The masking frame

Also called an easel they come in different sizes. It is a good idea to pick one that is larger than your current needs therefore not limiting the proportions of your enlargements. The main reasons for using a masking frame are to hold the paper flat, to reconfigure the composition, allow the margins to be adjusted to the various format sizes you wish to use and to crop out some of those bits that creep in at edges, that you didn't see before you pressed the shutter. 

The frames come with two or four independently adjustable blades on a yellow or white base. I have noticed that some blades are not set at right angles to each other so it is a good idea to check them at various settings with a set square to make sure they are true. Also make sure that the edges of the blades are not bevelled under. This will reflect the light and produce a thin black line around the edge of the picture. It can be a nice affect but one you should have control over. The light colour of the baseboard is so you can see the projected negative, enabling you to frame the image before you put the photo paper in place.

When using single weight papers on a white baseboard, it is possible for the light to pass through the paper and be reflected back, changing the value of the exposure. You can stop this by laying a dark coloured card on the baseboard with the light sensitive paper on top.

The most versatile of the masking frames is the four blade, it allows you to mask the image by only having to move the blades of the frame without having to re-a line the whole easel each time. It also gives better control over how big or small you make the margins and in some cases gives you the ability to produce borderless prints. The versatility of these frames makes them quite expensive to purchase.

Schaimpflug's rule.

This is the rule on tilting the easel and carries on from my last post.  The most accurate way of correcting distortion is to use Scheimpflug's principle: This states that you should tilt the negative as well as the baseboard and that they need to be canted over in opposite directions to each other. Additionally the incline should be such that the plane of the negative and the plane of the baseboard should meet in the plane of the aperture to give maximum sharpness over the whole image. 

You will find that the more expensive enlargers allow the plane of the negative to be tilted, add a tilting easel to the mix and the results produced can be remarkable.

Related posts:

Tilting the easel.

Tilting the easel

Is mainly used for correcting those converging verticals in pictures of buildings. The reason you get sloping upright lines is because the camera has not been held vertical to the view.  View cameras (large format) are the only cameras that can keep the film plane vertical and look slightly upwards at the same time with out this distortion. You can buy a shift lens which has the same ability or do it in Photoshop.

When enlarging you negative you can correct this by using a tiling easel.  Simply lift the easel by the appropriate amount and rest it on a block. Remember that you need to lift the easel on the side that has the converging lines. When doing this you should set the smallest possible aperture providing the greatest depth of field. When making the enlargement, part of the picture may be lost, it is just a case of cropping the picture to make it square. After processing the exposure may be different between the top and bottom this can be corrected by dodging to even up the overall exposure.

Related posts:

Scheimpflug's rule.