This section is from the book "Complete Self-Instructing Library Of Practical Photography", by J. B. Schriever. Also available from Amazon: Complete Self-Instructing Library Of Practical Photography.
Securing Sharp Focus. Always focus with your lens wide open. Be careful that your picture is placed both perpendicularly and horizontally to your camera. Focus as close as you can and then, if you find it necessary use a stop small enough to give you a perfectly sharp image.
Overcoming Reflection. Reflections are oftentimes caused by too strong light striking on some light article or wallpaper in the room, either of which may happen to be at such an angle that the light is thrown on to the pictures which you arc copying. A little careful observation on your part-covering up such articles with a dark cloth, or placing a screen between the light object and the picture-will readily enable you to overcome this reflection. If you are troubled with reflections when copying a picture which is framed, the glass should be removed if possible, or, by placing a black screen in front of the camera, with a small hole in it just large enough for the lens, you can readily overcome reflection on the glass. The use of a short focus lens is often responsible for this difficulty, as, the angle of view being a wide one, objects in front and a considerable distance from it on both sides are reflected onto the lens. Here again you will find the hood a very convenient accessory. Using a long focus lens the camera can be placed at a greater distance, thereby lessening the danger of reflection.
Overcoming Distortion. Distortion is generally caused by the picture not having been placed perfectly parallel to the ground-glass. If it is turned a trifle to one side or tipped backward, or forward to the camera you are bound to produce distortion. Adjust your camera and picture carefully, having them both perfectly aligned, and you will readily overcome this difficulty.
Overcoming Grain Of Paper In Original Picture. In some cases it is impossible to overcome the grain entirely, but careful lighting, use of proper plates, full exposure and full development will make it possible to at least not show the grain any more than it appears in the original picture. The lighting, exposure and development are important factors to be dealt with under such circumstances. (Read instruction carefully.)
Securing Proper Exposure. Only practice and close observation will enable you to judge proper exposure. Keep a memorandum of your exposures, noting carefully the conditions of light, length of exposure, and whether the plate appears to be under or over-exposed when developing. Examine your results carefully and then govern yourself accordingly the next time you are copying a picture under the same or similar conditions.
Plate Develops Flat. This is almost a certain sign that the plate was very much over-exposed. If the plate flashes up quickly in the developer you must immediately take means to overcome the effects of this extra over-exposure by restraining your developer. See instructions for developing over-exposures, Vol. II.