Lens help requested.

So, I'm fairly inexperienced with all of this, though I think I'm getting a fairly basic understanding of how my T1i and my lenses work. I'm going to Prince of Wales Island Alaska next month and I don't want to miss too many opportunities because I don't have the right lens(es). I'm planning on taking most of the lenses that I own, including the 18-55 kit lens, a Tamron 18-270 F35-6.3 VC and a Canon 55-250, though I suppose I could choose one or the other of the longer zooms. I'll also bring a set of cheap extension tubes in the event that I see any cool creatures that require some macro work.

I suppose I'll be OK for most stuff but not for the bears, whales, seals, puffins, etc. that I may see at fairly long distances (I really don't have a clue yet what ranges I'll be looking at but it will almost assuredly be too much for the 250 or 270mm lenses, even after cropping. I considered renting a 100-400L or a 400 plus teleconverter but frankly, I'm not sure I want to go to the expense since I'd probably need it for two weeks and the rentals rates seem through the roof (I know, I know, I don't have the lens that I need and they aren't cheap). To that end, I'm considering purchasing a teleconverter for one of the two zooms that I have but I have almost zero idea whether they'll work well or at all.

I know that the Canon TCs don't support the two lenses that I have. The Tamron would probably work but I'm sure I'll lose autofocus (not a big concern in my mind) and the Tamron specs suggest that their TC is not recommended for anything wider than 90mm. Does this mean that it won't work on my 18-270 or 55-250 or does it simply mean that it won't work at those distances but will work at full zoom?

Any help or insight would be appreciated. I realize that my equipment is serviceable but nowhere near the best but keep in mind that I simply CAN'T go out and spend hundreds or thousands of dollars right now on the "proper equipment" and everybody's got to start somewhere. I'm hoping someone can give me some advice that will give me some considerable potential for better photos while I'm there. Thanks in advance.

I now see that Tamron's 2X autofocus teleconverter is not recommended for lenses wider than 50mm. Does this mean that it would work acceptably on my 55-250? I know that I'd lose autofocus because of the smaller maximum aperture but would the 2X otherwise work and give acceptable results? Opinions appreciated guys, I'm really hoping someone can educate me a bit here.

First, the physical mounting problems:

Canon and Sigma teleconverters are limited to specific lenses because the teleconverter's front element protrudes into the back of the lens. This means that they can damage lenses (and themselves) if their front element contacts the lens's rear element. This can be deceiving, as many lenses will appear to have sufficient space, but have rear elements that move when focusing or zooming.

Tamron and Kenko teleconverters do not have protruding elements, and will therefore work on any Canon EF lenses (but not necessarily EF-S lenses), and all Sigma, Tamron, and Tokina lenses—at least in theory.

The latest Kenko Pro 300 series teleconverters (which I highly recommend) have recessed front elements, and will therefore (in theory) work on all Canon lenses, including EF-S lenses, plus all Sigma, Tamron, and Tokina lenses

Now, the optical problems:

All teleconverters, regardless of brand, are designed for use with telephoto lenses.

Telephoto lenses (70mm and up) are designed so the the image exiting the lens is already close to sensor size. That is, the light exiting the lens does not diverge much. This minimal divergence is taken into account in the design of a teleconverter.

Lenses shorter than 70mm, however, often have highly divergent light exiting the rear element. When this highly divergent light enters a teleconverter, the teleconverter is not quite sure what to do with it. Optical problems often result. These optical problems include some combination of flare, ghosting, vignetting, chromatic aberration, and barrel or pincushion distortion.

For the reasons described above, teleconverters often do not work well with short-focal-length lenses, especially ultra-wide-angle lenses, and especially prime lenses.

All is not lost, however. Many zoom lenses that have telephoto high-zoom ranges have minimal convergence throughout their range and work fine with teleconverters. You just have to try them and find out.

Another related problem:

Many high-quality wide-angle and ultra-wide-angle lenses use design tricks to get the desired short focal lengths. When used with a teleconverter, this short focal length is overridden and these design tricks work against the combined focal length, usually resulting in distortion. There is nothing wrong with either the lens or the teleconverter, just the combination of the two.

I hopes this helps.

I don't want to belittle your financial concerns, but putting a 2x TC on any of those zooms will likely cripple your image quality.

Renting the 100-400 will give your much better image quality. Plus, I have found that the 100-400 used with a 1.4x TC delivers quite acceptable image quality. I've used it with a Canon 2x TC, but the IQ is "iffy".

Here's a shot I took with the 100-400 and the Canon 2xTC at 800mm, uncropped:

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If money is an issue then just live with what you've got. You'd probably be better off with cropping, rather than put a tcon on those lenses.

Thanks for the thoughts and advice, especially 20droger for taking the time for a detailed explanation. I'm still completely uncertain what to do but at least I'm a bit better educated now about what to expect and how they work to a small degree.

OK, if anyone's still watching this thread, let's change the parameters a bit. Assuming I was able to get my hands on an EF 70-200f4/L, what would the recommendation then be? A 2X Kenko pro 300DGX? Would THAT set up give me acceptable or great shots? If not, would the Canon TC do the trick better?

The reason that I'm asking is that my wife just called to tell me about a barely used 70-200 Canon lens but I was in the pool and speaking through an interpreter so I'm not sure that it's the L but I think it is because she claimed that the retail was around $1300. I'm hoping that I could sell my Tamron and Canon 55-250 to make up most of the cost of this lens, if in fact it's what I want.

Again, any help is greatly appreciated. Money's always a concern for me right now since I'm "just a hobbyist" but I'd really like to take that next step forward if possible.

Which leads me to another question. I haven't talked to the individual who's selling this lens yet but I'd love opinions about the difference between the 70-200f/4 L with and without IS. Would the lack of IS be a deal killer to most of you? Would the non-IS lens be fine if used on a tripod all the time? What about handheld, at what shutter speeds would their begin to be a problem and would it be an issue for most nature/wildlife photography?

If retail was $1300 it's most certainly the f4 IS model. I have no direct experience with tcons, but I do know that with a 1.4 tcon you'll retain AF, with a 2x you'll loose AF. It's also generally accepted that 1.4 tcons are preferred over 2x ones for IQ reasons.

crn3371 wrote in post #14584908
If retail was $1300 it's most certainly the f4 IS model. I have no direct experience with tcons, but I do know that with a 1.4 tcon you'll retain AF, with a 2x you'll loose AF. It's also generally accepted that 1.4 tcons are preferred over 2x ones for IQ reasons.

Thanks. I spoke to the woman and it doesn't have IS, apparently there was some miscommunication somewhere. Furthermore, even though it's only very barely used (she claims three shutter releases), she wants retail for it. I recognize that for all intents and purposes it probably is new but for all I know, she could have played football with the lens. I guess the short story is that I won't be buying the lens but I will be keeping my eyes and my options open. I still am curious if the non-IS 70-200L lens would be good for my purposes with a TC or if I'm better off waiting for the 100-400L, the Sigma 150-500 or some other option. Sadly, it's unlikely that those options would happen anytime soon. Thanks for the help everyone.

Can you rent something for your trip and then buy what fits your longer term needs?

duane0524 wrote in post #14585287
Can you rent something for your trip and then buy what fits your longer term needs?

That was my original intention but when I looked, it was several hundred dollars to rent the 100-400L and that was for just one week. Because of the timing of my trip and the likelihood that I couldn't ship the lens back while I was there, I'd have to rent it for two weeks. While I'd love to have some better glass while I'm there, I just can't justify that expense, I'd rather save my money to buy a lens or two and use them on my next trip to Alaska (this is my first trip but I'm very hopeful that it won't be my last).

You can buy a used 70-200 f4 lens on this forum and resell it when you return if you don't like it. That will likely cost you less than renting. It's not much for low light, but other than that, it's a fine lens. If you decide on a TC, then I would recommend the Canon 1.4x. The 2x cuts out another stop of light, and the IQ is noticeably worse.

whuband wrote in post #14585377
You can buy a used 70-200 f4 lens on this forum and resell it when you return if you don't like it. That will likely cost you less than renting. It's not much for low light, but other than that, it's a fine lens. If you decide on a TC, then I would recommend the Canon 1.4x. The 2x cuts out another stop of light, and the IQ is noticeably worse.

Actually not a bad idea. I'd have to find the means to put the money up for the lens for several weeks or a month, even if I DID sell it after the trip but you know how those things go, I'd probably fall in love with it and have to find a way to pay for it.

whuband wrote in post #14585377
You can buy a used 70-200 f4 lens on this forum and resell it when you return if you don't like it. That will likely cost you less than renting. It's not much for low light, but other than that, it's a fine lens. If you decide on a TC, then I would recommend the Canon 1.4x. The 2x cuts out another stop of light, and the IQ is noticeably worse.

I was just going to suggest the same thing, but with a 100-400. The only issue with buying a used one with intention pf resllingit when you return is you may end up keeping it like I did.

It would cost you less then the few hundred to rent, if you are willing to put the effort in.