is it normal for tamron 90mm?
- Thread starter WatWatz
- Start date
Won't go into scientific explanations.
Take a black disc, say front opening is 20mm. This is the aperture (f/2.8)
Put it on a long, telescopic blackened tube. Put the tube over one eye. Aperture end is furthest away from you.
When you bring the aperture close to your eye, a lot more light gets in (infinity focus - the lens looks short, right?).
When you extend the aperture far far away, a lot less light gets in ... like the FAR end of a dark tunnel (min close focusing distance-lens becomes long long).
Hope this helps some.
Cheers!
Take a black disc, say front opening is 20mm. This is the aperture (f/2.8)
Put it on a long, telescopic blackened tube. Put the tube over one eye. Aperture end is furthest away from you.
When you bring the aperture close to your eye, a lot more light gets in (infinity focus - the lens looks short, right?).
When you extend the aperture far far away, a lot less light gets in ... like the FAR end of a dark tunnel (min close focusing distance-lens becomes long long).
Hope this helps some.
Cheers!
iguanavon
New Member
Actually, The aperture should remain at F2.8 no matter how close is your focusing. I've a Tamron 90mm macro and I've just tested it out. I can maintain F2.8 no matter focusing at min. distance or at infinite range.
There's 1 possibility which is that you're using Shutter spreed priority, Program mode or Auto mode
What you say is actually correct. 
The aperture, being a physical dimension 'Never' changes.
Only the AMOUNT of light that reaches the sensor//film plan DOES. :think:
I'm afraid I have no idea what you speak of in your second sentence and/or paragraph, though. My Bad. :embrass:
The aperture, being a physical dimension 'Never' changes.
Only the AMOUNT of light that reaches the sensor//film plan DOES. :think:
I'm afraid I have no idea what you speak of in your second sentence and/or paragraph, though. My Bad. :embrass:
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iguanavon
New Member
Dream Merchant said:What you say is actually correct.
The aperture, being a physical dimension 'Never' changes.
Only the AMOUNT of light that reaches the sensor//film plan DOES. :think:
I'm afraid I have no idea what you speak of in your second sentence and/or paragraph, though. My Bad. :embrass:
Erm... For my 2nd paragraph, what I wanted to say was that in S, P or Auto mode, the aperture will automatically change according to the amount of light available. So the issue that TS is facing might be caused by what I've mentioned.
NewbieInCS
Senior Member
I think it depends on what mount of the tamron you are looking at. IIRC, nikon bodies will show the change in effective aperture. My canon doesn't.
spree86
Senior Member
Yes it is normal to have very shallow DOF even at high f numbers, so try to fit the insect into the plane of focus if you want the whole insect sharp. Also, try not to shoot at above f16, it will cause diffraction, which will lower your image quality.
iguanavon
New Member
Hmm... Can know what mode are you shooting with? I'm using A33 and I shoot mostly in Manual mode, but I don't experience the aperature problem that both of you are facing.
For macro, I shoot mostly at F16 and yes, the DOF is still shallow. Therefore, you need to always think of how to position yourself to the subject. If you want a larger DOF on your photo, you can try focus stacking.
kentwong81
Senior Member
I think Canon camera will read the same f2.8 when mounted with the Canon 100mm f/2.8 L Macro, but the f aperture will change on Nikon cameras. Read from Ken Rockwell website:
Macro lenses lose light as focused more closely. I'll skip you the real reason, but suffice it to say that as magnification goes up, the light has to be spread further.
Canon EOS cameras don't show the true f/stop as these lenses are focused more closely. As one focuses to 1:1, one loses about 1 1/2 stops of light, but EOS cameras keep reporting the same f/stop regardless.
Because of this, you will have to compensate if using an external meter, which is very uncommon today. Most of us use our TTL meters, which work fine.
On the other hand, Nikon's AF cameras and macro lenses report the actual effective f/stops as one focuses more closely, so they always show the correct reading.
Macro lenses lose light as focused more closely. I'll skip you the real reason, but suffice it to say that as magnification goes up, the light has to be spread further.
Canon EOS cameras don't show the true f/stop as these lenses are focused more closely. As one focuses to 1:1, one loses about 1 1/2 stops of light, but EOS cameras keep reporting the same f/stop regardless.
Because of this, you will have to compensate if using an external meter, which is very uncommon today. Most of us use our TTL meters, which work fine.
On the other hand, Nikon's AF cameras and macro lenses report the actual effective f/stops as one focuses more closely, so they always show the correct reading.
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kei1309
Senior Member
i don't know about Ken Rockwell's camera testing techniques....:bsmilie:
neither do i use canon nor nikon. Mr Rockwell is a nikon fanboy, and anyone shooting with canon and knows the limitation will just use ringflashes/ringlights or external flashlights to get the shot.
what's Ken's beef with Canon? simply because it's not a Nikon.
kentwong81
Senior Member
I have a friend using Canon 100mm f2.8 Macro too. When I told him about the changing of apertures for Nikon, he was surprised as it doesn't happen for Canon and it always stay at f2.8. So what Ken Rockwell said might be true.
kei1309 said:
I think KRW as ridiculous as he sometimes is also owns and shoots a 5dm2. And he praises the hell out o it.
kentwong81
Senior Member
Rent a Canon 100mm Macro to try out or ask your Canon friends if they a Macro lens to prove KRW wrong in this case.
Doesn't really matter whether if it's NiCanOlyLeicaNyHasseyHoesemanSinarBlaBlaBla.
Whether the aperture readout registers as a variable scale or a constant going, your metering will clue you in if there IS a drop of EV when you go from infinity to MFD.
As far as I can recall, Nikons show that variation, whereas Canon does not. But the truth lies in the metering readouts, all things being constant, so it matters naught what the aperture readout says.
Whether the aperture readout registers as a variable scale or a constant going, your metering will clue you in if there IS a drop of EV when you go from infinity to MFD.
As far as I can recall, Nikons show that variation, whereas Canon does not. But the truth lies in the metering readouts, all things being constant, so it matters naught what the aperture readout says.
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