Use of X-ray film: technical discussion with example images

[Andrew O'Neill]

HC110 is fine and 1+32 dilution should be fine, providing you use effective EI. 5 minutes is too short. I would start at 10 minutes. Are you developing in trays?

[StoneNYC]

ndg, have you tested EI 400 on different lighting conditions? I would suspect there was some lens flare going on due to extreme brightness of sky. That tends to throw more exposure into the shadows. Less exposure would compensate for that, making one think that EI 400 was correct.

Lens flare? There's no sun in the shot... And the camera is under cover in the shade...

[premortho]

I THINK, but do not know, that it goes like this. f5.6 @ 1 second equals f8 @ 2 seconds, equals f11 @ 4 seconds. In other words, try 3 - to 3.5 seconds for f9.

Here are my results.
I used a 35mm camera (Nikkormat with a 110 mm lens).
I set on the camera a speed o 100 ASA
I used a Fuji radiographic film, I do not know if green or blue, the only thing I note is a bluish color of the substrate film.
The camera meter suggested, for a time of 1/4 sec an F of 5.6, and from there I started.
So I made several exposure, from 1/4 sec at F/5.6 to 4 sec F/2.5, developed in HC110 diluted 2:100 at 20°C for 10 minutes.

1) 1/4 sec F/5.6 underexposed
2) 1/2 sec F/5.6 well exposed
3) 1 sec F/5.6 well exposed
4) 1 sec F/2.5 well exposed
5) 2 sec F/2.5 well exposed
5) 4 sec F/2.5 overexposed

From test 2 to test 5 the overall density was obviously incrasing, but all negatives look printable.
From these results I am inclined to think that the speed of the film is around 50 ASA.

I made all these tests to get an idea of the good exposure for this film and used a 35mm camera because of convenience.
Now I like to extend this knowledge to another camera (large format, 18x24 cm) , which has a lens of 308 mm focal length and F/9 maximum opening.

I am asking you now a second naive question.
Having a diaphragm set at F/9, how long must be the exposure to have a negative with an optical density similar to the one observed in test n. 4 (1 sec F/5.6)?
Does a law exist predicting relative illumination as a function of lens focal length, diaphragm opening, and enlargement (or reduction)?

[Andrew O'Neill]

Stone. The camera is under what cover?? Were you there? Go back and look at it. Look at the sky. It's very bright. You do not need sun for lens flare. I've shot scenes where the brightness of a sunless sky has boosted zone II up to zone IV, even with a modern lens and a lens shade. I have thousands of negatives to prove it to you if like. I was only pointing out a possibility as to why such a high EI was used, and to be sure in other situations that it is correct.

[salvatore]

I THINK, but do not know, that it goes like this. f5.6 @ 1 second equals f8 @ 2 seconds, equals f11 @ 4 seconds. In other words, try 3 - to 3.5 seconds for f9.

What you say is true for the same camera and the same lens, but what happens if you change from a 24x36 mm camera with a 110 mm lens to a large format 8x10 inches with a 308 mm lens?
Probably your calculations are still true, but I would like to know why.

[Randy]

not bad How is grain?

That is one thing I have noticed with any of my attempts with X-ray film - noticeable grain when viewed through a magnifier. I mean, if I compare a 4X5 HP5 neg and an 8X10 X-ray neg, both processed in the same developer, the X-ray neg has much more pronounced grain than the HP5...but I don't really care because in the prints, since I am not going very big, it is not an issue.

Comparing two X-ray negs, one processed in HC-110 1:63, and one in the Arista liquid 1:18 - the grain is the same.

[towolf]

What you say is true for the same camera and the same lens, but what happens if you change from a 24x36 mm camera with a 110 mm lens to a large format 8x10 inches with a 308 mm lens?
Probably your calculations are still true, but I would like to know why.

F-number is ratio of pupil diameter to focal length. So 35mm camera f9 is the same as 8x10 f9.

8x10 lens has much larger diameter to reach f9.

Aside: The conventional f-number scale is stupid. It should be in stops, increment 1 to halve exposure. But we are stuck with square root of two based scale.

[ndg]

Funny you ask. Shortly after those test shots, I drove down to this creek. I wanted to capture the stream over the rocks on 14x20 Xray film for carbon. The foliage did not leave a lot of light through. I metered the scene at iso 400 and got absolutely no usable images! In bright sunlight, iso 400 give usable images. However, in low light situations, the iso drops into the 25 - 50 range. Again, that is my experience with my workflow and the experience of others may be different.

ndg, have you tested EI 400 on different lighting conditions? I would suspect there was some lens flare going on due to extreme brightness of sky. That tends to throw more exposure into the shadows. Less exposure would compensate for that, making one think that EI 400 was correct.

[salvatore]

F-number is ratio of pupil diameter to focal length. So 35mm camera f9 is the same as 8x10 f9.

8x10 lens has much larger diameter to reach f9.

Aside: The conventional f-number scale is stupid. It should be in stops, increment 1 to halve exposure. But we are stuck with square root of two based scale.

Thanks for your quick answer. Finally I will be convinced that you are right and my confusion comes from my limited familiarity with photography, but presently it seems to me that even with the same camera and lens and pupil diameter if you take a picture of a light source, the blackening of the film will be different according to the distance between the camera and the light source.
In fact the backening will be proportional to the intensity of light, and from my intuitive reasoning it will be proportional to the pupil area, and inversely to the square of the distance lens-source multiplied by the square of the enlargement, that is the ratio between the dimension of the source and that of the image on the film.
As an example, let me take a lens of 10 cm focal length, and at a F to reach a pupil of 3 cm (any value will however work for this example).
Let me place the source at 20 cm from the lens, I will see an image of the same size at 20 cm from the other side of the lens.
Now place the source at 10 cm from the lens, that is at its focus, and it will give an image at infinite ditance from the lens, with infinite size.
Infinitys are not fair, and we can consider a position near the focus, say at 11 cm from the lens, which will give a very large image.
If we make the calculations, we can easily see that a small nearing to the focus point will result in a very large image dimension, while the fraction of light entering the lens will be almost unchanged.
Obviously may be that my reasoning is wrong, and I will be happy to correct my thought.

[gsuser]

Here is one of my early attempts with Fugi HRT green and Rodinal. I just scanned into photoshop sized it and did a quick levels on the whole image. My DIY camera has the potential now I have to learn how to use it