[MichaelS]

I'm debating getting a teleconverter. I would use it rarely so can't justify spending a lot. I've seen many on Ebay anywhere from tens of dollars to hundreds and from manufacturers I'
ve never heard of. Also what's the difference between teleconverters and extension tubes? Any help or suggestions would be appreciated. I've got a K3 and K5. I would use the converter on my Pentax 55/300 mainly. thanks

[sergysergy]

Extension tubes do not have any glass while TCs do. Tubes are normally used for macro purposes while TCs give you more reach. The 55-300 is not that fast of a lens so a teleconverter might not work that well.

[gatorguy]

IMHO the only good ones on a budget that I'm aware of are the manual focus Kenko Teleplus MC7's. $50 or thereabout. Do not buy the even cheaper MC4's. They are worthless, thus the $20 prices.
The ones most frequently mentioned here, Pentax own AF1.7x and HD 1.4 are very good, and Tamron's 1.4x too, but are generally $150 and up due to autofocus capabilities.

[gatorguy]

Extension tubes do not have any glass while TCs do. Tubes are normally used for macro purposes while TCs give you more reach. The 55-300 is not that fast of a lens so a teleconverter might not work that well.

There are members here that are doing quite well with a TC/55-300 combo. I would suggest spending the money on one with auto-focus, perhaps the older Pentax 1.7 AF (non-HD) if the OP can find it. Tamron has another similarly priced.
Manual focus at 300mm with a cheap TC won't be fun or productive IMO but it WILL keep you busy.

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Last edited by gatorguy; 05-18-2020 at 09:31 AM.

[jgnfld]

Extension tubes do not have any glass while TCs do. Tubes are normally used for macro purposes while TCs give you more reach. The 55-300 is not that fast of a lens so a teleconverter might not work that well.

Agree. I have taken numerous pictures of some oil tanks from about 2 miles away which contain small regulatory writing on the side with the 55-300PLM w/ and w/o the 1.4 tele on my K-70. I can detect no increase in resolution to my judgement.

The one lens I own which to my eye does seems to get additional resolving power with the 1.4 added is the 100mm WR.

[Bob 256]

I'm debating getting a teleconverter. I would use it rarely so can't justify spending a lot. I've seen many on Ebay anywhere from tens of dollars to hundreds and from manufacturers I'
ve never heard of. Also what's the difference between teleconverters and extension tubes? Any help or suggestions would be appreciated. I've got a K3 and K5. I would use the converter on my Pentax 55/300 mainly. thanks

Let's say you have a basic 55mm lens. The 55mm applies for an object at infinity and is the distance between the lens and the film or sensor which gives a sharp focus. The aperture is what determines how much light is passed and what f-stop applies.

Now, if you move closer to an object, the effective focal length starts to increase. To compensate, you move the lens away from the film or sensor (focusing the lens). Let's say however that the lens doesn't have the ability to focus. You can put an extension between the lens and the film or sensor plane to compensate for the increased focal length. That's what an extension tube does and it is used primarily when a given lens runs out of its near focusing adjustability so you can focus on objects really close up.

In some cases, you just want a larger image (a longer focal length). In this case, a teleconverter is used. It has optics which increase the effective focal length of the lens it's attached to. It also keeps the new larger image in focus on the film or sensor.

In either case, a longer focal length without any changes in the original lens aperture means a higher f-stop and less light. If you double the focal length, the f-stop doubles and you get one-fourth as much light. With extension tubes, you can determine how much the focal length increases by the length of the tube. With teleconverters, the X1.4 or X2 is the multiplier for the focal length and the f-stop of the result. If you're shooting using a 55mm lens at f4, it becomes a 110mm f8 lens with a x2 teleconverter.

A good teleconverter will give image quality which essentially depends on the quality of the original lens but degraded slightly depending on how much magnification you choose. A poor teleconverter is just that and will degrade the image quality quite a bit more, particularly in the image corners. Good teleconverters don't perform well with poor lenses because any lens issues are also magnified by the teleconverter, and then some lens/teleconverter combinations just aren't the best and poor images result.

When using a teleconverter, just be prepared for dark images through the viewfinder and sluggish or disabled autofocusing because of the stretched focal length and higher f number. The metering system of the camera will usually take care of exposure issues due to the new f-stop range, but be aware that in some cases, manual compensation might be needed (and then some teleconverters don't couple the camera to the original lens so it's all manual in that case).

That's an Extension tube/Teleconverter 101 explanation.

[jatrax]

I would use it rarely so can't justify spending a lot.

The problem with that is that the cheap ones are (IMHO) less than worthless. Some of the MC7's are OK but the only TC I have used that I felt really helped was the Pentax HD 1.4x. The Pentax 1.7x autofocus adapter is also useful but it is a little different than a classic teleconverter as it was designed to be used with manual focus lenses.

The other issue is that the Pentax 55-300 is not a very fast lens and adding the TC makes it even slower. The 55-300 does work with the Pentax HD 1.4x in good light, but you are working right up to the edge of the AF ability.

"The Pentax 1.7x autofocus adapter is also useful but it is a little different than a classic teleconverter as it was designed to be used with manual focus lenses." But they worked best with the Pentax A series lenses. But moreover the 1.7x F was designed for the SF series camera's. On a new digital with APS-C they are less useful because they require then that you have manually prefocused and the converter does the finetuning. It is indeed an adapter and not so much a converter. I loved to use it on the SFX and the later MZ-5.
There is also a Takumar-A 2X converter to be used with manual focus lenses. I liked it on the Super A when using an A lens, but it is very difficult to use with long telephoto. You will notice that focusing will be hard, because 2X focal length results in about 1/2 of the leeway in sharp focusing, especially with that small APS-C viewfinder compared to full frame. So not recommended. And certainly not handheld, a tripod is needed. In some cases the result might be very soft. Does not get good reviews on this site.

[gatorguy]

"The Pentax 1.7x autofocus adapter is also useful but it is a little different than a classic teleconverter I loved to use it on the SFX and the later MZ-5.

Aha, THAT'S when I got mine. I could not remember.

[luftfluss]

It is indeed an adapter and not so much a converter.

[Lowell Goudge]

"The Pentax 1.7x autofocus adapter is also useful but it is a little different than a classic teleconverter as it was designed to be used with manual focus lenses." But they worked best with the Pentax A series lenses. But moreover the 1.7x F was designed for the SF series camera's. On a new digital with APS-C they are less useful because they require then that you have manually prefocused and the converter does the finetuning. It is indeed an adapter and not so much a converter. I loved to use it on the SFX and the later MZ-5.

It’s actually a little of both. It was brought out when Pentax released its first AF bodies to bridge between legacy lenses and af. As it is infinity corrected it requires magnification, so it becomes a 1.7x TC with internal AF.

It is actually very interesting for telephoto lenses, because it gives zone focusing capabilities I use mine with a K300/4. I agree A series lenses are most useful as they give full metering and flash support.

[kypfer]

The Kenko Pz-AF 1.5x is well worth considering, but only expect the autofocus to work well on a stationary subject in bright light. Unfortunately it is "dumb", so the camera won't "know" it's fitted, therefor the EXIF won't mention it, and, possibly more to the point, the Shake Reduction won't know about the increase in focal length! Take due precautions with a tripod, beanbag or whatever and the results can be very acceptable for those occasions when you "really need" that extra reach.
Good luck!

Aha, THAT'S when I got mine. I could not remember.

Glad to be of service. Just like me, you must be one of the first buyers. It is such a gem. One of the most original and unique Pentax ideas about using your legacy lenses, when AF came into swing.

[Wasp]

The short version is that a teleconverter enlarges the image formed by the lens in front of it. Imperfections are enlarged as well. This is the main reason why teleconverters have a bad reputation. In my experience, 2x converters are not worth the bother.

For guaranteed compatibility, this is pretty much the only game in town.

HD Pentax-DA 1.4x AW AF Rear Converter Reviews - DA Teleconverters - Pentax Lens Reviews & Lens Database

The cheaper options on the bay will be manual focus. There are third party auto focus options. YMMV as far as compatibility with the 55-300mm goes. Here are a few:

SIGMA APO 1.4x EX Teleconverter Lens Reviews - Miscellaneous Lenses - Pentax Lens Review Database

Sigma X1.4 Tele Converter AF Lens Reviews - Miscellaneous Lenses - Pentax Lens Review Database

Promaster Spectrum7 AF 1.7x Lens Reviews - Miscellaneous Lenses - Pentax Lens Review Database

[Lowell Goudge]

Snip......

Sigma X1.4 Tele Converter AF Lens Reviews - Miscellaneous Lenses - Pentax Lens Review Database

A caution to all. This teleconverter has a protruding front element and requires the rear of the lens it is being attached to to have a bore diameter of about 35 mm and the rear of the lens recessed 14 mm inside the bore.. it is only compatible with a very select number of sigma long & fast Tele photos Plus similar lenses from Pentax