Resolving power

[marameo]

I have read somewhere that flatbed scanners can't resolve film grain in depth. I thought that could be true because of the size of the grain. So, I was wondering if a scanner could resolve better a high grain film just like the Portra 800 instead of the Ektar 100. Do you think that makes some sense?

Thanks

 

[mdarnton]

The rule seems to be, perpetually, that flatbed scanners top out at around 2200 ppi no matter what the manufacturer says, and sometimes less than that. There are many, many tests out there confirming this. So basically the scanner will resolve what it can see at that resolution. If the grain's big enough it will see it; if not it won't.

Then on top of that there's something called grain aliasing, and you should probably just do a google search on that. What happens is similar to you trying to walk down the street missing all the cracks: it just makes things worse, never better, and you end up with a sort of "false" grain that's even worse than what's on the film.

You can't win.

 

[hanskerensky]

Flatbed scanner (Canon 8800F) against dedicated Filmscanner (Plustek Opticfilm 120) :


Canoscan 8800F versus Plustek Opticfilm 120 by Hans Kerensky, on Flickr

 

[hanskerensky]

Aliasing (False Grain) :


Plustek Opticfilm 120 Aliasing (02) by Hans Kerensky, on Flickr

 

[mfogiel]

You might find this discussion helpful:
http://www.apug.org/forums/forum37/131396-rollei-rpx-25-grain-resolution-2.html
The reality seems to be, that if you want high resolution, you should avoid scanning altogether. In case of colour photography, I hate to admit, digital is just so much more convenient from the technical point of view. An alternative would be to shoot MF, scan on a flatbed and send the best frames for rescanning on a drum. If you shoot colour negative, overexposing will limit the grain and extend the dynamic range. Try to shoot your Portra 800 at 200-400 and see what happens.

 

[philipus]

The rule seems to be, perpetually, that flatbed scanners top out at around 2200 ppi no matter what the manufacturer says, and sometimes less than that.

Well it depends on which flatbed. The old pro flatbeds like the iQsmarts and such go higher. But I guess you meant the consumer flatbeds sold today.

 

[marameo]

If you shoot colour negative, overexposing will limit the grain and extend the dynamic range. Try to shoot your Portra 800 at 200-400 and see what happens.

So, if I understand the way film works, overexposing the Portra 800 will not burn the highlight because of the log curve natrure of color negative film. Yet, it will raise low zones to medium zones thus extending dynamic range. The bonus add is that it also limits grain. Later on, when I process the scan I can capitalize on this extended dynamic range.

That's interesting.

 

[mfogiel]

Yes - mind you, this only works with negative film, particularly chromogenic, and to some extent with B&W ( the grain will not decrease). With slides, if anything, you should underexpose slightly, to avoid burning the highlights - a bit like with digital. One problem with overexposing in general, is that there is some loss of resolution due to light scatter in the emulsion.
For B&W a good tutorial on how to expose can be seen here:
https://www.youtube.com/watch?v=rlnt5yFArWo