IQ3 80 Long exposure mode

[Wayne Fox]

I keep getting the message to consider long exposure mode when taking shots with my IQ3 80 back. From what I can see it sets a minimum ISO of 200 which is 2 stops of light difference, but typically when I'm shooting these long exposures I have 4 to 10 stops of ND in front of the lens, so the ISO increase isn't something I'm wanting.

What's "special" about long exposure mode? I can't find anything in the manual that really explains what it is about. I can see some circumstances were it would allow a 4 min exposure to be cut to 1, but is there anything to be gained by adding two more stops of ND and then enabling this mode?

 

[Paul2660]

Hi Wayne:

On the IQ260, the LE mode takes you to ISO140, and as you pointed out on the 380, ISO200.

As I understand it, the LE mode, for both backs, is to allow exposures longer than 2 or so minutes at base iso. Where is gets frustrating, is it seems that on any exposure longer than 1 second, you get the prompt telling you to go to LE mode. Where as the real benefits are most likely in exposures starting around 3' and going to 1 hour. Of course there will also be the necessary dark frame which will be as long as the original exposure also.

My experiences with the LE mode in Arkansas, summer and fall evenings and night were not very good, even at exposures of 5 minutes, quite a bit of noise, but the ambient temp was around 75 degrees and I believe the cooler the ambient temp the better.

I think one reason Phase put the temperature gauge on the 380, so that you can see if the back is too hot to consider a very long exposure.

On the 260, LE mode has no effect on normal range exposures of ISO 140, 200, 400 and 800. Something I had hoped would be possible but after testing these ISO settings against the normal 100, 200, 400, and 800, I did not see any improvements. So it only seems to apply to longer shots.

I did notice that in the latest firmware for the 260 released last week, there was mention about a fix for noise in the dark frame processing. But I have not tried anything longer than 1 sec with the 260 since that update.

Paul C

 

[mjr]

I agree with everything Paul said, on the IQ260 I think the long exposure mode prompt must have something to do with the temperature of the chip too, here it is cold and I don't get the prompt for exposures under 8 seconds, so it's interesting to read that Paul gets it at 1 second.

Although I have yet to do a lot of testing, I have found that for exposures around 10 seconds in these ambient temperatures, I just stick with base ISO, especially if the length of exposure is related to an effect, eg. using filters because I want movement in a sky, if the exposures are longer because it's darker then I just switch to LE mode although often I will do both just to see what the difference is and I haven't found much. Anything longer than 30 seconds and I change over to LE mode anyway and up to an hour it seems to work well although standing around at -20 for an hour is much less pleasant!

I would test a little more and see if adding filters to allow use of a higher ISO has any benefit over not doing it and sticking at base ISO. I think it would be good if the prompt could be turned off though.

Mat

 

[tjv]

It's interesting, with my Credo 60 I've found 30 sec exposures and even 1 min exposures to be pretty good compared to what I was lead to believe the quality would be. I thought they'd be next to useless, but the detail and noise control is really good when using C1 v9. The dark frame is a pain in the arse especially when needing to stitch (eg for a pano), but other than that I'd certainly not hesitate in going this long. I wish the Credo had the LE mode though, even just to help cut the exposure time down when it's not needed for creative effect, especially if there is no loss in quality. Or is there?

 

[gerald.d]

Hi Wayne -

I don't think there are many of us about with the IQ3 80. Just a quick question to see if you have seen the same thing that I have noticed.

On your long exposure shots, are you seeing lots of dead pixels on the screen of the back? When I bring the file into C1, they're not there. It's almost as if the review on the back isn't taking into account the dark frame.

Kind regards,


Gerald.

 

[Paul2660]

Can't speak to the 380, but 260 sure has them. The "single pixel" noise reduction slider will remove the vast majority of them without much effect of the details of the selected image. I had always thought that the dark frame mapped these and then in the camera when the two files were combined the stuck pixels mapped out. But at least from what I have seen that doesn't happen.

Paul C

 

[gerald.d]

Can't speak to the 380, but 260 sure has them. The "single pixel" noise reduction slider will remove the vast majority of them without much effect of the details of the selected image. I had always thought that the dark frame mapped these and then in the camera when the two files were combined the stuck pixels mapped out. But at least from what I have seen that doesn't happen.

Paul C

Hi Paul -

The thing is that I don't have to use that at all - they just disappear in C1. But there are dozens and dozens of them.

It's certainly different from the IQ180 that I used to have as I never saw the same thing with that.

Kind regards,


Gerald.

 

[jagsiva]

From playing with the 380 in LE for a short time, and comparing files to the 260 and my 180, there is a difference. In C1, the files in LE looked fantastic, and LE was definitely better than "normal" mode (with less ND). From what I heard, there is some form of highlight masking that happens in the RAW file at capture that protects highlights and noise in LE mode that is unique to the 3xx. I have not read this any official spec, but it would not be far fetched for Phase to release something like that without an announcement. Subjectively, the LE files looked great.

 

[Paul2660]

Jag.
Did you try the 380 LE mode with exposures in the 1/30 to 1/250 range to see if they were any cleaner than similarly shot exposures at standard ISO 200?

This is something I had hoped for with the 260 but it did not happen.

Thanks
Paul

 

[GrahamWelland]

Per Gerald, with my IQ260 I would see a lot of hot pixels in long exposures (mins) on the LCD but the processing in C1 would all but eliminate them when the dark frame was applied along with careful use of the single pixel slider.

The biggest issue I had was the long exposure nag screen that would pop up at 8-10 seconds and it wasn't something that you could just disable. Using LE mode for shorter exposures I found the differences to be marginal, the main thing being that the LE mode at ISO 140 would shorten the exposure anyway which actually could be a pain in the a%% at times because guess what? I might actually WANT the longer exposure for artistic reasons and so upping the ISO and shortening the exposure wasn't what I wanted at all - I'd end up having to add filters when shooting under 60s for example to push out the exposure time again. When it came to shooting multiple minutes the impact was less of an issue and LE mode obviously improved things vs shooting in aerial mode (no dark frame) and using 3rd party noise reduction.

 

[jagsiva]

Jag.
Did you try the 380 LE mode with exposures in the 1/30 to 1/250 range to see if they were any cleaner than similarly shot exposures at standard ISO 200?

This is something I had hoped for with the 260 but it did not happen.

Thanks
Paul

Paul, I don't recall the specific ss, but I did find the especially highlights were better pretty much across the board. Take a look at the DT/CI samples in the IQ100 tests, where they also did some tests with the IQ260/380. I think they have some LE files in there. The still-life one with the large knife has some interesting peeping opportunities.

 

[Wayne Fox]

Thanks for the feedback. I guess I’m trying to understand the “goal” of long exposure mode. It appears it is an attempt to get similar quality images at 2 stops faster exposures by enabling ISO 200 and then doing some additional noise and processing.

In my case, I’m almost always interested in long exposures for the sake of the long shutter speed, with lots of ND and often small apertures. I just can’t see any reason to use it, since it would usually require adding two more stops of ND to maintain the long shutter speed.

The alert is sure annoying ... is there anyway to disable it?

 

[voidshatter]

In my case, I’m almost always interested in long exposures for the sake of the long shutter speed, with lots of ND and often small apertures.

You have picked the wrong product for that job. Even a Nikon D810 can do a lot better than the IQ3 80MP does in this territory, because the IQ3 80MP is a CCD and long exposure is the worst case usage.

For your information, the dedicated long exposure mode (LEM) improves dynamic range for long exposures on a CCD back, but is still far far behind modern Sony CMOS sensors..

Below shows what happens between LEM=off vs LEM=on:



It is also true that the IQ3 80MP's LEM has inherited the corner issues of the IQ260:

The troubles of using a CCD for long exposure:

a) It gives a warning which cannot be disabled if you shoot with LEM=off;

b) For a CCD back, you have to shoot with the long exposure noise reduction to prevent severe image degradation, but the long exposure noise reduction countdown is a deal-breaker as you would have to wait for N seconds after a long exposure of N seconds. For sunset / sunrise this is not acceptable as it would be impossible to do bracketing with the same set of ND filter.

c) If you take off the ND filter to bracket for the foreground then you run into alignment issues which is caused by change of angle of view (not tripod/head shake).

d) Thus by using a CCD for long exposure you are limited to shoot scenes with low contrast, or with constant light conditions.

e) I would recommend only Sony CMOS sensors for long exposure shots, e.g. IQ3 100MP, IQ250, Credo 50, Nikon D810 etc.

 

[Wayne Fox]

I'm familiar with all of this ... I've been shooting CCD since the original Kodak DCS 16mp and dealing with the issues of noise with long exposures. I also have a d800 system as well as a sony a7rII system, but I prefer the glass and resolutions with my XF and arca swiss systems. The majority of what I do doesn't require long exposure, and when I do long exposures it's almost always just for effect. I have no problem getting what I want out the files, prints look fine. I'm just trying to find out if there is any reason at all to switch to long exposure mode when the intent is to drag the shutter... this would require me to add two stops of ND or close the aperture down 2 stops. Doesn't appear to be, looks like it's more designed to allow a shorter exposure with perhaps better results than just switching to ISO 200.

My IQ3 100 should be showing up soon, I'm nervous I won't get what I want out of the files (I struggle with the nikon and sony files to get what i can get out of the phase files) but Phase says insuring good color rendition was a priority with the back. It has it's own issues which may limit shifting as far as I do with the current back, but that's sort of the nature of the beast with MF.

Also curious, I've never seen anywhere near that level of noise in any shot I've taken with an IQ180 or with then IQ380 as your example ... even with single pixel noise turned off and noise reduction off. Nothing even close. But your example does make me curious, I'd experiment more with Long exposure mode if i intended to keep the back.

 

[voidshatter]

Also curious, I've never seen anywhere near that level of noise in any shot I've taken with an IQ180 or with then IQ380 as your example ... even with single pixel noise turned off and noise reduction off. Nothing even close. But your example does make me curious, I'd experiment more with Long exposure mode if i intended to keep the back.

That was with shadow push +100 or something like that to abuse the files and stress test dynamic range of long exposure (which is quite essential when you do long exposure of backlight landscape). In this territory the D810 (not the A7R-II) can destroy the IQ3 80MP. If you only shoot low contrast scenes then it shouldn't be a problem.

 

[ondebanks]

I'm just trying to find out if there is any reason at all to switch to long exposure mode when the intent is to drag the shutter... this would require me to add two stops of ND or close the aperture down 2 stops. Doesn't appear to be, looks like it's more designed to allow a shorter exposure with perhaps better results than just switching to ISO 200.

Wayne, there is more to the long exposure mode than that.

First of all, the intent of the higher LEM "base ISO" is not to allow a shorter exposure, as you put it. The whole point of LEM is to facilitate exposures which are much longer than "normal", after all. No...the reason for the higher "base ISO" is to force underexposure, and therefore keep most of the pixel well depth unused. This frees up capacity in each pixel to store the additional electrons of dark current that build up in long exposures...from a low, gritty noise glow at most pixels, to very high intensities in the worst-case "hot" pixels. Without that capacity, the subtraction of the dark frame would riddle the final image with black, oversubtracted pixels.

Secondly, Phase One claim (but are characteristically vague about the specifics ) that starting with the IQ260, they have engineered the CCD sensor to effectively segregate "bad" dark current electrons from "good" image-forming photo-electrons, and they need this freed-up well capacity in the underexposing LEM mode to do so. It's no big deal to maintain enough capacity to accommodate the mix of "good" and "bad" electrons, but to somehow keep them apart from each other must be considered a really big achievement in sensor design.

BTW, the fact that the LEM ISO is higher for the 80MP backs (ISO 200) than for the 60MP backs (ISO 140) tells us that the 80MP sensors have an inherently worse dark current level. Using ISO 200 rather than ISO 140 reserves even more of the well capacity free for Phase One to manage the dark current.

Ray