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11-22-2007, 08:40 AM   #1
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Teleconverter?

I'm wondering what to expect if I were to get a 1.5 or 2x converter for my K100d and lenses. I have a nice Sigma 135-400mm f/4.5-5.6 APO that I can see might benefit from a converter occasionally. In the film SLR days, the rule of thumb I remember is I loose about half the "lens light" through a 2x converter, while my focal length doubles.

Specifically, I am wondering about static bird shots in my backyard. I'd like to be able to fill the frame with the bird. I plan to use a tripod even without the converter. My choices I'd think would be to crop the image using the current lens, or using a converter and not having to crop, but dealing with IQ issues?

What are your thoughts in the IQ, practicality and anything else I've not considered? I know that moving closer to the subject and/or getting a longer/faster lens are also choices, but let's leave them out of the discussion for now.

Thanks.

11-22-2007, 09:25 AM   #2
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95% of all 2x are crap. you get what you pay for. i've never been quite happy with any 2x on a zoom lens. too much glass and IQ loss. the 1.4x and 1.5x are better IMHO but you get what you pay for.
the pentax 1.4,2x-s and 1.4,2x-l are very good(and expensive) i've got a 1.4x-s and it gives great results on my primes. i do notice some IQ loss with it on my A70-210/4. the tamron, mc4 2x i have give acceptable results on my primes but i'd never use it on a zoom. the other 2 TCs i have are for adaptall 2 SP lenses and they were designed for tamron's SP lenses and are great on my 300/2.8 with practically no IQ loss but can not be used except on adaptall2 lenses. i'd suggest a quality 1.4, 1.5x and see how you like it. if you can test a 2x before you buy then i'd do that as well.

happy turkey day!!
11-22-2007, 11:25 AM   #3
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QuoteOriginally posted by Papersniper Quote
I'm wondering what to expect if I were to get a 1.5 or 2x converter for my K100d and lenses. I have a nice Sigma 135-400mm f/4.5-5.6 APO that I can see might benefit from a converter occasionally. In the film SLR days, the rule of thumb I remember is I loose about half the "lens light" through a 2x converter, while my focal length doubles.
As noted in the other thread, 2 is also two stops -- which means 3/4 of the light is lost.
11-23-2007, 01:32 PM   #4
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what you will get is a loss of autofocus.

the pentax cameras can work marginally with a 1.7x TC on f4.5 (they work well at F4.0) a 1.5x TC might be OK but a 2x forget it

11-23-2007, 03:23 PM   #5
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"JUST a little OT"...how do you like YOUR "Li'l Bigma"?

Dear Papersniper:

The PIPE Here again...I don't know if you saw my thread that's here already, at https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/14659-sigma-s-...-my-k100d.html . as I'm considering getting one of the latest versions of the Sigma DG 135-400 zoom telephoto lenses for my AVIATION photography needs sometime in the first half of 2008, for use with my own Pentax K100D...

...I was just wondering...how do you like YOUR own "Li'l Bigma" lens???

I've decided to call the 135-400 lens the "Li'l Bigma" because of its tripod mount making it SOMEWHAT resemble the much longer focal length Sigma 50-500mm telephoto lens, known by some here on the Pentax forum as the "Bigma"...but with the 135-400 being a bit "smaller", it gets the "Li'l Bigma" nickname.

I KNOW it's a small bit off topic, where you're looking for a teleconverter to use with your Li'l Bigma...by the way, the one teleconverter I've heard about in this forum being recommended for "general" use with Pentax DSLRs would be the Tamron 1.4x autofocus capable TC for the Pentax mount...but where I'm looking for user opinions on the "Li'l Bigma", particularly where you ARE apparently using it on the same Pentax DSLR as I've got already...generally, how do you like it, and what are your views on it. You could answer on this thread if you'd like, or please feel free to post your opinion up at the thread I started, that's the first link in this reply...hope to hear from you on either forum thread when you've got the time!

Yours Sincerely,

The PIPE...!
11-23-2007, 09:01 PM   #6
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Like some folks said you'll be losing a lot of light w/2x and you won't have AF. Sigma's own website states that TC with that lens doesn't have AF ; only the f/2.8 telephotos maintain AF with the 2x.
Sigma - Lenses - Teleconverters
(i'm guessing Sigma discontinued that lens as it's not on that table anymore like it used to be a few months ago, but you can see that even f/3.5 lenses don't maintain AF with the 2x)

The next thing is assuming you'll be using the quality Sigma TCs, in simple terms with the 2x, yes, your lens would be a 270 - 800mm, but also realize it will act as a f/9 - f/11+ lens in the amount of light it'll be letting through to the sensor. [!] Odds of you getting sharp pix @ 800mm is very questionable; cherish any you get IMO! From my experience, it was a lesson in futility even trying to use the 300mm f/2.8 + 2X TC + polarizing filter to shoot around a pond (that combo is about a 4 stop loss of light, making it act as a f/11+ lens) ... I'll never use the poli filter with the 2x TC again!!! Stick with only the 1.4X TC if you're going to use anything with your lens. The Sigma 1.4X TC is really excellent and not too much $.

edit! Pardon, a bit of a mistake on my part. I see that the 1.4x doesn't allow you AF either... it seems from this page Sigma doesn't even say your lens and its 1.4x TC are compatible... hence, the "--" in the matrix in this table: Sigma - Lenses - Lens Chart of Recently Discontinued Lenses .

Last edited by m8o; 11-23-2007 at 09:13 PM.
11-24-2007, 06:40 AM   #7
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Thanks for the good info on the TCs. I had not thought of losing AF, that is something to consider. I figured the loss of light was an issue also. Well, I may still get a "low powered" TC to use occasionally, with the tripod and with lots of light I might be okay. Since these pictures would be taken at home, at least I don't have to worry about hauling around a lot of gear! <g>
11-24-2007, 06:50 AM   #8
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QuoteOriginally posted by The PIPE Quote
Dear Papersniper:

.........................

...I was just wondering...how do you like YOUR own "Li'l Bigma" lens???

...................
............but where I'm looking for user opinions on the "Li'l Bigma", particularly where you ARE apparently using it on the same Pentax DSLR as I've got already...generally, how do you like it, and what are your views on it. ......


I've not had my Sigma 135-400 zoom long enough to be able to tell you much, but I will say what I can.

It is heavy enough that I think I'll only want to use it with a tripod or other support. It does have the tripod mount on it as you say.
The AF feature of the lens works smoothly enough that I can't tell much difference between it and the other 2 AF lenses I have. But I have only had the camera for a few weeks and the lens for a week! I've been recovering from some minor surgery and not had much time to play with the gear.

Since you mention aviation shots, while you be taking "action" shots, or just shots of the aircraft on the ground? Personally I don't plan to use that lens taking photos of birds in flight or aircraft in flight for that matter, but that's just my assumption at this time; I have not gotten out in "the world" to play with it yet!

So, listen little to me and much to others and you will certainly get good information!

11-24-2007, 07:37 AM   #9
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kenko 1.5x

Timely thread, I just used my kenko 1.5x and smc a70-210 (my 300mm was home ) for this one, they are handy to have for emergency taken at f5.6 on the lens
11-24-2007, 08:41 AM   #10
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Thanks for taking the time to post that, Tom. Looks darned good! I thought it initially was a red tailed hawk, but I'm not so sure now. It's not an eagle, is it?
11-24-2007, 10:58 AM   #11
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That's a "young" bald eagle, it takes 4 years (i've read) before they get their yellow beak/eyes and white head.
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