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Nikon Zoom Question

Sam Roberts

Sam Roberts

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Most of my experience with lenses is with Canon, Fujinon and ANGENIEUX broadcast zoom lenses. These leses hold their focus throughout the zoom range. You zoom in, focus and pull back to your selected focal length.

Today I purchased a used Nikon AFS Nikkor 28-70mm f2.8D from a very reputable camera store. It's about two years old and was rated an 8+ by the store and is in great shape, glass is clean and the housing looks new. Mechanics feel good although a bit loosey goosey but I expect that with still lenses.

When got home I put it on the RED (with factory installed Nikon mount) I zoomed the lens into it's top end, focused and zoomed out. Halfway through the zoom range the lens went out of focus. And not just a little..a LOT.

If this happened to me with a video lens I would suspect a back focus problem. But this Nikon has no back focus adjustment.

I did shoot stills with a couple of Nikon zooms back in the 80's and 90's and don't remember this happening but maybe I've forgotten..I was a weekend still photographer.

So I take the lens back to the camera store, the guy puts it on an SLR and tells me there is nothing wrong with it. He tells me NO Nikon lens will hold focus throughout it's zoom range. You have to refocus every time you change the focal length.

This sounds bizarre and counterintuitive but I didn't argue the point I wanted to hear what you guys had to say first.
 
So the guy...two guys actually, were talking sh*t about Nikon zooms not holding focus?

I really suspect the lens although I'm not sure how its back focus could be so out of whack unless it got damaged in shipping (it originally came to the camera store from their branch in another city) does this mean the rear lens elements are damaged?

As for RED Nikon mount and back focus, I just got the camera two days ago. You think someone at RED screwed up or is the camera back focus something that can easily get out of alignment?
 
I was under the impression that still lenses in general don't hold focus through the range. Hell, the RED 18-50 doesn't hold focus through a zoom.

In our era of autofocus, it makes sense that still lens manufacturers wouldn't spend extra effort to make sure lenses hold through a zoom.
 
I was also under the same impression as Brandon. For a stills lens manufacturer it's a case of "why bother?" as the autofocus takes care of focus at different lengths. I'm pretty sure that my nikon 17-35 does not hold through the zoom range. And yes, my camera is collimated.
Think of it more as a variable prime. I'd love to be proved wrong BTW.

Shane.
 
Well when I went back to the store and explained the problem these two guys (both under 30) didn't seem to understand what I was saying. I had to explain it two or three times. Afterwards it occured that in all likelihood these two had never used a manual focus lens in their lives, they probably grew up using autofocus cameras.

You guys are right of course ....with digital SLR's if the lens loses focus somewhere in the zoom range the camera automatically corrects for that. Indeed the lens I bought does have an auto manual switch for focus.

And since very few people would actually try and do a zoom while recording using a Nikon lens, it doesn't matter if it doesn't stay in focus.

I was under the impression that ALL zoom lenses PL-Broadcast and still, all held focus throughout the zoom range. I guess not.

It will make trying to stay in focus just that much harder. Instead of focusing once (on a scene with no movement or movement parallel to the lens) if I go from wide to medium to closeup I will have to refocus every time.

I guess the pricey glass spoiled me.
 
The still lenses do not hold focus throughout the zoom range. I have the 17-35 and the 28-70, and both of them don't hold focus thru the zoom.

It's one of the prices you pay for not having a 20 pound Optimo PL zoom (that costs as much as the Red body) hanging off the camera. :)
 
My experience is it varies from lens to lens. I used to run a camera shop and I know we used to zoom in, focus, pull back and shoot all the time.

The Canon 17-55mm I have on the Birger mount seems to hold focus well. I have a Sigma for Nikon 70-200 the holds pretty well, but not perfectly... but that is via an adapter ring to the Canon so it might not be collimated correctly.

You should be able to test the lens on a still camera to see what it's capable of... but the idea that no SLR Zoom holds focus is not true from what I've seen... but I do think each lens needs to be tested.
 
We did put the lens on an SLR in the store and it did the same thing which the guy said was normal. I guess he was right after all.

We don't hear much about the differences between the big glass PL lenses and the Nikon-Canon zooms. This one's a biggie.
 
This is why they are called still picture lenses, not motion picture lenses.
Also, their focus throw is usually insufficient for critical manual focusing. They are designed to be used with auto focus.

Good HD zoom costs $30k~$100k. Same with good zoom cine lens.

You get what you pay for.
 
Sam Roberts said:
We did put the lens on an SLR in the store and it did the same thing which the guy said was normal. I guess he was right after all.

We don't hear much about the differences between the big glass PL lenses and the Nikon-Canon zooms. This one's is a biggie.
Click to expand...

Yeah, it would be helpful to test a bunch of zooms and see which ones work. I'll shoot some zoom tests with the Canon 17-55 next week to verify what it is capable of. I've got the PL on for this weekend. I didn't realize the RED 18-50 didn't hold focus. Guess that's why people call it a variable prime.
 
We have the full series of Nikon 2.8 zooms and none of the them hold focus through the range. We knew this going and are happy with our "variable primes". For the record, you won't be unhappy about the images you'll get.

Nick
 
I was also really surprised to hear the RED 18-50 doesn't hold focus too.

But really I never actually used that many zoom shots when using a
Fujinon or Angenieux anyway. So it is really a matter of just wrapping my mind around having to refocus more. I'm sure it'll be second nature after awhile.

Just gotta keep repeating "variable primes...variable primes...variable primes...":tongue:
 
Sam Roberts said:
I'm sure it'll be second nature after awhile.
Click to expand...

This is exactly the case. Different tools need to be used differently. When you're used to using big HD and Cine zooms, then it takes a little getting used to to use still zooms, but it quickly becomes routine. It's simply the nature of still zooms. You'll notice that on the 28-70 there are different markings for 28, 50 and then the line is 70, simply because the focus changes when the focal length is changed. Stick with it though, because the more you use it, the more you'll see how nice this lens is.
 
Although it is true, that not all still zooms will not hold focus, however it does seems a-bit technically wrong.
ok with my nikon 17mm to 55mm zoom, i have focal length set to 20mm - the subject is 4 feet from my camera. set the focus on my lenses to be 4 feet, hence the subject is in focus, now i change the focal length to be 45mm the subject is still 4 feet from camera, so the subject should still be in focus??? but from what i'm reading in these post this is out of focus??? go figure.
 
I described it as "bizarre and counter intuitive"......although I understand it more now (thanks guys) I still believe that.
 
Streetlife said:
Although it is true, that not all still zooms will not hold focus, however it does seems a-bit technically wrong.
ok with my nikon 17mm to 55mm zoom, i have focal length set to 20mm - the subject is 4 feet from my camera. set the focus on my lenses to be 4 feet, hence the subject is in focus, now i change the focal length to be 45mm the subject is still 4 feet from camera, so the subject should still be in focus??? but from what i'm reading in these post this is out of focus??? go figure.
Click to expand...

Still lenses are designed to be used specifically for one reason, still photography. On top of that, most of these lenses that we're talking about were designed to be used with auto-focusing cameras. The focus marks on these lenses were never intended to be used for cinema style shooting, (measuring with a tape). They are not precise markings, they are close, but not precise. You will also notice that on many of these zoom lenses there are multiple focus marks indicating a different position for different focal lengths. These lenses were not designed to hold focus through pulling a zoom. Cinema style 35mm, 16mm and HD zoom lenses are designed for all this, but in order to achieve it, it requires much more precision in the design and build of those lenses, which is just one of the reasons why those lenses cost so much money. Some will argue that optically, these high-end still lenses can produce imagery that is just as good as the high-end cinema lenses and in many cases it's true, but while you can get stunning images from a $1600 still zoom lens, you can't expect it to act the same way as a $30,000 - $100,000 Cinema or HD lens. The fact that we can use these lenses is wonderful, but we need to keep in mind that this is not what they were intended or designed for, so we will have to adjust the way we normally do things with other tools in order to adapt them to fit our needs. In some cases it's just simply changing how you shoot, in others it's spending money and re-housing the lens to make it work more like what you are used to. There are simply many options available with thier pro's and con's and there are many perspectives of the whole situation. Sorry, I'll stop rambling now.
 
Nikon specifically states in their zoom manuals that the lenses will NOT hold focus as you zoom. It was simply a cost factor. No one would pay for such a lens since maintaining focus through the entire zoom range isn't something that a still photographer would ever need to worry about.

Nonetheless, the moving pictures rendered from a still lens are at least the equal of the very best cine lenses. A first-rate prime Nikon, Canon, or Zeiss will look every bit as good as the best Cooke or Angenieux. Still, I want to buy a Cooke or Angenieux just to have the option of a zoom and the faster shooting style that comes from not having to change lenses or camera distances all the time.

Stephen
 
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