Sigma 105mm 2.8 that won't go down to 2.8??

Nicola.P

Nicola.P

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Nicola
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We bought this lens a few weeks ago as my xmas prezzie and only just got round to having a play.
I have a Nikon D40X so Ii was already aware that it would not work with auto focus which is fine. However I tried using the lens earlier in Manual exposure mode and the lowest it would go down to was around f5?? The lens itself was set at the highest F stop as the details advised. When I changed the f stop on the lens itself the meter would not work.

Any ideas on why? or is it broken?
 
Nicola.P said:
We bought this lens a few weeks ago as my xmas prezzie and only just got round to having a play.
I have a Nikon D40X so Ii was already aware that it would not work with auto focus which is fine. However I tried using the lens earlier in Manual exposure mode and the lowest it would go down to was around f5?? The lens itself was set at the highest F stop as the details advised. When I changed the f stop on the lens itself the meter would not work.

Any ideas on why? or is it broken?
Click to expand...

How far from the subject/object are you trying to focus?

Macro lenses, whilst f2.8 in name, are not constant...the closer you get to the subject the higher the number will be.
 
I was pretty close to the subject, i was trying to get a leaf frozen in water, probably around 30cm away
 
sdb123 said:
How far from the subject/object are you trying to focus?

Macro lenses, whilst f2.8 in name, are not constant...the closer you get to the subject the higher the number will be.
Click to expand...


Not true - if its set at f2.8 then its f2.8 if you are 15mm away or 10ft away - its a constant aperture prime lens. (and a fine one at that)

Try setting the camera to Aperture priory and try setting it to f2.8 via the body.
 
ruvor said:
sdb123 is right, at ~0.3m the max aperture will be about f/5
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If that is so, could one of you explain why please.I thought a constant 2.8 prime would be just that,constant.I`m slightly confused now.......:wacky:
 
it's really complicated. The aperture isn't actually changing, it's the effective aperture, so the lens is sending that info to the camera so it exposes correctly.
 
ruvor said:
sdb123 is right, at ~0.3m the max aperture will be about f/5
Click to expand...

Crap.....if i set my Sigma 105mm to f2.8 in aperture priority mode and point it at a object 0.3m away it shows f2.8 in the view finder, if i then point it at the moon it still shows f2.8. were talking actual real life here not theory - a F2.8 prime lens set a F2.8 will display f2.8 throughout the focus range.
 
My Tamron 90mm 2.8 macro is exactly the same.
 
My Sigma 180 macro goes down to 3.5 wide open as it should whether i'm 1m or 100m away:shrug:
 
ruvor said:
sdb123 is right, at ~0.3m the max aperture will be about f/5
Click to expand...

b****x; I have the sigma 150 and can shoot f/2.8 and focus on a pin head at 1:1 magnification (0.38m) or the the car across the street 1:12ish (4m) and still have f/2.8

the only thing that chages is the DOF!
 
like i said, the aperture isn't actually changing, the metering system in the camera is just compensating for light loss due to close focus. the f/5 is what you need to use if you ate using a manual flash for example.
 
Some of the language in this thread is simply deplorable.........:D


Is this only for Macro/prime lenses or does it relate to all lenses?
 
the lenses i use (none macro) stay at say F2.8 throughout the range no matter how close or far away i am, surely marco lenses are the same
 
I agree the meter changes the closer you get to subject as less light able to be gathered from the surrounding (you will need a wider aperture for the same shutter speed to expose correctly.) but in manual the USER selects the aperture not the camera.

I also didnt see anything regards to flash being used in the OP
 
ruvor said:
like i said, the aperture isn't actually changing, the metering system in the camera is just compensating for light loss due to close focus. the f/5 is what you need to use if you ate using a manual flash for example.
Click to expand...


Why try confusing the OP ? ;)- the question asked was should the camera be able display a aperture of f2.8 in manual mode - the answer is yes- it should be able to display a aperture of f2.8 irrespective of focus distance.
 
The more you magnify the larger the effect of the aperture, this is not the problem I see here, the lens should stop down to F2.8 even if you have the lens cap on and focussed to the closest you can get the lens to go. Sounds like a faulty lens if it won't stop down to f2.8. Take it back to the shop.
 
sorry, got caught up in trying to explain effective aperture, rather than answer OP.

to the OP, check the aperture ring on the lens is set to the highest number (f/22 or whatever) on before you mount it on the camera and turn it on - then try again.
 
My Nikkor 60mm f/2.8 at the minimum focal distance shows a maximum aperture of f/5 and and a minimum aperture of f/55, even though it only stops down to f/32. The Sigma 150mm shows f/2.8 and f/22 at max and min apertures. The difference between the two is that the Sigma is internal focus and the Nikkor is not. As the article linked by Mr Pants says

"Except for lenses with internal focus, a macro lens will typically lose a full stop of light at half life size and two stops at life size (1:1) magnification."

so presumably the OP's 105mm lens is not IF and they are taking a photo near the minmum focal distance and the lens is reporting the true aperture.

as for changing the aperture on the lens itself, this won't work as the D40x controls the aperture and requires the aperture to be set to the minimum aperture and locked.
 
Dogfish_magnet said:
Crap.....
Click to expand...

Hmm. So that's crap is it. Or maybe not. Take a seat at the front of the class ruvor :) The rest of you doubters sit in the corner. Facing the wall. We'll come back to you later.

For all lenses, the f/number and focal lenth only hold absolutely true when focused on infinity. (That's what the figure 1 is referring to, when you see 1: 2.8 on the front of the lens, since you ask ;) ) When you focus closer, things change. They don't change much at normal focusing distances, but when you get down under say 1:4 magnification ratio they start to change a lot, and quickly. Normal depth of field calculations go wonky too. Macro is a whole different world in more ways than one.

When you get down to 1:1, which is where the OP is heading, the light loss is 4x, or two stops. Your f/2.8 lens is now effectively f/5.6. And this is regardless of whether the lens is internal focusing or not, and also holds true regardless of what that link to lowendmac appears to imply. The way I read it, that's not quite right either.

Not only does the f/number change, but focal length reduces a bit too. Especially on internal focus macros, but that is really very slight. It's a purely technical point anyway, and has no real world significance. The reason for the f/number changing is the Inverse Square Law - a fundamental of physics. It's the bane of flash photography too, but I won't go into that, and neither is this the thread to explain magnifications ratios.

The fact remains that when you get down to a magnification ratio of 1:1, even though the viewfinder may well still say f/2.8, it is effectively f/5.6. For those of you facing the wall, which is evenly illuminated I hope, set your camera to Av, select f/2.8 and focus on infinity. Note the shutter speed. Let's say it reads 1/125sec. Now focus the lens right down to 1:1 and check the shutter speed again. It will now read 1/30sec. Two stops different.

DogfishM, take 100 lines. "At a magnification ratio of 1:1, the marked lens aperture is effectively reduced by two stops and my camera is telling porkies."

Richard ;)
 
HoppyUK said:
Hmm. So that's crap is it. Or maybe not. Take a seat at the front of the class ruvor :) The rest of you doubters sit in the corner. Facing the wall. We'll come back to you later.

For all lenses, the f/number and focal lenth only hold absolutely true when focused on infinity. (That's what the figure 1 is referring to, when you see 1: 2.8 on the front of the lens, since you ask ;) ) When you focus closer, things change. They don't change much at normal focusing distances, but when you get down under say 1:4 magnification ratio they start to change a lot, and quickly. Normal depth of field calculations go wonky too. Macro is a whole different world in more ways than one.

When you get down to 1:1, which is where the OP is heading, the light loss is 4x, or two stops. Your f/2.8 lens is now effectively f/5.6. And this is regardless of whether the lens is internal focusing or not, and also holds true regardless of what that link to lowendmac appears to imply. The way I read it, that's not quite right either.

Not only does the f/number change, but focal length reduces a bit too. Especially on internal focus macros, but that is really very slight. It's a purely technical point anyway, and has no real world significance. The reason for the f/number changing is the Inverse Square Law - a fundamental of physics. It's the bane of flash photography too, but I won't go into that, and neither is this the thread to explain magnifications ratios.

The fact remains that when you get down to a magnification ratio of 1:1, even though the viewfinder may well still say f/2.8, it is effectively f/5.6. For those of you facing the wall, which is evenly illuminated I hope, set your camera to Av, select f/2.8 and focus on infinity. Note the shutter speed. Let's say it reads 1/125sec. Now focus the lens right down to 1:1 and check the shutter speed again. It will now read 1/30sec. Two stops different.

DogfishM, take 100 lines. "At a magnification ratio of 1:1, the marked lens aperture is effectively reduced by two stops and my camera is telling porkies."

Richard ;)
Click to expand...

Even I knew this,and the Inverse Square Law usually sends me to sle....zzzzzzzzzzzz ;)
 
HoppyUK said:
Hmm. So that's crap is it. Or maybe not. Take a seat at the front of the class ruvor :) The rest of you doubters sit in the corner. Facing the wall. We'll come back to you later.

For all lenses, the f/number and focal lenth only hold absolutely true when focused on infinity. (That's what the figure 1 is referring to, when you see 1: 2.8 on the front of the lens, since you ask ;) ) When you focus closer, things change. They don't change much at normal focusing distances, but when you get down under say 1:4 magnification ratio they start to change a lot, and quickly. Normal depth of field calculations go wonky too. Macro is a whole different world in more ways than one.

When you get down to 1:1, which is where the OP is heading, the light loss is 4x, or two stops. Your f/2.8 lens is now effectively f/5.6. And this is regardless of whether the lens is internal focusing or not, and also holds true regardless of what that link to lowendmac appears to imply. The way I read it, that's not quite right either.

Not only does the f/number change, but focal length reduces a bit too. Especially on internal focus macros, but that is really very slight. It's a purely technical point anyway, and has no real world significance. The reason for the f/number changing is the Inverse Square Law - a fundamental of physics. It's the bane of flash photography too, but I won't go into that, and neither is this the thread to explain magnifications ratios.

The fact remains that when you get down to a magnification ratio of 1:1, even though the viewfinder may well still say f/2.8, it is effectively f/5.6. For those of you facing the wall, which is evenly illuminated I hope, set your camera to Av, select f/2.8 and focus on infinity. Note the shutter speed. Let's say it reads 1/125sec. Now focus the lens right down to 1:1 and check the shutter speed again. It will now read 1/30sec. Two stops different.

DogfishM, take 100 lines. "At a magnification ratio of 1:1, the marked lens aperture is effectively reduced by two stops and my camera is telling porkies."

Richard ;)
Click to expand...

I know the theroy and i Know the camera lies but thats the point the camera should still show f2.8 in the display.... (well my D300 does) the OP asked if in manual the camera should stop down to f2.8 again i believe it should- why do people try to confuse or disregard the question :thinking: the OP didn't ask for a theory lesson in optics or what the effective aperture is at 1:1. they asked if they should be able to select F2.8 while in manual settings on the camera and have a F2.8 lens attached to the body.

i may take 10 lines for the use of a naughty word ;)
 
Gosh, don't people love to over complicate things. As some have said, you should be able to select an aperture of f2.8, whatever the distance from the subject. As far as an aperture ring goes though, I wouldn't know as the version of the lens that I have doesn't have one. ;)
 
fracster said:
...could one of you explain why please.I thought a constant 2.8 prime would be just that,constant.
Click to expand...

Sorry guys, I just think it's important to be clear and correct. I didn't mean to over-complicate in my long answer above (and only joking DogfishM ;) ) but macro photography changes a lot of things and an explanation was requested.

Richard <in the dog house :( >
 
HoppyUK said:
Sorry guys, I just think it's important to be clear and correct. I didn't mean to over-complicate in my long answer above (and only joking DogfishM ;) ) but macro photography changes a lot of things and an explanation was requested.

Richard <in the dog house :( >
Click to expand...


Richard thanks for the explanation (y) - And it may be that a D40's metering system isnt as deciving as other bodies :cautious: - anyone else got a D40 and a sigma 105mm ? -
 
My wife and I discovered this buying a macro lens for her D80 at RGB labs, every lens he tested on a D60, D90 and a D300 stopped down at minimum focussing distance (tamron 90, sigma 105 and the nikon 105). Put us off so we came home and did some research on it. Apparently they all stop down (like said above), maybe Canon just report the actual aperture and not the effective aperture?

Wife got her macro lens the next day once we knew it was normal and not just a defective lens (the guys in RGB tested all the nikon macros they had). RGB were very confused when we discovered it though.
 
Dogfish_magnet said:
Richard thanks for the explanation (y) - And it may be that a D40's metering system isnt as deciving as other bodies :cautious: - anyone else got a D40 and a sigma 105mm ? -
Click to expand...

This bit confuses me, and I don't think we've got to the bottom of it. I'm not Nikon, so can't help.

All I can say is that the f/number, technically, does not change. Or rather, it's a simple measurement that only strictly applies at infinity focus. It's only the effective aperture that changes. So I can kind of see that some cameras may report if differently. Assuming the camera knows what the focusing distance is in the first place, and I'm not at all sure that it has a clue there either.

So despite my finest wafflings, I am not yet clear on the OP! :thinking:

Richard.
 
eftpotrm said:
FWIW I've got this lens and a D80, and it reported f/2.8 all through the range perfectly happily.
Click to expand...

What do you mean all through the range, it's a fixed focal length, assuming your talking about the 105mm :thinking:
 
This has got me confused now, i have a tamron 90mm 2.8, when i tried it out i could rarely get 2.8 in AF, i read somewhere it was nothing to worry about and it was normal for it to fluctuate,i've just been to try it out again and used manual and it changes aperture in that mode to, so what i want to know is who is right and who is wrong, as their seems to be quite a difference of opinion here and should i be worried about this lens :shrug:
 
TG. said:
This has got me confused now, i have a tamron 90mm 2.8, when i tried it out i could rarely get 2.8 in AF, i read somewhere it was nothing to worry about and it was normal for it to fluctuate,i've just been to try it out again and used manual and it changes aperture in that mode to, so what i want to know is who is right and who is wrong, as their seems to be quite a difference of opinion here and should i be worried about this lens :shrug:
Click to expand...
Nothing wrong with the lens

I suspect that they are reporting effective aperture as the magnification increases

Fine explanation Hoppy - I already got it but I like the humour you injected into a somewhat boring topic :)
 
RichardtheSane said:
Nothing wrong with the lens I suspect that they are reporting effective aperture as the magnification increases
Click to expand...

So are you saying it is at an actual 2.8 aperture although it's not physically showing on the camera display, as this doesn't seem to make sense to me or am i missing something :thinking:
 
TG. said:
This has got me confused now, i have a tamron 90mm 2.8, when i tried it out i could rarely get 2.8 in AF, i read somewhere it was nothing to worry about and it was normal for it to fluctuate,i've just been to try it out again and used manual and it changes aperture in that mode to, so what i want to know is who is right and who is wrong, as their seems to be quite a difference of opinion here and should i be worried about this lens :shrug:
Click to expand...

When you were trying this were you in aperture priory of shutter priority ?
 
I'm not really following this.

I understand that the effective aperture changes as the focus distance shortens but how on earth is the camera working this out? Presumably it doesn't have a database of all lenses so it can recognise what one is connected and do the math based on the elements/grouping, extension, etc? I didn't think Sigma lenses reported focus distance anyway?

How else could the camera know the effective aperture has changed? A drop in light? But then how does it know that's not a cloud passing by, turning off the lights, etc, etc?

:thinking:
 
Hi it may not matter anyway in my opinion as at 1:1 you would stop down a bit normally say F8 or 10 to get a usable depth of field as even at F10 depth of field is small. Also the sweet spot for this lens is at around F10
Pete
 
TG. said:
Aperture priority.
Click to expand...

So what your saying is if you set the lens to manual focus at infinity and AP with a aperture of f2.8 it will read F2.8 then as you alter the focus upto the closest focusing distance you can see the aperture value change on the camera :thinking: - that doesn't happen on a D300 with a sigma 105mm macro if you set it to f2.8 then it stays at f2.8 - which is what i would expect to happen.
 
pxl8 said:
I'm not really following this.

I understand that the effective aperture changes as the focus distance shortens but how on earth is the camera working this out? Presumably it doesn't have a database of all lenses so it can recognise what one is connected and do the math based on the elements/grouping, extension, etc? I didn't think Sigma lenses reported focus distance anyway?

How else could the camera know the effective aperture has changed? A drop in light? But then how does it know that's not a cloud passing by, turning off the lights, etc, etc?

:thinking:
Click to expand...
I don't know for sure but I would think it is more likely to be the lens that reports it's maximum available aperture rather than the camera just knowing.
 
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