macro 1:1 extension tubes question

**gofour3** · 02-09-2021, 04:15 PM

Originally posted by Michael Piziak

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?

I use this tube for my K100/4 Macro to achieve 1:1 magnification:

PENTAX Auto Extension Tube K 50mm reviews - Pentax Camera Accessory Review Database

Phil.

Not a Number · 02-10-2021, 05:37 AM

According to the macro calculator I use the difference in magnification when using the Pentax Auto extension tubes in combination on the 100mm f/4 M macro

58mm = 1.08× ~1.1:1
46mm = 0.96× ~1.0:1
38mm = 0.88× ~1:1.1
32mm = 0.82× ~1:1.2
26mm = 0.76× ~1:1.3
20mm = 0.70× ~1:1.4
12mm = 0.62× ~1:1.6

BTW: The Pentax M 50mm f/4 max magnification without tubes is ~0.45/0.47×. So 26mm vs 25mm is 0.99× vs 0.97×. Maybe not significant (2.04%) but "a silly millimeter longer"* makes a difference. Minolta macro lenses (both 50mm and 100mm) had an included dedicated extension tube for !:1 reproduction.

* If you remember those TV commercials you are really dating yourself.

Wasp · 02-10-2021, 12:25 PM

Does the 1.5x crop factor apply to the above calculations when using an APSC camera?

**monochrome** · 02-10-2021, 01:19 PM

Originally posted by stevebrot

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

Don’t forget the

Reference also K-mount Page

stevebrot · 02-10-2021, 05:04 PM - **1 Like**

Originally posted by Wasp

Does the 1.5x crop factor apply to the above calculations when using an APSC camera?

No...both magnification and reproduction ratio are based on image size on the sensor and not on any crop applied by the camera. 1:1 (1x) is always 1:1, whether on APS-C, 24x36FF, 6x7, or 4x5. The photo below was taken with my 4x5 view camera with the film in a 6x7 roll film holder. The magnification would have been the same with a 6x6 crop or native 4x5 crop, despite different framing.

Think of 1:1 meaning a 1mm long subject will result in a 1mm long image of the subject to the sensor.

Steve

(...sort of like how focal length is always focal length regardless of crop factor...)

02-10-2021, 01:19 PM	#19
monochrome Loyal Site Supporter Join Date: Mar 2008 Location: Working From Home Photos: Gallery \| Albums Posts: 26,276	Originally posted by stevebrot 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 Don’t forget the Reference also K-mount Page

02-10-2021, 05:04 PM - 1 Like	#20
stevebrot Otis Memorial Pentaxian Join Date: Mar 2007 Location: Vancouver (USA) Photos: Gallery \| Albums Posts: 42,007	Originally posted by Wasp Does the 1.5x crop factor apply to the above calculations when using an APSC camera? No...both magnification and reproduction ratio are based on image size on the sensor and not on any crop applied by the camera. 1:1 (1x) is always 1:1, whether on APS-C, 24x36FF, 6x7, or 4x5. The photo below was taken with my 4x5 view camera with the film in a 6x7 roll film holder. The magnification would have been the same with a 6x6 crop or native 4x5 crop, despite different framing. Think of 1:1 meaning a 1mm long subject will result in a 1mm long image of the subject to the sensor. Steve (...sort of like how focal length is always focal length regardless of crop factor...) Last edited by stevebrot; 02-10-2021 at 05:10 PM. Reason: forgot photo!

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02-09-2021, 04:15 PM	#16
gofour3 Site Supporter Join Date: Oct 2008 Location: Vancouver, Canada Posts: 8,091	Originally posted by Michael Piziak 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? I use this tube for my K100/4 Macro to achieve 1:1 magnification: PENTAX Auto Extension Tube K 50mm reviews - Pentax Camera Accessory Review Database Phil.

02-10-2021, 05:37 AM	#17
Not a Number Moderator Join Date: Mar 2012 Location: Venice, CA Posts: 10,526	According to the macro calculator I use the difference in magnification when using the Pentax Auto extension tubes in combination on the 100mm f/4 M macro 58mm = 1.08× ~1.1:1 46mm = 0.96× ~1.0:1 38mm = 0.88× ~1:1.1 32mm = 0.82× ~1:1.2 26mm = 0.76× ~1:1.3 20mm = 0.70× ~1:1.4 12mm = 0.62× ~1:1.6 BTW: The Pentax M 50mm f/4 max magnification without tubes is ~0.45/0.47×. So 26mm vs 25mm is 0.99× vs 0.97×. Maybe not significant (2.04%) but "a silly millimeter longer"* makes a difference. Minolta macro lenses (both 50mm and 100mm) had an included dedicated extension tube for !:1 reproduction. * If you remember those TV commercials you are really dating yourself.

02-10-2021, 12:25 PM	#18
Wasp Pentaxian Join Date: Mar 2017 Location: Pretoria Photos: Gallery Posts: 4,661	Does the 1.5x crop factor apply to the above calculations when using an APSC camera?