Photograms directly on 4x5 film

[a77pardo]

Hi Everyone,

I'm trying to make some photograms by exposing film with a flash(speed light). I'm using the lowest power and my set up is simple. Place the negative on a table , cover the negative with semitransparent items and measure exposure. In order to affect the exposure I increase or decrease the flash distance or bounce it.

Now my question. Given that there is no lens involved, I am measuring at the widest aperture posible for the light meter (0,8) at the ISO of the film. However I'm still blowing up my exposure. How would you measure something like this in a light meter? Am I doing something wrong? If possible for the light meter, theoretically I should be using Aperture 0 in It?

I need some guidance, thank you in advance

[Wayne Fox]

I'm not sure you can get  flash power low enough. Maybe try a standard light source?

[a77pardo]

Thanks, even with continuous light how could I measure the needed exposure length?

[pflower]

 Trial and Error? I'm not sure a light meter is going to help you unless you can calculate the EV difference between f0.8 and f0 (which I can't).

 I would suggest that one approach would be to use the same technique as used to determine correct exposure for paper under an enlarger - i.e. a series of exposures of determined length, covering up part of the film after each exposure.  That way you will have what is effectively a step wedge.  I also think that direct flash, even on the lowest setting, would be too much for film.  I would start with a 25w bulb at a measured distance and then try a series of 2 second exposures up to say, 20 seconds.  Then look for the first strip that is pure black (assuming you are using B&W neg film).  That gives you the shortest time to completely expose uncovered film.  An enlarger timer connected to your light source would be helpful to control the exposures. 

[Rob C]

When film was king, we did something called a controlled test series...

Not being a smart-ass, but as everything is variable in photography, you really do, sometimes, have to suck it and see. In your specific case, I'd suggest masking your flash source with layers of tissue paper (toilet's just as good if you have far too much power) and keeping accurate records of distance of light from subject. Remember, you can also bounce light off walls etc. and if you are working in black/white the colour of the decoration won't affect you very much.

A big difference today, with digi, is that folks want everything now. With film, time is ever a factor. You have to get used to a different approach to time.

Have you tried using a photocopy machine instead? I've seen surprising images of secretaries making sitting selfies that way... maybe there are no more secretaries today.

;-)

Rob C

[billthecat]

Could you take the lens off a digital camera and aim it at your light source? Would the resulting histogram give you an idea of what the film will see?

Bill

[Chris Barrett]

I'd suggest buying a cheap enlarger to use as your light source.  With a decent timer, you will get much more accurate results.  Being able to stop down the enlarging lens will go a long way towards creating usable exposure times.  This is how we did photograms on paper in school, film should work the same way, just faster.

As other's have stated, start with a step wedge.

-CB

[tom b]

Showing my age, I taught students how to make photograms in Port Moresby in the early 80s.

Today I might approach the concept with using a flatbed scanner. They're old hat and you could get one relatively cheap.

The second thought is to use a copy stand.

Both processes are well worth consideration.

Cheers,

[Rob C]

Could you take the lens off a digital camera and aim it at your light source? Would the resulting histogram give you an idea of what the film will see?

Bill

Might that damage the sensor?

[billthecat]

Taking the lens off a SLR should not damage the sensor unless you touch the sensor. You might let some dust in. It could be done briefly.

Bright light like the sun can damage the sensor, but I haven't heard of a low powered flash hurting a sensor.

Bill

Might that damage the sensor?