3rd November 2004, 11:58 PM
4th November 2004, 12:13 AM
How wide the aperture can open depends on the lens. The body handles maximum shutter speed.
Originally Posted by club_de_oldman
4th November 2004, 04:10 AM
Thanks Xaler for explaining.
Originally Posted by Xaler
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.....
4th November 2004, 05:01 AM
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.
Originally Posted by eagles_creek
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.
4th November 2004, 06:19 AM
Okay....i'll try to explain here.....
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....
Last edited by sulhan; 4th November 2004 at 07:30 AM.
4th November 2004, 06:26 AM
4th November 2004, 06:39 AM
Getting more & more confusing...
4th November 2004, 09:21 AM
Thanks Sulhan for sharing, finally somebody who's not stingy in explaining
4th November 2004, 09:35 AM
4th November 2004, 10:55 AM
4th November 2004, 11:47 AM
Last edited by blurblock; 4th November 2004 at 12:19 PM.
4th November 2004, 01:58 PM
4th November 2004, 08:42 PM