Now this seems interesting - "seems" because I have no idea what you guys are talking about.
I'd appreciate it if you care to explain or point me to the relevant authority.
Edit: Just busy reading the article in that link from J-see an will need to read it a couple of times to understand it.
I still don't understand this.
So if I shoot with an aperture of f/11 using a lens that has an "effective aperture" of f/8 my D7100 won't focus?
I'm slow - can't get my head around the wording being used here.
I still don't understand this.
So if I shoot with an aperture of f/11 using a lens that has an "effective aperture" of f/8 my D7100 won't focus?
I'm slow - can't get my head around the wording being used here.
When you attach a lens to the cam, the aperture is always wide open. That is the effective aperture of the lens. The lens will only close down to the aperture you select the moment you push the trigger. After the shot, it opens up again.
The "selected" aperture plays no role during focus. Only the "effective" aperture.
All modern DSLRs auto focus at the maximum effective aperture i.e. with the lens wide open and only close down to the set aperture when you press the shutter. When you look through the viewfinder you are seeing the scene with the lens open. If you press the preview button you will see the scene at the set aperture.
So if you had the Tamron set at 600mm its maximum effective aperture would be f/6.3. If you have your aperture set on the camera to f/11 it would still focus first using f/6.3 then when you press the shutter it would close down to f/11 to take the shot.
Hope that helps.
I don't really get what you're asking.
The f/8 focus ability of the later Nikons is the ability to focus lenses to which a TC is connected. How many focal points depends on the specific cam. For the D7100 it was solely the center one but for other cam's it's up to 11 focal points (If I remember well).
Wider aperture lenses will use more points but you'd have to check how many which cam can use at what aperture.
I just checked and for the d7100 it seems only the center focal point is compatible with lenses slower than f/5.6 up to f/8.
Nikon | Imaging Products | Capturing power - Nikon D7100
The Tamron has an effective focus of f/5 to f/6.3 if my EXIF data is correct. I start to understand why you have more issues to focus the Tam than me.
To add: I read somewhere some "trick" is being used to have the Tam focus on certain cams but I'd have to think hard and dig deep to find that article again. It does focus on my D3300 but the results are poor. I'd have to check the max ability to focus of that cam.
View attachment 148789
Here's what Mike is asking. Current Nikons are said to be able to center focus at f8. I interpret that to mean that when using the center point of your 51 pt focus system you should be able to focus with a 300mm f4 and a 2X converter, which is effectively f8 at minimum aperture. If, however, you move away from the center point, will the camera still be able to attain focus with the same f8 minimum aperture?
I do not know the answer, but I would speculate that you might have an issue beyond the dark red circle above, particularly in a low contrast situation.
I suppose the next logical part of my question would be with a F6.3 lens if you chose multi point could this actually work against you achieving focus,or would the other points just not try to do anything,i think i need to wait for decent light and do some tests.
I only ever use the center point as i use my lens at 600mm a lot,wasn't sure if the surrounding points where F5.6 with a programed shut off or where capable of F8 in perfect contrast/lighting situations,in the early days a AF system would work until it didn't get enough light,although a manufacture would claim maybe F4 it would often hunt around at smaller stops and actually focus in the right conditions.
If its a programmed shut off there is no point in me considering using multi point,think i need to wait for a bright day and select an off center point and try it at F6.3.
All this makes sense and I fully understand it. BUT. If looking through the view finder and having the tamzooka attached with a teleconverter. You would still see the whole scene as apposed to having the edges cut away such as it vignetting. So if the whole scene is still in view than why do the focus points become inactive around the edges?