how many pixels is film equivalent to?

[Landrum Kelly]

My 14 megapixel Kodak does not equal the resolution of 35mm film, much less the color range. I suspect that the new digital sensors (18 to 22 mp) that are being touted as "medium format" are being oversold. They might approach (in resolving power) 35mm film. I will never know because I will never be able to afford one.

[vinayak_agrawal]

I'm not an expert, howere I'm going to attempt a reply (forgive me father for I'm going to sin):

 

25micron is the minimum grain size taken for DOF calculations for 35mm film, so let us say pixels separated by 25micron should do the trick. this means 24mm/25micron = about 1000 rows, and about 1500 columns which means 1.5Megapixel. Since there are three colours to be taken, we can multiply it by 3 and the new figure is 4.5Megapixel (This must be real Megapixel not some "effective megapixel"). So 4.5Megapixel should give resolution similar to 35mm film (for the same DOF).

 

Now some disclaimers:

====================

One important thing we have neglected here is the "fill factor", basically what percentage of pixel area really gathers light. This is close to 100% for film, but will be less than 50% for the best of CMOS sensors. This'll not degrade the amount of information so much but it'll reduce the sensitivity (whether you can take a picture in low light) and will appear piercing to eyes. In addition it'll give rise to something called "spatial aliasing" (search for aliasing, you'll find it in some article by Bob Atkins if I'm not making a mistake).

 

The 25micron criteria used above was, to the best of my knowledge and belief, used arbitrarily by a Zeiss engineer almost a century ago to calculate DOF tables. Film can (and good films do) do better than that. Now what this means is that THERE WILL BE LITTLE ALIASING for regions that are in very sharp focus when you're using a film. The regions that are not in sharp focus can not alias (because out of focus means blurred, which means low-pass-filtered already, and to understand what I've just written you must know what aliasing means). In contrast digital sensor will always alias if there is sufficient detail in a region. Now this should not be a problem unless you're going to enlarge too much but if you do you'll blame the resolution when aliasing is the culprit (increasing the resolution will decrease resolution).

 

Third, the calculation was for 35mm format only. The real thing depends on what kind of enlargement you want finally. For example I think pictures taken from my cellphone have enough resolution if all I want is a stamp-sized output (that the colour balance and dynamic range are screwed up is another matter).

 

Finally I really suspect that this question has been asked by someone who would do a "film Vs digital" on the basis of pixel-count. Now my advise is don't do that. For example if you're going to take long shots in dark I don't think any sensor can beat film whatever be the pixel-count. Moreover sensors have quit a few problems of their own, like dark-current, FPN, distortion etc. On the other hand film has real practical problems. I think digital will serve almost everyone's needs, if not today then in another couple of years and at an affordable price. On the other hand I also think film is not going out of the market for at least next half a decade and will be seen in at least a few stores for more than a decade (and I think may be forever) till the time you get a disposable digital camera SYSTEM (which means everything including a PC) for $10. People in good part of the world can yet not afford the latter but many, if not most, can afford the former and that doesn't give too bad a quality (and to the manufacturer not to bad a profit) so it'll just go on, may be not in the west but in the rest. (Oops, I fell in the film Vs. digital trap).

[vinayak_agrawal]

One thing I forgot to add:

 

A larger pixel-count will usually result in lower fill-factor (and/or exorbitant price) for CMOS sensors. This is because size of the sensor-chip will usually not be increased (because number of good chips produced goes down very sharply once you start increasing the area of the chip) as much as the number fo pixels and the average guy on street doesn't know/care about the specifications that are screwed up by such trade-offs (good for him, most of the time he shouldn't care but then most of the time he shouldn't care about pixel-count either).

 

Now I haven't recommended anything and this post was meant to give more info and confuse you even more (forgive me god for I have sinned).

[lemastre]

It's somewhat encouraging to see photographers discussing

film vs digital issues insofar as it implies that film is still a viable

choice. However, in my market, the number of places that do

professional film processing is down to about one lab, and

we've no guarantee it will survive. My longtime favorite, and

nearby, processor has just junked the wet gear on which his

business was founded and sequestered himself and his

computer and digital printer in an office building, where

customer contact is via telephone line rather than over the

counter. Now I have to drive across town to get a roll of slides

processed.

 

It's not that I mourn the disappearance of film so much as I

realize I'll have to junk thousands of dollars of cameras and

other film gear in a few years in the absence of any second-hand

market.