[UncleVanya]

All we need now is for someone to engineer a way to route the screw drive through the 2x-L Rear Converter A structure and make you a custom 2x-L that autofocuses...

I know pipe dreams...

[Lowell Goudge]

There may be instances where using TCs doesn't provide better results than no TC, because the original lens already resolves all relevant detail without the TC.

But, there is also a point where you back up so much the lens no longer resolves all relevant detail. At that point adding a TC will for a time continues to resolve all relevant detail, until you move back so far you need either stacked TCs or a better lens.

SO while I'm sure there are lots of instances where no improvement is seen with a TC, there are also many instances where a TC improves the image considerably. That's why people buy TCs.

Understanding folks saying a TC doesn't ad more detail. - PentaxForums.com

I'm using the Tamron SP AF 300 2.8 LD [Il} which is screw drive, and I'd definitely like to use the AF. And the lens is rated a 10 for sharpness on the forum, easily good enough to benefit from a 2x TC.

I found an original listing somewhere on the Tamron site that said it would not work well with stacked TCs, and it doesn't. So I'm looking to extend my reach past 1.7x. The Tamron site also listed the matched TC that was released with the camera, but months of watching eBay hasn't found me one, so I'm looking to see what else I might use.

When I bought the lens , of course I hadn't read the stacked TC warning. SO I was seriously disappointed when I couldn't get the same results with the 300 I got with stacked TCs with my DA*200 2.8 on the K-3 which gives me 2.4x magnification. So 2x wouldn't even be what i was hoping for. But it would seem to be really hard to come up with even that.

Especially bad since the only current Pentax TC vignettes on the K-1.

The good thing is the 1.7x gives me 510mm ƒ4.5 and is spectacular on the K-3. The focusing rotation on the Tamron is very loose and very short, probably the easiest lens you can buy for use with the 1.7x. One little pinky on the focus ring, it turns to close focus incredibly quickly, and then the 1.7x locks focus, usually immediately.

But I still want the option of 600 5.6 with AF.

Norm. Have you looked at / measured the available space at the rear of the lens. The best long telephoto screw drive TC you can get in production is the sigma APO 2x EX converter, BUT you need to be able to accept about 14mm deep 35mm in diameter protrusion into the lens because the sigma TCs have protruding front elements"

Not as bad as some of the old Pentax rear converters but close

[normhead]

The Tamron looks like it has about an inch and a quarter up in there, but I'm not finding the Sigma anywhere for Pentax.

[cyberjunkie]

I guess it's "finding" rather than "fining".
You typed it on a cellphone, isn't it?
I've seen few Sigma's in Pentax mount during the last few years. I think you just need to be patient. You'll eventually find one.

I have many converters in PK mount, most with electric contacts.
I haven't used most of them long enough to provide reliable and detailed informations about their performance with different lenses.
Most of them are in the lens list in my signature.
What I know about teleconveters is that it is not all about sharpness.
It is possible, and sometimes even evident, that a 1.4x, 1.5x or 2x crop equals or even beats the sharpness obtained by the use of a corresponding converter, but it's also true that the image is DIFFERENT.
The bokeh and the transition between in focus and OOF are rendered in a different way.
If you use the viewfinder the size of the subject makes a difference too. Focus and composition can benefit from a larger image, if the image is not too dark.

The 1.7x is a different beast, can't be compared with all the others because it gives AF to MF lenses. Using it as a "normal" converter is a nonsense.

I have found that the grey "-L" converters work very very well with the objectives they were designed for.
I have not enough experience with "-S" converters to go into details, but I'm sure that I have many lenses that work better (especially with the 1.4x) than cropped.

The 7 elements macro converters, like the Vivitar/Kenko/etc with helicoid, or the Panagor/Elicar/etc with floating elements are also quite good, and very useful.

In these days I'm using a Kenko AF PKA-Pz mounted on the the first version of the Tamron 90mm Macro AF, which shares the optics of the early 2.5/90mm MF ones.
It's a bit soft wide open, but the OOF rendition and the sharpness at medium apertures are really impressive.
You also won't get the "light spot" at the center of the frame that sometimes shows up in certain lighting conditions.

If I cropped the 2.5/90mm Macro many pictures would have been very different.

Cheers

Paolo

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Last edited by cyberjunkie; 02-09-2017 at 06:19 AM.

[normhead]

The 1.7x is a different beast, can't be compared with all the others because it gives AF to MF lenses. Using it as a "normal" converter is a nonsense.

I guess so is having a focus limiter on a lens. For my use in my blind I can set the the lens to focus on the front and back of the branches the birds land on and just fire away with very quick, AF. One person's nonsense is another person's genius. And the Pentax was also designed to be 1.7x TC, or are you thinking that happened by accident? What? They designed an AF converter and somehow it just happened to magnify 1.7x times?

but it's also true that the image is DIFFERENT.

Different can be good or bad. When you change from a 300 2.8 lens to a 500 4.5 lens, they will be different. Adding a TC is exactly the same thing, unless you were expecting it to be the same.

The 7 elements macro converters, like the Vivitar/Kenko/etc with helicoid, or the Panagor/Elicar/etc with floating elements are also quite good, and very useful.

Henry's has just informed me they can't get me the 7 element Bower. This is becoming quite tedious.

Anyway thanks for your input everyone...

[normhead]

I Just thought I'd add this TC, the 905 grams thing (over two pounds) is quite unappealing... that gives me two actual choices that go beyond "keep looking." Which I will no doubt do anyway. Now it's about a stop gap solution, not as good as the best but better than nothing. I still have no idea if either of these is better than nothing.

Choices to date.





It's just so odd, how the Canon 70-200 with the 2x TC is so popular among the wildlife guys around here, yet for Pentax it's not even a "thing."

[WPRESTO]

Kenko used to offer 1.5X and 2X AF converters in K-mount. Had both (one sold to another Pentaxian) and they were OK, and might be substantially the same if not identical to the Promaster units in the preceding post. An observation: no TC can improve on the IQ of the lens in use; the primary gain is in pixel density, not IQ as a crop from the same lens, same subject/distance etc. will be almost indistinguishable from an enlarged (what all I would call "pre-cropped") image taken with a TC. Teleconverters were devised during the film era to provide frame-filling on chromes using shorter telephotos when purchasing a lens of 50% to 100% greater focal length would be prohibitively expensive for most of us. The most satisfactory TC + telephoto combo is probably a 300mm f2.8 combined with a high quality 1.4X TC. The current 300mm F4 DA + the latest Pentax 1.4X TC is very good, but I'm skeptical that the TC provides IQ that matches a crop from the 300mm by itself - if you pixel-peep.

I used many telephoto + TC combos in the film era. These I found best:

1) 200 SMCA macro with either 1.4XL or 2XL converter
2) Nikon 500mm f4P with 2X Nikon long lens TC (model 301 as I remember). I really regret letting this lens and TC go.
3) Tamron 400mm f4 + Pentax 1.4XL converter, and I got some decent images using the 2XL as well

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Last edited by WPRESTO; 02-09-2017 at 09:48 AM.

[normhead]

OK, thanks for that opinion

Now for some actual testing and interpretation of facts, in this case images..
Understanding folks saying a TC doesn't ad more detail. - PentaxForums.com

But the simple reason TC out resolve non-TC images is, Lenses still out resolve sensors. Until sensors and lenses are equal, TC's will make a difference, in some cases.

It seems every time there's a discussion of TCs I end up posting this.

Have a Vivitar 135mm 2.8 M lens, and the TC does nothing for it but make the image bigger. Using a DA* or equivalent you will see at least a 30% increase in subject resolution.

I'm for now taking a used Promaster, that is reasonably cheap, hopefully that will keep me happy until I find the Tamron or Sigma. There will be extensive testing before I take it out to dinner. Stay tuned.

[WPRESTO]

OK, so the limitation on IQ is in the sensor, not the lens or TC. So the following two statements are correct: 1) a TC cannot improve the IQ of a lens; and 2) a TC + lens may record more detail in a digital image if the lens alone can out-resolve the sensor. My opinion of TC's comes from the film era, where in tests even the best TC always at least slightly reduced IQ (= a TC cannot make a lens better than it is, and addition of multiple lenses will almost always reduce contrast and resolution). With respect to the latter, there are photographers who advocate "never use any filter" because the addition of the glass will degrade image quality, and that is just one, very thin piece of glass.

[cyberjunkie]

I guess so is having a focus limiter on a lens. For my use in my blind I can set the the lens to focus on the front and back of the branches the birds land on and just fire away with very quick, AF. One person's nonsense is another person's genius. And the Pentax was also designed to be 1.7x TC, or are you thinking that happened by accident? What? They designed an AF converter and somehow it just happened to magnify 1.7x times?

Sorry, i should have worded it differently. Where're talking about buying a converter, isn't it?
I should have written "buying" instead of "using".
The concept remains the same though.
The AF 1.7x is expensive, more than any other, and in my personal experience inferior to the 1,4x -L and maybe also to the 2x -L.
My experience with the latter is limited, cause i didn't take many pictures with it, and it was film time.
Both were mainly used with a Pentax-A* 2,8/300mm. Which happened to be my only lens in need of a converter.
I don't see any good reason to buy one, given the price, unless you need AF (with an MF lens). Just because of the price, not because 1.7x is an unlucky number
If you want a converter that supports AF, there were a few Kenko converters that supported screwdrive AF, but not lenses with internal AF motor,
The Kenko Pz-AF 1,5x Teleplus SHQ i found second-hand on Ebay has the two contacts, but only to support PowerZoom.
I don't need a converter with support for non-screwdrive AF, so i haven't investigated any further.

The two Promaster shown in a previous post are obviously portrayed in a non-Pentax version (Nikon?).
It would be interesting to know if the 7-elements AF transmits data to modern lenses with internal AF.

cheers

P

[normhead]

OK, so the limitation on IQ is in the sensor, not the lens or TC. So the following two statements are correct: 1) a TC cannot improve the IQ of a lens; and 2) a TC + lens may record more detail in a digital image if the lens alone can out-resolve the sensor. My opinion of TC's comes from the film era, where in tests even the best TC always at least slightly reduced IQ (= a TC cannot make a lens better than it is, and addition of multiple lenses will almost always reduce contrast and resolution). With respect to the latter, there are photographers who advocate "never use any filter" because the addition of the glass will degrade image quality, and that is just one, very thin piece of glass.

WIth those two parameters I think we are on the same page.

But I have to tell you, Imaging Resources tests every camera that come out with Sigma 70 macro if they can. The K-5 tested at 2100 lw/ph, the K-3 at 2700. So far every test with a finer sensor has produced in increase in resolution. There is no indication that good lenses are going to be out resolved by sensors anytime soon.

With respect to the latter, there are photographers who advocate "never use any filter" because the addition of the glass will degrade image quality,

Once again a wives tale. Do those same photographers by 2 or 3 element lenses, instead of 11 or 12? I guarantee you not one of the uses a single element lens. You do what you need to do to get what you want. SO do the anti-filter crowd. But in terms of lens elements, CA correction requires more elements.So more glass actually aids IQ. The issue with the no filter guys is, they refuse to acknowledge adding a filter can improve your image.

I seriously don't understand folks getting all dogmatic about these things.

[WPRESTO]

WIth those two parameters I think we are on the same page.

But I have to tell you, Imaging Resources tests ever camera that come out with Sigma 70 macro if they can. The K-5 tested at 2100 lw/ph, the K-3 at 2700. SO far every test with a finer sensor has produced in increase in resolution. There is no indication that good lenses are going to be out resolved by sensor anytime soon.



Once again a wives tale. Do those same photographers by 2 or 3 element lenses, instead of 11 or 12? I guarantee you not one of the uses a single element lens. You do what you need to do to get what you want. SO do the anti-filter crowd. But in terms of lens elements, CA correction requires more elements.So more glass actually aids IQ. The issue with the no filter guys is, they refuse to acknowledge adding a filter can improve your image.

I seriously don't understand folks getting all dogmatic about these things.

We're on the same page V-A-V filters as well. The "never use a filter" advocates generally speak up when someone is considering a clear (or UV or skylight) filter to protect the front element of a lens, which apparently (ignorance of actual situation freely confessed) on big telephotos is sometimes made of special glass, maybe ED, and possibly not very resistant to scratching. I did once blemish the front element of a big lens by brushing it against an almost insignificant twig, and I'm inclined to use a protective filter on many of my lenses that have large front elements.

[UncleVanya]

We're on the same page V-A-V filters as well. The "never use a filter" advocates generally speak up when someone is considering a clear (or UV or skylight) filter to protect the front element of a lens, which apparently (ignorance of actual situation freely confessed) on big telephotos is sometimes made of special glass, maybe ED, and possibly not very resistant to scratching. I did once blemish the front element of a big lens by brushing it against an almost insignificant twig, and I'm inclined to use a protective filter on many of my lenses that have large front elements.

The problem with this is that there are many who have shown a negative impact to adding filters particularly for long telephoto use. My objections stem from people putting them on and never objectively testing them.

[cyberjunkie]

The issue with the no filter guys is, they refuse to acknowledge adding a filter can improve your image.

I seriously don't understand folks getting all dogmatic about these things.

I don't like dogmatism.
I don't use filters 99% of the times, but i would protect a valuable lens with a (good!) clear filter if i think i'm going to take pictures in an environment that could put the front glass at risk.

I don't follow you when you say that a filter can actually improve the image. What do you mean?
Of course a filter can't improve the optical quality of a lens.
Any element added to the original optical project degrades the image. Very very little or in a noticeable way, depending on the which filter (and lens) you use.
If you mean that a filter (mainly ND and polarizers with digital cameras) can give a kind of image that would be impossible to obtain without a filter... well, that's another thing.
If you need to blur running water, reduce metal reflections, or get a blue sky, it would be difficult and/or time consuming to get the same result in PP.

Going back to the subject of the thread, my own empirical impression confirms what you reported.
With most vintage lenses a converter can make focusing easier, but the quality of the image is not any better than the corresponding crop.
High performance lenses, which probably still outresolve the sensor, can perform pretty well with a 1.4/1.5 converter, better than the crop.
With the added advantage of easier focusing in manual, and a clearer view of the subject (which helps composition).
I want to try my 2.8/300mm A Star with the 1.4x-L and see if my original impression still holds true with the K-1.

cheers

Paolo

[p38arover]

There's a Takumar-A x2 teleconverter on Australian Gumtree for A$45 (about CAD45) Pentax-Takumar 2x teleconverter for KA mount lenses | Digital Camera Accessories | Gumtree Australia Knox Area - Rowville | 1074485333

If they won't ship, I'm happy to do it.