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EF-S lenses also multiply focal length ??

  • Thread starter Thread starter jim kelly
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And don't forget the advantages. If a lens is slightly soft at the edges in the 35mm format, it won't be soft in most digital formats because it doesn't use that part of the optical foot print. The lens will still focus to the same plane (hence the same exact focal length) but the offending edges are not within the bounds of the sensor.

It completely escapes me why there is such a crop factor hoopla, even though I have shot 35mm for decades. Might it be that I learned on 120,
2 1/4 square and sheet film??? I don't know. It was never a hang up.
 
grsharp said:
Now here's a question I've been thinking about...if you do consider
the "crop factor" between the various formats, do you get the same
amount of telephoto "compression"?
Click to expand...
The compression is due only to perspective. Take a picture of the same thing from the same position using any lens, and you will get the same amount of compression. The only difference is that with a wide angle lens, you have to crop to get the same image.

Don't believe me? Take your wide angle lens to a freeway overpass and photograph the traffic a mile away. Now blow up a 1/10 crop of the picture. It's compressed just like a full frame telephoto shot would be.

Taking a full frame using a smaller sensor size is the same as taking a crop of a larger sensor size, so looking at just full frame pictures, a smaller focal length will give the same compression effect that a larger focal length will produce on a full sized sensor. Why is this? Because to fill up the frame with the same subject, you have to move the camera, changing the position to one that will compress the image.

Regarding whether or not to use the 1.6X crop factor crutch, my recommendation is to learn the focal length of the standard lens for your camera. Then consider other lenses as multiples of this standard lens. For full frame 35mm cameras, the standard is typically 45-50mm. For the 10D and 20D, it would be 28-31. The number 30 is in the range and easy to use in computations, so that's what I recommend. For some medium format cameras, it depends what film you use and how you expose it (actually, this is true of 35 mm cameras as well -- remember super slides?).
 
DancePhotographer said:
And don't forget the advantages. If a lens is slightly soft at the
edges in the 35mm format, it won't be soft in most digital formats
because it doesn't use that part of the optical foot print.
Click to expand...
But the smaller sensor size demands a greater sharpness of the lens in the first place. If the lens is soft on the edges, it's likely it's soft in the center as well, to a lesser extent. But the smaller sensor size will magnify what softness there is. It's entirely possible that the apparent softness to the smaller sensor in the center is equivalent to the edge softness on the larger sensor.
 
RDKirk said:
Photographers who work with both 35mm and medium format aren't
wondering what the "crop factor" is when they shift between cameras.
Click to expand...
Well, I can't speak for others, but I used to primarily shoot 35mm film, and sometimes 6x6 or 6x7 medium format. I did have a habit of converting my MF lenses into 35mm equivalent, because that provided a familiar "scale" for me. I suspect other "part-time" MF users did the same. I never thought of it as a "crop factor", and still don't see much value in the "crop" idea in explanations of digital, as we already had the notion of a "format", but it is sometimes useful to keep in mind the size ratio of one format to another.

If you begin photography with a 1.6x camera, you can develop your internal "scale" using that format, but some day you'll find yourself using another format, and there's a good chance you'll find yourself converting in your head.

When you travel to a foreign country, do you develop a "feel" for what amount of their currency is a lot, or do you find yourself converting all the prices into your native currency? You probably start out converting everything at first, but if you live there for a while, you don't need to any more. If you travel frequently from country to country, you'll probably always convert back to "home" currency.
-harry
 
digirob said:
No. The compression will be the same as on a 35mm full frame.
That's because the optics are the same.

It's called "crop factor" because the result is the same as you'd
get if you cropped the image in Photoshop.
Click to expand...
Telephoto compression (and wide angle "distortion") has nothing to do with the optics, and everything to do with the shooting distance.

If you stay in the same place, it doesnt matter which lens you use, the compression/distortion will be the same. (shoot with a wide lens, and then crop the center out and enlarge it, and you will get the same picture (as far as compression is concerned) as if you'd used a longer lens without cropping.

--
Tony Collins
[email protected]
 
I stand corrected. Yes, you are correct. I was not considering the change in camera-to-subject distance as the mitigating factor.
Tony Collins said:
Telephoto compression (and wide angle "distortion") has nothing to
do with the optics, and everything to do with the shooting distance.

If you stay in the same place, it doesnt matter which lens you use,
the compression/distortion will be the same. (shoot with a wide
lens, and then crop the center out and enlarge it, and you will get
the same picture (as far as compression is concerned) as if you'd
used a longer lens without cropping.

--
Tony Collins
[email protected]
Click to expand...
--
dpreview & pbase supporter
http://www.pbase.com/digirob
 
You're trying to introduce facts not in evidence. If a lens is sharp at a 35mm footprint size, but soft at the edges, it will not be any softer in the center of a smaller sensor.
 
digirob said:
Ah, I misspoke. I should have not implied the markings were
modified to be 35mm equivalent -- just that they are marked 35mm,
and that the same math applies.
Click to expand...
Wrong again. The focal length of a lens is a physical constant nothing in the world changes.

What changes is the field of view that the sensor or film captures out of the lenses image circle. Everybody and his dog knows what a given focal length will deliver in terms of FOV on 35mm film, so we all are inclined to recalculate the focal length to the equivalent focal length to make heads and tails of any given lens on a DSLR.
A 50mm lens is giving you the FOV of
  • a moderate wide angle lens on MF.
  • a normal lens on 35mm (equivalent to your eye).
  • a short telephoto lens on a crop DSLR.
--
regards
Karl Günter Wünsch
 
RDKirk said:
Photographers who work with both 35mm and medium format aren't
wondering what the "crop factor" is when they shift between cameras.
Click to expand...
AMEN! Whoohoo thank you.

I try to tell non beleivers that a 50mm lens may act differently in medium format, than in a 35mm format, than in a APS-C or 1.6 DSLR format, but it is still a 50mm lens. No one gets it. I am glad you do.

Also it gets me when someone says their 100mm lens is giving you the "equivalent" of a 160mm lens, and people jump all over them. Um, it is true folks. No one is saying that it is a 160mm lens, but it is the APS-C equivalent of a 160mm lens. If they were making it just for APS-C they could realistically say it is a 160mm lens. but on a 35mm camera it is equal to a 100mm :D

Which brings me to a question, if EF-S lenses are only going to work on 1.6 APS-C typ DSLR's from Canon, why didn't they call it a 28-105 or whatever? Maybe because EF-S is going to have 1.3 or FF sensors?
 
DancePhotographer said:
You're trying to introduce facts not in evidence. If a lens is
sharp at a 35mm footprint size, but soft at the edges, it will not
be any softer in the center of a smaller sensor.
Click to expand...
True. But my point was that sharp in the center for a large sensor could be soft in the center for a small sensor because the smaller sensor has higher sharpness demands.
 
That can't be the case. If what you say is true than the lens was never really sharp in the center in the first place. It was simply "good". I am talking about lenses that are actually sharp with softness at the edges, which is a condition that is not uncommon. Even with eyeglasses it is tough to get edge to edge shaprnes, but the center can be perfect.
 
I elaborated at length in this thread about why it's important to know the cropping factor and using it to help determine the FOV one can expect from a given lens of FL x when mounted on a 1.6 crop camera -- if one is accustomed to the FOV that same lens delivers on a FF camera.

Sheesh. I give up.
Karl Günter Wünsch said:
Wrong again. The focal length of a lens is a physical constant
nothing in the world changes.
What changes is the field of view that the sensor or film captures
out of the lenses image circle. Everybody and his dog knows what a
given focal length will deliver in terms of FOV on 35mm film, so we
all are inclined to recalculate the focal length to the equivalent
focal length to make heads and tails of any given lens on a DSLR.
A 50mm lens is giving you the FOV of
  • a moderate wide angle lens on MF.
  • a normal lens on 35mm (equivalent to your eye).
  • a short telephoto lens on a crop DSLR.
--
regards
Karl Günter Wünsch
Click to expand...
--
dpreview & pbase supporter
http://www.pbase.com/digirob
 
DancePhotographer said:
That can't be the case. If what you say is true than the lens was
never really sharp in the center in the first place. It was simply
"good". I am talking about lenses that are actually sharp with
softness at the edges, which is a condition that is not uncommon.
Even with eyeglasses it is tough to get edge to edge shaprnes, but
the center can be perfect.
Click to expand...
But sharpness is a relative thing. A lens is sharp if it's at least as sharp as the precision of the recording medium. And with the same number of megapixels, a smaller sensor has tighter tolerance demands on the lens.

No matter how good the lens crafting skills are, there is always a limit to sharpness. At the very least, it's limited by the wavelength of light being focused.
 
But since good 35mm film is at least as accurate (if not more accurate) in recording sharpness as an 8.2mp sensor, then my point still stands.
 
RDKirk said:
In fact, you can mount Pentax medium format lenses on Pentax 35mm
cameras, and you'll find that 80mm is still 80mm, regardless which
camera format it's on.
Click to expand...
If you use a medium format 80mm lens on a medium format camera, the field of view would be close to that of a 50mm (or wider) camera (depending on film size) as the film is larger than 35mm film. If you could mount that 80mm lens on a 35mm camera, then it would give the same size image on film as an 80mm lens designed for 35mm film. If you could fit either if these lenses on a 10D (the 80mm MF or the 80mm for 35mm film) each one would give you a final image equivalent to a 50mm lens on a 35mm camera?

Clear now?

As someone else pointed out, 80mm is a physical characteric of the lens and the image size depends on the size of the sensor/film as long as the image cast by the lens is at least as big as the sensor/film. That comes into play if you were to use an EF-S lens on a full frame sensor (or 35mm film): theoretically, an 80mm EF-S lens would give the same size image on film as an EF lens except that the lens elements were designed for the smaller sensor and therefore you'd get significant vignetting on te 35mm film/sensor. (As you would if you used a 35mm camera lens on a medium format camera.)

Even clearer now?
--
Jeff Peterman

Any insults, implied anger, bad grammar and bad spelling, are entirely unintentionalal. Sorry.

 
Forget what went before.

Focal length does not change between full frame and 1.6 format.

The image magnification on a 1.6 sensor is exactly the same as a full frame sensor. You just need to enlarge the capture a bit more.

EFS lenses do not change focal length, or magnification. They just make it easier to manufacture wide lenses that work with 1.6 sensors.

1.6 is not the new format - it is just a format. 1.6 sensors will be with us for a very long time - perhaps for ever. If anything full frame is the freak!

When we only had 35mm, how many got hung up because theirs was not as big as the guy with the large format? exactly, some dabbled but generally we didn't care much. We were all nice and secure and confident in our 35mm world.

There is no benefit whatsoever in reverse thinking crops and magnifications. You are better off understanding what you have rather than trying to work out and compare what you don't have.
 
DigitalEOS said:
.... No one is saying that it is a 160mm lens,
but it is the APS-C equivalent of a 160mm lens.
Click to expand...
With respect to angle of view, it is equivalent. With respect to other attributes dependent on focal length, in particular depth of field, you need to consider it's true focal length (and the sensor size).
-harry
 
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