Effective aperture

[StuartC]

Although I have been taking photos for some time including macro it is only recently I have become aware of Effective aperture!
This has arisen because I have a Sigma 150mm f2.8 OS version that underexposes with my Canon 7D2 and requires up to about 2 stops of compensation when taking subjects at minimum working distance i.e about 1:1. Further investigation revealed that this effect is not repeated at focus distances over a metre or so. Initially I wondered if a firmware upgrade was available but initially Sigma said there wasn't but now they have told me one is available (although I am unable to find it in their lists)
I have now learnt a little more about Effective exposure (there is a short article on this site from some years ago) and suppose this is the phenomenon I am observing, oddly it doesn't seem to occur with a Canon 100mm macro lens.
My question is can this be compensated by firmware? Others have said that the camera should compensate and perhaps this is what is happening with the Canon lens which communicates focus distance more effectively.
I would appreciate any comments or observations to help me decide whether or not to get the firmware update offered by Sigma.

[xpatUSA]

Although I have been taking photos for some time including macro it is only recently I have become aware of Effective aperture! <>

My question is can this be compensated by firmware? Others have said that the camera should compensate and perhaps this is what is happening with the Canon lens which communicates focus distance more effectively.
I would appreciate any comments or observations to help me decide whether or not to get the firmware update offered by Sigma.

I have vague memories of my Micro-Nikkor 60mm on a Nikon D50 both displaying and accounting for the aforesaid Effective Aperture.

As to the Sigma lens firmware update, I would research what Sigma says about the update although, if they say anything, it's usually written in SMV (Sigma Marketing Vague). If Effective Aperture is not mentioned and if the lens is working well enough for you, I personally wouldn't bother. It is not unknown with Sigma stuff for a firmware update to result in a dead item that is only fixable by Sigma. Your call of course.

HTH

[DanK]

It happens with my Canon 100mm L macro.

If you are using Av or Tv, the camera's meter will compensate. If you are using M, just open the aperture or slow the shutter speed to whatever is appropriate at that distance.

[StuartC]

I have vague memories of my Micro-Nikkor 60mm on a Nikon D50 both displaying and accounting for the aforesaid Effective Aperture.

As to the Sigma lens firmware update, I would research what Sigma says about the update although, if they say anything, it's usually written in SMV (Sigma Marketing Vague). If Effective Aperture is not mentioned and if the lens is working well enough for you, I personally wouldn't bother. It is not unknown with Sigma stuff for a firmware update to result in a dead item that is only fixable by Sigma. Your call of course.

HTH

That is quite funny because all my communications with Sigma have resulted in a terse reply or as you say SMV!
Here is today's offering following my enquiry as to how the firmware works:

'What you are experiencing can be compensated for by the update which increases the exposure at the closer focusing distances'.

[DanK]

This may be brand-specific. Many Nikon bodies, if I recall correctly, actually do show effective f/stops, and if they do that, their meter can presumably compensate. Canon bodies show nominal aperture.

I have been doing macro for many years with Canon bodies, and I haven't found this inconvenient.

[Stagecoach]

I would appreciate any comments or observations to help me decide whether or not to get the firmware update offered by Sigma.

I shoot Nikon with a Nikon 105mm macro. The Nikon indicates 'effective' aperture, e.g. at closest focusing distance f/57 is indicated as opposed to f/32 the minimum 'actual' aperture.

A test shows that exposure is identical whether focused at minimum focusing distance or focused a metre away using a 'white' monitor screen.

It's an interesting problem you have found, in all my forum reading where many mention the 150 Sigma I have not seen this raised. How are you determining the 2 stop difference?

Edit;

I have since found a couple of references to the underexposing problem the closer you focus the Sigma that mention the software update solved.

[StuartC]

I judge the number of stops difference by the amount I move the exposure compensation to the right. This can be variable depending on the amount of light available but principally by how close I get.
Can you provide the links you have found to the underexposure being corrected by the firmware update? I have failed to find any reference to it.

[Stagecoach]

I judge the number of stops difference by the amount I move the exposure compensation to the right. This can be variable depending on the amount of light available but principally by how close I get.
Can you provide the links you have found to the underexposure being corrected by the firmware update? I have failed to find any reference to it.

https://www.dpreview.com/forums/thread/4025746

and a mention

https://www.talkphotography.co.uk/th...on-7d2.587891/

I found another but still looking ..............

[StuartC]

https://www.dpreview.com/forums/thread/4025746

and a mention

https://www.talkphotography.co.uk/th...on-7d2.587891/.T

I found another but still looking ..............

Thanks, the second one is particularly interesting since it mentions that Sigma were working on a firmware update. They both mention the problem but don't appear to say anything about the firmware rectifying the problem unless I've missed something.
My slight concern is that Sigma originally said they didn't have an update, although I may have confused them by mentioning using a 7D2 and a 5D4 with this lens. Now they say they have one for the 7D2 but I cannot find it in their update lists, perhaps it was so niche it never made it to the list! It is at least reassuring to read that they had been working on an update.

[DanK]

I think I misunderstood your post.

My Canon bodies and lenses don't display effective f/stops. However, the cameras' meters show the correct value--that is, they respond to the amount of light reaching the sensor, not the displayed f/stop. So I never have to use EC as a result of approaching MWD. As I get closer, the meter adjusts automatically.

On rereading your posts and Grahame's links, I realize that I misunderstood and that this doesn't happen with your Sigma lens. Sorry that my earlier post reflected a misunderstanding. But I am still puzzled. Presumably, the camera still has to recognize that it is receiving less light. Does the camera then display a reading that is off by 2 stops? And what mode are you shooting in?

[Manfred M]

There is a fairly good writeup on effective aperture in macro work that Sean (the CiC site owner) did about 11 years ago.

Have a look at the second entry in this thread:

Effective Aperture for Macro

[StuartC]

Thanks for your continuing interest, it is helpful to discuss it.

I use either AV or Manual but the effect occurs in either. I use the meter as a guide, so if I set this to near 0 (as I would do with any lens) the shot will be under exposed regardless of aperture, this is underexposure is corrected by adding up to 2 stops of compensation to the right. This occurs when photographing close to the subject, photographing subjects further away, say a metre or more the effect disappears.

None of this happens with a Canon 100mm macro lens.

According to Sigma the update corrects the underexposure when photographing close up. I interpret this to mean that currently the lens does not report the focus distance correctly to the camera but the update will correct it. The Canon lens, being on a Canon body does, so there is no error. I haven't contacted Canon yet but I suspect the camera simply reacts to the amount of light received and needs to know the focus distance in order to make the compensation but that is a real guess!

[Manfred M]

Thanks for your continuing interest, it is helpful to discuss it.

I use either AV or Manual but the effect occurs in either. I use the meter as a guide, so if I set this to near 0 (as I would do with any lens) the shot will be under exposed regardless of aperture, this is underexposure is corrected by adding up to 2 stops of compensation to the right. This occurs when photographing close to the subject, photographing subjects further away, say a metre or more the effect disappears.

None of this happens with a Canon 100mm macro lens.

According to Sigma the update corrects the underexposure when photographing close up. I interpret this to mean that currently the lens does not report the focus distance correctly to the camera but the update will correct it. The Canon lens, being on a Canon body does, so there is no error. I haven't contacted Canon yet but I suspect the camera simply reacts to the amount of light received and needs to know the focus distance in order to make the compensation but that is a real guess!

It sounds like the issue is the Sigma lens rather than something else. If you contact Canon, they will send you straight back to Sigma, The OEM manufacturers will back performance on how their lenses / camera bodies interact. That has always been the problem with third party accessories; lenses and flashes; they don't always work, especially with newer camera bodies.

[DanK]

I interpret this to mean that currently the lens does not report the focus distance correctly to the camera but the update will correct it.

Interesting. I had assumed that the lens needs to report only one thing to the camera: the aperture. The camera knows the shutter speed and ISO, so it needs the aperture value to calculate exposure. It doesn't need distance, except insofar as distance creates a difference between nominal and effective ISO.

So presumably either the lens firmware or the camera's firmware knows enough to adjust the aperture value when you get very close. I had never thought about this before.

[StuartC]

No, neither had I but if the firmware upgrade from Sigma works then that must be the explanation. Unless the camera receives information about focussing distance from the lens no compensation will be applied and the camera will just accept what it 'sees' i.e underexpose because the Effective aperture is smaller than set. I presume this is particularly a factor for macro lenses where we tend to work at very short focus distances.

The fact that my Canon macro lens doesn't exhibit this seems to support that theory, it is just my interpretation at present but have contacted Canon to see if they can confirm it.