Sunday, 30 September 2012

Alternative way to check your fix is still fresh.

Here are two simple and easy ways of checking that the fix is not exhausted. The bottom line is if in doubt, throw it out.

  1. Take a drop of fix and place it on some blue litmus paper, if it turns red the fix is still active, if the paper remains blue it is exhausted. Rapid acting fixes by their nature will get exhausted more quickly than an ordinary one. When fixing paper you may expect to get thirty to forty 18x24 cm ( 8”x10”) sheets per litre.
  2. Take ten ml of fix and add ten drops of potassium iodide solution to the measuring jar and stir. If the milky solution does not clear after it has been shaken then the fix is exhausted and a new batch should be made up. If it clears the fix is OK to use. Make up your Potassium iodide solution from two point five grams of powder and add a thousand ml of water and mix. This method does not apply to rapid fixes.

These methods will work for your film fixes as well. But the milk test you do for film will not work with paper as you cannot see this stage with paper.

Sunday, 23 September 2012

A fixing question.

This is the second most important part of the process after development. Proper fixation ensures the longevity of your prints and negatives. Fix works by removing the unused silver bromide particles from the film or paper. If not done properly, over time they turn black ruining the image.

The way the fix works on the emulsion is to chemically convert the remaining silver bromide into complex argentothiosulfate an insoluble  and unstable compound which after a few seconds can be seen on the film  as a milkiness (not visible on prints) this should be allowed to continue until it has disappeared otherwise the negatives will turn black. As the process continues the fresh hypo from agitation turns the insoluble into soluble sodium  argentothiosulfate which can be washed away in water. The fixing of the image is quite quick, it is turning the by products into a water soluble compound that takes the time.

The darkroom practitioner needs to be carefully when choosing a fix as some cause staining when being used with paper. There are three types: alkali, plain, and acid.

         Alkali are the most modern and efficient with today’s emulsions. They are the easiest to wash out of papers and cannot be over fixed.

          Plain is a mix of Hypo (thiosulfate) and water that should be used as part of a two bath system, then only as a second one as it can cause staining and other problems.

         Acid fixes are known to be quick and should be timed carefully as they can cause bleaching. Hence the reference rapid.

Some fixes come with hardening and should not be used if you are thinking of toning prints. Otherwise it is down to personal choice.

Film Fixing.

A lot of people ask how long will the fix stay fresh and how many rolls it will process. I mix up  1000 ml or 1200 ml  depending on how many rolls of 35mm and or 120 format I think will be processed at the same time. ( I  use a different fix for paper) I keep the fix until I have developed a mix batch of between twelve and fourteen rolls. Which can take some months to achieve.

The film has a milky look after one minute in the fix
There is a more scientific way of being sure what the limits of the fix are for yourself. It can only be done with a fresh batch of fix. After the film has been in the fix for a minute you open the process tank, checking to see if the milkiness has cleared. If it has then give the film a further three minutes this will also establish the time the film needs to be fixed for. You will need to do this check  with subsequent films until the clearing time is double what it was when the fix was fresh. Having kept a check on how many films you have processed this will give you a safe number per litre for the future, hence removing the need to check each time. There are other method for checking fix life which will be posted later.

Paper fixing.

There are two methods to choose from.

         Two bath method. This where two lots of fix are made up and set side by side. The first bath does all the work, with the second bath removing any argentothiosulfate that have not  been converted to sodium argentothiosulfate in the first place, making for a more complete final wash. Once the first bath is exhausted (which you will need to test for), the second bath becomes the first and a new one is mixed for the second. When the second now first bath is exhausted both should be ditched and two fresh fixes made up.

I use this method occasionally If I'm toning. To get round all the testing you need to know how many prints you can get out of the fresh  bath and the partly used second, for each of the sizes you print most often. It is a lot of work to start with.

         Single bath. Is a fast acting concentrated fix that takes one minute to do the job. This method needs to be timed exactly; to leave it longer will negate  its advantages. Most of the fixing is done in the first fifteen seconds, to leave it longer than one minute will allow complex compounds to build up making them difficult to wash out.

I use this method most of the time partly because I do not have a lot of time to spend when printing and the other is I do not do a lot of toning.

Sunday, 9 September 2012

To be sharp or not, how is the question.

Fg 1.
Film FP4+ developed in ID11 printed
on Ilford MG RC gloss.
A subject that is talked about by all photographers. No matter how you like to label it DOF or boken I am surprised that depth of field can be expressed by some in the terms of good and bad. Surely it is subjective and down to the person who has composed the picture.

So what is depth of field and how does it work?

Depth of field relates to the area of the image that is sharp. So the subject  you focus on in the view finder will be in the middle of the sharpness. How much this extends in front of or behind it, is dictated by the aperture you use. Small F number (large opening) very shallow, large F number (small opening) very wide. The other factor to have a bearing is the focal length of the lens used.  For example, with a wide angle 28mm lens you would not require the focus to be exact because the depth of field would be quite considerable in front of and behind the point of focus even at small f numbers (large apertures). But with a Telephoto lens of 200mm the point of focus needs to be precise as the depth of field is quite narrow even at large f numbers (small apertures).

Fg 2.
Kodak colour plus negative. scanned
 from print.
In understanding the way depth of field works you need to know that when you focus on the subject it is at that point the reflected light arrives at the focal plan as fine points of light (sharp). The subjects closer to the lens do not resolve as sharp until they are beyond this point and those further away reach pin sharp before they arrive, because of this they arrive as discs known as circles  of confusion. The larger the circles the softer the images appearance. By making the aperture smaller (large F number) you reduce the circles of confusion giving the picture the appearance of full depth of field. (sharp from front to back). The eye considers points of light as large as 0.25 mm diameter as sharp. The same applies to the dot pitch of a computer screen. When it come to the manufacturer of lenses for 35mm format cameras this figure is much smaller 0.08, this is because the maker has worked out  that on average a 35 mm negative will be enlarged by twenty times (a print size of 10 x 8.)

The good thing about using a film camera is that  you can check on how heavy the points of confusion will be by pressing the depth of field preview button. The advantage I have is I know what to expect from my lenses at particular apertures. This allows me to compose the picture with the amount of soft focus  I think will enhance it.

For example the three pictures included with this post.

         Fg. 1 The main reason for the cats paw being out of focus is to add depth and a sense of being very close.

Fg 3.
FP4+ developed in ID11 printed on
Iford MG RC gloss
         Fg. 2 The main reason for blurring the background is to exclude a large group of people walking towards me. They did not add anything to the picture I had in mind. By adjusting the aperture to a lager one (small F number) they have been removed making for a much better shot.

         Fg. 3 The depth of field in this picture is very narrow. It took a bit of time in making sure that the whole of the ball was sharp and nothing else.

When taking a picture I consider the 'out of focus' as important as the area to be sharp.