Sony A1 Revisiting the Spot vs multi-meter inconsistency

[GracieAllen]

Alpha 1, firmware 1.31.

I have always thought images captured using the spot meter were underexposed compared to images captured using the multi meter, which are GENERALLY pretty accurate.

I wanted to find out if it’s something I’M doing, or if there actually IS a difference in the metering, so I set up a very unscientific test to see. I do NOT know if there may be OTHER settings on the camera that would cause this – I only know what I’m seeing.

I put the alpha 1 with the 24-240 on a tripod with zoom at around 125mm, in single shot

• Manual mode with Auto ISO, eye AF and tracking at whatever they are when you're in manual focus - I presume off.
• Aimed from approximately a meter at a 50% gray screen on the computer
• Camera in manual focus, ZONE focus, focused near infinity
• Captured a single image using the standard spot and a single image using the multi meter.
• Switched the camera from Zone to Small SPOT focus.
• Captured a single image using the standard spot and a single image using the multi meter.

Ended up with 4 images. I displayed them in Imaging Edge and did a screen capture so you can see (attached somewhere) the metadata and histogram. Histogram on both Spot meter images is lower than multi, and the ISO drops from 640 to 500. Image name is in the Properties.

I put all FOUR images in Photoshop, created a set of guides that intersect in the middle of the image, then placed a 5x5 color sampler on the intersection – ALL this was done using an Action, so they’re as near identical as I can get. I then changed the color sampler size to 101 x 101 to see if there was any difference. There wasn't.
I then added an exposure layer and adjusted the exposure so the brightness of the spot meter would match the brightness of the multi-meter. In the Photoshop screen shots you can see the brightness values in the Info panel and the exposure adjustment in the Properties panel.

Meter	RGB values	correction to multi
Zone Multi	107, 107, 107
Spot Multi	104, 104, 104
Zone Spot	85, 84, 84	.75
Spot Spot	86, 86, 86	.6

In Zone mode, the multi meter read 107,107, 107. It took .75 stop to increase the brightness of the spot meter (85, 84, 84) to match the value from the Multi-meter.

In Spot mode, the multi-meter read 104, 104, 104, so very slightly lower than the Zone meter. It took 0.6 stops to increase the brightness of the spot meter (86, 86, 86) to match the value of the spot multi-meter, AND 0.7 stop to increase the brightness to the 107, 107, 107 value of the Zone multi-meter.

I cannot see any reason why the metered value should not be the same between the spot and multi-meter in this case. And yet, the metering drops 1/3 stop (ISO 640 - 500) when I switch to the spot meter, and the actual brightness of the image drops at least 2/3 of a stop.

I'm sure SOMEBODY is going to say "Well, just dial in 2/3 stop of exposure compensation." That's NOT a fix, it's barely a Band-Aid. And it's already bitten me in the rump several times 'cause I switch back and forth between multi and spot depending on subject, and I'm DEFINITELY not perfect a setting and resetting the exposure compensation every time I change the metering mode.

Is there some other setting in the camera that would cause the inaccurate spot metering?

If not, is this NORMAL - is everybody's Alpha 1 doing this? Or is it a problem with this body?

 

[LikesToys]

David - I don't think there is a problem with your A1. Mine experiences the same symptoms, I ran a test under similar circumstances to you yours and mine consistently reduces the exposure in Spot Metering Small Focus Point by ⅔ of a stop.

I noticed this problem in the field thus took interest in your post. Re my shots from the field, I was on firmware 1.30. Sometimes the exposure changed by 1 stop. I performed the test in a studio using a grey card, on firmware 1.31 with the same problem. So its not caused by firmware 1.31.

I have been thinking that perhaps there is not really anything 'not working' but simply that multi metering mode is considering factors that Sony has programmed in for Multi that simply increases the exposure. Multi is really an algorithm set up by each manufacturer. Its not actually just considering the light reading from the sensor but applies some other considerations to determine exposure.

The question remains, what to do if spot and multi produce different exposures. I Expose to the Right ETTR so with Spot that is not really working. I do use spot to correct for lost of focus in zone - the small AF area pulls the AF back to the subject (generally off the background) but I was not expecting the exposure to change. Since I live in an area with small birds hiding in branches, I thought that Spot Metering would be of help which it appears not to be.

I am thinking to turn off the spot metering and leave a smallish spot focus point. I might increase the size of the focus point as small is very hard to use for birds. I also read somewhere that Small Spot focus has a very small spot exposure, not the size of the circle in the viewfinder, but I may be wrong on that.

Attached are two shots, the first slightly overexposed ETTR that is correctable and better using Multi and the other 1 second later with Spot metering.

 

[Slug]

I have noticed that spot metering consistently underexposes with birds among branches on my A1. That surprised me having had a range of Sony mirrorless cameras over several years. The problem wasn't so evident with my A7R111 or with A6400. I'm often shifting off subject to darker areas just to get the exposure up on the subject and then cropping later. Often I don't have time to fiddle with settings on quick little birds.

 

[GracieAllen]

Thanks for the replies... They make a lot more sense than what I got elsewhere.

I've also done testing in the field where I can see how the two metering methods handle birds or whatever. The spot is ALWAYS at least 2/3 stop underexposed. In some cases, depending on what the multi-meter is seeing the spot will be 1 full stop under.

Unfortunately, having to compensate every time I switch back and forth is a pain, so I've resorted to just leaving it on the multi-meter 90+ percent of the time since I KNOW I'm not going to remember to put the exposure compensation back to zero when I switch back to the multi-meter.

I too ETTR, but there are a lot of situations where it's not practical to do that much fiddling. I have the zebras on and usually rely on those. If I'm getting zebras in white areas with it set at 109, I'm REASONABLY well exposed and in post the highlights, even though the jpeg zebras are showing them blown out, aren't.

 

[LikesToys]

For a custom button with Spot, It is possible to include a + 0.7 EC as part of the Custom Hold setting. Although it should not be required, that may solve the problem.

It seems to apply the +0.7 on top of any EC set using the EC dial (as an aside, I have set that to the back dial) so it might give us what we want. I only tested it in the studio however.

 

[GracieAllen]

I normally don't do settings I have to hold - the only custom hold I have is one on the lens button 'cause I know I'll only need it for one or two shots. I have a spare button and a number of things that toggle between the settings I need (like between zone and small spot focusing), but I've stayed away from things I have to hold.