Aperture issues

[ajmall]

I have a 24mm F/2.8 Macro film lens but when I put it on my D70s the widest aperture is F3?! I have re attached the lens and still the same and the aperture ring is locked at 22 which it needs to be to work.

Anyone know what the problem is?

 

[ajmall]

Does no-one know then?

 

[SLOShooter]

Can you manually open it up to 2.8?

 

[Artemis]

is it a non zoom lens? if so then I dont know, if its a zoom lens, zoom right out and then change aparature....

 

[kfoster]

Assuming that this is not a internal focus lens, but instead one that the front of the lens moves in and out as you focus. Yes?

I'm not positve but what I think is happening is that when the lens foucs toward 1:1 the lens loose some ability to caputure light. When you focus toward infinity you should get f/2.8. My 105mm f/2.8 Nikkor micro will only get f/5 when focused to 1:1 but easily achieves f/2.8 at infinity.

K

 

[ajmall]

it's non internal yes.

it's a Sigma 24mm F2.8 Marco "Super wide" II. I've tried it on Manaul, AP and SP modes and the widest i can get is F3. I'm rather miffed...

 

[airgunr]

I'm wondering if it has anything to do with the Magnification factor on the digital cameras. Is the reading for the f/stop on the display? Or, is it on the lens ring it'self? I think it may be that the digital image sensor in giving a magnification factor may decrease the percieved apature as well.

Just a guess, I may be totally wrong.