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PostPosted: Wed Jan 02, 2008 8:18 pm 
I have been browsing the lenses on offer but im having trouble understanding whats what.

I have put this topic in here because its just a general lense question and not many people reply to posts in the sony section

What does this f number (F4.5-5.6) represent on a lens and what is better?
Is there any way to tell the quality of the glass?
Is it best to get two different lenses(one low and one high distance) or one lense with a wide focal distance?

I have been looking at This list and im trying to work out the difference between the "G lens" and the "Carl Zeiss Lens" compared to the others in terms of quality.

Am I limited to just sony lenses or can I use more from other companys like nikkor and tamron?

What are Teleconverter?
Whats different about macro and fixedfocal length lenses?

Its all a bit baffling.

At the moment im thinking about the 75-300 lense for the thoes long distance pictres but now i have Found this So i guess i could just use one lens.


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PostPosted: Wed Jan 02, 2008 8:57 pm 
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I suggest you have a browse through the forums if you have a moment as a number of these questions have been answered pretty recently. You might also find the Lens buying guide feature over at our sister site DSLR Tips useful.

If you want to know more about individual lenses then the CameraLabs lens reviews are a good starting point. For lenses which Gordon hasn't had a chance to review yet the PhotoZone reviews are pretty reliable.

Bob.

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Leica D Vario-Elmar 14mm-150mm f/3.5 - f/5.6 ASPH.
OM-D E-M5, H-PS14042E, Gitzo GT1541T, Arca-Swiss Z1 DP ball-head.
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PostPosted: Wed Jan 02, 2008 9:15 pm 
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F Number:

Check this article out on wikipedia - http://en.wikipedia.org/wiki/F_stop - It should help you understand it a little better.

F Stops, numbers, aperture, are all the same thing; the size of the space in which light can enter the lens, and are measured in F-Stops/Numbers. The larger the Aperture, the smaller the F-Stop Number.

F/1.8 is a LARGE or FAST Aperture as it allows a lot of light in to the lens, but 1.8 (in numerical terms) is a small number compared to an Aperture of F/22 which is a SMALL or SLOW Aperture, and 22 is a larger number than 1.8.

So Small (F-Stop) Number = Large/Fast Aperture & Large (F-Stop) number = Small/Slow Aperture.

A Larger Aperture gives a smaller depth of field than a Smaller Aperture does. A better explanation than I can give of this effect can be found on Wikipedia and over at [url="http://www.dslrtips.com"]DSLR Tips[/url]


Quality of the Glass:

Better quality lenses are usually bigger, heavier and more well built on the outside than their lesser counterparts, but this is not always true. Reviews are always a good thing to check. Obviously Cameralabs and DSLR Tips do reviews on lenses but any that they don't have, I believe Thomas recommends [url="http://www.photozone.de"]PhotoZone[/url] for reviews.


Different Lens or One Lens:

Generally it is better to get different lenses, this usually minimizes distortion across the focal lengths, but there are exceptions such as the Nikkor 18-200mm which does a pretty good job across its focal length, but of course nothing can beat 2 or 3 good quality zooms or primes.


G Lens Vs. Carl Zeiss Lens:

I'm afraid I don't know enough about these lenses to pass a verdict, but like above, look for reviews of the lenses.


Lens Choice:

I'm not 100% but I think Sigma and Tamron offer lenses for the Sony mount, but you would have to double check that. (or hopefully someone else here can confirm/deny that) But you won't be able to use Canon or Nikkor lenses. (at least without a converter, but those are best avoided)


Tele-converter:

A Tele-converter is a "lens" which goes between the camera and the lens you are using and multiplies its focal length by usually 1.4x or 2.0x at the expensive of image quality and maximum aperture.


Macro & Fixed Focal Length:

Macro lenses are lenses that can focus to a distance which makes an object 1:1 - Life size or larger. Life size as in Life size on the cameras sensor, and when on a print or viewed on a computer screen, it becomes much larger than life size!

Fixed Focal Length lenses, also referred to as Primes, are lenses which can not zoom. They are generally much shaper and produce more accurate colours etc. than zoom lenses, but nowadays zoom lenses, especially good quality ones, aren't far behind in the sharpness and colour reproduction departments!


The Lens you are thinking about:

If you only want one lens, then from the face of it, should fit your needs. Depending on the lens you have just now, the 75-300 might be a better choice if you are willing to lug a second lens about.



Hope that helped 8)

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PostPosted: Wed Jan 02, 2008 9:24 pm 
CHeers for your reply, very usefull. So what does the F Number lables on the different lenses mean? Is is the minimum and maximum possible F stop on that lens?


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PostPosted: Wed Jan 02, 2008 9:36 pm 
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tobywuk wrote:
CHeers for your reply, very usefull. So what does the F Number lables on the different lenses mean? Is is the minimum and maximum possible F stop on that lens?

Maybe you didn't spot that there is more than one page on that DSLR Tips Lens buying guide? It's all explained there if you take the time to read it carefully. :idea:

Bob.

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Olympus OM-D E-M1 + M.Zuiko Digital ED 12-40mm f/2.8, Lumix 7-14mm f/4, Leica DG Summilux 15mm f/1.7 ASPH, M.Zuiko Digital 45mm 1:1.8, M.Zuiko Digital ED 75mm 1:1.8.
Leica D Vario-Elmar 14mm-150mm f/3.5 - f/5.6 ASPH.
OM-D E-M5, H-PS14042E, Gitzo GT1541T, Arca-Swiss Z1 DP ball-head.
Astrophotography: TEC 140 'scope, FLI ML16803 camera, ASA DDM60 Pro mount.


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PostPosted: Wed Jan 02, 2008 9:37 pm 
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If a lens is labeled - 18-55 F/3.5-5.6 - it means at 18mm its largest aperture is F/3.5 and at 55mm its largest aperture is 5.6. As you zoom from 18 to 55mm you will notice the maximum aperture has to drop gradually.

e.g. going from 18-55mm it may go something like this:

F/3.5 F/4.0 F/4.5 F/5.0 F/5.6

On a fixed aperture lens it will look something like 28-70 F/2.8 - only giving you one F/ number, since it is constant. Constant aperture lenses command more money than non fixed aperture lenses in the same class.



Stop getting in there before me Bob lol!

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PostPosted: Wed Jan 02, 2008 9:44 pm 
tobywuk wrote:
So what does the F Number lables on the different lenses mean? Is is the minimum and maximum possible F stop on that lens?


Take the Sony 18-250mm f/3.5-6.3 as an example. The part about the f-number refers to the maximum aperture available on the lens when zoomed fully out or in. So when this particular lens is zoomed all the way out to 18mm, the maximum aperture is f/3.5. When it is zoomed all the way in to 250mm, the maximum aperture is f/6.3.

You will only find this on some zoom lenses (other fixed lenses and more expensive zooms have a constant maximum aperture which can remain the same throughout the zoom range.) An example of a zoom lens with a constant aperture is the Sony 70-200mm F2.8G.

Hope this helps

Mark


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PostPosted: Wed Jan 02, 2008 9:58 pm 
Ah ok thanks.

Just to clarify, does this mean than with most lenses, Excluding the ones with a single max aperture, that the further you zoom in, the less F number you can get and so it is not possible to get as much background blur on an image than you would when you would be zoomed all the way out? From What I have read, people recommend zooming in to get a nice blurred background but this theory seems to go against this.


Bob, I have actually read and watched a lot of the content on the DSLR tips website, im just after some clarification and advice on some little aspects that im still unclear about.


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PostPosted: Wed Jan 02, 2008 10:13 pm 
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Well, the further you zoom in, the more extreme the effect is.

I am sure there is a formula for calculating it exactly somewhere, but by trial and error you eventually just know with your own lenses.

e.g my 70mm @ F/4 will give less of a background blur than when it zoomed all the way in to 300mm @ F/5.6

The longer focal length makes the depth of field smaller or just accentuates it, not sure which (might be both?)

Obviously though, 300mm @ F/22 will give less than 70mm @ F/4

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