Page 2 of 2 FirstFirst 12
Results 21 to 33 of 33

Thread: Len size???

  1. #21

    Default

    is getting more and more complicated liao I though the f-2.8 in on the camera itself and not on the len...??? how come there is 28-300mm with f2.8 len...


  2. #22

    Default

    Quote Originally Posted by club_de_oldman
    is getting more and more complicated liao I though the f-2.8 in on the camera itself and not on the len...??? how come there is 28-300mm with f2.8 len...

    How wide the aperture can open depends on the lens. The body handles maximum shutter speed.

  3. #23
    Member
    Join Date
    Apr 2003
    Location
    Land of the woods........
    Posts
    1,360

    Default

    Quote Originally Posted by Xaler
    No, it wouldn't make sense to get the 70-200mm f2.8 if you don't need it
    f2.8 gives a shallower depth of field and it's also a fast lens as Witness mentioned. Either way, you'll find that a wide aperture does come in handy.

    The 28-300mm is a good general lens but you might want to think of upgrading in the future. I have a Tamron 28-200mm f3.8-5.6, it's adequate, but not great.
    Thanks Xaler for explaining.

    No, I do not have a Sigma 28-300mm lens, just using an example to try to understand all this lens stuff. Trying to learn I should say...

    I am pretty confused by all these lens specs......

    I was looking at the spec sheet of the Sigma 28-300mm (f3.5-f6.3) lens and its written that minimum aperture is 22-41.

    Could you explain this 22-41 thingy and why is there a range and not a specific value like min aperture is 41 instead? I suppose this minimum aperture is the minimum aperture setting we can get with this particular lens?

    If I were to compare two lens of say (f3.5-f5.6) and (f3.5-f6.3), the one with f6.3 enables a smaller aperture setting(greater no.)?

    Why are lens rated in such a way as f3.5-f5.6? It seems that most lens are rated till f5.6....or am I wrong? Is this becos of the contraints of the aperture range when the lens are built and hence further changes of the aperture size has to be done through the camera body?

    My apologies for asking so many questions.....

    Thanks alot!

  4. #24

    Smile

    Quote Originally Posted by eagles_creek
    Thanks Xaler for explaining.

    No, I do not have a Sigma 28-300mm lens, just using an example to try to understand all this lens stuff. Trying to learn I should say...

    I am pretty confused by all these lens specs......

    I was looking at the spec sheet of the Sigma 28-300mm (f3.5-f6.3) lens and its written that minimum aperture is 22-41.

    Could you explain this 22-41 thingy and why is there a range and not a specific value like min aperture is 41 instead? I suppose this minimum aperture is the minimum aperture setting we can get with this particular lens?

    If I were to compare two lens of say (f3.5-f5.6) and (f3.5-f6.3), the one with f6.3 enables a smaller aperture setting(greater no.)?

    Why are lens rated in such a way as f3.5-f5.6? It seems that most lens are rated till f5.6....or am I wrong? Is this becos of the contraints of the aperture range when the lens are built and hence further changes of the aperture size has to be done through the camera body?

    My apologies for asking so many questions.....

    Thanks alot!
    Okay, let's use the Sigma 28-300mm f3.5-6.3 as explanation since you got the spec sheet in front of ya. Note we're talking about zoom lenses here.

    The range f3.5-6.3 refers to the MAXIMUM aperture opening size. There is a range because of the way the lens is contructed. Constant aperture zoom lenses cost more. At 28mm, the largest aperture is f3.5. If you zoom to the other end, at 300mm the largest aperture is f6.3. Anywhere in between will have a maximum aperture between 3.5 and 6.3 (e.g. at 80mm, max aperture could be f4.5)

    The range f22-41 is the MINIMUM aperture opening. Same idea as the max aperture. So to conclude, at 28mm, aperture size can be set from f3.5 to f22. At 300mm, aperture size can be set from f6.3-f41.

    When describing lenses, people are more concerned about the max. aperture size so only that is written together with focal length. If you take an old manual camera, you would see that aperture size is adjusted using the aperture-ring on the lens, not on the body. Nowadays controls/settings are located on the body (for ease of access), but max/min aperture-size still depends on the lens.

    Hope this clears up some doubts.
    Last edited by Xaler; 4th November 2004 at 05:04 AM.

  5. #25
    Moderator
    Join Date
    May 2002
    Location
    Melbourne, Australia
    Posts
    4,026

    Default Okay....i'll try to explain here.....

    Hiee there...

    Lens are build in many ways...(internal construction)
    I'm sure you have heard of lens that ar fast and lens that are slow.
    It basically means that:

    Terminology and Jargons....
    -------------------------
    - "Fast = large aperture = more light can come in for a particular shutter speed" &
    -" Slow = smaller aperture = less light can come in releative to the faster lens given the same shutter speed"


    Why not constant aperture through the zoom range?
    ---------------------------------------------------------
    Simply....these are true for "pinnochio type of lens which extends during a zoom (my personal way of describing)".

    As the zoom gets longer, the "lens barrel" gets physically longer and hence given that the front openning is already fixed - for example 58mm filter ring size...then if the barrel gets longer....the light needs to travel more into the barrel through the lens over a longer length......so the lens becomes "slower"


    (sorry from the rough sketch - super simplified ray diagram)

    Variable Aperture rated Lens:
    ---------------------------
    As you can see from the above diagram, for a lens like the 70-300mm f4-5.6mm. At its widest 70mm the largest aperture rating is f4. And at the 300mm point, its at 5.6. As you see here.........the "actual aperture leaves in the lens" is still the same as its on the same lens BUT.....the length of the lens changes hence resulting in less light. Also lengh may change if non-internal focus type of lens. Turning focussing ring extends the lens physically too....

    This is the reason why you have variable aperture rating. Mathematically for the same loss of light, the smallest aperture rating would also be something like f22@70mm and f32@300mm correspondingly - not fixed.


    Fixed Aperture Rated Lens:
    --------------------------
    Also from the above diagram, for a fixed aperture lens like the 70-200mm f2.8,
    which has internal focus + internal zoom, physically there isn't any change in barrel length. Only internal elements/groups move to achieve the zooms. Also the internal focus moving elements internally.


    Tip - Relation of Aperture rating based on Front lens Filter ring Size:
    -----------------------------------------------------------------
    In General.....aperture rating, normally corresponding to the front filter ring size - taking the front ring size and divide by the length of the max zoom of a given lens ....gives the "aperture rating ~ approximate".

    So at 200mm for the 70-200mm f2.8 lens with filter of 77mm ring gives 2.6 which is why rated f2.8.

    Similarly for a fixed 50mm lens with a ring of 49mm, its largest aperture possible is f1.02 - normally we fing 50mm fixed focal length lens at f1.4, f1.7 etc....

    Again for the 75-300mm f4-5.6 with a 58mm Filter Ring, at 300mm, the aprroximate maximum aperture would be about 300/58 = 5.17 ~ hence the f5.6 .

    -------------------
    Aperture sits in the lens......
    Different manufactureres have different ways to actuate this......e.g
    - Canon actualtes by a actuation mechanism in lens
    - Minolts uses a mechanical actuator from the body
    In the olden days, on manual focus cameras these aperture are adjusted by mean of ring.

    Nowadays, these apertures are electronically actuated. Each lens contain integrated circuit chips that talks to the cameras body to provide the values of the aperture given a particular zoom positions. These are fixed values already calculated by manufacturers and put into an IC chip. Thats why in a variable aperture rated zoom, physically the aperture leaves at a particular chosen f-number ...stays the same but if you zoom the "calculated f-number" displayed will change accordingly....


    So hopefully the above explanations would help clear off some doubts....

    rgds,
    sulhan
    Last edited by sulhan; 4th November 2004 at 07:30 AM.

  6. #26

    Thumbs up

    As usual, Sulhan gives very comprehensive and easy to understand explanations

  7. #27

    Default

    Getting more & more confusing...

  8. #28
    Deregistered
    Join Date
    Dec 2002
    Location
    Planet Nikon
    Posts
    21,905

    Default

    Thanks Sulhan for sharing, finally somebody who's not stingy in explaining

  9. #29

    Default

    Sulhan explanation is generally correct, for lenses that is 200mm and above ...... for those that is lesser then 200mm (or maybe lesser the 150), another factor has to be taken into consideration, Angle of View ...... .....

    which brings me to the point, Tamron 28-200 has a lens filter size of 72mm does that mean it is a f/2.8 lens ;D ... LOL ...... Angle of View ......

    Now you know why 12-24 lens has a lens filter size of 82mm ...
    Last edited by blurblock; 4th November 2004 at 09:41 AM.

  10. #30

    Default

    Hmmm I'm starting to think sulhan and blurblock design lenses for a living

  11. #31

    Default

    Quote Originally Posted by Xaler
    Hmmm I'm starting to think sulhan and blurblock design lenses for a living
    No, but we basically study the theory of light, including lenses. This allows us a better grip of the basics of lenses and we can pick better lenses that suits our needs ..... No overkill ..... No underestimate ....

    Most professional photographers, who had been through formal photography degrees will know this very basic, not to the extent of being a lens designer, but to the extent of being able to pick the right equipment for the required situation.
    Last edited by blurblock; 4th November 2004 at 12:19 PM.

  12. #32

    Default

    Sulhan, thank you for your very details explaination






  13. #33
    Member
    Join Date
    Apr 2003
    Location
    Land of the woods........
    Posts
    1,360

    Default Sincere thanks to all

    I would like to express my sincere gratitude to all who took the trouble to explain.

    Very informative and eye-opening....

    Really appreciate the effort taken by all.....

    Thanks alot!!!

    Cheers!

Page 2 of 2 FirstFirst 12

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •