New Micro Nikkor Lens....some advice, please

Msmoto

I need to be thinking about asking the right questions...I was thinking at infinity....yikes...mea maxima culpa

TaoTeJared

I just purchased a used Nikon 105 Micro VR yesterday, and when I got home and placed the lens on my body - I noticed that sometimes I cannot open up the aperture all the way. At times it would only go to f/3, sometimes f/4, and then another time I got the lens to open fully to f/2.8. Odd. Any reasonable explaination? I currently am using a D3200

100% normal. Mine does the same thing, and I have used it on 5 different bodies.

JJ_SO - I have never heard anything like you just said. Nor have I experienced any of that. Where is that info coming from?
One thing I know for sure, the focal length of the lens never changes. It doesn't have the capability too.

There is a reason why the lens stops down automatically and I have read it a ton of times - It makes perfect since, but I'll be damned if I can repeat it with due justice. It has something to due with the lens grouping design added with the extended focus range, at different distances less light is actually passed through. It has been that way with prior macros, but due to the limitations of technology, it just never showed up the "correct" way.

JJ_SO

Only two days ago I was laughing at "14 bit jpgs", which are impossible because of technical standards.

Now you tell me "focal length never changes", which goes the same way. How else you would get sharp images of things closer than "infinity" to the camera? Actually, that is, what focal length is for. Lenses are for specs reason - to compare them - described by focal length (at infinity) and nobody uses the words in brackets.

My "knowldege" comes from various so called "books" out of the pre-internet time . There were no forums but photoclubs can be the same collection of knowledge, rough guesses and being plain wrong. Best of these books to me was Ansel Adams' "The camera", "The negative", "The positive". But when I reread I discovered being to simple in my explanation. Of course the focal length is not the distance between film/sensor and front lens' highest peak. Also the aperture usually is inside, so the front lens' diameter will be a bit larger than the relation of diameter and focal length. But you can't have a 50/1.4 lens with a front lens diameter of 12.5mm - this will best be a 50/4 (=12.5).

Do you remember the days when turning the distance ring on a lens made the whole glass block inside moving away from the camera? This is the easiest way to understand the focal length will increase, but the aperture diaphragm stays the same size. Now, 10mm movement makes it a 60mm, aperture diameter still is 12.5 so the relation in between we usually call "aperture" or f-stop is 12.5/60 = 1/4.8 So, no longer f/4

But of course, if you never heard of that, it simply can't be true.

SquamishPhoto

From another forum:

"Originally Posted by RaZe42
All internal focus lenses change focal length(become shorter) when focusing closer.

While that is commonly true, that's not the same effect that is being discussed here, which is true for all lenses, whether internal focusing or not. It is known from older days as the bellows extension factor, and is simply down to the fact that as the lens moves away from the sensor to focus closer, so the light is more spread out, and therefore dimmer. So, the aperture size and focal length are unchanged, but you are getting less light. This is why they talk of "effective" aperture. When you're at 1:1 you've lost two whole stops of light compared with when you're focused at infinity.
__________________
Mark."

spraynpray

That explains a lot. I tried using a focusing rail to do a stack recently and watched the image getting further away (smaller) as I shot. I wonder then if I would be better using my 60mm f2.8D (non IF) on its own (without the rail) and focusing by guesswork?

Msmoto

Well, now that I have made my apologies for forgetting the f/stop changes as the lens focuses closer....I will add the fact that at 1:1 reproduction, an f/2.8 lens is an f/5.6 lens. And, for those of us who have done some close focused work, this is a very real problem, often compensated by adding a light source such as flash so as to have an lots of light directed where we want it.

sevencrossing

Given that most 1 :1 is done on a tripod, a stand and or, using flash. Does anyone shoot 1:1 at wider than f 8 ? The advantage of f 2.8 comes in, when using the lens for portraiture and for faster and more accurate focusing

MikeGunter

Hi all,

To compound the close focusing problem, Nikon is one of the few lens makers that 'report' the f-numbers to the user. Other makers will report the lens number on the barrel of the lens.

That was the point I obliquely made earlier in the posting. I don't know if Nikon think that Nikon users are smarter (good on us) or more inquisitive (maybe more good on us, or just plain oblivious - maybe leave that one alone.

The automatic nature exposure readings in any of the readings through the lens will continue to be read, and if one is doing the math, one will likely know the slight additional exposure.

My very best,

Mike

chakoo

I experienced the same behavior with my 105mm, look like it is normal.

DJBee49

A nice simple little formula to work out effective aperture is (1+M) squared (sorry, can't do little twos for the square) where M= Magnification ratio. Thus at 1:1 Mag. ratio (same size object and image) you must multiply the metered aperture by 4 times ie. +2 stops. If you are measuring the exposure in camera, as we usually do, this is done for you and you don't have to worry about it.

If though you were using the camera in manual exposure mode for a close-up, eg. using studio flash not metered in camera, you would have to do this little sum! It follows the inverse square law pretty much (although the projected light from the lens to sensor is not quite a point source etc.) I suppose you could just bracket like crazy but I think it is good to try to get stuff as right as you can. Then all the other possible errors don't just accumulate on top!

Sorry if you all knew that but if you have not come across it before it can come in handy and at least explains what is going on even if you never use it.