Jump to content

Constant aperture?

Elmerviking

By Elmerviking
in Fuji X-T3 / Fuji X-T30

 Share

Recommended Posts

Elmerviking Newbie

Elmerviking

Posted
Posted

I have a Fuji xt30 with the xf 18-55 kit lens. The lens has a variable aperture, but if you choose f-stop smaller than 4.5, the aperture is constant throughout all focal lengths! How come? Does the aperture change while zooming even if it shows the same f-stop?

 

Link to post
Share on other sites
Greybeard Experienced

Greybeard

Posted
Posted

Not quite sure what you mean.

The maximum shutter changes based on the focal length so if you set a manual aperture of f/2.8 at 18mm, say - then aperture would change as you zoom out.

Any manual aperture smaller than f4 will remain the same through the zoom range unless you change it.

Link to post
Share on other sites
Elmerviking Newbie

Elmerviking

Posted
  • Author
Posted
3 hours ago, Greybeard said:

Not quite sure what you mean.

The maximum shutter changes based on the focal length so if you set a manual aperture of f/2.8 at 18mm, say - then aperture would change as you zoom out.

Any manual aperture smaller than f4 will remain the same through the zoom range unless you change it.

Exactly....isn’t it strange that the aperture (the opening of the lens) remains the same when you zoom in.? Shouldn’t the aperture change the same way it does at f 2.8 at 18 mm  when you zoom?

Link to post
Share on other sites
Greybeard Experienced

Greybeard

Posted
Posted
49 minutes ago, Elmerviking said:

Exactly....isn’t it strange that the aperture (the opening of the lens) remains the same when you zoom in.? Shouldn’t the aperture change the same way it does at f 2.8 at 18 mm  when you zoom?

I don't think so - the variable aperture is just a physical limit of the lens when wide open.

If you set a specific manual aperture you'd want it to stay the same (if possible) across the zoom range.

Link to post
Share on other sites
Herco Rising Star

Herco

Posted
Posted

Aperture is the ratio between the focal length of the lens and the width of the iris (or aperture). So f2 at 18mm means an opening of 9mm. To reduce the size (and cost) of a lens, zoom lenses with longer focal lengths often have variable aperture. Your lens has a max opening of 6.4mm at 18mm (f2.8). To have the same aperture at 55mm the max. opening should be 19.6mm (55 / 2.8). That would result in a wider lens with larger glass elements and subsequently more costs and design issues. Hence the f4 at 55mm. It keeps the lens compact and cost efficient.

The downside of variable aperture is that the exposure changes while zooming in or out, which will need to be compensated by adjusting shutter speed or ISO. Professionals usually don't like that: e.g. a sports photographer being confronted with a longer shutter speed just because of zooming in. Another downside is that depth of field changes when zooming in or out which can lead to subjects being out of focus. Your camera will 'fix' that obviously in AF mode, but for most professionals it may ruin the effect they were looking for. That's why constant aperture zoom lenses are often referred to as 'professional grade lenses' or the 'holy trinity of f2.8 zoom lenses'...

Link to post
Share on other sites
Elmerviking Newbie

Elmerviking

Posted
  • Author
Posted
8 minutes ago, Herco said:

In fact it does. Whether it is mechanically or electronically I can’t tell, but yeah the ‘pupil’ widens.

Thank you Herco! That is what I think also. I just wonder how it works when you use a manual lens, like Nikkor 80-200 f 4.5.

The aperture (“pupil”) obviously is constant when you zoom. I have to check that!

Link to post
Share on other sites
jerryy Grand Master

jerryy

Posted
Posted (edited)

Usually the constant aperture lenses have different kinds of elements and lens groups than do the variable aperture lenses, it is a different design idea. One other side benefit that may matter, is that the lenses often do not extend or retract while zooming.

But try not to get too fixated on the idea, there are plenty of high quality variable aperture lenses out there. Canon makes some “L” grade red banded variable aperture lenses as does Sigma and Tamron and ... Lots of those Leica mount Carl Zeiss lenses, which are the mutterings of legend, are variable aperture builds.

Edited by jerryy
Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share
Go to topic listing

  • Similar Content

  • Posts

    • jerryy
      Fungus

      By jerryy · Posted

      A fungus in the forest.

      Welcome, dear visitor! As registered member you'd see an image here…

      Simply register for free here – We are always happy to welcome new members!

      (p.s. Open Topic.)  
    • Don Barar
      LUT doesn't works on resolve

      By Don Barar · Posted

      The backslashes you are referring are just symbols denoting path.  Once you import into these LUTS into Davinci Resolve those backslashes are removed by default and you only see is the true file name which has no backslashes.  Convince yourself of this by opening the LUT folder from the Davinci Resolve Project Settings.  Do you see any backslashes in those LUT names? Of course not.  The only name you see is the one that has the underscores and the periods. These LUTS work as designed without having to change any path names.  However, they need to be set up properly through CSTs and by what is supported in Davinci Resolve.  Hence, the FLog2C film simulation LUTS cannot be used because Davinci Resolve does not support Fuji Gamut color space and the FLog2C gamut. Alternatively, Davinci Resolve does support Flog2 film simulation LUTS because the color space for FLog2 is Rec 2020 and there is an FLog2 gamut. If all you are doing is changing the path names then you are not getting the correct results.
    • PoorAlchemist
      LUT doesn't works on resolve

      By PoorAlchemist · Posted

      I found the reddit topic i refere to :  https://www.reddit.com/r/davinciresolve/comments/1pc3f1e/cant_apply_new_fujifilm_gfx_55_lut/ "Update for y'all, It's just like what @ExpBalSat said, it's because of the backslashes in the names break them. I changed the file name and it works now. "   For me it was the solution. Realy annoying if it doesn’t work for you 😕  
    • Don Barar
      LUT doesn't works on resolve

      By Don Barar · Posted

      Here is the solution to using the Eterna 55 file simulation LUTs in Davinci Resolve.   In general, do not use the FLog2C to film simulation LUTs as they are not supported by Davinci Resolve for two reasons: 1) Davinci Resolve does not support Fuji Gamut Color Space and 2) Davinci Resolve does not support FLog2C gamma.  Instead, use Flog2 which is supported by Davinci Resolve.  Here is an example.  Let's say that you want to use Classic Chrome simulation.  Do the following: Complete your color grade and use a CST to get to Rec 709. Add a node.  Use a CST to convert from Rec 709 to FLog2.  Output Color space is Rec 2020 and Outout Gamut is FLog2. Add a node.  Apply the FLog2 to Classic Chrome LUT Create a combination node from node in steps 2 and 3. Apply a Key to the combination node and adjust the Key Output Gain to get the amount of the combination node that you want applied. So that you do not have to do this over and over again, generate a LUT for the combination node.  Remember to turn off all other nodes before generating the LUT. Hope this helps others. Don  
    • crazyfields
      Please save me from insanity 23mm f2 vs F1.4r

      By crazyfields · Posted

      Thanks for the insights. I think it's really hard to make a decision without having the two side by side! 
×
×
  • Create New...