amfoto1 Loc: San Jose, Calif. USA

A 1.4X "costs" one stop of light, while a 2X TC "costs" two stops.

In other words, if a lens is f.2.8... adding a 1.4X will make it an f/4... or adding a 2X will make it an f/5.6.

The camera's TTL metering system automatically accounts for this, as far as exposure is concerned. With Canon teleconverters (which they call Extenders) on a Canon lens and Canon camera even the correct focal length and aperture are included in image EXIF data. When I add my EF 1.4X to my EF 500mm f/4 and shoot with the lens wide open, the EXIF reports 700mm focal length and f/5.6 aperture.

It's more of a concern how adding a teleconverter will effect autofocus.

Some Canon DSLRs' AF systems are "f/5.6 limited", which means you will lose AF if you add a 1.4X to an f/5.6 lens or a 2X to an f/4 lens. Other Canon DSLRs' AF systems are "f/8 capable", often with some limitations. For example, the 45-point AF systems used in various models are able to focus a lens/TC combo that results in an f/8 aperture, but in most cases will be limited to using only the center AF point. A few very specific f/8 lens/TC combos allow more points to continue working.

Canon mirrorless are another matter. The R-series can autofocus with much less light than the DSLRs, so are able to AF with f/11 and possibly even f/16 combos. The reason for this is the DSLRs use a semi-transparent mirror that "splits" light entering the camera, sending some of it to the viewfinder and some of it to the AF sensor array. The mirrorless cameras, on the other hand, have no mirror (d'oh!) and their AF sensors are built right into the imaging sensor, which they use both for an image in their electronic viewfinder and to capture the photo or video.

Another possible concern with teleconverters is whether the added optics will effect image quality. Better quality TCs have relatively little effect, especially weaker 1.4X. TCs also typically work best on prime lenses, instead of zooms. And they work best on high quality lenses. There may even be physical fitment issues, since many of the highest quality TCs have a protruding front element that has to fit inside the rear barrel of the lens.

Bridges Loc: Memphis, Charleston SC, now Nazareth PA

Maybe it is a communication problem between the extender and camera/lens. Try cleaning the contacts with a pencil eraser making sure the pieces of the eraser fall away from the lens/extender by holding the contacts so they are at the bottom end of the lens as you hold it horizontally.

VietVet Loc: Brooklyn, NY

👍

TriX Loc: Raleigh, NC

Contact cleaner, NOT a pencil a eraser, which can abrade the thin gold finish on the contacts and leave residue besides.

VietVet Loc: Brooklyn, NY

I think I’ve read that somewhere.

Bridges Loc: Memphis, Charleston SC, now Nazareth PA

Good advice, but I hope the cleaning of the contacts will do some good.

TriX Loc: Raleigh, NC

Me too!

VietVet Loc: Brooklyn, NY

Me most of all!!!😀

robertjerl Loc: Corona, California

35 years teaching Jr & Sr High School so I am used to being around people who "know everything" already.

From your user name I assume you are about my age and a past member of Uncle Sam's SE Asia Resort Club.

Me=Army, Camp Granite, Qui Nhon, Binh Dinh Province early Dec 66 to early Jan 69 HQ Company 593rd General Support Group acting as HQ Qui Nhon Sub-Area Command of 1st Logistical Command(Nov 66 on USNS Gordon for a cruise in the Pacific then at Camp Granite Dec 66 to Jan 69).

one_eyed_pete Loc: Colonie NY

I see you have the vII 100-400 and the vIII 1.4 converter. (seems like some didn't read your post) I would think you should be getting very sharp images with only a slight loss relative to image sharpness w/o the converter. I have the vI lens and vI converter yet I've been satisfied with the sharpness using my 80D. Perhaps you should do some bench testing at different settings to rule out some variables. Perhaps you do have some issue with the converter. How does it perform with other sharp lenses?

VietVet Loc: Brooklyn, NY

When I get home I intend to do some testing.

VietVet Loc: Brooklyn, NY

Yes. Infantry pathfinder attached to 222nd Air Force battalion in Ben Cat. Was there at a much calmer time than you in 1971. In my time we had the lottery instead of the draft and to this day it’s the only lottery I’ve ever won lol. Thanks for your service Robert.

robertjerl Loc: Corona, California

A bit quieter, we had the fun of Tet and the post Tet festivities. They didn't draft me, I had to drop out of college to work to buy another car when mine blew the engine. My draft board back home in Kentucky informed me I had lost my deferment and going back in the draft pool. My reaction was "Hell No! You aren't drafting me." so I enlisted in the Regular Army with a contract for admin type MOS's (I already wanted to be a teacher so that seemed a fit.) I got trained as a Clerk Typist and got orders to "HQ Company 593rd Combat Engineer Group" at Granite City Army Engineer Depot, Granite City Illinois.

Our oldest has a room with us when he is in town. He is an Army Reserve Civil Affairs (after 6 years active as a Combat Engineer) logistics NCO and his unit is airborne to work with special forces. He is Pathfinder and a Jump Master for his company.

The day I arrived they changed the sign on the gate to "HQ Company 593rd General Support Group" (manual to follow once it is written) a new type of unit. We did know we would supervise the building of and then run a division size basecamp on the Cambodian Border. The unit was loaded with a bunch of former combat arms senior NCOs and officers, many of them Rangers etc., as well as a lot of Combat Engineer types. Those of us in the lower ranks were all from the top 10% of our MOS schools. So for six months we trained and organized to do just about anything anyone could imagine as being involved in building and running a division size basecamp. Plus all those former combat types decided that they would trust the Army to have trained us for our MOSs so they drilled and trained us like we were infantry or scouts for over half of our training time. We even had a Chaplain who jumped as a private with the 82nd at Normandy and was a Sgt Major by the end of the war-then he got ordained.

We shipped out by transport in Nov 66 with "our" division to follow 60 days later. In mid-Pacific we got the word the division failed their pre-deployment quals and were going to do a 90 day retraining. Since they didn't want us stuck on the Cambodian border with a whole division size base camp to our selves for 90 days we would be broken up and assigned as replacements and another of the new "General Support Groups" would take our job and division.
Our Colonel got off the ship at Naha when we stopped to pick up fresh food and flew to Saigon to see some of his buddies from West Point. He got us reassigned to the 1st Log as a sub-area command HQ company and we also got our support group so things got weird. As a support group we were under a Combat Engineer Brigade, which in turn was under the Sub-Area Command. I worked in the Tac Ops Center so we sent out orders to the Engineer Brigade (and were already doing our part as a Support Group) who resent them to us, reports going the other way we just filed and sent a copy to the Brigade. Brigade inspections they treated us very nice because they knew the next week we would be inspecting them as Sub Area Command.
Since a General Support Group was a new thing we got all kinds of sub-units assigned to us that no one knew what to do with. A platoon of Armor with M-42 Dusters, two battalions of Yard Mercs with their SF advisors, a platoon of Nung Mercs run by a 101st Lt who was also our Asst Intel Officer and Night Duty Officer in Tac Ops - I was his clerk and Jr NCO for 6 months on the night shift. A pile of specialty units - base camp engineers, depot units, Computer Units who ran the computers with all the records for II Corps' northern half, transport units and a battalion of convoy escort MPs among others. We had several "Mini Support Groups" who moved around running LZs and temporary bases all over the Central Highlands. And several groups of guys in jeans and civilian shirts who called each other Mr Johns, Mr Green, Mr Smith etc. One of them walked in one day and my section NCO recognized him. Later he told me he had worked for him at NATO HQ's intel section a few years before but back then he wore a Navy Uniform and was addressed as Admiral.

Ah, I will shut up now. A year and a half of being a Covid POW (Prisoner of Wife-her term) has left me severely lacking in people to talk to. The wife is a retired Surgical RN and OR Charge Nurse = germaphobe on steroids. None of us have gotten Covid, I think the viruses are scared of her.

VietVet Loc: Brooklyn, NY

COVID had us all Locke at home. I was lucky because right before covid hit my eldest daughter gave birth to a baby girl and six months later my youngest (son) and his wife gave birth also to a baby girl. So I finally became a grandfather at 69 now 71.
The base I was on in Vietnam which we lovingly called BearCat was split between us (Americans) and The Thailand regular infantry. Our Sid had most of the Huey’s, cobra’s and other suppor choppers along with other air support planes. After seven months in country I was transported to Tan Son Nhut Air Base and had surgery for kidney stones. Than to Clark Air force Base in the Philippines and finally to Okinawa for recovery. When I was about to return to Vietnam my order were to a new unit, 101st but all orders were rescinded by President Nixon and we were all sent state side. I got out of the service three months early and got a 10% disability. It’s nice talking (texting) to you.

Charles 46277 Loc: Fulton County, KY

I have read some of the replies, and am surprised. I have tried teleconverters a number of times over the years and the result was always quite bad. I will have to reconsider. Many books and articles say they introduce aberrations, so I figured they were just for snapshots. But respectable people here seem happy with them...