What aspect ratio are slides intended to be?

Question

My father-in-law was cleaning out his basement recently and discovered a cache of slide carousels taken in the 1960s that his deceased wife left behind. He sent them to my wife and I and we have had them scanned and are cleaning them up now. The question I have is what the intended aspect ratio was? Some of the slides are clearly 3:2 and have no border around them. However, a large batch of them appear to be almost, but not quite 5:4 with a black border to pad them to 3:2. They are just slightly too tall to be 5:4. Was this just some "slop" that the format supported or was there some other well-known aspect ratio that they represent? (They also aren't 1:1.)

There's also some black fringing on the sides that makes it look like torn paper. The original images are about 3120x2048 pixels. Once I've cropped them to 5:4, they are around 2472x1976 pixels. (It's inexact because I'm cropping each one separately by hand.) So there about 72 pixels of extra height, or about 3.5%. What's the reason for the extra? Or is it not extra, and I'm missing something?

Answer 1

The Kodak Carousel projector design accepted 2 inch by 2 inch slides. Most of these were made with a 35mm film camera. The format was most often 24mm height by 36mm long. This length to height ratio can be stated as 1.5 to 1 or 3:2. In that period of time, several camera models made half-frame images, the idea was to squeeze more pictures out of a roll.

About that time, Kodak and others introduced a 126 film size. This was 35mm wide film in a plastic cassette. This camera format was easy to use and practically foolproof to load. The 126 was 35mm perforated on just one side. The format was 28mm by 28mm thus it was square. During manufacture, the film makers pre-exposed a boarder around the film. The idea was to make it easier for photofinishers. When negative film was loaded, the finished results were prints on paper either 3 ½ X 3 ½ inches or 4 inches by 4 inches. The pre-exposed border allowed high speed printing as the black border and the perforation location forced the frame to fall in perfect alignment during high-speed printing and then perfect alignment for high-speed negative cutting and packaging. The 126 slide had the black border, the actual dimensions when placed in a 2 X 2 cardboard slide was 26 ½ mm X 26 1/2mm. Depending on the make of the cardboard slide frame, some came out slightly off square. This I think is your 5:4 slides.

There was also a 127 super slide as described in Jerry’s answer. Also, the Rollieflex twin-lens-reflex was quite popular. Their was a Rollieflex that accepted 127 film and the 120 film size camera sported metal mask insert that masked off the normally 60mm by 60mm image to 28mm by 28mm. The idea was to make high quality slides to fit in the Kodak Carousel projector. This projector design dominated that period.

There were 60mm by 60mm cardboard slide material for the film from the Rollieflex. Many slides were mounted in sandwiched in glass using duct tape to seals and there were aluminum slide mounts also. These fit in a 2 ¼ X 2 ¼ projector. The imge qualitywas outstanding.

Answer 2

Standard 35mm full frame size was 24 x 36, which gives you the normal 3:2 format. If the 5:4 ish ones are a larger area than the normal 36x24mm slides, they may be transparencies from 127 film, which allowed images up to 40x40mm to be fitted in 2" x 2" slide mounts (the same size as 35mm film slides). These larger slides were known as "superslides" (see https://en.wikipedia.org/wiki/127_film#Superslide).

If the film area is the same size as the normal 35mm 3:2 images, but just with a black border, there are two possibilities: They may have been copied from 8 x 10 (or 20 x 16 (see note 1)) inch prints, or (if home mounted, or commercially processed with a clip shut plastic mount that can be opened and resealed) may have been masked down to that aspect ratio for artistic reasons.

Back in the film days, I used to do that with some of my slides - you could buy special slide mounts with a metal mask built in, or make your own mask from tinfoil (or possibly paper or card, but tinfoil was (a) opaque, and (b) non flammable - potentially important given that projector lamps can run pretty hot...).

You could also get APS slide film for the short lived APS cameras - these allowed a choice of the different APS aspect ratios, but - although they used the same 2" x 2" mounts, the film area was significantly smaller than 35mm.

note 1: 20 x 16 was a common size for mounted prints for photo society competitions (in the UK, at any rate - though that's probably shifted to the metric near equivalent (40 x 50 cm?) these days.)