I own a Sony 100a and have Sigma lenses a 17-70 and a 70-300.
I am very pleased with the pictures I get from my set up. I would like however to be able to do a bit of wildlife work and find that even with the 300 I can't get anything that is worth while. My friend who has an Olympus set up has recently bought a teleconverter which gives him a decent range, although not seen any of the results yet. I am thinking of getting a teleconverter for myself, has anyone got one? if so which size and are they any good?
I don't have a lot of money to invest but think this might be the best way forward without breaking the bank, any advice would be welcome.
T/Cs vs f/4 lenses ... buzz! Nope.
Buy enlarge (I know, I know ... very punny) ... hey, it's that time of year.
Anyway, I have a 1.4x and a 2x teleconverter (T/C). The main problem with these devices and low-cost lensing is that a teleconverter takes out a certain amount of light for the extension.
1.4x T/C = 1 full stop of light (making a basic f/4 lens seem like a f/5.6 lens to your camera.
2x = 2 full stops of light (making a basic f/4 lens seem like a f/8 lens to your camera) The problem here is that your camera's autofocus(AF) becomes intermittant or non-functional around f/8.
And the good Lord help ya, if you are also using a Circular Polarizer (CP) on the front of your lens (that's another full f-stop of light lost).
Your 70-300mm is a guaranteed f/4 lens at 70mm ... so adding the 2x T/C to the lens is really is gambling on your camera's AF-response as you zoom. You "automagically" pass f/4 and darken with the variable aperture of the lens, as you "zoom in", going toward 300mm. You may even notice that your autofocus just stops working around 100mm+. It drifts back and forth, right past the focal point ... unable to stop.
"Oh heavens, what's wrong with this darn thing?" you ask, of course, forgetting that you placed the teleconverter in between your lens and the body.
If you want to talk about "missing the shot" in a natural setting, this is probably the perfect way to do so, as you struggle to throw the MF/AF switch on your lens collar to the "MF" setting, to try and manually focus on Mr. Chipmunk, who's bobbing and weaving to see what the heck you're doing, over there.
I mean, of course, Mr. Chipmunk has to look up to see what the heck all the noise is from with all your foolin' around and, in due course, takes off for the hills.
Hmmm, a 2x T/C, huh? Best try forgetting this idea, altogether, with that particular lens. Even the 1.4x T/C, which only robs you of 1 stupid f-stop of light may cause AF to fail somewhere between 180-300mm.
You said you wanted to shoot long, right? Let it be known that the 70-300mm f/4-5.6 lens does not lend itself to any kind of extension. You either need a longer lens, by design
- TAMRON SP AF 200-500 f/5-6.3 Di LD
- Tokina AT-X 840 80-400mm f/4.5-5.6 AF
or even a
- SIGMA AF 135-400mm f/4.5-5.6 DG
- SIGMA AF 170-500mm f/5-6.3 DG
Nope, there is no "or" ... that's the real solution. Sorry ... you're on "manual focus" for the long shot with a 2x T/C + 70-300mm f/4-5.6 combo.
Now, if someone out there made a 70-300mm f/2.8 ... then ... oh yes, then the T/C could be a reasonable solution. It would be slow as "molasses in January" to autofocus, because T/Cs also slow down AF to a crawl. If you thought the 70-300 was slow as it is ... that T/C will give you a whole new paradigm. You'll start thinking your batteries are failing or dying ... but, when you peek at the battery indicator, it'll say "FULL."
Anyway, just so you don't think I'm making all this bad news up, JDH ... here's YOUR tool suggestion, in the flesh, so to speak:
A rather useless AF
tool, at that ...
SONY α100 + Bower 2x T/C + TAMRON AF 70-300mm f/4-5.6 LD
effectively (in 35mm-film terms) a 210-900mm f/8-f/11 Manual-focus monster
I sincerely hope this response answers your question.
Last edited by DonSchap; 12-27-2007 at 09:23 PM.
- BFA, Digital Photography
A Photographer Is Forever
Look, I did not create the optical laws of the Universe ... I simply learned to deal with them.
Remember: It is usually the GLASS, not the camera (except for moving to Full Frame), that gives you the most improvement in your photography.
70-300 =105-450 +2x Would Be 210-900
Last edited by SONYNUT; 12-29-2007 at 04:47 PM.