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07-28-2019, 03:21 PM   #1
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Variable Aperture lenses

Hello,
What exactly does variable aperture mean. I've always preferred fixed aperture lenses in the f/2.8 range, but am looking at lenses for my Sons Canon Rebel and a lot of them are variable aperture. He would like to have a nice UWA lens.
Thank you.

07-28-2019, 03:28 PM   #2
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It's one of the trades lens designers have to deal with when making a lens.
It's common among all brands, generally for all but the most expensive zoom lenses.

For a zoom lens, a variable-aperture lens will have a slower aperture at the long end than it does at the short end.
You might see something like an 18-55 f3.5-5.6, which would have a maximum aperture of f3.5 at the 18mm end and f5.6 at the 55mm end.
It is extremely common... especially for UWA and other specialty lenses...

-Eric
07-28-2019, 03:43 PM   #3
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QuoteOriginally posted by TerryL Quote
He would like to have a nice UWA lens.
Thank you.
Sigma makes a 10-20mm F3.5 that currently sells for $399. You can find them used for less. The Sigma 10-20mm F4-5.6 was discontinued some years ago and it can be found for less than $200 used. IMO there is not much difference between them.

SIGMA 10-20mm CLUB - PentaxForums.com

Sigma also has the 8-16mm F4.5-5.6 is generally more expensive $400 and up. It has more distortion at the wide end than the 10-20 and can't use filters.

Older versions of the Tamron 10-24mm F3.5-4.5 can be found for less than $200, the newer version with VC is more expensive.
07-28-2019, 04:38 PM   #4
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QuoteOriginally posted by boriscleto Quote
Sigma makes a 10-20mm F3.5 that currently sells for $399. You can find them used for less. The Sigma 10-20mm F4-5.6 was discontinued some years ago and it can be found for less than $200 used. IMO there is not much difference between them.

SIGMA 10-20mm CLUB - PentaxForums.com

Sigma also has the 8-16mm F4.5-5.6 is generally more expensive $400 and up. It has more distortion at the wide end than the 10-20 and can't use filters.

Older versions of the Tamron 10-24mm F3.5-4.5 can be found for less than $200, the newer version with VC is more expensive.
Thank you, Ben,
I was looking at the Tamron, newer version, do you happen to know if it's any good?

---------- Post added 07-28-19 at 04:39 PM ----------

QuoteOriginally posted by TwoUptons Quote
It's one of the trades lens designers have to deal with when making a lens.
It's common among all brands, generally for all but the most expensive zoom lenses.

For a zoom lens, a variable-aperture lens will have a slower aperture at the long end than it does at the short end.
You might see something like an 18-55 f3.5-5.6, which would have a maximum aperture of f3.5 at the 18mm end and f5.6 at the 55mm end.
It is extremely common... especially for UWA and other specialty lenses...

-Eric
Perfect, Eric,
Thank you very much.

07-28-2019, 05:01 PM   #5
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QuoteOriginally posted by TerryL Quote
Thank you, Ben,
I was looking at the Tamron, newer version, do you happen to know if it's any good?

---------- Post added 07-28-19 at 04:39 PM ----------


Perfect, Eric,
Thank you very much.
I have no experience with the Tamron, the new version isn't made in K-mount. I have the 10-20/3.5 but I broke the filter ring when my tripod fell over...
07-28-2019, 11:55 PM   #6
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QuoteOriginally posted by TerryL Quote
What exactly does variable aperture mean. I've always preferred fixed aperture lenses in the f/2.8 range, but am looking at lenses for my Sons Canon Rebel and a lot of them are variable aperture. He would like to have a nice UWA lens.
The f/stop = the focal length of the lens divided by the diameter of the aperture. So with a 35mm prime at f/4 the aperture will have a diameter of 8.75mms (35mm/4). But on a typical 18-55mm zoom, because the focal length is not a constant, it is not cost effective for the lens to be designed to maintain the same effective aperture. At shorter focal lengths it may be f/3.5 and at the long end it could be f/5.6 or f/6.3.

"Constant aperture zooms" for any camera will generally be more expensive. For the Canon, Meike makes an UWA constant aperture 6-11mm f/3.5 for under $300:
Meike MK-6-11mm f/3.5 Fisheye Lens for Canon EF

Tamron, Sigma, Tokina, and Canon also make constant aperture zooms in the 16-50mm range for $300-$500 that you can filter to find on the B&H's website for Canon mounts.

Based on your description, I'd recommend the Sigma 10-20mm f/3.5 that is currently on sale for $400:
Sigma 10-20mm f/3.5 EX DC HSM Lens for Canon EF 202101 B&H Photo
07-30-2019, 08:48 AM - 2 Likes   #7
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Variable aperture lenses became much more viable on the photography marketplace when flash systems became TTL.

Until then, if your flash had a automatic sensor parked on its front, you set the lens aperture according to what exposure the flash asked for. Typically, if you were using the longer "red" range, the flash said you had to set f4.0 (or something like that, depending on the ISO of your film). Thus set, you got decent flash exposures from, say six feet to 30 feet, for instance. What you didn't want was a lens that varied that f4.0 setting if you zoomed around. In theory, if you zoomed to where your aperture was now an effective f5.6, you had to open the aperture back up to a true f4.0, or risk an underexposed shot.

When TTL (through the lens) flash systems put the flash sensor inside the camera, any change in lens brightness was automatically compensated for. Flash output was dosed out in real time, with real lens brightness factored in.

All of a sudden, lens designers were let off the leash, and could come up with wider range, more complicated, more compact, less expensive, better corrected zoom designs - or so it was said.

However, professional photographers working in studio conditions, or those who never trusted autoflash systems anyway (ever try to photograph a bride in a white dress beside a bunch of guys in black tuxes with autoflash?), those guys wanted consistent lens apertures, no matter how they zoomed. So fixed aperture lenses became "pro" tools in the minds of photographers. You wanted one, even if you didn't really know why you wanted one.

What a lot of people may not realize is that many "pro" grade zooms actually have variable apertures. That f2.8 wide angle zoom may have a true 2.8 aperture at the long end, but when you zoom back a little cam physically closes down the aperture a little bit to stop it from becoming a f2.5 or so. The Canon 24-105 f4.0, even has a secondary aperture unit inside that closes down as it nears 24mm, keeping the max at f4.0.
07-30-2019, 11:48 AM - 1 Like   #8
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Variable aperture lenses are way smaller than fixed aperture lenses. That was apparently why companies started making them. With program auto it isn't a big deal. When people were complaining about slow lenses on point and shoot zoom cameras Ricoh made a camera with a larger aperture zoom lens. It was a slow seller and they only made one model. Most people don't know what aperture numbers mean and smaller and cheaper win out.

07-30-2019, 12:58 PM - 1 Like   #9
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QuoteOriginally posted by TerryL Quote
What exactly does variable aperture mean.
It means that the lens maintains a constant physical aperture diameter throughout the zoom range when focused to infinity. Constant maximum aperture zooms have design features that "throttle" the physical aperture as the zoom moves to the short end to allow the same relative aperture (f-number) at all focal lengths...again, when focused to infinity.


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