# Sigma 24-70 2.8  Macro



## ratssass (Feb 6, 2014)

Forum dedicated to discussions and photos of Macro Photography


...not sure if this belongs here,or the "Products" tab,but here we go.
I own the above mentioned lens,and have a few questions.
I was recently in possession of the "Lens Across America Pt. 3" lens.It was the Nikkor D-AF 28-105/3.5-4.5.On that particular lens,was a switch for "Normal/Macro". My Sigma has no such switch,only an Aperture locking switch. Any Thoughts??
 Another question,I have is regarding DOF. I was just blown away at how narrow the DOF was.I'm using a DX body,so If I went FF,would the DOF become even narrower?That may sound like an elementary question,and I'm pretty sure I know the answer,but would like confirmation.
I'm really quite excited about discovering Macro,but having never played with the genre,I'm afraid most of my questions may sound like "Hi...new to photography.What camera should I buy".
Any thoughts would be appreciated.Especially about the Sigma,for now.


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## charlie76 (Feb 6, 2014)

I like macro


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## Derrel (Feb 6, 2014)

Here is a good article that might be of some interest.Common Macro Questions Answered by Thom Hogan

A fair number of older zoom lenses used to use a rotating switch system for their macro range. I think that might have been a way to mechanically move an element or element group into a position that would help eliminate some optical faults, like curvature of field, at close focusing distances. Newer lenses have pretty much dispensed with this mechanical switching system.

Depth of field *at macro distances* is more closely correlated to the degree of image magnification than it is to format size or lens focal length, which is one of the oddball things about depth of field.

I'm interested in seeing your Lens Across America Pt. 3 shots. Have you uploaded them to the site yet?


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## Overread (Feb 6, 2014)

"macro" as a term used on zoom lenses nearly always doesn't actually mean "true macro". It's a marketing term used to denote  a close focusing system. Some lenses will achieve this natively, others will have a switch which allows the lens to switch in a closer focusing setup, whilst often locking it at a certain focal length and focusing range band. 

True macro is understood as a ratio of 1:1 

Size of the subject reflected on the sensor : Size of the subject in real life

Whilst most "macro zooms" will at best get to around 0.5:1 which is half life size on the sensor. 

In rough real terms that means the difference is like this;

Result from a macro zoom






Result from a true macro lens






Pretty much all true macro lenses on the current market are primes (one focal length) which means that you can roughly assume that if its a zoom then its only close focusing, whilst if its a prime its true macro. Though always check as there are likely to be a few exceptions to that rule out there.



Derrel has touched on depth of field and that when it comes to macro photography the magnification of the lens defines the depth of field. If you've got to 1:1 magnification it doesn't matter if you used a lens - extension tubes on a leans - reverse mounted etc.. the magnification will be similar. Adding fullframe and you'll typically find that your depth of field at 1:1 will also be smaller; however you'll also be showing more of the frame. The magnification ratio is still the same, but you'll capture more edge content because the subject is being reflected onto a bigger sensor area. As a result if you print two shots, one from a crop and one from a fullframe camera body the one from the crop (at the same physical size as the one from the fullframe) will appear to be more magnified.


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## scotts2014se (Feb 6, 2014)

I am also interested in macro but don't know where to start. What did you think of the nikkor lens? and what benefits do you see from the sigma?


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## ratssass (Feb 6, 2014)

Thanks,Derrel...I had read the Hogan article,and will give it another re-read.I've never had a problem reading something many times,in the hopes I will have an "AHA" moment.Quite honestly,everything I shot for the "Lens Across America Pt 3" is very uninspired,though I will post a few up tomorrow.
I appreciate your thoughts on this.


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## ratssass (Feb 6, 2014)

Overread said:


> "macro" as a term used on zoom lenses nearly always doesn't actually mean "true macro". It's a marketing term used to denote  a close focusing system. Some lenses will achieve this natively, others will have a switch which allows the lens to switch in a closer focusing setup, whilst often locking it at a certain focal length and focusing range band.
> 
> True macro is understood as a ratio of 1:1
> 
> ...




OK...I think....basically,the DOF will remain the same (DX VS. FX),however the FOV will be affected as a normal DX VS. FX ?Am I understanding that correctly?


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## Overread (Feb 6, 2014)

ratssass said:


> OK...I think....basically,the DOF will remain the same (DX VS. FX),however the FOV will be affected as a normal DX VS. FX ?Am I understanding that correctly?




Depth of field is a nightmare question here (partly as a result of the fact that most people don't actually know how DoF works because its put together by bits of information rather than a structured information packet - self learning has its downsides ). 

The rule I've always heard is that you'll get around one stops worth of aperture in depth of field loss with fullframe. So at 1:1 you'll have more frame coverage, but also a slightly smaller depth of field. However diffraction (the softening of detail as you decrease the aperture beyond the lenses peek of sharpness) reduces its effect with fullframe. So whilst you've got around 1 stop less in depth of field you've also got the capacity to close the aperture down by another stop and still retain a similar level of sharpness so it cancels each other out. 

If you want a more technical answer read a book - seriously because the story here gets muddled.

However you approach it though the depth of field will be small - that is part of macro life, though there are tricks to get around like like using tilt shift lenses or focus stacking


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## ratssass (Feb 6, 2014)

...thanks,Overread.Trust me on this,a Readers Digest version is sufficient.I just wanted the jest of it,to get me going in the right direction.More questions will follow...lol.

....and thank you for your time   

"The rule I've always heard is that you'll get around one stops worth of  aperture in depth of field loss with fullframe. So at 1:1 you'll have  more frame coverage, but also a slightly smaller depth of field. However  diffraction (the softening of detail as you decrease the aperture  beyond the lenses peek of sharpness) reduces its effect with fullframe.  So whilst you've got around 1 stop less in depth of field you've also  got the capacity to close the aperture down by another stop and still  retain a similar level of sharpness so it cancels each other out. "

^^been re-reading this.....the addled brain is making sense of this....


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## greybeard (Feb 14, 2014)

Many lens companies throw the word MACRO around when they really mean close up.  At any rate, if you want razor sharp 1:1 images, you can't beat a dedicated MACRO lens.  Macro zooms will let you get close up but the resolution is usually mediocre at best.


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