macro 1:1 extension tubes question

**Michael Piziak** · 02-09-2021, 08:01 AM

Using the Asahi Pentax M 100mm macro 1:4 lens that takes 1:2 macro photos.

Which extension tube or combination of tubes would take a 1:1 macro photo?

From the web: The Asahi Pentax Auto Extension Tubes are a three piece set consisting of tube #1 of 12mm in length, tube #2 of 19mm, and tube #3 of 26mm. Combined the three tubes have a total extension of 57mm.

Read more at: Asahi Pentax Auto Extension Tubes - Influential Photo Gear | PentaxForums.com

**SamirShah** · 02-09-2021, 08:50 AM

You read my mind! I have the same question!

**baro-nite** · 02-09-2021, 08:54 AM - **1 Like**

A lens needs total extension (including that provided by the focus helicoid) equal to its focal length to achieve 1:1 magnification. Your lens at closest focus already gives you 50mm of extension (hence 1:2 magnification), so adding 50mm gets you to 1:1.

**Michael Piziak** · 02-09-2021, 09:43 AM

ok thanks!

I wonder what logic was behind the choice of tube #1 of 12mm in length, tube #2 of 19mm, and tube #3 of 26m

**UncleVanya** · 02-09-2021, 10:14 AM

Originally posted by Michael Piziak

ok thanks!

I wonder what logic was behind the choice of tube #1 of 12mm in length, tube #2 of 19mm, and tube #3 of 26m

I'm not sure what specific change would be more logical. Remember these are for use on any lens not just 50mm.

**Michael Piziak** · 02-09-2021, 10:26 AM

Originally posted by UncleVanya

I'm not sure what specific change would be more logical. Remember these are for use on any lens not just 50mm.

You have a point. I was just thinking that even numbers would be more logical, like 10mm, 20mm, & 30mm, but the people that made them are much smarter than me.

**stevebrot** · 02-09-2021, 10:32 AM - **1 Like**

Originally posted by Michael Piziak

ok thanks!

I wonder what logic was behind the choice of tube #1 of 12mm in length, tube #2 of 19mm, and tube #3 of 26m

They want to mess with your mind.

I have two sets of extension tubes, one from Soligor (12mm, 24mm, 32mm) and one from Vivitar (12mm, 20mm, and 36mm). Both total to 68mm. If it were 42 (the ultimate answer to life, the universe, and everything), it might make sense, but 68? I have had many sleepless nights due to this issue.

Sleepless nights aside, probably the easiest way to attain 1:1 with your lens is with a bellows. Leave the lens focused to infinity, rack the bellows out 90mm or so, and fine tune the magnification using the focus ring or bellows nobs to attain 1:1 (focus on a millimeter scale to a frame width of 36mm or 23.5mm depending on camera).

Steve

**Michael Piziak** · 02-09-2021, 10:48 AM

Originally posted by stevebrot

They want to mess with your mind.

I have two sets of extension tubes, one from Soligor (12mm, 24mm, 32mm) and one from Vivitar (12mm, 20mm, and 36mm). Both total to 68mm. If it were 42 (the ultimate answer to life, the universe, and everything), it might make sense, but 68? I have had many sleepless nights due to this issue.

Sleepless nights aside, probably the easiest way to attain 1:1 with your lens is with a bellows. Leave the lens focused to infinity, rack the bellows out 90mm or so, and fine tune the magnification using the focus ring or bellows nobs to attain 1:1 (focus on a millimeter scale to a frame width of 36mm or 23.5mm depending on camera).

Steve

Big Smiles!

Well, achieving a perfect 1:1 doesn't bother me that much, and I know the extension tubes weren't made specifically for *my* lens.

**stevebrot** · 02-09-2021, 11:22 AM

Originally posted by Michael Piziak

Which extension tube or combination of tubes would take a 1:1 macro photo?

I found a definitive answer! The Auto Extension Tube K (100mm)!

Reference found at: Pentax Close-up Accessories | The K-Mount Page

There is also an Auto Extension Tube K (50mm) if that option is preferred.

Steve

Not a Number · 02-09-2021, 11:28 AM

I think the minimum has something to do with the K-mount specifications. On all the Pentax lenses I checked the flange to tip of the aperture actuator lever is 12mm. So it would probably follow to use even numbers for the other tubes. My Pentax Auto Extension tubes measure out at 12, 20 and 26mm.

Edit: Ah yes, I forgot about the 100 and 50mm tubes. And the Dental version comes with a set of close-up lenses to get 1:1+ reproduction. I guess they thought an even longer lens would be intimidating to patients.

**UncleVanya** · 02-09-2021, 11:38 AM

Adding the Raynox dcr-150 gives slightly more than 1.2:1, the dcr-250 gives 1.7:1 without loss of light. This is the same approach used by Codina with their 100mm f3.5 that came with a dedicated 1:1 closeup lens.

On an f2.8 macro adding tubes isn’t too bad for focus and exposure. The f4 lens will get very dark very quickly as you add extension. Both methods are viable however.

**AstroDave** · 02-09-2021, 01:54 PM - **1 Like**

Originally posted by Michael Piziak

I wonder what logic was behind the choice of tube #1 of 12mm in length, tube #2 of 19mm, and tube #3 of 26m

Originally posted by Michael Piziak

even numbers would be more logical, like 10mm, 20mm, & 30mm,

Well, 10 and 20 would combine to make 30 - Which you would already have!

So, a mixture of lengths that don't add up to each other in any combination gives you the widest range of possibilities. 12 / 19 / 26 gives you length options of 12, 19, 26, 31, 38, 45, and 57.

**Michael Piziak** · 02-09-2021, 03:33 PM

Originally posted by AstroDave

Well, 10 and 20 would combine to make 30 - Which you would already have!

So, a mixture of lengths that don't add up to each other in any combination gives you the widest range of possibilities. 12 / 19 / 26 gives you length options of 12, 19, 26, 31, 38, 45, and 57.

Yes, but 30+20 = 50mm, which is what it would take to achieve 1:1 macro

Not a Number · 02-09-2021, 03:37 PM

If you are using a macro lens you can adjust the extension on the lens.

**Michael Piziak** · 02-09-2021, 03:57 PM

Originally posted by Not a Number

If you are using a macro lens you can adjust the extension on the lens.

Right.
I'm not that worried about it. Just was curious.

02-09-2021, 11:22 AM	#9
stevebrot Otis Memorial Pentaxian Join Date: Mar 2007 Location: Vancouver (USA) Photos: Gallery \| Albums Posts: 39,515	Originally posted by Michael Piziak Which extension tube or combination of tubes would take a 1:1 macro photo? I found a definitive answer! The Auto Extension Tube K (100mm)! Reference found at: Pentax Close-up Accessories \| The K-Mount Page There is also an Auto Extension Tube K (50mm) if that option is preferred. Steve

02-09-2021, 11:28 AM	#10
Not a Number Moderator Join Date: Mar 2012 Location: Venice, CA Posts: 7,832	I think the minimum has something to do with the K-mount specifications. On all the Pentax lenses I checked the flange to tip of the aperture actuator lever is 12mm. So it would probably follow to use even numbers for the other tubes. My Pentax Auto Extension tubes measure out at 12, 20 and 26mm. Edit: Ah yes, I forgot about the 100 and 50mm tubes. And the Dental version comes with a set of close-up lenses to get 1:1+ reproduction. I guess they thought an even longer lens would be intimidating to patients. Last edited by Not a Number; 02-09-2021 at 11:38 AM.

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02-09-2021, 08:01 AM	#1
Michael Piziak Site Supporter Join Date: Dec 2013 Location: West Virginia Posts: 1,596	macro 1:1 extension tubes question Using the Asahi Pentax M 100mm macro 1:4 lens that takes 1:2 macro photos. Which extension tube or combination of tubes would take a 1:1 macro photo? From the web: The Asahi Pentax Auto Extension Tubes are a three piece set consisting of tube #1 of 12mm in length, tube #2 of 19mm, and tube #3 of 26mm. Combined the three tubes have a total extension of 57mm. Read more at: Asahi Pentax Auto Extension Tubes - Influential Photo Gear \| PentaxForums.com

02-09-2021, 08:50 AM	#2
SamirShah Site Supporter Join Date: Dec 2020 Location: Stamford, Ct Photos: Albums Posts: 97	You read my mind! I have the same question!

02-09-2021, 08:54 AM - 1 Like	#3
baro-nite Loyal Site Supporter Join Date: Aug 2011 Location: North Carolina, USA Photos: Gallery \| Albums Posts: 5,134	A lens needs total extension (including that provided by the focus helicoid) equal to its focal length to achieve 1:1 magnification. Your lens at closest focus already gives you 50mm of extension (hence 1:2 magnification), so adding 50mm gets you to 1:1.

02-09-2021, 09:43 AM	#4
Michael Piziak Site Supporter Join Date: Dec 2013 Location: West Virginia Posts: 1,596 Original Poster	ok thanks! I wonder what logic was behind the choice of tube #1 of 12mm in length, tube #2 of 19mm, and tube #3 of 26m

02-09-2021, 10:14 AM	#5
UncleVanya Loyal Site Supporter Join Date: Jul 2014 Photos: Gallery \| Albums Posts: 18,647	Originally posted by Michael Piziak ok thanks! I wonder what logic was behind the choice of tube #1 of 12mm in length, tube #2 of 19mm, and tube #3 of 26m I'm not sure what specific change would be more logical. Remember these are for use on any lens not just 50mm.

02-09-2021, 10:26 AM	#6
Michael Piziak Site Supporter Join Date: Dec 2013 Location: West Virginia Posts: 1,596 Original Poster	Originally posted by UncleVanya I'm not sure what specific change would be more logical. Remember these are for use on any lens not just 50mm. You have a point. I was just thinking that even numbers would be more logical, like 10mm, 20mm, & 30mm, but the people that made them are much smarter than me.

02-09-2021, 10:32 AM - 1 Like	#7
stevebrot Otis Memorial Pentaxian Join Date: Mar 2007 Location: Vancouver (USA) Photos: Gallery \| Albums Posts: 39,515	Originally posted by Michael Piziak ok thanks! I wonder what logic was behind the choice of tube #1 of 12mm in length, tube #2 of 19mm, and tube #3 of 26m They want to mess with your mind. I have two sets of extension tubes, one from Soligor (12mm, 24mm, 32mm) and one from Vivitar (12mm, 20mm, and 36mm). Both total to 68mm. If it were 42 (the ultimate answer to life, the universe, and everything), it might make sense, but 68? I have had many sleepless nights due to this issue. Sleepless nights aside, probably the easiest way to attain 1:1 with your lens is with a bellows. Leave the lens focused to infinity, rack the bellows out 90mm or so, and fine tune the magnification using the focus ring or bellows nobs to attain 1:1 (focus on a millimeter scale to a frame width of 36mm or 23.5mm depending on camera). Steve

02-09-2021, 10:48 AM	#8
Michael Piziak Site Supporter Join Date: Dec 2013 Location: West Virginia Posts: 1,596 Original Poster	Originally posted by stevebrot They want to mess with your mind. I have two sets of extension tubes, one from Soligor (12mm, 24mm, 32mm) and one from Vivitar (12mm, 20mm, and 36mm). Both total to 68mm. If it were 42 (the ultimate answer to life, the universe, and everything), it might make sense, but 68? I have had many sleepless nights due to this issue. Sleepless nights aside, probably the easiest way to attain 1:1 with your lens is with a bellows. Leave the lens focused to infinity, rack the bellows out 90mm or so, and fine tune the magnification using the focus ring or bellows nobs to attain 1:1 (focus on a millimeter scale to a frame width of 36mm or 23.5mm depending on camera). Steve Big Smiles! Well, achieving a perfect 1:1 doesn't bother me that much, and I know the extension tubes weren't made specifically for my lens.

02-09-2021, 11:38 AM	#11
UncleVanya Loyal Site Supporter Join Date: Jul 2014 Photos: Gallery \| Albums Posts: 18,647	Adding the Raynox dcr-150 gives slightly more than 1.2:1, the dcr-250 gives 1.7:1 without loss of light. This is the same approach used by Codina with their 100mm f3.5 that came with a dedicated 1:1 closeup lens. On an f2.8 macro adding tubes isn’t too bad for focus and exposure. The f4 lens will get very dark very quickly as you add extension. Both methods are viable however.

02-09-2021, 01:54 PM - 1 Like	#12
AstroDave Loyal Site Supporter Join Date: May 2007 Location: Flagstaff, Arizona Posts: 832	Originally posted by Michael Piziak I wonder what logic was behind the choice of tube #1 of 12mm in length, tube #2 of 19mm, and tube #3 of 26m Originally posted by Michael Piziak even numbers would be more logical, like 10mm, 20mm, & 30mm, Well, 10 and 20 would combine to make 30 - Which you would already have! So, a mixture of lengths that don't add up to each other in any combination gives you the widest range of possibilities. 12 / 19 / 26 gives you length options of 12, 19, 26, 31, 38, 45, and 57.

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02-09-2021, 03:33 PM	#13
Michael Piziak Site Supporter Join Date: Dec 2013 Location: West Virginia Posts: 1,596 Original Poster	Originally posted by AstroDave Well, 10 and 20 would combine to make 30 - Which you would already have! So, a mixture of lengths that don't add up to each other in any combination gives you the widest range of possibilities. 12 / 19 / 26 gives you length options of 12, 19, 26, 31, 38, 45, and 57. Yes, but 30+20 = 50mm, which is what it would take to achieve 1:1 macro

02-09-2021, 03:37 PM	#14
Not a Number Moderator Join Date: Mar 2012 Location: Venice, CA Posts: 7,832	If you are using a macro lens you can adjust the extension on the lens.

02-09-2021, 03:57 PM	#15
Michael Piziak Site Supporter Join Date: Dec 2013 Location: West Virginia Posts: 1,596 Original Poster	Originally posted by Not a Number If you are using a macro lens you can adjust the extension on the lens. Right. I'm not that worried about it. Just was curious.