[SylBer]

One advantage of the Tamron 90mm over the Pentax 100mm WR is aperture ring. You can use it with old vivitar extension tubes and still maintain the ability to use your camera in Av mode. I don't think one can do that with the new Pentax 100mm WR. Achieving ratios bigger than 1:1with a relative ease of use is really cool. Correct me if I am wrong.

[dgaies]

One advantage of the Tamron 90mm over the Pentax 100mm WR is aperture ring. You can use it with old vivitar extension tubes and still maintain the ability to use your camera in Av mode. I don't think one can do that with the new Pentax 100mm WR. Achieving ratios bigger than 1:1with a relative ease of use is really cool. Correct me if I am wrong.

No question it's a lot easier and cheaper to use extension rings with the Tamron (vs the 100WR) because it has an aperture ring. I used to have a set of Vivitar AT-23 tubes which I could use with the 100WR (worked quite well actually) as they have electrical contacts that allow you to control the aperture from the body. They're expensive ($150-200) where as you can use just about an extension tube with a lens like the Tamron due to the fact that is has an aperture ring to control the aperture directly.

That said, and someone can correct me if I'm wrong, but I think you'd need quite a bit of length on your tubes (and light) to really increase the magnification of either of these 1:1 lenses much beyond 1:1.

[SylBer]

I am not familiar with the optical mathematics. I am sure someone will find an answer to that one. I looked for these extension tubes for a long time before buying the AT-22 version I think for 60 $ or so.

I have this model:

https://www.pentaxforums.com/forums/sold-items/32342-sale-%5Bsold%5D-vivitar-...eplus-mc4.html

[SylBer]

This guy (Hin) seems to have the answer:

Hin's Tech Corner: Vivitar AT-22 Macro Extension Tubes

According to his calculation, two extension tubes (36mm + 20mm) give a ratio of 1,56:1 on a 100mm 1:1 macro lens.

[dgaies]

I am not familiar with the optical mathematics. I am sure someone will find an answer to that one. I looked for these extension tubes for a long time before buying the AT-22 version I think for 60 $ or so.

I have this model:

https://www.pentaxforums.com/forums/sold-items/32342-sale-%5Bsold%5D-vivitar-...eplus-mc4.html

As far as I understand, to achieve 2:1 magnification with a 1:1 lens that is 100mm lens, you'd need 100mm of extension tubes. Again, if that's not right, please someone correct me on that.

As for the tubes themseleves, the AT-22 version will let you do stop-down metering but won't actually let you control the aperture from the body as they don't have electrical contacts. It basically turns your lens into a manual lens and you have to operate like you would a Pentax-K or Pentax-M series lens. With the AT-23 version, it basically turns your lens into a Pentax-A series lens. So with the AT-22 tubes and the 100WR you would not be able to control the aperture and would always be shooting wide open. With the AT-22 tubes and the Tamron 90, you would set the aperture on the ring itself and then just shoot it like a manual lens.

[dgaies]

This guy (Hin) seems to have the answer:

Hin's Tech Corner: Vivitar AT-22 Macro Extension Tubes

According to his calculation, two extension tubes (36mm + 20mm) give a ratio of 1,56:1 on a 100mm 1:1 macro lens.

That is how I was calculating it as well, so in the above post I suggested you need 100mm of extension to get to 2:1, or 56mm to get to 1.56:1.

[SylBer]

You were right.

[Blue]

One advantage of the Tamron 90mm over the Pentax 100mm WR is aperture ring. You can use it with old vivitar extension tubes and still maintain the ability to use your camera in Av mode. I don't think one can do that with the new Pentax 100mm WR. Achieving ratios bigger than 1:1with a relative ease of use is really cool. Correct me if I am wrong.

That has already been pointed out and the Sigma 105 also has the aperture ring. However, I have a kenko 25mm af extension tube and am looking forward to trying it out with the D FA WR later this summer. It works well with the Sigma 105 and FA 77.

[GeneV]

One advantage of the Tamron 90mm over the Pentax 100mm WR is aperture ring. You can use it with old vivitar extension tubes and still maintain the ability to use your camera in Av mode. I don't think one can do that with the new Pentax 100mm WR. Achieving ratios bigger than 1:1with a relative ease of use is really cool. Correct me if I am wrong.

That is also the reason why it works with older film bodies.

[Blue]

That is also the reason why it works with older film bodies.

You can use the WR on certain af film bodies that allow aperture adjustment via the body or if not, you can use them in autoprog, or Tv mode. Of course with macro, the Av is a big deal. That is the only negative thing I can say about my MZ-3 is that it doesn't allow Av control from the body which was not a problem until they did away with the ap ring.

[6hzzz]

我选择了100wr.