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04-09-2010, 07:45 AM   #1
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How does a teleconverter change the macro 1:x range?

Hi there, first post

I've been reading about the effects of a teleconverter on a macro lense and I am just not confident that I am thinking of this right.

I have a vivitar mc tele converter 2x and a sigma mini-zoom 39-80mm which can macro to 1:3.5.

When using the tele converter with this lense, does that mean:

3.5 / 2 = 1:1.75?

And so if I wanted to get a 1:1 ratio, i would need to get an extender then.

My secondary question is how large of an extender do I need to get 1:1 here and/or what is the math to determine this?

Thanks all!

04-09-2010, 07:51 AM   #2
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On your first question: yes, you are correct.

On your second one, I'm sure there are but that's far too precise for me. If you get an extension tube set, you don't need the 2x tele converter, by the way. You can get to 1:1 or beyond just with the tubes, and with better image quality.
04-09-2010, 07:55 AM   #3
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nesster,

awesome, i am glad i figured that right per the first part.

as far as extension tubes. This is where i am a bit hazzy. how do i determine what the proper size extender is to get a 1:1.35 lense to 1:1?

similarly, i'd imagine that if i purchased an extender that brought that lense to 1:1, then that would mean using a 2x teleconverter with that setup would bring the total to 2:1?
04-09-2010, 08:00 AM   #4
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I don't know the math, google or someone wiser here will provide, no doubt.

The tubes often come in sets of 3, and you can use them singly or in combinations for different magnifications and working distances. And yes, adding the 2x will double the magnification yet again. I've played with screwmount 2x and tubes - there's a slightly different look depending on whether you put the 2x in front or behind the tube(s). But with just the tubes you'll be able to get closer than 1:1, I'm certain.

04-09-2010, 08:04 AM   #5
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Interesting.

so is what i am looking for something like this?
Extension Tube Macro Ring for Pentax K K100D K110D - eBay (item 270559720550 end time May-06-10 19:54:05 PDT)

It's only $8, I am new to photography and i know lenses are really expensive. I know these are not lenses but $8?...
04-09-2010, 08:22 AM   #6
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That might do - but note: it has no electrical contacts, so you'll be doing manual metering. It also has no aperture linkages, so you'll have to have a way to stop the lens down yourself, though the adapter on the lens end may hold down the aperture pin for you. Therefore, you need an aperture ring on the lens.

Something like this would be more useful, as it has aperture coupling:
VIVITAR AUTOMATIC EXTENSION TUBES, PENTAX K FIT CAMERAS - eBay (item 110514986026 end time Apr-09-10 12:19:49 PDT)

Unfortunately, the KA type of tube is very rare and therefore expensive. One more area where being a pentaxian means wearing a hair shirt

Here's a real Pentax item:
PENTAX MANUAL EXTENSION TUBE SET WITH CASE MINT - eBay (item 220586362544 end time Apr-18-10 12:19:49 PDT)
04-09-2010, 09:17 AM   #7
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Hi Nesster,

Thanks for the links, i will certainly consider them.

For what it's worth, the lenses i own do not have electical contacts and are fully manual; they came from a user of the k1000. so any advantage I would get from the extension tubes that do have electrical contacts would only be realized when i buy new lenses; someday.
04-09-2010, 09:27 AM   #8
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Ok actually now I am a little more confused here.

I found that "total extension / focal length = magnification"

So if I had my zoom set to 68mm and i had 68 extension, i would achieve a 1:1.

What effect then, does the macro option on the zoom lense do to this figure?

So let's say the above, i have 68mm focal and 68 extension, THEN i hit the macro button and slide it to the 3.5- what would that mean? 3.5:1?

04-09-2010, 09:53 AM   #9
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I found here a formula that states M=((mLxF)+E)/F stating:
QuoteQuote:
M = magnification
mL = the magnification of the lens alone (see lens manual)
F = the lens focal lenght in millimeters
E = added extension in millimeters
My Nikkor AIS 105/2.8 can achieve 1:2 (= 0.5) magnification by itself. We can calculate the magnification of the system, when using this lens and two extension tubes totalling 80 millimeters, the PN-11 (52.5 mm) and PK-13 (27.5 mm).
M = ( (0.5 x 105) + 80 ) / 105 = 1.26 1.3
Magnification of AIS Nikkor 105/2.8 with 80 mm extension is 1.3X.
So, with my example of 68mm focal, 68 extension, and a macro option on the lense of 3.5 then i would end up with a 1:4.5 ratio?

Last edited by Capslock118; 04-09-2010 at 10:01 AM.
04-10-2010, 02:18 AM   #10
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Let's see, 1:3.5 at 68mm is about 92mm (mL*F). Add 68mm extension and you get 160mm ((mLxF)+E). Divide 160 by the 68mm FL and you get a magnification of 2.35:1. (I just figured this the way I normally do, then looked at the formula and saw it's the same. Whew.) I usually don't calculate the exact magnification. I just try to fill the frame with what I want.

Now, some truths. Macro zooms (ANY zooms!) don't do macro nearly as well as primes on tubes. Macro tubes with electrical contacts or even just PK (bayonet mount) aperture linkage are few and expensive. US$8 is a fair price for a set of manual tubes. Get two sets, or three -- you'll need more extension in order to use longer lenses for macro work. And the extra mount pieces can come in handy. (I ordered two sets, they sent me four -- wheeee!!) In fact, if you have any non-Pentax primes (Nikon etc), you can order a set of tubes for that mount, then interchange the mount pieces and use those Brand X lenses on your Pentax camera!

Those look like standard black-painted tubes, about the same as I have. Scrape off the paint on the mounts' bases. Or add some thin metal tape. Why? To (safely) short out the electrical contacts on the camera body, so you can use Catch-In-Focus (aka trap-focus) if you wish. Trap-focus is REALLY REALLY GOOD when you're shooting macros handheld. Have fun!
04-10-2010, 01:00 PM   #11
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QuoteOriginally posted by Capslock118 Quote
I found that "total extension / focal length = magnification"

So if I had my zoom set to 68mm and i had 68 extension, i would achieve a 1:1.

What effect then, does the macro option on the zoom lense do to this figure?
The formula above, and other simialr formulas, tell you the magnification *when focused at infinity. But of course, lenses don't have to be focused at infinity. the closer you focus, the more magnification you get. So lenses that already offer unusually close focusing for their focal length (ie macro lenses) will allow more magnification still. Not sure if there is an easier formula to say how much, though.
04-10-2010, 03:27 PM   #12
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QuoteOriginally posted by Marc Sabatella Quote
The formula above, and other simialr formulas, tell you the magnification *when focused at infinity. But of course, lenses don't have to be focused at infinity. the closer you focus, the more magnification you get. So lenses that already offer unusually close focusing for their focal length (ie macro lenses) will allow more magnification still. Not sure if there is an easier formula to say how much, though.
Hi Marc. I just checked my authority on this subject, FIELD PHOTOGRAPHY by Alfred Blaker, which deals extensively with usable math for extreme closeups. He gives the same formula, with M (magnification), F (focal length of lens) and E (camera extension - LENS TO FILM DISTANCE) (my emphasis). When you've added extension, you CAN'T focus to infinity! So magnification is ONLY dependent on focal length, and total extension.
04-12-2010, 05:47 AM   #13
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So while we're on this topic, I wonder if using a converter affects the minimum focusing distance of the lens?

Anyone know???

Rodney ...
04-12-2010, 06:34 AM   #14
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A converter - no - it just magnifies the image
Extension tube - yes - it reduces minimum focus ( and you lose infinity or even anything a bit further out, depending on how deep the tube)
04-12-2010, 07:21 AM   #15
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Thanks Nesster, Thats what I thought, but I wasn't sure if I had my head wrapped around it in the right direction.

Rodney...
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