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Help with Tamron 2x teleconverter
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PostPosted: Mon Jun 20, 2011 3:32 pm    Post subject: Help with Tamron 2x teleconverter Reply with quote
Can someone with one of these help me please?

As I understand it, I lose 2 stops of light through the teleconverter, so if I set the lens aperture at say f8, then the value entering the camera is f16. I'm finding that with any AD2 mount on my 2x TC, the aperture reading in the window on the TC correctly shows f16 but the mount is still at f8. You can see this is this pic - the lens @ f8, the TC @ f16 and the mount @ f8. This shows a Minolta MD mount but the same happens with the PK mount:



Is this normal? The Minolta camera's open-aperture metering is being told the lens is at f8 but the light value is really f16, and surely this messes up the exposure. You'd expect this to result in 2 stops underexposure, but the shots on my first roll with this setup are actually over-exposed! What's going on?


PostPosted: Tue Jun 21, 2011 8:41 am    Post subject: Reply with quote
I've no idea what's going on, but I have just bought one of these units and, coincidentally, it came with a Minolta MD adaptall mount. It behaves exactly as yours does. Confirmation, but not very helpful, sorry !


PostPosted: Tue Jun 21, 2011 1:59 pm    Post subject: Reply with quote
Thank you Martyn, at least I now know my mount and lens aren't mechanically faulty. I'm reserving judgement on a design fault till I get to the bottom of this.


PostPosted: Tue Jun 21, 2011 3:15 pm    Post subject: Reply with quote
Hi Peter. Very Happy

Maybe have a look at this topic :
http://forum.mflenses.com/tamron-sp-500-f8-some-birds-in-the-garden-t36581.html

Mo asked about the doubler and I answered with a picture, nearly 2/3 from the bottom of the topic.

I hope it could help. Smile


PostPosted: Tue Jun 21, 2011 4:03 pm    Post subject: Reply with quote
My PK works the same. No problem for film cameras, or exposure measurements, only EXIFs will not have correct f/#.


PostPosted: Tue Jun 21, 2011 4:25 pm    Post subject: Reply with quote
Olivier wrote:
Hi Peter. Very Happy

Maybe have a look at this topic :
http://forum.mflenses.com/tamron-sp-500-f8-some-birds-in-the-garden-t36581.html

Mo asked about the doubler and I answered with a picture, nearly 2/3 from the bottom of the topic.

I hope it could help. Smile


Olivier, thanks for that, at least it shows I have mine assembled correctly Smile

BTW, the xxx for which you don't know the word could be a "TAB" (general term for something sticking out, like in your browser etc) or a "SPIGOT" (more specific engineering term) or simply a "DOOFER" (as in "don't know what it is, but it will DO FOR this as well as DO FOR that" [said quickly] Smile Smile)

I believe the french have the word "truc" ???


PostPosted: Tue Jun 21, 2011 4:28 pm    Post subject: Reply with quote
Hi Peter

I have the same lens and converter. What you are seeing is quite correct. For example, if you set f8 on the lens then your effective aperture is f16 because you are losing two stops of light due to the 2X teleconverter. My lens has a Pentax ES mount on it at the moment and I have coupled it with my Bessaflex TM. Outside this afternoon with the lens wide open at f2.8 I am getting a camera reading of 1/60 sec. With my handheld meter set to 1/60 sec I am getting a reading of f5.6.


PostPosted: Tue Jun 21, 2011 5:47 pm    Post subject: Re: Help with Tamron 2x teleconverter Reply with quote
peterqd wrote:
Can someone with one of these help me please?

As I understand it, I lose 2 stops of light through the teleconverter, so if I set the lens aperture at say f8, then the value entering the camera is f16. I'm finding that with any AD2 mount on my 2x TC, the aperture reading in the window on the TC correctly shows f16 but the mount is still at f8. You can see this is this pic - the lens @ f8, the TC @ f16 and the mount @ f8. This shows a Minolta MD mount but the same happens with the PK mount:



is that black tab (lower left corner of the photo) correctly connected between mount and tc, like it is between tc and the lens? i have only AD2 OM mount which doesn't have aperture numbers on the mount


PostPosted: Tue Jun 21, 2011 5:56 pm    Post subject: Reply with quote
This is really simple! Laughing

Use the camera adapter on lens without the TC -- now the aperture numbers reported to the camera match those written on the adapter, right? Very Happy

When camera adapter is put on TC, the aperture numbers on the adapter are now low by 2 stops. Laughing Tamron could have printed a second set of numbers for use on TC, but they didn't.

At issue is how the mechanical aperture setting coupling to the camera works. There is a fixed range of movement. The same full range of movement is used regardless the lens f/# specifications, 50/1.4, 300/5.6 both use full range of movement, with 50/1.4 @f/1.4 the lever is in the same position as with the 300/5.6 @f/5.6. The coupling is reporting lens aperture setting relative to the lens aperture range, not a specific f/# number, to the camera.

Last edited by visualopsins on Tue Jun 21, 2011 7:19 pm; edited 1 time in total


PostPosted: Tue Jun 21, 2011 6:51 pm    Post subject: Reply with quote
I'll add my hopefully simple answer as well.

The TC is simply showing the equivalent F-stop when it is being used since 2 stops of light are lost. That's all.

The camera adapter shows f/8 because it is meant to correspond to what the lens shows. It wasn't designed to reflect what a TC shows. But the TC reminds you what the actual aperture value will be.

It's real easy to confirm this. Take a reading of a simple, evenly lit scene with your camera's meter using the lens only. Install the TC and take a reading of the same scene. Your camera's meter should be indicating 2 stops less of light.


PostPosted: Wed Jun 22, 2011 1:20 pm    Post subject: Reply with quote
cooltouch wrote:
I'll add my hopefully simple answer as well.

The TC is simply showing the equivalent F-stop when it is being used since 2 stops of light are lost. That's all.

The camera adapter shows f/8 because it is meant to correspond to what the lens shows. It wasn't designed to reflect what a TC shows. But the TC reminds you what the actual aperture value will be.

It's real easy to confirm this. Take a reading of a simple, evenly lit scene with your camera's meter using the lens only. Install the TC and take a reading of the same scene. Your camera's meter should be indicating 2 stops less of light.

OK, thanks for all the help. I think I it makes sense now. Idea Of course, when I'm looking through the TC, the light level is already reduced by 2 stops, and the meter reacts accordingly.

Not thinking straight, I was expecting the mount to add 2 stops to the lens aperture setting! I even went to the bother of experimenting with my X500, using a Minolta lens, a Tamron lens and the Tamron + the TC, and comparing the position of the open-aperture metering tab on the camera. Of course it was the same for all three. Doh! I guess my age is showing Smile


PostPosted: Thu Jul 07, 2011 9:50 am    Post subject: Reply with quote
Thought I'd add a finale to this thread. These two shots were taken with the Tamron 80-210 103A on the 400D, from the beach at Seaview on the Isle of Wight, looking across to the Spinnaker Tower in Portsmouth Harbour on the mainland. The distance from the camera to the tower is exactly 5 miles/8 kilometres. Pic 1 is included to show a sense of the distance with the lens at 80mm and no TC, and Pic 2 is at 210mm with the TC, so effectively 420mm (not counting the crop factor).

Something happens to the camera metering with the TC in place as the 2nd shot was at least 1 stop OVER exposed and I've reduced the exposure in RAW to compensate, plus resizing and adding a little sharpening.

I'm rather pleased with this. I was expecting a fair bit of degradation using the TC, but I'm pleasantly surprised. Smile

(PS Please excuse the sensor dust - now removed.)

80mm

210mm + 2xTC


PostPosted: Thu Jul 07, 2011 10:20 am    Post subject: Reply with quote
Peter, as far as I'm concerned, that's a great result ! Smile Shocked

About metering, the TC multiplies by 2 the aperture either.
So, we have to compensate between 1 and 2 stops.

Thinking again about your 2 pictures above, I repeat that I'm really impressed.
I'm wondering what result it would give if I try with mine on Dover cliffs seen from Wissant.

Have a nice day. Smile


PostPosted: Thu Jul 07, 2011 10:57 am    Post subject: Reply with quote
Peter, that's a cracking result! I will have to try mine again, it certainly hasn't been that good up to now Sad


PostPosted: Thu Jul 07, 2011 11:25 am    Post subject: Reply with quote
OK, I must have a bad copy of the teleconverter. I know it's grey and raining here at the moment, but to my eyes this is a significant degradation in image quality. Shot using Tamron 103A at f8. Without and with TC.




PostPosted: Thu Jul 07, 2011 11:27 am    Post subject: Reply with quote
Olivier, be sure to let me know when you go to Wissant and I'll be on the cliffs at Dover waving to you! Laughing

Thanks very much Martyn. I had the camera mounted on a tripod on the top of the sea wall, with the legs fully retracted to make it as solid as possible and I used the remote release. I really like the 103A a lot. Although it's non-SP, I think it outshines my SP60-300 and it's a lot easier to use.


PostPosted: Thu Jul 07, 2011 12:18 pm    Post subject: Reply with quote
I have the 103A as well and it is a lovely lens...must admit I had not thought of using the adapter with it! Rolling Eyes ...great shots Peter.


PostPosted: Thu Jul 07, 2011 12:37 pm    Post subject: Reply with quote
martyn_bannister wrote:
OK, I must have a bad copy of the teleconverter. I know it's grey and raining here at the moment, but to my eyes this is a significant degradation in image quality. Shot using Tamron 103A at f8. Without and with TC.

That image isn't so bad as it looks, you know! It can be improved a lot with PP. There seems to be some kind of flare reducing the contrast, and like mine maybe a little overexposure. I also think it's quite permissible to add a little sharpness. Here's my very quick go at it:


Thank you Mo! Smile


PostPosted: Thu Jul 07, 2011 3:10 pm    Post subject: Reply with quote
I tried mine too. Wink
But with the Tamron 03A 80-210mm.
It's clearly worse than the 103A at 210mm.

1/ on the 400D
at 80mm F8

at 210mm F8

at 210mm F8 + doubler


2/ on the 5D MkII
at 80mm F8

at 210mm F8

at 210mm F4 + doubler


Not too bad.
I too observe a difference in white balance, metering and contrast.


PostPosted: Thu Jul 07, 2011 3:48 pm    Post subject: Reply with quote
peterqd wrote:
That image isn't so bad as it looks, you know! It can be improved a lot with PP. There seems to be some kind of flare reducing the contrast


I agree. What is annoying is that this was taken when it was grey and raining, so it cannot be flare! It seems to affect all the shots I have taken with this TC, so I put it down to a bad copy. It doesn't seem overly dirty, but I might take it apart to see if there is any misting or hazing on any of the internal elements.


PostPosted: Thu Jul 07, 2011 3:59 pm    Post subject: Reply with quote
Super shots Olivier! So now I know mine wasn't a fluke. I have a 03A too, and it isn't far behind the 103A at all. Anyway, I can't grumble about it as it only cost 99p! Smile

The 5D seems to handle the contrast a lot better, assuming you didn't do any PP.


PostPosted: Thu Jul 07, 2011 4:06 pm    Post subject: Reply with quote
mo wrote:
I have the 103A as well and it is a lovely lens...must admit I had not thought of using the adapter with it! Rolling Eyes ...great shots Peter.


Yep..... like the 46a, the 103a is good zoom.


PostPosted: Thu Jul 07, 2011 4:37 pm    Post subject: Reply with quote
peterqd wrote:
Olivier, be sure to let me know when you go to Wissant and I'll be on the cliffs at Dover waving to you! Laughing

Laughing
Be sure I'll let you know, Peter !!! Very Happy

About my pictures, they are raw converted to Jpeg. I just compensated exposure and tightened light and dark levels (on the Jpeg histogram).
On the 5D at 210mm with doubler, this is a F4 picture (F8 on the doubler) and I increased contrast one stop.

I take photos in Raw mode and Adobe RVB.
To post them here, I change the colours to sRVB and push sharpness a bit.
I don't heavily PP any of these pictures.

I think that the 5D MkII sensor is far better than the 400D's and the image treatment has been greatly improved with a better processor.
I would be a pity if it were different when I look at the price difference. Wink


PostPosted: Thu Jul 07, 2011 4:46 pm    Post subject: Reply with quote
Olivier wrote:
It would be a pity if it were different when I look at the price difference. Wink

That's true! I'm perfectly happy with the 400D but wish I could afford a 5D, that's for sure! Smile


PostPosted: Thu Jul 07, 2011 5:09 pm    Post subject: Reply with quote
peterqd wrote:

Something happens to the camera metering with the TC in place as the 2nd shot was at least 1 stop OVER exposed and I've reduced the exposure in RAW to compensate, plus resizing and adding a little sharpening.


That was an excellent shot, Peter. As for your above comment, this might be attributable to Canon's reliance on electronic feedback from the lens in order to compute correct exposure. With my EOS, I have some lenses -- usually telephotos -- that require up to two stops of underexposure compensation the further they are stopped down. And I have others that require zero. It's practically a case-by-case basis.

Your results are similar to what I've been getting with my Tamron 01F 2x TC.

I have a 103A that's just sitting on a shelf since I bought it at a second hand store. Almost mint condition, even came with a Tamron case. Paid $20 for it, and given how little they sell for on eBay, and especially given how good of a lens it is, I've just decided to keep it. Need to go out and exercise it, though.
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