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Author Topic: Wide angle digital zooms f-stops  (Read 3174 times)
giles
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« on: July 12, 2005, 08:18:17 PM »
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I think you may be confused.   The widest open aperture is the one primarily quoted in specifications.  For zoom lenses this can be "fixed" meaning that it doesn't change as the lens zooms, or variable.

An example of "fixed" is Canon's 70-200 f/2.8 IS lens, which can be used at 2.8 at 70mm and at 200mm.  It can be stopped down to f/32, probably far smaller than is practical. A lens that is not "fixed" is Canon's 10-22mm f/3.5-4.5 EF-S zoom.  At 10mm its widest aperture is f/3.5.  At 22mm its widest aperture is f/4.5.   Smallest apertures (again, probably unusably small) are f/22 at 10mm and f/29 at 22mm.

For a 10D you might be interested in Tamron's new wide angle lens, which Michael has posted a "quick look" article about today:

Tamron SP 11-18 f/4.5-5.6 Di II LD

Regards,

Giles
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mdijb
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« Reply #1 on: July 13, 2005, 09:11:23 AM »
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I stand corrected--I checked out Tamron's website and their new 11-18 zoom will stop down to f22.

Now my interest is stimulated.

MDIJB
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mdiimaging.com
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« Reply #2 on: July 14, 2005, 04:33:06 AM »
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Zoom lenses with fixed MAX aperture are e.g. Tokina 12-24/4, Canon 70-200/4 etc. In each of these lenses you can open the lens to f/4 (not more) or close it to f/5.6, f/8, f/11 etc.

Lenses with fixed aperture are mirrors e.g. Tamron 500/8, Sigma 600/8 etc. In these lenses you can NOT change the aperture at all.

HTH.

Happy shooting,
Yakim.
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boku
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« Reply #3 on: July 14, 2005, 02:32:08 PM »
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As Howard said, sometime you need to stretch to achieve. Don't be afraid of small aperture + focal length. Just be aware. The following shot was taken at 10mm at f/16. I knew this was in the "diffraction-compromized" zone, but went ahead anyhow because that's what it called for:

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Bob Kulon

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boku
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« Reply #4 on: July 14, 2005, 03:15:10 PM »
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Quote
Quote
A picture is worth a lot of words, or something like that.
One rock, two rocks, three rocks, four rocks ...

Yep. ::

Good illustration, Bob! How big can you print that before the illusion doesn't work anymore, or is it simply not an issue?
Well, I printed it to 11x14. The detail held like there wasn't even a hint of diffraction. I suppose it could go 16x20, but after that the 8MP is more of an issue, no?

I was very careful with the noise, sharpening, and tonal adjustments to prevent diffraction artifacts, so let's not assume that the Canon EF-S 10-22 is flawless, just very useful.
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Bob Kulon

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mdijb
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« Reply #5 on: July 12, 2005, 07:40:26 PM »
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I really want a wide angle zoom for my 10d.  All the alternatives seem to have an f/stop that is fixed in the rane f4.0-f5.6.  i know that these focal lengths have an OK depth of field fo distant scenes, but will they provide enough for closer objects.  I want to be able to stop down to f/8 or higher to assure max sharpness and depth of field, to take advantage of what these widae angle lenses can do, but these lense do not seem to provide that capability.  Is this relatively wide aperture limitation a concern?

MDIJB
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howard smith
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« Reply #6 on: July 13, 2005, 07:44:16 AM »
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I take exception to giles comment that the smallest apertures are unusable.  They are there for a purpose and should be used for that purpose.  Just like the widest aperture.

"... these focal lengths have an OK depth of field fo distant scenes, but will they provide enough for closer objects."

Depth of field is determined the same way for all lenses and is a function of the focal length, f/stop used, circle of confusion and focus distance.  What is "OK" and "enough" is a rather personal and application question.

f/4 to f/5.6 is only one stop.  The range is usually not a problem, if f/4 and f/5.6 are fast enough for your use.
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giles
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« Reply #7 on: July 13, 2005, 05:25:38 PM »
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I take exception to giles comment that the smallest apertures are unusable.  They are there for a purpose and should be used for that purpose.
In the context of the question, introducing discussion of diffraction and other issues seemed inappropriate, but I didn't want the original poster to jump to the conclusion that the smallest aperture is automatically "best" when substantial depth of field is wanted, either. I'm sorry you didn't like my compromise!

Cheers,

Giles
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howard smith
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« Reply #8 on: July 14, 2005, 02:20:50 PM »
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giles, my only objection was that I use the small apertures when needed, rather than limit myself to the "optimum" aperture for diffraction.  If I need f/22 or f/32 for the image I want, I use it fearlessly.  Same for wide open.  Some things are more important (at least to me) than lines per millimeter.
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howard smith
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« Reply #9 on: July 14, 2005, 02:37:33 PM »
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A picture is worth a lot of words, or something like that.
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jani
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« Reply #10 on: July 14, 2005, 02:50:40 PM »
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A picture is worth a lot of words, or something like that.
One rock, two rocks, three rocks, four rocks ...

Yep. ::

Good illustration, Bob! How big can you print that before the illusion doesn't work anymore, or is it simply not an issue?
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Jan
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« Reply #11 on: July 15, 2005, 05:49:24 AM »
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Well, I printed it to 11x14. The detail held like there wasn't even a hint of diffraction. I suppose it could go 16x20, but after that the 8MP is more of an issue, no?
Thanks.

That's certainly good. "16x20 should be enough for anyone" ::

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I was very careful with the noise, sharpening, and tonal adjustments to prevent diffraction artifacts, so let's not assume that the Canon EF-S 10-22 is flawless, just very useful.
Yes, absolutely. From my meager experience, I'd say that this lens gives what you're paying for, and I mean that as a positive.
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Jan
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