[Studor13]

I never said that it couldn't be done. I even said that I have done it myself.

 

But 400mm in say the early morning light means that you are on a tripod since I seriously doubt that you can handhold this thing. Even if you could, unless you have VR you are going to need around 1/400 seconds, which is not a lot of light.

 

So, you are in fact as crazy as me and all others who do this, right?

[Brightcolours]

You don't necessarily need to know the nodal points, as long as you know focusing distance, size of object, size of object in the image, maximum image size and therefore magnification anf FoV. I guess you could calculate the nodal points based on those, but I was just trying to figure out the effective FL

 

Kind regards, Wim

Then you do not calculate correctly, using a wonky formula.

[Brightcolours]

I never said that it couldn't be done. I even said that I have done it myself.

 

But 400mm in say the early morning light means that you are on a tripod since I seriously doubt that you can handhold this thing. Even if you could, unless you have VR you are going to need around 1/400 seconds, which is not a lot of light.

 

So, you are in fact as crazy as me and all others who do this, right?

I shoot the close ups handheld.

[wim]

Then you do not calculate correctly, using a wonky formula.

 

Nope. When you work with magnification, you get the exact resulting FL.

 

I remember now what I did as well. I had a few photographs of tape measures across the entire viewfield, photographed at the above distances. In short, based on magnification and focusing distance (from exif), knowing the sensor width, and knowing the tape length in view in the image, it is then very easy to calculate the resulting FLs.

 

For all intents and purposes, my method is a very practical one, and it works. With magnification you do not need to know the nodes anyway, one can calculate the resulting FL purely based on focusing distance, image size, object size, and magnification.

 

Kind regards, Wim

[Brightcolours]

Nope. When you work with magnification, you get the exact resulting FL.

 

I remember now what I did as well. I had a few photographs of tape measures across the entire viewfield, photographed at the above distances. In short, based on magnification and focusing distance (from exif), knowing the sensor width, and knowing the tape length in view in the image, it is then very easy to calculate the resulting FLs.

 

For all intents and purposes, my method is a very practical one, and it works. With magnification you do not need to know the nodes anyway, one can calculate the resulting FL purely based on focusing distance, image size, object size, and magnification.

 

Kind regards, Wim

No, you do not get exact focal length values without. Give the formula you use?

 

Take ANY lens that does not change focal length (any lens that moves the entire lens system to focus will do). When one looks through the view finder and one goes through the focus range, one will notice focal breathing (the subject becomes "larger" when you go towards MFD). FOV changes, while focal length does not.

This makes a simplified method like you use very useless to determine sort of exact focal length (needed to say with any real authority how much focal length is lost). 

 

In order to exactly calculate effective focal length you will need the front and rear nodes of the lens, and those are not that easy to measure (and usually not provided by the lens manufacturers). 

 Interesting articles:

http://www.pierretoscani.com/echo_focal_length.html

http://www.panohelp.com/thinlensformula.html

[wim]

No, you do not get exact focal length values without. Give the formula you use?

 

Take ANY lens that does not change focal length (any lens that moves the entire lens system to focus will do). When one looks through the view finder and one goes through the focus range, one will notice focal breathing (the subject becomes "larger" when you go towards MFD). FOV changes, while focal length does not.

This makes a simplified method like you use very useless to determine sort of exact focal length (needed to say with any real authority how much focal length is lost). 

 

In order to exactly calculate effective focal length you will need the front and rear nodes of the lens, and those are not that easy to measure (and usually not provided by the lens manufacturers). 

 Interesting articles:

http://www.pierretoscani.com/echo_focal_length.html

http://www.panohelp.com/thinlensformula.html

 

Thank you for the links, I love reading about optics.

 

As to the calculations: I used single lens formula equations, and to be very honest, all I am interested in is effective FL, not theoretical FL based on node calculations. This simply because it does not matter for the end result. A given magnification at a giving shooting distance with known object size and known size of that object in the (sensor) image makes it possible to calculate the effective FL This takes the FoV into account automatically as well.

 

To be very honest, all any extra node calculations provide is potential bragging rights for the manfacturer, as this generally overstates the effective FL, certainly for telelenses. In principle any lens can be replaced by a specific single lens FL, at any distance and magnification, which essentially provides the end result for the photographer. That is to me what it all is about.

 

As to focus breathing in your statement above: in that case the only way to prevent focus breathing is actually to change magnification ver the focus range in such a way that FoV stays exactly the same, no matter where the lens is focused. That is only possible with an IF-type of lens, whether prime or zoom. This is easier to achieve with a zoom lens, in principle, because focusing and zooming can be combined in these lenses. However, it makes a lens with absolutely no focus breathing effectively a zoom lens under all circumstances, as the FoV has to stay the same at all times. The lens therefore has to shorten FL with decreasign focusing distance.

 

From a photographic POV, for me, especially when shooting macro and portraits, this is unacceptable, as it obviously changes magnification and perspective at close focus drastically.

 

HTH, kind regards, Wim

[Brightcolours]

Your post is confusing. You say that to have no focus breathing it needs to shorten focal length (correct), but then you say that is unacceptable to you because it changes perspective. 

 

If you talk about perspective as it is talked about in art, that actually changes when FOV changes.

If you talk about perspective as in point of view, it will not change, either with focus breathing or shortening of focal length.

 

As for your calculations, they still do not make sense (well, the outcome you typed). Version 1 of the Nikkor 70-200mm f2.8 VR has a narrowing FOV towards MFD. Your post just above seems to assert that that changing FOV will mean a longer focal length.

 

Also, for a single lens calculation you still need to know the front nodal point to judge the subject distance.

 

And yes, to have no focus breathing, one has to take care of that in the lens design. That is why specialized film lenses which have low to no focus breathing are very expensive.

 

About that Nikkor 70-200mm f2.8 VR:

1.5m MFD, max. mag. 0.16x

Taking a 1.3m object distance (assuming a single 200mm lens), gives a focal length of 179mm.

[davidmanze]

I used to shoot macro using a 400 mm lens and tubes. Was great for insects. Great working distance, excellent subject isolation. You may be unfamiliar with this way of shooting close-ups, but that doesn't mean it's no good. In fact it's probably the best way for some subjects.

 I shot a load of butterflies with the Nikor 500mm F4 and a 32mm extension tube, AF worked fine, as you say I was shooting from just  2 meters, otherwise the MFD is 2.8 mts. 

[JJ_SO]

poor little critters, must have made feel them like pointed a Hubble telescope on me... wait, you just made me do equivalencing  <_< Aaargh! 

 

:lol:

[davidmanze]

poor little critters, must have made feel them like pointed a Hubble telescope on me... wait, you just made me do equivalencing  <_< Aaargh! 

 

:lol:

 I of course was wearing my camouflage suite and told them what pretty buttie-flies they were.........

 

                  you know you have to wax lyrically to critters!