Sigma 150mm f2.8 won't stop down past f6

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diggerz

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Hi
Has anybody got any idea as to why my Sigma 150mm f2.8 APO macro DG HSM won't open any further than f6 in any modes on my Nikon D80. It's not the camera as my Nikon 80-200 f2.8 works fine. I have given the contacts a good clean and the lens is as good as new with very little use, I've never had any problem with it before and it seems to work apart from not stopping down past f6. Any advice would be greatly appreciated.

Cheers Paul
 
i don't know mate sorry, but hopefully someone else will be along shortly to help you
 
I'm a bit confused when you say "won't stop down past f6" and then say "won't open any further than f6", could you clarify - is the problem that it won't stop down (you can't get f/8, f/11 etc) or that the aperture won't open further (you can't get f/4, f/2.8 etc)?
 
Has it been like this since you got it or was it once OK?

The item below was in a review of the lens I read.
Don't know if it is of any significance. Hopefully not.

* Nikon mount of this lens is not equipped with an aperture ring, therefore, depending on the camera model some functions may not work.
 
Hi Arclight
Yeh It was fine, I've not not used it for a while maybe 3 months, but whichever mode I use it won't go wider than f6. It hasn't been dropped or banged so I just can't understand it.

Cheers Paul
 
Could it be a case of some grit or something stopping the shutters from opening past that point, have a good luck and see what you can see. Maybe a good drop or bang would fix it?! (Probably best to ignore that last bit of advice)
 
Can't see it being grit or anything like that as ithas only been as far as the garden but never put down there. How and where do you suggest I drop it and how would I explain this rather extreme remedy to Sigma if I end taking it back to them/
 
I accept zero responsibility for any actions taken from advice taken off the internet.

I used to have a TV where the ONLY way to fix the dodgy screen was to bang it on either side, obviously that's of no use here but goes to show it sometimes works lol.
 
When you look through the lens can you see the aperture blades. If so then it sounds like a good old fashioned mechanical fault. If the blades are fully retracted and you can see edge to edge when you look through the lens then it's something in the software and camera/lens communication that's the trouble.

If it's not mechanical then some form of reset on the camera may help but it sounds like it could well be a back to sigma affair. They do get very good customer service reports on here, so there is a small bright side.
 
I guess it's worth finding out whether it's really at f/6 or just reporting f/6. Take a shot in Av at f/6 whilst looking into the lens and check if the aperture moves.
If the aperture blades are sticking then it's sometimes possible to free them by stopping down a long way and then toggling the DoF preview button several times.

Bob
 
Thanks Bob
The DOF button seemed to do the trick (in stages) do you think its a case of a new lens not being broken in yet? Anyhow Thanks again Bob :thumbs::clap::clap:
 
Out of curiosity ... does/did this problem still occur when you're trying to photograph something in the distance, or only when focussing on something close?
 
Spoke too soon now won't go down past f4 but as you auto focus it goes up to f6 again, I'm confused!!!!! Help.

Cheers Paul
 
diggerz said:
Thanks Bob
The DOF button seemed to do the trick (in stages) do you think its a case of a new lens not being broken in yet?
Click to expand...


You shouldn't have to "break-in" a lens....

Are you trying to adjust the aperture when it's in P,A,S, or M?
 
In every mode, if you set it at say f6 it can wander as it's auto focusing but will come back to f6 when it locks on, but if you manage to set it on f2.8 it wanders around the same but could be on f3.6 when it locks on if that makes any sense? same thing happens at distance. Sorry for taking so long to get back but the Mrs just phoned from her sisters.

Cheers Paul
 
diggerz said:
In every mode, if you set it at say f6 it can wander as it's auto focusing but will come back to f6 when it locks on, but if you manage to set it on f2.8 it wanders around the same but could be on f3.6 when it locks on if that makes any sense? same thing happens at distance. Sorry for taking so long to get back but the Mrs just phoned from her sisters.

Cheers Paul
Click to expand...

If you set it on manual, or Aperture it can't "wander", if you're using P or S or full auto it can though....
 
Flash, take it from me it does, but something else that I've noticed is with the manual focus ring, that at both its limits it has a distinctive clunk, but turns past this point, and by turning it past the clunk point I can sometimes achieve f2.8 but can't keep it. If that makes sense? Perhaps some thing has come loose within the lens?

Cheers Paul
 
What I want to know is what happens when you're focussed at infinity, and what happens when you're focussed close up. Bear with me, and I'll explain why.

Macro lenses employ tricks to obtain really close focus. As you focus closer, what hapens is that the focal length effectively increases. Without this trick, a 150mm lens would only give you 1:1 reproduction if the subject was at 150mm from the sensor, which is right about where the front element is. In fact the minimum focus distance (MFD) for this lens is 38cm, which suggests that by the time you've focused at the MFD the effective focal length has increased to around 380mm.

Now the f/2.8 aperture means that, wide open and focused at infinity, the aperture is 150/2.8 = 54mm. But when you're focused at the MFD the effective maximum aperture is around 380/54 = f/7.

Different cameras can report this in different ways. But it's entirely possible that your camera will tell you that you can achieve f/2.8 at infinity but you can't achieve anything better than about f/7 at MFD. In other words, this "problem" you're having may be entirely normal behaviour.

I think you need to be a bit more disciplined in your approach to testing, so we can tell whether you really do have a problem. Here's a suggestion.
1. Choose a nice well lit subject. Set the lens to manual focus. Set the camera to shutter priority.
2. Focus the lens to infinity. (It doesn't matter if your target isn't in focus.)
3. Work through all the shutter speeds from fastest to slowest. For each shutter speed, meter on the target, and note what aperture the camera selects.
4. Focus the lens to MFD. (Again, it doesn't matter if your target isn't in focus.)
5. Repeat step 3.
6. Tell us what you found.

If the results of step 3 are that the aperture ranges from f/22 to f/2.8, and the results of step 5 are that the aperture ranges from f/22. to about f/7, then that's perfectly normal behaviour.
 
Hi Stewart
I set the camera on the tripod, ISO was set at highest (only way to get f2.8) Here are the results

Speed Inf Mfd
4000 f2.8 HI
3200 f3.2 HI
2500 f3.5 HI
2000 f4 HI
1600 f4.5 HI
1250 f5 HI
1000 f5.6 f6
800 f6.3 f7.1
640 f7.1 f8
500 f8 f9
400 f9 f10
320 f10 f11
250 f11 f13
200 f13 f14
160 f14 f16
125 f16 f18
100 f18 f20
80 f20 f22
60 f22 f25
50 HI f29
40 HI f32
30 HI f36
25 HI f45
20 HI f45
15 HI HI

Looking at these results given your explanation there doesn't seem to be much wrong. What do you think? Am I imagining a problem that doesn't exist?

Cheers Paul
 
Both, if you look at the top of the list you'll see Speed, Inf and Mfd, and the three figures for each in the descending list. Sorry, I did set them out in 3 seperate columns but when I posted it they all got pushed together.

Cheers Paul
 
StewartR said:
Were you focussed at infinity or at MFD?
Click to expand...

diggerz said:
Both, if you look at the top of the list you'll see Speed, Inf and Mfd
Click to expand...
Doh. :bonk:

Anyway, what that's saying is that, focused at infinity, the lens adjusts from f/2.8 to f/22; but at MFD it adjusts from f/6 to f/45. That is exactly (*) the behaviour I said you should expect, and it's perfectly normal for a macro lens.

To be honest, I'm surprised that some of the other people who had contributed to this thread didn't pick up on that. You must have caught them on an off day.


(*) OK, I said about f/7 rather than f/6. But that's a minor detail.
 
Thanks for your help regarding this Stewart, I remember reading something about this a good while back now but had totally forgotten it until you mentioned it again. :bonk::bonk::thumbs::thumbs:

Cheers Paul
 
It may be different on a Nikon but my Sigma 150 will remain at f/2.8 whether it's focussed at MFD or infinity. The physical aperture size may well vary as the focal length changes with focal plane distance but the maximum aperture should remain regardless.

Bob
 
Canon Bob said:
It may be different on a Nikon but my Sigma 150 will remain at f/2.8 whether it's focussed at MFD or infinity.
Click to expand...
I hate to contradict you Bob, because you're usually right, but in this case I don't think you are.

On Canons the behaviour is quite different from Nikons. The lens still reports an aperture of f/2.8 as you approach MFD, but I don't think it is f/2.8. Of course this would be pretty easy to confirm or refute, and next time I get my hands on a macro lens (probably around October, they've been in so much demand recently) I'll give it a try.
 
Stewart,

With the lens off the body and in MF, turning the focus ring towards MFD has the effect of closing down the aperture blades....visible through the rear element. The aperture is mechanically coupled to the focus ring to maintain constant aperture. If I read your description correctly then you appear to be assuming that the aperture remains a constant diameter irrespective of where the focus ring is....hence the aperture ratio would increase as the focal length shortens. The aperture definitely varies to counter this.

Bob
 
I have (and love) this lens which I use on Canon's. I can't comment on what Nikon's do, but on a Canon it reports & maintains a constant aperture of f2.8 irrespective of focussing distance.

My instinct is that the 150mm lens in question is faulty, but it would be better for a Nikon user who also owns the same lens to confirm/deny that.

Phil
 
Wife has the Nikon 105 VR and it does the same thing (well I think it's 4.8 or so it reports), when in the shop buying it we also tested a Sigma 105 and a Tamron 90 and they both did the same. It's just Nikon reporting the aperture differently to Canon it would seem, bloke in the shop tried a Sigma and Tamron on a Canon and they reported 2.8 straight through.

Just one of those things. If you search the net there's a whole pile of physics related stuff about it available to explain it.
 
I had the 150mm on a Nikon D300 and the aperture changed from F2.8 as you moved closer to 1:1 - its reporting effective aperture, i also have the 150mm on my Canon 50D which will report f2.8 at 1:1
 
OK, this is getting a bit confusing.

My understanding is as follows:
(a) the effective focal length of a macro lens increases as you get close to MFD;
(b) Nikon cameras report the aperture relative to the effective focal length, so they indicate that you can't achieve f/2.8;
(c) Canon cameras report the aperture relative to the nominal focal length, so they indicate that you can achieve f/2.8;
(d) but what's going on inside the lens is essentially the same regardless of whether it's connected to a Canon or Nikon.

It looks like Dogfish_magnet and chimponarope agree, but Canon Bob and philthe juggler disagree.

So here's a thought experiment which I hope would settle it.

(1) Point the camera at a uniform subject (eg a blank wall).
(2) Focus the lens at infinity, set f/2.8 in aperture priority, note the shutter speed.
(3) Focus the lens to MFD, and note the shutter speed again.

If the settings in (2) are, say, 1/60th at f/2.8, then I think we all agree that in (3) the Nikon will give us something like 1/25th at f/6.3. But what will the Canon give? If it's still 1/60th at f/2.8 then the Canon really is behaving differently to the Nikon. If it's 1/25th at f/2.8 then it's actually behaving the same as the Nikon, but just reporting what it's doing in a different way.
 
Trying to pick the bones out of this :thinking: I seem to recall the Nikon/Canon macro thing has come up before, but I'm not sure. Some comments:

All lenses change focal length when they focus closer. Some internal focusing lenses, eg some macros and zooms, change quite a bit, but only a few percentage points. It's not massive, and they get shorter.

The f/number is also only true when focused on infinity, but that does change massively when focusing very close. It's two stops down at 1:1 magnification, which takes an f/2.8 to an effective f/5.6.

I guess you can look at that two ways - the f/ratio hasn't changed, so the the f/number should technically remain the same - I know that Canon works like this. However, since we use f/numbers to set exposure, the effective f/number (or T/stop) is the one that matters for exposure - maybe this is how Nikon does it? The f/number is needed for depth of field calculation.

Confusing isn't it.
 
StewartR said:
My understanding is as follows:
(a) the effective focal length of a macro lens increases as you get close to MFD;
....snip....
Click to expand...

I think you may find that the focal length decreases as you approach MFD. I haven't measured the Sigma 150 but tests with my Canon EF100 show that the focal length is 98mm at infinity and 79mm at MFD.

The Sigma may well work on a different principal (ie, not having free movement of the internal elements) but my theories above have assumed that has this design.

Bob
 
Hi
Just tried 2 things. 1) as suggested by Bob remove lens, holding the aperture lever up so it's wide open f2.8 at inf as I turn the focus ring to mfd the aperture closes somewhat but smoothly. 2) as suggested by Stewart, point at wall focus at inf,result 1/20 @ f2.8. without moving anything focus at mfd result 1/80 @ f6. Please discuss.

Cheers Paul
 
diggerz said:
Hi
Just tried 2 things. 1) as suggested by Bob remove lens, holding the appeture lever up so it's wide open f2.8 at inf as I turn the focus ring to mfd the appeture closes somewhat but smoothly. 2) as suggested by Stewart, point at wall focus at inf,result 1/20 @ f2.8. without moving anything focus at mfd result 1/80 @ f6. Please discuss.

Cheers Paul
Click to expand...

That makes no sense. Are you sure? Is the lens diaphragm still sticking :thinking:
 
I don't know if it was sticking, from what Stewart is suggesting (I think) is that this shutting of the diaphragm and upping of the shutter speed is all part of the natural phenomenon of the lens, and I think these results bear this out.
 
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