[borisbg]

Hi Zoners, I need your advices on this:

I purchased used Sigma 150mm f2.8, tried it on arrival and it can't open more than 3.0... Sometimes 3.3. Otherwise everything else works. Is this easy fix? Should I keep it? Or more surprises might come?

[Rainer]

A Sigma 150mm f/2.8 Macro?

 

On which camera do you use it?

 

Just a guess: You are using the lens in macromode (where the effective

aperture begins to drop down) and the lens is reporting its real maximum

aperture (at the focus distance in use) to the camera.

 

To find out if this is the case, make your tests with fokus set to infinity.

Then you should be able to open up to f/2.8.

 

Rainer

[JJ_SO]

Focus on infinity, then you'll have your f/2.8

 

Focus closer means focal length increases - but maximum front lens diameter doesn't. f (focal length) divided by 2.8 is 53.6mm lens diameter, more or less. That is, why apertures are correctly written as f/x.

 

 

So, all what's happening is your camera (Nikon?) is giving you the correct aperture to calculate manual flash lights or other light sources for macro shots.

[borisbg]

I use it on D800. I test it at approximately 3m.

[Brightcolours]

I use it on D800. I test it at approximately 3m.

It is normal on a Nikon camera with Macro lenses. The camera will report what it thinks the effective aperture will be. Some find this confusing, and for instance Canon does not approximate the effective aperture, but just shows the selected aperture setting. So with Canon you can only figure out that light gets lost at closer focus distances, by looking at the exposure times.

 

If you test it at infinity, you will/should see f2.8. If you test it at MFD, you will probably see something towards f5.6?

 

My old and lovely Nikkor AUTO 55mm f3.5 shows it on the lens barrel. It is a shorter lens, so not totally comparable as to when the bellows effect starts to have a significant impact (the longer lens has more magnification at the same distance), it becomes f4 at 0.7m, f5.6 at 27cm, f5.6 at about 23cm and f7.1 at 21.4cm (when it delivers 1:1).

 

You get even smaller effective apertures when using bellows, that is why it is known as bellows effect. 

[borisbg]

It has to be at its infinity setting... More than 10m to show 2.8, is this normal? I used 100mm before and didn't notice this. 100mm lens showed the effective aperture at macro settings only.

[Brightcolours]

It has to be at its infinity setting... More than 10m to show 2.8, is this normal? I used 100mm before and didn't notice this. 100mm lens showed the effective aperture at macro settings only.

Yes, it is normal. The longer the lens, the higher magnification it reaches at a certain distance, and the sooner you get a noticable bellows effect.

 

Whether or not the Nikon cameras show the right approximation with all macro lenses, I do not know, since it is unknown how the effective aperture actually is derived. 

[borisbg]

BC, I know about the effective aperture, but I was surprised to see it kick in under 10m. I have Sigma 85 1.4 it never shows effective aperture at 2m. Some photographers use 150mm as portrait lens... Anyhow one more thing to learn.

[borisbg]

Thank you all for helping me understand this.

[Brightcolours]

A lovely new toy you have there... A lens to be envious about