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SENS-UP in Liveview with DSLR/Mirrorless cameras?


paolos

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Hi all!, I'm a new entry!

I'm doing some video astronomy lately, expecially to show faint Messier Objects to people with a public telescope ( Newton 12"-F5).

I've just tested two methods:

  1. Using a Samsung CCTV video camera connected to a laptop ( via USB Video Grabber)
  2. Using a Sony NEX-5R Mirrorless camera connected to a wide monitor wall-mounted

and here are my first comments:

CCTV Video camera :

  • OK: 1) high sensibility with SENS-UP feature : you can show "almost Liveview" faint objects, even if the movie is not smooth due to long  exposure time of each single frame, and you can "go around" the target with micro-movements of the motors, always watching it ( this is necessary when you have to find an object with Go-To procedure but the polar alignement is not perfect)
  • KO: 1) the sensor size is too small for a focal lenght of 1.500 mm : it's difficult to center the faint targets and big nebulas/galaxies go out of the FOV. 2)The need of a laptop in order to save still images to send later to partecipants.

SONY NEX-5R camera:

  • OK: 1) big sensor size ( I'm dreaming to use full size models like Alpha 7S....!). 2) Live view option: perfect for the moon, the planets, the sun. 3) Possibility to store videos and images on the camera, and then send them to the partecipants at the star-party. 4) Possibility to shoot still images with long exposures ( 1-10 seconds) and show them immediately at the wide monitor: you can show to the people more than what they could see at the eyepiece ! this is the only way to really appreciate nebulas and galaxies ( see attached file).
  • KO: 1) Live view mode: even if sensibility is going higher and higher ( see Sony Alpha 7s for example), it is still not sufficient to watch in Liveview mode what you could see through the eyepiece: this is a pity because Liveview mode would be the best way to manage a public session of visual obervation ( centering the targets, showing various details of wide objects, no need to shoot continuously new images, set the camera in PLAY mode and send them to the monitor,....)

--> So now my question is clear:

Why is not possible to modify Liveview shutter time ( increasing it), io order to reach a "SENS-UP" effect also in DSLR/Mirrorless cameras?

Is there any technological limit or is it just a matter of sensor-control programming?

Has anyone already tried to do something about this topic?

Thanks!

post-46158-0-89742900-1438260926_thumb.j

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I would say the answer is that the camera is not and never was intended to operate as a cctv device.

A camera is intended to take an image - one off. Then repeat the process and take another SINGLE picture.

The circuitry and software inside it is not meant to take a continuous video of a panorama.

I would guess the chip is different, I think a CCTV chip would need to be along the lines of a KA device where one column absorbs photons from the object and the one along side it is used to shift the collected data into for them to be shifted up and out while the "read" column collects the next "exposure", thus it is a more or less continuous operation without the need to block the incoming image to read the collected data on the whole chip.

There is a club here at Cambridge that run a presentation for the public in conjunction with the University and they use a webcam type camera to a laptop then to a projector and onto a screen. The scopes used are Meade 8" and 14" scopes so the final image is bigger then the 12" f/5 Newtonian and they show the objects without problems. Maybe what you are using is simply not ideal or best suited.

As a webcam is the obvious item to connect to a laptop you should be able to go: Scope, webcam, laptop. Keep it simple.

Then people view the laptop screen.

May need to track down a "webcam" with a biggish chip (QHY5 I think had one) as I doubt that a standard PC one will be adaquate.

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What I would like to do, in view of max. semplicity, is to connect directly the camera to the monitor and set the camera in Liveview , so I don't need any computer, video-grab interface, etc...

This is possible and it perfectly work with bright objects.

So I'm asking to modify Liveview parameter, like the shutter frame time, in order to increase visibility of faint objects.

In theory it seems to be a simple thing, but actually I don't know if it is feasible by programming, for example via "API", the camera firmware ( like has already been done with app like Time-lapse, Noise Reduction in Multiple Shots, etc...)

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Paolos,

Most of the cams that have high sensitivity and work well for EAA have small sensors. Except for a few smaller objects, your 1500mm FL will have too narrow a FOV for most DSO's. You will need something in the 400 to 1000mm range. Newts are difficult to get focal reducers to work, so you may have to consider a different scope. The SCB2000 is a good starter cam, but is limited in exposure/integration time. To get fainter DSO's, you may want to consider something like the SX Lodestar used with software called Lodestar Live. If your interested, just post here and I can provide more details. I'm sure others will join in as well.

Don

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