Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
06-11-2010, 11:45 AM   #16
Junior Member




Join Date: Nov 2009
Location: Norfolk
Posts: 40
Original Poster
QuoteOriginally posted by Asahiflex Quote
By the way: I also tried the Sigma 500/4.5 with the SMC Pentax-F 1.7x AF adapter and I was really underwhelmed with the results. IMHO this combination is not recommended.
I won't bother trying then.

I don't know about the optics but I think the Sigma TC is a nice piece of engineering.

06-22-2010, 09:03 AM   #17
Inactive Account




Join Date: Feb 2010
Photos: Gallery
Posts: 488
I have the sigma 300mm f2.8 lens and use the 2.0 tc whenever i can. The 1.4 is a shoe in.
But in low light. And i mean with some sun and the subject in the shade it is a very bad af problem.
I shoot birds and often in dark places. The 1.4 at f4 is great but the 2.0 at f5.6 is very slow on my k-7. I would hate to take it to 6.3 and try. But I have thought about this lens and wondered how it would work.
Thanks
06-23-2010, 03:23 AM   #18
Junior Member




Join Date: Nov 2009
Location: Norfolk
Posts: 40
Original Poster
QuoteOriginally posted by garyk Quote
I have the sigma 300mm f2.8 lens and use the 2.0 tc whenever i can. The 1.4 is a shoe in.
But in low light. And i mean with some sun and the subject in the shade it is a very bad af problem.
I shoot birds and often in dark places. The 1.4 at f4 is great but the 2.0 at f5.6 is very slow on my k-7. I would hate to take it to 6.3 and try. But I have thought about this lens and wondered how it would work.
Thanks
It would be interesting to try the combination on a K-x.

Are you pleased with the lens? I was thinking about it but saw a used 500mm at a good price & I had to grab it if I wanted it.

With the 1.4x you have 420mm at F4 while I have 500mm at F4.5 but it is about 1Kg heavier.
06-23-2010, 04:33 AM   #19
Veteran Member
PePe's Avatar

Join Date: Nov 2007
Location: Helsinki, Finland
Photos: Gallery | Albums
Posts: 452
QuoteOriginally posted by PMunks Quote
It would be interesting to try the combination on a K-x.

Are you pleased with the lens? I was thinking about it but saw a used 500mm at a good price & I had to grab it if I wanted it.

With the 1.4x you have 420mm at F4 while I have 500mm at F4.5 but it is about 1Kg heavier.
I have both the Sigma 300/2,8 and the 500/4,5 and use them frequently.
As such the 300/2,8 is a pretty good lens, but wide open the 500/4,5 is slightly sharper.
Combined with a TC the 300/2,8 is way behind in terms of optical performance, even with a 1,4 x TC.
Despite the weight penalty I would not consider this as a real alternative to the 500/4,5.

The 500/4,5 works reasonably well with the 1,4 x TC. AF is somewhat slower, but it usually works.
With the 2 x TC it is a MF lens.


Last edited by PePe; 06-23-2010 at 04:40 AM.
06-23-2010, 06:06 AM   #20
Junior Member




Join Date: Nov 2009
Location: Norfolk
Posts: 40
Original Poster
I have a Pentax 300mm F4 which AF's quite well with my Pentax 1.7X TC so from what you say, I think I made the right choice for me.

When I want 500mm without the weight I use a Tamron 500mm F8 Mirror. With CIF & SR I find it a pretty good combination though obviously not as sharp.
06-23-2010, 07:18 AM   #21
Veteran Member




Join Date: Jun 2007
Location: Owego, NY
Posts: 976
QuoteOriginally posted by Lowell Goudge Quote
impossible re AF limit

the bigma would not AF if this was the case.

Not sure where you got your info but there are just too many lenses at F6.3 to 6.7 which are sold by all lens makers for this maximum aperture to be a limit.

If you follow the forum threads frequently you will see a lot of dicsussion about the SMC-F 1.7x AF TC.

This works reliably on any F4 lens and the 1.7x factor translates to 510mm F7.1 I think. It has been reported to work on the SMC 500 F4.5 also, which would take you to F8 although I have no first hand experience of that. I do have first hand experience with the 1.7x TC on AF bodies back as far as the PZ-1 with no issue so the F7 limit for AF working has been around for some 20 years.

Where ever you got it, it is bad information.
It's a soft limit, and 5.6 is all Pentax will guarantee their AF system to. You can almost always go to 6.3 without problems, and sometimes even f/8 but at that point you'll be on the edge in any lighting condition.

Third-party manufacturers do extra testing to certify that their lenses work beyond the specified limit.

It's not about available light, it's actually about the lens physics - think of the classic split-prism viewfinders and how they would just go completely dark beyond a certain aperture regardless of the available light. Same concept for AF failing beyond a certain limit.
06-24-2010, 07:55 AM   #22
Forum Member




Join Date: Apr 2009
Location: Canada
Posts: 75
Re: Canon and the F5.6 limit for AF - I have read (and can't find the link right now) that the Canon firmware includes a self-crippling mechanism where if the camera body can determine that the combination of lens and TC will result in smaller aperture than F/5.6 (F/8 for the 1D series) it will disable AF. Read that carefully - the camera body is programmed to kill AF without trying if it thinks the aperture is smaller than a pre-defined limit. This is why some Canon users talk about various hacks to trick the camera body into believing it's just a lens attached by shorting pins so that the camera still tries to AF (which it often does successfully, within reasonable limits).
06-26-2010, 12:57 AM   #23
Inactive Account




Join Date: Feb 2010
Location: thailand
Posts: 45
I must have a good copy of the 300mm f2.8 lens. I bought it new, it is the Ex DG Apo, about 6 months old now. But at 2.8 it is great close. But stopped down to 3.5 to 4 it is absolutly stunning.
And that goes for the T.C's. It follows the lens exactly. At 4.9 with the 1.4 T.C. It doesn't get any sharper. At F7 with the 2.o T.C. It is at it's sharpest.
Here is a pic I took last week.

I use the lens on a gimble mount almost always for good sharp and consistent pics. But with the 1.4 and shake enabled on the camera it is very good also. If you can punch up the shutter speed. I am getting old and have a hard time holdint it for very long.
Many times with the 300 and the 2.0 attached i focus manually first on the subject then switch over to auto focus and it hits very fast. If not sometimes it is very slow. In low light it is a must to manual focus first I have found on my copy. But then it will hit after MF is close usually.

When used properly I don't see how the eye can pick up anymore detail.
I have many pics this good and better.

But I am thinking seriously about getting the 500mm f4.5 because with a T.C. on a pentax it will give me a 700mm lens. with minumum drop off in imige i hope.
With the 1.4 T.c. on the 300mm it is better but you must get very close to birds.
That is my copy if the 300 mm f2.8.

If the O.P. will PM me or give me links to your pics with the 500mm and the 500 with the 1.4 attached i would very much appreciate it.

This is with the 300mm + 2.0T.C. F7 and -.7.



Last edited by gary1952; 06-26-2010 at 01:17 AM.
06-26-2010, 02:23 AM   #24
Junior Member




Join Date: Nov 2009
Location: Norfolk
Posts: 40
Original Poster
QuoteOriginally posted by gary1952 Quote
If the O.P. will PM me or give me links to your pics with the 500mm and the 500 with the 1.4 attached i would very much appreciate it.
A very nice picture.

Both the 500mm F4.5 & the 1.4x TC are pretty new to me & I haven't put anything online yet, but when I do, I will certainly send you a link.
06-26-2010, 02:31 AM   #25
Veteran Member
PePe's Avatar

Join Date: Nov 2007
Location: Helsinki, Finland
Photos: Gallery | Albums
Posts: 452
QuoteOriginally posted by gary1952 Quote

But I am thinking seriously about getting the 500mm f4.5 because with a T.C. on a pentax it will give me a 700mm lens. with minumum drop off in imige i hope.
With the 1.4 T.c. on the 300mm it is better but you must get very close to birds.
That is my copy if the 300 mm f2.8.

If the O.P. will PM me or give me links to your pics with the 500mm and the 500 with the 1.4 attached i would very much appreciate it.

This is with the 300mm + 2.0T.C. F7 and -.7.
Just PMīd you a longer description of my experience with the Sigma500/4,5.
You might also want to have a look into
https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/59187-sigma-50...est-shots.html
Please bear in mind that these pictures were sent as attachments and have therefor been compressed quite alot, leading to a significant loss of colour intensity.
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, k-mount, pentax lens, sigma, sigma 500mm f4.5, slr lens, tc
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
For Sale - Sold: Sigma 170-500mm f5-6.3 APO Autofocus PKA photobizzz Sold Items 7 10-26-2009 02:03 PM
For Sale - Sold: Pentax AF-540FGZ Flash, Sigma 10-20mm F4-5.6, Sigma 170-500mm F5-6.3 davebest Sold Items 12 06-25-2009 02:48 PM
For Sale - Sold: Sigma 50-500mm APO DG EX Autofocus lens dubjay Sold Items 1 11-11-2008 12:05 AM
For Sale - Sold: FS: Samsung GX10, Sigma 50-500mm (Bigma), Sigma 400mm AF chirpy Sold Items 4 03-24-2008 11:07 AM
A little longer... Sigma Bigma vs Sigma 170-500mm Buddha Jones Pentax SLR Lens Discussion 1 01-15-2008 11:20 PM



All times are GMT -7. The time now is 11:50 PM. | See also: NikonForums.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