Color shift on R4 prints

[coops]

I plan on making some 16x20 R4 prints this week when the paper arrives and was hoping to first make the print on 8x10 (same paper) and get the color right, then print on the larger paper and only needing to make changes to exposure. Is this a fair assumtion? Or will the color shift a little as I go to a larger print. Just trying to save paper.
Also, as a general rule with color paper, how much extra exposure should I expect to give 16x20 from 8x10? Cheers

[Robert Ley]

If you are using the exact same paper (same emulsion #) then there should be no change in color. I have used a rule of thumb that give it one stop of extra light for each rise in size...8X10 to 11X14= one stop 8x10 to 16x20= two stops. I would add two stops and use an 8x10 sheet or smaller to check exposure.

[coops]

Thanks Robert.

[Scotty230358]

If the sole object is to get the colour right would it not be a good idea to size your image to 20x16 and make a 10x8 sectional print of the most important area. Thus you will get your colour and exposure locked down in one go.

[Robert Ley]

I find it somewhat difficult to judge color balance from a small section of a large print.
Also if the negative requires any dodging or burning or other print manipulations, it is easier to translate that knowledge to the 16x20 after getting a good 8x10.

[hka]

@Robert: I agree with you. That's also my way of working.

When you have find the right color balance and exposer time for the smaller print then it is easy to blow up to a 16x20 or so. To avoid color shift play with the aperture to keep the exposure time around the time you found for the smaller print.

[Greg Blank]

Some good info provided so far. The only time color will shift is if you go to a different emulsion - or a new film base, like making prints from Kodak film to Fuji or if your chemical strength declines. However if the paper is the same maker and same exact type more likely you will not see a dramatic shift. My color photo teacher always said, print your density correct and then color balance. A difference in exposure from 810 to 1620 is about 4x. Beyond the 18 second sweet spot for exposure you may not see small shifts up to 32 seconds using the same aperture @1620 those 32 second exposures are more likely if you have a average density color negative or slightly dense one -thus keeping the exposure time as the only variable. I have a analyzer that measures the light output at the base board so adjusting the aperture is easy as long as you started in the middle of the aperture range.

[tgtaylor]

I always use the same time whe enlargening from 8x10 to 11x14 or beyond by opening the aperature to comepnsate. If you change the time you will change the density.

Thomas

[gary mulder]

If you have a enlarger with a shutter, ore better a closed loop light, going from 8x10 to 16x20 with a compensation in exposure time will not be a problem. Maybe a color shift ± cc 01. But if you have a enlarger without a shutter try use the same exposure time and compensate with the aperture.
This is one of the reasons why pro's use closed loop enlarger's. In the time the bulb needs to reach it's temperature it will give a different color.

[coops]

Thanks for all the advice. Great stuff.


Cheers