Similarly, four times the object distance yields sixteen times the depth of field. If you can not achieve the depth of field you need by other methods, consider increasing the object distances to the camera. Later, when you crop the negative to achieve the perspective had before increasing the object distances, the loss in sharpness due to cropping will be linear, not exponential like the gain in depth of field. Grain might become an issue due to the increased magnification of the negative, but the desired depth of field will have been achieved. Halving the focal length quadruples the depth of field, for a given format.
Depth of field is directly proportional to the f-number.
If you double the f-number, you double the depth of field. Thus far, we have assumed that all viewing distances would be equal to the print diagonal. This is not an unrealistic assumption, but it is said that the best perspective is achieved at a viewing distance determined using the formula above. It should be apparent by now that the constant 1750, is really a variable. Only the focal length component of this equation presents a threat.