Tele-converters???


Ralphpiano

Link Posted 19/03/2013 - 16:36
Hi Folks,

I'd like a little (simple) explanation about tele-converters please. I have a 400mm Sigma APO MC and would like to enhance it's capabilities, what can I expect from a tele-converter, is there a sacrifice in IQ, what's the difference between say a sigma x2 and a old pentax x2???

I would appreciate any help the forum can give.

Kindest Regards
Jason

johnriley

Link Posted 19/03/2013 - 17:02
Think of the teleconverter as being a magnifying glass, in which case x2 makes perfect sense. 400mm becomes 800mm. However, there is a two stop light loss, so f/5.6 would become f/11, so camera shake may be a problem. Then we are magnifying the faults in a lens, so quality will suffer to some degree.

Having said that, a x2 converter will convert 50mm f/2 very nicely to 100mm f/4 and as the minmum focus stays the same, suddenly we have a makeshift macro lens.

So there is a place for them, but they need to be the highest quality possible. A 1.4x converter, losing only one stop of light, would be my first choice.
Best regards, John

Mike-P

Link Posted 19/03/2013 - 17:12
Also the newer Sigma converters have a protruding front element and only fit their fastest lenses whereas I believe the Pentax will fit any lens.

Personally I wouldn't use a converter on anything slower than F4 as in less than perfect conditions it would seriously degrade the image ... you would be better off cropping harder.
No equipment list here but thanks for taking an interest. My Flickr

Ralphpiano

Link Posted 19/03/2013 - 17:16
Thanks for the tips. I find that my 400mm is sharper around f11 but would that be bumped up as well, would I be looking at f22 to get same level of sharpness?

I've only seen a Sigma 1.4x converter, are there other ones that a more reasonably priced?

Mike-P

Link Posted 19/03/2013 - 17:23
Ralphpiano wrote:
Thanks for the tips. I find that my 400mm is sharper around f11 but would that be bumped up as well, would I be looking at f22 to get same level of sharpness?

I've only seen a Sigma 1.4x converter, are there other ones that a more reasonably priced?

With a 1.4x I would think around f16 and a 2x f22 ... I would imagine that's nigh on impossible to get a reasonable shutter speed. Not sure how you would get on with AF though.

SRS have a Tamron 1.4x for 109 which should work as your lens is screw drive. Resist the urge to buy the 2x .. it will be manual focus only and you will be wasting your money (imo)
No equipment list here but thanks for taking an interest. My Flickr

Ralphpiano

Link Posted 19/03/2013 - 17:28
My lens is so old it's manual focus already, no AF on it. I'll take your combined advice and have a look out for a 1.4 x converter or maybe stay away altogether and dream of a 150-500mm lens

Algernon

Link Posted 19/03/2013 - 17:32
That Sigma 400mm isn't that hot to begin with so a
converter isn't really feasible.

You would be better buying something like a
Sigma 150-500mm and using it with or without
a TC.

-
Half Man... Half Pentax ... Half Cucumber

Pentax K-1 + K-5 and some other stuff

Algi

Ralphpiano

Link Posted 19/03/2013 - 17:43
I'm sure it does fall into catagory "not that hot" when compared to other lenses, but I've been impressed with it, I did a sharpness test with a box of swan vestas and was blown away how sharp it was at 4 metres. And then I went out and about with it and caught a smashing shot of a Red Kite. What do you think of the IQ after looking a these pics?





Algernon

Link Posted 19/03/2013 - 18:26
The bird looks sharp enough, but there isn't really any
fine detail on the match box to indicate how sharp it
is.

Quite a few people on here have had the same lens and
it hasn't shown much promise, also a TC on a 400mm lens
is very difficult to hold steady. If your happy with the
results just use it as it is and crop slightly.

-
Half Man... Half Pentax ... Half Cucumber

Pentax K-1 + K-5 and some other stuff

Algi
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