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06-08-2007, 05:01 AM   #1
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Pentax a converter (and Tamron adptall one too)

Perhaps I have understood something wrong but when I attach Pentax-A 2x converter and lens to my K10D, the largest aperture viewed does not change.

Pentax-A 35-105 f:3.5 + Pentax-A 2x converter and body still shows largest aperture 3.5......

Same happens with Tamron SP 180mm f:2.5 and Tamron SP adaptall-2 2x converter, with or without converter it is 2.5....

Is this correct ofris one/some of these equipments faulty? cleaning the connections do not help.

06-08-2007, 05:09 AM   #2
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try cleaning the contacts with an eraser. sounds like you are not getting a good contact. try cleaning them also with some lens fluid applied to a cloth. DO NOT squirt the fluid onto the contacts.
i have just the opposite prob with my A1.4x-s and my manual lenses. the TC will not close the lens down to meter unless i short out the contacts between it and the manual lens.
06-08-2007, 05:23 AM   #3
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I allready tried to clean the contacts....

I also made some exposure experiments. Conlusion is that when using 2x A converter I have to dial at least -1,5 EV correction to get correct exposures.... very strange....

Does you your k10D:s show proper values for widest aperture when using converters?
06-08-2007, 05:36 AM   #4
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I'm pretty sure that unless you use the 1.7x-F AF converter, the camera won't know what lens is mounted and will therefore not adjust the aperture. I'll have to double-check that, though, as I'm not 100% sure.

When I used my 300mm F4.5 with the 1.7x TC, the maximum selectable aperture was F8, and when I used my 300mm F2.8, it was F4.5.


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06-08-2007, 05:54 AM   #5
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Yes, indeed...... now I think I understand.... in the KA-bayonet the max aperture value is an information made by shortcircuiting the contacts.... it is nothing more, nothing less.

Converter cannot "know" what lens is attached and thus cannot know what pins should be open and what closed to achieve the proper result... and it does not even try.

We really dont have any other means to play with KA-bayonet converters than dial - (minus) correction according what converter is attached. Simple, 2x needs -1,5-2 EV correctionand 1,4X needs obviously -0.5-1 EV correcton.
06-08-2007, 06:01 AM   #6
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QuoteOriginally posted by Mo Quote
I'm pretty sure that unless you use the 1.7x-F AF converter, the camera won't know what lens is mounted and will therefore not adjust the aperture. I'll have to double-check that, though, as I'm not 100% sure.

When I used my 300mm F4.5 with the 1.7x TC, the maximum selectable aperture was F8, and when I used my 300mm F2.8, it was F4.5.
These lenses were A-lenses? if they are K or M-lenses I do not understand where the converter gets this info :-)
06-08-2007, 06:16 AM   #7
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With the 1.7x-F, the lens you're using has to be an A, F, FA, FAJ, FA, or DA for the aperture connecton to be reflected in the viewfinder. If you use one of these lenses with an A-series converter, the loss of two stops will be compensated for by the camera, but it will not be shown in the viewfinder.

If you decide to use a manual (M or K) lens with any converter, you're on your own with exposure settings.

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06-08-2007, 08:02 AM   #8
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The 1.7x AF-TC or any TC (with automatic contacts) will not modify the behavior of the camera when using manual lenses. It cannot "create" an apature independantly as this information comes from the lens itself.

The AF TC will work from my experience up to F4, and from what I have seen from others, up to F4.5 but definitely not F5.6 lenses.

I have suggested to Pentax (I am not sure they listened) to make a new 1.7x TC / AF adaptor that could read the apature position from manual lenses and convert them to automatic. It would be a great selling product. probably 1:1 sales ratio to camera bodies.

06-08-2007, 08:26 AM   #9
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QuoteOriginally posted by Lowell Goudge Quote
What I have seen from others, up to F4.5 but definitely not F5.6 lenses.
I second that. F4.5 lenses can only be used in strong daylight with the AF converter.

QuoteOriginally posted by Lowell Goudge Quote
I have suggested to Pentax (I am not sure they listened) to make a new 1.7x TC / AF adaptor that could read the apature position from manual lenses and convert them to automatic. It would be a great selling product. probably 1:1 sales ratio to camera bodies.
That, in addition to the re-introduction of the aperture coupler to new DSLRs, would be very useful. I don't understand why Pentax only produces "crippled mounts" nowadays...

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06-08-2007, 08:31 AM   #10
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QuoteOriginally posted by Mo Quote

That, in addition to the re-introduction of the aperture coupler to new DSLRs, would be very useful. I don't understand why Pentax only produces "crippled mounts" nowadays...
I think it is a cost and space issue. With new lenses it is not really needed but it would be nice in some ways.

Note however, that you can get metering activated by stopping the lens down, or via the green button, and as a result work like many did with the origonal K series lenses. Matched needle mode on KX, K1000 etc, just not apature priority mode.

I think to some extent we are getting lazy/spoiled?
06-08-2007, 08:38 AM   #11
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Heh, we might be getting lazy with the desire for auto-everything, but the lever would allow cameras such as the K10D to more accurately meter the light with manual lenses, and it would also let us use the aperture rings instead of just the wheel on the camera. According to our December forum survey, more than half of the community uses M or K lenses- that should be a motivation for Pentax!

What I'd like to see is a digital PZ-1, lol- that camera has everything!

Let's not get sidetracked from the main thread topic, though, so back to teleconverters

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06-08-2007, 09:28 AM   #12
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QuoteOriginally posted by Mo Quote
With the 1.7x-F, the lens you're using has to be an A, F, FA, FAJ, FA, or DA for the aperture connecton to be reflected in the viewfinder. If you use one of these lenses with an A-series converter, the loss of two stops will be compensated for by the camera, but it will not be shown in the viewfinder.

If you decide to use a manual (M or K) lens with any converter, you're on your own with exposure settings.
Well, according my tests, camera does not compensate the light loss due to a Pentax-A converter automatically. You have to dial the EV compensation yourself. Do you have different experiences?
06-08-2007, 10:16 AM   #13
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QuoteOriginally posted by Harald Quote
Well, according my tests, camera does not compensate the light loss due to a Pentax-A converter automatically. You have to dial the EV compensation yourself. Do you have different experiences?
The camera compensates for the light loss symply by being a TTL metering scheme. It sees the light through the lens and sets exposure accordingly.

What I have found the camera DOES NOT do is compensate in the focal length, when using a TC, and as a result, the focal length for shake reduction is wrong.

Also when the camera displays F Stop number, it is that of the lens, not the effective f stop of the lens plus TC. It works this way on my sigma 1.4x and 70-200 mm F 2.8 zoom in any case.
06-08-2007, 11:20 AM   #14
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I tested it quite a lot today and it seems that this wrong widest aperture information confuses the measurements quite a lot.

I got it corrected only by dialing appropriate amount EV correction (-2) manually. After that measurements were consistently correct.

I thought that TTL measurement alone could do the compensation but it didnt.

Is there any other possible explanations? your cameras dont behave this way when Pentax A converters are used?

Lowell Goudge, you didnt mention what bayonet version your converter and lens was.
06-08-2007, 12:08 PM   #15
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QuoteOriginally posted by Harald Quote
I tested it quite a lot today and it seems that this wrong widest aperture information confuses the measurements quite a lot.

I got it corrected only by dialing appropriate amount EV correction (-2) manually. After that measurements were consistently correct.

I thought that TTL measurement alone could do the compensation but it didnt.

Is there any other possible explanations? your cameras dont behave this way when Pentax A converters are used?

Lowell Goudge, you didnt mention what bayonet version your converter and lens was.
I have 3 teleconverters, one sigma to go with my autofocus 70-200 F2.8, one pentax 1.7x autoficus adaptor, and one 2x Pentax A TC
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