Why is my aperture changing while zooming?

T

TajJackson

Active member
I don't know if this is normal or not or if there is any way to combat it with the A1. When I am completely zoomed out, I can open up the aperture all the way to 1.6 in manual mode. But as soon as I start zooming in, the aperture also starts closing up and the aperture number begin to slowly increase. Why won't it just stay where its at? I am trying to keep it wide open for my 35mm adapter, which I need to zoom in to.
Thanks in advance.
Taj
 
As the lens shifts, the ratio of which the aperture or f stop is, changes. So, without going technical on how a lens works, I can just say you won't be able to achieve a f/1.6 at full zoom at all.

It's normal. You'll just have to work with it, one of the toughies with a 35mm adaptor, you lose light on top of the light you lose zooming in. Which is why you'll have to blast continuous lighting like the sun (if you want to avoid high gain control).
 
Just to add to Mayodaze's explanation. If you are ever lens shopping and you notice that the lens has a number like 4.0 - 5.6 the 4.0 represent what the aperture is at the wide end of the lens fully open and the 5.6 represents what the aperture is fully zoomed in fully open
 
does the lens on the hvx respond the same way in terms of light loss when zoomed all the way in?
 
The Canon 16x manual lens will hold a f/1.6 all the way and it looks surprisingly good in HD, as well as SD. (H1 and XL1/2)

It's one reason I bought the lens. It definitely makes a difference for 1/3" DOF .

Not sure if the 16x for the JVC HD100/200/250 holds it's f-stop too. I would think it does, but it's got rather nasty CA when wide open.
 
TajJackson said:
I don't know if this is normal or not or if there is any way to combat it with the A1. When I am completely zoomed out, I can open up the aperture all the way to 1.6 in manual mode. But as soon as I start zooming in, the aperture also starts closing up and the aperture number begin to slowly increase. Why won't it just stay where its at? I am trying to keep it wide open for my 35mm adapter, which I need to zoom in to.
Thanks in advance.
Taj
Click to expand...


Cheap video zoom lenses do this when shooting wide open.

I first noticed this with my old XL-1.

The trick is to NOT shoot wide open if you don't want this to happen.

I'm not sure why you need to change the focal length though if you're using an adapter...
 
TajJackson said:
It's when I initially zoom into the M2 to properly set the backfocus. Just noticed that the aperture goes from 1.6 to 2 something as I slowly zoom in to the grain. :-)
Click to expand...



I hadn't even noticed that you lose almost 2 full stops from the wide end to the long end, but really I never thought of it as being an issue with the adapter since once your focal length is set, it doesn't change.

.
 
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