Extension tubes

axl · 12-02-2008, 01:43 AM

Hi all,
just a few quick Q's about extnesion tubes.
1 - is there any way to calculate by how much will extension tube (say 20mm) cut the closest focusing distance?
2 - with extension tube the lens will not be able to focus to infinity, right?
3 - again is there any way to calculate what will be the biggest distance that the lens will by able to focus to?

why I'm asking, I have SMC 400/5.6, and it's shortest focusing distance is 8m, and I saw cheap 20mm extension tube. So I'm wondering how it might/might not help me to cut the 8m down.
TIA for all your replies.
BR
Peter

MoiVous · 12-02-2008, 03:36 AM

Some quick answers can be found at these two sites

:

Lens Tutorial - photo.net
and
macrophotography.org - Calculating Exposure Compensation

Good luck!

**Lowell Goudge** · 12-02-2008, 04:49 PM

there are lots of sites that give you all the formulas you need, at least to calculate the maximum working distance (lens at infinity) and the minimum magnification.

It takes a little imagination to repackage the calculations knowing the minimum focusing fdistance of the lens in question to develop the maximum magnification at the new minimum focusing distance .

I worked it out once and programmed a spreadsheet to do all the calc's

bottom line, however is that you get true macro, (1:1 image) with the lens at 2x the mominal focal length away from a subject and an equal amount of extension., therefore a 100mm lens needs an additional 100mm of extension to get 1:1

**Canada_Rockies** · 12-02-2008, 05:10 PM

Originally posted by Lowell Goudge

bottom line, however is that you get true macro, (1:1 image) with the lens at 2x the mominal focal length away from a subject and an equal amount of extension., therefore a 100mm lens needs an additional 100mm of extension to get 1:1

When the lens is focused at infinity. My M 100 macro gets 1:2 on its own, and 1:1 with 50 mm extension tube - the other 50 mm is in the lens focusing helical.

Just to make things clear.

LaRee · 12-18-2008, 11:19 PM

Originally posted by Canada_Rockies

When the lens is focused at infinity. My M 100 macro gets 1:2 on its own, and 1:1 with 50 mm extension tube - the other 50 mm is in the lens focusing helical.

Just to make things clear.

So, what would using a 25mm extension tube do to the DA 35mm macro?

**Canada_Rockies** · 12-18-2008, 11:49 PM

Originally posted by LaRee

So, what would using a 25mm extension tube do to the DA 35mm macro?

Here's an approximation of the formula. It's close enough for rough work.

The 35 macro gets to 1:1 on its own, so it has 35mm of extension built in. Adding 25mm to that should give you (35 + 25)/35 = (60/35) = 1.7:1. A 10 mm object would be 17 mm on the sensor.

Blue · 12-19-2008, 08:30 AM

Originally posted by Canada_Rockies

When the lens is focused at infinity. My M 100 macro gets 1:2 on its own, and 1:1 with 50 mm extension tube - the other 50 mm is in the lens focusing helical.

Just to make things clear.

Are you sure you don't have that backwards?

Edit: what I'm getting at is different formulas are used with non-macro primes and macro lens.

Last edited by Blue; 12-19-2008 at 09:40 AM.

Blue · 12-19-2008, 08:37 AM

Originally posted by axl

. . .

why I'm asking, I have SMC 400/5.6, and it's shortest focusing distance is 8m, and I saw cheap 20mm extension tube. So I'm wondering how it might/might not help me to cut the 8m down.
TIA for all your replies.
BR
Peter

Another thing an extension tube does is make the lens focus closer. For example, I have a 400mm A lens that has a minim focus distance of 2.8 meters. I can use a small amount of extension and get that closer (12mm or 19mm). However, when I do that, I loose infinity focus.

Edit: Here is another formula for you, Effective aperture = (Set Aperture) x (1 + Magnification ratio)

Edit Edit: I like to use the 12mm extension with min A series lens but sense yours has 8 meters, I think 20mm would be better for your K series lens.

LaRee · 12-19-2008, 09:02 AM

Originally posted by Canada_Rockies

Here's an approximation of the formula. It's close enough for rough work.

The 35 macro gets to 1:1 on its own, so it has 35mm of extension built in. Adding 25mm to that should give you (35 + 25)/35 = (60/35) = 1.7:1. A 10 mm object would be 17 mm on the sensor.

Thank you for doing the math for me. I'll have to get out an extension tube and give it a go to see how that translates into use.

**Canada_Rockies** · 12-19-2008, 03:31 PM

Originally posted by Blue

Are you sure you don't have that backwards?

Edit: what I'm getting at is different formulas are used with non-macro primes and macro lens.

Not backwards, but confused.

Try that again: My 100/4 M series macro will focus from infinity to 1:2 with no accessories. It will focus between 1:2 and 1:1 with the 50mm extension tube. The helical in the M 100/4 gives 50mm of extension, and adding another 50mm gives 1:1 when the lens is focused to its close focus distance, 1:2 when at its infinity focus mark. The tube gives 50mm of extension to the lens.

12-02-2008, 01:43 AM	#1
axl Veteran Member Join Date: Mar 2007 Location: Nove Zamky, Slovakia Photos: Gallery \| Albums Posts: 7,183	Extension tubes Hi all, just a few quick Q's about extnesion tubes. 1 - is there any way to calculate by how much will extension tube (say 20mm) cut the closest focusing distance? 2 - with extension tube the lens will not be able to focus to infinity, right? 3 - again is there any way to calculate what will be the biggest distance that the lens will by able to focus to? why I'm asking, I have SMC 400/5.6, and it's shortest focusing distance is 8m, and I saw cheap 20mm extension tube. So I'm wondering how it might/might not help me to cut the 8m down. TIA for all your replies. BR Peter

12-19-2008, 08:37 AM	#8
Blue Moderator Site Supporter Join Date: Jun 2008 Location: Florida Hill Country Photos: Gallery \| Albums Posts: 17,377	Originally posted by axl . . . why I'm asking, I have SMC 400/5.6, and it's shortest focusing distance is 8m, and I saw cheap 20mm extension tube. So I'm wondering how it might/might not help me to cut the 8m down. TIA for all your replies. BR Peter Another thing an extension tube does is make the lens focus closer. For example, I have a 400mm A lens that has a minim focus distance of 2.8 meters. I can use a small amount of extension and get that closer (12mm or 19mm). However, when I do that, I loose infinity focus. Edit: Here is another formula for you, Effective aperture = (Set Aperture) x (1 + Magnification ratio) Edit Edit: I like to use the 12mm extension with min A series lens but sense yours has 8 meters, I think 20mm would be better for your K series lens. Last edited by Blue; 12-19-2008 at 09:39 AM.

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12-02-2008, 03:36 AM	#2
MoiVous Veteran Member Join Date: Sep 2008 Location: Adelaide, South Australia Photos: Gallery Posts: 677	Some quick answers can be found at these two sites : Lens Tutorial - photo.net and macrophotography.org - Calculating Exposure Compensation Good luck!

12-02-2008, 04:49 PM	#3
Lowell Goudge Site Supporter Join Date: Jan 2007 Location: Toronto Photos: Gallery \| Albums Posts: 17,891	there are lots of sites that give you all the formulas you need, at least to calculate the maximum working distance (lens at infinity) and the minimum magnification. It takes a little imagination to repackage the calculations knowing the minimum focusing fdistance of the lens in question to develop the maximum magnification at the new minimum focusing distance . I worked it out once and programmed a spreadsheet to do all the calc's bottom line, however is that you get true macro, (1:1 image) with the lens at 2x the mominal focal length away from a subject and an equal amount of extension., therefore a 100mm lens needs an additional 100mm of extension to get 1:1

12-02-2008, 05:10 PM	#4
Canada_Rockies Loyal Site Supporter Join Date: Nov 2007 Location: Sparwood, BC, Canada Photos: Gallery \| Albums Posts: 12,385	Originally posted by Lowell Goudge bottom line, however is that you get true macro, (1:1 image) with the lens at 2x the mominal focal length away from a subject and an equal amount of extension., therefore a 100mm lens needs an additional 100mm of extension to get 1:1 When the lens is focused at infinity. My M 100 macro gets 1:2 on its own, and 1:1 with 50 mm extension tube - the other 50 mm is in the lens focusing helical. Just to make things clear.

12-18-2008, 11:19 PM	#5
LaRee Veteran Member Join Date: Nov 2006 Location: San Diego Photos: Gallery Posts: 2,225	Originally posted by Canada_Rockies When the lens is focused at infinity. My M 100 macro gets 1:2 on its own, and 1:1 with 50 mm extension tube - the other 50 mm is in the lens focusing helical. Just to make things clear. So, what would using a 25mm extension tube do to the DA 35mm macro?

12-18-2008, 11:49 PM	#6
Canada_Rockies Loyal Site Supporter Join Date: Nov 2007 Location: Sparwood, BC, Canada Photos: Gallery \| Albums Posts: 12,385	Originally posted by LaRee So, what would using a 25mm extension tube do to the DA 35mm macro? Here's an approximation of the formula. It's close enough for rough work. The 35 macro gets to 1:1 on its own, so it has 35mm of extension built in. Adding 25mm to that should give you (35 + 25)/35 = (60/35) = 1.7:1. A 10 mm object would be 17 mm on the sensor.

12-19-2008, 08:30 AM	#7
Blue Moderator Site Supporter Join Date: Jun 2008 Location: Florida Hill Country Photos: Gallery \| Albums Posts: 17,377	Originally posted by Canada_Rockies When the lens is focused at infinity. My M 100 macro gets 1:2 on its own, and 1:1 with 50 mm extension tube - the other 50 mm is in the lens focusing helical. Just to make things clear. Are you sure you don't have that backwards? Edit: what I'm getting at is different formulas are used with non-macro primes and macro lens. Last edited by Blue; 12-19-2008 at 09:40 AM.

12-19-2008, 09:02 AM	#9
LaRee Veteran Member Join Date: Nov 2006 Location: San Diego Photos: Gallery Posts: 2,225	Originally posted by Canada_Rockies Here's an approximation of the formula. It's close enough for rough work. The 35 macro gets to 1:1 on its own, so it has 35mm of extension built in. Adding 25mm to that should give you (35 + 25)/35 = (60/35) = 1.7:1. A 10 mm object would be 17 mm on the sensor. Thank you for doing the math for me. I'll have to get out an extension tube and give it a go to see how that translates into use.

12-19-2008, 03:31 PM	#10
Canada_Rockies Loyal Site Supporter Join Date: Nov 2007 Location: Sparwood, BC, Canada Photos: Gallery \| Albums Posts: 12,385	Originally posted by Blue Are you sure you don't have that backwards? Edit: what I'm getting at is different formulas are used with non-macro primes and macro lens. Not backwards, but confused. Try that again: My 100/4 M series macro will focus from infinity to 1:2 with no accessories. It will focus between 1:2 and 1:1 with the 50mm extension tube. The helical in the M 100/4 gives 50mm of extension, and adding another 50mm gives 1:1 when the lens is focused to its close focus distance, 1:2 when at its infinity focus mark. The tube gives 50mm of extension to the lens.