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PROBLEMS with SIGMA 50-500mm Zoom Lens on Red-One ??

George D.

George D.

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At the advise of others on this forum, I have purchased a Sigma 50-500mm Zoom Lens for use on our Red-One. It is a beautiful lens in mint, like new condition. This is the model without the OS and with an aperture ring for external control.

Since other Red owners have used this lens, I just want to make sure you guys are having the same issues I'm having with it. Therefore, my question is this:

I have owned or used many, many lenses in my life, but never one quite like this. It was obviously designed for still use, but most others made for still cameras do not have these restrictions.

This Sigma lens does NOT hold focus throughout the zoom range. In other words, when focused on the subject at full extension, as you zoom back it goes in and out of focus. No, it is not the back focus adjustment on the camera lens port. As such, this lens can only be used theoretically as a series of fixed lenses and has to be focused at each separate focal length.

If this is normal for this lens, then so be it, and I can live with it. I was hoping I could use it as a zoom lens as well though, but if not, OK. It would be more like having many different lenses all in one.

Another thing I noticed. Most zoom lenses, when an object is too close, you just can't focus on it. But, with this Sigma it "jumps" out of focus when it's past the zoom range it can handle. For instance, it will focus at 300mm, but as soon as you've passed that, to 350mm or beyond, it "immediately" goes super-soft.

Are these things typical of this lens? Is it just the norm because of the design?

If you have any knowledge and experience with this lens I'd appreciate knowing if you have the same issues.

Thanks for your time.





 
The inability to hold focus throughout the zoom range is normal for most stills zoom lenses.

Stephen
 
Stephen Pruitt said:
The inability to hold focus throughout the zoom range is normal for most stills zoom lenses.

Stephen
Click to expand...

Not really Stephen.

I have several Nikon zooms that hold focus throughout the entire zoom range. They DO change exposure as you zoom them, which is not good for cine use, but focus IS held.

.
 
To put it another way, there is less incentive for a manufacturer to spend the extra money to design and build a zoom lens for a still camera that holds focus as you zoom, or holds the center in the same spot (i.e. tracking), or doesn't have an exposure change -- all of those things adds to the cost of the lens. Doesn't mean that there aren't still zooms that do some, most, or all of those things, just that it's less of a priority or it adds to the cost (and size sometimes, in the case of a consistent aperture that is fairly fast).
 
I believe Sigma lenses come with a four year warranty. So I'd contact Sigma and see what they say. You also might want to search out some photography sites and ask the same ?. There are probably aren't all that many users of that lens for cine work. Haven't owned a lot of still zooms, but the ones I have owned held focus while zooming, AFICR.
 
David Mullen ASC said:
To put it another way, there is less incentive for a manufacturer to spend the extra money to design and build a zoom lens for a still camera that holds focus as you zoom, or holds the center in the same spot (i.e. tracking), or doesn't have an exposure change -- all of those things adds to the cost of the lens. Doesn't mean that there aren't still zooms that do some, most, or all of those things, just that it's less of a priority or it adds to the cost (and size sometimes, in the case of a consistent aperture that is fairly fast).
Click to expand...

True David, very true.

I was just hoping someone who'd used that exact lens would give me some feedback on it. But, I'm sure it IS as you say.

Thanks.

.
 
I have been using the Sigma 50-500 on the RED One since 2008, it will not hold focus while zooming in or out.
You have use it as block lens. But there is no other lens out there which has this range, and for wildlife
its been a great asset.

Yusuf Thakur
VFX, Dubai.
www.vfxme.com
 
Thank you very much Yusuf.

That is EXACTLY what I wanted to know.

And, that is exactly what I'll be using it for too. Wildlife.
 
You are welcome, one more tip. If you can buy the 120-300 2.8, its the sharpest lens
you can get at the price performance and is a zoom too. I am going to try one on the
Epic soon with the auto function and canon mount. All my present glass is either nikon
or PL mount.

Yusuf
 
The Sigma 50mm - 500mm does go a bit soft at the 500mm end. Stills lenses are not born equal. Some models hold focus through the zoom more than others. There is another factor at play and it is the anti-aliasing filter/infrared filter. I don't know how thick this is on the RED but on the SI2K which is a smaller sensor, this does have subtle effects on realworld lens flange to focal plane distances and ability to infinity focus compared to the same lens performance to film. I don't know enough about the lens to know if it possible to recollimate the lens to the RED camera via removal of shims or spacers between the lens body and the mount. Maybe the RED NIkon mount adaptor has a facility for collimation or backfocus adjustment. It this is possible, then it may be possible to improve the focus behaviour of the lens.

What you need to watch out for is the airflow through the lens body when the zoom extends or pulls in. You preferably should keep the mount and nearby camera body clean of dust and avoid operating in a dusty environment. There is otherwise a risk of dust on the sensor or dust getting inside the lens itself.

Here is a bit of SI2K footage through this lens. ( Guru Jim. Please forgive me for sullying this environment with the "SI" word. ) It is to a 2/3" sensor, which is analagous to the RED in 2K cropped mode. The lens was operated in the aperture range f11-f16. Wider apertures may aggravate any tendency to softness or loss of focus through the zoom range.

http://www.youtube.com/watch?v=yCIFj1NVR08
 
The vast majority of zooms designed for still cameras are varifocal (focus changes as focal length changes) not parfocal (focus remains the same as focal length changes) but while some varifocal zooms are way out (the Sigma 50-500mm) many are pretty close, and appear to be parfocal, but actually aren't. So you want to very carefully test before you assume they are parfocal. I've seen it before - an operator believes from their small LCD that their lens is parfocal, zooms in telephoto to focus then zooms back wide, and it's not until they see it full-res on a larger monitor that they realize every single wide shot is slightly out-of-focus, and just enough to render the shots unusable.
 
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