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10-27-2007, 02:46 PM   #1
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Bigma Question

I've just purchased a Bigma lens, and find that the aperture at 500mm opens only to 6.7 as opposed to the shown and advertised 6.3. Is this significant enough to warrant either shipping the lens back to the dealer for replacement or to Sigma for repair? (Sure is a heavy sucker, isn't it?)

CN

10-27-2007, 03:31 PM   #2
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Well, this is one of those maybe, maybe not answers. If the dealer will cover the cost of replacing the lens then I certainly would. If not then I'd contact Sigma and find out what their policies are. I just wonder how accurate the lens data/metering is to the body. Mine is spot on and I've never encountered this type of issue with any lens. So I can't offer a reason for the difference.

Have you tested it out at all? Does the lens show the correct aperture at 50mm or other settings? How do the tests shots look? Exposed OK? The 0.4 difference at 500mm may make very little difference in many scenes. What does it say if you pull it back to 480mm, the same?
10-27-2007, 06:28 PM   #3
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Peter:

At 50mm I can open it up to f4. At 100mm it goes to 4.5; at 200mm to 5.6, and from 300mm up it's at 6.7. The weather here has been completely overcast (what time it wasn't raining) since I got the lens so I haven't had much chance to play with it, but what test pictures I've taken (mostly at 500mm) are properly exposed. Interestingly, I purchased a Sigma 17-70mm f2.8/4.5 new a few months ago, and at 17mm it would only show a maximum aperture of 3.5. I sent it to the Sigma repair facility in New York, and on return a couple of weeks later it would go to 2.8. Needless to say, I have no idea what they did or whether it was a "hardware" or "software" problem. I'd be very interested to know if your lens shows the same maximum aperture from 300mm on. Thanks for your help. (If memory serves me correctly I think I read either here or on the DPreview Pentax SLR forum where someone made a comment about their Bigma only going to 6.7 as opposed to the advertised 6.3)

CN

Last edited by Clem Nichols; 10-27-2007 at 06:31 PM. Reason: Additional comment
10-27-2007, 06:41 PM   #4
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My Bigma is the same up to 300mm where it is at 6.3 So I guess you might want to have them look at it. I think I would since it's under warranty now and presumably you want to keep it for awhile and if you ever decided to sell it you can say with confidence that it's functionally as it should be. But of course that's your call.

10-27-2007, 07:05 PM   #5
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Mine has always been at 6.7. I have read in a few places that the Bigma is 6.7 w/Pentax only. I have the EX model (not the new DG)....the DG may be different. Truthfully, the difference is there, but its pretty negligible.
10-28-2007, 06:29 AM   #6
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It is important to note that the lens data regarding maximum and minimum apature (as determined by 5 of the electrical contacts on the lens do not provide for 6.3 as a maximum apature.

to see the range of possible values, see the following site

Pentax Lens Modifications for Matrix Metering - Mark Roberts Photography

as a result you will probably not get this 1/2 stop.
10-28-2007, 10:50 AM   #7
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That is the way mine behaves as well, ie. f6.7 at the long end instead of f6.3.
I suspect it is a readout issue. At the long end it is only supposed to be f36 minimum but mine goes down to f38.
The camera still appears to expose correctly with this minor descrepancy, but you could dial in a little ex comp if you find differently.
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10-28-2007, 10:55 AM   #8
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Lowell:

I read the info on the Mark Roberts site, but to be honest, I probably didn't comprehend much of it. Moreover, that wouldn't explain why Peter's Bigma will open to 6.3 whereas Paul's and mine won't open past 6.7. My basic question is whether or not this discrepancy is likely to make any difference in the real world, and I'm inclined to agree with Paul that it probably won't inasmuch as this is pretty much a bright light only lens to begin with. (DBH, thanks for your reply. I feel more comfortable knowing that others have the same experience. I've been very favorably impressed with the lens so far, and believe that after a few months of weight training in the gym I'll get a lot of use with it. :-)

CN


Last edited by Clem Nichols; 10-28-2007 at 11:02 AM. Reason: Additional comment
10-28-2007, 01:05 PM   #9
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I may need to amend my earlier comments. I never thought of this before posting the first time. I bought my Bigma used with a couple other pieces from a professional. There's no way for me to be sure that he didn't send the lens to Sigma to have it checked and adjusted. So my lens may not be a good indicator of the norm for this lens. Possibly this is how it reacts on a Pentax and as long as shots beyond 300mm are properly exposing then you're probably fine since everyone else is reporting the exact same thing.
10-28-2007, 03:16 PM   #10
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Mine also only opens to f/6.7 at the long end.
10-28-2007, 07:03 PM   #11
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I just checked, and mine also closes down to f/38 at the long end.

CN
10-29-2007, 11:54 AM   #12
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As an after thought you may wish to check / change your exposure steps in the camera.

Depending on whether you have 1/3 or 1/2 stops, you may not be able to adjust to maximum apature on the lens.
10-29-2007, 01:35 PM   #13
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QuoteOriginally posted by Lowell Goudge Quote
It is important to note that the lens data regarding maximum and minimum apature (as determined by 5 of the electrical contacts on the lens do not provide for 6.3 as a maximum apature.

to see the range of possible values, see the following site

Pentax Lens Modifications for Matrix Metering - Mark Roberts Photography

as a result you will probably not get this 1/2 stop.
If you read the note at the bottom of the page you will see, " It will not have any effect on any of the Pentax digital cameras ".

Apparently the digital camera does not use the five electrical contacts to establish maximum and minimum aperture, instead it uses a serial data contacts to communicate with the lens.

If you're not seeing the correct aperture values, check your camera and make sure it is set up to use one third stop.
I am not sure but This may make a difference.

If this does not help, and it is still under warranty contact the vendor and get it repaired.

It's better to have it working right, than to try to live with it.

joe1955
10-29-2007, 01:58 PM   #14
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QuoteOriginally posted by joe1955 Quote
If you read the note at the bottom of the page you will see, " It will not have any effect on any of the Pentax digital cameras ".

Apparently the digital camera does not use the five electrical contacts to establish maximum and minimum aperture, instead it uses a serial data contacts to communicate with the lens.
Not true.

The reason it does not have any impact on a DSLR is that the DSLR assumes that if the Automatic apature connection is missing, that it is not connected. I have successfully modified a K mount to KA mount and it does use the se contacts. Note the automatic apature connection requires a pin, not just contact surface on the lens, and the camera pin does not stick out sufficiently to contact the lens base.

Please see my later post, where depending upon exposure steps you may not be able to use the f/6.3 stop because it is 1/3 of a stop from f/5.6
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