Canon 90D: Today I was photographing with a Canon 90D and a 1.4ext. on a Canon 500mm, f4, IS, USM lens. I decided to switch to a 2x extender and found that by doing so I was only able...

will47 Loc: Indianapolis, IN

Today I was photographing with a Canon 90D and a 1.4ext. on a Canon 500mm, f4, IS, USM lens. I decided to switch to a 2x extender and found that by doing so I was only able to use single point focusing. The expanded focusing I was using (for tracking etc.) was unavailable. I put the 1.4 back on and was ok. Why can't I use a 2x extender and get the expanded focusing? And would this be true if I was using a 6D Mark ll? Thanks.

bleirer

With the 1.4 you lose a stop. With the 2x you lose 2 stops. Every camera has its own limit as to what wide open f stop it can auto Focus at. Some cameras use only the center autofocus point at f8. You'd have to check the manual. Mirrorless can autofocus at f11 because each pixel has 2 focus points built in, but with a mirror the light has to pass to the focusing sensor, unless you are in live view.

You should be able to autofocus that lens on the center point with the 2x, I'd think.

https://shuttermuse.com/canon-cameras-autofocus-extenders-f8-aperture/

TriX Loc: Raleigh, NC

I took a brief look at the 90D manual, but didn’t immediately find the chart I’m used to seeing in other Canon manuals showing how many AF points are available with various lens and TC combinations. If I read it correctly (and 90D users please correct me) it appeared that 27 AF points (and 9 cross points at f8) were available up to and including f8. If that’s true, I would expect more than a single AF point to be available With a 2x TC on the 500mm f4 lens IF you were using it wide open. However, I will reread the manual and see if I can find that elusive chart that I expected. You ARE shooting wide open at f4 aren’t you?

bleirer

It should be focusing wide open no matter what aperture he is using, no?

This quote is from the link I posted above:

EOS 90D, 80D, 77D & 800D (REBEL T7I)
Lenses providing this broader 27-point coverage at f/8 effective maximum apertures with the EOS 80D/90D/77D/800D are:

EF 100–400mm f/4.5–5.6L IS II + Extender EF 1.4x III
EF 200–400mm f/4L IS Extender 1.4x lens + Extender EF 2x III (built-in extender not used)
If you are not using one of these combinations, you will be limited to a single central cross-type AF point. This is often a point of HUGE confusion for Canon users because Canon makes a big deal about f/8 autofocus being available for “up to 27 AF points”. What they hardly ever mention is that it only works with these two lenses, and if you don’t have either of those, you just get one central AF point. It’s still not bad, though. It wasn’t long ago that you got no AF points at f/8 in this level of camera

TriX Loc: Raleigh, NC

bleirer wrote:

It should be focusing wide open no matter what ape... (show quote)

And there you have the correct answer!

will47 Loc: Indianapolis, IN

bleirer wrote:

It should be focusing wide open no matter what ape... (show quote)

Thank you for taking the time to reply.

jeep_daddy Loc: Prescott AZ

will47 wrote:

Today I was photographing with a Canon 90D and a 1.4ext. on a Canon 500mm, f4, IS, USM lens. I decided to switch to a 2x extender and found that by doing so I was only able to use single point focusing. The expanded focusing I was using (for tracking etc.) was unavailable. I put the 1.4 back on and was ok. Why can't I use a 2x extender and get the expanded focusing? And would this be true if I was using a 6D Mark ll? Thanks.

You are lucky you get one focus point. Older bodies would not autofocus AT ALL with a 2x . The newer bodies will allow autofocus, but it limits it to a certain number of focus points. Keep in mind, even if you could get more focus points, focusing will be much slower and will prove to be much more difficult to track moving subjects such as birds in flight.

PS - some older bodies will not focus AT ALL with a 1.4x

will47 Loc: Indianapolis, IN

jeep_daddy wrote:

You are lucky you get one focus point. Older bodies would not autofocus AT ALL with a 2x . The newer bodies will allow autofocus, but it limits it to a certain number of focus points. Keep in mind, even if you could get more focus points, focusing will be much slower and will prove to be much more difficult to track moving subjects such as birds in flight.

PS - some older bodies will not focus AT ALL with a 1.4x

Thanks for the reply. I AM learning.

Architect1776 Loc: In my mind

jeep_daddy wrote:

You are lucky you get one focus point. Older bodies would not autofocus AT ALL with a 2x . The newer bodies will allow autofocus, but it limits it to a certain number of focus points. Keep in mind, even if you could get more focus points, focusing will be much slower and will prove to be much more difficult to track moving subjects such as birds in flight.

PS - some older bodies will not focus AT ALL with a 1.4x

Like my old 7D.

amfoto1 Loc: San Jose, Calif. USA

will47 wrote:

Today I was photographing with a Canon 90D and a 1.4ext. on a Canon 500mm, f4, IS, USM lens. I decided to switch to a 2x extender and found that by doing so I was only able to use single point focusing. The expanded focusing I was using (for tracking etc.) was unavailable. I put the 1.4 back on and was ok. Why can't I use a 2x extender and get the expanded focusing? And would this be true if I was using a 6D Mark ll? Thanks.

With a 1.4X on an f/4 lens, it becomes an f/5.6 (one stop light lost).... the Canon 90D can focus an f/5.6 lens at all 45 AF points.

With a 2X on an f/4 lens, it becomes an f/8 (two stops of light lost to the teleconverter)... and the 90D can only focus that lens/teleconverter combo at the center AF point (same with my 7D Mark IIs, as well as 80D, 6DII, and some other Canon DSLRs).

There are a few specific f/8 lens/teleconverter combos the 90D can utilize up to 27 of its 45 AF points.

One I know for certain is the EF 100-400mm f/4.5-5.6L "II" with the EF 1.4X "III" teleconverter.

There are only a few other combos that allow more than the single center point to work at effective f/8. There's a list in the manual, I believe. I think they all only involve the "III" series Canon teleconverters.

jeep_daddy Loc: Prescott AZ

Architect1776 wrote:

Like my old 7D.

Yes, the old 7D wouldn't focus at all...even with the 1.4x

bleirer

amfoto1 wrote:

With a 1.4X on an f/4 lens, it becomes an f/5.6 (o... (show quote)

Or the list is posted a few posts from the beginning of the thread....

Architect1776 Loc: In my mind

jeep_daddy wrote:

Yes, the old 7D wouldn't focus at all...even with the 1.4x

It will slowly in live view though but not worth the pain.

PHRubin Loc: Nashville TN USA

bleirer wrote:

It should be focusing wide open no matter what ape... (show quote)