Discovery on why Sigma Long zooms aren't always sharp

I have spent the last two days working with a Sigma 150-500 f/5-6.3 OS lens while teaching and using a 7D. As many of you know, reviews of this lens have been mixed where some people feel it is very sharp and others feel it is very soft and their pictures bear that out. Most of us thought that this is due to large sample variation but I discovered something today that makes me question that diagnosis. I noted today, that unless the lens collar is firmly tightened so that the lens can not rotate, there is a very large amount of flex in the lens collar that causes enough shake that the OS can not correct it. Unless you put your hand on the top of lens and push down while pulling down on the camera, as good long lens technique dictates, there is quite a bit of vibration in the system unless the collar is really tightened down. Even with it tightened down, tapping the front end results in a vibration that takes several seconds to dampen out. My theory based on this is that technique may be a bigger factor on whether this lens is sharp on the long end than sample to sample variation. The Sigma 120-400 has the same design for the collar and the same variation from review to review.

This is most definitely not a lens you want to shoot hands off with or with a cable release, you definitely want to place a hand on the lens to dampen any vibration. I would love to see somebody like 4th Generation design or ReallyRightStuff design a replacement lens collar without so much flex for this lens and I would bet that many of the long end sharpness complaints would go away.

Just food for thought on this lens. Based on my experience with it this weekend, I think it is a very good lens with superb versatility but an under designed lens collar.

Appreciate the information that you have provided. I have a friend that has the Sigma 150-500 and he swears by its sharpness. Pop Photo's lens tests showed it to be sharp also. One lesson that can be taken from this is to always use flash when you do your lens tests. You want to eliminate all the variables that you can so that you are testing only the optical performance of the lens. I've always used a resolution chart and flash for my lens testing. Another key is to make sure image magnification is identical when you are comparing different lenses. It is harder to distinguish differences in resolution when the comparison images are at different magnifications.

Yes that is true for lens tests but in real life field use one has to be careful to tighten down the collar and use even better long lens technique then you would with say a 600 f/4 with 1.4x because of the flex in the collar and foot.

With my Sigma 50-500 I always found that the focus distance was important. I could get razor sharp images at 500 mm (well pretty darned sharp, anyway) on close-up subjects, but using 500 mm for further away subjects, the images always seemed a bit soft. I know that technique is extremely important, but I think on that lens anyway, there was some optical effect at longer focus distance.

-Paul

I think EJ is wright about this lens. I own the 150-500 OS for some time and have noticed the same problem. Only difference is that handheld images were sharper than on tripod. On tripod the OS can not be used and I had the good (or not so good )technique problem that EJ mentioned.
I did put my hand a little to far to the front of the lens and so the lens did show a serious amount of flex, I could see the image vibration trough the viewfinder when placing my hand (when lens is fully extended the problem gets bigger). You have to place your hand almost against the camera body to avoid the flex and than paying attention not to touch the focus ring.

Thanks EJ for doing this test, I'm feeling somewhat reassured about this lens now.

Jos

I use the 150-500 on the Nikon d300 hand held with good results, however when I read your comments I put it on a tripod and it definately has a poor collar design. The Nikon 300 f/4 also has a similar problem but not to that extent. Kirk makes a replacement collar for the 300 that is just a perfect upgrade. A third party replacement collar would be the answer.

Thanks for your testing.

Thanks for the tip on the Nikon 300 collar!!!

E.J.
You got my attention with your 7D review as that is a camera I plan to get soon. I was surprised in that review that you mentioned the 150-500 in a favorable way, I have never taken the lens seriously, and I have always valued you opinion. You have me thinking now. I do much of my photography from a 23 inch wide kayak. On partial day trips I carry my 500 f4, on longer trips I often use my 400 5.6 but I miss the IS plus I do not have anything between that and my 28-135 which is a great kayak lens (I am still searching for a good quality lens that is not overly bulky in that mid-range category, I have the 75-300 IS that I don’t like and seldom carry and am contemplating the 70-300DO.). This lens could replace my long lens and give me the middle range and possibly replace my 100 macro with a 500D. That is appealing; I am interested in more observations on this lens if you have time to give me some thoughts.

Well it certainly won;t be as sharp as the 400/5.6 - no zoom is though so it's the convenience factor. I was pleasantly surprised by this lens though. I do think the lens colar's flex is a liability though but opne that can be mitigated with excellent technique. I would not get the 70-300DO - it is very expensive and doesn't have as good of image quality as the non DO version of the lens but is lighter and more compact.

A downside of the 150-500 is that you really can't use a TC on it and expect AF performance or image quality.

So it comes down to a convenience call. Certainly it would replace carrying both your 400 and 500 on a kayak which would be good.

On the Nikon 300mm f/4, I much prefer the RRS Collar over the Kirk Collar because I use Wimberley flash brackets.

DavidRamey wrote:On the Nikon 300mm f/4, I much prefer the RRS Collar over the Kirk Collar because I use Wimberley flash brackets.

David,

I did not know that RRS made a repalcement lens collar for the Nikon 300 f/4. Do you have a link to it?

I was talking about this: http://www.kirkphoto.com/Lens_Collar_fo ... 4_AFS.html

EJ.,

Thanks for sharing us with this great finding. Almost like a Christmas gift for Nikon bird shooters. It seems this Sigma will fit this big hole in Nikon's modern line of lenses.

Eric

Just remember my analysis is based on a sample of 1. Sigma has a long history of high sample variation.

EJ,

I had an older 150-500 and found the same issue with the collar, then I bought a Bogen long lens attachment and with a minor mod it supported the the lens and the camera body at the same time reducing all vibration but the results were still far from useable even after mirror lockup etc. It was a great lens 150 to about 350, but was definitely soft beyond that in my copy.

YWguide wrote:EJ,

I had an older 150-500 and found the same issue with the collar, then I bought a Bogen long lens attachment and with a minor mod it supported the the lens and the camera body at the same time reducing all vibration but the results were still far from useable even after mirror lockup etc. It was a great lens 150 to about 350, but was definitely soft beyond that in my copy.

Yup, that's why i think there is still a sample variation issue. But it is also possible that Sigma has cleaned this up as this was a brand new lens purchased last week.

Mike Gallo wrote:

DavidRamey wrote:On the Nikon 300mm f/4, I much prefer the RRS Collar over the Kirk Collar because I use Wimberley flash brackets.

David,

I did not know that RRS made a repalcement lens collar for the Nikon 300 f/4. Do you have a link to it?

I was talking about this: http://www.kirkphoto.com/Lens_Collar_fo ... 4_AFS.html

http://reallyrightstuff.com/rrs/items.a ... =0&Tp=&Bc=

Does anyone have any experience/thoughts about using this lens on a full frame camera (i.e. 5dII)? I'm specifically thinking relative to a reasonably sharp copy of the 100-400.

Cheers,
Sam.

Hi,
I have one more question about the Sigma lens: Do you switch the OS off, when putting the lens on the tripod ?

E.J. Peiker wrote "I noted today, that unless the lens collar is firmly tightened so that the lens can not rotate, there is a very large amount of flex in the lens collar that causes enough shake that the OS can not correct it. " So I presume, he had the OS switched on - or am I misunderstanding it ?

Please help me get it right: is it better to switch the OS on or off when mounting the lens on the tripod ?

Thanks, Miha.

According to Sigma's instructions that come with the lens, they say to turn it off, however since there is so much flex in the collar, I found that OS on in Mode 1 helps stabilize the image quite a bit.

Thank you for a well written article that should be helpful to thousands. I am amazed that in this day and age (sounding like my father again) that multimillion dollar companies can release and successfully market products with obvious design flaws. We see it often. I wonder about the history of recalls of lenses...and if any recalls were or could be consumer initiated. Maybe it's time? The lack of comment on this aspect of your article suggests to me a degraded level of expectation as it relates to purchases we make. Consumers deserve better.