Clarification on Maco lens, extention tubes & magnification

[AcidBurn003]

I have been reading up on macro techniques and related information on these forums. However i still have a question.

I recently purchased the sigma 180mm macro lens. Now i know this lens has a maximum magnification ratio of 1:1. If i were to purchase and attach a set of extension tubes that when stacked would add to 68mm and attach it to the lens it would increase the magnification.

According to the wonderful information on this thread:
http://photography-on-the.net/forum/showthread.php?t=807056

If i use the formula to figure out ratios with extension tubes it would be:

180 + 68/100 = 2.48 or about 2.5:1 magnification

or would it be:

180 + 68/180 = 1.37.

I think its the first way but I'm not 100% sure.

Thank you for your help!

[LordV]

I have been reading up on macro techniques and related information on these forums. However i still have a question.

I recently purchased the sigma 180mm macro lens. Now i know this lens has a maximum magnification ratio of 1:1. If i were to purchase and attach a set of extension tubes that when stacked would add to 68mm and attach it to the lens it would increase the magnification.

According to the wonderful information on this thread:
http://photography-on-the.net/forum/showthread.php?t=807056

If i use the formula to figure out ratios with extension tubes it would be:

180 + 68/100 = 2.48 or about 2.5:1 magnification

or would it be:

180 + 68/180 = 1.37.

I think its the first way but I'm not 100% sure.

Thank you for your help!

For the 180mm at min focus with ext tubes you need to use a better estimate of the focal length at min focus= 460/4 =115mm.
(460 is the min focus distance)

So the max mag by calculation= 1+ (68/115) = 1.6:1
This is probably a slight underestimate.
The calculation is existing magnification + (length of tubes/actual focal length of lens).
You can actually get much higher magnifications using a reversed lens on the front so a 50mm lens reversed onto the front would give a max mag= 1+ (180/50) or 4.6:1

Brian v.

[dicklaxt]

How come I stayed confused,where did the 460 and the 4 come from?

dick

[LordV]

How come I stayed confused,where did the 460 and the 4 come from?

dick

This is why it's best to measure the mag with a photo of a ruler :)

Calcs involving extension tubes with a macro lens do not work well (they do work well with normal prime lenses). This is because the focal length of a lens is normally measured at infinity focus. Macro lenses because of their optics shorten their focal lengths as you get near to 1:1. An estimate of the revised focal length at min focus happens to be the minimum focus distance/4 which in the above case= 460/4

Brian V.

[dicklaxt]

So what happens if you reverse a 50mm onto a 90mm macro lens?

I guess that would be 2.8 : 1,,,,,,,,now in theory adding tubes to this would once again add magnification and further would a TC in the mix add magnification as well.I guess this is a suck it up and see.LOL

AB didn't mean to hijack your post but while Brian was here,,, thought I would hold his feet in the fire a bit too.

dick

[LordV]

So what happens if you reverse a 50mm onto a 90mm macro lens?

I guess that would be 2.8 : 1,,,,,,,,now in theory adding tubes to this would once again add magnification and further would a TC in the mix add magnification as well.I guess this is a suck it up and see.LOL

AB didn't mean to hijack your post but while Brian was here,,, thought I would hold his feet in the fire a bit too.

dick

This will confuse you Dick - it confuses me. :)
Calcs involving add on reversed lenses or diopters do not seem to require you to use the revised focal length at min focus distance. Just using the quoted one seems to work fairly well in practice.
So in your example a reversed 50mm onto a 90mm macro lens at min focus should give pretty close to 1 + (90/50) = 2.8:1 as you suggest.

Funnily enough I asked about this discrepancy of using a revised focal length for calcs involving macro lenses with extension tubes but not when using macro lenses with reversed lenses or diopters on another forum recently. The answer seemed to be that the use of the revised focal length for extension tube calcs was correct and it really should be used for the reversed lens situation as well but then you also seem to have to take into account the absolute position of the two lenses which makes a difference. It just so happens that leaving the position information out seems to cancel out the error of using the wrong focal length in the calculation.

As I've often said- it's always best to measure the mag using a ruler shot :) - all these calcs have assumptions/simplifications etc in them and are therefore only approximate.

Brian v.

[dicklaxt]

You know ,I really thought that to be true because of all the variables involved for example to adapt a 50mm to the 90mm took two adapters, a male-male and a female -male, which added 3/16th's to the gap between lens on the other hand some one else may have the correct male-male adaptor and not being adding that 3/16th's gap to the mix..

Yes you are right the combined focal length being divisible by 4 doesn't seem right to me as the subject is presenting a magnified image thru the 50mm to the surface area of the macro lens which in turn presents it to the sensor,,,,,,,,,,,I don't see where the divisor of 4 comes to play.I suppose the play on optics is the culprit and thus confusing me as you said

dick

[AcidBurn003]

For the 180mm at min focus with ext tubes you need to use a better estimate of the focal length at min focus= 460/4 =115mm.
(460 is the min focus distance)

So the max mag by calculation= 1+ (68/115) = 1.6:1
This is probably a slight underestimate.
The calculation is existing magnification + (length of tubes/actual focal length of lens).
You can actually get much higher magnifications using a reversed lens on the front so a 50mm lens reversed onto the front would give a max mag= 1+ (180/50) or 4.6:1

Brian v.

I understand what your saying and I thank you for the clarification. I suppose then it wouldn't be worth it to get the extension tubes for use with that lens. Oh well.

Thank you for the help! :)

[LordV]

I understand what your saying and I thank you for the clarification. I suppose then it wouldn't be worth it to get the extension tubes for use with that lens. Oh well.

Thank you for the help! :)
Well that depends on what you are trying to shoot. I think I used tubes on my sigma 105mm to give 1.5:1 more than I did at 2:1 - you start getting good fly eye resolution at 1.5:1
Brian V.

[AcidBurn003]

Well that depends on what you are trying to shoot. I think I used tubes on my sigma 105mm to give 1.5:1 more than I did at 2:1 - you start getting good fly eye resolution at 1.5:1
Brian V.

I would eventually like to shoot pics of fly's, spiders etc. with the same detail as some on the macro forum. I just thought i should try to master a "regular" macro lens first before getting say the canon MPE65 5:1 macro lens. That's why i was wondering about the extension tubes and my lens. I was just thinking if they really won't magnify my lens much than they may not be worth the money. Anyways, thank you for your help in understanding all of this, i really appreciate it!

--AcidBurn003

[LordV]

You know ,I really thought that to be true because of all the variables involved for example to adapt a 50mm to the 90mm took two adapters, a male-male and a female -male, which added 3/16th's to the gap between lens on the other hand some one else may have the correct male-male adaptor and not being adding that 3/16th's gap to the mix..

Yes you are right the combined focal length being divisible by 4 doesn't seem right to me as the subject is presenting a magnified image thru the 50mm to the surface area of the macro lens which in turn presents it to the sensor,,,,,,,,,,,I don't see where the divisor of 4 comes to play.I suppose the play on optics is the culprit and thus confusing me as you said

dick

Can't remember where I found the min focus distance /4 to get the actual focal length but it was from a lovely big equation where to a first approximation everything cancelled out just leaving min focus distance/4 as the new focal length. So it does have a mathematical basis and more to the point seems to work roughly in practice.

[LordV]

I would eventually like to shoot pics of fly's, spiders etc. with the same detail as some on the macro forum. I just thought i should try to master a "regular" macro lens first before getting say the canon MPE65 5:1 macro lens. That's why i was wondering about the extension tubes and my lens. I was just thinking if they really won't magnify my lens much than they may not be worth the money. Anyways, thank you for your help in understanding all of this, i really appreciate it!

--AcidBurn003

It is a good idea to gradually stepup the magnification when learning macro- you see quite a few MPE-65's for sale where people jumped in feet first and found the lens almost unusable.
Unfortunately the 180mm macro lens is not what I would call a starter lens either - harder to handle than a lens around 100mm and has few advantages compared to the disadvantages.
Much easier with a 100mm lens and then use a full set of ext tubes.

Brian v.

[AcidBurn003]

It is a good idea to gradually stepup the magnification when learning macro- you see quite a few MPE-65's for sale where people jumped in feet first and found the lens almost unusable.
Unfortunately the 180mm macro lens is not what I would call a starter lens either - harder to handle than a lens around 100mm and has few advantages compared to the disadvantages.
Much easier with a 100mm lens and then use a full set of ext tubes.

Brian v.

I kinda figured that the MPE-65 would take a lot of knowledge and experience to use correctly. I was originally going to get the 100mm with a set of extension tubes for the very reason's you have given me. However i found the sigma 180mm for the same price as the canon 100mm and since i could use my friends 100mm with little to no problem I figured the 180mm would be the same way. I was wrong. I having a bit of a hard time with the 180, and I don't know why. It not the lens, my mother is able to use it without a tripod and get great closeup shots. I just need to practice. Would using live view be better with the macro? I do use a remote too, which i know helps.

Thanks,
AcidBurn003

[LordV]

I kinda figured that the MPE-65 would take a lot of knowledge and experience to use correctly. I was originally going to get the 100mm with a set of extension tubes for the very reason's you have given me. However i found the sigma 180mm for the same price as the canon 100mm and since i could use my friends 100mm with little to no problem I figured the 180mm would be the same way. I was wrong. I having a bit of a hard time with the 180, and I don't know why. It not the lens, my mother is able to use it without a tripod and get great closeup shots. I just need to practice. Would using live view be better with the macro? I do use a remote too, which i know helps.

Thanks,
AcidBurn003

I think it takes a lot of practice to use a 180mm macro lens without a tripod. Not sure if you are mainly shooting natural light or flash but if natural light on a 1.6 crop camera handheld you really need to keep your shutter speed up around 1/500th sec or higher. Live view could be useful for focusing but i suspect only if you are on a tripod. Holding a 180 lens/camera combo away from your head would be very difficult to stabilise.