Can you lock exposure completely with

T

Tameside

Well-known member
the GH1? unless I'm doing something wrong there is still visible exposure shifts with ae lock/manual settings etc if I zoom, why is that? if I set the ap to 6.3 and lock exposure and iso what is the camera adjusting inside the lens?
 
The lens has no choice but to adjust the F stop through it's range. For example at the 140mm it is physically impossible for it to have an F stop value lower than 5.8, just as it is impossible for it to be lower than F4 at 14mm.

The only way around this is to buy a different lens. The cheapest zoom with a constant aperture is the Canon FD 75-200mm F4. It goes for about £30 on eBay!
 
There is another thread about this. My understanding is that the zoom lens, in order to maintain a constant f-stop while zooming, has to open or close the iris. Apparently the kit lens doesn't do that so well.
 
so its impossible to zoom with the 14-140 without any noticeable exposure shift? irrespective of setting the f@6.3 and loccking shutter, ae lock etc etc, you will still see an exposure bump with the 14-140, unlike with say a conventional video camera?
 
Read the other post, see my comments, seems as if in normal pasm modes, expousre is locked and clicking stops, you can zoom freely, to some extent anyway, as I believe iso may move in this mode, either way theres something wrong with cmm mode as the clicking is obvious when zooming but not with pasm modes.
 
Well I just did a 15 second test...not scientific or anything...


Set f4.0, hit record, zoom in all the way -- lose a couple stops as it stops down.
(I couldn't really tell on the image, but watching the histogram)

Set at f6.3, hit record, zoom in all the way -- I lost 1/3 a stop at 1 point, but I think that was just because I was handheld and the image was bouncing around.

You need to set the f-stop before you zoom in though. If you are at 4.0 and zoom in, it stops down, and then as you zoom out, it comes back up to 4.0 automatically.

If you want to be open as far as you can without the aperture shifting, zoom to the point you want to zoom to, note the f-stop number, zoom out, and set the f-stop to the nearest number. (If you can't hit it exactly, like if it's f4.7 (Roughly 23mm) -- then you'll have to go up to 5.0).
 
see my comments above, cmm is flwed for zooming, it needs a fix! std pasm modes work fine, lock ae and see!!
 
If you want to be open as far as you can without the aperture shifting, zoom to the point you want to zoom to, note the f-stop number, zoom out, and set the f-stop to the nearest number. (If you can't hit it exactly, like if it's f4.7 (Roughly 23mm) -- then you'll have to go up to 5.0).
Click to expand...

Right -- set the lens at f/5.8 and you'll have a constant aperture throughout the zoom. Set it to more open than 5.6 (like 4.0) and you'll see it change. But at 5.8 it'll stay constant.

If you're not zooming all the way in, you might be able to get away with a slightly more-open iris. But if you want guaranteed constant aperture throughout the zoom range, use 5.8.
 
Yes, but in cmm mode it still bumps/clicks inside the lens, doesnt matter wher you set the ap/what you lock, if you zoom it bumps the exposure with a nasty flicker, go to std pasm modes lock ae and zoom it doesnt happen, whats going on?
 
seems as if you need to be f7.1 to almost eliminate the exposure bump, this is very high obviously, but the lack of clicking between cmm modes when you zoom in and out and on std pasm modes is very noticeable. I wish I'd recorded the first set of numbers in pasm mode because on closer inspection there is still some minot flicking but imo its way better than zooming in cmm mode, why would they be different?
 
Its nothing particularly wrong with the kit lens. It's pretty common on 95% of lenses to have a variable aperture through the zoom range.
 
Yes, but why is the clicking so obvious and loud in cmm mode and not in std PASM settings, this is what I dont get! fit the 14-140 and swtich between cmm and PASM and zoom, notice any difference in noise/clicking?
 
I think what you are looking for is a cine lens. Thats what they do.
They are constructed to maintain exposure through out the zoom.
As opposed to still lenses which don't and are consequently much cheaper.
Read the reviews tho, some still zooms are close to cine when it comes to this
 
Tameside - I just ran a test through every set and at first look it did seem this was correct. However the true story here is this goes away once you hit record. This is another one of those preview things we see go away during recording. Go ahead and give it a try and confirm.
 
I find zooming the kit lens problematic at best just from a steadiness standpoint. Even locked down on a tripod, it's really difficult to get a smooth zoom action.

Cheers,
 
The kit lens compensates for zoom, no doubt about it. I guess I'll have to put up a sample to prove this once and for all.
 
Hmm, some eating of words here - I used mine for quite some time before doing the firmware upgrade about a week back, and I now don't see the change in illumination when doing a full aperture zoom in full manual that I used to see. Smells to me of a silent fix. The effective aperture is clearly maintained where it can (eg if aperture wasn't wide open in the first place) when you zoom in on a light coloured wall right in front of the camera (it doesn't darken with zoom) but that's good.
 
Ozpeter said:
Hmm, some eating of words here - I used mine for quite some time before doing the firmware upgrade about a week back, and I now don't see the change in illumination when doing a full aperture zoom in full manual that I used to see. Smells to me of a silent fix. The effective aperture is clearly maintained where it can (eg if aperture wasn't wide open in the first place) when you zoom in on a light coloured wall right in front of the camera (it doesn't darken with zoom) but that's good.
Click to expand...

See my earlier response. I believe the culprit is preview.
 
It'll always have to adjust the aperture. The size of the iris at f7.1 for 14mm is not the correct size to get f7.1 for 140mm, it's basic optics. You'd have to change to stay the same.
 
FWIW this isn't limited to the kit lens. I've had the same clicking/bumping while zooming my 4/3 lenses, which have aperture communication via the adapter. Again this goes away once stopped down past the min. f-stop at the long end of the zoom.
 
You must log in or register to reply here.
Back
Top