I was told in school that "he who asks a question may seem a fool for the moment, be he who fails to ask, remains a fool forever".
Here I go with my foolish question! Can you please help me with how focusing motors work? I will tell you what I understand at the moment, and please correct me on anything I have got wrong.
Some Nikon cameras have focusing motors built in to their bodies, and these are normally the higher end models? To enable auto focusing you need either a motor in the body or the lens? Lower end bodies without motors, need to be used with modern lenses that have them in the lens? How does the body communicate auto focus with the lens? Is it through the row of gold pins on the mount? I know that aperture is selected via the small round screw head on the lens. Why (or is) there not a conflict when mounting a modern lens on a high end body? Surely there must be two motors in play?
Sorry for so many questions, but I would prefer to try and limit the number of times I make my foolishness public! Any clarification you can give would be appreciated, and would help end my shameful ignorance.
Ask the question or remain a fool!
(10 posts) (6 voices)-
Posted 2 years ago #
-
ill try and explain it.
Yes you need either a motor in the lens or the body. The way to find out how its done is if its an af-s lens (ie af-s 50mm f1.4) then it will focus on all nikon digital cameras.
If its an af or an af-d lens (ie af 50mm f1.8) then it will need a motor in the body.The body communicates using the little balls on the back of the lens as you said.
As for aperture there is a little lever which is used to control aperture, you can play around with this yourself and find out :)There isnt a conflict because on the afs lens the af motor drive goes into a indent in the metal where it wont move. And because the camera sences the lens has a motor it doesnt spin it.
Hope this helps.
The only stupid question is a question un asked. :)
Posted 2 years ago # -
You've got most of it right. The row of contacts is how the camera communicates with the lens. The aperture is controlled by a lever that moves the aperture electronicly or manually depending on the camera and lens. Older lenses had aperture rings that you had to set manually. G lenses don't have aperture rings so the lens tells the camera electronically how far to open the aperture using the same lever.
All AF cameras in the late 1980s, 1990s, and early 2000s had focus motors in the body. The reason Nikon moved the motors to the lens was to make the camera bodies smaller and the autofocus faster and more responsive. AF-S lenses are virtually quiet while screw driven lenses are very noisy.
The pro cameras today still have motors in the body because most pros have a large collection of older lenses that aren't AF-S.
Posted 2 years ago # -
The 90 and above (now 7000 and above) have built-in AF motors; unlike the lower end cameras that don't have the motor, they don't need lenses with built-in motors, allowing the use of older AF lenses. The impression I get is that these are a tad slower than lenses with the built-in motors; the onboard AF motor is also not as quiet as the in-lens kind. And yes, either one or the other (lens or body) needs the motor to AF. The lens has a chip built in that allows not only for AF, but also metering. You'd need to check the compatibility of the camera (not just its motor or lack thereof, but I guess also its chipset) to see if it'll meter with your camera. Ken Rockwell comes in for a lot of flak on this site -- some of it well deserved -- but one resource his site has that's very useful is a chart explaining lens compatibility with different bodies... what'll focus, meter, etc., and what won't.
As to the "conflict", I'd guess that if the camera senses that the lens has a motor, it "lets" the lens handle AF.
I'm sure someone else will have more to add to this. :)
"Marx was skint but he had sense
Engels lent him the necessary pence..."Sorry. Couldn't help it. :) Keep thinking of that song when I see your screen name.
Posted 2 years ago # -
I'll try to help You with understanding.
the modern dslr (lower models) lack the AF motor, which is commonly called as "screwdrive" instead they use hypersonic motors which are build into the lens - they are faster and in higher model lenses allow You to override AF, which can't be done with regular AF motors, unless You use a lot of force, and break some mechanisms, as that kind of motor works like a screwdriver - turn it one way and You will make the af closer, turn it other way and You will defocus.
the communication works though the gold pins and camera distinguishes what kind of lens it's using and what kind of motor should be used, basically if body AF motor is in use, there's a hole in the lens to allow the screwdriver to operate, if there's no hole = AF-S or manual, which is distinguishable through the gold pins.
as for the aperture, no it's not selected through a small screw on the lens (that's the AF motor), instead on older lenses it was selected through a level bar (which is located on the lens mount)Posted 2 years ago # -
Wow 3 replies in minutes, I'm impressed! Thanks for all your help. It makes sense what you say about pro level bodies having the motor built in so as to be compatible with older lenses. 2 things I'm still not 100% clear on, what stops the conflict between a motorised body and AFS lens setup, and is there a physical/visual difference between a body with a built in motor, and one without? If you look at the body is there anything visual that shows you the presence of the AF motor?
Posted 2 years ago # -
There is a screw that sticks out of the camera bodies with motors and it is spring loaded so when a AF-S or manual focus lens is attached the pin is forced to retract and the built-in camera motor disengages. The screw sticks out at about the seven o'clock position when you look at the metal lens mount.
Posted 2 years ago # -
Sorry Adamz, you posted your reply, at the same time as me. You have answered my first question, you all seem to be saying that lens based AF is better than body?
Posted 2 years ago # -
AF-S lenses tend to focus faster, and are always quieter than lenses that require the screw driven motor, but that isn't always the case. Case and point the 50mm F1.4D focuses faster than the 50mm F1.4G, although the latter tends to focus more accurately from the accounts that I have read.
Posted 2 years ago # -
All questions answered! I am now enjoying total enlightenment! Thank you all for your time in helping me. :-)
Posted 2 years ago #
Reply
You must log in to post.
