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Does anyone have quantitative data of the focal length of the new AF-S 80-400 at distances between MFD and 6 meters at max zoom? I have read one owner's comment that the focal length dropped to ~250mm at MFD (1.75m). Assuming the owner is correct in that the lens does have a focus breathing issue at max zoom, has anyone measured at what focus distance the focal length drops below ~380mm (5%) or so?
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There are basically 2 methods of focusing a lens. With "traditional" lenses, the whole optical assembly is moved forwards away from the film/sensor to focus closer. Many lenses now use "internal focusing" where the outside dimensions of the lens remain constant and the focal length is reduced as we focus closer.
Your lens has to do one or the other.
All of my lenses, with the exception of my AF 50mm 1.4D are internal focus. I am considering, but have not purchased, the AF-S 80-400. The AF-S 80-400, like the AF-S 70-200 are also internal focus lenses. Still, one of the Cons in the dpreview of the latest AF-S 70-200 variant is "Pronounced focus 'breathing', i.e. widening of the angle of view on focusing closer" This widening of the angle of view is analagous to a decrease in the focal length on focusing closer (less magnification of the subject).
I have read owner reviews, but not professional reviews, which state the AF-S 80-400 also suffers from this widening of the angle of view/reduction of focal length when focusing near the MFD. My question is, "does anyone know how much and at what distance?"
With lenses intended for movie cameras, "breathing", where image scale changes during focusing, is considered a cardinal sin. Designers just accept that lenses are going to be more complex to eliminate breathing and they are going to cost a lot more.
The Zeiss 100mm Makro Planar is descended from a movie lens and has floating elements to but eliminate breathing. This lens isn't exactly cheap but it's a lot easier to use for close-up than the 105mm Nikon AFS that we also have.
You can make a rough guess from basic optical theory. For a macro lens, the physical extension at life-size will be equal to the focal length. By focusing internally, the focal length would need to halve. At any image scale, the focal length is reduced by a factor equal to magnification plus one. At half life-size (magnification +0.5), focal length is reduced by a factor of 1.5 so a 300mm lens would act as a 200mm.
Quote: You can make a rough guess from basic optical theory. For a macro lens, the physical extension at life-size will be equal to the focal length. By focusing internally, the focal length would need to halve. At any image scale, the focal length is reduced by a factor equal to magnification plus one. At half life-size (magnification +0.5), focal length is reduced by a factor of 1.5 so a 300mm lens would act as a 200mm.
Thanks. My basis of comparison is my 300 + 1.4x TC, or 420mm. What I'm trying to appreciate is just how close the 80-400 at max zoom would be to my 420mm at the distances I am currently shooting. From what you state, it could be that I am already experiencing the effect of breathing with my 300 + TC, in which case the 80-400 at max zoom would lose only about 5% in terms of subject image size. It seems easy to check out shooting a fixed length target at various distancesdown to MFD and comparing test target length in pixels as a function of distance to target to be able to determine quantitatively how much breathing I am currently experiencing. Perhaps I am concerned about nothing of significance.
Conducted my experiment and found the results interesting. The focal length dropped from 420mm by only 3% (407mm) between 135 and 15 feet. By ~ 5 feet the focal length was down to about 350mm, a 17% drop from 420. Of course, the error in my subject to camera distance grew as the distance shrank, so my focal length at MFD measurements could have significant errors. Still, at that distance less than 2 inches fills the frame from top to bottom, so the modestly reduced focal length is of little concern to me.
Thanks TrailorSailor for your post on my forum topic on the same lens. I have just bought one today from Wex and should have it by the weekend. I will attempt testing when I have it to assess the extent of focus breating and get back to you on this forum.
Enjoy your lens. I look forward to your future post.
Quote: Assuming the owner is correct in that the lens does have a focus breathing issue at max zoom,
Part adding to comments by thewilliam and others there is a lot of internet myth about "focus breathing" affecting only specific lenses.
Symmetrical lenses always have focused to 4 times their focal length at half their infinity angle of view and with 2 stops loss of light transmission by 1:1 magnification.
Because of the problems of getting good optical quality at infinity, medium distances and 1:1 only some expensive macro lenses cover this focus range.
If you want lenses which "focus breathe" in exactly the same way as a symmetrical lens you cannot have it if you want retrofocus wide angles (the only ones that fit an SLR or DSLR), modern lighter weight closer focussing telephotos, macros that auto focus to 1:1, many fixed aperture zooms and variable aperture zooms.
This is probably why in the Nikon line up only the 50mm f1.8 and 85mm tilt and shift lenses appear to be symmetrical optical designs.
All other Nikon AF lenses focus breathe in the sense of internet comment referred to, though not always in the same direction or by the same amount...
The original 80-400 also "breathes" quite a lot.
Variable aperture zooms often "breathe" more than other lens designs though not always in the same direction at all zoom settings.
Recently in the age of video as thewilliam mentions Nikon, Canon, Zeiss etc have been introducing angles of view which do not change (or change very little) when you change focus when updating lenses.
The Nikon zoom which "breaths" the most is probably the 18-200. Despite this it is not stopped more than 1,250,000 copies being sold.
Macro primes also breathe a lot by 1:1 focus.
The Nikon zoom which "breathes" least at 400 is the 200-400. On FX it covers a 6 inch wide subject at 2m. It costs twice as much and is bigger and heavier.
The 80-400 AF-s on FX should cover an 8.5 inch wide subject at 400mm at 1.75m focus.
As a matter of curiosity and for what it's worth, I repeated my breathing experiment with my AF-S 70-300 at 300mm, assuming that it might have similar breathing behavior to the far more expensive 80-400 at max zoom, considering that both are Nikon large zoom range internal focusing lenses. To my surprise I found that it's breathing behavior was quite similar to that of the 300 F4 +1.4x TC. Specifically, at 30 feet and above the focal length varied by less than 1%, and dropped by about 3% at 15 feet and by about 15% at 5 feet. With the lens at max zoom (300mm at infinity) for FX it would cover a 4.0" wide subject at 5'. That would equate to 6" at max zoom and 5' if the 80-400 behaved similarly. That's about the same as what LenShepherd lists for the 200-400 at 2m.
I personally am nolonger concerned about the potential beathing issure of the new 80-400mm. The actual maximum focal length when compared to my 300 F4 +1.4xTC is of greater concern. Here is one review that indicates that I would be loosing more than the 5% in max focal length axxociated with dropping from 420mm to 400mm. http://www.backcountrygallery.com/photography_tips/nikon-under-3k-tele-compariso... The author suggests that the 80-400 is more like a 75-385. I used my pixel-counting technique with the comparison pictures of the 80-400 compared to the 300 + 1.4x TC and calculated that the 385mm figure may be overly optimistic. My current lens combo is already shorter than I would like for a reasonable weight field lens. I guess I'll continue cranking the ISO to up the shutter speed until a VR version of the 300 F4 is available - and justifies what will likely be another huge price jump.
Thanks, all, for the comments. Regrettably, I've ended up where I anticipated I might, just not for the same reasons.
Just recieved my lens today and have done some initial test shots of a test chart and graduated ruler. It will close focus to an object 1.27m perpendicular from the front element of the lens, at this distance, the horizontal width of the full frame is 13.5cm. Full size images of my test chart indicate similar results in sharpness and chromatic abberation to a 200-400mm F4 Nikkor which I had borrowed last weekend under similar lighting conditions. I will do some more tests in due course, if you would like some images of the tests I have done ( for this and the 200-400 if you want), I could email them to you if you send your details via the private message service. The lens is very managable by hand, especially compared to the 200-400mm which is over double the weight.
Results of my tests on this lens:
1.27m from front element/ 1.52m from sensor = 13.5cm image width ( with Nikon DX sensor 1.5x crop) equates to 20.25cm on full frame.
1.75m from front element / 2m from sensor = 15.0cm image width
2.59m from front element = 20.6cm image width
4.1m from front element = 29.7cm image width
Examining Nigeve1's data I discovered that I had made a serious error in calculating focus breathing for my 70-300 and 300 F4 lenses. I have been calculating the angle of view and determining focal length from that by comparing my calculated angles of view to the AoV and focal length at infinity published by Nikon. Previously finding my results consistent with what I had expected I did not question them until I used the same technique on Nigeve1's data. That's the danger of blindly plugging data into a spreadsheet vs. conducting old fashioned pencil on paper calculations. It's easy to overlook simple math errors.
In the case of the 70-300 and 300 F4 the angles of view actually shrink as MFD is approached, while for the 80-400 the AoV increased. As a result I found that the focal length for both the 70-300 and 300 F4 grew by ~ 20% as I approached MFD, while Nigeve1's 80-400 shrank by ~ 25% between 4.1 and 1.27m.
Note that Nigeve1 used the lens front element as his frame of reference. I added .2m to his distance for my AoV calculations as a reasonable correction factor based on the Nikon published lens length of 203mm. However, I did a simple sensitivity analysis varying the correction factor between .1 and .3m. Over this range the focal length changed by only a few percent from the .2m correction factor results.
It is a minor detail but Nikon regard focus distance as being measured from the sensor, and working distance as being measured from the front element (without a lens hood) to the subject.
The distance between the front element and the sensor when the lens is zoomed to 400mm is actually 31cm, this may affect your calculation ( it is 25cm when zoomed to 80mm ).
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