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How to Tell Which Type of Slides You Have

By Dillon Wallace

Not all slides are created equal.

That may seem like a simple concept, but similar to today’s laundry list of digital photo formats (PDF, JPEG, PNG, etc.), there’s definite differences. Only for slides, those differences are even easier to notice as they’re tangible objects that all look slightly different. That is, if you know what to look for.


Picture this scenario. 

You’ve just stumbled upon your grandparents’ old box of slides buried at the bottom of their ornate walnut chest they got as a wedding gift back in 1949. As you dig through the Red Wings boots shoebox, you notice they’re not all the same. Similar, but not the same.

Not to fret, we’re here to help you decipher what type of slides are what.


Mounted Slides & projectors

Your grandparents’ photo slides are most likely mounted individual transparency slides used in yesteryear’s slide projectors. The most common form of these slides is a rectangular 35mm bit of film placed in a small square piece of cardboard or plastic shell for protection. Sometimes, these might be glass transparencies but that’s not as common.

Introduced in the 1930s, 35 mm film quickly rose to prominence in the 1960s as the go-to standard. Slide projectors were a mainstay in academic facilities and typically used either Kodachrome, Ektachrome or Ansochrome 2” x 2” transparencies throughout the 50s, 60s and 70s.


Identifying 35 mm formats

Now that you know a little about the background of your treasure chest of slides, how do you know what 35 mm slide format you have? After all, there is quite a variety, including 126, 127 and 110 slide films? Not to mention, almost all 35 slides are 2” x 2” mounts, except for the 110 which is a 1” x 1” mount – it can get a little tricky.

Let’s start with the most standard of the bunch and work our way down the list.

Standard 35 mm Slide

  • Slide Mount: 2” x 2”
  • Transparency Film Size: 24mm x 36mm
  • This slide is going to look as if the transparency fills the mount like a TV screen. There will be more room on the top and bottom than on the sides.

Half Frame 35 mm Slide

  • Slide Mount: 2” x 2”
  • Transparency Film Size: 18mm x 24mm
  • Like the name suggests, this slide is nearly half of the standard slide size. The transparency is just a tiny rectangle in the middle.

126 Slide

  • Slide Mount: 2” x 2”
  • Transparency Film Size: 28mm x 28mm
  • Produced by Kodak in 1963, this film’s transparency is a perfect square (not a rectangle) within the mount.

127 Slide

  • Slide Mount: 2” x 2”
  • Transparency Film Size: 40mm x 40mm
  • Another slide produced by Kodak, this film’s transparency is also a perfect square but fills out the mount much more than the 126 format. It was produced as early as 1912 all the way up until 1995.

127 Superslide

  • Slide Mount: 2” x 2”
  • Transparency Film Size: nearly 2” x 2”
  • This is a rare slide for personal images, but if you do stumble across this slide it should be easy to identify as the film transparency fills out nearly every millimeter of the 2” x 2” mount.

110 2” x 2” Slide

  • Slide Mount: 2” x 2”
  • Transparency Film Size: 13mm x 17mm
  • This tiny little slide is easily identified as the smallest film transparency on a 2” x 2” mount.

110 1” x 1” Slide

  • Slide Mount: 1” x 1”
  • Transparency Film Size: 13mm x 17mm
  • Similar to the 110 2” x 2” slide, except this slide’s mount is half the size. The smallest all-around slide of the bunch.

Digitize your slides

Now that you’ve got the 411 on identifying your nana and papa’s slide collection, your next move is paramount. There’s a strong chance that you found the slides but probably no projector (at least not a working one) in sight. It’s okay, because what you should do is preserve those memories by digitizing them today for future generations to view and share. It may not have the same click through slide feel as they would viewed in a retro projector, but they’ll be safe and future-proof. And if you really want the full projector-like experience, you can always view them in slide show mode on your computer for that authentic feel.

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