AFD 105mm f2.8 micro

[Henessy]

Hi, I notice that this lens does not stay at f2.8 unless it is focusing at 3m and above, which is next to the infinity mark. Most of the time, it stops down automaticall to F3 and below. I know that a micro lens will perform in such a way by stopping down automatically to achieve certain depth of view.

My concern is whether a normal 105 mm f2.8 lens minimum focusing distance is 3m? If it is less than 3 m, I am wondering why the AFD 105mm f2.8 lens micro perform in such a manner.

Currently., i own a AF 55mm f2.8 micro. The lens stays at f2.8 most of the time, until I really go very close like 20+ cm.

So this lens quite disappoints me in the area where it does not stay at f2.8 most of the time just like my AF 55mm f2.8 micro does.

Pls explain to me why the AFD 105mm f2.8 micro is unable to do just like what my AF 55mm f2.8 micro is doing currently.

Your views are very much appreciated.

Thanks

[longkangman]

Originally Posted by Henessy Hi, I notice that this lens does not stay at f2.8 unless it is focusing at 3m and above, which is next to the infinity mark. Most of the time, it stops down automaticall to F3 and below.

Not too sure what you mean, are you using 'A' mode.

[Henessy]

Originally Posted by longkangman Not too sure what you mean, are you using 'A' mode.

Yes, I am using aperture mode.

[Henessy]

From what I have find out, nikon's 105mm F2 DC minimum focusing is 1.1m. So I find it strange that my 105mm f2.8 micro is unable to get a f2.8 aperture even at 1.5m.

[Henessy]

For a 50mm f1.4 lens, the minimum focusing distance is about 0.45m , and my AF 55mm f2.8 micro is able to get a f2.8 reading even at 0.45m.

What I am trying to say that is since 105 mm F2 DC is able to focus at 1.1m at F2, why the AFD 105mm f2.8 micro is unable to do it at even 1.5m, but only 3m.

Thanks

[catchlights]

when you go 1:1, you will have light loss of 2 stops, read your owner manual for more info.

[Henessy]

Originally Posted by catchlights when you go 1:1, you will have light loss of 2 stops, read your owner manual for more info.

The problem is I did not go 1:1 . When it focuses at about 30cm, then the ration is 1:1

Thanks

[lsisaxon]

Originally Posted by Henessy For a 50mm f1.4 lens, the minimum focusing distance is about 0.45m , and my AF 55mm f2.8 micro is able to get a f2.8 reading even at 0.45m. What I am trying to say that is since 105 mm F2 DC is able to focus at 1.1m at F2, why the AFD 105mm f2.8 micro is unable to do it at even 1.5m, but only 3m. Thanks

This has to do with the optical construction of the lens. Nothing we can change.

[zac08]

Originally Posted by Henessy Hi, I notice that this lens does not stay at f2.8 unless it is focusing at 3m and above, which is next to the infinity mark. Most of the time, it stops down automaticall to F3 and below. I know that a micro lens will perform in such a way by stopping down automatically to achieve certain depth of view. My concern is whether a normal 105 mm f2.8 lens minimum focusing distance is 3m? If it is less than 3 m, I am wondering why the AFD 105mm f2.8 lens micro perform in such a manner. Currently., i own a AF 55mm f2.8 micro. The lens stays at f2.8 most of the time, until I really go very close like 20+ cm. So this lens quite disappoints me in the area where it does not stay at f2.8 most of the time just like my AF 55mm f2.8 micro does. Pls explain to me why the AFD 105mm f2.8 micro is unable to do just like what my AF 55mm f2.8 micro is doing currently. Your views are very much appreciated. Thanks

Btw, can you pls show me a AF 55mm f2.8 macro?

The only closest AF is 60mm micro and the 55mm micro I know of is a manual focus lens.
Due to the movement of the lens groups internally, the lens will shift and cause the aperture to stay constant at a fixed diameter but as the length is now not the same, it will now reflect a smaller aperture (lens length vs diameter ratio)

[Henessy]

Originally Posted by zac08 Btw, can you pls show me a AF 55mm f2.8 macro? The only closest AF is 60mm micro and the 55mm micro I know of is a manual focus lens. Due to the movement of the lens groups internally, the lens will shift and cause the aperture to stay constant at a fixed diameter but as the length is now not the same, it will now reflect a smaller aperture (lens length vs diameter ratio)

You may do a search in google. Nikon(Nikkor) AF 55mm F2.8 micro. There is really such AF lens. But it is quite old.

[Henessy]

Actually, I thought this lens can go f2.8 all the way until when it focuses damn close object, then it will stop down, just like what my AF 55mm f2.8 micro does.

I know that micro lenses will stop down eventually when it focuses close object. But it is the distance when it starts to stop down that matters.

The 105mm micro starts to stop down from f2.8 when focusing at around 2.8m...

[psychobiologist]

so.. are you intending to do a macro at f2.8?

[catchlights]

that's is call effective aperture, like it or not, it will go down anyway.

[Henessy]

Originally Posted by psychobiologist so.. are you intending to do a macro at f2.8?

No. I am not intending to do micro at f2.8. I bought this lens so that it can do a bit potrait and micro photos. So some soft of all round lens.

[SNAG]

Originally Posted by catchlights that's is call effective aperture, like it or not, it will go down anyway.

Yes, this is intended to be normal.

If I'm not wrong, I've read somewhere in Nikonians that only Nikon cameras effectively compensate for this by reflecting the correct aperture values at close focusing ranges. The other camera makes just simply show you f/2.8 values, which is misleading.

I stand corrected on this though.

[gooseberry]

This question has been asked before or at least similar questions have - can do a search.

The difference you are seeing is the difference between the effective aperture and theoretical aperture. The aperture for the lens is reported when the lens is focused at infinity. If you take a look at the mathematical formula to calculate the lens' aperture, you will see that it varies with focus distance (actually subject magnification). The difference between effective aperture and the theoretical aperture is negligble until you focus fairly close where it starts to become significant.

All modern Nikon bodies will report effective aperture (instead of theoretical aperture) when you mount a Micro-Nikkor with a D CPU (and other third party macro lenses that have reverse engineered the D CPU and communication protocol between the lens and the body). All other lenses report the theoretical aperture.

[zac08]

Originally Posted by Henessy You may do a search in google. Nikon(Nikkor) AF 55mm F2.8 micro. There is really such AF lens. But it is quite old.

Thanks... didn't know there was one which only had a production run of 3 years. No wonder it's not common.

But looking at the image, doesn't it protrude out when you focus closer as well?? This will make it somewhat like the 60mm micro already.

[Henessy]

Originally Posted by zac08 Thanks... didn't know there was one which only had a production run of 3 years. No wonder it's not common. But looking at the image, doesn't it protrude out when you focus closer as well?? This will make it somewhat like the 60mm micro already.

Ya,it will protrude out when focus very close( going macro mode)

[Henessy]

In that case, I should buy the 105mm F2 if I want to have a large aperture at 1.1m?

Cos the 105mm f2.8 micro will never be able to have a f2.8 aperture at that focusing distance.

[Henessy]

Anyway,may I know will the Tokina 100mm f2.8 macro lens stopped down automatically when focusing at around 1.5m?

Thanks