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by kiwijohn on Mon Nov 06, 2017 4:05 am
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Here in New Zealand much of our wildlife displays what is called ecological naivety or a lack of fear of humans (and many introduced pest predators). This means many species of our forest birds can be approached quite closely without provoking a flight response. Great for photography!

However, my Nikon 600mm f4 telephoto has a minimum focusing distance of approx 16 feet, and I am constantly having to move away from birds in the forest in order to get them into focus.

Would it be worth using a small extension tube to help shorten this minimum focusing distance? Or would it introduce other problems, for instance:

1. Would it cause problems with existing focus fine tuning settings for this lens on my D810. (It had originally front focused and needed a 15 point correction in-camera)

2. Degrade the image in some way due to the altered light path.

3. Drastically reduce the depth of field.

I would be interested in your thoughts as I have not heard of this being done with long telephotos.

If its a bad idea, can you suggest an alternative workaround for this problem?

I am due to travel out to one of our pest free offshore island "arks" where many of out rare birds are found next week and will do some extension tube experimentation.

Your advice in advance would be appreciated!

Thanks!
John
 

by E.J. Peiker on Mon Nov 06, 2017 8:12 am
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1. Possibly, the only way to know for your exact camera and lens and extension tube is to do a focus cal specific to that combo and then dial it in when youa re using extension tubes.

2. No, the light path is merely longer, there are no additional optics. Do realize that your DOF gets shallower the closer you get to a subject but that isn't IQ.

3. Yes it will reduce it but only if you are physically closer to the subject. DOF is a function of subject magnification and aperture only!
 

by photoman4343 on Mon Nov 06, 2017 9:10 am
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John, these were great questions. I never would have thought about the AF fine tuning issue. EJ, thanks for the answers.

I will share some of my experiences with extension tubes on my 500mm f4 Nikon lenses. I loved using the Nikon all metal extension tubes when I had a manual focus Nikon 500mm. f4. I used the PK-11A tube, only 8mm thick and it had minimal impact on exposure. Sometimes I just left it on the lens all day long. When I really had to get close, I used the PN-11 tube, about 52mm thick. This tube is no longer made by Nikon. Of course I had to manually focus as AF is not supported.

I have used some of the tubes that support AF, but some have broken (came apart) while in use. And sometimes I got vignetting with them. Maybe someone can recommend the "best" electronic extension tube to use for the latest Nikon long lenses and digital bodies.

Joe
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by Mike in O on Mon Nov 06, 2017 12:13 pm
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I believe you will also lose light...not sure how much, probably depends on the size of the tube. I played a bit with my 500 & 600 in various combinations and they seem to work great (Kenko auto)
 

by signgrap on Mon Nov 06, 2017 1:06 pm
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There is some light loss but not all that much. I use to put a 25mm extension tube on my Canon 400mm f/5.6 all the time with little light loss. Doing so never changed the way I used the lens (tripod use mostly). With an extension tube as the lens gets longer the light loss lessens. The converse is true for wide angle lenses, the wider the lens the greater the light loss. With through the lens metering you don't need to think about light loss or f stops as the camera takes all that into consideration for you; unlike in the days before before through the lens metering when you had to do the math yourself (what PITA).
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by kiwijohn on Mon Nov 06, 2017 1:53 pm
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Thanks fellas for your valued input.

I will report back when I have done some trials at home and on the island next week.

I feel a little ashamed I have never thought of doing this before especially as I have had the 600mm for 4+ years!

I would think I will lose the ability to focus to infinity using extension tubes, but we will see. Maybe not with the smaller tubes?

I have a set of auto tubes by Kenko (Medium quality) with all the electronic contacts. Why does Nikon not make their own high quality auto tubes? As far as I know the only Nikon ones available are ancient manual only tubes. Correct me if I'm wrong.

Thanks again guys!
John
 

by Wildflower-nut on Mon Nov 06, 2017 2:37 pm
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Your light loss with a tube is a function of the magnification you get from the tube. Magnification is the ratio of the tube length to the length of the lens. I'm going from memory but light loss I think is 1/(1+m). For the length of tube you are likely to use, light loss is insignificant. While not quite the same thing, I had an 800mm canon FD lens that had a long minimum focusing distance. I found that I could just put a tube on there and leave it as I never needed to focus further than 150 ft or so anyway for birds A real short tube, you may still be able to focus to infinity with some lenses that focus "beyond" infinity. My guess such a tube would be too short to help with your main problem.
 

by E.J. Peiker on Mon Nov 06, 2017 2:54 pm
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Yup the light loss will be minimal due to the long focal length of the lens you are using. You will most definitely lose infinity focus, even with a 12mm tube.
 

by ChrisRoss on Tue Nov 07, 2017 1:28 am
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Use extension tubes all the time with my 500mm, Use the 25mm Canon tube which is quite robust and maintains all functions. Unfortunately Nikon never produced tubes after going AF. Yes you lose infinity but is very rarely an issue as you can normally focus out to 30-40 m or something like that, most big teles focus beyond infinity a little which helps.
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by Wildflower-nut on Tue Nov 07, 2017 1:29 am
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I agree with EJ and Chris Ross  My suggestion is more theoretical than realistic.  You are going to lose infinity but this for me was not a problem for bird photography.
 

by Gary Irwin on Wed Nov 08, 2017 2:07 pm
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I'm wondering if it wouldn't be simpler to rely on the TC14EIII to increase magnification?  The 600 can certainly take it.

if you can get really close, consider the 200-400VR....2m MFD is killer for closeups.

BTW, that's a nice problem to have.  :)
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by DChan on Wed Nov 08, 2017 3:06 pm
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If the birds are closer than 16 feet away, I would have used shorter focal length lenses like a 300mm, a 200-400 or even a 70-200 (plus TC if necessary). With a 600 at such close distance, you may have another problem to deal with, i.e., not enough depth of field.

I don't think a TC would get you a smaller MFD.
 

by ChrisRoss on Wed Nov 08, 2017 6:29 pm
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The extension tube is definitely the answer in cases like this, a 1.4x you are still inside MFD and in the case of small birds you definitely need 600mm FL. The issue is they are not always inside MFD, they are birds so they move around but if you move to get back outside MFD they could well leave.

The other advantage of a tube is the image is slightly larger at the same subject distance because you are using extension to focus not the internal focus which reduces focal length as you get closer. There was a post with sample shots taken which showed the effect of using a tube on magnification. The bird is noticeably larger in frame.
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