Stacking two (2) Pentax 1.4X HD AW TC's.

Started Mar 27, 2014 | Discussions
brandrx Forum Pro • Posts: 28,337
Stacking two (2) Pentax 1.4X HD AW TC's.

Hi folks,

I received my second Pentax 1.4X HD AW about 30 minutes ago. Before I did the tests below I made sure that each Pentax 1.4X HD AW worked properly. They do.

Stacking two of these Pentax 1.4X HD AW teleconverters corrects the aperture as if only one of them was attached. In other words, it is no different than stacking a Pentax 1.4X HD AW on top of a Tamron-F 1.4X Pz_AF. It's the same on SDM or screwdrive.

Stacking two of the Pentax 1.4X HD AW TC's shows the following for autofocusing as compared to stacking one Pentax 1.4X HD AW on top of one Tamron-F 1.4X Pz_AF.

(1) - Pentax DA*300/4 sill works crappy with stacking two.

(2) - Pentax DA*60-250/4 still works good with stacking two.

(3) - Sigma 300/2.8 still works good with stacking two.

I have not looked at IQ other than on the back of the camera. However, I predict that the IQ is not going to be that much different than stacking the Pentax 1.4X and the Tamron 1.4X.

In a nutshell, the purchase of two Pentax 1.4X HD AW teleconverters for stacking purposes is not worth it IMO.

Cheers.

Ron

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Ron - 'We don't have time to go take pics this afternoon Carl.'
Carl - 'What do you mean? It will only take 1/1000s.'
'Keep your eyes looking forward. However, glance back now and then to see where you've come from. It will put a smile on your face.' ~ brandrx

MightyMike Forum Pro • Posts: 38,596
Re: Stacking two (2) Pentax 1.4X HD AW TC's.

Interesting Ron, this means that the TC doesn't actually alter the aperture signal coming from the camera, it rather informs the camera that there is a 1.4x TC and the camera displays the new aperture. so in order to make this work on a 3rd party TC that TC would have to report the same code as the Pentax TC to get the aperture to change. I still think there is a big flaw happening to those who have a 1EV shift in metering with the TC

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Mike from Canada
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OP brandrx Forum Pro • Posts: 28,337
Re: Stacking two (2) Pentax 1.4X HD AW TC's.

MightyMike wrote:

I still think there is a big flaw happening to those who have a 1EV shift in metering with the TC

Mike,

As far as I know that much shift in metering only applies when attached to the Sigma 500/4.5 lens. I don't see a shift in metering when used on the DA*60-250/4 or the DA*300/4 lenses.

Ron

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Ron - 'We don't have time to go take pics this afternoon Carl.'
Carl - 'What do you mean? It will only take 1/1000s.'
'Keep your eyes looking forward. However, glance back now and then to see where you've come from. It will put a smile on your face.' ~ brandrx

snostorm Senior Member • Posts: 2,044
Ron. . .

Hi Ron,

The lack of support for the Av conversion is pretty strange, IMO. IIRC, stacking 2 1.7x AFAs resulted in a close approximation of the correct converted Av for the combination with Pentax lenses (and with Sigma lenses with contacts taped to provide a corrected max Av with the AFA). They seemed to be able to get this part right with the AFA.

Perhaps it has something to do with the information transmitted by the Info contact which is blocked by the absence in the AFA. . .

Scott

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Russell Evans Forum Pro • Posts: 12,617
Ron, do you own the DA * 55mm f1.4 and FA 77mm f1.8?

The 1.4x TC with the DA * 55mm would give you a 77mm f2, so I'm wondering how that would compare to the FA 77mm f1.8. I think the DA * 55mm f1.4 has rounded aperture blades, so it might be more interesting a comparison than just which is sharper.

Thank you
Russell

MightyMike Forum Pro • Posts: 38,596
Re: Ron, do you own the DA * 55mm f1.4 and FA 77mm f1.8?

Russell Evans wrote:

The 1.4x TC with the DA * 55mm would give you a 77mm f2, so I'm wondering how that would compare to the FA 77mm f1.8. I think the DA * 55mm f1.4 has rounded aperture blades, so it might be more interesting a comparison than just which is sharper.

Thank you
Russell

Actually due to the limitations of the TC you end up with F2.4 when on a lens F1.7 and faster

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Mike from Canada
"I am not a great photographer! God is a great creator! All I do is capture His creation with the tools He has provided me."
'I like to think so far outside the box that it would require a telephoto lens just to see the box!' ~ 'My Quote :)'
http://www.michaelfastphotography.com/galleries/VP-BDI_3a.jpg
http://www.airliners.net/search/photo.search?sort_order=views%20DESC&first_this_page=0&page_limit=180&&emailsearch=mighty_mike88%40hotmail.com&thumbnails=

OP brandrx Forum Pro • Posts: 28,337
Re: Ron. . .

The aperture is not corrected when attaching a Pentax "A" lens to the Pentax 1.4X HD AW. I can also attach a Pentax-A 1.4X-S (to either side of the Pentax 1.4X HD AW) then to the DA*60-250/4 and the aperture reads f4 when wide open.

So, the camera "knows" that a 1.4X teleconverter is attached via the Data pin which is only on autofocusing lenses. But then, not all autofocusing lenses, because it doesn't give corrected focal length and aperture for HSM lenses.

I'm through trying to make any sense of this. I will just continue to muddle my way through stuff as I always have. Then I will decide at the time of use whether or not to use them, or it, or not 

Ron

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Ron - 'We don't have time to go take pics this afternoon Carl.'
Carl - 'What do you mean? It will only take 1/1000s.'
'Keep your eyes looking forward. However, glance back now and then to see where you've come from. It will put a smile on your face.' ~ brandrx

OP brandrx Forum Pro • Posts: 28,337
Russell...

Russell Evans wrote:

The 1.4x TC with the DA * 55mm would give you a 77mm f2, so I'm wondering how that would compare to the FA 77mm f1.8. I think the DA * 55mm f1.4 has rounded aperture blades, so it might be more interesting a comparison than just which is sharper.

Yes Russell, I do own the DA * 55mm f1.4 and FA 77mm f1.8. Sometime in the future I might get around to making a comparison. Right now I am only interested in going long for wildlife shooting.

Ron

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Ron - 'We don't have time to go take pics this afternoon Carl.'
Carl - 'What do you mean? It will only take 1/1000s.'
'Keep your eyes looking forward. However, glance back now and then to see where you've come from. It will put a smile on your face.' ~ brandrx

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