The Benefits of Recording Your 35mm Slide’s Exposure Number

by | Last updated Apr 21, 2017 | Organizing Digitals, Scanning Photos | 4 comments

35mm slide on desk — showing exposure number and date markings at top

35mm slide I just scanned from my collection.

Did you ever notice those little 2-digit numbers printed at the top of your 35mm slides?

I have to keep in mind some of you reading this may have never even touched a roll of film in your life!

It's scary for guys like me to think that's even possible, but it really is!

Digital cameras have been affordable since about 2000.


For the uninitiated, [cough]  when you shot pictures that would be developed as those little plastic or cardboard slides, that you later projected onto a large screen for family nap times viewings, you used a special roll of film in your camera.

One of the choices you had to make when picking out a box of film was how many exposures you wanted.

Kodak Kodachrome film box

Kodak Kodachrome film box

Usually they came in divisibles of 12 — so 12, 24 or 36 images (or exposures) were most popular.


Isn't it funny to think that back then we were actually “limited” to the number of shots we could take!


Okay, so now we are back to those funny little numbers that are usually printed somewhere on your old slides.

Yes! Thanks for keeping up. These numbers represent what frame from the roll of film is inside this slide mount.

35mm slide magnified to show exposure number marking

Magnified view of the exposure number (24) at the top left edge of a slide developed in 1984.

Now, this number could seemingly be irrelevant to many now that we are moving along in the digital era.


But, I am proposing to you now to consider recording this exposure number somewhere in your “digital” records for one of many possible reasons that could eventually come up for you.


Now if you are doing any of the other techniques I revealed in my file naming system and my numbering system, you may be a little upset with me for suggesting yet another thing to keep track of. [laughing]  I'm Sorry!

But even though this would benefit anyone who is scanning their 35mm slides, it's possible this is more of a suggestion for those with advanced goals for their photo collections.

Why Even Record This Info

The main reason to type this information someplace in your records is because of chronology.

We all rely on this kind of time-based order more than we're probably really aware of.

For example, if someone asks us how our vacation or holiday was, what do we do? We show them our photo collections on our laptops or smart phones and we say something like:

It was incredible! First we did this, and then we did that, and here we are eating this — oh and THEN you won't believe what we saw!

The chronology of the images is important because it reveals the experience as an entire story. Otherwise, it just becomes a bunch of single random memories.


We are all spoiled in the digital camera age when all of our photos are automatically “date stamped” for us. When we want to know when a photo was taken, we just “right click” on it and look at the properties or information window and we can find out the exact date and time it was taken. It's fantastic!

And better yet, if you want to sort a whole group of digital images in the order they were originally taken, it's usually just clicking one button or “heading bar” at the top of the list and boom, they are sorted in order!


But, if you're holding a physical slide in your hand, all you have to go on is that exposure count and (if you're lucky) part of the date when it was developed stamped at the top to help you determine when the photo was taken.

And don't get me started on sorting a group of slides by chronological order in your image manager software. Without knowing the exposure number, you are pretty much completely out of luck unless you were actually there when the photos were taken and your memory is remarkable!


It may take some work moving the images around in your image manager, but with these numbers recorded, you will eventually be able to put unsorted slides back into their original chronological order.


When Should You Record It

The best time to record this number is right after you've scanned them, or gotten them back from a photo scanning service.

Chances are, once you put them back in their little boxes, slide trays or whatever you have them stored in, and then put them back way in the dark place of your bedroom closet or whathaveyou (that's a fun word isn't it?), I can almost guarantee you will never want to obtain this information.

I am right aren't I?

This is especially true for those of you who are thinking about throwing your original slides and prints in the trash after you have scanned them. For the very small percentage of you who are working towards this “minimalistic” goal, recording this information as soon as possible is imperative.

How You Might Choose to Record It

Keep in mind we are in the process of moving our analog collections into the digital world. So while recording this information in a paper log somewhere is of course possible, I would highly recommend you type this information into your computer in an appropriate place that will be associated with each particular image.


My favorite place to enter the exposure number is in the image's actual filename.

I type it in right after I pull the slides out from my scanner. They are right in front of me on my desk so why not.

And if I need to, I can easily double check and compare the slide to the digital file that was just created (by holding the slide up to a source of light) just to make sure I'm labeling the correct image.


If your operating system allows characters like parenthesis and brackets, I recommend you try using them around the number because they can differentiate the numbers and make them so much easier to read.

Here is a basic and an advanced example of how you could add them to your filenames:


Grandpa Holding Up Leaning Tower Pisa (24).jpg

1962-07-xx Leaning Tower Pisa (ES-3200-UM-48b-#01390) [SL-24].tif


In the advanced filename, I added “SL” for slide. This could help you quickly identify this image later as being made from a slide versus a negative (NG) or a print (PR).

Description / Caption Field

Another place you could enter the number is in the caption or description field in your non-destructive image manager of choice.

To me, this isn't as favorable as the filename. But, it's an option nonetheless.

And for example, for those using iPhoto and who have already imported in their photos, modifying the description field is far easier than modifying the filename at this point.

Example of a slide exposure number written in the caption field of a photo in Google's Picasa

Here's how you might add the exposure number in Google's Picasa in the caption field.

Example of a slide exposure number written in the caption field of a photo in Apple's iPhoto

Here's how you could add the exposure number in Apple's iPhoto using the description field.

Just know that in some applications, the caption may not be immediately written (saved) inside of the master image file. It's possible it will just be stored in the software's database until the image is eventually exported out of the program for various purposes.

Regardless, the number is still being stored with each digital image and that is our goal. Just make sure your library (database) is being backed up regularly.

Metadata Fields

For those using more professional programs like Lightroom or Aperture, you could easily pull up the standardized IPTC fields where you can freely enter in any information you would like.

There isn't a specific IPTC field called “Exposure,” but you could use one of the more generic fields like “Category” and place your exposure numbers there.

Slide exposure number entered in the IPTC metadata field "Category" in Adobe's Lightroom

Here's an example using the standard “Category” IPTC metadata field to store the exposure number in Adobe's Lightroom.

Or, you could create your own customized metadata field. Here in Apple's Aperture, I created a “custom” metadata field and was able to label it “Exposure.”

Slide exposure number entered in a custom field called exposure in Apple's Aperture

Custom metadata field “Exposure” created in Apple's Aperture.

Update: As pointed out by Art Taylor in the comments, calling the metadata field “Exposure” might be confusing as you might later think it's referring to shutter speed, Aperture, and ISO/ASA. His suggestion of “Exposure Number” or “Frame Number” would be better, especially if you're mixing it with other (EXIF) camera fields.

A downside though to custom fields as opposed to the standardized “IPTC” fields is that they may not carry over to other photo applications you may wish to use. I would advise you to experiment with this if your workflow involves moving from one application to another.



Okay, so who's with me!? Who else is recording this information or is now thinking about doing so?

Tell me why in the comments below. I would love to hear your thoughts!

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Dave Robinson
Dave Robinson

My favorite place to enter the exposure number is in the image’s actual filename.

I type it in right after I pull the slides out from my scanner. They are right in front of me on my desk so why not.

And if I need to, I can easily double check and compare the slide to the digital file that was just created (by holding the slide up to a source of light) just to make sure I’m labeling the correct image.

If your operating system allows characters like parenthesis and brackets, I recommend you try using them around the number because they can differentiate the numbers and make them so much easier to read.

Here is a basic and an advanced example of how you could add them to your filenames:

Grandpa Holding Up Leaning Tower Pisa (24).jpg

1962-07-xx Leaning Tower Pisa (ES-3200-UM-48b-#01390) [SL-24].tif

Hi Curtis!
I’m definitely one to follow chronology! I like to document everything I can the best way I can. I too would prefer to have the exposure numbers in the file name.

I shot film for a lot of years before I went digital in 2008. Very often I’d shoot multiple rolls of film for a given event. Because of this, I kept track of rolls and frame numbers. So, I thought I’d put something like this at the end of the file name: [NG R-01 F24A].

I probably never had more than 9 rolls of film on a given shoot, but I wanted to give myself two digits for the roll number just in case. Depending on how a roll of 35mm film got loaded into the camera, sometimes your first frame was frame 1, and other times your first frame was 1A, or maybe even 0A, So I thought I’d give myself three digits for the frame number. For consistency, I thought I’d use the same numbering system for prints and slides as well, although I don’t think I ever saw more than 2 digits on a slide frame number.

I have no earthly idea how large my photo collection is. I have lots of old family photos on my side of the family and lots of old family photos on my wife’s side. Those photos are the highest priority, and I need to start there.

So It maybe years before I get around to scanning my own photo collection, but this is how I plan on documenting the exposure numbers when I get there.

Art Taylor
Art Taylor

Thanks, Curtis, for your response.

One excellent reason for adding the frame number and processing date to digital images from scanned slides or negatives is that information may be the ONLY information readily available to help with establishing the date a particular image was made. If both prints and negatives are available for a roll of film, it should be possible to match each print with its corresponding negative and determine the sequence of similar shots. This might be important, or at least very interesting, for shots of a particular event such as a wedding. If shots are taken of various individuals making speeches, and the names have been written on paper in a program or just a casual note, it should be easy to match the sequence of names and faces to identify these people. Another possible sequence would be one such as the series of shots I took back in 1986 as CNR’s Spadina roundhouse and coach yard in Toronto were demolished to permit the construction of Skydome, now known as Rogers Centre, the domed stadium that is home to the Toronto Blue Jays. My series of shots was taken over a period of several months as the process proceeded, with shots being taken at least once a week, sometimes several times per week, on different days. A similar sequence might have been taken to document the construction of the new stadium.

If prints and negatives are initially stored in the envelope from the processing lab, the date the envelope was received either at the drop-off store or at the lab, most likely was written or stamped on it. Lacking other evidence of dates taken, this would provide at least an approximate date the shots were exposed. However, unless one is familiar with the photographer, and knows how frequently he/she got film exposed and processed, the processing date may be only approximate. An avid photographer may have shot a dozen or more rolls (particularly of slides) on one day and maybe even a hundred rolls on a 3-week trip. Such rolls would likely have been sent in for processing within a few days of their exposure so the processing date would be fairly accurate. However, if photos of 2 different Christmas trees appear on one roll of film, with a variety of outdoor, summer shots between them, chances are that photographer didn’t shoot much film in any one year. In this situation, the processing date is likely closer to the date of the last group of negatives on the roll but the film may have been stashed in a drawer for safe keeping and forgotten about for months or even years, so the processing date on an envelope or on slide mounts would serve only as a reliable ‘NOT AFTER’ date. It would not provide a reliable ‘ON’ or ‘NOT BEFORE’ date.

If photos in an album are known, or at least suspected, to be entered in chronological order, it may be possible to match these photos with negatives with a known processing date, thus providing at least some indication of dates.

Curtis raises an excellent point about the standardized IPTC and EXIF data fields used in various programs. Not all programs that support IPTC and/or EXIF, provide complete support for all the available fields. Some older programs won’t support the newer, extended fields because such fields did not exist at the time such programs were written. Even current programs that offer some support for this data don’t follow the ‘standard rules’ very well and some programs ignore such industry standards completely, going their own way with proprietary data fields, compatible only within related programs from the same company. As Curtis suggests, experiment with COPIES of your images in various programs you might be considering using, now and in the future. Also, think about how future users of your data base and images might be able to access the data you spend time and effort entering. Stick with a program that provides the closest support to the existing standards to ensure maximum future accessibility to your data.


Art Taylor
Art Taylor

Hi Curtis,

Another good post!

It’s only been since about the early 1970s that 24 exposure rolls of film were available. Before then, we had a choice of 12, 20, or 36 exposures per roll. While they were theoretically available, I don’t recall ever seeing, much less using, a 12-exposure of 35 mm film. Medium format films, sizes 120 and 620, were available in different lengths, but the number of exposures per roll depended on the particular camera’s format. Each camera, generally, had a fixed image format, although there may have been a few high-end (read expensive) cameras that could be used with different formats on the same roll of film. Usually a camera exposed one of these size negatives: 6.0 x 4.5 cm (645); 6.0 x 6.0 cm (6-by-6); 6.0 x 7.0 cm (6 by 7); or 6.0 x 9.0 cm (6 by 9). A few cameras could shoot panoramic photos of 6.0 x 12.0 cm or longer. Often, photographers referred to 6 by 6 as 2 1/4 (inches) square; 6 by 7 as 2 1/4 by 2 3/4 (inches); and 6 by 9 as 2 1/4 by 3 1/2 (inches) before Canada officially converted to metric measurements.

Your use of the term ‘Exposure’, by itself instead of ‘Exposure Number’, could lead to confusion. People might think of it in terms of ‘Exposure’ as related to Shutter speed, Aperture, and ISO/ASA. It could reasonably be called ‘Frame Number’ or ‘Exposure Number’.

While it’s usually visible on the slide mount, if somebody has re-mounted a slide at some time, as happened with camera club members who often re-mounted particular slides in special mounts to crop the image for composition or other reasons; or if a slide has been transferred to a glass and plastic mount but the data printed on the original mount has not been copied; or if the processing lab’s printing is simply not legible, as has been known to happen; the original frame number is visible on the film rebate (the black strip beside the sprocket holes) once the film is removed from its mount. The frame numbers for negatives are also visible in the same location, at least for 35 mm, 126 Instamatic, and 110 Pocket Instamatic films.

Because different format cameras could use 127, 120, 620, medium format films, frame numbers were generally not printed on these films because a single length of film would give a different number of frames, depending on which format the camera used.

A few 35 mm cameras had the ability to imprint the time/date/sequence number on every frame of film. Occasionally, this feature was built-in to the camera body but often, a separate ‘data back’ was required. This was the case with several models of Minolta cameras I owned and used. The original camera back was removable and the optional data back was attached in its place. Such data backs usually had their own battery or batteries which required periodic replacement. Of course, once the battery power was removed, the clock and calendar had to be reset when power was restored with a fresh battery. Otherwise, the default date and time would be imprinted and this would seldom give correct information.

Sometimes the imprint would be clearly within the image area. At other times, depending on the particular camera, it would be imprinted in the black strip between film frames, at least in theory. Depending on how carefully the slides happened to be mounted, it was sometimes visible in the image area, at the very edge of the frame. Other times, it would be covered by the slide mount.

Users of Photoshop Elements or Lightroom have the option of writing all captions and other IPTC data to each image file, even before any attempt to export a file. In Elements, (at least on Windows), the command is in the File menu. This option should be used after every change to data, whether new data is added or existing data is edited. That way, the data is saved both within the PSE/LR catalog/data base AND within the image file so it’s accessible to other programs outside of PSE or LR.

Keep up the good work on the blog.