A7c ISO 100 significantly softer than ISO 200!

[Zedster]

I recently purchased a Sony A7c mainly for street photography and I have been testing a 7Artisans 35mm fixed aperture F5.6 pancake lens for its suitability. I have been finding the images unsuitably soft, then I made an interesting discovery that has left me baffled.

I set up some photographs at a harbourside, chosen as iot had a lot of mid distance and long distance detail. Although the day was bright I mounted the camera on my sturdy Manfrotto tripod for good measure. I then checked the focus on some lettering in the distance using the focus magnifier and took my first photograph. I realised the camera was still set on multiple shot at ISO 200 from the previous day. So I changed the shutter mode to single shot and the sensitivity to 100 ISO and proceded to take a series of photos of the harbour. When I returned to view the photographs, all the images shot at 100 ISO were soft despite focusing with the focus magnifier, using a shutter speed of 1/320 s or faster and a sturdy tripod. Then I noticed the burst of 4 images I sook at the start on 200 ISO were a lot sharper.

I am now really confused how can 100 ISO images be much softer than 200 ISO despite the exact same setup? and is the issue of softness down to the camera or the lens or me?

I have compared the image properties in Sony viewer, the only difference between the two images are ISO, shutter speed (obviously), and long exposure NR which is off for the 200 ISO image but on for the 100 ISO image. This also confuses me because I did not enter the menu to change this.

I have attached a close up from each of the two images, these have been opened up in Affinity Photo 2, developed without making and changes , cropped and then exported as 95% quality jpg images. No other changes have been made.

Any thoughts appreciated.

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[Pieter]

12 minutes ago, Zedster said:

Although the day was bright I mounted the camera on my sturdy Manfrotto tripod for good measure.

...

the only difference between the two images are ISO, shutter speed (obviously)

Did you disable image stabilization? On a tripod it should be disabled otherwise the camera will try to compensate for motion that isn't there. Could be the ISO 200 shot has such a fast shutter speed that it negates the IBIS mechanism.

Edited October 2 by Pieter

[Zedster]

Hi Pieter thanks for your reply. That is interesting, this the first camera I have had with a steady shot feature and I did have it switched on, I hadn't realised it should be switched off. I will wait for the right day and then go and try it again, I hope you are right. It would certainly explain why the images are not sharp anywhere! I had even pre focused the manual lens to 8m (the hyperfocal distance is about 7.3m) and left a sticker on the focus ring so I could shoot at 8m and should have got everything from 4m to infinity with an acceptable amount of sharpness.

I am also curious though why the 200 ISO show "long exposure NR" to OFF and the 100 ISO show "long exposure NR" to ON but I never made any changes to this.

 

[Cameratose]

You should be able to get that shot without a tripod. If you really want to test the lens, do as Pieter says, but also shoot handheld as fast a shutter as possible. 

Are you sure Auto ISO isn't turned on?

If everything else were equal, then the only difference would be the sensor's sensitivity due to ISO. Reviews for that lens say it's a bit shy on color and contrast, could be that what we're seeing is better contrast due to the change in ISO? 

Lastly, on the weird things like NR on and off, did you purchase the camera used? If so, did you start by doing a reset to factory defaults? That should always be the first step with a used camera, a previous owner could have programmed odd settings that are affecting your own.   

[Pieter]

1 hour ago, Zedster said:

I am also curious though why the 200 ISO show "long exposure NR" to OFF and the 100 ISO show "long exposure NR" to ON but I never made any changes to this.

No idea, but it shouldn't affect images with a shutter time shorter than 1 sec anyway.

[Zedster]

Hi Cameratose, I kept my original explantion simple. In reality I was doing back to back tests of the 7A vs an existing 35mm lens. I used a tripod so I could: compose; take shot with one lens; switch lens; take it with the other and have the same scene for both lenses. I can confirm the lens is shy on contrast colour and contrast and that is what prompted me to do the back to back tests. The previous day I had taken the lens out for the first time on a casual shot and I was dissapointed with the lack of impact of the raw images, they appeared flat and soft compared to what I am used to from Sony and Samyang primes. So I thought I would do a back to back. I think I will repeat the comparison using my A7 and see how the lenses compare, then try again on the A7c making sure i have image stabilistion off.

It is a strange lens, on the one hand it is quite a practical as a street lens, compact, light and F5.6 gives a hyperfocal distance of around 7m so prefocusing to 8m means in theory everything from 4m to infinity should be sharp enough. On the other hand when you do need to focus, it is very fiddly, the lens is so short that the grip gets in the way of the focus ring and the focus itself has way too much sensitivity (it came with a stick on lever for the focus ring, so this must be recognised). The difference between infinity to 8m is only around 1mm of radial turn, so when you do need to focus on something specific it is easy to end up with focus overshoot in both directions.

I bought the camera new, but have only just started using it, so still getting used to the differences from my A7. I don't find Sony manuals to ve a very easy read, so tend to rely on the internet. I missed the point about switching off stabilisation on a tripod.

 

[Cameratose]

Usually, the advice to switch of IS when using a tripod is in the lens manual. I have also noted that once your shutter gets above 1/1000 or so, IS is not only useless but can be detrimental. Some lenses also provide that advice. I think my Tamron 50-400 says to turn it off when the shutter is over 1500. 

Sony has online user manuals that are searchable and can be very helpful once you sort out how to use them, they change the format over time (thanks, Sony) so they will probably have a different layout between your two cameras.

Have you seen Viltrox has released a 28/4.5 pancake with AF? Early reviews are promising for that kind of a lens, looks to be plenty sharp in the center. It's selling for $99 US, so maybe worth a shot.  

[Zedster]

I hadn't paid too much attention to that at that becuase I already have a samyang 24mm f2.8 A/F which is small enough for me and I can live with the 1 stop difference.