I don't quite get this 1.5x mutliplier thing
I think I'm overlooking something obvious, but when I see this description of the D series camera bodies that the effective focal length is increased by 1.5, what exactly does that mean?
For example, the D100 review by thom uses the illustration that the '20mm lens shows roughly the same angle of view as a 30mm lens'. Why is this so? I have the sense that the smaller-than-full-35mm size of the sensor is effectively cropping the field of view; so, if I take a photo with my 50mm f/1.4 on my F100, and crop/enlarge the resultant image in Photoshop Elements to the same angle of view as I would have gotten with a 75mm lens from the same spot, have I effectively done the same thing?
#1. "RE: I don't quite get this 1.5x mutliplier thing" | In response to Reply # 0genec57 Basic MemberSat 10-Aug-02 07:28 PM
You aren't missing a thing. You have it right. The advantage is that any loss of sharpness due to edge distortion will be remedied. The obvious disadvantage is that your wide angle lens will no longer be as wide.
#2. "RE: I don't quite get this 1.5x mutliplier thing" | In response to Reply # 0BJNicholls Charter MemberSun 11-Aug-02 03:32 AM
That's why many folks including Phil Askey in his reviews refer to it as a "crop factor" instead of a "multiplier".
Oh, and the crop is a lot more dramatic on wide angles than it is on teles. 1.5 isn't much "multiplier" in terms of angle of view on a 300mm lens. Your angle of view is reduced from 8.3 degrees to 5.5 degrees by the crop factor. That's 2.8 degrees of change.
But take a 20mm wide angle that has an angle of view of 94.5 degrees. Put it on a D100 and you get only 71.5 degrees, a whopping loss of 23 degrees of wide angle coverage!
#3. "RE: I don't quite get this 1.5x mutliplier thing" | In response to Reply # 2lordnikon Registered since 17th Feb 2002Sun 11-Aug-02 01:42 PM
So really then the crop factor is pretty minimal past the 50mm mark, as angle of view is not really altered then, if i am understanding this correctly.
Aaron J. Heiner
Team Coast Guard Photographer
US Department of Homeland Security
#6. "No..." | In response to Reply # 3Sun 11-Aug-02 10:10 PM
The FOV crop is proportionally the same at every focal length. You get the same approximately 50% of the image frame compared to 35 mm film for every lens. That is, the image will appear to be "magnified" by 1.5X at every focal length. You will notice the difference just as much at the long end as the short end.
#18. "RE: No..." | In response to Reply # 6BJNicholls Charter MemberWed 16-Jan-08 12:01 PM
Field of view (FOV) is a complex calculation of a how much linear distance you can view using a particular focal length, on a particular film or imaging chip size, at a particular distance from the camera. Field of view dimensions for wide angle lenses will be much larger than for teles on a given format.
What is consistent for any image made with any lens is the image crop. The crop trims 33% of the image dimensions - how that relates to FOV depends on the focal length of the lens if the other factors are equal.
The crop is the same, but the effect on the angle of view you can capture in an image is dramatically more on wide angles than on tele lenses. FOV dimension changes are proportionally more the shorter the focal length you use for a given calculation. The horizontal field of view at 100 m (328 ft.) with a 16mm lens on 35mm film is 225 m (738 ft.). The field of view at 100 m with a 400mm lens on 35mm film is 9 m (29.4 ft.) horizontally.
If I substiture APS film dimensions in my handy f/calc program (APS is close to the 1.5X crop factor) the FOV for the 400mm lens is 7.5 m (24.7 ft.). That's a reduction of 4.7 feet FOV. For the 16mm, the APS FOV is 188.7 m (619 ft.). That's a reduction of 119 feet FOV.
1.5X with a tele lens brings a critter at a distance a little closer to filling the image frame. 1.5X on a landscape shot with a 20mm lens crops out enough of the image to make the view the same as if you were using a 30mm lens on film. If you have any experience with wide angles, you know that 30mm isn't anything like shooting with a 20mm.
A 16mm lens would be even more cropped as a percentage of angle of view. You lose the same amount of area from the image rectangle, but at superwide angles, the crop means losing many degrees of the scene you would otherwise be able to capture.
I'm attaching a couple of examples. The arch is shot with a 16mm fisheye. The crop is a 33% reduction but the angle of view loss is like shooting with a 24mm lens. The eagles were shot at 800mm. The crop is like adding another 1.5X teleconverter and shooting at 1200mm. The extra tele doesn't really bring the eagles in a heck of a lot "closer" but on the fisheye shot the difference is seeing the arch or not seeing it.
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#8. "We are confusing absolute FOV with proportional FOV..." | In response to Reply # 18Mon 12-Aug-02 12:10 PM
...differences. BJ, in your example, the FOV ratio between 35 mm film and APS is exactly 1.19X in both cases: 738/619 or 29.4/24.7. Proportionally the FOV crop is exactly the same at every focal length.
That is not to say that the operational differences of the FOV crop will be the same at every focal length. When shooting wide angles on a digital camera, you can't work with what you can't get in the frame, whereas in tele shooting with film you can always crop out the "extra" image you don't need.
While the physical image in digital isn't any larger than it is in film, what is important is that the image produced by the digital sensor is on a par (somewhere between 75%-100% of image resolution) with a full 35 mm film frame for enlargements not exceeding A3 size.
I know this is probably niggling, but the FOV crop certainly doesn't "go away" at long focal lengths, and anyone contemplating "going digital" should realize this. One of the things I am learing with my D100 is that it is all too easy to "overfill" the frame when shooting with lenses you normally relied on in 35 mm format. As I go through my learning curve with the D100, I am finding that I often have a too long a lens attached for my shooting, and it is taking me awhile to re-orient my lens choices when out and about. That is, some days I should really be thinking "28-105" when I have the "70-300" attached, etc.
#4. "RE: I don't quite get this 1.5x mutliplier thing" | In response to Reply # 2
From your explanations, it makes sense that the effect proportionally lessens with longer focal length lenses.
But can you explain why statements such as this are fairly common (this also from the D100 review by thom):
"Your 300mm f/4 lens just received the angle of view of a 466mm f/4 lens! Wildlife and bird photographers love the focal length changes the D100 makes to their lenses."
Because you really don't have a 466mm lens, and presumably you don't get the same optical quality as you would with a 300 mm with a 1.5x optical teleconverter (?). By the way, I'm not 'picking' on thom, but just using this as a recent example. I can see the built-in cropping helping to eliminate some edge of frame lens issues; which, again, you could also do by enlarging and cropping.
I'm also not attempting to compromise the very good things about the D100 or other D series bodies, but this particular 'benefit' seems to be an unnecessary exageration.
#5. "The FOV crop factor" | In response to Reply # 4Sun 11-Aug-02 10:06 PM
You can fill the frame with the subject in a way you can't with the same lens at full 35 mm film coverage, at approximately the same (actually just slightly less--the best estimate is that 6 Mpixel digital has about 75% of the image resolution of a 35 mm film frame) effective image resolution as film for enlargements up to 10x15" (Beyond that and the 6 Mpixel digital images really start to fall apart.)
You can utilize the best 50% of the focused image from the lens, and a cropped lens image will have better image quality than for the same lens at 35 mm full frame with a 1.4X teleconverter, for example.
You get a longer effective focal length without any maximum aperture penalty.
You could achieve the first of these three advantages, and part of the second, by heavily cropping a full frame of 35 mm film, but that will probably reduce the effective resolution of the film shot to below that achievable with 6 Mpixel digital.
As a practical example, a consumer f/4.0-5.6 70-300 mm zoom lens at ISO 200 on a D100 becomes quite competitive with an 80-200 mm f/2.8 zoom with 1.4X teleconverter using ISO 100 film. In fact, at an effective focal length of 300 mm (or as close to it as you can get), they will have identical exposure settings, with the exception that the 80-200 mm lens can go to a maximum aperture of f/4.0, while the 70-300 mm lens is limited to a maximum aperture of maybe f/4.5. While the 80-200 lens is objectively a better lens, the FOV crop of the digital lens makes the consumer 70-300 mm lens a much better optic than it would be for a film camera. Now, while the 80-200 mm lens will be somewhat brighter and probably autofocus faster even with a teleconverter, the 70-300 mm zoom is no longer at such a serious disadvantage as it would be on a film camera, and is a reasonable choice for a "105-450 mm" lens.
This will all change and go away if and when there are full 35 mm frame digital sensors, but for now the FOV crop confers a curious and real advantage to digital cameras. On the other hand, you have no option to get ultrawide with something like a D100. Even with an 18-35 mm lens, you can only get an effective 28 mm at the short end, and this only at the expense of the extra distortion and flare-proneness of what is actually an ultra-wide angle lens. (You get something, you lose something. There is no free lunch here.)
#7. "RE: The FOV crop factor" | In response to Reply # 5Chirotk Registered since 23rd Apr 2002Mon 12-Aug-02 07:03 AM
Forgive me for butting in.
As I understand you, by using a digital I get only the FOV at a 1.5 factor on my lens than if I use a film camera, and I do not get a 1.5 factor magnification of the object. If that is correct, filling the frame with a narrower feild of view is not necessarily an improvement over filling the frame with a magnification. If I'm wrong on this please correct me as soon as possible.
This question has likewise been a problem for me. The FOV term, aka " crop factor " , seems more accurate than the multiplier effect that has been bandied about. Your explanation also sounds more correct than the hazy double speak I have heard elsewhere.
Please correct me if I'm still wrong.
#9. "You are correct in that..." | In response to Reply # 7Mon 12-Aug-02 12:21 PM
...the physical image is not any larger. But the quality (image resolution) of the cropped digital image is about 75-100% of that of a full 35 mm frame of film for enlargements up to about A3. So you do gain some real advantage in "filling the frame" with your subject in digital that you can't completely replicate by simply cropping the 35 mm film frame. And you're also getting the sweet spot of the lens to boot, but that is harder to quantify.
Please note that if your image sensor was only 2-3 Mpixels the advantage of the crop factor is more than eaten away by the loss of image resolution compared to film.
#10. "RE: You are correct in that..." | In response to Reply # 9Wed 14-Aug-02 11:45 AM
“So you do gain some real advantage in "filling the frame" with your subject in digital that you can't completely replicate by simply cropping the 35 mm film frame.”
Understand your point, but true only when the digital sensor resolution is comparable to the resolution provided by a section of film of the same dimensions (all other factors being equal), correct? And, presumably, resolution is dependent on the ISO rating of the film and the comparable setting used on the digital camera? I don’t mind cropping / enlarging: from experience I can look at a full frame image and ‘see’ the composition I want to end up with (I envy those who have the skills to consistently capture good compositions full frame).
I think part of my confusion comes from the assumption that film resolution is significantly greater than that of the D100 or other similar digital bodies, even when enlarged to A3 size or so; but from what you’re describing, that may be a false assumption.
#11. "That's right..." | In response to Reply # 10Wed 14-Aug-02 01:27 PM
of film (Provia 100F) vs. digital imaging and has concluded that the current generation of 6 Mpixel sensors are about 72% the resolution of film, so we are near par with 35 mm film now. But there is a non-quantifiable factor about digital in that it is substantially noise-free (no grain) so that in perception digital images may actually look sharper than one would expect from looking at the MTF performance. And of course if you go to higher speed film (with the attendant increase in grain) digital may compare even more favorably.
Of course, anyone who has been shooting digital awhile already knows that 3 Mpixels is enough to make excellent letter-size prints and 6 Mpixels is enough to go to A3. In the end, if you can fill the frame with the desired image and print it at the desired size, you have what you need. There is no real necessity to drag in the film vs. digital debate, although it is certainly very entertaining. It turns out that you only need around 200 ppi to make decent prints (although there are some real benefits to printing at higher ppi when possible) because that's about the effective resolution of paper anyway. At this stage, I think image resolution is the least compelling reason to differentiate digital and film these days: more substantive issues, in my opinion, are exposure latitude, highlight rendering, long exposure noise, and the effect of FOV crop on wide angle composition.
#12. "Film vs. digital" | In response to Reply # 11Wed 14-Aug-02 07:12 PM
Agreed, and a 'vs.' debate wasn't my intent, so I apologize if my wording led that direction. Not having a digital camera and the experience to go with it, I've found some of the discussions to be somewhat inscrutable. It's been helpful to try and relate my questions to my film experience. If the digital SLR startup costs weren't quite so steep, I'd probably be there. I would disagree with the '200 dpi and decent' pairing, but that would be quibbling .
I couldn't get the link to work, even when copying to a new window. ???
#13. "I've fixed the link..." | In response to Reply # 12Thu 15-Aug-02 09:57 AM
I'm glad you have enjoyed the discussion. Being a scientist by training, I enjoy the theory but still realize there is no substitute for empirical observation. A session at the Nikon School convinced me to try printing at lower resolution (as low as 180 ppi) when required by extreme enlargement or low resolution images. What I saw at the Nikon School was a series of beautiful prints done by the instructors that were 180 ppi. So, while I prefer to print at ppi densities of 240-300 ppi, I have no qualms about printing at 180-200 ppi if required.
#14. "A bit off topic, but..." | In response to Reply # 13JoeSlotz Registered since 17th Jul 2002Thu 15-Aug-02 12:07 PM
So you are saying that printing at 300 ppi makes as good a print as 1200 ppi? (assuming that quality glossy paper is used and your printer is decent and set properly)
This I must try and see for myself.
#15. "RE: A bit off topic, but..." | In response to Reply # 14JoeSlotz Registered since 17th Jul 2002Tue 20-Aug-02 09:23 AM
I did the test last night. I printed (2) 8.5 x 11 sheet with (2) 5x7 images (both 5x7 images had different contrasts and color schemes) on Kodak Glossy Photo paper using a Lexmark Z65 color printer w/ 1 tricolor cartridge and 1 Black.
Printer Resolution - 1200x1200 dpi (2400x1200 is max)
Image Res.: (D100 standard ppi)
Paper setting - Glossy Photo
Color - Automatic
Results - Images are clear and sharp but slightly darker than the screen image. (need to reset gamma later)
Printer Resolution: 300x300 dpi
Image Res.: (D100 standard ppi)
Paper setting - Glossy Photo
Color - Automatic
Results - Images are very light and washed out. About equal to the brightness up +50 and contrast down -50 than normal (being zero). These are PSP7 setting referrences.
Conclusion: When using a Lexmark printer and color photo paper, printing resolution has a direct affect on image darkness and contrast.
My scanner is down right now. I will try and upload samples later.
Printer & Image data corrections added for clarity
#17. "You are confusing image pixels and printer dots..." | In response to Reply # 15Tue 20-Aug-02 12:20 PM
ppi (pixels per inch) = number of image elements (pixels) printed per inch at the final output size. This number has nothing to do with the printer. It relates to how large individual pixel elements of the original image are printed on the page. This measurement is quantified the same way for ever image/printer combination.
dpi (dots per inch) = number of ink dots the printer will lay down per inch to render the image. This number has nothing to do with the image. It relates how finely and accurately the printer will be able to render the individual image pixels when printed. Manufacturers play fast and loose with this number, and 2880 dpi by one manufacturer may actually be less print density than 1200 dpi quoted by another manufacturer. There is no "standard" way of quantifying dpi
I know this is arcane and confusing, but it is actually a fundamentally important point in digital imaging. The ppi setting controls the ultimate quality of the images. No amount of dpi can save a pixelated image. The dpi controls how accurately the printer can translate the image to paper.
Some oversimplified rules of digital printing:
Choosing an image ppi setting. Generally use the highest ppi setting possible as determined by the original digital image, but at extreme enlargements don't be afraid to drop down to lower ppi values. There is no compelling reason to have files much greater than 300 ppi, although it doesn't hurt up to a point.
180-240 ppi - acceptable images, comparable to image resolution of photographic paper
240-300 ppi - sweet spot of digital output for the current generation of inkjet printers. Excellent images
300+ ppi - Superb images, but in the area of diminishing returns. Files sizes become very large with only minimal improvements in image resolution, but demonstrable improvement up to at least 360 ppi. Some contributors to this board have noticed image degradation at very large (>400-500) ppi, presumably due to printer driver downsampling artifacts.
Choosing a printer dpi setting. I can't help with non-Epson printer (I'm an all-Epson shop) but the general principles will apply to any printer (only the numbers will be different). Experiment. Here are my Epson comments:
360 dpi - unsuitable for photographic images. The printer cannot lay down enough dots to properly define the color of each pixel at even 180 ppi.
720 dpi- absolute minimum for photographic images, and suitable for proofing prints for color correction or approximate monitor-to-printer color fidelity. Significant banding is seen upon close inspection, but passable quality for some purposes and economical on ink.
1440 dpi - sweet spot for photo printing. Very smooth color rendition, and virtually no observable banding or other digital print artifacts. Uses a lot of ink but the most economical setting for serious work.
2880 dpi - virtually indistinguishable from 1440 dpi except upon extremely close inspection with a loupe. Very profligate with ink. I hardly ever use this setting, but it offers the most image quality.
I hope this explanation helps.