[slackercruster]

Looked at the reviews at B&H for Sigma and Vivitar. Reviews were pretty dismal. Although many complaints were about the auto camera functions. I am concerned with sharpness, not auto features.

Do you use a teleconverter? What was your experience?

[bjake]

For many years while using Spotmatics I had three lens,35mm,50mm and 135mm.Would occasionally use a converter on the 135mm when it wasn't long enough.With the price of fairly good manual zooms these days for Pentax don't think converters are worthwhile.One should be able to pick up a manual converter for $15 or less so you may want to get one and try it.
Jake

[reeftool]

It's going to depend on the particular converter you're using and the lens. The combination may work well or it may degrade the IQ considerably. Some converters (Sigma) are designed to work with certain lenses and are an excellent combination but only with the lenses they are intended to work with. It's hit and miss with others and may not even mount on other lenses. I have a Pentax A 2x converter and the results are acceptable. I use it on a 300mm lens mostly. A crop is just as good for most viewing but the TC will allow a very large print to be made which I may not get with a tight crop.

[Nowhere Matt]

It depends on the lens. Some lenses are not that sharp to begin with and naturally the magnification of a teleconverter will only amplify that.
With digital, often times you can take an image, crop it and the image will appear just as sharp as if you had muddied it with a tc.
I don't use a tc all that often. I sometimes get the urge to use one tc or even two on a 500mm lens when shooting the moon but usually end up getting images that I could still obtain through simply cropping a normal image taken with the 500mm and no tc.
But again, I'm not nearly as fussy as many around the forum so I don't believe there is any real harm in buying an inexpensive teleconverter and seeing for yourself.

[Marc Sabatella]

Depends on the specific converter and the specific lens. You'd have to tell us what specific combinations you have in mind. But generally, when using a TC that costs less than several hundred dollars on a lens that costs less than a thousand, you can expect results worse than cropping, plus of course the loss of a stop of light and the reduction in focusing efficiency. In particular, there is probably no TC ever made that will produce better results than cropping with the consumer zooms like the DA50-200, DA55-300, or the various older design xx-300 zooms from Pentax, Tamron, and Sigma.

I will say that manual focus is sometimes easier with the larger viewfinder image, despite that image being dimmer. So even though there is really no advantage to the TC optically over cropping with my M200/4, I will sometime use my TC with that lens. Plus when viewing distant small objects, it can be fun to see the image larger, not even taking a picture but just considering the camera like a pair of binoculars.

[RKKS08]

Back in the 1980s, I used a Vivitar MC 2X-22 quite frequently. As far as I remember, at that time it was probably the most sold one in my country. It was a more simple construction (4 elements in 2 groups, as far as I remember), but better ones were VERY expensive. It reduced contrast quite a lot, and there was some reduction in sharpness, too. These multi-purpose TKs were usually optimized for tele lenses 100~300mm, which made it very difficult to focus properly without using a tripod (2 steps of reducing light). But I always took it with me when I had a SMC-A 1.4/50 attached, as it was small enough to even carry it in a shirt pocket. But to get fairly good results, I had to use F5.6 or smaller, so ended up with a F11/100mm (but for focusing, it was 2.8, of course). However, the results were better than working without it and do cropping afterwards (and also cheaper), and the only way when doing slides.

Now I have sold this TC and got a Kenko 7-element one which is an A-type, so I don't need to do stop-down metering. I have not used it often enough to state a qualified opinion, but first impression is that the results are better than with the old 4-element TC.

Be careful buying the near-to-pancake sized Sigma (can't remember the exact name of that one): it is so small because it has a produding front element. With some lenses, you could damage the rear element of the lens. There used to be a compatibilty chart at the Sigma homepage; not even all Sigma lenses could be used with it.

[rvannatta]

I've written about this fairly often,, usually suggesting that they aren't worth it, but then I do use them as well. My take is this. If you have zoom lens or a slow lens (anything slower than f4) forget it. depending on how strong a one you get they will use 1 to 2 f stops
of speed and you get out beyond the range where much works right.

The only circumstances I find that worthy of consideration is if you own an exotic high speed extreme telephoto.---and you get a really good converter.....

All the converter realy does is to crop the picture some. You can crop it in photoshop as well. I call it optical cropping vs. digital cropping. The significance difference is
that the sensor is infront of the digital crop and behind the optical crop.

In theory if your sensor is as good as your lense-----it won't make any difference which place
the cropping takes place. If you have a K5 and use it to the max you shouldn't and won't
see much benefit from the converter as opposed to digital cropping.

I do have some exotic long lenses, and (as listed in my signature line). I do consider
using the Pentax AF 1.7x adapter or the dedicated 1.4x-L TC with someof them, but even with the best of the best its hard to see much benefit. Mostly the TC's make you feel better
when you are using the camera, and the most significant benefit I can see--is that they help
you focus on the real target more accurately whether you are using Auto focus or manual focus because the real target is bigger in the viewer.

I have an additional article and a number of sample photos on a page in my website at:
http://www.vannattabros.com/photo9.html
(this is not a commercial site)

---

Last edited by rvannatta; 02-13-2012 at 10:23 AM.

[RioRico]

Except for matched high-end long-teles and converters, IQ is probably so diminished that you'd be best just enlarging and cropping a non-TC'd image. Otherwide. it depends. If content is more critical than quality, such as for surveillance, blackmail, crime planning, etc, then go for it. One of these days (I keep threatening) I'll put a 3x and two 2x's on my Rubinar 1000/10 mirror for a 12000/120 optic. That should be fun!

[newarts]

All a teleconverter does is optically enlarge the image the primary lens projects on the sensor; I can't see how that can possibly give better results than magnifying the image after it is captured by the sensor. I hope someone can explain this to me.

I know there are some cases where an image with TC is measurably better than enlarged without TC. I just bought my son a gift of a Canon 1.4x III Extender which to improve image quality on the Canon70-200:4 L. I hope it turns out to be true because it was expensive!

[reeftool]

All a teleconverter does is optically enlarge the image the primary lens projects on the sensor; I can't see how that can possibly give better results than magnifying the image after it is captured by the sensor. I hope someone can explain this to me.

I know there are some cases where an image with TC is measurably better than enlarged without TC. I just bought my son a gift of a Canon 1.4x III Extender which to improve image quality on the Canon70-200:4 L. I hope it turns out to be true because it was expensive!

Your son's set up is probably fine. I have a friend who shoots sports professionally and uses a Canon tele/TC combo and it performs great. As you said, it's expensive. His setup is close to the price of a new car. The problems arise when folks on a budget want to buy and expect the same results on cheap imported TC's they see advertised in magazines and on Ebay. You get what you pay for.

[Lowell Goudge]

this subject has been hotly debated many times, with the comments againts teleconverters ebeing that it is generally better to crop than use a TC.

the counter argument is that bigger is better, and a Good TC on a good lens can produce stellar images.

I can't comment on the former, but here are two shots that demonstreate the latter.

the first is an SMC Pentax 300F4 (K300/4) with SMC-F 1.7x AF converter



this was shot using flash on my *istD

the second is with a Sigma APO 70-200F2.8 EX non DG Non Macro and sigma APO 2x Teleconverter EX DG



the chickadee is slightly cropped (about 10-20% of the area cut out, the merlin is not cropped.

Is a TC worth it, I say yes, on a good lens if it is a good TC

[rvannatta]

All a teleconverter does is optically enlarge the image the primary lens projects on the sensor; I can't see how that can possibly give better results than magnifying the image after it is captured by the sensor. I hope someone can explain this to me.

I know there are some cases where an image with TC is measurably better than enlarged without TC. I just bought my son a gift of a Canon 1.4x III Extender which to improve image quality on the Canon70-200:4 L. I hope it turns out to be true because it was expensive!

It is part depends on the quality of the sensor. If the sensor is the limiting factor
in the quality of the photo---all the 'processing' that is done before it gets
to the sensor is a plus. However when we are looking at sensors of every
increasing capabilities, which are approaching or equaling the resolution of the optics (where we are with the K-5) the usefulness is diminished.

The point I try to get accross is that if you pile on the TC's the ability to enlarge
in photoshop or other post processes is limited, You can generally do one
or the other, but if you use a TC don't expect to be able to enlarge/and implictly crop as much as you can if you don't use a TC.

[Lowell Goudge]

my take on the issue, specifically for birds and other small subjects is that bigger on the sensor is better, because the lenses still out perform the sensor.

[normhead]

I guess I just have to keep posting this..



As Mark said... the lens is over $1000 and has amazing MTF numbers....(DA*60-250), the converter cost me over $300 (Pentax A 1.7)

The results mean about 50% more sharpening in post production, when you consider it turns my F4 60-250 into a 425 mm 6.7 lens, this is the bargain of the century. Using a DA lens on an FA converter you're definitely making use of the best part of the converter. I had a Sigma 120-400, and I like these images better, the combination is lighter and I still have a razor sharp 60-250 when the teleconverter isn't on the lens.

[slackercruster]

I was looking at the Sigma APO converter and a high grade Pentax zoom. But from the replies, does not sound worthwhile.