[RioRico]

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Most of the cheap tubes I've seen are like these. According to the ad: "This Macro Extension Tube set does not have electrical contacts and does not preserve the automatic diaphragm." Wouldn't there be an aperture stop-down pin on the rear mount of the tubes if it had that feature?

More of a lever than a pin, but yes, these are the kind of cheap foolproof PK-zero tubes I use. Zero automation, neither electrical nor mechanical. I have six or seven sets. I use them for weird-lens mods as well as for macros. The price has risen since I last bought them.

Tubes of this type are NOT suitable for extending DA-type lenses lacking aperture rings. They do NOT allow pTTL flash use. Stick these on a dSLR and it defaults to Av mode. You control the exposure by arranging lights and setting the aperture. For more automation, you need different extension.

[GibbyTheMole]

Hi, RioRico...

I'm not concerned with exposure automation, and the lenses I will be using are standard MF lenses.

What I specifically need to know is: If I use these tubes, will I have to manually open up the lens to focus, and then manually stop it down to shooting aperture before pressing the shutter release to take the picture? If I'm taking a handheld closeup of a bug or something out "in the wild", it won't be practical to do that.

Maybe I'm wrong (which is why I'm asking) but it doesn't look like these cheap tubes have the lever on the rear required for the camera to stop the lens down from wide open to shooting aperture in the instant before the shutter fires, just like it does with a totally manual Pentax M lens.

On the other hand, all of the PK teleconverters I've seen have the aperture stop-down lever on the rear mount which is coupled to the aperture lever on the lens, so it should be possible to de-glass them and still have the auto stop-down function still work.

[baro-nite]

Maybe I'm wrong (which is why I'm asking) but it doesn't look like these cheap tubes have the lever on the rear required for the camera to stop the lens down from wide open to shooting aperture in the instant before the shutter fires, just like it does with a totally manual Pentax M lens.

Looks that way to me too. Hard to be 100% certain from that photo, but I can't see an actuator lever and the listing says nothing about "auto".

[newarts]

Hi, RioRico...

I'm not concerned with exposure automation, and the lenses I will be using are standard MF lenses.

What I specifically need to know is: If I use these tubes, will I have to manually open up the lens to focus, and then manually stop it down to shooting aperture before pressing the shutter release to take the picture? If I'm taking a handheld closeup of a bug or something out "in the wild", it won't be practical to do that.

Maybe I'm wrong (which is why I'm asking) but it doesn't look like these cheap tubes have the lever on the rear required for the camera to stop the lens down from wide open to shooting aperture in the instant before the shutter fires, just like it does with a totally manual Pentax M lens.

On the other hand, all of the PK teleconverters I've seen have the aperture stop-down lever on the rear mount which is coupled to the aperture lever on the lens, so it should be possible to de-glass them and still have the auto stop-down function still work.

You are right in all the above. But you may not need to stop down after focus. As I understand it, you'll be using the tubes with a 100mm 3.5 lens. At 1:1 this is already a f:7.0 lens and any further increase in magnification due to tubes will increase the effective f-stop ( effective f-stop = f-stop(1+m)). Increasing the effective f-stop much above f:11 will soften images.

Here's an example of how a lens is usually removed from a TC: See the holes on the perimeter of the lens?

Stick the tips of a pair of scissors in them and turn - the lens assembly will come out. Like tihis-


If the TC is a macro-focus, "A type" like that shown above, removing the lens will convert it into an A type variable length extension tube (ie. with electrical & aperture control). This about the best one might expect for a macro extension device!

Regarding lenses stuck on tubes, all the times I've heard of (and experienced) were when the user hadn't figured out how to properly move the release button on the side of the tube (it varies from tube to tube). To be sure a lens won't get stuck, one could learn how to release the lens from the tube by mounting the camera end of the tube set to the lens end - figure out how to press the button on the tube to release the lens end.

It isn't yet clear to me what you are trying to accomplish; your initial post about the 3x focusingTC and 100mm 1:1 macro lens implied you are looking for quite high magnification; is that not true? I'm surprised you found the image quality satisfactory using the 3x TC - if it was, I'd hang on to that TC. How does it perform for far away subjects?

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Last edited by newarts; 04-03-2012 at 08:22 AM.

[GibbyTheMole]

I'm surprised you found the image quality satisfactory using the 3x TC - if it was, I'd hang on to that TC. How does it perform for far away subjects?

It performs from far away pretty much like up close. I think it looks pretty good. Here's an example of the result of the rig: (Promaster 100mm macro + 3x Magnicon TC + ring flash)



So.. Before I buy something, whaddya think? TC or tubes?

[newarts]

It performs from far away pretty much like up close. I think it looks pretty good. Here's an example of the result of the rig: (Promaster 100mm macro + 3x Magnicon TC + ring flash)



So.. Before I buy something, whaddya think? TC or tubes?

That's a pretty good looking photo for a 3x TC I'd say!

Plain old tubes are so cheap and foolproof that you might get a set just to try them. You really should to see how image quality compares with your TC approach.

Personally, I would convert a vari-focus A-type TC to a variable length tube (I'm going to buy one and try it.)

Or if you were happy with your old TC, buy another just like it. (did you use the focusing capability of the TC or use the focusing ring on the Macro lens?... it isn't clear to me if the focusing feature of the TC is useful with your macro lens, although it certainly would be useful with a non-macro lens.)

I guess my answer to your question whaddya think? TC or tubes? - both - at worst you'll learn something and not be out much money.

[GibbyTheMole]

did you use the focusing capability of the TC or use the focusing ring on the Macro lens?

I just cranked the TC down to 1:1, cranked the focus on the macro lens to it's minimum distance & focused by moving the camera.

With a set of tubes, can I expect the same level of magnification as with the TC?

[newarts]

Thinking about this a little more leads me to believe the main benefit of the TC approach is a big increase in working distance compared to tubes alone. Basically a 3xTC means you can be 3x the distance from the subject for the same size image. That's very important in some cases.

That advantage goes away with tubes alone.

[newarts]

I just cranked the TC down to 1:1, cranked the focus on the macro lens to it's minimum distance & focused by moving the camera.

With a set of tubes, can I expect the same level of magnification as with the TC?

Less mag with the tubes.

The TC you used gave you a big mag factor to start with and just a little mag increase due to setting it to 1:1 I think. What happened in real life? Does changing the TC focus ring make much difference?

[baro-nite]

With a set of tubes, can I expect the same level of magnification as with the TC?

To get a 100mm lens to 3x on bare tubes, you need a lot of extension, an impractical amount I would say.

Basically a 3xTC means you can be 3x the distance from the subject for the same size image.

Very true.

I just cranked the TC down to 1:1

OK, what actual magnification are you getting? 1:1 or 3:1? I don't quite get the nomenclature for macro-focusing TCs. A photo of a ruler scale at max magnification would answer it.

[GibbyTheMole]

Does changing the TC focus ring make much difference?

Yep. A lot.

OK, what actual magnification are you getting? 1:1 or 3:1?

Dunno... That TC is actually designed to give 1:1 with a regular 50mm prime. That's what the "1:1" on the barrel indicates. I'm guessing it's much higher with a 100mm macro lens, but I'm not sure on the math.

One thing is certain: the increased working distance is a big plus when shooting bugs. I'll look for another copy of the TC, then maybe try the tubes or better yet - bellows, later.

[newarts]

To get a 100mm lens to 3x on bare tubes, you need a lot of extension, an impractical amount I would say.

The Baron is right. The math is simple:

extension = mag*Focal.length

so for a 100mm lens, and mag=2:1

extension = 2 * 100mm = 200mm .........that's a lot!

And as extension goes up, working distance goes down.

It is a little more complicated with your macro lens because it is an internal focus type and when it is cranked all the way its focal length is shorter, maybe 70mm so the extension needed is a bit less.

[baro-nite]

That TC is actually designed to give 1:1 with a regular 50mm prime. That's what the "1:1" on the barrel indicates. I'm guessing it's much higher with a 100mm macro lens, but I'm not sure on the math.

A typical 50mm has a maximum magnification around 1:6 or 1:7 on its own. Hence a typical 50mm would get around 1:2 with an ordinary 3x TC. So the macro TC needs to add enough extension to make that 1:1, another 35mm or so??? Put the TC on a 100mm 1:1 macro and you now have enough extension for about 4:3 and then the TC makes it about 4:1. Just my guess based on my very limited knowledge of how these things work.

[newarts]

A typical 50mm has a maximum magnification around 1:6 or 1:7 on its own. Hence a typical 50mm would get around 1:2 with an ordinary 3x TC. So the macro TC needs to add enough extension to make that 1:1, another 35mm or so??? Put the TC on a 100mm 1:1 macro and you now have enough extension for about 4:3 and then the TC makes it about 4:1. Just my guess based on my very limited knowledge of how these things work.

That's about what I was thinking, but that doesn't quite fit with gibby's saying the tc focus ring makes a big difference.

I need to do some numbers....

[Philoslothical]

By far the easiest way to figure out this TC would be for Gibby to take a couple shots of the millimeter gradations on a measuring tape, or ruler. One focused fully out, another in, etc. Then it'd be really easy to just calculate by dividing into the sensor width. That's what I do whenever I try a new method or lens pairing. Even on normal lenses the extension caused by focusing in can have quite an effect.