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12-25-2009, 08:23 PM   #1
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Extension Tube Question

I was reading up on the DA 35 Limited Macro. It supposedly has a focus distance of .45 inches. What are the benefits to using an extension tube to a lens that already has such a short focus range? Or are these tube reserved for ones that do not have such close ranges?

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12-25-2009, 09:51 PM   #2
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Its 5.4 inches, not 0.54

According to the specs on Pentax USA's website:

PENTAX DA Limited Macro Lens for Digital SLRs and Compacts: smc PENTAX DA 35mm F2.8 Macro Limited

the minimum focusing distance is 5.4 inches, not .54 inches. That's pretty close focusing, but its still not 1:1 or larger magnification. For that, you need extension tubes.
12-25-2009, 10:08 PM   #3
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QuoteOriginally posted by noblepa Quote
According to the specs on Pentax USA's website:

PENTAX DA Limited Macro Lens for Digital SLRs and Compacts: smc PENTAX DA 35mm F2.8 Macro Limited

the minimum focusing distance is 5.4 inches, not .54 inches. That's pretty close focusing, but its still not 1:1 or larger magnification. For that, you need extension tubes.
I just checked the link above and it clearly says the mag = 1.1

To simplify the question, will an Extension Tube somehow enlarge the magnification rate of 1:1 [DA 35] by getting you a closer focusing distance? In other words, does ET's increase your mag ratio?

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12-25-2009, 10:11 PM   #4
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I just checked wiki, and it does say that ET's increase the mag ratio, which makes sense ^^ But how much more of an increase in Mag ratio would you achieve with a DA 35 on ET? To me it seems ET's are more suited for 100mm macro lenses, if so how much more mag ratio would you achieve? Would it depend on how many ET's are being used? If so, what would each ET's get in terms of mag ratios?

12-25-2009, 10:17 PM   #5
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If you put 35mm of extension tubes on a 35mm lens you will double the magnification.
12-25-2009, 10:41 PM   #6
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that's was easy ^^ ty for the to the point answer
12-25-2009, 11:09 PM   #7
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But Gary, what about for a 70-300mm lens I am planning to get? Do they even have extension tubes that go up that high? If I did use the 35mm extension tube you mentioned on this 70-300mm lens, what mag ratio would I achieve? I'm talking about the Tamron 70-300 DI LD Macro [i know this is not a true macro] I probably won't be getting an extension tube for this but just for the sake of asking.
12-25-2009, 11:28 PM   #8
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QuoteOriginally posted by joodiespost Quote
But Gary, what about for a 70-300mm lens I am planning to get? Do they even have extension tubes that go up that high? If I did use the 35mm extension tube you mentioned on this 70-300mm lens, what mag ratio would I achieve? I'm talking about the Tamron 70-300 DI LD Macro [i know this is not a true macro] I probably won't be getting an extension tube for this but just for the sake of asking.
The answer is, "it depends". What it depends on is the close focus limit on the lens without the tubes and the focal length of the lens. In the case of a zoom lens, it gets complicated, so I will use a 50mm and 100mm lens for the purpose. Nit pickers and pixel peepers, I realize fully that this is a gross simplification of things, but it will point the OP in the right direction.

I own and love the M 100/4 macro lens. The problem is that it only gets up to 1:2 magnification. The full extension of the helical is 50mm. To get 1:1, I need the lens nodal point (the real optical centre) to be 100mm from the film or sensor. I own and add an extension tube whose length is 50mm to get the full 100mm extension when my 100mm lens is at its closest focusing point. When the lens is focused at infinity, with the 50mm tube, it is the same magnification as when the lens is focused all the way in with its 50mm helical. So with the tube attached between the camera body and the lens, I have my choice of magnifications from 1:2 through 1:1.

If I put the 50mm tube on the back of a 50mm lens, it will be 1:1 with the lens helical focused at infinity, and some other number when the lens is refocused with its helical to the minimum focus distance.

In grossly simplified terms, the nodal point of the lens (where a single element lens would be) is a certain distance from the film/sensor when the lens is focused at infinity. This is the focal length of the lens. Magnification is approximately the focal length divided by the extension.
To obtain 1:1 with my 100mm macro, I need 100mm of extension. The lens itself includes the equivalent of 50mm, so adding 50mm more gives me 1:1.

Hope this long worded explanation helps the concept. In the case of your 70-300mm zoom, at 70 mm, 70 mm of extension will give you 1:1 - you hope. Zooms don't work the same as prime lenses, so the only way you can ever figure out the true magnification is to take pictures of a ruler.

A true macro lens is also optically corrected to provide a flat field, particularly at close focus distances. They are much more difficult to build, optically, which accounts for some of the high price. The rest of the price increase over the equivalent non macro lens of the same focal length is the much smaller number of macro lenses that are ever sold.

12-25-2009, 11:40 PM   #9
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QuoteOriginally posted by joodiespost Quote
I was reading up on the DA 35 Limited Macro. It supposedly has a focus distance of .45 inches. What are the benefits to using an extension tube to a lens that already has such a short focus range? Or are these tube reserved for ones that do not have such close ranges?

Thanks
QuoteOriginally posted by noblepa Quote
According to the specs on Pentax USA's website:

PENTAX DA Limited Macro Lens for Digital SLRs and Compacts: smc PENTAX DA 35mm F2.8 Macro Limited

the minimum focusing distance is 5.4 inches, not .54 inches. That's pretty close focusing, but its still not 1:1 or larger magnification. For that, you need extension tubes.
No, you probably do not want to use tubes on a 35ltd. The reason is the Minimum WORKING Distance (note this is not minimum focus distance) is somewhere around 0.5" - 1" from the front element. By adding tubes you might, well probably...no for sure, move the MWD INSIDE the lens. This is, well, bad for photography.

The 5.5" or so distance is the lenses MFD which is measured from the focal plane not the front element. From my experience with the 35ltd its at it's best when thought of as a close focus lense rather than trying for 1:1 true macro. I have used it for both and it excels in either case but the MWD is so tiny that it can be problematic in getting the shot.

It is probably my favorite lense of all time though.
12-26-2009, 12:12 AM   #10
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Thank you Canada Rockies and Breckludin. And thanks to all the helped out for this tread, I can now sleep peacefully ^^

i currently am trying to obtain a Tamron AF 70-300mm f/4-5.6 LD Di macro for 70 dollars used, in top condition wish me luck
12-26-2009, 02:23 AM   #11
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glad to help...

And have fun with the 70-300 and some tubes...
12-26-2009, 07:09 AM   #12
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QuoteOriginally posted by joodiespost Quote
what about for a 70-300mm lens I am planning to get? I'm talking about the Tamron 70-300 DI LD Macro

The first thing you'll want to know about extension tubes is that auto tubes are hard to find and very expensive because of it. The cheap extension tubes that you can find aren't auto aperture, so that means the lens is going to need to have its aperture set by the aperture ring to be useful. The DA 35mm macro nor the Tamron 70-300 DI LD Macro have an aperture ring.

With a 1:2 lens like the Tamron, your best bet would be to try to use a 2x teleconverter to bring the magnification ratio close to 1:1. I have a Sigma 70-210 F3.5-4.5 APO 1:2 macro that, with a 2x TC, I can get to about 1:1.1. I measure a horizontal 25-26mm on a ruler to the 23.4mm horizontal of the sensor. Working distance is about 20 inches.

The TC approach will require a lot of light however and AF is not an option. I bought the Sigma for $35 and the Quantaray 2x TC for $12 so this was a very inexpensive way to get to almost 1:1 for me. I now need to find an older MF 2x TC so that I can try trap in focus with this setup.

You can also use a close up, supplemental, lens (diopter) to get closer. I have never tried this so can't really say anything about this approach. I have looked for a cheap two element diopter and have not found any. The Canon and Nikon diopters are usually over $100 and can be up to $180 for the 62-77mm sized ones.

Thank you
Russell

Last edited by Russell-Evans; 01-25-2010 at 11:52 PM.
12-26-2009, 11:33 AM   #13
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Thank you Russel for that. I had a quick question, I know that in my K-x Kit Lens the aperture is set automatically in relation to whatever setting my focal length is. Which is to say I can't set the aperture to 3.5 at 55mm. I can only do that at 18mm. With a manual aperture lens, is there a locking mechanism that will keep me from turning the aperture to a 3.5 while at 55mm focal length? I am sorry if this sounds stupid as I have never touched a manual lens before, well I probably have but never gave it a thought
12-26-2009, 12:25 PM   #14
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QuoteOriginally posted by joodiespost Quote
Thank you Russel for that. I had a quick question, I know that in my K-x Kit Lens the aperture is set automatically in relation to whatever setting my focal length is. Which is to say I can't set the aperture to 3.5 at 55mm. I can only do that at 18mm. With a manual aperture lens, is there a locking mechanism that will keep me from turning the aperture to a 3.5 while at 55mm focal length? I am sorry if this sounds stupid as I have never touched a manual lens before, well I probably have but never gave it a thought
not a stoopid question at all...a Pentax AF/Auto lens will have a "A" on the aperture ring. The ring will physically lock into that position so you can use is as and auto-aperture lens. But if you want manual control you simply rotate the ring out of that position to the aperture you want. Pretty simple if you ever used a 35mm in the 'old' film days in the "before time"...hehehe....

If you ever try using a reversed lense for macro, ya want a lense with an aperture ring for sure. It is a real PITA to set the aperture otherwise and, in fact, you can't on a Pentax body. On a Canon body you need to do a "preview/liveview" so that the aperture blades close down...then remove the lense while the blades are still closed down to whatever you set the camera to use...it's tricky because you need to hold a couple buttons the hole time while removing the lense...then when you want to use a different aperture you need to do the whole dance all over again. That is why it's important to use only manual aperture (the ones with an aperture ring) on those cheap manual tubes.

BTW, for the price of the full auto tubes, just buy a cheap old manual 50mm (or any other lense) and get a reversing ring...a lot easier for sure and cheaper, plus you get another lense you can use. but the reversed lense does not need to be for a Pentax mount as you are not connecting from that end. it only needs be a K-mount if you want to use it as a a 'normal' lense on the body.

You can reverse a lense at the end of another lense or directly on your current body...your choice both require at lease on adapter that fits the threads on the lense to be reversed as well as the k-mount or the threads on the second lense.
12-26-2009, 12:32 PM   #15
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I have used lenses reversed on my film cameras. A 28mm lens reversed on the body gives you about 2X magnification. My reversing ring was 52mm filter ring, and my M 28/3.5 was a 49mm filter ring, so I needed a 49 >52 adaptor ring. The extra extension of the adaptor included, my magnification was around 2.1X. The wider the lens, the more magnification.
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