[reh321]

No TC is better than some kind of TC.

That is your opinion. My DA 55-300mm + 1.4X TC serves me fine - is better than just a 55-300mm for me.

[zapp]

DA* 200mm and DA* 300mm are true FF designs. DA560mm is FF capable.
We are expecting two TC from Pentax.

I totally disagree. No DA or DA* lens is a true FF design by default. We are looking at an optical formula that was inherited from FF designs (film era btw), but Pentax released both lenses as DA -> APS-C glass. That implies tha FF compatibility was not a priority in the design process. I know that the lenses do OK on FF..., but I would not claim that they are true FF designs. Was optical quality and vignetting really checked for digital FF during design phase? What cameras were used to test the lenses in real life. Not even all Pentax resources call them FF capable as of today:
Lens list for Digital single-lens reflex camera / Lens lineup/ Lenses / Products | RICOH IMAGING
The DA560 was obviously not designed for FF - so marketing invented FF "capable" afterwards.

All APS-C glass physically fits FF cameras and is capable of producing an image. Where do we draw the line?
Lens designations should be chosen carefully by the manufactrurer at release.

Bottom line. FF TCs are allways welcome, but make sure they work well with the future of lens designs and not with the (distant) past.

[Kunzite]

zapp, if you take a FF optical design, you put it in a FF-compatible barrel, but stick on it a DA label - does that make it an APS-C design?
The only difference between FF and APS-C lenses is coverage.

[normhead]

All APS-C glass physically fits FF cameras and is capable of producing an image. Where do we draw the line?
Lens designations should be chosen carefully by the manufactrurer at release.

We draw the line at what we find functional on an FF camera. Most APS-c lenses vignette on FF, because they were designed for APS-c. But there is a certain amount of DA glass that was designed for film FF and the design was just carried over to APS-c. They were designed for FF, they cover the FF circle without undue vignetting (even some FF lenses vignette, that's not necessarily a criterion.

My old screw drive Tamron 300 and Tamron MC7 2x give me 600mm 5.6 on FF. That's very nice and on my K-1 the IQ is quite acceptable.
But what other lenses would be useul?

The 300 2.8 lets me stop down a bit to ƒ8 to avoid fringing and CA) , but what other Pentax glass would even be functional for 2x TC? The 200 2.8, the 70-200 2.8 (and possibly the DFA 100 macro) are the only ones I can think of.

My experience would suggest you will get optimum use of a 1.4 TC for ƒ4 glass and a 2x for 2.8 glass. Without more longer 2.8 glass, my question would be "why?" What lenses would you actually want to use it on?

Just in terms of possible sales, a 1.4 FF TC could be used on both APS-c and FF, with all the ƒ4 lenses (300, 60-250, 70-210) giving it a much broader market the a 2x. I would expect to see that one first. It makes little sense to release a TC that pushes lenses past ƒ5.6. Practically, AF is negatively affected when a lens combo wide open is ƒ8 or slower. Making a TC for that purpose would in my opinion cause customer dissatisfaction. Among my Nikon and Canon shooting acquaintances, 1.4 is used on ƒ4 lenses. 2x is used on ƒ2.8 lenses. There's no way Pentax users interested in optimum performance are going to find things work differently just because they use Pentax. And those buying a 2x for their ƒ4 glass are going to run into some serious limitations. The 1.7 for ƒ4 glass is functionally better than 2x for AF. Especially since it acts as a focus limiter and gives you extremely fast AF within it's focus range.

IMHO most of the dissatisfaction with TCs is people use them on glass for which they aren't appropriate (not sharp enough, or not fast enough). Just because you can use them on given lens, doesn't mean you should. On the other hand, if you can't afford the long glass you need to make good use of the TC, I guess it's better than nothing.

But hey, no one at Pentax asked me for an opinion, they'll do what they want.

---

Last edited by normhead; 09-24-2020 at 06:58 AM.

[weverka]

...
The 300 2.8 lets me stop down a bit to ƒ8 to avoid fringing and CA) , but what other Pentax glass would even be functional for 2x TC? The 200 2.8, the 70-200 2.8 (and possibly the DFA 100 macro) are the only ones I can think of.

My experience would suggest you will get optimum use of a 1.4 TC for ƒ4 glass and a 2x for 2.8 glass. Without more longer 2.8 glass, my question would be "why?" What lenses would you actually want to use it on?

You can go a little further than that. How about pair the SMC Pentax-F 1.7x AF Adapter with the SMC Takumar 6x7 600mm F4, and the 6x7 to K mount adapter?

[normhead]

You can go a little further than that. How about pair the SMC Pentax-F 1.7x AF Adapter with the SMC Takumar 6x7 600mm F4, and the 6x7 to K mount adapter?

I'm not saying you can't do it. It takes until 5.6 to become pretty much nonfunctional, and I've used the 1.7x on the 60-250 as well as the stacked 1.4 and 1.7 on a 2.8 lens, but if you're used to faster glass, there is a difference in accuracy of AF and ease of use.

[TwoUptons]

I'm not saying you can't do it. It takes until 5.6 to become pretty much nonfunctional, and I've used the 1.7x on the 60-250 as well as the stacked 1.4 and 1.7 on a 2.8 lens, but if you're used to faster glass, there is a difference in accuracy of AF and ease of use.

With decent light, I've had good focusing results with the F 1.7x and the SMC-A 400mm f5.6

-Eric

[normhead]

I had the same lens and couldn't get any decent results at all with the A-400 and 1.7x. So YMMV. If I could have found a way to make it work, I probably would have kept mine so you have my congratulations.
Pentax AF is calibrated for ƒ2.8, and there's quite bit more DoF at ƒ8, which should make focussing a lot less precise if you're going for an exact focus point. But if your set up works through whatever combination of factors, more power to you. Don't sell anything.



---------- Post added 09-25-20 at 03:18 PM ----------

You can go a little further than that. How about pair the SMC Pentax-F 1.7x AF Adapter with the SMC Takumar 6x7 600mm F4, and the 6x7 to K mount adapter?

That is just sooo cool, are there any pictures taken with it?

[stihlmania]

I agree with Norm, best results are with the best lenses with TC”s....Cardinal image with this setup, 952 mm at minimum focus distance [ with 1/64 inch depth of field! ]

[Zygonyx]

Wow, exifs please !

[stihlmania]

Zygonyx, top left of my photos for EXIF..

[totsmuyco]

I agree with Norm, best results are with the best lenses with TC”s....Cardinal image with this setup, 952 mm at minimum focus distance [ with 1/64 inch depth of field! ]

Beautiful capture.

[SunnyG.]

Finally we know a new TC will come 🔭
When it happens, it'l be the first FF TC from Pentax who uses the AF of the lens. The AF of the F 1.7X was independend from the lens.

So if there are no surprises, a possible name can be D FA 1.4X AW.

Since the price for the DA was around $400, the D FA could be around 500$.
Pentax HD DA Rear Converter 1,4x AW | In der Grafik - in the? | Flickr
Pentax AF-Adapter 1,7x ebay | In der Grafik - in the chart: ? | Flickr

I hope it performs according to its price!

---------- Post added 12-07-20 at 07:01 AM ----------

I agree with Norm, best results are with the best lenses with TC”s....Cardinal image with this setup, 952 mm at minimum focus distance [ with 1/64 inch depth of field! ]

What a beast! Hope I can find one someday!

[reh321]

I'm not saying you can't do it. It takes until 5.6 to become pretty much nonfunctional, and I've used the 1.7x on the 60-250 as well as the stacked 1.4 and 1.7 on a 2.8 lens, but if you're used to faster glass, there is a difference in accuracy of AF and ease of use.

Which cameras is your experience based on?
My DA 55-300 f/4.5-6.3 PLM focuses well when used at 300mm with a DA 1.4X TC {where f-stop is reported as being something like f/9.5} on my KP, but hunts endlessly when used under same conditions on my K-30 {yes, I know it will be ‘wide-open’ in that case, but we are talking about focusing only}. It focuses on both cameras when used without a TC.

[davesofnj]

The original price of the current 1.4x was $600. Given the size of the glass that would be necessary for a 1.4x to be full frame, I'd expect it to cost at least $800 and I've been bracing myself for a $1000 price ticket.

I've taken to using a preset in Lightroom that scales up to 120% my images taken with the 150-450mm lens combined with the 1.4x. That gets rid of the vignetting and if an image isn't good enough to stand that much post-processing magnification then it probably isn't worth keeping anyway, so I'm kind of getting a 1.68 full-frame with the current setup.

Dave