gvarner Loc: Central Oregon Coast

I’ve seen everything from 300 to 3200. Aside from slow scan times, what’s the pros and cons of low versus high? Full disclosure: I did mine at 600 with the plan to scan at much higher if I had a real good one that I wanted to make a large print with.

BebuLamar

I do it at 3200 but if you ask CHG_CANON he would say none of your numbers mean anything.
In my opinion scanning a 35mm slide at 3200 would give you about 13.5MP image which is sufficient to get all the details there are in the slide. But that my opinion.

rmalarz Loc: Tempe, Arizona

I just finished scanning some 120 color slide film with an Epson V850. I simply used the default 3200. I a light table to choose the exposures to scan and then scan them. No use in scanning twice.
--Bob

CHG_CANON Loc: the Windy City

Look at the pixel resolution of the resulting JPEGs. However you want to fiddle with the numbers of the scanner settings, the pixel resolution of the resulting digital files is the ultimate measure of success.

f8lee Loc: New Mexico

That is not quite accurate - and Paul (@CHG_CANON) never implied it was - when it comes to scanning, which in effect is making an original digital copy of an analog original, the higher the resolution used the better. So 3200 is the way to go - when I scan slides on a Nikon 4000-ED I use the 4000 dpi resolution.

Look at it this way - say you want to make a print from a scan that is 8x10" in size. At a nominal 300 dpi print setting that calculates out to a need for 3000 dots on the long edge, right?

So if you were to scan that 35MM slide at 200 dpi, and again at 2000 dpi (just to make the math simple), even you can see that the former, lower resolution scan will require the printer driver software (or poet procesing softwaer) to interpolate a lot of dots to fulfil the total of 3000 dots required. Meanwhile, the straight scan file at 2000 dpi would already be 3000 dots!

See how that works?

CHG_CANON Loc: the Windy City

If I've said it once, I've now said it a 1,000 times: there are no dots in pixel-based images.

Your scanning process creates pixel-based digital files, no matter the target file format of JPEG, TIFF, DNG, etc. If you want a 24MP digital file, one like if you had photographed the negative or slide with your 24MP DSLR instead of scanning, you need to find the scanner setting that yields 6000x4000 pixels. Adjust the scanner settings for different target pixel resolutions and / or the clock-time needed to scan the negatives.

BebuLamar

Read what he said.

burkphoto Loc: High Point, NC

Think of it this way. If you scan an 8x10 print at 300 dpi, that yields an output file of 2400 by 3000 pixels. That is sufficient to make an 8x10 print that is nearly indistinguishable from the original, IF you have everything set correctly for color and tonal scale. But if you scan a 1.42" by .94" (36x24mm) frame of 35mm film at 300 dpi, that yields only 426 by 282 pixels! That will make a nice "large postage stamp" sized print, or a "yearbook portrait panel page print." And because slide mounts crop the original film a bit, you will probably have even fewer pixels than the theoretical 426x282.

The benefit of scanning at resolutions much higher than the 300 or 600 dpi is that you will have a file you can actually use for something other than social media or a "for position only" placeholder in a book or magazine layout. A "300 dpi scan" means you are capturing just 300 samples per inch of original film, which means it makes one inch of photo quality output. If you want to scan for printing, you have to capture a lot more than 300 dots per inch of original. (Really, those "dots" are square "grid cells" mapped from the scanner glass).

So scan for the target print size:

5 inches on the short side and smaller: Scan for 300 PPI output (i.e.; make a file with 1500 pixels by 300 x [the longer print dimension])
8 inches on the short side: Scan for 240 PPI output (i.e.; make a file with 1920 pixels by 240 x [the longer print dimension])
12 inches on the short side: Scan for 200 PPI output (i.e.; make a file with 2400 pixels by 200 x [the longer print dimension])
16 inches on the short side: Scan for 180 PPI output (i.e.; make a file with 2880 pixels by 180 x [the longer print dimension])

Most of my negatives and slides are 3:2 aspect ratio frames of 35mm film. I "camera scan" (copy them with a macro lens on a 16 MP camera) to as close to 4608 x 3072 pixels as I can capture, knowing I can make about a 24" by 16" print from that at a minimum. If I were scanning them, that would equate to about 3200 dpi at 100% on the film.

In reality, most flatbed scanners cannot resolve 3200 dpi, even if they are advertised as scanning to much larger file sizes. Most of them effectively resolve somewhere between 1800 and 2400 dpi from film. That's plenty for medium format film, but marginal for 35mm film, which is why I turned to camera scanning.

With my 1:1 macro lens, I can scan a 17.3mm by 13.0mm area of film, to 4608 x 3456 pixels. So I can crop away roughly 3/4 the area of a 35mm slide...

The benefit of camera scanning is the ability to capture files as fast as you can load the film or slide in the holder. The detriment of it is having to clean the film first, and having to still do some spotting, negative conversion, and/or tonal or color correction in post-processing. To learn more about that method, read the attached PDF file.

The slide is Kodachrome 64 camera scanned and processed in Lightroom Classic. View download on 4K monitor at 100% if possible.

Attached file:
(Download)


(Download)

CHG_CANON Loc: the Windy City

Or, if you're using an Epson Scanner, you can consider using the Professional Settings in their software and setting up a scanning profile, where ideas on the settings are described and discussed on this post about the v600: https://www.uglyhedgehog.com/t-689142-1.html#12074449

bwana Loc: Bergen, Alberta, Canada

I normally scan slides at 2400 dpi. BUT do a few test runs, some resolutions can result in moire patterns.

bwa

f8lee Loc: New Mexico

And I suggest you understand what he said - "you need to set the scanner to deliver the required pixel count" - and scanners, my boy, are set in dots per inch, because the stepper motors that move the platen or laser or whatever do not know what a "pixel" is, in that it is an artifact of digital imagery.

BebuLamar

What did he mean by "There is no dot in pixel based image" so how your DPI goes?

f8lee Loc: New Mexico

Okay, sir, let me flip that around...why do ALL scanner settings relate to DPI? DO Epson, Nikon and the rest not know of this trade secret?

DPI is a physical measurement - and when you scan a physical slide with a physical device, well, duh, physical measurements are involved. Pixels are without dimension - it takes three to make a visible color, but there is no inherent size to them.

Two different concepts that meet in the form or the scanning process, but ought not be confused.

BebuLamar

Ask CHG_CANON he is the one that said that not me. Didn't I said I use my scanner at 3200dpi? But if you asked CHG_CANON he would say all those DPI numbers mean nothing.

burkphoto Loc: High Point, NC

In Scanner World, a 'dot' is a square cell of a rectangular grid on the scanner glass (platen). If the scanner bed is 8.5x11.7 inches and you scan at 300 dpi, the scanner bed is divided into 2550 by 3510 square cells, each of which is read and processed to numbers, separately. That creates 2550 by 3510 PIXELS in the output file.

If you scan a 56x56mm (nominal 6x6cm or 2.25" square) negative from 120 film, at 3200 dpi, you get about 7055 by 7055 pixels in the output file (more if you include a little border area of the film to aid in white balance).

There are no dots in Digital Image Processing World. Digital files created in scanners are derived from "conceptual" dots — those tiny square areas of the scanner glass, electro-optically converted from light to voltages. The voltages are digitized and processed to pixels — sets of numbers representing red, green, and blue light.

A scanner will have a fixed OPTICAL resolution, which is its absolute number of discrete sensing areas. For lower SET resolutions, the scanner software combines adjacent sensors to create a coarser grid of larger "grid cells" or dots. At higher resolutions, the software interpolates.