Optimal scanning res for Portra 4x5?

[feppe]

I'm considering buying an LF 4x5 and shooting glamour in studio with Portra, and some limited landscapes with Provia.

Previously I've had my Velvia and Provia 6x6s scanned by a service, but a local photolab has an Imacon Flextight 848 scanner, which goes up to 8000 ppi (!). That would result in a 1.28 gigapixel file if my math is right, which not only sounds like massive overkill, but I doubt that any lens or film can produce such resolution. Or am I underestimating LF performance - formerly 35mm film and digital, and 6x6 film experience here.

From your experience, what should I expect from an 4x5 camera with very old but good quality 300mm lens? I haven't bought a lens, yet, but am wondering what kind of resolution I should expect.

Also, if anyone has experience with the Imacon, I'd be glad to hear your experiences. The lab offers scanning, or they sell use of it by the hour for a reasonable cost (40 EUR per hour).

[gary mulder]

The Flextight 848 will go up to 2040 on 4x5

[feppe]

The Flextight 848 will go up to 2040 on 4x5

Yep, appears to be correct - I just checked the lab's website but the 8000 ppi seems to be for 35mm only. So the 2040 ppi results in a much more manageable 84 megapixels.

But the question remains: how much resolution can I expect? If the Flextight can't go to the res, I could get them drumscanned at higher res by my service.

[Bruce Watson]

This topic has been discussed many times before. Use the site search and you'll uncover many threads on this topic.

The first question is: how do you personally define optimal? The reason I ask is that there's no standard definition of "optimal" when it comes to scanning.

The next question is: what do you intend to do with the scan file? IOW, how big a print are you going to make? The reason I ask is that there's little point in scanning a piece of 5x4 film at 1500 s/cm (about 3800 spi) if your final print is going to be a 50 x40 cm print. It's just a lot of expensive overkill at that point.

Another pertinent question is: how did you make the exposure? Handheld? Tripod? Wide open? Stopped down? Equipment? Format? Film? That kind of thing.

What I'm saying is, you can't solve a problem unless you can first define it. If you can define for us what you are trying to accomplish, we can perhaps help you toward your goal.

[feppe]

The first question is: how do you personally define optimal? The reason I ask is that there's no standard definition of "optimal" when it comes to scanning.

The next question is: what do you intend to do with the scan file? IOW, how big a print are you going to make? The reason I ask is that there's little point in scanning a piece of 5x4 film at 1500 s/cm (about 3800 spi) if your final print is going to be a 50 x40 cm print. It's just a lot of expensive overkill at that point.

Another pertinent question is: how did you make the exposure? Handheld? Tripod? Wide open? Stopped down? Equipment? Format? Film? That kind of thing.

What I'm saying is, you can't solve a problem unless you can first define it. If you can define for us what you are trying to accomplish, we can perhaps help you toward your goal.

By optimal I mean getting the most out of the film, lens and exposure combination. I'm not really concerned about the ultimate print size - I'll be downrezzing it 99% of the time. But I want the "full" data that's available, without the need to rescan when/if I need to print BIG. Megabytes are dirt cheap these days. But there's no need to go beyond the image chain's weakest link, ie. it's pointless to increase scan resolution if it merely makes the grain larger without improvement in data.

4x5 Portra and Provia. I'd be using tripod, mostly studio with flashes, but some travel photography work as well. I'm a newbie to LF, but how I shoot 35mm and 6x6 is stopped down to the lens's sweet spot as much as the subject matter allows, although some portraits are wide open. I rarely stop down beyond f/8 on 35mm. In short, I try to get the most out of my equipment.

So to recap: what's the highest scanning resolution a good, but old LF lens used in well to highly controlled environment with top-of-the-line slide film is likely to benefit from?

[Gordon Moat]

A good rule of thumb is 60 lp/mm based upon results from Chris Perez et al of various lenses. So scanning near 3048 ppi would be another good choice, except when you consider that some details could be off axis and not purely horizontally nor vertically aligned, in which case you could double that to 6096. On a more practical matter, I have rarely seen much benefit in scanning above 6000 ppi, other than tonal transitions can really smooth out nicely in the final prints. Quite often you can get away with 2540 ppi scanning, and meet many printing needs with that.

Often when I see these questions, it is because someone is looking for a MegaPixel equivalent, or it is strictly for the sake of argument. The reality is that often prints are smaller than the maximum possible, scanners in use are not high end, and the person asking such questions is unlikely to ever test the limits. Even if one does test the limits, it can have little to no bearing on the popularity of the final print.

One definite benefit I have seen with larger film sizes is an improvement in tonality and tonal transitions. Obviously there is not much resolution in an expanse of blue sky, but that smoothness can appear more compelling when captured on larger film. This is where I see a benefit to using large format, beyond the idea that there are benefits to the movements possible on many of the cameras, and beyond that composing on the ground glass is very different than using a viewfinder.

Ciao!

Gordon Moat Photography

[Bruce Watson]

By optimal I mean getting the most out of the film, lens and exposure combination. I'm not really concerned about the ultimate print size - I'll be downrezzing it 99% of the time. But I want the "full" data that's available, without the need to rescan when/if I need to print BIG. Megabytes are dirt cheap these days. But there's no need to go beyond the image chain's weakest link, ie. it's pointless to increase scan resolution if it merely makes the grain larger without improvement in data.

4x5 Portra and Provia. I'd be using tripod, mostly studio with flashes, but some travel photography work as well. I'm a newbie to LF, but how I shoot 35mm and 6x6 is stopped down to the lens's sweet spot as much as the subject matter allows, although some portraits are wide open. I rarely stop down beyond f/8 on 35mm. In short, I try to get the most out of my equipment.

So to recap: what's the highest scanning resolution a good, but old LF lens used in well to highly controlled environment with top-of-the-line slide film is likely to benefit from?

Even at this, it depends on what you believe "getting the most out of the film, lens and exposure combination" means to you. And I'm really not trying to be difficult here.

I tell people that there are three general "schools" of scanning. I categorize them as 1) capture just the image information, 2) capture up to the average film grain clump (dye cloud) size, and 3) scan at the maximum the scanner can do and downrez, the idea being that you'll also be downrezing some scanner noise.

I can make the arguments for all three. All three are useful in their own ways. But I can't tell you which method to use because too much depends on you, the individual photographer, your workflows, your subjects, etc.

For the first school, you'll want to figure out how many line pairs per millimeter your particular camera, lens, film, processing, tripod, aperture choice, etc. can deliver on fully processed film. That will basically be the "limit" and you'll normally be getting somewhat less than that (in the corners for example, or if you use lots of front rise). The resulting number will vary from lens to lens, aperture will make a huge input because of diffraction, etc. So there's not a single number that will work for every piece of film.

For the second school, you'll perhaps just want to figure out your max print size and scan for that. IOW, a 12.5x enlargement (gives you some room to crop), for an output resolution around 120 ppcm, will give you a scanner resolution of about 1500 spcm, or 3800 spi. Off the top of my head that's around 6.5 microns for an average grain clump size, so a good modern medium speed color negative film like 160PortraNC.

For the third school, you just need to find someone with a scanner that has a small enough aperture (if you are going to do this, you might as well do it with a drum scanner IMHO, but that's another flame war altogether). The Aztek Premier, ICG 380(?), the latest Screen drum scanners all have minimum apertures of 3-ish microns. That'll give you an optical scanning resolution in the 2700+ spcm range, around 7500 spi. And of course you'll have to use a scanner who's software will let it generate a file larger than 2GB, another reason for the scanners listed above, but check first.

If all that's not enough of a pain, remember that the appearance of grain in the final print varies a great deal between color negatives and color positives. With trannies, most of the grain shows is in the shadows where the human visual system has more trouble seeing it. With negatives, it's in the highlights where it's pretty easy to see. This typically means that even when modern color negative films have smaller RMS grain size ratings (which they often do), you'll want to enlarge them somewhat less. Which also will effect how you scan.

[Garry Madlung]

Your question seems to be identical to the question I've tried to have answered. That question is, "what is the pixel per inch equivalent of film grain/resolution?". Somewhere I read that with Velvia (my main film) it is around 3200 dpi, though I'm not sure that this is accurate. Portra might not be that fine.

Ideally, yes, I want to scan a neg/transparency at 100% and at a resolution that matches the film's resolution.

Scanning on an Imacon 848, I am limited to 2040. From there I re-size to 300 dpi for working files, maintining file size through re-sampling. I often re-size printing files to anywhere from 180-260 for a print around 47"x60". I prefer to decrease the resolution rather than up-size a file trying to maintain 300 dpi. I can honestly say that I am more than pleased with the results from a Chromira printer.

Like you, I would appreciate finding a reliable source to find out a particular film's pixel equivalent so that I can match it when scanning.

[sanking]

Bruce Watson's replies to this thread show why the answer to that question is difficult to answer. The resolution on film depends not only on the film but on the camera and lens system and on the conditions of exposure. And second, the term "pixels per inch" is not a measurement of resolution. If the equivalent resolution in the film was absolute, and if the scanner was perfect in its ability to pull every bit of the resolution out of the film, then the formula lp/mm X 25.4 X 25.4 would work fine. For example, if the film has detail equivalent to 60 lp/mm, and the scanner is capable of reading and recording 100% of that detail, then the scan should be at 3048 spi, as Gordon Moat already indicated for resolution of 60 lp/mm.

However, odds are your 160 VC Portra film does not contain anything close to 60 lp/mm. The real optimal figure is probably closer to 40 lp/mm, which means that a scan of 2000-2540 spi would pull out all the detail.

Issues of how the scanner deals with grain are complicated and depend not only on the scanner but on the operator. Grain is controlled with drums scanners by the choice of scanning aperture, and with CCD flatbeds by use of fluid mounting.

The other reason the question is difficult to answer is that people just don't agree on some of the issues, probably because their materials, goals and equipment are different.

My own experience is that if you are scanning color negatives or transparencies, and assuming a professional quality scanner, a scan about 3000 spi gets it all, about 98% of the time.


Sandy King

Your question seems to be identical to the question I've tried to have answered. That question is, "what is the pixel per inch equivalent of film grain/resolution?". Somewhere I read that with Velvia (my main film) it is around 3200 dpi, though I'm not sure that this is accurate. Portra might not be that fine.

Ideally, yes, I want to scan a neg/transparency at 100% and at a resolution that matches the film's resolution.

[feppe]

Indeed it's quite a bit more complicated than I was expecting - and I was expecting quite a bit... But good info, thanks for the input! Sounds like the Imacon might be able to pull out most of the info, with perhaps drum scan being needed for some resolution-critical BIG prints.