Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
05-30-2009, 12:32 PM   #1
Site Supporter
Site Supporter
dadipentak's Avatar

Join Date: Jul 2008
Location: Baltimore, Maryland
Photos: Gallery
Posts: 10,475
AF 1.7x Adapter not working with SMC 1000mm f/8

Yeah, I know: that's 1,700mm and on a K20D it's the film equivalent of 2,550mm. But, heck, I have 'em so why not try it?

I'm shooting in M mode and the problem is that while the adapter AF works as expected, the shutter refuses to activate. I don't have this problem with other lenses. I thought maybe it was insufficient light but I stopped another lens down to f22 indoors and it snapped away just fine, giving me a photo of total darkness (blinkie OD)

Any clues?

Based on what I've seen in the viewfinder, btw, this may not work well in any case--heavy green/magenta fringing (LCOA?) but still....

05-30-2009, 12:35 PM   #2
Loyal Site Supporter
Loyal Site Supporter
Canada_Rockies's Avatar

Join Date: Nov 2007
Location: Sparwood, BC, Canada
Photos: Gallery | Albums
Posts: 9,623
Your problem is that you have the camera set to AF.S, and the focus system cannot confirm focus at f/13.6. Once you have the AF 1.7X on the camera, the camera expects to auto focus. Set the camera to MF and all will be well.
05-30-2009, 01:54 PM   #3
Site Supporter
Site Supporter
dadipentak's Avatar

Join Date: Jul 2008
Location: Baltimore, Maryland
Photos: Gallery
Posts: 10,475
Original Poster
QuoteOriginally posted by Canada_Rockies Quote
Your problem is that you have the camera set to AF.S, and the focus system cannot confirm focus at f/13.6. Once you have the AF 1.7X on the camera, the camera expects to auto focus. Set the camera to MF and all will be well.
Thanks but that doesn't seem right. I want AF and the adapter is supposed to deliver that (and, in fact, it does its focusing thing.) Also, it worked fine at f22 with a different lens so why not this one?

UPDATE: It may not seem right but you certainly set me on the right track! I did the AF and then switched to MF and the shutter activated! Then, I tried it with AF-C and the problem was resolved: I got the AF and shutter activation.

I don't understand but then there are all sorts of things I don't understand ;~) Thanks!
05-30-2009, 02:20 PM   #4
Loyal Site Supporter
Loyal Site Supporter
Canada_Rockies's Avatar

Join Date: Nov 2007
Location: Sparwood, BC, Canada
Photos: Gallery | Albums
Posts: 9,623
QuoteOriginally posted by dadipentak Quote
Thanks but that doesn't seem right. I want AF and the adapter is supposed to deliver that (and, in fact, it does its focusing thing.) Also, it worked fine at f22 with a different lens so why not this one?

UPDATE: It may not seem right but you certainly set me on the right track! I did the AF and then switched to MF and the shutter activated! Then, I tried it with AF-C and the problem was resolved: I got the AF and shutter activation.

I don't understand but then there are all sorts of things I don't understand ;~) Thanks!
You are welcome. I think from this reply that you are confusing the f/stop you have set with the wide open f/stop of the lens. For AF, the aperture that counts is the wide open aperture used while attempting to focus. I can sometimes get the 1.7X to auto focus with my M 400/5.6, but it is definitely "sometimes". Most of the time it will not. If you get AF with the 800/8 you will be seeing a very contrasty subject in very bright light. Don't confuse the red flashing light with the AF signal that is the green hexagon at the bottom of your viewfinder. The red square is just an indicator that the camera is trying to AF with that AF detector.

05-30-2009, 02:41 PM   #5
Pentaxian
Just1MoreDave's Avatar

Join Date: Feb 2007
Location: Aurora, CO
Photos: Gallery | Albums
Posts: 4,874
QuoteOriginally posted by dadipentak Quote
Thanks but that doesn't seem right. I want AF and the adapter is supposed to deliver that (and, in fact, it does its focusing thing.)
If you read the manual, it says AF only works with f2.8 or faster lenses. That's not a hard limit; it doesn't stop dead at f3.5, it just gets less and less reliable at locking focus. Focus is harder at f8. The other problem may be that it does not have an unlimited range. You have to set the manual focus ring somewhere close to the actual focus. That's probably harder at 1000mm.
05-30-2009, 02:44 PM   #6
Loyal Site Supporter
Loyal Site Supporter
imtheguy's Avatar

Join Date: Mar 2009
Location: Virginia Beach
Photos: Gallery | Albums
Posts: 2,950
I believe the reason you get your shutter at AF-C and not AF-S is the K20d WILL NOT allow shutter w/o focus lock at AF-S but WILL at AF-C so you may just be getting shots as it drifts in and out of lock. I missed what body you are using.
05-30-2009, 02:45 PM   #7
Pentaxian
Marc Sabatella's Avatar

Join Date: Sep 2006
Location: Denver, CO
Photos: Gallery
Posts: 10,686
QuoteOriginally posted by dadipentak Quote
Thanks but that doesn't seem right. I want AF and the adapter is supposed to deliver that (and, in fact, it does its focusing thing.) Also, it worked fine at f22 with a different lens so why not this one?
You mean you actually forced this other lens to stop down to f/22 before pressing the shutter? Simply setting the aperture to f/22 doesn't normally stop it down until the shutter is pressed, unless you're talking about a screw mount lens. And with screw mount lenses, I'm not sure the camera will refuse to fire just because focus hasn't been achieved (maybe that depends on the the setting of the custom option having to do with focus indicator and screwmount lenses?). So without knowing exactly what strings you pulled, I'm guessing you weren't really asking the camera to do the same thing at all with this other lens.

Anyhow, while the AF system of the TC may have moved the lens, and may have even achieved semi-decent focus, it may well have given up before true "lock" was achieved. And if there isn't enough light for the AF sensor *in the camera* to judge that focus lock has been achieved, it won't fire when in AF-S mode. For a lens that is presenting f/13 to the focus sensor (as I believe yours is), I'd be really surprised if it was able to judge a focus lock, unless maybe you were focusing on the sun.
05-30-2009, 04:47 PM   #8
Site Supporter
Site Supporter
dadipentak's Avatar

Join Date: Jul 2008
Location: Baltimore, Maryland
Photos: Gallery
Posts: 10,475
Original Poster
Ah, ok, I'm starting to get it. It's a K-mount lens, btw, mounted on my K20D. And You're right, Marc, the other lens was a f/3.5.

I have gotten the AF to work on f4 and f4.5 lenses so forgot about that caveat in the manual. Obviously I'm pushing the AF function well beyond its limits.

AF aside, the real question is whether combination will render better IQ than shooting with the lens alone and cropping. Quite frankly, I rather doubt it but figured it was worth a try--I am a pentaxian after all ;~)

Thanks everyone!

UPDATE: Well, actually, the resolution ain't too shabby.

Attached Images
View Picture EXIF
PENTAX K20D  Photo 

Last edited by dadipentak; 05-30-2009 at 05:25 PM.
05-30-2009, 06:02 PM   #9
Pentaxian
jgredline's Avatar

Join Date: Oct 2007
Location: LosAngeles, Ca.
Photos: Albums
Posts: 10,587
Dave, those wood peckers have no chance now
05-30-2009, 06:31 PM   #10
Loyal Site Supporter
Loyal Site Supporter
Canada_Rockies's Avatar

Join Date: Nov 2007
Location: Sparwood, BC, Canada
Photos: Gallery | Albums
Posts: 9,623
QuoteOriginally posted by dadipentak Quote
... <snip> ...

UPDATE: Well, actually, the resolution ain't too shabby.
As rear converters go, the AF 1.7X rates right up there with the best. It seems to have an ever so slight edge over the A 1.4X-S when used with my M 400/5.6 lens, not to mention a bit more magnification, nicely offset by the loss of another half stop of light.
05-31-2009, 12:30 PM   #11
Site Supporter
Site Supporter
dadipentak's Avatar

Join Date: Jul 2008
Location: Baltimore, Maryland
Photos: Gallery
Posts: 10,475
Original Poster
Well, I tried it this morning on AF.C and the focus worked fine. The light was pretty good but not great so I got a fair amount of noise (which Neat Image refused to treat for some reason.) I'm quite pleased with the resolution.
Attached Images
View Picture EXIF
PENTAX K20D  Photo 
05-31-2009, 01:06 PM   #12
Pentaxian
jgredline's Avatar

Join Date: Oct 2007
Location: LosAngeles, Ca.
Photos: Albums
Posts: 10,587
QuoteOriginally posted by dadipentak Quote
Well, I tried it this morning on AF.C and the focus worked fine. The light was pretty good but not great so I got a fair amount of noise (which Neat Image refused to treat for some reason.) I'm quite pleased with the resolution.
Dave, for what you put together, that is a great shot. i am pleasantly surprised. those lenses are not known for their sharpness and let alone with a 1.7tc.
05-31-2009, 01:27 PM   #13
Site Supporter
Site Supporter
dadipentak's Avatar

Join Date: Jul 2008
Location: Baltimore, Maryland
Photos: Gallery
Posts: 10,475
Original Poster
Thanks, Javier. Of course, it shortens the min and max focusing distance of the lens but I can live with that.
05-31-2009, 01:43 PM   #14
Pentaxian
jgredline's Avatar

Join Date: Oct 2007
Location: LosAngeles, Ca.
Photos: Albums
Posts: 10,587
QuoteOriginally posted by dadipentak Quote
Thanks, Javier. Of course, it shortens the min and max focusing distance of the lens but I can live with that.
When I first read your post on my cell phone, I thought to myself. No way can you have a usable image, then when I saw it on my Laptop, I was amazed.

I have that TC but have not used it in many months, but it is time to experiment.
05-31-2009, 02:26 PM   #15
Site Supporter
Site Supporter
dadipentak's Avatar

Join Date: Jul 2008
Location: Baltimore, Maryland
Photos: Gallery
Posts: 10,475
Original Poster
I was really surprised myself. I get the feeling the way TCs and lenses match up can be quite variable --sometimes by design but other times, by chance.
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!
adapter, af, af 1.7x adapter, k-mount, pentax lens, slr lens
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Success with the SMC 1000mm f/8 rfortson Pentax SLR Lens Discussion 11 01-22-2010 10:00 PM
7 large shots from SMC 1000mm f/8 rfortson Pentax SLR Lens Discussion 9 01-20-2010 05:20 PM
SMC 1000mm f/8 dadipentak Pentax SLR Lens Discussion 10 06-18-2009 10:27 AM
ASAHI SMC PENTAX 1000mm F8 $$? quenched Pentax SLR Lens Discussion 11 04-19-2009 01:02 AM
Pentax SMC 8/1000mm? Gimbal Pentax SLR Lens Discussion 14 10-30-2007 04:21 PM



All times are GMT -7. The time now is 03:50 AM. | 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