Questions re Multi Frame Noise Reduction on Sony a6X00

I'm trying to get a good handle on the Multi Frame Noise Reduction feature on my Sony a6300, and would really appreciate some guidance on the following.

When you select the MFNR option, the camera then gives you two choices under "NR Effect" -- 1) selecting a specific ISO value, and 2) selecting "high" or "standard."

I'd love some advice in understanding when it's best to make which of those choices. In what circumstances would you select a specific ISO when using the MFNR feature (and what factors would you use in setting that number), and in what circumstances would you not select a specific ISO but instead choose "high" or "standard" (and what would be the factors in deciding between those two choices)?

I think what may be confusing me a bit is that if you set a specific ISO, say 6400, when using MFNR, is the camera taking all of the multiple frames at that same ISO? If so, what is making each of the stacked frames different, such that the resulting final image is different from/better than just shooting a single image at that same ISO without using MFNR?

I've tried to research this on line but have not been able to get these specific questions clarified, so I'd really appreciate any help!

Thanks!!

I have always set the option to a specific value, 6400, 12800, etc.. The camera then takes a rapid burst of images all at that ISO (all images at the same ISO regardless of option chosen) and stacks them, computing noise reduction based on comparison.

I have found it works best tripod mounted but have had many a great image turn out from a handheld "impossible"shot.

Dave

I've looked at the math. I can't see a benefit to doing that, rather than taking a slower shutter-speed shot at lower ISO.

Of course, there's an exception. If I want to get a better ISO than my camera is capable of delivering (or if it requires a slower shutter speed than my camera can deliver), then that's the way to go.

The idea of multiple frames has to do with averaging - noise is random when it appears in a shot, which means the noise is in different parts of the frame with each shot taken. The more frames you take, the better the chance that some particular part of the scene that was obscured by a noisy pixel in frame 1 will be visible in one of the subsequent frames...and so merging together multiple frames into one allows the random noise to be reduced, even eliminated, and also allows fine detail that had been obscured behind noise in one frame to be restored in the merged shot. So although you're taking all the frames at the same ISO, the stacking of multiple frames pays off in reducing the noise and rebuilding the detail.

There are two ways to use it - one is of course when handheld in low light, where a tripod or monopod or flat surface is unavailable - a slow shutter won't be an option, and the only remaining option is raising the ISO. Once you're pushing it up to ISO3,200, 6,400, even 12,800 - especially in low light with plenty of underexposed shadows, the noise becomes ever more intrusive. But use MFNR at those higher ISOs, and the noise can be reduced by at least 3 stops, sometimes more...meaning an ISO6400 shot can have the noise of an ISO400 shot...and good detail in the shadows...and the shutter speed can be set to a hand-holdable level.

The other way to use it is combined with long-exposures - but in situations where you would need to exceed 1 minute or more, or would still have to use a higher ISO in extreme low light even with a long exposure. Stacking multiple frames will help reduce that noise and also allow better detail retention with hot-pixel removal. Astrophotographers have used multiple image stacking for a long time - though it wasn't done in-camera as that technology didn't exist.

Most of the time, setting your own ISO level will be best - even if you want to use 'auto ISO' to meter the scene initially in standard ISO mode - see what ISO the camera wants to pick, and if it's a high ISO, switch to MFNR, set it to that ISO, and shoot the scene.

Also, most of the time the standard MFNR setting is best - it stacks 4 frames which will usually be enough for most walkaround subjects, and for most ISO levels at 6400 or less. The high mode would be used when you have to really go mega-high with the ISO - I'd not even bother until I'm at ISO 12,800 to 51,200...then the 11 frames that it stacks might be needed to really try to average out the high levels of noise at those extreme ISOs.

I've done some tests with and without MFNR a while back, to give an idea. This is on the 'standard' setting - this first shot is in low light, taken at ISO 25,600 (I'm providing the link because you can go to 'original' and see the 6000x4000 resolution shot as it came out of the camera, shot in JPG Fine:

https://www.dpreview.com/galleries/3702150612/photos/3425669/a6300-iso25600-bottles

Now, with MFNR standard mode, ISO 25,600, shot in JPG, straight out of camera:

https://www.dpreview.com/galleries/3702150612/photos/3425670/a6300-iso25600-mfnr-bottles

You can see the noise is reduced nicely - but also look at the light grey writing at the top of the Malibu bottle - the text is mostly obscured and hard to read in the first shot due to noise which blocks and pixellates the writing - but in the MFNR mode it has restored the text by building back detail behind the noise, enough that you can read 'twelve' and 'shipping' above and below the circle.

An example of when MFNR can be useful. A night scene of a lovely sunset color while walking around Epcot center - I had a kit lens, F5.6 max aperture, no tripod, and nowhere to put the camera on a level surface, but wanted the shot. At ISO100, I'd have needed a 4-second exposure - way beyond handheld range. But using MFNR, I could use a 1/15 shutter and ISO 6,400...and with the MFNR stacking, ISO6400 could have roughly the same level of noise as an ISO200 to 400 shot:

It can still give you some of that long-exposure night shot look, but done handheld.

Probably one of the most extreme examples I attempted with MFNR was pulling out of San Juan after 11pm at night, no moon, rough seas, moving boat...I wanted to try to catch El Morro with some big storm clouds behind it only visible in the reflected light of the city - near black to the naked eye. I was using an F1.8 lens wide open, ISO 12,800, and a shutter speed of 1/6...6 frame stacking MFNR mode. Surprisingly the camera was still able to align and stack despite a little movement - I still had to increase the exposure 200% in post processing! So this is effectively an ISO 51,200 equivalent at F1.8 and 1/6 shutter:

Not great. But pretty extreme conditions. And a long exposure on tripod would not be remotely possible from the deck of a moving ship.

It's great for handheld interiors too - when you want to capture as much detail in a low lit room but don't have a tripod or don't have time to set one up - and want to preserve that low light feel and atmosphere that would be lost with a flash. This is one example of where Auto ISO can be useful too - you know you want max aperture, and want a hand-holdable shutter speed, so letting the camera pick the ISO necessary with the ceiling set to something like 6,400, you often end up not needing quite that much. Here's a link to a shot, where you can look at the original JPG from the camera at 6000x4000, taken with MFNR at ISO2,000 picked by the camera, handheld:

https://www.dpreview.com/galleries/3702150612/photos/3777383/zzzdisney-june2018-067

The details in the very dark plants in the vase, the pine tree outlines on the lampshade, details in the painting on the walls, patterns in the chairs and carpets, all nicely retained with little to no noise - and straight out of the camera with no processing needed.

Thank you Dave, Flip, and Justin!

And Justin, HUGE thanks for taking the time to provide that incredibly detailed and helpful tutorial on MFNR, along with the examples from your beautiful photos. Also, your explanation of what the camera is doing with those stacked frames (the fact that noise appears in different places on multiple images shot with the same ISO) made me understand why there is logic in selecting a specific ISO value when using MFNR.

This seems a useful alternative to Hand-Held Twilight (giving the photographer more control over the settings), and I'm glad to finally understand it!

Thanks again!!

You're welcome - glad to help. I've been using the stacking modes since they first debuted on Sony P&S models, and on all my cameras since...it's a very useful tool. And you're right - handheld twilight is the same thing - but not as useful since it's a scene mode and doesn't allow any settings to be controlled. MFNR is great because not only can you set the ISO, but you can use it in any of the P, A, S, or M modes, and change focus areas, focus modes, white balance, EV - pretty much anything you want. The first camera I had with MFNR was the DSLR-A580 back in 2011...then it migrated to the E-mount cameras with the A6000...and also on the RX lines.

Before that, it was only HHT and AMB (anti-motion blur) that had been around since some P&S models and onto early DSLRs with the A550 and the first NEX models - which I still used, but always wished I could have more control over settings. Since MFNR, I've never used HHT or AMB again. I still love a good long exposure night shot, on a tripod, but there are many times where it's either not convenient or not possible, and I still like to take low light scenics.

BTW - it's even usable for moving things - if they're moving slowly - an animal sitting still rather than walking, and maybe eating something, or looking around, can be captured if the frames are close enough together. I took a snap of an opossum in my backyard, 60 feet away, near midnight, in extreme low light with a 70-300mm F4.5-5.6 lens wide open at ISO 12,800 and a 1/160 shutter, through a thick hurricane-glass window. I was mostly just trying to ID what was out in the yard, so not trying to get a serious wildlife photo - and it was good enough to easily identify what the animal was, that couldn't be determined with the naked eye:

We're just back from 20-nights on the HAL Zuiderdam's Viking Passage, and I decided to try out the MFNR feature on my a6300 one night from our balcony when the full moon was playing peekaboo behind the ship. It was actually pretty dark out. I also pulled out my a6000 and took a similar shot at the same ISO. I can definitely see far more noise (especially in the sky) in the latter, without MFNR. Very interesting, and I thank everyone again for all the info on this feature.

Sony a6300, using MFNR, ISO 12800, f/3.5, handheld on a moving ship at 1/5 sec:

Sony a6000, ISO 12800, F/3.5, 1/4 sec:

That's definitely an example of when MFNR is quite useful. Though you used it while moving, which can sometimes trip up the multiple frames, I find with slower movement it can still cope well. Not only is the noise lower, you also have nicer contrast, deeper shadows but still with detail, better colors and saturation, and you probably can inspect the details at 100% and find some spots where fine details are kept better too.