Aspect ratio of scanned 35mm slides

As mentioned in another thread I currently spend some time scanning a selection of my slides I had taken many years ago. I therefore have reactivated my Nikon Coolscan 4000 film scanner and use the current version of the Silverfast Scan Software. I optionally want to provide a mixture of the scans and images taken with my DSLRs for different tasks, i.e. future talks and digital presentations, prints for exhibitons, web galleries etc. That means the dimensions of both outputs basically should be identical.

It has been my expectation that the aspect ratio of the slides is 36:24mm = 3:2. However, if I exactly place the scan frame within the black boundaries of the slides, the dimensions (proportions) in the preview window and the resulting scan considerably differ from that 3:2 aspect ratio I get from the processed files of the DSLRs: Let's say I want the output dimensions to be 30:20 cm, the content of the scan frame for example is 30,65 : 20cm, though, (given I lock the width to 20 and vice versa). By then, the input dimensions of the slide are 3,45x 2,26 cm, btw

To get the aspect ratio of 3:2, I either need to lock both the length and width of the output dimensions in the scan program (Silverfast) to 30:20 by keeping the scaling factor identical for both sides - or crop/cut the scan in PS afterwards. Of course, both ways identically result in loss of image content which can be relevant - or not.

Based on both output dimensions locked to 30:20cm again, I can alternatively unlock the scalingfactor (to 869x and 884x in this example). That doesn't cut the image then but leads to distortions, of course, which can be barely visible or evident depending on the image content. It's probably even more obvious if the output is set to 45x30 cm.  Again, I can also tweak the given scan output of 30,65 x 20cm later in PS by resampling the scan without keeping the orginal proportions.

I had expected slight deviations from the aspect ratio of 3:2. But based on 30:20 cm the lengthwise amount of 0,6cm is considerable and surprising for me. I could realize that there are very small differences between the slides, probably caused by the framing. But the proportion is never 3:2.

I guess the subject posted here is a bit "outdated " in the digital age and it's a long time since I dealt with slides and scanning, too. But the pandemic gives me the time and opportunity to revive my archives. So maybe there's a basic error of reasoning in my initial expectation regarding the aspect ratio. As for the settings and procedure of the scan process, I don't see an user error, though. I'm also unsure of the best alternative to circumnavigate the problem.
That said,  I'd appreciate comments and experiences of other photogs who made the transition from the analogue age and maybe had scanned their slides in the past, too.

Thank you in advance

Wolfgang

 

When I have wanted to scan a slide at full dimensions, I have always used a slide mount that reveals the full image. Most slide mounts cover part of the image and may change the proportion ratio if not cut to those proportions, i.e. 36x24.(https://en.wikipedia.org/wiki/35_mm_format). Slide mounts are often about 34x23(http://www.pearsonimaging.com/articles/about/filmformats.html). I think this is the one I used, although in the description, it says 35.8x24.4. The frame is prominently marked in raised letters “Original”.

Joe

Thank you for your comment and informative links, Joe. Interesting and basically a possible reason for the problem. However, I clearly see the black boundaries in each direction of the slide in the preview window and I'm using it for adjusting the scan frame. But I will unmount one of my slides to check if there's in fact a coverage of the image by the mount. If so, it wouldn't be a good thing  given ten thousands slides in my archive. I occasionally used Wess mounts for slide shows, too. But just for quick mounting and archives I used the glassless Hamafix mounts, https://de.hama.com/00001032/hama-hamaf ... rgetLang=1, probably not distributed in the US.

Wolfgang

This is an example of a slide that only revealed the full image by using the full frame slide mount. With a standard slide mount, the turkeys were cut off and the frame was tighter as well. (BTW, I still have never been able to get the digital processing right on that image, but the slide is perfect in my eyes.)

https://www.naturescapes.net/forums/viewtopic.php?f=3&t=227121

If you do try the Wess mount, make sure it is the full frame or “Original” mount. The others will still cut off image area. Usually, most images won’t need the extra, unless you have to have it. I always shot a bit wider if it was possible just with the mounted image in mind. I always mounted my own slides because I could never get my mounted slides back from any developer without scratches. I used Gepe mounts if I didn’t need the extra room around the edges.

Joe

Thank you again, Joe ! Very nice image, btw.
I now unmounted one of my slides and also checked (measured) the inside dimensions of the different slide mounts I had used over the years such as Gepe, Rowi, Revue and Hamafix - the latter for 95% of the archive of ten thousands of slides. In my rapid search I couldn't find my slides mounted with Wess, so I cannot tell which kind I had. But you definetely hit the point : The frame size of all the mounts I have checked so far is about 34mm x 23mm - or even a bit less on the small side. In consequence I also can see from the comparison of the unmounted slide that those mounts in fact cover a small part of the image. So the "black boundaries" in the preview window of the scan that I use to exactly frame the scan evidentally are caused by the mount and not based on the borders of the slide content itself. Strange enough, that in 25 years of photographing film I never had realized the limited inside dimensions of the standard mounts and the cut off of image content . I therefore didn't come across the alternative of full frame mounts in that analogue age though I always had mounted my slides by myself, too, - for the same reason you did. I also cannot remember how I dealt with the dimensions when I first had scanned some of my slides 15 years ago.

At least, the input dimensions of the slide of 3,45x 2,26 cm in the scan preview that I had referred to in my first post make sens now and I'm glad that the difference from the 3:2 proportion is not caused by a wrong setting in the scan program. Over the last couple of weeks I already scanned around 500 slides - each individually with appropriate settings for tonal balance, color, dust removal etc. and I don't want to redo everything, the more as the Wess mounts aren't available here anymore. There is an offer of some used Wess mounts on ebay, though, but they're not the full frame Originals you mentioned. And I also wouldn't want to remount thousands of slides for optional future scans. So as pointed out in my first post - if I in fact need the 3:2 proportion, there's only the alternative to further cut off the scan to those dimensions or accept a small distortion by locking the output dimensions and unlocking the scaling factor and thus keeping the visible image content, at least.

In any case thank you again !

Wolfgang