Maybe this has been discussed here before, but I wonder if the D100's 1.5x effect on lenses (field of view crop 1.5x, also known as focal length multiplier) is a true telephoto effect or just a crop of the field of view? Grateful for clarification on this matter. Julius
Just a crop of the field of view: no actual magnification involved.
A lens (any lens) produces an image that is actually a circle. This circle has to be big enough to cover a 35mm film format both horizontally and vertically. Obvioulsy then, there is some portion of the image that hangs off the sides and is not captured on film. In digital (current digital such as the D100 at least) the recording medium (the CCD) is even smaller, meaning that even more of the lens's image circle falls off the sides and is not recorded. The CCD only captures the center portion of what the lens produces. Hence, the image is cropped more than film simply due to the relative size of the sensor versus the size of a film frame.
Just a crop, exactly as Bob says. The whole "1.5 magnification" thing is misleading and is intended to make you think you're getting something for nothing, when in fact you're getting less from the same.
Dave! What do you mean? BTW I like your homepage, great work!
I made a somple test by using D100 and a F100 and two 20mm lenses. I could not notice any magnification effect on the D100 so I have to agree that the 1,5 factor is just a simple crop. The owner's manual which came with the D100 is a bit misleading in this respect, at least so it seems (to make us happy).
What I meant was that the D series cameras although cobbled together from exisiting 35mm bits are in reality not 35mm but a new smaller format. So if you change your 'film' format you get different magnification from the same focal length (assuming you use the whole frame available). My 90mm Super Angulon on my 5x4 monorail is a great wideangle but if I could glue it on the D100 it would be a nice little telephoto (a tad expensive tho'!)
Don't you think that a lot of the anxiety about small CCDs is because we think of them as digital 35mm cameras. When Nikon eventualy completely restyle pro digital cameras (as they will!) and they don't look anything like F5s we won't even need to know what the physical dimensions of the chip are.
After all 35mm only came about 'cause someone had a load of old cine film kicking around and they built a camera around it....
Exactly! It's just different. Period. If a spec is given for a medium format, you wouldn't ask, "What's that in 35mm equivalent." It's a silly question. Like, "Do you walk to work or carry your lunch."
It's funny to hear so many people complain about the 1.5 crop. With Nikon making lenses to cover the wide, isn't a lighter camera more ideal for all day shooting? So what if you have to think of your 300mm as a 450mm. Once you get a feel for it, it is easy to adjust. For most of us that have gone to all digital we never even think twice about it.
OK...I have a question. I understand the 1.5x crop and field of view. Now for my question; does a 300mm lens on an f5 and a 200mm lens on a d100 produce the same photographic image. In other words (and I don't exactly know how to say this) if I take a photo of a bird in a tree with a 300mm on f5 and 200mm on d100, and print them both out (not resized) to 4x6 prints (or any equal sized print for that matter), would the bird appear the same size in both photos?
The crop and image magnification issue somewhat confuses me in that is the field of view and magnification the same thing? If I reduce the field of view am I in essence magnifying?
What would be identical though, would be to use that same 200mm lens on both cameras, then crop the F5 image to only be the central section of the image and enlarge it to match the dimensions of the D100 image.
Bob's answer is precise and accurate. Here's the math:
1. 1/u + 1/v = 1/F
2. M = v/u = I/S
where; u is distance from focal plane to subject, v is distance from focal plane to image, F is focal length, M is magnification, I is image size, S is subject size.
In fact, the whole debate about focal length is settle in equation 1, because u and v held constant means F is determined. Said in D100 terms, the focal length of a lens on the D100 (image plane located right where it is on a 35mm cousin) is equal to focal length of the 35mm cousin.
Magnification is settled by equation 2. Again, u and v are constant so M is equivalent for D100 and 35mm cousin.
Confusion comes when you make the print. The same size IMAGE in print (see bob's example) will occupy more of the D100 frame. This is another way of saying the portion of the image circle used is bigger for 35mm.
Instead of saying the, "focal length is greater," D-SLR makers should have said, "You get to use the center of the image circle." That's the very best part--lowest distortion, least fall off, etc."
In your example, you made the same size PRINT image and frame. You did that by magnifying the D100 print 1.5 times as much as the 35mm print. Think about the circle of confusion and you will understand why Bob says that DOF is different. DOF and Magnification have the same relationship to CoC.