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Old Jun 22, 2005, 5:30 PM   #1
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Hey everybody,

Well, I've been sitting around with my XT for almost two months. I could say I learned a lot within the time, but there are still some things I'm not so sure and I was hoping you guys would be able to fill in the gaps

-Could someone explain the lens construction detail; the "X elements in Y groups". What does that really mean and is this concept somehow proportional to the optical quality of a lens?

-How does a lens affect the colour/saturation/contrst/etc. of a picture? Isn't glass just glass? I might understand how an UD or ASP glass may alter it, but if you look at the cross-sectional diagram of the canon 50mm 1.4, there is no "special" glass but people keep saying the colouring is good.

-What's this "distance scale" from some number to infinity?

-For a crop factor of 1.6x, would I only consider up to ~15mm in MTF charts?

-How many of you actually use filters?

And lastly

-Which lens which you pick: the EF 85 1.8 or EF 50 1.4? At first I was only looking at the 50 until I started noticing the 85... With the 85 I could still see a reason to use my kit lens, but the focal length might be too long since I never tried it... :O
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Old Jun 22, 2005, 11:04 PM   #2
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BoYFrMSpC wrote:
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-Could someone explain the lens construction detail; the "X elements in Y groups".
X - is the total number of glass pieces inside the lens (7 total for the 50 f/1.4)

Y - is howseveral element are mated together to form a particular correcting function (6 for the 50 f/1.4 -> only 2 elements are linked)



Quote:
What does that really mean and is this concept somehow proportional to the optical quality of a lens?
I doubt this...



Quote:
-How does a lens affect the colour/saturation/contrst/etc. of a picture? Isn't glass just glass? I might understand how an UD or ASP glass may alter it, but if you look at the cross-sectional diagram of the canon 50mm 1.4, there is no "special" glass but people keep saying the colouring is good.
Actually the less glass the better here since each time alight raypass from one medium to the next - i.e. glass/air/glass/air each color (wavelenght) is diffracted/refracted differently creating more problem/loss


->Look throughyour lens(es) at a white piece of paper - don't they all have different tint? :shock:




Quote:
-What's this "distance scale" from some number to infinity?
Do you mean the DOFmarkers engraved next to the distance scale?





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-For a crop factor of 1.6x, would I only consider up to ~15mm in MTF charts?
13.52mm to be exact (square root of the sum of 1/2 the sides squared) :-)



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Old Jun 23, 2005, 10:39 AM   #3
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thanks for that . I would of never thought about the diffraction/refraction reason... And I thought I knew my physics...
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Old Jun 23, 2005, 4:10 PM   #4
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On top of that, glass is not just glass! Most of the pro series lenses are manufactured from much purer glass and different glass recipes to attain higher optical values. For instance, most standard glass in the world has a fair amount of arsenic in it, you'll see many higher end lenses advertise arsenic free glass, it providesbetter optics. Each additional ingredient or trace element in theglassaffects the way the glass allows light to pass through it and to a smaller degree the weight of the glass and its properties at different temperatures.

There are lots of other things in glass (usually metals like lead or iron or potassium) that also affect the way light is refracted.

Then, once you've got your glass, it has to be polished and coated with various compounds to protect it or modify the way it plays with light.
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Old Jun 23, 2005, 8:29 PM   #5
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G35Guy wrote:
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... you'll see many higher end lenses advertise arsenic free glass, it providesbetter optics.
Oh, man. I thought it just meant it was just more environmently friendly because they always mention that in release announcements... :shock:
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Old Jun 24, 2005, 8:24 AM   #6
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BoYFrMSpC wrote:
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G35Guy wrote:
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... you'll see many higher end lenses advertise arsenic free glass, it providesbetter optics.
Oh, man. I thought it just meant it was just more environmently friendly because they always mention that in release announcements... :shock:

That is true, as well...but, it does alter the optics, also
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Old Jun 24, 2005, 11:06 AM   #7
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FYI - http://www.osa-opn.org/view_file.cfm?doc=%24)%3CK-J0%20%20%0A&id=%24*%2CO%2BK%20%20%20%0A
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Old Jun 25, 2005, 5:41 PM   #8
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:O

Whow... very techy, I need to take that one in small doses... I'm still on summer vacation... :roll:

But I got another question... What's "light fall off"?
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Old Jul 1, 2005, 9:48 AM   #9
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Quote:
-Which lens which you pick: the EF 85 1.8 or EF 50 1.4? At first I was only looking at the 50 until I started noticing the 85... With the 85 I could still see a reason to use my kit lens, but the focal length might be too long since I never tried it...
Both of these are excellent for the money. Its really a personal choice about which focal length you think you require most.

The 85 will give you nicer portraits.

Heres an idea: how about getting the 85 and opting for the 50 f1.8 also. This is a very inexpensive lens, but optical quality is good.
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Old Jul 1, 2005, 1:32 PM   #10
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i agree with the 85 1.8 (or you could go 100mm f2.0, whichever you can find cheaper, the 85 is sharper but the 100 controls CA better)... and if you do decide to pick up the 50mm 1.8 check out ebay and see if you can find the mk I edition which has a metal mount and is generally built better..
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