cannon lenses

[bdieguez]

i new learning photo lens tecniques if some one can help me understand lenses. 1rst question whats 28- 300 mm means on lens.(what this numbers means when taking pictures.
thanks
bernie

[djwixx]

28-300mm is the zoom range relative to 35mm film. The widest point is 28mm, with the 300mm being the furthest length you can zoom to. On a digital camera, because the sensor is smaller than 35mm film the relative zoom range will be higher.

At 28mm you'll be able to focus on a few feet in front of you, but at 300mm it'll be nearer 20 feet. In terms of a point and shoot camera range will be equivalent to about 2X-7X.

[gilp]

28-300....it also means you got yourself one really soft lens!

[uplander]

28-300....it also means you got yourself one really soft lens!

Expain soft to me. I belive I know what you mean, but please clarify.
Thank you

[djwixx]

28-300....it also means you got yourself one really soft lens!

Expain soft to me. I belive I know what you mean, but please clarify.
Thank you

Personally I would say it depends on the quality of the lens, but I'm no expert. I would assume that the longer the zoom range the more you compromise from wide to long to try to satisfy the needs at both ends.

I have 70-300 and personally I think it's sharp at both ends - starting at 28 would probably reduce that.

Feel free to correct me - all useful information appreciated.

[bdieguez]

28-300....it also means you got yourself one really soft lens!

Expain soft to me. I belive I know what you mean, but please clarify.
Thank you

Personally I would say it depends on the quality of the lens, but I'm no expert. I would assume that the longer the zoom range the more you compromise from wide to long to try to satisfy the needs at both ends.

I have 70-300 and personally I think it's sharp at both ends - starting at 28 would probably reduce that.

Feel free to correct me - all useful information appreciated.

thanks it is very helphul for me all this information
i learning more every day
thanks again
bernardo

[gilp]

Ok, In simple terms:

There is a mathematical equation that you can use to see how "sharp" your zoom lens will be from one end to the other (many lenses have a "sweet" spot and can be very sharp at a certain focal range and very soft everywhere else)

as we know, Prime lenses are the sharpest of the bunch... if you divide the Prime lenses focal range ie: 50mm lens = 50 divided by 50 = 1 ... 1 being the magic number as sharpness goes...

start from 1 and upward sharpness decreases... and it's generally accepted than any number larger than 4 is quite soft... and that anything between 1 and 3 will be very sharp.

as an example, the EF 70-200L 2.8 will give you a sharpness factor of 2.85 (200/70 = 2.85) very good sharpness. but when you get to lenses that will have a wide zoom range things get "blurry" ! a 28-300... will give you a 10.71 sharpness factor....


I know many people will say... "my lens is very sharp".... but sharp compared to what?

I think that trying to stay under 4 or makes for wise purchasing.


1= perfect
1-3 = great
3-4 = a bit soft...a bit of fringing.. but generally very aceptable
4-6= quite soft, more fringing.
above 6 = well...not that good.

[djwixx]

Excellent info - thanks.

[uplander]

Thanks gilp, I figured it was about not being able to stay sharp over such a broad zoom range. Your answer went beyond expanation and actually quantified it. useful info for sure

[madlights]

Thanks gilp...very informative. I had a photography instructor once who said don't buy zooms that the high number is much over 3X the low number of the zoom. I guess he must have been making a generalized statement based on this equation? When you think of it going from a 28-300 zoom is MUCH different than a 70-300. I would also imagine that's why some of the sharper digicams have a lens that's somewherein a range 30-95 or thereabouts? Thanks...interesting.

[gilp]

There are ofther factors that come into play of course, but this equation is valid for all lenses...

of course, when you compare a 300$ with a 3000$ zoom lens...there are obviously other important diffences... things like Glass, coatings and aperture all have dramatic impact on sharpness.

when you shop for an affordable lens...you do want to put all chances on your side... so remaining within a factor of 3x will defintily help compansate for the other little flaws the lens will have.

[dick_haynes]

28-300mm is the zoom range relative to 35mm film.

28-300mm is 28-300mm regardless of whether it is 35mm, APS-C, 1.5x sensor, etc. The number stands for the distance from the rear nodal point of the lens (usually close to the aperture plane) to the plane where subjects at infinity come into focus.

Essentially the point where light stops traveling straight, and turns to head toward the sensor.

The difference is in the image size. A 35mm negative is larger than a APC-C sized film or sensor. Therefore at 20mm you will get a different image size between the two. But the focal length is the same.

There is no need to convert crop factors if you just get used to knowing what your lenses look like with your camera. I am now totally digital and know that if I am using a 30mm lens it will look like a normal perspective. I don't pick it up and say that this will look like a 50mm lens. Just get used to what you are using and don't worry about the past!


Key point- when you double the focal length, you will double the image size. So if you go from 28mm-280mm it will be a 10x zoom, whether or not it is 35mm format or not.

As for sharpness, well. sometimes with the "affordable lenses" you have to give it a few goes. They generally have less quality control so your might get a lemon the first time. I have a Sigma 18-200mm and find that it is quite sharp for a what? 10x factor.

I had a Canon 70-300mm and the sharpness was sub-par. Now, the 24-70mm L-series on the other hand. . . WOW!!!!

So my experience with the equations has been hit and miss, but generally you get what you pay for. If you want the ultimate sharpness, Canon L-series is peerless!

[dang]

I've learned my lesson about being to general when talking about the difference in lenses, so I've begun passing out this link which should help. It's always good to have something visual, so here's some explanations with example shots. It's a great read, I think you'll enjoy it:
http://www.photonomics.com/chooselensa.htm