleared in 3 minuets.

I am guessing that thick emulsion will capture more light then a thin one and then hide the image under the unexposed excess white halides. Trees in the Frick Park Wedge Test photo have more gray details than the trees in the Field house photo. Development was one min in the Wedge Test and three min in the Field house. I will develop 2 min both new plates.

Two new plates were coated. The glass is new single strength with the sharp edges knocked off with a black diamond pad underwater. Two different methods of coating plates were used. One coating was applied thinly and the other was applied thickly.

The thin coating used glass edge strips of the same thickness, single strength, and a puddle pusher glass rod. The ends of the glass rod were wrapped with three layers of scotch tape. A thicker, double strength, glass strip was used to guide the glass rod pulling down emulsion over the plate. The glass set up was heated with a hair dryer. Emulsion was dumped onto one four inch edge and emulsion ran over the edge strip and the plate. Emulsion was pulled down over the plate in one slow pass then past the edge at the other end so to prevent emulsion from backing onto the plate. Excess was put back into the film canister; emulsion was kept warm for reuse on the next plate. The plate appeared light gray and dull.

About a third of a canister of emulsion remained and was used to coat the thicker plate. A marble slab was extended out over the edge of the table and a hot plate put under it. The stone end was heated to warm to the touch. Uncoated glass was preheated on the stone then held on my finger tips. Emulsion was about 110 F and carefully poured into the center. I was looking into the safe light in order to see to keep the glass level. No emulsion was allowed to pour off. I slowly tipped the plate this way and that so the emulsion ran into corners and edges. Then I rotated it some and placed it back onto the warm stone. While it sat for one minuet on the warm stone, I pushed the glass in circles with a popsicle stick. After I had counted to 60, I pushed the coated glass plate to the cold end of the stone without lifting it. It was allowed to solidify there. The plate appeared very white and shiny.