Extension Tubes
- Rogerdodge
- Posts: 1177
- Joined: Tue Jan 31, 2006 6:06 pm
- Location: North Devon
Extension Tubes
I have looked a little bit on the web for this, but am still a bit confused.
So, here's hoping that we have a knowledgable person on this group who can help.
I am thinking about getting a set of extension tubes to use with my 180mm macro lens (1:1 magnification on 35mm), the lengths are - 35, 20 & 12 mm.
So, what effect will these have, singly and combined, on the magnification factor?
Is there a calculation for this?
I am hoping for 5:1 or bigger (yes - I will be using flash and a tripod!)
Thanks
Roger Harding
So, here's hoping that we have a knowledgable person on this group who can help.
I am thinking about getting a set of extension tubes to use with my 180mm macro lens (1:1 magnification on 35mm), the lengths are - 35, 20 & 12 mm.
So, what effect will these have, singly and combined, on the magnification factor?
Is there a calculation for this?
I am hoping for 5:1 or bigger (yes - I will be using flash and a tripod!)
Thanks
Roger Harding
Re: Extension Tubes
Roger,
The magnification factor of a lense can be determined using the equation:
Magnification = Extension/Focal Length
So your 180mm lens already has a built in extension of 180mm (using crafty optics) to achieve 1:1 reproduction. So using your rings, you can increase the extension to 192mm, 200mm, 212mm, 215mm, etc... to a maximum of 247mm.
This would give a maximum magnification of 247/180 = 1.37:1
Theoretically, you would need 720mm additional tubes to achieve 5:1. Practically, I think this would be impossible as the minimum focussing distance would get nearer and nearer to 0.
To achieve 5x magnification, you're better off starting with a shorter lens and bellows... sorry, I hope I'm wrong!
Regards,
Chris
The magnification factor of a lense can be determined using the equation:
Magnification = Extension/Focal Length
So your 180mm lens already has a built in extension of 180mm (using crafty optics) to achieve 1:1 reproduction. So using your rings, you can increase the extension to 192mm, 200mm, 212mm, 215mm, etc... to a maximum of 247mm.
This would give a maximum magnification of 247/180 = 1.37:1
Theoretically, you would need 720mm additional tubes to achieve 5:1. Practically, I think this would be impossible as the minimum focussing distance would get nearer and nearer to 0.
To achieve 5x magnification, you're better off starting with a shorter lens and bellows... sorry, I hope I'm wrong!
Regards,
Chris
- Rogerdodge
- Posts: 1177
- Joined: Tue Jan 31, 2006 6:06 pm
- Location: North Devon
No - you are right!
My calculations also told me that there was a 'built in extension' of 180mm
(bie = focal lengthXmagnification = 1x180)
However, I thoght this could not be right considering the physical length of the lens.
I thus got the same answer as you -
Long extension, loss of a couple of stops of light, and no real increase in magnification. I just hoped my calculations were wrong...........
Now...where did I put that old 50mm lens?
Thanks for your reply.
Roger
My calculations also told me that there was a 'built in extension' of 180mm
(bie = focal lengthXmagnification = 1x180)
However, I thoght this could not be right considering the physical length of the lens.
I thus got the same answer as you -
Long extension, loss of a couple of stops of light, and no real increase in magnification. I just hoped my calculations were wrong...........
Now...where did I put that old 50mm lens?
Thanks for your reply.
Roger
- Trev Sawyer
- Stock Contributor
- Posts: 851
- Joined: Sun May 07, 2006 8:37 am
- Location: Cambridgeshire
- Trev Sawyer
- Stock Contributor
- Posts: 851
- Joined: Sun May 07, 2006 8:37 am
- Location: Cambridgeshire
Hey Gruditch,
I've picked up a Sigma 1.4 x APO tele converter, but the Sigma 150mm APO lens is not on the list of lenses it is designed for (in the instruction sheet). Is it OK to use... the instructions say if used with the wrong lens it can damage both the lens and converter. I'm pretty sure it SHOULD be OK, but just wanted to check. Presumably it will only work on manual focus setting too.
Cheers.
Trev
I've picked up a Sigma 1.4 x APO tele converter, but the Sigma 150mm APO lens is not on the list of lenses it is designed for (in the instruction sheet). Is it OK to use... the instructions say if used with the wrong lens it can damage both the lens and converter. I'm pretty sure it SHOULD be OK, but just wanted to check. Presumably it will only work on manual focus setting too.
Cheers.
Trev
- Gruditch
- Moderator & Stock Contributor
- Posts: 1689
- Joined: Mon Apr 09, 2007 3:30 pm
- Location: Hampshire
- Contact:
Hi Trev, it works great with the 150mm, For piece of mind check this link to the Sigma site, it says you can use the 150mm Macro with the x 1.4.
http://www.sigma-imaging-uk.com/lenses/macro/150mm.htm
Gruditch
http://www.sigma-imaging-uk.com/lenses/macro/150mm.htm
Gruditch
- Trev Sawyer
- Stock Contributor
- Posts: 851
- Joined: Sun May 07, 2006 8:37 am
- Location: Cambridgeshire
- Rogerdodge
- Posts: 1177
- Joined: Tue Jan 31, 2006 6:06 pm
- Location: North Devon
Hi all,
would the Sigma 2x tele converter also work with a sigma 150mm macro or would it become an unwieldy beast? I'm unsure whether to get the sigma 150 and try with teleconverters or whether to try extension tubes on my canon 28-135mm EF IS. Don't know if this will allow me to go tripod free or whther the IS is knocked out by the extension tubes. My wife has just read this and accused me of being a nerd. Any ideas? (on the lens gear, not the wife!!)![Confused :?](./images/smilies/icon_confused.gif)
would the Sigma 2x tele converter also work with a sigma 150mm macro or would it become an unwieldy beast? I'm unsure whether to get the sigma 150 and try with teleconverters or whether to try extension tubes on my canon 28-135mm EF IS. Don't know if this will allow me to go tripod free or whther the IS is knocked out by the extension tubes. My wife has just read this and accused me of being a nerd. Any ideas? (on the lens gear, not the wife!!)
![Confused :?](./images/smilies/icon_confused.gif)