[KingInfo]

Been searching for a while now, but am getting very confused with all the details so was wondering if someone could help me out.

I have a Pentax K-5, and the longest lens I have is a 50-200mm WR AF but I want a longer/zoom lens.
I was hoping to get a 75-300mm or similar lens for under £70, obviously second hand and probably on eBay. Otherwise I was thinking of getting a 2x converter but got really confused by it all, I understand that by using a converter I will use some f stops and picture quality, but that doesn't bother me to much. And if there's a difference of ~£50 between a converter and lens then I'll definitely be getting the converter
Finally, the loss of auto focus or whatever is okay.

Any help is appreciated!!

[eonb]

Quality loss with a 2x converter is quite large, apart from the 2 stops of light that you lose. Personally, I'd look at getting the 75-300 or similar. I've also got a Kenro 1.5x which has the AF contacts (or my version has). There's a slight loss of quality with this, but not that much.

What are you looking for specifically in the lens is more of an issue? What do you want to shoot?

[jatrax]

Using a 2x TC with a consumer zoom is an exercise in futility. You will almost certainly not be able to autofocus but in addition the viewfinder will be darker making it even harder to manually focus. Might be able to get it to work in Live view by zooming in. But really it's not worth the aggravation.

Take a look at the FA 100-300 models (4.5-5.6 and 4.7-5.8) the latter is supposed to be somewhat better and both can usually be found for under $150usd.

[Lowell Goudge]

Generally speaking, here is what you win and lose with a teleconverter

Depending on the magnification1.4x or 2x you get 1.4 times or 302 times the image size on the sensor, but the illumination is 1 to 2 stops lower, therefore, you need much slower shutter speeds under the same lighting conditions, BUT the longer focal lengths require faster shutter speeds to eliminate shake and camera motion from blurring the image. A a result you really wind up losing 2-4 stops not 1-2.

On a high quality fast lens(I use a sigma APO 70-200/2.8) there is not much, if any noticible loss of image quality with sigmas 1.4x and 2x TCs BUT they cost $200-$300 so they are not cheap. They also do not work on many lenses due to the design.

On your 50-200, a teleconverter will make the lens so slow at the longer focal lengths that AF does not work. In addition, the $50 teleconverters you are looking at a really cheap, and you would not be happy with the result. If you want to get to 300mm or longer, go out and purchase any 300mm F4 or F4.5 lens you will be happier with it

[RKKS08]

Since my film days long ago I know that using a TC with zoom lenses is not a good idea for many reasons.

The only exception is, if both the lens and the TC were designed to be used together. In this case, IQ may even improve as one of the two may compensate for optical deficits of the other

Before you buy an old 4/200 or 4/300, have a look at size and weight! Many of the 1970-80 teles are optically quite good (Takumars, Pentacons, CZJs), but VERY BIG and VERY HEAVY.

[halfspin]

tele with a zoom is barely a step up from taping a monkey to a long stick and have him draw what he sees in green crayon.

[VisualDarkness]

tele with a zoom is barely a step up from taping a monkey to a long stick and have him draw what he sees in green crayon.

I wholeheartedly disagree. There are many nice tele zoom options out there with Pentax DA (or DA-L) 55-300mm as a great option for the price.

[jatrax]

Maybe he meant TC with a zoom? A creative description at any rate.

[halfspin]

Yeah, sorry - tele(converter) used with a zoom. I agree tele(photo)s zooms can be awesome! I love the DA* 60-250 like a child.

[Ponosby Britt]

Yeah, sorry - tele(converter) used with a zoom. I agree tele(photo)s zooms can be awesome! I love the DA* 60-250 like a child.

So can a Sigma 100-300/4 with a Kenko 1.5 TC from the rear of the theater.

[KingInfo]

Quality loss with a 2x converter is quite large, apart from the 2 stops of light that you lose. Personally, I'd look at getting the 75-300 or similar. I've also got a Kenro 1.5x which has the AF contacts (or my version has). There's a slight loss of quality with this, but not that much.

What are you looking for specifically in the lens is more of an issue? What do you want to shoot?

I'm mainly looking for long range shots, especially for taking photos of birds.

Okay then, as the majority of people have said not to bother with a converter then i'll have a further look into lenses.

[ivanvernon]

Been searching for a while now, but am getting very confused with all the details so was wondering if someone could help me out.

I have a Pentax K-5, and the longest lens I have is a 50-200mm WR AF but I want a longer/zoom lens.
I was hoping to get a 75-300mm or similar lens for under £70, obviously second hand and probably on eBay. Otherwise I was thinking of getting a 2x converter but got really confused by it all, I understand that by using a converter I will use some f stops and picture quality, but that doesn't bother me to much. And if there's a difference of ~£50 between a converter and lens then I'll definitely be getting the converter
Finally, the loss of auto focus or whatever is okay.

Any help is appreciated!!

I have three different zooms that might work for you:

Sears 80-200 mm f 4.0
Phoenix/Samyang 75-300mm f 4.5-5.6
Samyang 28-200 mm f 4.0-5.6

All three are in excellent working condition and all are immaculate cosmetically. I do not have much money tied up in any one of these, mostly they are lens I got in a package with some film cameras I purchased. The Samyangs both have the Ricoh post on the K-mount, but the post is a round one and has caused no problem at all with any of my Pentax DSLR or film cameras. If interested, send me a private message, and we can work out details.

[Lowell Goudge]

Since my film days long ago I know that using a TC with zoom lenses is not a good idea for many reasons.

The only exception is, if both the lens and the TC were designed to be used together. In this case, IQ may even improve as one of the two may compensate for optical deficits of the other

Before you buy an old 4/200 or 4/300, have a look at size and weight! Many of the 1970-80 teles are optically quite good (Takumars, Pentacons, CZJs), but VERY BIG and VERY HEAVY.

Ok fine, a 300/4 is big and heavy, but did you know that a K300/4 is actually lighter than the DA300/4, the M/A 300/4 is lighter still. I am tired of the ongoing myth that old glass is heavy.

[jatrax]

I am tired of the ongoing myth that old glass is heavy.

+1 Even the S-M-C Takumar 300/4 is lighter than the DA*300

[TER-OR]

I can advise going for the DAL 55-300 over a Tamron 70-300. The Tamron suffers from excessive purple fringing in high-contrast settings. If you can control that, the Tammy might be worth buying if you can get it for under $80.