What size (resolution) scan is optimal for medium format negatives?

[Tom Pinchenzo]

I get my film developed and scanned by filmdev.co.uk and they offer three scan sizes 1545x1024, 3091x2048 and 6774x4493 for £4, £6 or £8 respectively. I’m shooting med format (6x4.5). My D610 is 24mp which is 6000x4000 so if I wanted equal resolution on my film images It would be the ‘large’ scans, but I’m unsure whether my 6x4.5 bronica ETRSI will resolve enough detail to make the larger scans worth it...

would you go for larger scans with a larger format? E.g. for 35mm, would the small scans be enough??

£2 difference isn’t much but it all adds to the cost per shot! What are your thoughts?

Cheers,
Tom

 

[Kevin Allan]

Thinking about how you want to output your images is a bigger factor than the negative size, when considering what size of scan you want.

For example, if you want to produce a digital print (ie not a wet darkroom print) sized 8 inches * 10 inches, at a resolution of 300 dpi, then you need a file measuring 2400 * 3000 pixels. This is true whether the negative was 35mm, 645, or even 8*10.

However the larger the negative size, then the bigger the print you will ever be able to create from that file; and you can print a smaller file if you wish to.

A 1545* 1024 file will produce, at 300 dpi, a print of 5.15 inches by 3.41 inches
A 3091* 2048 file will produce, at 300 dpi, a print of 10.3 inches by 6.82 inches
A 6744* 4493 file will produce, at 300dpi, a print of 22.48 inches by 14.97 inches

If necessary you could drop the resolution a little below 300dpi to fit a common paper size, so for example you might squeeze an A4 print (11.69 inches by 8.7 inches, if I remember correctly) out of the 3091*2048 file, by dropping the resolution.

Showing an image on screen is a different matter. I rarely publish images on-line bigger than 2000 pixels on the long side, because it just isn't necessary; but a 2000 pixel image which has been downsized from a larger image may look nicer than one which was only ever that big.

Finally, the sizes that you quote seem to be in the 2:3 ratio, which would work for a 35mm negative; but 6*4.5 is a different ratio so the actual file sizes wouldn't be the same. my 645 negs, when scanned, have a ratio of about 1:1.28. The actual film size is 59mm * 41.5mm.

Most of my (home-scanned) 645 negs are in the region of 3900 * 5200 pixels. I probably scanned them at 2400 dpi.

 

[Harlequin565]

What size are you wanting to view it at?

A4 at 300 ppi (magazine quality) requires a file size of around 2400 x 3300 (8x11 inches x 300)
My 4k screen is 3840x2160. That's how big an image needs to be to fill it with no upscaling.
The iPhone 10 is 2436x1125 and an Instagram image takes up about half of it and is square (guess at about 800x800?)

In short, 1500x1000 is fine for any kind of web use. 3000 x 2000 is fine for printing where you're not getting your nose up to examine pixels. 6700 x 4500 is your "super" quality for up close scrutiny of large (A3+) prints.

(Edit - Kevin has given a more comprehensive reply)

 

[Harlequin565]

Edit to add, I've just double checked a shot of Tom which is from a Pentax 645N I scanned in at 3400 x 2500. It's printed to A3+ (13 x 19") and comes out at 165ppi after cropping and fitting to the paper. It looks sharp as a tack.

But my eyesight is pants...