Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
5 Days Ago   #1
New Member




Join Date: Nov 2021
Location: Fredericton
Posts: 2
Can a camera autofocus with a f/5.6 lens through a teleconverter?

I've seen it said that autofocus doesn't work for a 1.4x past a aperture of f/4 and so on, but is that a hard limit, or can good strong lighting still allow for it? I don't expect fully sharp images, or fast autofocus, I just want to get an idea as to whether autofocus could work on a f/5.6 lens, under conditions like good sunlight or if I should think about a cheap manual one to mess with.

5 Days Ago   #2
Administrator
Site Webmaster
Adam's Avatar

Join Date: Sep 2006
Location: Arizona
Photos: Gallery | Albums
Posts: 50,351
QuoteOriginally posted by MDRatliffe Quote
I've seen it said that autofocus doesn't work for a 1.4x past a aperture of f/4 and so on, but is that a hard limit, or can good strong lighting still allow for it? I don't expect fully sharp images, or fast autofocus, I just want to get an idea as to whether autofocus could work on a f/5.6 lens, under conditions like good sunlight or if I should think about a cheap manual one to mess with.
In good lighting it should be possible only at the expense of speed, especially if you use a modern body that can otherwise focus in -3 or -4 EV (K-3 III, K-3, K-1, K-5 II, etc.).

Adam
PentaxForums.com Webmaster (Site Usage Guide | Site Help | My Photography)



PentaxForums.com server and development costs are user-supported. You can help cover these costs by donating. Or, buy your photo gear from our affiliates, Adorama, B&H Photo, KEH, or Topaz Labs, and get FREE Marketplace access - click here to see how! Trusted Pentax retailers:

5 Days Ago   #3
Pentaxian
bertwert's Avatar

Join Date: Jun 2015
Location: Golden, BC
Posts: 14,805
Some people use a TC on the 55-300 which is a third stop slower at f/6.3 with great results, so it's possible. I believe @normhead; is one.
5 Days Ago   #4
Pentaxian




Join Date: Dec 2011
Posts: 2,979
QuoteOriginally posted by MDRatliffe Quote
I've seen it said that autofocus doesn't work for a 1.4x past a aperture of f/4 and so on, but is that a hard limit, or can good strong lighting still allow for it? I don't expect fully sharp images, or fast autofocus, I just want to get an idea as to whether autofocus could work on a f/5.6 lens, under conditions like good sunlight or if I should think about a cheap manual one to mess with.
My experience is that Pentax DSLR cameras with their F5.6 sensors can function down to "wide open" F9 lens/converter combos.
But that needs bright and contrasty subjects (due to the effective area of the remaining AF sensor now being so small; I guess the size of the AF cross then is less than 1/3 of the full thing and within that tiny area there needs to be a good contrast edge).

5 Days Ago   #5
New Member




Join Date: Nov 2021
Location: Fredericton
Posts: 2
Original Poster
QuoteOriginally posted by Adam Quote
In good lighting it should be possible only at the expense of speed, especially if you use a modern body that can otherwise focus in -3 or -4 EV (K-3 III, K-3, K-1, K-5 II, etc.).
Alright thank you, I'm not to concerned about autofocus speed, more that it can work for simplicities sake. I'm using the K-S2, so assuming it would be fine since it's newer than the K-3 and K-5 II
5 Days Ago   #6
Pentaxian
Wasp's Avatar

Join Date: Mar 2017
Location: Pretoria
Photos: Gallery
Posts: 3,818
I have the SMC Pentax 1.7x AF converter. It works fine with my SMC Pentax A 400mm f/5.6, as long as the light is good.
5 Days Ago   #7
Administrator
Site Webmaster
Adam's Avatar

Join Date: Sep 2006
Location: Arizona
Photos: Gallery | Albums
Posts: 50,351
QuoteOriginally posted by MDRatliffe Quote
Alright thank you, I'm not to concerned about autofocus speed, more that it can work for simplicities sake. I'm using the K-S2, so assuming it would be fine since it's newer than the K-3 and K-5 II
The K-S2 has the K-5 II's AF system, so yes you should be in good shape.


Adam
PentaxForums.com Webmaster (Site Usage Guide | Site Help | My Photography)



PentaxForums.com server and development costs are user-supported. You can help cover these costs by donating. Or, buy your photo gear from our affiliates, Adorama, B&H Photo, KEH, or Topaz Labs, and get FREE Marketplace access - click here to see how! Trusted Pentax retailers:

5 Days Ago   #8
Site Supporter
Site Supporter
vector's Avatar

Join Date: May 2015
Location: Alberta
Posts: 464
It can also help if you have a quick shift lens to manually get the focus into the ballpark before pressing the AF button. I have done that with stacked 1.4TCs which generally doesn't work but will if you help it out by getting close first.
5 Days Ago   #9
Pentaxian
Paul the Sunman's Avatar

Join Date: Aug 2011
Location: Melbourne
Photos: Gallery
Posts: 3,671
What is the experience with the DFA 150-450 and the 1.4 DA TC? I guess it would work with the K3iii in decent light.
5 Days Ago   #10
5ks
Pentaxian




Join Date: Feb 2011
Location: Southern Finland
Posts: 460
QuoteOriginally posted by Paul the Sunman Quote
What is the experience with the DFA 150-450 and the 1.4 DA TC? I guess it would work with the K3iii in decent light.
This is what interests me a lot, too (not quite yet being able to try myself...). Depending mostly on the amount of light, I guess?
5 Days Ago   #11
Pentaxian




Join Date: Jan 2018
Location: Jersey C.I.
Photos: Albums
Posts: 1,395
I use my Sigma 150-500mm f/5-6.3 with a Kenko 1.5x tele-converter, in AFS and central spot focussing, with good light on a contrasty static subject, with little problem, provided I can wait for the focus confirmation to "lock", which can take a couple of tries sometimes.
My K-3iii is better in this regard than my KP, the K-70 often struggles (all with the latest firmware).
Hoping to get a bird in flight or similar with the 1.5x fitted is relying on a very great lump of luck, though it can happen sometimes
As mentioned, quick-shift focus and/or manually pre-focussing can be a great help … the ergonomics of the lens being a factor here. My "bigma" isn't optimally designed to be hand-held and manually focussed!
To be honest, the resultant image can be very similar to a heavily cropped image without the tele-converter on a 24 megapixel camera, in some circumstances, though this may be due to heat haze or shimmer (over water, especially).
For the price of the "genuine" Pentax item I really would like to "try-before-I-buy", though I would expect it to perform better than my "budget" option, especially on a Pentax lens.
The main criteria for reliable results seems to be good contrast, rather than necessarily bright light, though, obviously, in lower light conditions, high ISO noise may become a factor if the shutter speed needs to be kept up.
Good luck
5 Days Ago   #12
Site Supporter
Site Supporter




Join Date: Jun 2008
Location: Idaho
Photos: Gallery
Posts: 1,526
It all boils down to the camera and lighting conditions. I've used my K-1 with a x2 TC and it auto focuses satisfactorily when there's enough light available. As the light decreases, AF can become sluggish or quit altogether. Some cameras need more light than others. In fact, the K-1 has issues if the contrast AF is used and a slower maximum aperture lens is attached, but the phase (viewfinder) AF is much better. I doubt however that you will have any issues with an f5.6 lens and a x1.4 TC in bright daylight. Note that you'll need a coupled TC which will open the lens all the way while obtaining a focus. If the lens stops down for any reason during AF (e.g., manual aperture and set at f11), then it may not work.
5 Days Ago   #13
Loyal Site Supporter
Loyal Site Supporter




Join Date: Jun 2009
Location: Melbourne Australia
Photos: Albums
Posts: 1,331
QuoteOriginally posted by Paul the Sunman Quote
What is the experience with the DFA 150-450 and the 1.4 DA TC? I guess it would work with the K3iii in decent light.
QuoteOriginally posted by 5ks Quote
This is what interests me a lot, too (not quite yet being able to try myself...). Depending mostly on the amount of light, I guess?
I just tried it, it's currently a solid 'neutral grey' overcast day in Melbourne and it worked fine on the K3 (maybe a little slow) even in darkish shadows. The K3-iii was even better, as expected.
4 Days Ago   #14
New Member




Join Date: Feb 2021
Location: Havant
Posts: 24
I've just had a quick test with my camera.
K1 ii, FA28-70MM F4, Kenko DG P/AF Teleplus MC7 converter.
Indoors at 28mm F10 ISO400 AF set to spot auto auto focus works but I can't
hand hold for 5 seconds without moving a little, so the image is more than a little blurry.
4 Days Ago   #15
Pentaxian
35mmfilmfan's Avatar

Join Date: Oct 2016
Location: Norfolk, UK
Posts: 2,431
If my memory serves, the intended use of a TC is on a telephoto lens - short range zooms lenses are not considered ideal.
Reply

Bookmarks
  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Tags - Make this thread easier to find by adding keywords to it!
autofocus, camera, camera autofocus, f/5.6, f/5.6 lens, lens, pentax help, photography, troubleshooting
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
645 Teleconverter Conversion with Autofocus? TDvN57 Pentax Medium Format 4 05-04-2021 07:14 AM
K70 will only autofocus and shoot in monitor mode, not through viewfinder snobrewer Troubleshooting and Beginner Help 8 02-06-2021 03:06 AM
For Sale - Sold: Nikon F-801 AF film camera w/ TC 16A teleconverter-autofocus with manual lenses 17dew Sold Items 4 05-08-2016 08:10 AM
For Sale - Sold: quantaray 2X Autofocus teleconverter; Pentax 18-55mm kit lens idler Sold Items 9 07-02-2009 12:06 PM
In-Body autofocus vs In-Lens autofocus Gooshin Pentax DSLR Discussion 7 02-05-2008 11:10 AM



All times are GMT -7. The time now is 07:38 PM. | See also: NikonForums.com, CanonForums.com part of our network of photo forums!
  • Red (Default)
  • Green
  • Gray
  • Dark
  • Dark Yellow
  • Dark Blue
  • Old Red
  • Old Green
  • Old Gray
  • Dial-Up Style
Hello! It's great to see you back on the forum! Have you considered joining the community?
register
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]
Top