[willywalker]

Hi

If this thread exists - please point me in the right direction.

If not, does anyone have experience using a converter?

I have just ordered a Vivitar's 1.4x Teleconverter for Pentax and would like to know as much about it as possible. ie, does the camera need to be set in a specific way in terms of focal length?

Any other info would be welcome.

Many thanks
William

[Wildturkey]

Hi! I've been using a Kenko 2x-Ka-X teleplus for years. You'll need to go to manual settings . I found really no problem with focal length. Have fun.

[willywalker]

Hi! I've been using a Kenko 2x-Ka-X teleplus for years. You'll need to go to manual settings . I found really no problem with focal length. Have fun.

Thanks a lot for the reply - I'm sure I will have fun!

William

[willywalker]

I have received the converter, now I have another question.

I have read that one loses a stop with an extender. I am using a Pentax 300mm FA 4.5 lens. With the extender fitted, I am still able to set the aperture to 4.5. What is happening and what don't I understand?

William

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Last edited by willywalker; 09-19-2011 at 01:06 AM.

[falconeye]

I have read that one loses a stop with an extender. I am using a Pentax 300mm FA 4.5 lens. With the extender fitted, I am still able to set the aperture to 4.5. What is happening and what don't I understand?

William,

X-times converters increase a lens' focal length and aperture F-stop by X.

But a camera (except with a converter doing the math in an embedded chip which don't exist for Pentax) won't know. So, EXIF and camera readings are still the unmodified (and false) values.

With a manual lens (or all manual converter), the camera at least allows you to dial in the increased focal length to make shake reduction work properly.

[willywalker]

Hi Falk

Thanks for the reply.

Am I correct then in saying that when the camera says 4.5, it is in fact 5.6 and so on?

Or when the camera says 4.5 it is 5.6, and when it says 5.6 it is also 5.6? in other words, 4.5 falls away and it simply starts at 5.6 and continues normally?

Thanks
William

[falconeye]

Am I correct then in saying that when the camera says 4.5, it is in fact 5.6 and so on?

You have a complicated way to talk about "times 1.4"

btw, 4.5 times 1.4 was 6.3 when I last checked...

[Flick]

Have any you experienced a noticable loss in quality / sharpness when using a converter on say a 300mm zoom lens, and can someone direct me to some sample images? I need more reach; options are 1) get a converter, or 2) fork out the money for a larger lens...?

[falconeye]

Have any you experienced a noticable loss in quality / sharpness when using a converter on say a 300mm zoom lens, and can someone direct me to some sample images? I need more reach; options are 1) get a converter, or 2) fork out the money for a larger lens...?

There will be a significant loss in image quality.

A tele converter however still delivers more resolution than a good prime lens alone. You'll have to use the lens at its sweet spot (like f/5.0), and you'll have to sharpen more which means you better shoot at low iso when using a converter. So, a converter "eats" at all ends: less aperture, faster shutter speed and lower iso.

However, if for some reason you absolutely need the resolution, a good prime with a converter can't be beaten by a longer consumer zoom at its long end (or a bargain 4 element tele lens). So, the only alternative to a converter then is very expensive glass ($4000+ range). For all camera systems. This is why in my blog, I proposed Pentax to make a $2000 500/5.6 lens to make a fresh and unique offering to the market.

In practice, it means that longer reach is impossible except at sunlight with a converter and the DA* 300mm or the DA*60-250 at 250mm. However, converters supporting autofocus with SDM lenses are rare (some very specific Tamron 1.4x and the Pentax 1.7x) and AF then is slow.

Therefore, you are normally better off cropping. Note that a 4MP crop from a K-5 with a DA*300 corresponds to a lens which is at 35mm film equivalent to a 900mm lens ... And only very few long tele shots resolve better than 4MP...

I have a 500mm lens but believe me, it is hard to use with a moving subject like a bird. Framing becomes an art, not to speak about focussing With a static subject, you can also shoot a short burst of 4-6 frames and use super-resolution (cf. PhotoAcute) to extend your reach.

[Flick]

There will be a significant loss in image quality.

Thanks, I guess that confirms my suspicion.

A tele converter however still delivers more resolution than a good prime lens alone. You'll have to use the lens at its sweet spot (like f/5.0), and you'll have to sharpen more which means you better shoot at low iso when using a converter. So, a converter "eats" at all ends: less aperture, faster shutter speed and lower iso.

I can't have that happening; loss of IQ and sharpness along with limited use of apperture and iso is asking a tad too much! I certainly want to be able to use those at slightly higher values, especially with moving objects.

So, the only alternative to a converter then is very expensive glass ($4000+ range).

Well, Canon's luxury zoom lenses come to mind; they're outrageously expensive, but the speed and quality is yours if you can afford it!

This is why in my blog, I proposed Pentax to make a $2000 500/5.6 lens to make a fresh and unique offering to the market.

Would be nice if Pentax did so Meanwhile we are forced to look at offerings from other brands. For me personally a single lens with further reach sounds like the better option, and this should also circumvent the issue with loss of EXIF data.

I have a 500mm lens but believe me, it is hard to use with a moving subject like a bird. Framing becomes an art, not to speak about focussing

Yes I believe it ain't easy, but doable! Would you mind sharing which 500mm lens you're using, and why?

Thanks once again for the reply, much appreciated.

Elizme

[garyk]

I would like to see a pic with the 1.4. If you have any now. Please post. Just browsing. I have not seen any good 1.4 pics with Pentax glass. I don't know if Sigma is just allot better or Pentax is not being used properly. Browsing the 300mm+ thread. I see some very bad shots there. There are a few using Sigma that are excellent. But not any consistent using the large Pentax glass. That I have seen. Some of the big Pentax old glass is sharp but the antiquated AF and weight outshines it image quality in my opinion.
Pentax is the worst camera for wildlife you can buy. While the IQ is #1 in my opinion and sigma can produce outstanding shots. The speed of AF and poor AF, which is probably 5-10 years behind the leaders.

[willywalker]

You have a complicated way to talk about "times 1.4"

btw, 4.5 times 1.4 was 6.3 when I last checked...

Yep Falk, your'e right!

The reason my talk is complicated is because I simply did not understand it! I now understand the multiplication of the aperture - thank you!

I still do not understand the practical application of this when using the lens. Does it matter where the aperture is set (on the camera) - from between 4.5 - 6.3 at any rate? Or do I start by setting the camera from 6.3, disregarding everything below that?

Let me put it another way. How would you set your K5 with the 300mm FA and the extender? I use it mainly for wildlife/birding.

I used it for the first time on Sunday, in very good light, and I was very pleased with the results. (Garyk - I'll try and post a few samples later this evening.)

In December I'm going to a game reserve where the chances of a cheetah-kill are not an impossibility (however unlikely!) - but what would your settings be under such circumstances? I'm thinking here in particular of higher iso's capable with the K5.

Thanks for the info.

William

PS.. Am I right in saying that on the K5, the 300mm lens and the 1x4 converter equals 630mm?

[sprint06]

Here is a shot taken with pentax 300 f4 and 1.4 converter.I think you will find that a 300 lens with 1.4 converter = 420mm

[falconeye]

The reason my talk is complicated is because I simply did not understand it! I now understand the multiplication of the aperture - thank you!

I still do not understand the practical application of this when using the lens.

I think it is the other way round: You don't understand because you think it is more complicated than it actually is. Anyway.

The lens has a focal length and F-stop. The F-stop [dimensionless figure] is the focal length [mm] divided by the lens' aperture diameter [mm]; it's that simple.

A tele converter increases the focal length by a factor, like 1.4x. This is why it is an 1.4x converter, not an 1x4 converter which is another sign that you complicate matters in your thinking.

But a tele converter doesn't change the lens aperture blades (cannot) which is why the F-stop (focal length / aperture diameter) is increased by the same factor, like 1.4x.

But the camera doesn't know that there is a converter. So, all the 1.4x multiplications happen in your brain (only). The lens aperture ring (if it has some) may say f/4, the camera may say f/4 in the display and EXIF may say f/4. But it will be f/1.4x4=f/5.6.

[willywalker]

I think you will find that a 300 lens with 1.4 converter = 420mm

I was thinking of the crop-factor of the sensor too.