Auto shutter speed limitation?
 

Suppose I want to shoot with constant (fixed) aperture (Aperture priority mode); in changing light conditions it might be preferable to use Auto Shutter (even more so when doing unattended time lapse, without ND filtering).

However, the fastest speed of Auto Shutter mode is limited to 1/250th. Can anyone explain why? With ND off, this is simply not fast enough to keep aperture at say F4 or 5.6, and not overexpose!

Also, another doubt I have with regard to the TLCS settings: I understand the "A.SHT point" setting is there to limit the minimum aperture when in auto, and increase the shutter speed instead. So if I want to never close below say F5.6 (in order to avoid diffraction softening, or increased DOF, or both), I am setting A. SHT point to F5.6 - and the iris should never close further. Do I get it right?

I'm not sure, because it simply doesn't work that way (i.e. in auto iris, it can stop much more than the above parameter's value). This may be related to the Auto Shutter speed no being able to get faster than 1/250th, which makes my first point even more valid: why is this limitation present?

comment deleted.

Yes - but not in Auto Shutter mode; this is what I mean!

Can anyone confirm, or deny, my observations in the first post of this thread? Am I missing something? Comments, please!

I can confirm it Piotr. I have the exact same questions.

In general, it seems it will override the min aperture to maintain correct exposure, as a safety net.

I almost always shoot manual, but was shooting auto to see how reliable it could be. I think it works fairly well, if you can remain attentive to the need for adding ND when the aperture closes down beyond F5.6.

But as you stated, it questions why it has a seemingly arbitrary limitation of 1/250th.

Coming from the Canon perspective, I also don't understand why you also can't have shutter speeds below 1/48th (or 1/60th) without putting it into an accumulation mode, or why there aren't more shutter speeds between the coarse ones provided, for finer control. The Canon has finer adjustment of shutter speeds in manual.

If so, I wonder why everyone else are so forgiving about it - I mean, the whole concept of limiting the iris while increasing shutter speed (when necessary) doesn't work as advertised.

Of course we don't use auto settings often, but sometimes it'd be desirable to run in the "Aperture Priority" mode (term from the Canon A1 - do other use it, too?), and without ND filtering (unattended), this is simply impossible! And the camera won't even issue a warning when it needs to change the aperture (or stop below the "A.SHT point" threshold)!

1/250
 

Maybe for the same reason why our still cameras limit to 1/250th at aperture priority when we use a flash without setting up the high speed sync?

Piotr,
I agree completely. It's lame. Do you think the coarse shutter speeds are the reason for including TLCS into the feature set? Because with only a few auto shutter speeds available for the cam to select from when the iris is off, you don't have fine control within aperture priority mode, so TLCS could have been the fix, since it would allow some movement of the shutter and aperture in combination, to result in less coarse exposure than aperture priority alone would have.

What Sony could have done at the minimum, (if not for making all the shutter speeds available) is to at least display the shutter speed and gain when full auto is engaged, or flash the ND1 or ND2 indicator rather than permit the aperture to stop down when the scene's exposure goes higher than the shutter limit.

I'm surely wrong about putting the shutter into auto. Switching the iris off maintains the correct stepless exposure regardless of the ND setting, therefore the EX1 must have the full range of shutter speeds to work with in that mode. That would be equivalent to the Canon aperture priority mode.

In other words, shutter auto, iris off.

Full auto would be more like Canon's "Programmed Automation" but with a soft preference to stay within a range if possible.

Yes, I checked it and you're right.

But the "A.SHT point" threshold setting doesn't seem to work as expected, or am I missing the point again?

No you're not missing the point. The devil is in the details. "Limit" means hard limit, and "point" is a soft preference but not a rule.

A.SHT point is the largest iris opening before continued increasing scene brightness forces the iris to stop down smaller than the soft limit, since the hard shutter limit has been reached.

Here's how I see TLCS working. I don't have the cam in front of me, but assume for example:

1.) You set the lower iris setting to f2.8.
2.) You set the gain limit to +6db.
3.) You set the upper shutter limit to 1/200th sec.
4.) You set the upper iris setting to f5.6.

In the above scenario, the cam will try to stay between f2.8 and f5.6 if possible, by using variable shutter and variable gain.

If the scene is darkening, it will reduce the shutter speed and add gain to preserve the iris opening to f2.8. But if the scene is still too dark, it will open the iris as far as f1.6, sacrificing your iris preference but preserving enough exposure. At that point, your shutter speed will be at the camera's unspecified minimum, (1/50-1/60th etc.), and the gain at +6db.

If the scene is brightening, it will stop down the aperture as far as f5.6, and increase the shutter as far as 1/200th, but if there is still too much light, it will override f5.6, going as far as f16 but keep the 1/200th shutter as the hard limit.

The cam will try and work within your range of apertures , adjusting shutter speed and gain for the scene, but will not exceed 1/200th at the fastest or +6db at the slowest.

To get below f2.8, the gain will have to go up to +6db first. To get above f5.6, the shutter has to be maxed out at 1/200th first.

Your understanding of how it should work ic 100% the same as mine, Tom (with one correction - the shutter hard limit is 1/250th, not 1/200th). But why Sony didn't allow TLCS to use higher shutter speeds beats me...

If they had, it certainly would have been more versatile, agreed.

(What's a millisecond between friends ;-)

I just noticed something useful in manual operation, if you use "ECS" shutter mode, you get access to all the shutter speeds inbetween the discrete ones. You could for example, choose 1/93 sec by setting the ECS to 93.02 for example. the ECS frequency is just the reciprocal of the shutter speed.