bglick,
I was just thinking of you when reading this thread...
As from your previous pos, the maximum resolution a lens theoretically can resolve in lines per mm (lpmm) by averaging wavelengths is 1500/f-number. So, for common f-stops, the diffraction limits to resolution are:
f/stop : max lens resolution : max lens/film resolution
- f/2.8: 536 lpmm : 80 lpmm
- f/3.5: 429 lpmm
- f/4.0: 375 lpmm : 90 lpmm
- f/4.5: 333 lpmm
- f/5.6: 268 lpmm : 95 lpmm
- f/6.5: 231 lpmm
- f/7.7: 195 lpmm
- f/8: 188 lpmm : 100 lpmm
- f/9: 167 lpmm
- f/11: 136 lpmm : 95 lpmm
- f/16: 94 lpmm : 80 lpmm
- f/22: 68 lpmm : 70 lpmm (should be 68 lpmm)
- f/32: 47 lpmm
- f/64: 23 lpmm
Those are theoretical maximums, but no LF lens performs at 429 lp/mm at f/3.5. Also, Chris Perez quotes from his website the maximum film/lens combined resolutions at various f-stops. Bryan Guyer says that maximum film-resolution increases as f-stops are increased:
>"However, film resolution has also been shown to vary appreciably with
>aperture, and resolving power is always highest when the light source
>area is minimized, to retard dispersion. This presents a troubled
>dichotomy: Best lens resolution is achieved when shooting wide open, but
>best film resolution is at ~ f22 (or smaller)!"
I'm not sure I understand that, but he does quote the maximum lens/film combination as being 100 lpmm at f/8 (I quote these film/lens combination max's above).
Best Lenses Wide Open
Some of best lenses wide open, like the Xenotar 135/3.5 or 150/2.8 have been measured to get 20-30 lp/mm wide open at f/3.5 (I don't know about the Carl Zeiss ones); they've been measured at 60-70 lp/mm at f/8. Both of these are at center; outside of center, resolution drops to 10 wide open and 30 at f/8 for both lenses. The Kodak Ektar 203/7.7 has been measured at 67 lpmm average from 0-20 degrees from the axis, and 78 lpmm average from 0-10 degrees from the axis (calculated from the table at the bottom of this page).
Wide open, and even at f/8, these lenses would most likely be doing portraiture work, where relative center is the most important. So, assuming human eyesight of 5 lpmm, maximum enlargements from 4x5 are as follows (for apertures f/11 and below, I assume it is used for portraiture or other isolation work, and that the middle part of the image is most important, thus discard edge-resolution; for the Xenotar 135/3.5 and Kodak 203/7.7, I assume full-use of the film from center to edge after f/11).
- Schneider Xenotar 135/3.5 (~$400 - $800)
- @ f/3.5: 20 lpmm / 5 lpmm = 4x (20" x 16" portraits) [5 megapixels]
- @ f/8.0: 60 lpmm / 5 lpmm = 12x (60" x 48" portraits) [46 megapixels]
- @ f/11: 40 lpmm / 5 lpmm = 8x (40" x 32" portraits) [20 megapixels]
- @ f/16: 58 lpmm / 5 lpmm = 11.6x (58" x 46.4" portraits or landscapes) [43 megapixels]
- @ f/22: 54 lpmm / 5 lpmm = 10.8x (54" x 43.2" portraits or landscapes) [38 megapixels]
- Schneider Xenotar 150/2.8 (~$1500)
- @ f/2.8: 30 lpmm / 5 lpmm = 6x (30" x 24" portraits) [11 megapixels]
- @ f/8.0: 70 lpmm / 5 lpmm = 14x (70" x 56" portraits) [63 megapixels]
- Kodak Ektar 203/7.7 (< $150)
- @ f/7.7: 78 lpmm / 5 lpmm = 15.7x (78" x 63" portraits) [78 megapixel print]
- @ f/11: 75 lpmm / 5 lpmm = 14.9x (75" x 60" portraits)* [72 megapixels]
- @ f/16: 67 lpmm / 5 lpmm = 13.5x (67" x 54" portraits or landscapes) [58 megapixels]
- @ f/22: 57 lpmm / 5 lpmm = 11.5x (57" x 46" portraits or landscapes) [42 megapixels]
It seems like the Ektar 203/7.7 would be an excellent portrait lens if you can compose with f/7.7, and if that doesn't provide too much dof. Also an excellent "normal" lens. Likewise, the Xenotar 135/3.5 and 150/2.8 seems excellent for portraiture and landscape.
* Measured aerial resolution for the Kodak Ektar 207/7.7 at f/11 was 103 averaged from 0 to 10 degrees from axis, as done by Larry and Linda Whatley; but 64 lpmm as done by Chris Perez (ctr + mdl).
I have heard, but not seen any test results, some people say that the Kodak Aero-Ektar f/2.5 resolves hundreds of lp/mm wide open; but this is apparently at infinity focus, whereas at portraiture focus, it is much much softer (it didn't measure as sharp as the Xenotars). Maybe a good lens for astrophotography? (if you can tolerate the color).
Nikon Nikkor-SW 90/4.5 or 90/8
I assume these lenses effectively have the same optical performance (but data is from the 90/8):
- @ f/11: 80 lpmm / 5 lpmm = 16x (80" x 64" portraits) [83 megapixels]
- @ f/11: 73 lpmm / 5 lpmm = 14.6x (73" x 19" portraits or landscapes) [69 megapixels]
- @ f/16: 65 lpmm / 5 lpmm = 13x (65" x 52" portraits or landscapes) [55 megapixels]
- @ f/22: 56 lpmm / 5 lpmm = 11.2x (56" x 45" portraits or landscapes) [40 megapixels]
Maybe a good environmental portraiture lens, but of course it's designed with landscape photography in mind, for which it is perfect.
Diffraction Limits at f/32 and f/64
Assuming all of the above lenses are diffraction limited at f/32 and f/64 (this is reasonable as the Kodak Ektar 203/7.7 pulls in 46 lpmm at f/32, just under the 47 lpmm diffraction limit), the maximum print size will be:
- @ f/32: 47 lpmm / 5 lpmm = 9.4x (47" x 38" portraits or landscapes) [29 megapixels]
- @ f/64: 23 lpmm / 5 lpmm = 4.7x (23" x 19" portraits or landscapes) [7 megapixels]
By contrast, a Phase One P45 39-megapixel P45 back is 7216 x 5412 pixels. That corresponds to a 57" x 43" print at 5 lpmm. Of course, this is a favourable estimate, as it assumes any lens on the P45, no matter the f-stop, will actually resolve the full 39 megapixels. But the above estimates of maximum print sizes for LF were also favourable, as they didn't account for the film part of the 1/R equation.
But yea, all of that kind of pretty much confirms what you said. The equivalent megapixels of a 4x5 range from 5 to 83 megapixels. If the numbers for the fast Xenotars wide open are representative of most Xenotar 135/3.5 and 150/2.8 samples, then if you need to shoot portraiture in low-light situations and can't have longer exposures, then you're probably better off with a DSLR (like my E3 + 58/1.2)...unless you want that uber uber narrow DOF (58/1.2 on an Oly E3 is very narrow dof...135/3.5 on LF is equivalent to 18/0.47 on Olympus 4/3rds, or 36/0.93 on 35mm in dof).
If you're doing portraiture where you can stop down a little bit, to f/7.7 (and compose there for the Kodak Ektar), f/8, or f/11, then large-format will deliver absolutely stunning resolution (if you really want that much detail) that will be superior to the best MF backs.
Landscapes where you can get everything you want in focus via tilts at f/11 or f/16 will be superb; more likely is f/22 which will also be great; if, due to the 3-dimensionality of your picture, you need f/32 even with tilts, then large-format will be equivalent to 29 megapixels. If you need to stop down to f/64, you might as well use a DSLR; enormous hit.
Originally Posted by
bglick
As mentioned previously, before you get too caught up in file size, you should instead pursue the IQ you desire...
There is some posters on this list that will mistakenly advise you 4x5 scanned film contains 200 - 320 MP of data.... the realists are in the 30 - 50 MP range, which supports basic imaging fundamentals. It's not unusual on these forums for numbers to be off by a factor of 10x. You may want to glance at this current thread if your interested in a better understanding of the "recorded Mega Pixels" subject...
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