Sun exposure...

[Guillaume Zuili]

Hi all,

I'm ready to do some 16x20 VDB. As my light unit isn't large enough to handle the frame I'm going to use mother nature. Being in south california helps.
I was talking about that with a friend and he advised me to create a difuser above the frame to avoid any zoning due to variation of the sun.

I have doubts about that. If there is any variation (and there is) it should be on the whole frame. I don't see his point.

Is he paranoiac ? Am I missing something ?

Thanks for your responses in advance.
Guillaume

[David A. Goldfarb]

I don't use any kind of diffuser for my albumen exposures. I do move the frame occasionally since I'm usually exposing indoors through a window.

With albumen (contrary to what one might expect) direct sun produces a slightly lower contrast image than indirect sun. Direct sun is also about 3 stops faster.

Here's my usual high-tech exposure setup--

http://www.apug.org/forums/attachmen...3&d=1151344340

If I prop my printing frame up on a scanner, is it a hybrid print?

[micek]

I don't know if a diffuser might help, but without one I have had a charming butterfly's silhouette on a cyanotype, and a cat also managed to ruin another one by sitting on the same chair against whose back my printing frame was resting...
On a more constructive note, if the edge of your VDB image is too close to the the frame of your printing frame, depending on the time of the day you are exposing it, it might be affected by the shadow cast by the frame. If it is a short exposure you can check and alter its position, but if it is a longer exposure and you are not going to stand and watch over it a diffuser might help.

[TheFlyingCamera]

Also check to make sure that your diffusion material is not also a UV-blocker.

[Guillaume Zuili]

Thanks.
1) Check for my cats... 2 + their buddies !
2) No UV blocker
3) Move it from time to time.

It's a full time job !

[Guillaume Zuili]

I'm going to use the reflection of a white wall. There are so many electric lines, didn't realize that their shade would ruin the exposure. This is the only spot that seems even.

[Guillaume Zuili]

I did a 16x20 test today. Very weird day with the sun diffused by a lot of smog. Amazing how fast the exposure was. 5 minutes top and for sure it was over exposed.
Was it because of this huge diffused light ?

[Sparky]

It's because the smog ate away all the UV-blocking ozone!!!

[Guillaume Zuili]

Damn yes !

[z-man]

I did a 16x20 test today. Very weird day with the sun diffused by a lot of smog. Amazing how fast the exposure was. 5 minutes top and for sure it was over exposed.
Was it because of this huge diffused light ?

YES

the use of a difusing material in many different ways in contact printing may be found in literature from 1800's to present day

when u have a large difuse light source,, the time factor comes in to play

the longer the exposure the more the difusion of the light inside the layers of materials in the frame-this can goto positive feed back --the opposite of self masking

also: the contrast of the finished print was controled back in the day by using direct sun or open shade(large difuse light source)-

the speed of the materials was different under direct sun from skylight which was usualy faster-depends on the process

you have discovered for yourself a most important technique in contact printing- -if you take detailed notes every time you make a print you will have a journal that will be your own cookbook with recipes for success-

vaya con dios