Enlarging times for bigger size papers

[Shaggysk8]

Hello I have a print done at 8x10 with dodge and burns all times worked out nicely, now I want to print it bigger, how can I work out my times by doing bigger prints and does it need any adjustment?

Paul

 

[Steve Smith]

It's proportional to the print area. i.e if you know the time for a 10 x 8 print then a 20 x 16 print will take four times as long. 80 sq. inches : 320 sq. inches.


Steve.

 

[ic-racer]

(there was a url link here which no longer exists)

 

[ROL]

"Now that I already know where I am going and how to get there - by following the PRINTING RECORD's recipe - the TEST PRINT can often be skipped when making greater enlargements. The first exposure for a STRAIGHT PRINT may be estimated by..." - from the section, Making Larger Prints, part of my article, Making a Fine Print.

 

[Christopher Walrath]

Think of it in terms of aperture. 5.6, 8, 11, 16, 22. Increase a stop for print sizes. 5x7, 8x10, 11x14, 16x20 and so on. It's not exact but it will be really close. Adapt as needed.

 

[MattKing]

One minor caution - if you are working with very low light levels and very long exposure times, you may begin to have trouble with reciprocity failure.

 

[Vaughn]

Using math will get you close, as suggested above. Adjustments might (should?) be made as a matter of expression. A print at 16x20 may not "say" the same thing even though it has the exact same light values as the 8x10. For example, small deep shadow areas that work well at 8x10 all of a sudden become large information-less black areas at 16x20. And those small pure white highlights that gave the 8x10 life can become distracting white specks at 16x20.

 

[Bob-D659]

http://www.darkroomautomation.com/da-main.htm has a nice exposure ruler you print and tape to a ruler, it is hiding in the support files page.

 

[Shaggysk8]

Thank you very much every one, today I made my first 16 x 20 print and it's beautiful

 

[jeffreyg]

I agree with Vaughn. I always make a new test print. The math can be a starting point but once you see larger prints after they dry down you will find there is something that will need a change. Usually the larger prints will be viewed from a different distance and the ambient light may not be the same as when you are up close and personal with your print.

 

[Rom]

Think of it in terms of aperture. 5.6, 8, 11, 16, 22. Increase a stop for print sizes. 5x7, 8x10, 11x14, 16x20 and so on. It's not exact but it will be really close. Adapt as needed.

Thanks a lot Chris, it is a good starting point for a newbie like me. I have some 13x18 enlargements that i like a lot and i will start asap to enlarge it at 20x30. I wanted to find the calculation for the time but i think your process could be useful & also more easier for me.

Many thanks

++

Rom

 

[Casey Kidwell]

Test. Unless you're wealthy. In which case send me some paper!

 

[Ronald Moravec]

easiest is open the lens stop. From 35 mm, 3 1/2x5, 5x7, 8x10,11x14, & 16x20 each require one stop more.

Another way is to proportion the area of the two papers. 4 8x10 fit on a 16x20 so you need 4x the light or 2 stops.

1 stop is 2x. 2 stops are 4x, 3 stops are 8x.

If you start changing times rather than light quantity, reciprocity factors come into play and bigger prints will be too light.

So my formula is 8x10 is f11, 11x14 is f8, 16x20 is f5.6, 5x7 is f16

It is also possible to use neutral density filter. B&H sells Roscoe light modifying ones. .3 is one stop. .6 os 2 stops .9 is 3 stops. $6 for 20x24 sheet.

Finally I have an Aristo resistor made for their cold lights that dims to 3.5 stops constantly variable. Use a wall light dimmer for 1/10 the money.

 

[Bob-D659]

Have a look at the exposure ruler here. http://www.darkroomautomation.com/support/index.htm

 

[jeroldharter]

You might find that increasing exposure alone when going from 8x10 to 16x20 is not enough. Sometimes you need a slight bump in contrast with the larger print.

The Darkroom Automation timer looks nice. The Ilford exposure meter is an inexpensive option too. Just calibrate it to a zone on the 8x10 print and then when making the 16x20 you open up the aperture until the meter nulls out.

 

[youngrichard]

I agree with Vaughn. I always make a new test print. The math can be a starting point but once you see larger prints after they dry down you will find there is something that will need a change. Usually the larger prints will be viewed from a different distance and the ambient light may not be the same as when you are up close and personal with your print.

It ought to be simple but it isn't. See Sticky Thread at top of this forum - pages of agonising about essentially the same thing. For some reason a mathematical approach just doesn't work - in the event contrast is not quite the same, exposure not quite the same, burn times as proportion of exposure not the same; and even if, as pointed out, a highlight or shadow is just as in the 10 x 8, in the bigger size it doesn't look right any more. And of course there are lots of reasons, especially if you are lengthening the exposure rather than opening up the aperture - reciprocity failure, maybe a little flash effect from the safelight that was meant ot be safe, light spill from the enlarger, light leak through the ceiling, your lovely pack of 20 x 16 is older than your fresh 10 x 8; need I go on?
So, I always start again; at least you know what you are after. I start again with my trusty RH Designs Analyser to give me a basic exposure, then put two or three or four 5 x 7s onto key areas (ideally cut from the pack of 20 x 16, but as I use MGIV RC I can usually just use tailor-mades), dev and fix; then maybe a test strip with my Ralph Lambrecht test strip printer to fine tune exposure; then Bob's your uncle, a final print and it's not even supper time yet. It's not really a hassle, after all most of us don't make 20 x 16s of every neg; I may go months without feeling I have a negative worth the treatment, but when I do, it's special.
youngrichard
PS I've done all that midnight oil burning; I'm retired now, so I can do it in the afternoon.