Here an interesting scientific analysis. It works.
Finally a free afternoon. I went out with the (black) Cameradactyl 4×5 to try a few shots with the cheaply aquired, cleaned and mounted 127 lens.
Of course as soon as I arrived with my bicycle the weather went to light rain.
The tripod mount I glued in is not stable (looking for an idea to get it right) and while composing the camera was rather wobbly on the tripod.
Fuji X-ray film (Fuji AD-M 18×24 100 Bl. mammography film, one side emulsion), Rodinal 1:100, 20 Celsius, about 10min under red light with visual control.
The pic shows part of the eremitage, a long forgotten place where some monks once lived in solitude near the Nahe valley, Bad Kreuznach.
This is my quick cheat table if I take my pinhole with me.
|DETERMINING EXPOSURE TIME FOR PINHOLE CAMERAS |
You have to work with small apertures (high f numbers) and long exposure times and the reciprocity law failure (Schwarzschild effect) must also be taken into consideration.
Taking photographs with a pinhole camera is always something of an experiment and requires a bit of playing around. Achieving perfect results is not always the most important aim.
Many pinhole photographers simply use estimated exposure times. Also, many commonly used films have high exposure latitude and therefore are less sensitive to incorrect exposure.
One option is to prepare a simple table for each pinhole camera whereby the time measured by a light meter can be quickly converted to the required time for the given pinhole camera and film stock.
You can use the PinholeDesigner program to help you with the following calculation. f number In order to calculate an exposure time, it is important to know the f number of the pinhole camera.
Using a lightmeter the problem is that the high f numbers on pinhole cameras are not available on light meters.
The way round this is to set the light meter to a different aperture, usually f 22, and then convert the measured exposure time for the aperture of the pinhole camera.
This is done by dividing the f number of the pinhole camera by the f number set on the light meter; this number is squared and the result is used to multiply the measured exposure time.
For example, if the measured exposure time for f 22 is 1/60 second, the calculation for our pinhole camera with an f number of 250 is: (250/22)2 = 129. The measured time is increased 129 times, therefore the exposure time for the pinhole camera will be 2 seconds (rounded).
Reciprocity law failure (Schwarzschild effect)
For long exposure times, usually for exposures longer than several seconds, it is necessary to extend the measured time.
The majority of film stocks indicate in their specifications by how much the exposure times should be extended; if not you have to experiment.
Tips for correct exposures
Choose a material with high exposure latitude, this increases the probability of obtaining a useful negative. In general, conventional light-sensitive layers (which do not use T-grain emulsions) have a higher exposure latitude, such as Ilford FP4 Plus, and also the majority of commonly used colour negative films.
Indoors the times are very long, often more than one hour.
Usually, the only possible method to obtain a correct exposure is trial and error.
The sensitivity of the photographic paper is to be tested. The light meter should be set to somewhere between 2 and 10 ISO.
A good idea for simplifying exposures is to create a table for each pinhole camera and type of film stock.
„A film that can only see blue and green spectra of light doesn’t get
along very well with light reflecting off of red objects.
Red leaves go dark grey, red bricks go darker, and red shirts and skin blemishes become quite prominent and dark.
Top things to avoid with x-ray film: red backgrounds, red shades of lipstick, and hot lights!“
„X-ray film, when processed in standard developers, builds contrast very quickly.
A quick glance at any x-ray shooters‘ developing times will show you that even very dilute solutions have a time of < 10 min.
Taming contrast with green x-ray film can be accomplished with some yellow/pale yellow filtration during exposure.
In otherwise „flat“ light, x-ray film at „N“ (normal processing) will provide you contrast equal to N+1 development with conventional films.
„Personally, I’ve found shooting somewhere between ASA 100-200 gives me acceptable prints with silver, and ample density for carbon printing. And with the addition of a yellow filter (see image right), even more contrast can be controlled, and a little darkening of the sky can be obtaining with this naturally contrasty x-ray film“
Above quoted from Mat Marrash
I had my „new“ 18×24 now functional and did (its dark and cloudy here) a testing with some x-ray sheets I got as a gift because they are to old for medical use.
Development in Rodinal, x-ray film is orthochromatic so under safe light red.
R09 1:25 worked much to fast, in the 2 minutes range, but this cheap old (stored at room temperature) film is not bad at all.
You see small scratches and the dust, I did a careless quick test job cutting and loading and scanning – and the tray development which followed is alway dangerous for this film because the film is coated on both sides.
Because of the coating I was really careful loading the film, taking it out of the holder and especially moving it in the tray while developing, stop in water, fixing and washing.
A small tip is to put the glas of some cheap frames at the bootom of the trays, so no more scratching at the bottom.
The coating is of course very vulnerable when wet, but I managed to get a few 8×10 sheets very well developed without any scatches.
Contact printing works very well.
Be aware that Tim Layton uses another x-ray film, rates it at 100 ISO, developes in Rodinal 1:100 for 6 min., his blog here :
his tips :
Fuji AD-M 18x24cm @ ISO 100, Ilfosol 3 1+14, 20°, 8′, Rotation
Fuji AD-M 18x24cm @ ISO 64, Kodak HC110 (1+47), 20°, 5’30“, Rotation
Fuji AD-M 18x24cm @ ISO 100, Kodak HC110 (1+47), 20°, 7′, Rotation
Fuji AD-M 18x24cm @ ISO 100, Pyrocat HD, 5ml+5ml+500ml, 20°, 7’30“,
Fui UM MA @ ISO 25 Rodinal 1:50 , 10min
Fixierer Moersch ATS, Rotation
Gregg wrote this in our Lensless group on FB:
Gregg Obst I use the single-sided blue-based Carestream Ektascan B/RA in my 8×10 and have also cut it down to 4×5 on occasion….
I rate it at ISO 80 or 100 and generally dev it in Rodinal at a 1:100 or 1:150 dilution at room temp (20 C/70 F). I’ve tried various times using rotary processing but around 6 minutes at the 1:150 dilution seems to control the contrast well and still gives good shadow detail….
If you choose tray development do yourself a favor and get some cheap 8×10 glass sheets and line your trays with those to mitigate scratching if you want to experiment with the cheaper double sided X-Ray films like Fuji. A good source of cheap glass for this purpose can be found in dollar store picture frames.
You can develop under a 7w red bulb placed no closer than about 4 feet from the working surface….
Some examples: https://www.flickr.com/search/?user_id=25235850%40N03…
Here is a copy of the email James Guerin shared with me the other day to help me along my x rayfilm journey
Hopefully others will find it equally helpful
Details on x ray – pasted from a previous email..
> The pros and cons of X-ray are:
> You can develop under safe light. This mean that if you under exposed you
> leave it longer and wait for the image to appear… and if you over-expose
> you pull it out of the developer early. Simple!
> Your iso is 100. Not too fast..not too slow.
> Load cassettes in any direction (note for single sided x-ray emulsions such
> as Kodak Eka-scan BR then you need to use the notches as per normal).
> Chemistry dilution is very weak so very economical. I use rodinal at 1:100,
> and 1 litre will develop about 8 sheets. (the time normal increases from 5
> minutes for the first 2 sheets up to about 6 mins for the last sheets. At 20 deg C
> This stuff is cheap! About $39 for 100 sheets of 8×10″ – or 400 sheets of
> 4×5″ (I use a paper crop to chop down 8×10 to 4×5 under the red light).
> This film scratches very easily during developing.
> The film is double sided, this decreases the sharpness slightly and makes
> for a dense negative if you’re not careful.
> This film is orthographic.. it is only sensitive to one colour (green or
> blue depending on the one you buy – green is nicer). Modern film is
> panchromatic, so will record the colour red as a grey mid-tone. Green
> sensitive x ray film will record red as black. Green is recorded brightly
> (trees/foliage) which works well.
> The film base has a blue tint.
> The main trick to avoid the scratches is to develop in a regular tray but
> lining the bottom of the tray with either a glass sheet (so the film slides
> over it) or a sheet of pvc (the chemistry will not annoy the pvc sheet – the
> trays are made from PVC). After a while the glass will become etched by the
> acidic developer but this doesn’t seem to cause any issues. you should use
> these glass liners on all three 4 trays – pre-wash, develop, water stop and
> Times and concentrations are as follows for green sensitive x ray film. (20
> degrees C all solutions)
> Pre-wash – tap water; 5 mins, turn over the film at least once (2.5min per
> side). The pre-wash is essential, you will get horrible unevenly developed
> negs if you omit this step.
> Develop – Rodinal or R09 equivalent – 1:100; 6 mins, turn the film over
> every 1 min, this is the only agitation required (otherwise you will make a
> very dense negative).
If you’ve underexposed and are waiting ages for an
> image you can start agitating.. also consider upping the concentration of
> developer (bear in mind you might have other sheets to develop after so maybe
> keep this tray separate and start another standard solution
> Stop – Tap water (or stop bath – I never use stop bath). 30 secs with agitation, get as much developer off so you don’t contaminate your fixer.
> Fix – Any fixer at recommended film concentration. 1 min with agitation. (x ray fixes very quickly)
> Washing – as per your normal film process.
Generally there are massive differences in ISO, coating and responding to developers. You have to find a solution for every single brand…
Here is an example of the Fuji UM MA HD, 15 ISO (not enough light), R09 1:100 15 Min:
Fuji UM MA HD rated ISO 25 with flash, Rodinal 1:50 10 min
More light & shorter dev = less contrast…