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09-16-2020, 08:52 AM - 1 Like   #1
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What is a "fixed" lens?

I have been reading on this site about lenses and one thing I keep running into is "fixed" lenses what does this mean? Thanks as always.

09-16-2020, 08:57 AM - 1 Like   #2
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QuoteOriginally posted by dipo 1 Quote
I have been reading on this site about lenses and one thing I keep running into is "fixed" lenses what does this mean? Thanks as always.
depending upon the context, a fixed lens could refer to a prime (or single focal length) lens or a camera with a non-interchangeable lens...
09-16-2020, 09:06 AM   #3
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A lens usually has three rings.

1 - focus ring
2 - aperture ring (might be absent on modern lenses)
3 - zoom ring (might be absent if the lens is only single focal length (prime/fixed)

For prime lenses, one would 'zoom' with their feet

For instance, a lens could be a zoom, say 18-50mm. But a prime/fixed lens would be something like 50mm only.

While not always true, a prime/fixed lens needs less glass in the lens than a zoom lens. This makes it 'easier' to create sharper lenses with wider apertures.
Also, while not always true, zooms commonly have variable widest apertures to reflect the zoom length.

For reference, you can see in my signature that I have 3 zooms and 5 primes.

Last edited by FozzFoster; 09-16-2020 at 09:14 AM.
09-16-2020, 09:26 AM   #4
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another possibility might be a zoom with a constant aperture such as this one

HD Pentax-D FA* 70-200mm F2.8 ED DC AW Reviews - D FA Zoom Lenses - Pentax Lens Reviews & Lens Database

you can use F2.8 regardless of the focal length selected as compared to a variable aperture zoom where the maximum aperture changes based on the focal length selected


HD Pentax-DA 16-85mm F3.5-5.6 ED DC WR

https://www.pentaxforums.com/lensreviews/hd-pentax-da-16-85mm-f35-56-ed-dc-wr.html

09-16-2020, 09:34 AM - 3 Likes   #5
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Usually it means non-zoom i.e. prime lens, or a zoom with constant aperture. It could also be something that been picked up from the repair shop recently.
09-16-2020, 12:19 PM - 3 Likes   #6
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QuoteOriginally posted by dipo 1 Quote
I have been reading on this site about lenses and one thing I keep running into is "fixed" lenses what does this mean?
QuoteOriginally posted by pepperberry farm Quote
depending upon the context, a fixed lens could refer to a prime (or single focal length) lens or a camera with a non-interchangeable lens...
QuoteOriginally posted by aslyfox Quote
another possibility might be a zoom with a constant aperture
QuoteOriginally posted by Wasp Quote
It could also be something that been picked up from the repair shop recently.
...in summary a "fixed" lens can mean:
a) A non-zoom lens that has only one focal length.
b) A non-interchangeable lens fixed permanently to a camera.
c) A constant aperture zoom lens.
d) A repaired lens.
e) A sterile lens where the fungus or mold has been removed

It all depends on the context. Without context, a fixed lens is probably "a" a.k.a. prime lens.
09-16-2020, 12:40 PM   #7
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Then there are mirror lenses that only have one, non-adjustable aperture opening. The aperture is 'fixed' at one value.
09-16-2020, 01:08 PM - 2 Likes   #8
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Succinctly, with a few essential qualifiers:
  • A fixed lens is permanently affixed to the camera
  • If not a zoom or multi-focal, it's fixed focal length
  • If it's maximum relative aperture does not change, it's fixed maximum aperture
  • If no aperture adjustment, it's fixed aperture
  • If not focus-able, it's fixed focus
Most cheap plastic cameras feature fixed lenses that are also fixed focal length, fixed maximum aperture, fixed aperture and fixed focus. That is, of course, assuming the lens is not broken. In which case, it may be in need of fixing as well as all of the above.


Steve

09-16-2020, 01:44 PM - 2 Likes   #9
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Thanks guys and gals great info as always.

---------- Post added 09-16-20 at 01:57 PM ----------

Ok guys I blew it what I was talking about is a 'preset'. Sorry still learning the lingo.
09-16-2020, 04:24 PM   #10
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A preset lens has an aperture ring (manual aperture) and a construction/linkage/second ring on which you select the aperture you wish to use. Selecting an aperture here creates a hard stop to the aperture ring so when turning that it will stop at the selected aperture.

So you'd do this when shooting:
- Preset your aperture value of choice, say f8
- Focus with the lens wide open (for instance f2 for a 50mm f2)
- Close your aperture by turning the aperture ring until you can't turn further, this will be f8.
- repeat

or you focus, then adjust the aperture to get the DOF you want, meter and shoot.
The lovely thing about presets are that they have no "hard" stops, so you can technically shoot at fπ instead of f2, f2.8, f4 etc.
09-16-2020, 10:13 PM - 1 Like   #11
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QuoteOriginally posted by dipo 1 Quote
Ok guys I blew it what I was talking about is a 'preset'. Sorry still learning the lingo.
Do we bite?

Answer: A lens is not preset, but its aperture actuation might be. Google: "preset lens aperture"

Expansion: Compare and contrast to "automatic aperture", "semi-automatic aperture", "manual aperture".


Steve
09-17-2020, 01:59 PM - 1 Like   #12
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Boy are guys good or what? I really liked the answers about repairing the lens. Thanks again now I know more than I did yesterday always a good thing.
09-17-2020, 03:20 PM - 1 Like   #13
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as I tell newcomers -

you will find friendly members and a lot of knowledge here at the Pentax Forums
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