[Stone G.]

My motivation for using a teleconverter is almost always to get a larger image of a subject that's too far away. Therefore the test that applies to me is if the cropped photo without TC is as good or better than with TC.

+1

One area, where I find TCs useful is astrophotography, in particular lunar and solar photography with longer telephoto lenses: The lens outresolves the sensor and cropping to get the "last, minute detail" is not an option.

Another, more subtle, is certain, mostly hand-held, macro work: An extension tube - without disturbing extra glass elements - may appear better and will often be so, but in certain situations I appreciate that the TC retains a comfortable working distance + better lightning conditions, with or without flash.

[demp10]

This is all very interesting for people who print images. All of mine are displayed digitally, either on websites, in digital photo frames, or via the screensaver on my 40" TV.

So you are limited to about 2 MPixels for output (1920x1080) at best. Interesting.

BTW the little bird reference was an analogy. I could have used a plastic one that will stay put.

[pacerr]

One issue often overlooked is exposure accuracy. If you . . . crop in PP to accomplish the same FOV, the metering will have been done on the full image possibly leading to different exposure results.

Certainly true -- and I'd note that once again we come full circle to the fact that automation and kit don't replace practical knowledge of how one's equipment works. In practice, many variables besides optical qualities affect the intrinsic "value" of an image.

Whether a TC serves as 'training wheels' for exploring tele-photography, a momentary MacGyver-it lens solution, or simply the best long FL kit one can afford, the resulting image should be judged on its own merits, not in comparison with an alternative that wasn't available.

H2

Someday I'd like to sculpt (in the field!) a close-up lens from clear ice and use a piece of white birch bark and a torch for a fill-light reflector to capture a once-in-a-lifetime 'macro' shot. And then watch the forums declare that it would have been oh, so much better if I'd just lugged the "right" lens and lighting kit through the blizzard.

[thoughton]

BTW the little bird reference was an analogy. I could have used a plastic one that will stay put.

That's hardly the "real world" test you were banging on about earlier.

[newmikey]

Whether a TC serves as 'training wheels' for exploring tele-photography, a momentary MacGyver-it lens solution, or simply the best long FL kit one can afford, the resulting images should be judged on its own merits, not in comparison with an alternative that wasn't available.

Whisper words of wisdom, let it be....

You nailed it.

[ripit]

Pixel peeping and tests to see if there is a measurable difference aside, I think this thread shows one thing. Teleconverters don't deserve the blanket bad reputation for severe image degradation they seem to have. Under the right circumstances and or with the right combination with a lens, they are usable tools that can yield good results. As with any optics, cheap glass is not going to produce results like good glass and good glass is often the very expensive ones, not the cheap 4 element variety you find on ebay for 5$ used. I have a lot more experience with front mount tele and wide converters from my days of using fixed lens cameras. They likewise get the same bad rap. Front mount converters always degrade the image significantly and will not yield good results. The statement about adding glass always degrades the image is often brought up. Perhaps its true, but the question is how much will it degrade it and is it a significant amount? I have front mount converters ranging from the worst made to one that originally sold for 600$. The better ones are perfectly usable and can produce very good results. Is there image degradation from the good ones? Probably. Is it enough to matter? I don't think so and people that have used them don't seem to think so either.

There is one issue that was touched on here but I think it might be a much bigger issue than some may think. With front mount converters they are an afocal lens design so they will basically work with any lens by just mounting it in the front, right? That not always true. I have an old canon 3x teleconverter (9 elements, long tube as heavy as a brick, its own focus, not your typical teleconverter). It likes to be mounted about 3 inches away from the front of the camera. If you don't image quality suffers a lot.
While it has been touched on a bit here, I think likewise, compatibility issues may be responsible for a lot of the bad rap teleconverters get. Matched ones are said to work better, but I am getting the impression, they are all matched to a certain configuration lens. Even the generic unmatched ones are matched to a particular configuration, and will work with a general range of lenses, but the further you get from that ideal lens for that particular teleconverter, the worse the results are going to be. My experience with slr teleconverters is quite limited. The only longer term experience I have is with a couple of older quantaray auto focus 2x pk converters. They always seemed to work fine with longer lenses. There was some image degradation but it was usable. I have recently learned that they do not work as well with shorter lenses and in fact will not work at all with some (won't focus to infinity). I now have several recently purchased teleconverters (many have had little or no use yet), but I am quickly learning, how well they perform can be drastically changed by what lens they are attached to, and it doesn't seem to correlate with the the quality of the lens.

Is it possible that a lot of the bad rap slr teleconverters get is from the teleconverter not being well matched to the lens? Is it possible that the average teleconverter is only going to perform its best with a few certain lenses, weather it was intended to be a matched teleconverter or not? If nothing else, perhaps they will only work to the best of their potential with a particular focal length? Again, I have little experience with slr teleconverters so this is just a theory based on recent experience and what others have said.

[Kerrowdown]

Are teleconverters worth using?

Yes they are, when you need the extra reach and they don't take a up much space in the bag.

Downside, you may lose a stop or two.

[Lowell Goudge]

So you are limited to about 2 MPixels for output (1920x1080) at best. Interesting.

or he pixel peeps and looks at the image mapped pixel to pixel

BTW the little bird reference was an analogy. I could have used a plastic one that will stay put.

actually they need to be stuffed real birds, plastic lacks the fine detail of feathers necessary to really judge sharpness

[Lowell Goudge]

Is it possible that a lot of the bad rap slr teleconverters get is from the teleconverter not being well matched to the lens? Is it possible that the average teleconverter is only going to perform its best with a few certain lenses, weather it was intended to be a matched teleconverter or not? If nothing else, perhaps they will only work to the best of their potential with a particular focal length? Again, I have little experience with slr teleconverters so this is just a theory based on recent experience and what others have said.

With the sigma TCs and the pentax rear converter that protrude into the rear of the lens, this is certainly true, the TCs were developed to be used exclusively with a few select fast and long primes and zooms. these TCs work well but don't even fit on most lenses.

as an all round TC, the pentax AF converter si quite good, but it should be at its current price. There are a couple of "matched multipliers" as well that are very good on the lenses they were designed for. The rest, test and be satisfied they work on the lens you plan to use them on, and even then, use them only when you don't have the needed focal length at hand

[pacerr]

Downside, you may lose a stop or two.

Yeah, but if you're usin' a TC it's probably because the financial alternative would have been an econ consumer zoom at f 8 or bloated ISO to get comparable IQ anyway -- or a serious crop from a lens shorter by 50%. So is it actually a con, or just the price of a longer FL set-up?

And I've no doubt that some of the bad-mouthin' of TCs comes from folks that simply don't understand, and/or fail to compensate for, the significantly increased motion blur that accompanies longer focal length lenses. That and the misguided attempt to use TCs at infinity and expect that inherent limits and faults won't be enlarged accordingly.

Motion blur from one source or another accounts for the great majority of my unsatisfactory long FL shots even though I'm careful to double-down on stability when usin' tele modes.

Smoke 'em if ya got 'em but collect the butts when you're done.

H2

[ripit]

With the sigma TCs and the pentax rear converter that protrude into the rear of the lens, this is certainly true, the TCs were developed to be used exclusively with a few select fast and long primes and zooms. these TCs work well but don't even fit on most lenses.

as an all round TC, the pentax AF converter si quite good, but it should be at its current price. There are a couple of "matched multipliers" as well that are very good on the lenses they were designed for. The rest, test and be satisfied they work on the lens you plan to use them on, and even then, use them only when you don't have the needed focal length at hand

I didn't really want to post too far off topic, but my interest is in making canon fd to pk and minolta md to pk adapters, with better glass than the Chinese ones. In theory, it should work, but it may be a matter of having an assortment of adapters, each with corresponding lenses they work well with (didn't know about the compatibility issues when I started). Of course the cost of good teleconverters, and not wanting to chop up expensive glass is the major obstacle. I'm just experimenting with cheap ones right now. I'm kind of wondering if going to 7 element converters might help. I have completed one such canon fd to pk adapter. The results are not the best, but there are several reasons that may explain that (I don't even know where I got that teleconverter for sure, it may have been a fungus lens). It does work...

[Lowell Goudge]

Yeah, but if you're usin' a TC it's probably because the financial alternative would have been an econ consumer zoom at f 8 or bloated ISO to get comparable IQ anyway -- or a serious crop from a lens shorter by 50%. So is it actually a con, or just the price of a longer FL set-up?

this is really just the price of a higher FL set up in my opinion.

And I've no doubt that some of the bad-mouthin' of TCs comes from folks that simply don't understand, and/or fail to compensate for, the significantly increased motion blur that accompanies longer focal length lenses. That and the misguided attempt to use TCs at infinity and expect that inherent limits and faults won't be enlarged accordingly.

Motion blur from one source or another accounts for the great majority of my unsatisfactory long FL shots even though I'm careful to double-down on stability when usin' tele modes.

this is why I came back to this point several times. when considering a TC, you need to consider what you get, relitive to a lens at the new FL, of equal speed to the lens you used with the TC inthe first place.

My Sigma 70-200f2.8 with the addition of a sigma 2x TC for a couple hundred, far exceeds what you can get to cover even 400mm on its own with equal quality at f5.6 for the same price and is a whole lot cheaper smaller and lighter than an equal IQ 400F5.6

I am playing now with a tamron 200-500F5.6 manual focus zoom, that weighs almost 3 kilos, and is clearly tripod bound. I need a little more time to determine if it is better than my sigma with TC or my K300/4 and 1.7x AF TC,

for me it is an intermediate play with serious size and weight glass. I may, read the word may carefully, look at the new proposed pentax 560mm F5.6 but that will only add to my current long lenses, not replace them

[RioRico]

Pixel peeping and tests to see if there is a measurable difference aside, I think this thread shows one thing. Teleconverters don't deserve the blanket bad reputation for severe image degradation they seem to have. Under the right circumstances and or with the right combination with a lens, they are usable tools that can yield good results. As with any optics, cheap glass is not going to produce results like good glass and good glass is often the very expensive ones, not the cheap 4 element variety you find on ebay for 5$ used. I have a lot more experience with front mount tele and wide converters from my days of using fixed lens cameras. They likewise get the same bad rap. Front mount converters always degrade the image significantly and will not yield good results. The statement about adding glass always degrades the image is often brought up. Perhaps its true, but the question is how much will it degrade it and is it a significant amount? I have front mount converters ranging from the worst made to one that originally sold for 600$. The better ones are perfectly usable and can produce very good results. Is there image degradation from the good ones? Probably. Is it enough to matter? I don't think so and people that have used them don't seem to think so either.

I think we have a consensus that 1) cheap glass ain't great, and 2) 2x and 3x TCs are significantly worse than 1.4x-1.7x TCs, whether front- or rear-mounted. Front-mounted TCs don't eat light as do the rear-mounted sort, but they do impact contrast and sharpness a bit, maybe even a little more than non-expensive rear-mounted TCs. But sharpness and contrast can be fixed somewhat in PP. What, me worry?

I use a front-mounted 1.5x Sony VCL-1546A to good effect on a Fast Fifty for ultra-thin-DOF portraits but I'm not expecting edge-to-edge flatfield sharpness there. Alas, my only rear-mounted tele TCs are 2x so I can't adequately test IQ vs the Sony. I *do* know that all the front-mounted wide converters I've used show more aberrations and edge-effects than front-mounted tele converters.

Besides tele-TCs are also front- and rear-mounted variable-macro TCs. I have a couple, both labeled Paragon. They're fun but not ultra-sharp. Ratz.

I *will* echo a point made earlier: The IQ degradation may not matter. If an image DEPENDS on the absolute best IQ, then we want the cleanest optics possible. If content trumps quality, then even cheap TCs can be very useful. But because of the light-eating properties of rear-mounted TCs, they're still best on good fast lenses.

[pacerr]

. . . but my interest is in making canon fd to pk and minolta md to pk adapters,

I haven't given this much thought myself but I have converted both Oly and Minolta lenses for PK use by simply accepting the longer flange distance as an extension ring effect and using them for close-ups only. Too lazy to shave the coupl'a mm's from the mount base. I'd note that transplanting cannibalizing lens mounts and caps to extension rings, bellows and short sections of PVC tubing makes 'hermaphrodite' adapters easy.

The rear element in many of the cheaper TC's you might scavenge for such a project are assembled with threaded sleeves. I DO know that a miss-adjusted or loose TC element can have quite an effect on focus but I've not attempted to intentionally re-calibrate a TC to compensate for a different registry distance -- you might try that.

H2

[ripit]

I think we have a consensus that 1) cheap glass ain't great, and 2) 2x and 3x TCs are significantly worse than 1.4x-1.7x TCs, whether front- or rear-mounted. Front-mounted TCs don't eat light as do the rear-mounted sort, but they do impact contrast and sharpness a bit, maybe even a little more than non-expensive rear-mounted TCs. But sharpness and contrast can be fixed somewhat in PP. What, me worry?

I use a front-mounted 1.5x Sony VCL-1546A to good effect on a Fast Fifty for ultra-thin-DOF portraits but I'm not expecting edge-to-edge flatfield sharpness there. Alas, my only rear-mounted tele TCs are 2x so I can't adequately test IQ vs the Sony. I *do* know that all the front-mounted wide converters I've used show more aberrations and edge-effects than front-mounted tele converters.

Besides tele-TCs are also front- and rear-mounted variable-macro TCs. I have a couple, both labeled Paragon. They're fun but not ultra-sharp. Ratz.

I *will* echo a point made earlier: The IQ degradation may not matter. If an image DEPENDS on the absolute best IQ, then we want the cleanest optics possible. If content trumps quality, then even cheap TCs can be very useful. But because of the light-eating properties of rear-mounted TCs, they're still best on good fast lenses.

That all sounds reasonable to me. I have a sony vlc-1452h 1.4x that does a respectable job. I'm guessing its easier at only 1.4x though. Olympus glass still seems to be some of the best you can get (for front mount converters). While decent front mount teleconverters are common enough and resale value is pathetic so you can get them very cheap, wide converters are another story. Very good quality ones are a lot harder to find at all and a lot harder to find cheap. That goes doubly so for ones large enough for dslr use (I have noticed that oversize lenses where you are shooting through the middle have less edge problems but then lens weight becomes an issue).

I know you have a lot of lenses but have no idea if you have a lot of teleconverters. If you know (or if anyone else knows), do the 7 element 2x converters tend to be significantly better than the 4 element ones? I would love to have a pentax 1.7x af converter but I'm on an ebay MF budget. Seems the pentax ones are going for 500$+ new now.