Yes, but why?
Since tripod is required, and there is no shutter speed constraint, there does not seem any need for shooting at ISO higher than base ISO. What am I missing?
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IQ4 frame averaging vs ND filter
- Thread starter Maxx9photo
- Start date
Since tripod is required, and there is no shutter speed constraint, there does not seem any need for shooting at ISO higher than base ISO. What am I missing?
Ray Harrison
Well-known member
If you're on something that's vibrating where a longer shutter speed affects the image quality, shooting at a faster shutter speed allows for an average of sharper images rather than an average of less sharp ones. Also, if there are time constraints where I am, a shorter overall frame average time setting packing in more frames at faster shutter speeds is great flexibility. Let's say I've got 5 minutes available to me to capture an image and at base ISO 50, f8, 2 seconds I might get ~150 frames. Depending on what's going on in the scene, it may be better to have more frames, so cranking up the ISO gets that.
Bill Caulfeild-Browne
Well-known member
In shots of the night sky stars will appear as ovals unless you keep the exposure short - hence the need to crank up the ISO.
Increase generally, or only from extended (50?) to native (100?).
If something is vibrating it will affect the IQ of frame averaged result as well, wouldn’t it? Phase One does not have in-camera frame alignment, do they?
The vibration in a single 5 sec. shot should have the same IQ issues as in a 5 frame averaged 1 sec shot.
But if you run frame averaging, you are extending the shutter speed and get the same issue. What is a difference between a single 10 sec shot and ten one sec. shots that are frame averaged (first at native, second at higher ISO)?
vieri
Well-known member
Just my .02:
- Increase ISO: Phase recommends to use it at ISO 100 rather than ISO 50 on the IQ4. However, there is no warning to increase ISO from base ISO on the IQ4 Achromatic;
- Movement: if the tripod vibrates during Frame Averaging, your selected base shutter speed is of no consequence and you will have micromovement regardless of what base shutter speed you use; what makes a difference is the final amount of time your camera is recording an image;
- Similarly, in shots of the night sky averaging or shooting longer than 20 seconds (give or take) will start showing stars as elongated lines rather than dots;
All of the above is the result of extensive Frame Averaging use, both on my IQ4 and IQ4 Achromatic (I use FA for a vast majority - almost all - of my images).
Hope this helps, best regards
Vieri
- Increase ISO: Phase recommends to use it at ISO 100 rather than ISO 50 on the IQ4. However, there is no warning to increase ISO from base ISO on the IQ4 Achromatic;
- Movement: if the tripod vibrates during Frame Averaging, your selected base shutter speed is of no consequence and you will have micromovement regardless of what base shutter speed you use; what makes a difference is the final amount of time your camera is recording an image;
- Similarly, in shots of the night sky averaging or shooting longer than 20 seconds (give or take) will start showing stars as elongated lines rather than dots;
All of the above is the result of extensive Frame Averaging use, both on my IQ4 and IQ4 Achromatic (I use FA for a vast majority - almost all - of my images).
Hope this helps, best regards
Vieri
Thank you for sharing your experience, Vieri. Based on your report, I assume that with Frame Averaging, you use only ISO100 on your IQ4.
Do you use Frame Averaging only to simulate long exposures (motion blurs) or also to reduce noise (how many frames typically)?
Both Image Stacking and Frame Averaging are commonly used terms.
kdphotography
Well-known member
I always thought of "image stacking" as in stacking images in order to increase depth of field.
Frame averaging is just another tool in the shed, and am happy to see that the IQ4 has implemented it well. It doesn't replace my use of filters, but certainly does lighten the load a little. I just returned from Lofoten recently and found that Frame Averaging actually helped me obtain a shot that would have been difficult for me to do traditionally with filters. Glad it is an option on the IQ4 menu.
One other item not often mentioned, although I don't find it to be a significant issue but some are much pickier than me---is with Frame Averaging you avoid the potential for image degradation by placing a filter over the lens.
That is often called focus stacking and probably belongs to the family of image stacking, like frame averaging.
vieri
Well-known member
You are very welcome, always happy to help.
- I normally stay at ISO 50 on IQ4, Phase warns about potential overexposure but I never found that to be a problem.
- Only to do long exposure, not to reduce noise. About this, it could be interesting to compare two shots, one done with a single long exposure of x seconds at base ISO, the other done with Frame Averaging, shorter exposure, higher ISO, and see which one is cleaner. If nobody else does it before that, I might look into it when I am back home (currently traveling leading Workshops, won't have the time until a couple of weeks after Easter at the earliest).
Best regards,
Vieri
Bill Caulfeild-Browne
Well-known member
Because you can increase ISO to the maximum so your 10 sec. shot becomes 1 sec, for example.
This was at ISO 28600 - no noise.and only slight star movement. At lower ISOs the exposure would have been much longer and stars more oval. (Comet Neowise)
You misunderstood my question about frame averaging. I wondered why to use high ISO with frame averaging. For example, I wondered why you would use 10 frames with 1 second per frame (high ISO) instead of 2 frames with 5 seconds per frame (low ISO). In both cases, the motion blur will be the same.
You would not use frame averaging to avoid motion blur, on the contrary.
vieri
Well-known member
Just a note about star movement - if your resulting exposure is always 10 seconds, regardless whether you'll get there with one 10 seconds shot at ISO 5000, two 5 seconds shots at ISO 2500, four 2.5 seconds shots at ISO 1250, etc, the resulting movement in the stars is always exactly the same.
Best regards,
Vieri
Bill Caulfeild-Browne
Well-known member
I agree. My point is that with frame averaging you get much lower noise, thus enabling a higher ISO and a shorter exposure. Instead of two five second shots at ISO 2500, you could do one five second shot at ISO 5000 (total exposure might be ten frames) and noise is reduced because it is averaged over those ten frames.
Ray Harrison
Well-known member
I can only speak from my own personal experience in cities and urban landscapes, but if I have a high contrast scene exposing to protect highlights and where I know that I’m going to want to pull out deep shadow detail, then the more frames I have in the calculation, the cleaner the shadows (which I know is obvious). This can also be useful if I have to stop the FA in the middle for whatever reason. Also, as often happens in urban areas, when light intensity can change quickly, especially at night with vehicles going by or any variety of lighting changes as the city settles in to the dark, I want to avoid "additive" components of any exposure. If the sensor is open long enough to blow the well, it's blown out. Fewer images with overblown highlights can have the affect of overblown highlights in the averaged image.
I can choose to get those extra frames a couple of different ways, either by extending the length of time I record or, if I'm time limited, increasing ISO (to a point), assuming I want a constant aperture. The caveat is that once the shutter speed exceeds the sensor scan speed, then the number of frames that can be captured in a specific time interval becomes constant which is where you end up with gapping. There's a fairly quick point at which increasing ISO doesn't really help in the "maxing out the number of frames" scenario, for how I shoot.
To keep the math easy, if not always realistic, I can get 120 shots in a two minute frame average at an exposure of f8, ISO 100, 1 second, I can get (because of the above caveat) an upper limit of ~275 at 1/4 second at ISO 400 over those same two minutes and the resulting raw file is super clean with no real penalty except maybe gapping. Whether that matters is scene dependent. I’d need an additional two minutes or so to get those frames at ISO 100. That may seem like a petty amount of time, but sometimes being able to move scenes reasonably quickly is of value to me, especially as light and other factors around me change.
Do I really need those additional frames to pull super clean shadow detail? In most cases, probably not, but having that flexibility is nice. In my early testing a couple of years+ ago, I did find there to be differences in certain scenes as to the number of images per interval as regards averaged noise in shadows. Because I've matured over that time, it may be that I wouldn't find it to be true now. To me it's less about equivalences, but having more than one way to get there. That may not be important to many people but I appreciate it, nonetheless.
To be clear, most of the time, if I do use AFA (which isn't that often), I do shoot at ISO 100 because my shutter speeds are typically reasonable and I hit close to the max limit of frames per time interval anyway. The key for me is that there’s flexibility when I want it. I’m not invested or interested in proving AFA is the best thing since sliced bread, or that anyone should run out and pick up an IQ4150, or that if they don't have one, they're not going to be successful. Clearly, that's not true and some cameras have a variation of it, and honestly, I don't have the back because of AFA. It just showed up in my firmware one day
. AFA is just a tool in the tool belt, as was noted elsewhere. I do appreciate the flexibility.