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Andante_2

D5600 Shutter Frame Rate vs Live View *.avi Rate

Question

Hello,

This question refers to a D5600 body and BYN v2.1.0 using Planetary Mode and 5x Live View.

When recording using 5x Live View, BYN and my computer (2018 Apple Air, dual boot w/Windows 10, Thunderbolt port) are downloading frames at a rate of ~100 fps, actually 91.8 fps or some such. This is indeed what is recorded within the *.avi file, EXCLUSIVE OF THE SHUTTER SETTING. For example, a 600 frame collection at 1/10 s integration time should require 60s of clock time plus a bit of additional time for downloading each subframe window. However, the actual collection is complete in ~ 600 frames / 100 fps = 6s! I can only conclude that Live View is being sampled at ~100 fps regardless of the shutter time. This means the same actual frame (which is integrating over 1/10th s) is being displayed by Live View and captured into *.jpg files (which are subsequently compiled into an *.avi movie) multiple times per actual camera integration (i.e., shutter "open") interval.

Some background follows.... The iso level appears to be properly set within BYN because the planetary image brightens or darkens as appropriate within the Live View window of BYN. The same is true for the shutter time setting: increase the shutter time and the Live View image brightens, as it should. Take my previous example: if BYN is sampling the Live View stream at, say, 100 fps (or directly reading it out at that rate), I am essentially collecting 10 of the same images for each 1/10th s exposure. I obviously want to know how to collect a single Live View frame per camera integration time.

For what it is worth, and this may not be relevant: the download rate of ~100 fps is the same whether or not I turn the manual movie mode "on" or "off" in the BYN settings block. The difference here is that, with manual "off," the camera seems to set it's own iso and shutter speed, and the images are often overexposed. So ... I turn manual "on."

Thank you in advance,

Don

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There is no frame rate per say and NOTHING is preset.  BYN/BYE is limited only by your physical setup (USB speed / cable / computer).

BYN/BYE will try to download as many frame as possible as fast as possible.

 

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You are correct, the shutter setting does not control the duration of each frame or the frame rate. It may only affect the brightness of each frame.

I would also say that the Nikon SDK does not download or create AVI video files. It downloads individual LiveView frames and BYN controls the assembly of those individual JPG frames into a video file by means of DCRAW, a video tool that is installed with BYN.

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Thanks for the quick response,

OK, so the download rate of LiveView frames is "controlled" only by the diameter of the data firehose. In my case, the data rate is ~92 fps of 640 x 424 pixels per each frame. This means I am grossly oversampling my desired integration interval of ~1/5 to 1/50 s (depending upon the planet). Given that I can download in one burst only 2000 or so frames, and that concatenating smaller *.avi files into a single longer one requires 3rd party S/W I don't have, I am limited to 2000 fr/image. Oversampling reduces the number of "different" images, so that say, at 1/10th s integration time and 1/100th s frame capture time, I would reduce independent images by a factor of x10 to an equivalent stack of 200 images. Here are some possible fixes, and I'd like you opinion:

(1) jack up the iso, perhaps to 3200 or even 6400. Assuming 13-bit significant data at iso=200, I would lose a factor of 2^5 = 32 dynamic range at iso=6400 BUT preserve 13 - 5 = 8 bits of full-well dynamic range, which is the bit width of a *.jpg pixel anyway. However, I am unlikely to fill the well, so I may end up with only something like six bits, or a dynamic range of a factor of 64 ... not good,

(2) get an older, slower downlink somehow,

(3) perhaps (and I need your advice here), readout the entire frame instead of using the 5x option. Hopefully, this would slow down the downlink frame rate by ... a factor of as much as (depending upon the binning and thus resolution loss) x25? 'Trouble is, I'd lose resolution, right?

(4) Simply take a bunch of short exposure *.NEF images and combine them in Registax6. This cycles the mirror and kinda beats up the camera. I hate this option.

Your thoughts,

Don

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The atmospheric distortion due to seeing varies rapidly and the purpose for taking lots of short images for planetary photography is to allow you to get lucky and capture a few images when the seeing is extraordinarily good. You use those good images and discard the rest. The images do not need to be too bright. You just need the planet to be bright enough that you can stretch it into a pleasing picture. Making it too bright by increasing the ISO or increasing the exposure setting limits how much you will be able to stretch the image once it has been stacked.

You might try increasing the Live View Throttle setting value to slow down the captured frame rate. However, if you slow down the fire hose, I do not believe that it will result in longer exposures. You would just have fewer of them over the same time period.

I do not believe that Registax6 can deal with RAW images. It needs JPGs or an AVI.

 

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Thanks for responding,

Planetary Imaging Pre-Processor (freeware) can combine *.NEF (i.e., *.RAW) files into an AVI movie. Still, I heartily dislike doing this because it cycles the camera mirror way, WAY too much.

Changing the iso and "shutter speed" does affect the brightness of the image on the Live View feed. So ... better to have a lower iso balanced with a higher "shutter speed," even if the "shutter speed" is notional: the important thing is to get the brightness of the planet correct.

Right, I want to extend my "movie" over a longer time to better capture the changing seeing (which also oscillates over a few seconds between slightly poorer and better). I agree, basically, there is no way to change the "shutter speed" using the Live View modality, only to space out the frames that are collected.

Thx much,

Don

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