RF 28-70 F2 IS STM f-stop range question

[Cantrell]

All,

Considering purchasing the above lens. Because there is not a range in F stops. The F2 is the F stop at 28mm as well as 70mm. Is that correct?

Thank you in advance for your response. 

[Cantrell]

vantage,

Thank you for the links in your previous post.

Reese

[MrWalleye73]

Almost jumped on the 28-70 F2 last week when Canon released a bunch of refurbished lenses for the sale. Something like ~$2100. Somehow Holiday spending on other gifts stopped me. But that was a deal!

[Cantrell]

MeWalleye73,

Looking at the RF 28-70mm F2.8 IS STM. Canon has none in their refurbished inventory at this point. The price was reduced during the Black Friday Sales and looks as if they are going to honor that price. If so it will be a nice reduction. We will see.

I would like the RF 24-70mm F2 L USM, but that is out of my price range.

Hope that you and your family had a wonderful Thanksgiving.

Reese

[normadel]

There's something screwy here. No such thing as an RF 28-70 F2 IS STM. Are you talking about the RF 28-70 F2 L USM? Or the RF 24-70 F2.8 L IS USM? Or what?

In any case, why isn't anyone pointing out to the OP that the F-whatever is the MAXIMUM aperture, not he ONLY aperture?

[Cantrell]

normadel,

It was my mistake. My brain works faster than my fingers. I use the Christopher Columbus method of typing. The lens should have read RF 28-70mm F2.8 IS STM. I am interested in a constant aperture lens.

Reese

[normadel]

I'm not sure what you are looking for: unchanging f/ number across the zoom range, or lens with only one fixed aperture, period (no adjustable diaphragm). Lenses I know of fitting the second description are mirror lenses (single focal length) and old 400mm  manual lenses having fixed maximum and variable aperture.

Here's a good article on constant-aperture zoom lenses:

https://photo.stackexchange.com/questions/7365/how-do-constant-aperture-zoom-lenses-work

[ebiggs1]

"I am interested in a constant aperture lens."

The magic happens because of lens elements. The factors controlling it are two main ones. First costs, can we sell the lens for what it is going to cost us to manufacturer it. And two, how big and heavy (elements are heavy) will it be so are folks going to be able to hold it and use it. Variable aperture is easier to make and makes a lighter zoom lens.

[Cantrell]

normadel,

Thank you for the link.

Reese

[Cantrell]

ebiggs1,

Thank you very much for this explanation.

Reese