Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
01-06-2011, 09:10 PM   #16
Pentaxian




Join Date: Jun 2009
Location: Chicago Suburbs.
Photos: Gallery
Posts: 500
Original Poster
Is there a model # for the Tamron 1.4?? It might be "good enough" for my needs.
GA

01-06-2011, 09:14 PM   #17
Veteran Member
dgaies's Avatar

Join Date: Oct 2009
Location: Maryland / Washington DC
Posts: 3,917
QuoteOriginally posted by goldenarrow Quote
Is there a model # for the Tamron 1.4?? It might be "good enough" for my needs.
GA
It's the Tamron 1.4x Pz-AF MC4. I'll post a picture of both it and the Pentax 1.7x AF-A below. FYI, the Tamron is no longer made and can pretty much only be bought used. They typically sell for $150-200, which is almost double what they sold for new when they were in production.

01-06-2011, 11:42 PM   #18
Pentaxian




Join Date: Feb 2009
Location: Alameda, CA
Posts: 3,198
QuoteOriginally posted by goldenarrow Quote
Is there a model # for the Tamron 1.4?? It might be "good enough" for my needs.
Not sure what your needs are....

But the Tamron does not modify any data from the lens, so the body doesn't know there is a 1.4X TC between it and the lens. For example, when the lens is set at 200mm FL, the effective FL is 280mm, but the body still thinks the FL is 200mm. When you use the body to set the aperture at F/4, the effective aperture is F/5.6.

Also, in my experience, when the DA* zoom lens is at the long end of the FL (there is no reason to use the TC at the short end of the FL), the autofocus of the body most times keeps hunting back and forth as if it can't decide where to lock focus on. When you remove the finger from the shutter release half press, and then half press again, the focus may lock. It is annoying and I can't really call that "working."

The symptom is the same with the DA* zoom lenses I have: 16-50, 50-135, and 60-250.

I personally prefer the Pentax 1.7X AFA. I haven't used the Tamron 1.4X since I got the Pentax 1.7X.
01-07-2011, 12:09 AM   #19
Pentaxian
littledrawe's Avatar

Join Date: Jan 2010
Location: Red Rock
Photos: Gallery | Albums
Posts: 2,454
Just got the Kenko 1.5x in the mail today. I am excited to go try it out.
1.5X Teleconverters | Teleconverters | 1.5X & 1.7X Teleconverters

looks like they are out of stock now but this is the best deal I could find. Seems like build quality is decent.

01-07-2011, 04:57 AM   #20
Pentaxian




Join Date: Jun 2009
Location: Chicago Suburbs.
Photos: Gallery
Posts: 500
Original Poster
Thank you for the pictures and descriptions, very informative reading! Using "zooms w/TC with respect to SR" is mostly what I am concerned about in this thread but I also like the descriptions of how it actually works in practice. Seems like a premium price put on just 1.4x of magnification for the Tamron. I really like the AFA, at least on fixed lenses. Since I am trying to be careful with my currency, I will have to think about the worth to me of that premium.

I like the concept that I would probably not use a TC at the lower end of the zoom range. Definitely affects where I set the SR manually. Let's see, with a 50-135, halfway is 92.5. Then multiply by 1.4 = 129.5. 135 is the closest setting on the menu for a conservative SR manual setting. By contrast, the long end = 135*1.4= 189 (about 200 on the menu). So, I see that at least a fairly good amount of SR is possible when one thinks about it carefully (and stays at the longer half of the zoom range). So, perhaps instead of 3 stops of SR in a perfect world, I might get 2-2.5 stops SR if I happen to be using it at the farthest end of the range (with the SR setting at 135). I have been known to be lazy and not take off the TC the whole time. So if something did pop up close by, I might have to deal with SR induced blur, which means more post-processing. So, not a perfect solution but might be acceptable.

I would prefer not to have to think at all about this. Just took up half an hour of my time just sitting here thinking and writing this post. A more ruthless person would ditch this problem and go for the expensive lens-built stabilization and never look back. But that is a different discussion altogether......

GA
01-07-2011, 03:34 PM - 1 Like   #21
Veteran Member




Join Date: Apr 2009
Location: Blacksburg, VA
Posts: 485
I have some information about teleconverters to share.

1. Quantaray 2x
- Power contact available
- SDM works on KAF3 lens (but hunt a lot)
- SDM not working on KAF2 SDM lens
- Screw-driven AF works on older DSLR and KAF2 SDM lens combination
- Focal length transmitted untouched
- Aperture value transmitted untouched
- Metal construction

2. Sigma APO 2X DG
- No power contact
- SDM not working on KAF2, KAF3 with newer DSLR
- Screw-driven AF works on older DSLR and KAF2 SDM lens combination
- Focal length transmitted untouched
- Aperture value transmitted untouched
- Metal construction
- Bug: If use with any SDM lens and newer DSLR combination, cannot enter camera menu, LF or play mode.

3. Pentax 1.7X AF
- No power contact
- SDM not working
- Focal length blocked
- Aperture value transmitted modified
- Overexposure with AF-540FGZ, but not built-in flash
- 2 variants available, older plastic barrel and newer metal barrel

4. Pentax 2X-S
- No power contact
- No AF at all
- Focal length blocked
- Aperture value transmitted untouched
- Metal construction

Last edited by arm_jstp; 01-07-2011 at 03:41 PM.
01-08-2011, 12:42 PM   #22
Veteran Member
Ben_Edict's Avatar

Join Date: Jul 2007
Location: SouthWest "Regio"
Photos: Albums
Posts: 3,303
QuoteOriginally posted by goldenarrow Quote
Ben,
Thanks for echoing my sentiments. I hear rumors that professionals snicker at the name of Pentax. Now I can see tangible proof that Pentax does not currently have the resources to compete on a pro level in certain areas. And that gives the willies to any budding pro, not wanting to get caught with a system that lacks anything one might need to get business and keep it.
There are some areas, were the Pentax system is lacking. A tc with a fl corrector is my least concern here. For wildlife a choice of long lenses beyond 300mm seems to me much more important. Another shortcoming was the Pentax AF system, which made it not exactly a preferred choice for sports photography and other high speed action.

But wildlife and sports represent only a small part of the spectrum of professional photography and there are enough other areas, where you could excel with Pentax equipment.

QuoteOriginally posted by goldenarrow Quote
As an amateur, I can live without a fully functional TC for now. But I can see a day when I may not be so amicable. If the lack of this feature in a TC sways me away from the 50-135 I was thinking of getting, how little it would take to sway me to get the Nikon system I might want to switch to, dumping Pentax in the process because of lack of money. I don't have the money to switch, and I have no need to also. Just saying, if the opportunity arose, who knows? But that is also the amateur legacy of Pentax which keeps them around and makes uniquely useful products that they DO make. So, I appreciate what they are accomplishing with digital but also keeping my eyes open, too.
To be honest: combining a zoom lens with a tc is rarely a good idea. I never do so, except when I have a dedicated tc available for a certain lens (which is the case with my Sigma 70-200 and the 2 Sigma Apo tcs). A universal tc is always a trial and error thing with each lens - it may work acceptably or not. So, the lack of the one Pentax tc seems to me highly irrelevant, even if I can see, that there might be applications for it.

Anybody should keep his eyes open and be informed about products which may help his job or which are more satisfying to use. That is sensible. But it does not constitute any proof, that a certain system (be it Pentax or otherwise) is inferior. It is just a matter of personal choice as is the the preference for either an Arca Swiss or an RRS ball head.

Ben
01-08-2011, 12:47 PM   #23
Pentaxian




Join Date: Jun 2009
Location: Chicago Suburbs.
Photos: Gallery
Posts: 500
Original Poster
Ben,
Thanks for your thoughts, well described. Nothing is perfect and I try to live with any limitations. And I appreciate a well-rounded discussion, if I have the time.


01-09-2011, 02:44 AM   #24
Veteran Member




Join Date: Jan 2010
Location: Southern England
Posts: 495
Be very careful when choosing a "compromise" FL value for a zoom lens!

I did some work on this here:

https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/119297-what-fo...al-zoom-2.html

For example, using the formula given, a 50-135mm zoom would become an 85-230mm zoom, and the best compromise value would be 120mm. But this assumes the lens will be used at all FLs, including at the wide end, and this may not be the case, given the use of a TC. Nevertheless, it's worth bearing in mind that, if you operate at FLs less than half the value that you entered, you'll magnify any camera shake.

So, if you were to operate at minimum FL, and had entered 250mm, you would almost double any camera shake.
01-10-2011, 07:51 AM   #25
Pentaxian




Join Date: Jun 2009
Location: Chicago Suburbs.
Photos: Gallery
Posts: 500
Original Poster
That is an interesting thread

Re-read the thread on calculating formulas for a manual zoom. I will have to experiment. There is also the notion of changing the formula when a TC is attached AND one is sure to use the longer half of the range, since (presumably) the TC is there for more "reach", the lower half of the zoom range will not be used. Not always true, but in some cases it is.
01-10-2011, 08:00 AM   #26
Pentaxian




Join Date: Jun 2009
Location: Chicago Suburbs.
Photos: Gallery
Posts: 500
Original Poster
Thanks arm_jstp for the table of information. I wonder if anything like it exists on the internet!!! Very very nice info to have.
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!
1.7x, afa, body, camera, info, k-mount, length, pentax 1.7x afa, pentax lens, question, slr lens, theory
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Sigma UC Zoom 28-70mm 1:2..8-4 info required please Just Me Pentax SLR Lens Discussion 2 11-08-2010 11:54 PM
Hood info required for 100-300mm zoom samski_1 Pentax SLR Lens Discussion 6 05-16-2010 09:37 PM
Any info on Sigma Zoom AF 70-300mm f4.5-5.6? EsBee Pentax SLR Lens Discussion 3 05-30-2009 11:53 AM
RE: Need info on Zoom lens cruiserlan2000 Pentax SLR Lens Discussion 5 12-28-2006 03:10 PM



All times are GMT -7. The time now is 09:23 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