[csa]

TC's are pretty confusing. I want to get one that is auto, but don't know about which power is best. I would primarily be using it with the Tokina 400 lens. Is this even recommended?

Thanks in advance for any assistance.

[KevinR]

By Auto, what do you mean? Auto focus, or auto aperture?

TCs normally come in 1.4x 1.5x 1.7x and 2x which increase the effective FL of the lens but reduce the light by 1 stop for every 1.4x factor. So 1.4x on 400 f4 will give you about 560mm equivalent field of view but at f5.6 equivalent light. Beyond that the light level will get difficult to focus or affect the AF system to the point of non-functioning.

As a general comment, 1.4x or 1.5x would be about the most you can use on a 400mm f4 and still preserve AF. Beyond that you will be MF and best in Live View on tripod to be accurate. If lens f5.6 then will drop to f8 and AF will most likely not work.

Hope this of some help.

[csa]

Sorry; auto focus.

Thanks Kevin, that helps.

[jeallen01]

Definitely don't go beyond 1.4x - get a Tamron/Kenko (whatever - look at the PF converter tests for other brand-names for same item!) - as the K-10 has relatively poor low light autofocus.

[slowhands95128]

Traditional teleconverters are rear converters, and lose light by 1 or more F stops. There is another option, a teleconverter lens on the front of the lens. They do not lose any light, but they may vignette and can be heavy, so need support.

The problem is most of the available ones are simply poor quality, since they are aimed at the point and shoot consumer market. And to avoid vignetting, for large teles we need a large thread mount from 67-77mm, so they are big and heavy. However, some of the better Camera Makers built some good ones. Raynox makes a few good ones at the high end too, maybe not as good as the major camera makers but better than average.

Years ago, Canon made a 1.4x 67mm TC for its C-8 16mm movie film camera. It's good, and not expensive - and easy to find and try. You get these on ebay from $20, and they are surprisingly good. (Beware, there was a 1.6x C-8 for 8mm movie cameras with 43mm threads only fits small lenses.) For most people, the C8 1.4x 67mm lens this is the best option, considering low cost and availability. It does a good job and because of the huge rear mount, is less prone to vignetting.

The Nikon TC-15ED lens is good but has 50mm rear threads; unusual matching step rings can be found on ebay. Another is the Nikon TC-E17ED. This exquisite lens is expensive ($300-500) and rare, but worth a try. It has 5 elements in 3 groups and is very sharp. People know about this lens and hunt for it. The TC-E17ED has 60mm rear threads. Birders sometimes stack these two Nikons with good results (2.55X).

The Olympus TCON 17 is worth mentioning. It has good optical quality too. It has 55mm rear threads.

A final option is from Sony, the DEH-17R, for the Sony DSC-R1 camera. This is a "High Grade" lens, according to Sony (use, $50-250). It has 5 elements in 5 groups. It also has a custom bayonet mount that only mates with Sony's lens support, the VAD-RA, which is tailored to the DSC-R1 camera and may not fit well on others. It may be best to glue a ring or machine threads on the DEH-17R to suit your lens if the VAD-RA does not work out.

All of these front mount converters stress the lens and must be supported, to avoid ruining the lens. A Manfrotto 293 may suit, or you may have to improvise.

[jeallen01]

Front-mounted T/Cs are relatively large and pretty heavy, and designed for fixed lens cameras - why would you want to use one on a DSLR when a rear-mounted T/C is much smaller and lighter, and more likely to be optically-compatible with your existing lenses?

[csa]

Front-mounted T/Cs are relatively large and pretty heavy, and designed for fixed lens cameras - why would you want to use one on a DSLR when a rear-mounted T/C is much smaller and lighter, and more likely to be optically-compatible with your existing lenses?

Agreed. I wouldn't be interested in a front-mounted T/C at all. I'm familiar with these "front mounted" T/Cs from my Panasonic days. I don't want something heavy hanging off any of my lenses.

[slowhands95128]

I agree these are heavy and need support. The reason to consider them is you don't lose F stops, and some are optically good and quite cheap. A good rear converter, 1.4x, will cost you $500, while the C8 1.4x 67mm runs about $20-40. I use mostly manual focus lenses that are all metal and can easily handle these. They generally won't suit the plastic lenses.

[csa]

"All of these front mount converters stress the lens and must be supported, to avoid ruining the lens. A Manfrotto 293 may suit, or you may have to improvise. "

I still only want to get a rear TC, to use with my long lenses. I found a Sigma, but it says it is not compatible with the K10D, only SLR. (Pentax autofocus 1.4 Sigma APO EX DG.) This is what is confusing to me, to find one that will work with the K10D.

[jeallen01]

"All of these front mount converters stress the lens and must be supported, to avoid ruining the lens. A Manfrotto 293 may suit, or you may have to improvise. "

I still only want to get a rear TC, to use with my long lenses. I found a Sigma, but it says it is not compatible with the K10D, only SLR. (Pentax autofocus 1.4 Sigma APO EX DG.) This is what is confusing to me, to find one that will work with the K10D.

The Sigma 1.4x TC does NOT work with the newer HSM versions of the Sigma long lenses, whereas the KENKO/Tamron 1.4x "Pz" TC (but not the ones without "Pz" in the name!) works with both the older screw-drive AND the HSM versions of most Sigma lenses - so which (exactly) long lenses are to be used with a TC?

(I have both the Sigma 1.4 TC and the KENKO 1.4x "Pz" TC, and have done some checks with both screw-drive and HSM Sigma lenses - and also the PENTAX 18-135 with the DC motor, and the KENKO "Pz" TC works with that as well).

[csa]

For now, the TC would be used with the Tokina 400 AT-X SD.

[jeallen01]

For now, the TC would be used with the Tokina 400 AT-X SD.

Not familiar with that lens, but - having had a quick look at the PF review - I suspect it is a screw-drive lens. As such, any TC with screw-drive capability should work with it, but the Sigma might not because its protruding front element might foul the rear element of the main lens.

OTOH, whilst a particular combo may physically work, the optical compatibility may or may not be very good as some TCs (e.g. the Sigmas) are only designed to be used with a particular manufacturer's lenses - and even then the lenses with which they work well may not include every one in that manufacturer's range.

Others may be able to provide more specific info on TCs for use with this lens.

---------- Post added 01-12-15 at 07:03 PM ----------

Definitely don't go beyond 1.4x - get a Tamron/Kenko (whatever - look at the PF converter tests for other brand-names for same item!) - as the K-10 has relatively poor low light autofocus.

Carol

Look in this part of the forum:
Miscellaneous Lenses for Pentax: Teleconverters (All Brands) - Pentax Lens Review Database