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03-16-2009, 07:08 AM   #16
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QuoteOriginally posted by Samsungian Quote
I'll point out nikon never made a screw drive teleconverter. Pentax and Nikon both share this screwdrive autofocus technology. I know Tamron made screw drive af TC as I own it. But I have no SDM motor glass to see how it does on my K20D. I read it works fine with SDM glass. Its odd third party created a product that pentax cannot or will not. I think the tamron 1.4x for Pentax mount were discontinued in 2003. They are still available for other mounts.
I have the big-brother of the 1.5x Kenko tc, a 2x version. It works fine on all my screwdrive lenses from excellent on the FA50/1.4 to OK on the more darkish zoom lenses. Funny thing is that it didn't want to engage the SDM focus on the DA*50-135 despite that it had the SDM contacts (or once in a time long ago "power zoom" contacts). Not hunting like others were complaining on some other Kenko or Tammy tc's, but the SDM engine was completely dead.

So I oppened it, found a small electronical circuit inside, removed it, found a way to get the 7 A contacts to connect through the tc without the removed circuit. With this modification, the SDM was activated on the DA*50-135, but it hunted so much and never realy stopped in a good focus, so it was useless. When the SDM focus wont work on a f2.8 lense while the screwdrive focus work on f4 lenses or worse with the same tc, this makes me think that the SDM focus for some reason is more sensible to light losses than the screwdrive focus.

Thinking that since the screwdrive focus worked on slower lenses, it would be better than nothing if I could engage the screwdrive focus on the DA*50-135, so I tried disconnecting the SDM contacts and/or part of the A contacts, but no combination worked. Either, with A contacts, the camera (a K20D) does know that it is a SDM lens and refuse to activate the screwdrive, or, with the A contacts off, it believes it is a manual lens and refuse to activate any autofocus Just to irritate me, the DA*50-135 and this 2x Kenko TC worked well (with screwdrive focus) on my old MZ5 and *istDS. It tells us that it is something in the new DSLRs that prevent it from activating screwdrive focus on a SDM lens.

https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/38514-converti...erter-sdm.html

03-16-2009, 07:57 AM   #17
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Isololated view on crop format does not give extra reach

Take a lens like a 200-500mm 5.6 Tamron Adaptall and use same lens on Eos 5D full frame and Pentax K20D and the central images are identical. The isolated view the smaller sensor provides or gives no extra reach. You could argue the 15mp residing in aps-c would offer more photoshop potential over full frame 12mp. For me, my eyes aren't what they used to be. On crop viewfinder I am reminded of this. On full frame with biggie sized viewfinder I have NO manual focus/autofocus problems at all. I find with 5D I no longer have to chimp my images which then requires me to get my reading glasses out each time to see if I think I got the shot. Anyways once I gave the K20D to the wife for the last day of our 20th anniversary she customized it to her tastes. I don't want to reset it to factory settings so I don't use it now. I've considered getting me one but I've got other things on my $700 per item want list that I'm ignoring too.

If sensors were never pricey to begin with I'd guess there would have never been a 1.5x crop format, or a 1.3x format or a smaller than full sized medium format. Thus no need for the popular myth that smaller sensors give additional reach to sell photographers cameras at reasonable prices. The camera manufacturers continue the myth by modifing metadata to continue this illusion inleiu of offering affordable full frame cameras and full frame designed glass.




QuoteOriginally posted by kenyee Quote
Lindy: out of curiosity, why aren't you using an APS-C cam instead of FF when you need a TC? Seems like you effective get a 1.5x TC when you use APS-C.
I've always thought that I'd keep an APS-C cam if I ever got FF just for telephoto ranges because of this...

Last edited by Samsungian; 03-16-2009 at 09:13 AM.
03-16-2009, 08:08 AM   #18
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I use my 1.4x tamron with the 80-320 FA 5.6 successfully

All but one of my pentax lenses are manual focus. I experienced an irratating hunting session using tamron 1.4x paired with 80-320mm FA. Its kinda crazy that each time I wanted to take a pic the lens would hunt all the way out and back again. But image quality wise I was very impressed with results I got from 320mm + 1.4x= 450mm~ish or for you croppers that think aps-c means extra reach "675mm". To be fair using a 1.4x with a 5.6 lens would shut down af function on a canon body. One of thesedays it would be nice to try the Tamron 1.4x with a 200mm SDM or a 300mm SDM but as of now I have zero shops locally that carry pentax equiptment. But i live in a small 1/2 million person area so its too small a market for Pentax to be concerned with. In past 4 years I lost all 3 proshops, closed due to their inability to adapt and they carried pentax off and on and now they're all gone.


QuoteOriginally posted by Douglas_of_Sweden Quote
I have the big-brother of the 1.5x Kenko tc, a 2x version. It works fine on all my screwdrive lenses from excellent on the FA50/1.4 to OK on the more darkish zoom lenses. Funny thing is that it didn't want to engage the SDM focus on the DA*50-135 despite that it had the SDM contacts (or once in a time long ago "power zoom" contacts). Not hunting like others were complaining on some other Kenko or Tammy tc's, but the SDM engine was completely dead.

So I oppened it, found a small electronical circuit inside, removed it, found a way to get the 7 A contacts to connect through the tc without the removed circuit. With this modification, the SDM was activated on the DA*50-135, but it hunted so much and never realy stopped in a good focus, so it was useless. When the SDM focus wont work on a f2.8 lense while the screwdrive focus work on f4 lenses or worse with the same tc, this makes me think that the SDM focus for some reason is more sensible to light losses than the screwdrive focus.

Thinking that since the screwdrive focus worked on slower lenses, it would be better than nothing if I could engage the screwdrive focus on the DA*50-135, so I tried disconnecting the SDM contacts and/or part of the A contacts, but no combination worked. Either, with A contacts, the camera (a K20D) does know that it is a SDM lens and refuse to activate the screwdrive, or, with the A contacts off, it believes it is a manual lens and refuse to activate any autofocus Just to irritate me, the DA*50-135 and this 2x Kenko TC worked well (with screwdrive focus) on my old MZ5 and *istDS. It tells us that it is something in the new DSLRs that prevent it from activating screwdrive focus on a SDM lens.

https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/38514-converti...erter-sdm.html
03-16-2009, 11:58 AM   #19
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QuoteOriginally posted by kenyee Quote
Lindy: out of curiosity, why aren't you using an APS-C cam instead of FF when you need a TC? Seems like you effective get a 1.5x TC when you use APS-C.
I've always thought that I'd keep an APS-C cam if I ever got FF just for telephoto ranges because of this...
There is another thread here talking about this but in short a crop sensor doesn't actually give you an image that has 1.5x more magnification. It is only the FOV that is different. If you take that FF image and crop it by 1.5x you have the same exact photo.



John

03-16-2009, 03:00 PM   #20
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QuoteOriginally posted by huqedato Quote
Yes indeed.
The only thing can be changed with the K-Mount is either something electronical or related to to the optics (image circle).
Otherwise, the mechanical K-mount could not be changed keeping the back compatibility in the same time.
It could also be they are moving the lens closer to the sensor. That way the lenses would be smaller and native compatible with the Samsung NX. This would be the same generation shift as m42 to K. An adapter will be provided for the camera so that older lenses can be used. If this is it, it indicates Pentax will remove the mirror. Right now I don't feel very happy about that, but I will have a look at it with open eyes. The G1 is sooooooo much better than my old A2, so if Pentax/Samsung has another evolutionary step like that, hmm why not.
03-16-2009, 03:39 PM   #21
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QuoteOriginally posted by quarc Quote
It could also be they are moving the lens closer to the sensor. That way the lenses would be smaller and native compatible with the Samsung NX. This would be the same generation shift as m42 to K. An adapter will be provided for the camera so that older lenses can be used. If this is it, it indicates Pentax will remove the mirror. Right now I don't feel very happy about that, but I will have a look at it with open eyes. The G1 is sooooooo much better than my old A2, so if Pentax/Samsung has another evolutionary step like that, hmm why not.
Don't think so. It would render those lenses incompatible with any prior K-mount body.
03-16-2009, 04:19 PM   #22
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QuoteOriginally posted by quarc Quote
I get the impression Pentax has decided not to put anything on the roadmap unless it si very close to being launched. They probably want to avoid people sitting and waiting for future lenses rather than buying what is available today.
It also avoids people getting into the Pentax system, and has people like me looking at buying into the other systems and deserting Pentax.
03-16-2009, 04:44 PM   #23
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I really think people should wait 'till summer, and not switch just because of that roadmap. We may see something interesting then

03-17-2009, 01:29 AM   #24
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QuoteOriginally posted by Arpe Quote
It also avoids people getting into the Pentax system, and has people like me looking at buying into the other systems and deserting Pentax.
Other brands do not show roadmaps, does that prevent them from Buying those brands?
I'm not sure I understand...
03-17-2009, 06:04 AM   #25
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QuoteOriginally posted by Samsungian Quote
Take a lens like a 200-500mm 5.6 Tamron Adaptall and use same lens on Eos 5D full frame and Pentax K20D and the central images are identical.
The central images may be identical, but the issue is the final destination. The APS-C sensor maps the center portion of a full frame image to N mpixels. The full frame sensor maps the same area to a fewer number of pixels. So while it's not quite "you get a free 1.5x zoom" w/ APS-C because of DOF issues, you're effectively getting the cropped area mapped to the digital pixels of your sensor. If it's purely analog w/o digitization, yes, you're right, it doesn't matter. You'd just zoom the film in later and develop for it (assuming you're not hitting film resolution limits when cropping).

That's how I understand it at least...

btw, I just found out an old screw drive Nikon 300/2.8 is under $2K. Makes me wonder if running a dual system for tele is really a better idea since a used Pentax 300/2.8 runs $3.5K and new Sigma 300/2.8 is $3K :-P
03-17-2009, 06:08 AM   #26
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The Pentax Roadmap...

I thought for sure 3 years ago the roadmap was designed to keep people from switching from pentax to other brands. I recall how slow the 200mm SDM and 300mm SDM were to launch. And when they did they of course start at full retail which put the 200mm SDM several hundred above Canon 200mm 2.8 and a 300mm SDM couple hundred above Canon 300mm f4 IS.

Living with the Pentax Roadmap concept of selling items that do not exist was one of the few reasons I in Feb 2008 began building my Eos Full Frame System. By January 2009 I completed My Eos Kit and moved on to add Nikon D700 to specifically use their 14-24mm 2.8. I own 3 full frame dslrs now along with 3 K-Mount dslrs. Still the K20D I bought is a very nice Camera and the best way I know of to drive old K Mount lenses. When the wife travels she takes Pentax K20D and 3 or 4 lenses. When we travel together by car only the Canon and Nikon equiptment go with us. She uses and has customized to her tastes the 2nd 5D and I use a 5D and D700.

Luckily for me, adding lenses last year saved me a hundred here a couple hundred there. Now the devalued dollar has been intergrated into the prices and most everything I bought, except for two 5D, costs a bit more, like 10% to as much as 25% more.


Had it not been for the Pentax Roamap Experience I would have likely never bought so much gear in a 11 month period. so in a very real way I have pentax to thank for the lovely gear choices I have inhand today.







QuoteOriginally posted by thibs Quote
Other brands do not show roadmaps, does that prevent them from Buying those brands?
I'm not sure I understand...

Last edited by Samsungian; 03-17-2009 at 07:20 AM. Reason: added total K mount dslrs
03-17-2009, 06:19 AM   #27
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Yeah K20D is pixel rich enviroment, but the 6mp & 10mp are not

You finding a Nikon screwdrive 300mm 2.8 for $2,000 is commonplace Ken. If you keep your head inside the pentax system all is good. If you look around at everything everyone else made and what these items cost now second hand it becomes easier to want to add another brand of system based on what pro quality pentax lenses cost thesedays in aftermarket.

300mm 2.8 AF nikon buy it now $1890 plus $122 express to your door:

NIKON AF NIKKOR ED 300mm f/2.8 IF Exc+ D3 D700 D300 D80 - eBay (item 380108478057 end time Apr-04-09 22:00:00 PDT)


QuoteOriginally posted by kenyee Quote
The central images may be identical, but the issue is the final destination. The APS-C sensor maps the center portion of a full frame image to N mpixels. The full frame sensor maps the same area to a fewer number of pixels. So while it's not quite "you get a free 1.5x zoom" w/ APS-C because of DOF issues, you're effectively getting the cropped area mapped to the digital pixels of your sensor. If it's purely analog w/o digitization, yes, you're right, it doesn't matter. You'd just zoom the film in later and develop for it (assuming you're not hitting film resolution limits when cropping).

That's how I understand it at least...

btw, I just found out an old screw drive Nikon 300/2.8 is under $2K. Makes me wonder if running a dual system for tele is really a better idea since a used Pentax 300/2.8 runs $3.5K and new Sigma 300/2.8 is $3K :-P

Last edited by Samsungian; 03-17-2009 at 07:29 AM. Reason: added 300mm 2.8 link
03-17-2009, 03:10 PM   #28
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QuoteOriginally posted by thibs Quote
Don't think so. It would render those lenses incompatible with any prior K-mount body.
That is how the generation shift was done last time. You can use old lenses on the new bodies not the other way around, just like when they changed from screwmount to bayonet. With the new body there will be an adapter allowing old k-lenses, but if you buy the new lenses you will get more compact lenses, and i understand especially wide angle lenses can exploit being closer to the sensor.
03-17-2009, 04:54 PM   #29
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QuoteOriginally posted by thibs Quote
Other brands do not show roadmaps, does that prevent them from Buying those brands?
I'm not sure I understand...
They don't really need roadmaps as they already produce everything I, and others, generally need.
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