Teleconverter advice

Hopefully a quick query...

I'm thinking of purchasing a teleconverter for my airshow trips but how will they affect the images? For example with my K20 I normally use centre weighted metering and between +5/+1 EV and for propeller aircraft an ISO of 100 and a shutter speed of 1/350 or 1/500. For jets the ISO is 400 and shutter speed of 1/1000 The mode is always on TV.

Can someone explain to me that if I was to use a 2x TC then if I loose 2 stops of light how would I change the settings described above to obtain a correctly exposed image? Likewise if a 1.4x or 1.7x TC was used what would be the expected effect and how would I rectify this? I would probably be using a TC combined with a DA*300mm or a zoom lens up to 300mm.



Regards

Rob

To be honest it's mainly trial and error getting the exposure right as each TC seems the have a different effect. I have to dial in -1 when I use the Sigma 1.4x or 2x EX converters on the 70-200mm f2.8 but only - .5 when I use the Tamron 1.4x on the Pentax F* 300mm f4.5.

That's about all I do .. when you have done it once the settings you use rarely change.

Not sure if you would even have to do anything with the Pentax 1.7x as its more compatible than the other makes.

I have the Kenko 1.5 and it seems to over expose so I dial in -2 on av on the 18-250 lens and -1 on the tamron 70-300 as Mike says it's mainly trial and error getting the exposure right but once set it seems to be OK.

Have a look at 'jackitec's' images in the gallery on Pentax PU website, as stated he uses the Kenko teleconverter and his images speak for themselves.

How come that the camera exposue so differently with teleconverters, I thought the camera meters through the lens so it shouldn't matter how many filters you use, extension tubes or teleconverters.

No idea but a friends D90, 300mm f4 and 1.4x TC doesn't have the same problem as my Pentax.

Not a great problem but a bit annoying.

Perhaps the same issue with stop down metering and M series lenses. Why is it OK wide open, over exposed in the mid range and back to OK shut right down? And why is OK on my K 135 f/2.5 but a stop out with the Tammy? I am just glad with digital that one can check on the spot, with film I would be getting fed up.

Anyway, I think we have not answered the OP. I think the OP asked, how much will the TC impact on exposure (i.e. two stops would make 1/500 -> 1/125) rather than how bad is the error from the TTL metering... or I may be wrong!

Correct Kris! Although Mike-P and jackitec have provided some of the answers I was after thanks to you all for your advice.

Hi Rob

May I ask, do you use AF when you are shooting the subjects in flight or otherwise? Or you mostly use MF?
The only reason I ask is if you are planning to use mostly AF and specifically with the DA*300 (my experience limits to this one only with the Pentax AF 1.7TC, so i am strictly speaking about this lens), I would suggest you to do a bit more research work, practically I mean.

If you are going to rely mostly on AF using this lens I would really suggest you to try your hands on this combination so that you dont get disappointed. Its a superb combination but its way different if you are using the DA*300 alone on its own compared to the TC combination when it comes to focusing.

It does require nudging to close focus and then it hunts and locks, but its not always that it happens also. Many times I have reverted to manually moving the focus ring of the DA*300 (setting on AF.S on my K20) as the shutter wouldn't fire and while keeping the index finger pressed I have to still keep moving the focus and then it suddenly releases. So that quick ability to just nudge and then let the TC do the final job is not always there, nor it is perfect.

Having said all that I have to reiterate that this TC is superb and I am over the moon with it, both quality wise and in the way it performs. But I mainly shoot birds and have used it for macro only, never tried flying aircraft.

Mike, you got to give it a spin so that you can have a more indepth input about this, with your experience you are a great candidate to try it and give a more technical view on it. And if I remember you got an arsenal of MF lenses that you could test it on .
I just use it for extra distance as my lenses are all AF, so drop me a line when you are ready and we can swap the TCs and give them a go when its convenient for you.

Regards

Amin

Amin.
Ready when you are.. I tried my converter this morning on the DA* 16-50mm that I just bought and SDM works fine.

You mean SDM function with the TC attached or just normal AF? And which TC is that?

Am dropping you a PM
Thanks
Amin

SDM with the TC attached works fine with the Tamron 1.4x
The Sigmas will not fit the lens.

Mike, the term SDM sounds magic, truly, after experiencing that silent and fast focusing mechanism one really learns to appreciate it.
keen now in wantint to give it a spin.

I don't know about anyone else,but I find converters /adapters work best on Prime lenses!.....on zooms I think the image quality is effected for the worse!......only my opinion mind!

TRUE!

Teleconverters are not designed for zoom lenses which are optically compromised anyway. I have tried a few over the years and the results have always been very disappointing and that was on primes.

I have one TC, a Pentax SMC-A 645 2X, other than the loss of speed you wouldn't know it was there but you would expect that from one that retailed at £500 wouldn't you?