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09-14-2013, 09:29 PM   #1
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Macro ratio confusion

I picked up my first dslr last November and still consider myself new despite the shutter count on my K-30 (Shutter Count 14,081). There is a lot to learn and I seem to accumulate lenses which of course adds to the learning process.

Today I managed to confuse myself and I still remain confused.
I have a Tamron 90mm macro lens which offers a maximum 1:1 ratio. The K-30 has a sensor that is 23.7mm wide. I had this lens since early January and have not actually measured what I could shoot, I just assumed I shoot something that was 23.7mm wide and it would fill up the picture........

Then today I picked up ($6 at a Thrift store) a Vivitar MC Tele Converter 2x - 22 and after playing with a manual 50 lens I had with me, came home and grabbed the Tamron. Still can't find a way to meter the light (green button works fine with my 50mm M lenses) but was more surprised by the size of the image I am able to shoot.

Maybe I am just tired and bad at math tonight but I can shoot a ruler and 7/32s of an inch fill my frame at maximum focus. That works out to just under a quarter of an inch or 0.21875 of an inch. More math tells me that the 23.7mm censor converts to 0.933071 of an inch.

By my math, that works out maxing out at 1/4 of the censor or 4:1. Maybe this will make more sense when I have more time to play tomorrow but for now I am confused. I've included to uncropped pics below......

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09-14-2013, 11:28 PM   #2
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Did you put the vivitar on the 90mm tamron?

Here is what is happening.

The vivitar macro converter is targeted for a 50mm lens. It does 2 things, first it contains a tele converter so your 50mm becomes a 100mm lens.

Second it has a focusing helix, which allows you to focus much closer. Between the two, it converts a 50mm lens into one that gives 1:1 macro

If you put this on your tamron, and use minimum focus distance on the tamron plus the minimum focus of the adaptor, plus then2x image enlargement I can easily see much higher magnification being possible. Likely 3:1 or more. Perhaps your 4:1 is about right
09-15-2013, 08:33 AM   #3
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QuoteOriginally posted by Lowell Goudge Quote
Did you put the vivitar on the 90mm tamron?

Here is what is happening.

The vivitar macro converter is targeted for a 50mm lens. It does 2 things, first it contains a tele converter so your 50mm becomes a 100mm lens.

Second it has a focusing helix, which allows you to focus much closer. Between the two, it converts a 50mm lens into one that gives 1:1 macro

If you put this on your tamron, and use minimum focus distance on the tamron plus the minimum focus of the adaptor, plus then2x image enlargement I can easily see much higher magnification being possible. Likely 3:1 or more. Perhaps your 4:1 is about right
Yes. I "just had to" try it with the Tamron. Time will tell how useful it will be in the field and what the IQ is like but will certainly try it.

I am guessing this Tele is only useful with lenses that have an Aperture ring as well, as there is no other way to change that?

Thank you for the explanation as well there Lowell. I thought I just might have been confused.
09-15-2013, 09:01 AM   #4
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If the TC is the version with electrical contacts and it is an "A" lens or newer you can control the aperture through the e-Dial.

09-15-2013, 09:30 AM   #5
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QuoteOriginally posted by Not a Number Quote
If the TC is the version with electrical contacts and it is an "A" lens or newer you can control the aperture through the e-Dial.
There are no contacts at all on Tele Converter. I checked out pictures of the Vivitar Tele here with 6 or 7 contacts but this one has none......
09-15-2013, 01:15 PM   #6
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QuoteOriginally posted by Mistlefoot Quote
There are no contacts at all on Tele Converter. I checked out pictures of the Vivitar Tele here with 6 or 7 contacts but this one has none......
There were two versions of the teleconverter. A long time at , without really thinking I passed on one with aperture contacts for $30. That was in something like 2004, when I had an *istD which could support TTL flash. I had no idea pentax would not continue to support TTL in the future. I bought the unit I have now, without contacts for $20 which was not a bad deal, but I should have ( in retrospect) bought the KA mount

In the same 20/20 hind sight, I should have bought many more M42 lenses than the 16 or 18 I have collected.
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