Who Can Expose And Develop Planfim Material For Me?

ImperatorRex · 2012-11-11T19:40:17+00:00

Liebe Forummitglieder, wer kann "Planfilme" wie nachfolgend beschrieben belichten & entwickeln? Ich beschäftige mich privat mit Mikroskopie und benötige...

ImperatorRex

Dear forum members, Does anyone know how to expose and develop ‘sheet films’ as described below? I am a keen amateur microscopist and need the exposed film for a modulation contrast technique on my microscope. I am unable to produce the film myself. Perhaps someone here in the forum is willing and able to produce such film? If not, do you know anyone I could contact? I will, of course, reimburse you for your time and expenses by mutual agreement. Instructions: A sheet of film (9x12cm) is cut lengthways. This yields two pieces measuring 12x4.5 cm. A strip of film approximately 3 cm wide is covered with a piece of card, and the remaining strip is exposed. A low-wattage incandescent bulb is sufficient for this; an enlarger is not required, but does make the work easier. After the first exposure, the covering card is pushed back by about 2 mm. A further exposure is carried out. This must be considerably shorter than the first, as this narrow streak must only turn grey after development. As we cannot usually measure the transmittance of the grey area – a densitometer would be required for this – the density should be chosen so that the printed text can just about be read through the grey area. The wider streak, which was exposed first, must be completely blackened. No specific guidance can be given regarding exposure time, as the light intensity will vary from case to case. A test strip should be produced to determine the correct exposure time. To do this, cover a scrap of the sheet film with a piece of cardboard, leaving a small section exposed. After half a second of exposure time, move the cardboard back slightly and expose for another half second. Repeat this several times. After developing the test strip, you will obtain a so-called step-grey scale. Now the required exposure time, at which the correct grey value has just been achieved, can be determined. If the film strip turns out too dark in all cases, the lamp brightness must be reduced or the distance from the lamp increased. The development time used for the test strip must be the same for all trials, otherwise the results will not be comparable. Sheet film (e.g. Labalith, manufactured by LABAPHOT, or NP515, manufactured by AGFA) must be processed under red darkroom lighting. It is developed in standard document developer. The development time should be 3 minutes. Many thanks Jochen

Urnes

Am I wrong, or isn’t this procedure usually done with two crossed polarising filters? Creating a step-grey scale ‘blind’ (i.e. without a densitometer) seems rather time-consuming. http://www.grossformatfotografie.de/viewtopic.php?f=12&t=9814 Are the films you mention orthochromatic films? Hardly anyone will have those at home. Why don’t you describe exactly what you want to do with the film. Otherwise, you could also develop the film at home in a darkened room in a tray. Regards, Sven.

ImperatorRex

Sven, In the USA, the Hoffman modulation contrast method – named after its inventor – is used to enhance contrast in microscopes. Here in Germany, this method is relatively unknown. One component (the so-called modulator) consists of the film described above. You can find a description here: www.micro.magnet.fsu.edu/primer/techniques/hoffman/hoffmanintro.html . The modulator is also pictured in the middle of the article. There is also a good Java tutorial showing how the contrast method affects the microscopic image. I have no idea whether the film material needs to be ‘orthochromatic’. I only know that the film material exposed to light has three zones: a light, a grey and a dark zone. Their corresponding transmittance values should be approximately 100%, 15% and 1%. It doesn’t have to be adhered to quite so precisely. Unfortunately, I don’t have any photographic lab equipment at all and I’m also a complete novice when it comes to film exposure and development. Best regards, Jochen

Urnes

Hi Jochen, I’ll have a proper read through this and see what can be done. It might take until the weekend, though. Best regards, Sven.