Aperture : My brain hurts (Page 2): I'm not a math wiz, but I know from shooting from 1969 to present a 1.4 EX will reduce light by 1 stop. When I use my 300mm F:4 with a EX1.4EII my...

Larryshuman

I'm not a math wiz, but I know from shooting from 1969 to present a 1.4 EX will reduce light by 1 stop. When I use my 300mm F:4 with a EX1.4EII my light meter readout reads 5.6. One stop of light loose from F:4 to F:5.6. This is the same from all 1.4's. I have sigma's 1.4 on my 800mmF:5.6 and the light meter read out was F:8. Again one stop loose. All camera companies use basically similar construction for 1.4 ex's but might vary coatings and etc. Sigma, Nikon and Cannon all have EX 1.4's and I've used them all and they all have the same readout of 5.6 on F:4 300's

Rich1939 Loc: Pike County Penna.

Larryshuman wrote:

I'm not a math wiz, but I know from shooting from ... (show quote)

How does the number of lens elements change the depth of field?
Ans They don't. the depth of field change is because of the increase in lens length (which has enlarged the image on the film/sensor).

Larryshuman

We are not talking DOF. We are talking light going thru a stack of glass. When using a 1.4 on a 300mm lens you will get the equivalent view of a 420 mm lens. Meta data information confirms that. DOF occurs when the lens aperture is set to F:8, F:11 or lower. When in the woods chasing little birds I would be at 5.6. At Indianapolis speedway I might be using F:8, In Florida where there is tons of light the aperture might be set around F:11. Any lower setting would be bring in LENS DIFFRACTION.

Rich1939 Loc: Pike County Penna.

Larryshuman wrote:

We are not talking DOF. We are talking light going thru a stack of glass. When using a 1.4 on a 300mm lens you will get the equivalent view of a 420 mm lens. Meta data information confirms that. DOF occurs when the lens aperture is set to F:8, F:11 or lower. When in the woods chasing little birds I would be at 5.6. At Indianapolis speedway I might be using F:8, In Florida where there is tons of light the aperture might be set around F:11. Any lower setting would be bring in LENS DIFFRACTION.

If you are talking about tele extenders you have to include DOF. It is a inherent part of the subject.
Yes changing the f stop changes the amount of light reaching the sensor and it also changes the DOF.
Lens construction also affects light transmission. Adding an extender adds some more glass but its effect on LT is not by a factor 1.4 or more. Very little in fact for practical consideration.

DirtFarmer Loc: Escaped from the NYC area, back to MA

The focal length of a lens is rarely equal to the linear dimension of the lens. The internal optics modify the focal length. In the case of the teleconverter, most of them add maybe 20-30 mm to the physical length of the lens, but it's the effective focal length that is important, not the physical length. The teleconverter changes the effective focal length by the multiplication factor of the teleconverter so that's what's important in calculating the f/ number.

Hammer Loc: London UK

Thanks very much for all you Hoggers that have pitched in .

Both my brain cells hurt even more now.

Had a quick look at some of the maths involved re circle of confusion , have decided to stop and do something more exciting , like watching the grass grow.

Fotomacher Loc: Toronto

The aperture is a physical measure based on the size of the lens opening and the focal length. Increasing the focal length will reduce the ability of the lens to transmit light to the film/sensor thereby reducing the effective f/stop. It is an inverse relationship.

rmalarz Loc: Tempe, Arizona

Why limit it to salespeople? As an engineer (mechanical / aerospace) one of my favorites is never arguing with an engineer. Arguing with an engineer is like wrestling with a pig in a mud puddle. Sooner or later one will come to the realization that the pig is enjoying itself.
--Bob

jerryc41 wrote:

Right! You can spend hours exploring the physics that cause a rainbow, or you can just enjoy the sight.

A friend (an engineer) told me that salespeople hate dealing with engineers. : )

BebuLamar

Hammer wrote:

Thanks very much for all you Hoggers that have pitched in .

Both my brain cells hurt even more now.

Had a quick look at some of the maths involved re circle of confusion , have decided to stop and do something more exciting , like watching the grass grow.

Then don't think about why just knowing what it does is fine.

Hammer Loc: London UK

BebuLamar wrote:

Then don't think about why just knowing what it does is fine.

Can't do that : I am ever so slightly deranged .

anotherview Loc: California

Good morning. By your question, you seem to have a misunderstanding of how a teleconverter functions.

Simply put, a teleconverter increases the effective focal length of the lens in use. For example, using a 2x teleconverter doubles the lens' focal length.

The information at these Web-links may help you to inform yourself.

https://digital-photography-school.com/the-pros-and-cons-of-using-tele-converters-extenders-on-your-dslr/

https://www.lensrentals.com/blog/2009/01/teleconverters-101/

https://en.wikipedia.org/wiki/Teleconverter

Good luck.

Hammer wrote:

I understand that when attaching a teleconverter to a lens the aperture is altered by the factor of the converter . ie a 1.4 converter will turn a f2.8 lens into an f4.

The aperture for a lens is altered from within the camera . When I attach a teleconverter the aperture is already is reduced/affected by the converter. What is happening?

I accept that my photography will not be affected by this knowledge but my brain is really hurting and I need to resolve this .

billnikon Loc: Pennsylvania/Ohio/Florida/Maui/Oregon/Vermont

Hammer wrote:

I understand that when attaching a teleconverter to a lens the aperture is altered by the factor of the converter . ie a 1.4 converter will turn a f2.8 lens into an f4.

The aperture for a lens is altered from within the camera . When I attach a teleconverter the aperture is already is reduced/affected by the converter. What is happening?

I accept that my photography will not be affected by this knowledge but my brain is really hurting and I need to resolve this .

Because light has to go through more glass (in the teleconverter) this reduces the amount of light reaching the sensor. The longer the teleconverter, the further and more glass light has to travel. The 1.4 converter reduces the amount of light by ONE stop. A 2X converter (longer than the 1.4) lets in ever less light reaching the sensor of the camera for a TWO stop difference. A 3X converter (even longer) lets in even less light for a 3 STOP difference. Think of like entering a cave, the further you go in, the darker it becomes. The further light has to travel, the less bright it is.
Remember this fact: There is not a teleconverter on the market that IMPROVES image quality.

Hammer Loc: London UK

Hi,

Thanks for your help. I think I understand these issues but what I am trying to establish is that my camera adjusts to base aperture to take into account the aperture adjustment. How does it do this .

I realise that it will not affect my photos but I cant help being deranged!

billnikon Loc: Pennsylvania/Ohio/Florida/Maui/Oregon/Vermont

Hammer wrote:

Hi,

Thanks for your help. I think I understand these issues but what I am trying to establish is that my camera adjusts to base aperture to take into account the aperture adjustment. How does it do this .

I realise that it will not affect my photos but I cant help being deranged!

The coupling of the teleconverter (provided it is the correct one) communicates to your body the correct minimum F stop to be used. It is all in the pins and couplings.

GrandmaG Loc: Flat Rock, MI

Bill_de wrote:

While many newer cameras will focus (some only center point) at F/8.0, the current Nikon 800mm comes with a dedicated 1.25 tele extender. It works great on the D4s and D500. On the D500 it's the equivalent of 1500mm @ F/7.1

--

Holy crap. That lens weighs over 10#, is 1 1/2 feet long and costs over $16,000. Do you have one?