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10-04-2015, 01:41 PM   #1
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Teleconverter for sigma 70-300mm to k100d

I've recently bought a Tamron MC 2x Teleconverter for my K100D ($15 - I hope I wasn't ripped off), and I want to use it to take pictures of the moon and some wildlife. I have a Sigma DG 70-300mm that I'd like to use with the teleconverter.

Now the problem is that I don't really know how the teleconverter will work with the lens. Will I have to mount it to the lens first? To the body first? Does the aperture setting matter when I'm mounting it? It doesn't have an actual ring, just the setting for adjusting electronically.

I do know that there are no electronic components to the teleconverter, so I'll have to focus and set the aperture manually. But is that all I need to know?

Any help is greatly appreciated! Hopefully I can get those moon pictures where I can actually see some craters!

Joseph

10-04-2015, 01:56 PM   #2
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Does the Sigma have an aperture ring? If not you will be stuck using the minimum aperture. The TC also adds 2 stops to that...

As for wildlife, forget about it. A manual TC with an AF lens just isn't worth trying.
10-04-2015, 02:02 PM - 1 Like   #3
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A few points about tele-converters:
1) A 1.4x TC costs you one stop. A 2x TC costs you two stops. So your 70-300 which I think is f/4-5.6 would end up being a f/11 lens with a 2x TC
2) $15 for a TC is not a rip-off However, consider that a good TC costs $200 - $250 and the Pentax one is over $450 so I would not expect too much
3) Using a TC with a slow consumer lens like the 70-300 can be a challenge. They are designed to work with fast prime lenses and work best with those.
4) As to mounting it makes no difference. I usually mount the TC on the lens first but it does not matter
5) You say the 70-300 has no aperture ring if I understood you correctly. If so this is an additional challenge as there is no way to control the aperture and it will always shoot at smallest aperture. That might be OK for your purpose but it limits what you can do
6) Since there are no electronics in the TC you will need to set the focal length, focus manually and use stop down metering

Bottom line, it is not impossible to use this for your purpose but you have a lot of hurdles to overcome.

Read through this it might help: https://www.pentaxforums.com/forums/58-troubleshooting-beginner-help/110658-u...x-dslrs-f.html Both the links and the video have important info.
10-04-2015, 02:04 PM   #4
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It does have an aperture ring. I think when I set it to A the camera will adjust it electronically with the dial, or otherwise I could use the ring itself. I'll have to use the ring to set it with the teleconverter. Does that change the way I need to mount it?

10-04-2015, 02:07 PM   #5
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QuoteOriginally posted by joseph_me Quote
It does have an aperture ring. I think when I set it to A the camera will adjust it electronically with the dial, or otherwise I could use the ring itself. I'll have to use the ring to set it with the teleconverter. Does that change the way I need to mount it?
Makes no difference in how you mount it. But you do need to use the ring with the TC mounted.
10-04-2015, 02:17 PM   #6
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Thanks boriscleto and jatrax for your help! I think I have an idea as to what I need to do.

That raises another question though: the 2x TC will cost me 2 stops, so f/4-5.6 becomes f/8-11? Does that actually change the way the aperture ring moves or is it just blocking some light?

Sorry for the dumb questions, and thanks for your insight!
10-04-2015, 02:29 PM   #7
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Just double the F-stop ..

F4.5 becomes F9 , and so forth ..

Does the Teleconverter have the electrical contact for Aperture ? If not then its a fully manual converter and that is how you need to run things , Manual .
10-04-2015, 02:55 PM   #8
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QuoteOriginally posted by joseph_me Quote
Does that actually change the way the aperture ring moves or is it just blocking some light?
Just blocks more light. So if you set the ring at f/5.6 the amount of light actually reaching the sensor is what you would see at f/11 without the TC. Note this continues with each setting and the f/5.6 number is only "wide open". If you set the aperture ring to f/8 then the light passed will be as if you were at f/16. But you need to use stop down metering so the camera will read the light passing through when you do that.

10-04-2015, 03:17 PM   #9
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Ahh I see, everything now makes sense. Thanks everyone for your help. I'll post some pictures of the moon if I get a clear night tonight
10-04-2015, 04:30 PM   #10
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I feel its only fair to warn you that the results from marrying a 2x tc to a slow consumer zoom typically disappoint.

Some more info:

Teleconverters (Multipliers) - how well do they work?

PhotograFun (click Tips 'n Tricks - teleconverters)

edit PS I have written several reviews for 400mm lenses, and posted pics in the 300mm plus lens club. IQ of the best 400mm vintage MF lenses (and bear in mind you are unlikely to get AF working with 70-300mm + 2x tc) will certainly be better than the tc combo.

And an interesting look at stacked tc's showing that although the iq deteriorates the combos are pulling through more info.

http://forum.mflenses.com/fun-with-teleconverters-t72307.html

Last edited by marcusBMG; 10-06-2015 at 01:32 PM.
10-04-2015, 05:52 PM   #11
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QuoteOriginally posted by marcusBMG Quote
I feel its only fair to warn you that the results from marrying a 2x tc to a slow consumer zoom typically disappoint.
This. You'll probably get better results at 300mm stopped down a little bit, than with a TC.

Or get a cheap 300mm or 400mm prime - that will probably be even better.

Adam
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10-05-2015, 01:56 AM   #12
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I have an older Pentax-mount Sigma 5-element 1.4x AF teleconverter mated to Tamron's earliest AF 70-300 lens (58mm filter threads). These both came out at least around the time of the PZ series, if not earlier, and were made in Japan.

I still use this set up today to shoot wildlife with a K200d. The autofocus is slow, but works reasonably well in most situations.

Tamron also used to make a 5-element 1.4x teleconverter for Pentax AF, but it was discontinued a long time ago.
10-05-2015, 06:38 AM   #13
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QuoteOriginally posted by bobore Quote
Pentax-mount Sigma 5-element 1.4x AF teleconverter mated to Tamron's earliest AF 70-300 lens
Yes this works better, only one stop lost, less image degradation.. but 1.4x is only a small jump. I have drifted away from using my adaptall 1.4x because between the gain in mag versus slight loss of IQ and greater difficulty of nailing focus, avoiding shake the gains at best tend to be marginal, even though I have good lenses to use it with: 300mm f2.8 for example.

You know what: you're way better off upgrading from the 6MPx K100 to eg a 12Mpx K-X or K-r. Or try a cheap mirrorless like a s/h lumix G1: 12MPx AND 2x crop factor (as a general suggestion - limited utility with KAF mount lens w/o aperture ring). This first gen M4/3 camera was a great success when it came out meaning there are lots on the s/h market and it is easily acquired off ebay for around a hundred bucks. More MPx, higher crop factor: it's all more magnification in the end technically incorrect, cropping is not magnification, I should say it's all a bigger picture of your subject at the end.

Last edited by marcusBMG; 10-05-2015 at 07:03 AM.
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