Contact printing...misinformation?

[ic-racer]

Yes, math errors.

Your enlarge can only go 90 mm? That's about 3 inches. I'm sure you meant 90 cm, or 900 mm. That makes your incorrect 0.022 result become 0.0022.

At least someone read the 'jpg.'

Interesting error...looks like the enlarger light should perform better than was suggested.

As far as degree of separation, in the tests I posted it was 'best' at the edges where things were held together in a projection printing frame.

I think that not accounting for diffraction is an issue but the one of the light passing through the film base is relevant .

I saw Kodak had some patent for a system with no on-lay glass but it involved using laser light.

I think I can say that unless I missed something that others are doing, the posts I ran across on NOT using a contact glass may have been with respect to printing "PROOF PRINTS" rather than fine art contact prints.

 

[richard ide]

Specific gravity variations in the frame materials would also have a small but not neglidgable effect on the pressure gradients of the system with the possibility of newton ring development at points where the pressure is less than optimum. Newton rings will not form in the close proximity of dust particles of course; which suggests that dust in itself is not a bad thing when carefully controlled in the contact printing matrix.

 

[ic-racer]

hey ic


20 sheets of glass would just be silly

20 sheets of framing glass; about a stack under 2 inches high. Pretty much what I had lying around to test as I am still waiting for my thick single sheet from the glass co. As I posted before, isolated pressure on the edge of a single thin sheet bends the glass, so this was the best way I could cobble up to get pressure in the center also.

As far as the foam goes, Shore A is the rating for the softer foams. McMaster Carr has a conversion chart showing common items like 'mattress' and 'pencil eraser' on their site.

I suspect not everyone has a Shore guage to measure the foam tires for their RC racing cars, but when you go to order foam from McMaster Carr (or other source) knowing the firmness of something someone has tested and shown to work can help.

 

[ic-racer]

If you first clean the glass of the frame with a cleaner as I do, give ample time for drying.

I then dust the glass and negative under white light with an anti static brush. I put the negative in the frame, check it again for dust, switch to safe light, take the paper from the safe, place it in the frame, put the back on, expose and process. I have no problems. Comes out as sharp as a contact print. Occasionally I have to spot one that got by.

Good, this was what I was thinking about trying. Well, I will see how the glass and foam work out and if to much of a hassel, will try the contact frame.

Now if someone would just donate a nice frame I could end this miserable thread....

 

[JBrunner]

Good, this was what I was thinking about trying. Well, I will see how the glass and foam work out and if to much of a hassel, will try the contact frame.

Now if someone would just donate a nice frame I could end this miserable thread....

One thing that you may find is that the contact print frame tends to stay cleaner, for longer, after a thorough cleaning, than the glass and foam.

 

[ic-racer]

Actually, this would best be done using a matrix of strain gages mounted in all three planes (x, y, z) at each corner of the frame, in the middle of each frame member, then a matrix at several points on the back and on the glass sheet. That would allow actual deflections to be be measured. The forces applied and bending moments could be calculated from those direct measurements. Of course that depends on the properties of the frame's materials, so then we get into the type of woods being used, wood grain orientations, saw orientation, and of course, moisture content at time of testing.

Once the first test is complete, then we can vary the types of woods and joint constructions used in the frame, along with glass types and thicknesses. I'm excited!

Actually, I saw some pretty well thought-out contact printers in use for aerial photography. I am enticed by the possibility of having the negative DOWN and the paper UP, so I can just open the lid and stick the proof strips down and pick them up again, without having to dissasemble a frame.

 

[ic-racer]

. Not the best but it works....

I have "paper clips and cardboard" also, but this is the point: if it's "not the best" then it doesn't work for me.

 

[ic-racer]

In working with contact printing LF negatives I found I got sharper results with 8x10 and larger film sizes by using a vacuum frame. 5x7 and 4x5 were fine with a normal spring back glass contact printing frame.

Thank you (and I'm not being sarcastic), this is exactly the kind of thing what to know.

 

[ic-racer]

I would urge the OP take a class somewhere and see the process done.

Some things really are simple at their essence,

C

Actually would like to do that, there is a alt process workshop in my local area but this season's schedule is over.

 

[CBG]

Actually would like to do that, there is a alt process workshop in my local area but this season's schedule is over.

Thanks - but - I would beg you to stay away from alt processes till you are rock solid with basic silver based contact printing - too many new variables - my suggestion is that you do not need to add more to think about.

Keep it simple. All this complexity: collimated light, twenty sheets of glass, ad infinitum is an albatross that will keep you from getting what you want.

Thirty years ago, I used the exact opposite of collimated light. I contacted with a sheet of flashed opal glass and a pad of foam rubber. Long time ago, but it worked like a charm. The light coming out the back of flashed opal glass is what I imagine the inside of a ping pong ball would be. As diffuse as possible.

C

 

[ic-racer]

Thirty years ago, I used the exact opposite of collimated light. I contacted with a sheet of flashed opal glass and a pad of foam rubber.
C

Why did you change?

 

[DBP]

For over 30 years I have made contact prints the way my father, and his father before him, made them. 1. Place a piece of paper, emulsion side up, on a flat surface. 2. Place negative on paper, emulsion side down. 3. Cover with a clean sheet of glass (these days I wipe it with a microfiber cloth to clear off dust - TP was the old solution). 4. Expose to a light source (this ranges from my enlarger - racked all the way up so I lessen the chance of banging my head against it - to an old Kodak contact printing box - which admittedly reverses the order of the stack so paper is on top). If the curl of the negative or the paper is an issue I hold the glass down with my fingertips.

If this worked in my grandparent's attic, my uncle's attic, my parent's bathroom, my pre-renovation basement, and my current combination basement and laundry room (and yes, I do have to deal with dust issues), then it should work anywhere.

 

[bruce terry]

In working with contact printing LF negatives I found I got sharper results with 8x10 and larger film sizes by using a vacuum frame. 5x7 and 4x5 were fine with a normal spring back glass contact printing frame.

ice-racer - If one feels better using a vacuum frame for 8x10 negs, fine, but something equivalent to a B&S mid-size 12x15 exposure-area split back contact frame is all you need. Pressure distribution against the thick, stiff back is even throughout and the interior glass and backing felt are always protected from external crap by the framed structure. Glass cleanliness and dust are a non-issue ... with a little logic.

You do need the extra room of an oversized frame, be it for ease of handling just 8x10 silver paper, or for employing the necessarily-oversized 11/11.5 x 14/14.5 alt-process papers – an area you're guaranteed to enter once you see those beautiful contacts ... once you throw out the math you learned past sixth grade.

PS - My math is PRE-sixth-grade! I have trouble keeping count of the drops coming out of an eyedropper much less determining the matrixical forces extant within a compounded medial plane that ecliptically reciprocates the inverted mass of american black cherry and 3/8" thick hyperventilated non-ultraviolet glass – an issue that dearly needs clarification by someone way smarter than me. Meantime, amazingly, I find my 8x10 plat prints perfectly sharp.

 

[JBrunner]

I have a vacuum frame, but I feel that 8x10 can be happily printed with a good quality springback frame. The quality of a frame is important. I haven't seen an advantage to the vacuum frame until 11x14, and it's sloooow.

 

[John Bartley]

For over 30 years I have made contact prints the way my father, and his father before him, made them. 1. Place a piece of paper, emulsion side up, on a flat surface. ... snipped ...

If this worked in my grandparent's attic, my uncle's attic, my parent's bathroom, my pre-renovation basement, and my current combination basement and laundry room (and yes, I do have to deal with dust issues), then it should work anywhere.

Yup ... me too ... exactly .... works perfectly ... no math req'd.

cheers eh?

 

[DBP]

BTW, a lot of us who fiddle with alt processes use a very highly collimated pinpoint light source - the sun.

 

[CBG]

Why did you change?

Didn't. It just worked.