External zoom, what are the pros and cons?
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hef19898
Well-known member
For the user? External zooms are more at risk regarding dust and moisture being sucked in, or put differently, they rely more on hood weather sealing. Compared to internal zooms that is, doesn't mean external zooms are bad.
Regarding IQ, no difference. External zooms tend to be lighter and overall shorter than internal ones.
Mostly, weather a zoom is external or internal is an engineering constraint / trade-off.
Not to forget, even internal zooms pump air when zooming.
Regarding IQ, no difference. External zooms tend to be lighter and overall shorter than internal ones.
Mostly, weather a zoom is external or internal is an engineering constraint / trade-off.
Not to forget, even internal zooms pump air when zooming.
To me the big things are:
- Internal zooms don't change length as you zoom which also minimizes big center of mass shifts which means less readjusting of things like mounting location when shooting from a gimbal as you zoom. Long focal length external zoom lenses in situations like that can be frustrating as the gimbal or other mount has to be rebalanced as we zoom in and out.
- External zooms can pump dust and moisture in and out as you zoom the camera leading to stuff inside your lens that shouldn't be inside the lens.
Good external or internal zooms can both deliver excellent images so it's not really an image quality thing but in the field I much prefer a good internal zoom.
TurtleCat
Well-known member
For my typical case of handholding it makes no difference. I also don’t tend to be in super dusty environments, either. And I find that dust concerns are a bit overblown in general except for resale purposes. If I’m using camera support then it matters a little more to me but not much more. Generally the lenses are sealed against basic stuff but remember all the terms from all the manufacturers about weather sealing is a marketing term unless they give a waterproof rating.
hef19898
Well-known member
On non-gimbal heads, I never had problems with any of the now four Nikon 24-120 zooms on tripods. Neither did I encounter issues with dust / water, and that includes litteral snow, rain amd dust storms (the latter with the old AF-D and the f4 f-mount). I'd rather see probpems with external zooms that develop barrel wobble over time (read: years if not decades). And the f4, 24-120 Z and 100-400 Z, I'd say, should be pretty much immune to that kind of wear. Unless the have an impact on the extended zoom barrels. I prefer to carry them zoomed in.
Only real advantage to an external zoom is ability to take less space in camera bag when zoomed close for storage.
That being said, any given lens only comes in one or the other configuration as far as I know. Both seem to work fine so I would not make this a deciding factor in which lens to get (though I must admit I do love the internal zoom of my Z 70-200).
That being said, any given lens only comes in one or the other configuration as far as I know. Both seem to work fine so I would not make this a deciding factor in which lens to get (though I must admit I do love the internal zoom of my Z 70-200).
There are some very good answers here. A few other things that are also worth considering:
Exotic zooming mechanisms and exotic glass and other things are generally employed with internal zooms where they may not be necessary on an external zooming lens. An internal zoom maybe a compromise in that to fit it into a (usually) shorter lens barrel it might mean that they cannot be as good at things like focus breathing without making the zoom larger and heavier or using more exotic glass and mechanics to achieve a top quality result. It might mean that more exotic glass is needed to iron out other issues like CA or other distortions due to the need to fit it into this smaller space where moving the zooming lens elements more (as in an external zooming mechanism) would normally allow for easier corrections. It might mean that the zoom ring needs to go forward instead of aft (and opposite for the focus ring) like the F 70-200 f2.8 E FL VR and the new Z 70-200 f2.8 VR S.
An external zoom may give the lens designer more freedom in how they construct the zoom and hence why external zooms are generally cheaper, lighter and smaller, but that does not always apply to all aspects. Some may not necessarily be smaller, and/or lighter and/or cheaper. An external zoom also generally moves the weight forward when zooming to the longest zoom range meaning that the balance may change. However, a well-designed external zoom lens - read more expensive as well! - may allow for the balance to remain constant or near to it, like the Z100-400 f4.5-5.6. I have this lens and can attest to the fact that it is a great lens simply for that fact, a very well-balanced lens at the shortest or longest focal length. Again, there will either extra and/or more exotic lens elements and/or special mechanisms employed to achieve this adding to cost. Possibly why this lens is not as cheap as other lenses of similar zoom range and aperture value.
The need to be internal or external will come down to a compromise between the marketing department, the engineering department and the accounting department. If we take the Nikon Z 24-70 f2.8S. Top quality results in a relatively light weight and small package compared to the old F mount 24-70 f2.8 lenses and they are both external zooms. I would guarantee that if they were internal zooms, they would be heavier, larger and more costly, which is not what the marketing dept would like, nor the accounting dept. There is also another consideration with regards to the F mount version, and that is that the lens hood is a constant size yet you are zooming from very wide angle at 24mm to short telephoto. This does not allow for optimal shading throughout the zoom range as the hood would not shade enough at the tele end but enough at the wide end. Nikon had come up with a neat almost solution in that the lens hood was mounted at front of the lens barrel, yet the front lens element/s moved back and forth inside the hood which remained stationary. So, when at 24mm, the front lens element was furthest forward meaning that the hood was shallowest in relation to the front element/s and thus no vignetting. As you zoomed the lens from 24mm towards 70mm, the front element retracted back behind the stationary lens hood where the barrel of the lens itself afforded part of the shading as well as the hood left on the end of the lens. Not perfect but better than nothing and quite ingenious in a way. They may have actually made the lens an external zoom simply to employ this method in order to get a decent amount of shading throughout the zoom range. It is difficult to make a zooming lens hood for best shading, but this system seemed to work. It was also employed to a degree on the F mount 14-24 f2.8 and very well with the Z 14-24 f2.8S. Unfortunately, the new Z 24-70 f2.8S doesn't employ this system as they were probably after the smallest and lightest they could get, maybe the new lens coatings do a better job of reducing flare etc.
Exotic zooming mechanisms and exotic glass and other things are generally employed with internal zooms where they may not be necessary on an external zooming lens. An internal zoom maybe a compromise in that to fit it into a (usually) shorter lens barrel it might mean that they cannot be as good at things like focus breathing without making the zoom larger and heavier or using more exotic glass and mechanics to achieve a top quality result. It might mean that more exotic glass is needed to iron out other issues like CA or other distortions due to the need to fit it into this smaller space where moving the zooming lens elements more (as in an external zooming mechanism) would normally allow for easier corrections. It might mean that the zoom ring needs to go forward instead of aft (and opposite for the focus ring) like the F 70-200 f2.8 E FL VR and the new Z 70-200 f2.8 VR S.
An external zoom may give the lens designer more freedom in how they construct the zoom and hence why external zooms are generally cheaper, lighter and smaller, but that does not always apply to all aspects. Some may not necessarily be smaller, and/or lighter and/or cheaper. An external zoom also generally moves the weight forward when zooming to the longest zoom range meaning that the balance may change. However, a well-designed external zoom lens - read more expensive as well! - may allow for the balance to remain constant or near to it, like the Z100-400 f4.5-5.6. I have this lens and can attest to the fact that it is a great lens simply for that fact, a very well-balanced lens at the shortest or longest focal length. Again, there will either extra and/or more exotic lens elements and/or special mechanisms employed to achieve this adding to cost. Possibly why this lens is not as cheap as other lenses of similar zoom range and aperture value.
The need to be internal or external will come down to a compromise between the marketing department, the engineering department and the accounting department. If we take the Nikon Z 24-70 f2.8S. Top quality results in a relatively light weight and small package compared to the old F mount 24-70 f2.8 lenses and they are both external zooms. I would guarantee that if they were internal zooms, they would be heavier, larger and more costly, which is not what the marketing dept would like, nor the accounting dept. There is also another consideration with regards to the F mount version, and that is that the lens hood is a constant size yet you are zooming from very wide angle at 24mm to short telephoto. This does not allow for optimal shading throughout the zoom range as the hood would not shade enough at the tele end but enough at the wide end. Nikon had come up with a neat almost solution in that the lens hood was mounted at front of the lens barrel, yet the front lens element/s moved back and forth inside the hood which remained stationary. So, when at 24mm, the front lens element was furthest forward meaning that the hood was shallowest in relation to the front element/s and thus no vignetting. As you zoomed the lens from 24mm towards 70mm, the front element retracted back behind the stationary lens hood where the barrel of the lens itself afforded part of the shading as well as the hood left on the end of the lens. Not perfect but better than nothing and quite ingenious in a way. They may have actually made the lens an external zoom simply to employ this method in order to get a decent amount of shading throughout the zoom range. It is difficult to make a zooming lens hood for best shading, but this system seemed to work. It was also employed to a degree on the F mount 14-24 f2.8 and very well with the Z 14-24 f2.8S. Unfortunately, the new Z 24-70 f2.8S doesn't employ this system as they were probably after the smallest and lightest they could get, maybe the new lens coatings do a better job of reducing flare etc.
jcollins
Member
Lots of comments about external zooms being worse about dust, but I'd note that internal zooms aren't perfect either. I've used my Z186 extensively for about 5 months now (i.e. 3hrs+ a day) and there are a few specks of dust inside... Nothing that I've noted makes any difference in image quality, but eventually it'll reach a breaking point where it becomes notable and I'll have to get it sent for servicing.
This is inaccurate. There is no volumetric change and therefore no air exchange. For an internal zoom to draw in/expel air the moving parts would have to be sealed against the lens barrel(i.e. like an engine piston with sealing rings). Which is not the case.
All lenses "breath" due to thermal cycling. The greater the temperature differential, the more often that it cycles, and the larger the lens is the more likely it is to ingest particulates.
hef19898
Well-known member
As I said, all zooms pump air. And I'd argue primes as well when focusing, but less so. You move a lens element, or multiple ones in new Z mount Nikkor glass, you move air.
External zooms are at risk getting dust on the lens barrels past whatever sealing is in place. I did use an old 24-120 AF-D, next to my travel mates 24-120/4, during a dust (as opposed to a sand strom, dust particles are significantly smaller) in Sahara. No visible amount of dust ended up in the lens. Dust does, as you noted, build up over years and years of use inside each and every lens. Usually has no visible impact on IQ, no matter how much pixel peeping one does.
External zooms are at risk getting dust on the lens barrels past whatever sealing is in place. I did use an old 24-120 AF-D, next to my travel mates 24-120/4, during a dust (as opposed to a sand strom, dust particles are significantly smaller) in Sahara. No visible amount of dust ended up in the lens. Dust does, as you noted, build up over years and years of use inside each and every lens. Usually has no visible impact on IQ, no matter how much pixel peeping one does.
hef19898
Well-known member
Internal zoom and (!) focus lenses doe pump air: they move lens elements around, creating over pressure at one side of the element and inder pressure at the other. That pressure delta sucks and pumps air, simple physics. The do less so than external ones, they still do so. I am not aware of any lens that has valves and hoses / vent lines to minimize that effect.
Example: a pump bicycle tire doesn't change volume neither, and yet it pumps air quite well, doesn't it? All by moving an internal element up and down. Same for lens elements, minus the intentional sealing of the moving element against the barrel, a lens is not designed to be pump after all.
It is indeed simple physics. Without a seal between the moving element and barrel there is no pressure differential generated. No differential no motive force. No motive force no air movement.
The piston in a bicycle pump has a seal on it. Comparing it to a camera lens is nonsensical. Take you bicycle pump apart, take the seal out of it, put it back together and give it a try. How's that work for you?
hef19898
Well-known member
Oh dear... Move your right hand fast down on your left one, you feel an airflow. Now imagine that in a weather sealed barrel. There very much is a pressure differential... Physics never go away.
Marketing material is one hell of a drug it seems...
The only way to prevent this effect is to have the moving element not blocking any air, aka having a very slim and aerodynamically perfectly neutral ring, or no element at all.
Marketing material is one hell of a drug it seems...
The only way to prevent this effect is to have the moving element not blocking any air, aka having a very slim and aerodynamically perfectly neutral ring, or no element at all.
The laws of physics are indeed immutable. The trick is understanding how they manifest themselves in practical application.
So true. Exacerbated by the fact that our system of higher learning educates a lot of people well beyond their level of intelligence.
hef19898
Well-known member
Not sure how I should read your comment...
Edit: Now that I think of it, the only way to completely avoid air being pumped around would be a vaccum sealed lens. Would have the benefit of being ultra fast as well, no internal air resistence to work against. Just how long the vaccum seals would last so is a different topic. Such a lens would also be almost completly sealed against water, rain at least. And very resistant to heat effects, a vaccum doesn't transfer temperature. Not sure how much that would weigh or cost!
Edit: Now that I think of it, the only way to completely avoid air being pumped around would be a vaccum sealed lens. Would have the benefit of being ultra fast as well, no internal air resistence to work against. Just how long the vaccum seals would last so is a different topic. Such a lens would also be almost completly sealed against water, rain at least. And very resistant to heat effects, a vaccum doesn't transfer temperature. Not sure how much that would weigh or cost!
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macwalter
Well-known member
I do think internal zooms will ingest less air and I can say that in my experience I had the f 80-400 external zoom and took it to Africa where it was very dusty and the lens sucked in quite a bit and it ruined the lens for all practical purposes. I spent hundreds of dollars trying to get it working right and it never was the same. So if I were to go back to similar situations I would be more cautious about covering amy lens when dust is stirring up like in Bosque NM when other vehicles are passing by. Lots of fine dust. So far my primes are fine but I do try to protect them as well. It will get on the front element ar least and you have to clean it off meaning contact with the glass that sometimes requires more than just blowing it off.
As noted by others internal and external variable focal lenght (zoom) lenses pump air when focusing. More of an issue for me than dust in the lens is that they can actually pump dust to the sensor, but and a big but, a prime (fixed focal length) lens can do the same. I had no clue about this until a lens rep and then one of the few SPT Certified Camera Technicians in Idaho got my attention about how the focusing elements in the lens move and have to displace air to operate and that air and dust can end up on my sensor. I got educated when I was trying to figure out how I go dust on my sensor without have had a high end prime lens of the camera for months before the sudden appearance of dust spots.
macwalter
Well-known member
Yeah I didn’t know that. I always assumed it was due to changing lenses. Interesting to know.
That was what I always thought.
macwalter
Well-known member
I guess its important to know best how to minimize the chances of getting dust on the sensor or just accept that it is going to happen and deal with it accordingly.
Happily so far I have not had much problem with my Z lenses and a quick blow off with my rocket blower usually takes care of it.
macwalter
Well-known member
So far so good here as well. I did have some spots after a trip to Brazil last year using the 100-400z nd the 1.4tc. But the blower blew it off. Didn’t have to do any other cleaning. Nothing since.
Roy
Well-known member
External zooms are cheaper to make.
But on longer lenses that belong on a tripod they throw the balance off as they extend ..
hef19898
Well-known member
Only on Gimbals, other tripod heads are unbalanced anyway.
For me, the external zoom provides a much shorter length for travel and such. In the nearly 25 years I’ve been shooting I’ve never had an issue with an external zoom lens, so they are pretty tough to say the least. Two of my favorite current zooms are the Sony 24-70 GMii and 100-400gm which are both external. Typically the internal zoom lenses have a smoother zoom action as well.