Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
04-19-2010, 05:48 AM   #1
New Member




Join Date: Oct 2009
Location: Hastings, Ontario
Posts: 21
Sigma telephoto lens converters.

I am thinking of buying a teleconverter for the Sigma 50-500mm 1.4-6.3 APO DG lens that I have bought. (Also known as BIGMA.) This lens does not have the newer HSM motor in it. I am assuming that it is the screw type motor.

From what I have been told by the Sigma manufacturer if I get their 1.4 teleconverter I will have to use the lens in manual mode only. I would like to be able to use all the automatic features the lens has when it is attached directly to the my K10D, but alas from what I have been told I cannot do it with the Sigma teleconverter.

I have read on the forum of other teleconverters from other manufactuers that members are using. My question is this, is there a teleconverter available
from another source that will work with this lens and give me the ability to use all of the lens automatic features?


Hopefully I can source one here in Canada, but I am willing to buy outside of the country.

I am also thinking of buying the new Sigma 70-200mm HSM lens, so it would be nice if the teleconverter would work with it also.

Yes, I know I am asking for a lot, but one can always hope for the best.

04-19-2010, 07:46 AM   #2
Pentaxian




Join Date: Oct 2006
Location: Chicago suburb, IL, USA
Posts: 1,535
Hi oddie,

There are two issues with the Sigma TCs with the Bigma.

1. The front element of the TC (either the 1.4x or the 2x) protrude into the are normally occupied by the rear lens element of many lenses. In the case of the Bigma, the read element moves while zooming, and towards the short end (I believe it's at @ 100mm), the rear element of the lens moves back enough to potentially contact the front element of the Sigma 1.4x TC, and the 2x protrudes more, so the contact point would be at a higher FL. This is not a good situation, as you could damage the lens, the TC, or both by unthinkingly retracting the zoom. I wouldn't use either of these TCs with the Bigma, ever. Possible optical damage to a $1K lens and a $200-300 TC while retracting the lens to its smallest length (as most will normally do to carry it) is not an option for me.

2. The Bigma's widest aperture at the long end is f6.3-f6.7. TCs "eat" light proportional to their magnification factor causing the max aperture to get effectively smaller by the same factor as the magnification. A 1.4x TC will "slow" down the lens 1 stop, a 1.7x TC will cause a 1.5 stop loss and a 2x TC will cause 2 stops loss. Using the Bigma at the longest reach, the mac apertures become f8.8, f10.7, and f12.6 respectively. Pentax's AF system is designed to work optimally at max apertures of f5.6 and larger (smaller f stop values). It will, of course work at slower apertures with decreased speed and accuracy, but f8 has always been the practical limit (this is stretched by the K-7, and maybe the Kx tho). This means that if the TC will allow AF at all at the longest FLs of the Bigma, you'll need very bright conditions with a lot of contrast for it to have any chance.

The Kenko and Tamron 1.5x and 1.4x AF TCs respectively would work with the Bigma without the potential lens element damage, but the restrictions to functionality caused by the light loss would still be there. Then there is optical performance. Many zooms do not perform well with TCs because of optical compromises that are made in the zoom's multiple FL design. When people talk about the image degradation caused by TC use, zooms are more prone to display this unacceptably than primes. I think that the Bigma is good enough optically, to stand up to TC use, but I haven't seen any results that have impressed me -- and there are still the AF limitations. . .

Scott
04-19-2010, 08:15 AM   #3
New Member




Join Date: Oct 2009
Location: Hastings, Ontario
Posts: 21
Original Poster
RE: Bigma teleconverters

Thanks Scott for the valuable information. When I was in Henrys and also talking to some of the dealers from Alberta. No-one mentioned the potential damage to the lens or sigma teleconverter.

Would you possibly know where I could pick up either a Kenko or Tamron teleconverter?
04-19-2010, 08:44 AM   #4
Pentaxian




Join Date: Oct 2006
Location: Chicago suburb, IL, USA
Posts: 1,535
QuoteOriginally posted by oddie1990 Quote
Thanks Scott for the valuable information. When I was in Henrys and also talking to some of the dealers from Alberta. No-one mentioned the potential damage to the lens or sigma teleconverter.

Would you possibly know where I could pick up either a Kenko or Tamron teleconverter?
Hi oddie,

Look at the Sigma TC compatibility chart on their site, and note the *** exception for the Bigma ("***Zoom control range is limited to 100-500mm, when the teleconverters are used with this lens.") I've been told by trusted Bigma users that this is the case -- I have no direct experience.

As to where to get the Kenko or Tamron. Unfortunately, I believe that they were both discontinued a while back. The forum Marketplace here would be one of the more reliable sources, but as always, be very aware of bogus online sellers. These TCs have gotten to be much sought after items by many, and as such, are presented as bait by scammers. I'd keep an eye on KEH and both B$H's and Adorama's Used departments as other reliable sources.

Scott

04-19-2010, 08:53 AM   #5
Pentaxian
Lowell Goudge's Avatar

Join Date: Jan 2007
Location: Toronto
Photos: Gallery | Albums
Posts: 15,314
according to sigma's documentation,, the TCs are useable but the zoom range is limited to 100-500 not 50-500mm.

I do not know how they achieve this unless the BIGMA has a some mechanical device that cona tacts the TC but which protects the rear element of the lens.

They also note that the lens is MF only.

This is not really true, but simply that the loss of the additional stop will reduce the aperture, especially a t the long end, such that AF is unreliable., not that it does not work, just that performance is very poor.
04-19-2010, 09:09 AM   #6
Pentaxian
Mike.P's Avatar

Join Date: Mar 2008
Location: South Coast .. UK
Photos: Gallery
Posts: 1,734
QuoteOriginally posted by snostorm Quote
Hi oddie,

There are two issues with the Sigma TCs with the Bigma.

I wouldn't use either of these TCs with the Bigma, ever. Possible optical damage to a $1K lens and a $200-300 TC while retracting the lens to its smallest length (as most will normally do to carry it) is not an option for me.
That is where the zoom lock comes into operation. Extend the Bigma to 500mm, lock using the switch on the lens and then fit the teleconverter. The Bigma will not drop below around 100mm (guess) which allows the converter to be used. Works fine with mine.
04-19-2010, 11:59 AM   #7
Veteran Member
Ben_Edict's Avatar

Join Date: Jul 2007
Location: SouthWest "Regio"
Photos: Albums
Posts: 3,303
QuoteOriginally posted by oddie1990 Quote
Thanks Scott for the valuable information. When I was in Henrys and also talking to some of the dealers from Alberta. No-one mentioned the potential damage to the lens or sigma teleconverter.

Would you possibly know where I could pick up either a Kenko or Tamron teleconverter?
There is no damage risk, if you use the 100mm lock provided!

The only thing, that won't work reliably is AF and that with any tc (Sigma, Kenko, Tamron), because the Bigma is a bit slow on the long end.*Anyway, I never used the Sigma (or any other) tcs with the Bigma, as I find thew combination way too slow to be useful. Even manual focusing get a bit tricky with such a "max" aperture. I personally think, using a tc on the Bigma is something like a last ressort, when you need to image that crashing airplane from 2 miles away, but nothing to use under normal circumstances.

Ben
04-19-2010, 12:18 PM   #8
Veteran Member
Tuner571's Avatar

Join Date: Mar 2008
Location: Ohio
Photos: Gallery | Albums
Posts: 1,550
QuoteOriginally posted by snostorm Quote
Hi oddie,

There are two issues with the Sigma TCs with the Bigma.

1. The front element of the TC (either the 1.4x or the 2x) protrude into the are normally occupied by the rear lens element of many lenses. In the case of the Bigma, the read element moves while zooming, and towards the short end (I believe it's at @ 100mm), the rear element of the lens moves back enough to potentially contact the front element of the Sigma 1.4x TC, and the 2x protrudes more, so the contact point would be at a higher FL. This is not a good situation, as you could damage the lens, the TC, or both by unthinkingly retracting the zoom. I wouldn't use either of these TCs with the Bigma, ever. Possible optical damage to a $1K lens and a $200-300 TC while retracting the lens to its smallest length (as most will normally do to carry it) is not an option for me.

2. The Bigma's widest aperture at the long end is f6.3-f6.7. TCs "eat" light proportional to their magnification factor causing the max aperture to get effectively smaller by the same factor as the magnification. A 1.4x TC will "slow" down the lens 1 stop, a 1.7x TC will cause a 1.5 stop loss and a 2x TC will cause 2 stops loss. Using the Bigma at the longest reach, the mac apertures become f8.8, f10.7, and f12.6 respectively. Pentax's AF system is designed to work optimally at max apertures of f5.6 and larger (smaller f stop values). It will, of course work at slower apertures with decreased speed and accuracy, but f8 has always been the practical limit (this is stretched by the K-7, and maybe the Kx tho). This means that if the TC will allow AF at all at the longest FLs of the Bigma, you'll need very bright conditions with a lot of contrast for it to have any chance.

The Kenko and Tamron 1.5x and 1.4x AF TCs respectively would work with the Bigma without the potential lens element damage, but the restrictions to functionality caused by the light loss would still be there. Then there is optical performance. Many zooms do not perform well with TCs because of optical compromises that are made in the zoom's multiple FL design. When people talk about the image degradation caused by TC use, zooms are more prone to display this unacceptably than primes. I think that the Bigma is good enough optically, to stand up to TC use, but I haven't seen any results that have impressed me -- and there are still the AF limitations. . .

Scott
Wow, thanks for that great write-up. However, I do find it odd that Sigma would design a TC that won't fully work with a lens that they sell. Is it because there is just no way around it? I mean I know Pentax made TC and I have never of this happening with them.

04-19-2010, 01:45 PM   #9
Forum Member




Join Date: Dec 2008
Location: West Sussex, UK
Posts: 62
Personally I think Sigma including the bigma in the list of lenses for the TC is more down to it not requiring any real effort on their part rather than the lens being specifically designed to work with one.

As others have noted the bigma simply isn't fast enough to work well with a TC attached. Trust me, it's an absolute pig to manual focus as there simply isn't enough throw in the focus ring to get the sort of precision you need given the depth of field you'll be working with. Plus the viewfinder can get pretty dark making it even harder.

I picked up the 2X Sigma TC a while ago when I came across one that was dirt cheap, but I didn't really expect much from it. I've only used it a few times, but generally it's only worth it when the alternative is no photo at all. Forget about even trying it if it's not a bright day, and you'll need a steady tripod too. Even then you lose an enormous amount of contrast compared to the lens normally, and forget about pixel peeping.

You might have better results with a 1.4X or 1.5X TC, but I would suspect you might do just as well with simply cropping.
04-19-2010, 04:51 PM   #10
New Member




Join Date: Oct 2009
Location: Hastings, Ontario
Posts: 21
Original Poster
Bigma teleconverter answers

Thank you everyone for the insite on potential pitfalls and issues with the Bigma. If I was to buy the teleconverter I would have to remember to use the lock and then not forget to take the teleconverter off the lens before retracting it. A bit of a pain in the butt.

Now does anyone know where I can source a Kenko or Tamron teleconverter that maybe would not have the same issues as the sigma teleconverter.
04-20-2010, 02:26 AM   #11
Veteran Member
Ben_Edict's Avatar

Join Date: Jul 2007
Location: SouthWest "Regio"
Photos: Albums
Posts: 3,303
QuoteOriginally posted by Tuner571 Quote
Wow, thanks for that great write-up. However, I do find it odd that Sigma would design a TC that won't fully work with a lens that they sell. Is it because there is just no way around it? I mean I know Pentax made TC and I have never of this happening with them.

The best Pentax tcs - may be, even the best tcs of all makes are the two Pentax A 1.4x-L and 2x-L modells - both of which fit only a few select lenses, quite like the Sigma Apo tcs. They are by no means universal.

Also, I cannot find a problem with limiting the Bigma's zoom range, when a tc is used. A tc should be used to increase the max. focal length. not to convert a 50mm lens to a 70mm or 100mm one. The Bigma already has a big zoom ratio of 1:10 and that affporeds some quality compromises. I would think, that on the short end, adding a tc, will show clearly in the resulting images.

Ben
04-20-2010, 04:42 AM   #12
Pentaxian
Mike.P's Avatar

Join Date: Mar 2008
Location: South Coast .. UK
Photos: Gallery
Posts: 1,734
QuoteOriginally posted by Ben_Edict Quote
The best Pentax tcs - may be, even the best tcs of all makes are the two Pentax A 1.4x-L and 2x-L modells - both of which fit only a few select lenses, quite like the Sigma Apo tcs.
Hmm, I have both these for my A* 300mm f2.8 .. wonder if they will fit my Bigma with the lock on.
04-20-2010, 11:19 AM   #13
Forum Member




Join Date: Dec 2008
Location: West Sussex, UK
Posts: 62
QuoteOriginally posted by Mike.P Quote
Hmm, I have both these for my A* 300mm f2.8 .. wonder if they will fit my Bigma with the lock on.
I would expect so, the rear element is recessed more than half an inch at 100mm.
04-20-2010, 11:21 AM   #14
Pentaxian
Lowell Goudge's Avatar

Join Date: Jan 2007
Location: Toronto
Photos: Gallery | Albums
Posts: 15,314
QuoteOriginally posted by Mike.P Quote
Hmm, I have both these for my A* 300mm f2.8 .. wonder if they will fit my Bigma with the lock on.
I don't think so, the sigma TC extends about 12 mm forward, the pentax I believe about 30 mm
05-29-2010, 07:26 PM   #15
Pentaxian
littledrawe's Avatar

Join Date: Jan 2010
Location: Red Rock
Photos: Gallery | Albums
Posts: 2,434
Other lenses

Do the sigma teleconverters work with pentax brand lenses? Are they fully functional with AF or does it need to be switched to MF?
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!
features, hsm, k-mount, lens, motor, pentax lens, sigma, sigma telephoto lens, slr lens, source, teleconverter
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Sigma APO 400mm f5.6 Telephoto Lens that is foggy jack56 Pentax SLR Lens Discussion 6 07-30-2009 11:16 AM
For Sale - Sold: Sigma 135-400mm F4.5-5.6 super telephoto lens with case SouthShoreRob Sold Items 2 07-04-2009 01:21 PM
Sigma telephoto lens with K200D rzarector Troubleshooting and Beginner Help 5 04-15-2009 04:24 PM
Info on 400mm Sigma APO telephoto lens SOldBear Pentax SLR Lens Discussion 7 04-06-2009 09:56 PM
For Sale - Sold: Sigma Zoom Telephoto 100-300mm f/4 EX DG IF AF Lens with 1.4X and 2.0X TCs MikeDubU Sold Items 5 02-23-2009 01:56 AM



All times are GMT -7. The time now is 01:03 AM. | 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