The third and last method of bellows making which we will describe is that devised by Mr. Bierstadt, and called the truncated cornered pyramidal bellows, for the reason that the corners of the folds are truncated. The advantage that this form possesses over any other is that it may be folded up into smaller space than others, and at the same time it is so elastic that its folds do not adhere to each other.
In Fig. 66 will be seen a plan of a bellows of this form for a 4x5 camera. The peculiar manner in which this kind of bellows is folded is best ex plained by Fig. 67. The inside measurement at the back is five inches, and at the front three inches. We draw a centre line C and measure off the side corner line D ; we then divide the centre line into inches, and draw lines parallel to A, extending them on either side as far as line B. We next determine the position of the intermediate line I by deducting from half the distance between E and A the amount of space between G and H, obtained by dropping a line from the intersection of fold line E with corner line D to the base line A, the said line E F being parallel with the centre line C. Just here is an important difference. Instead of stopping the intermediate
line at the corner line D, we extend it to point J, or a distance be yond the perpendicular line I F, equivalent to the space between I and F, or between E and I. We then draw the line J parallel with corner line D, and have a guide where to draw the zigzag lines like A and E to line D. By drawing a diagonal line from H to J across the square K, and from J to E across the square L, we have the proper location and angle for the corner crease lines. From the point H we measure off half the width of the inside of the intended side of the bellows. Draw a centre line perpendicular to its base, and measure off on that the position of the fold lines as described for the top of the bellows. It will be noticed that on the sides of the bellows the intermediate lines stop at J, while the other fold lines cross the line J, and meet at E. By this method a curious skew shape of the cross lines, especially between lines D and J, is observed, but is necessary in order that the folds may come out in unison. A bellows constructed after this plan requires a little more leather, but is far superior in appearance to any other.