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AV FLAT


FERRAN_BOSCH

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If you try to capture an image with the shooting mode set to M and the Shutter value in BYE set to AV-Flat, BYE will complain that the shooting mode must be set to Av.

In Av mode, the aperture is fixed and the camera's exposure is determined by its internal exposure measurements. If you are shooting sky flats or t-shirt flats when the sun is setting or rising this can help to provide some consistency in brightness for a series of exposures taken over time.

When I was actively imaging I used an artificial light source so the brightness was fixed. I initially used AV-Flat to get an the camera's idea of what my exposure should be and then switched to Manual and adjusted that exposure to shift the histogram to where I wanted it to be. Then I used that exposure for my flat frames going forward.

I hoped this helps.

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On most camera models, you have to turn the dial to M or Av for AvFlat.

On the higher end camera models, BYE can set the dial mode programmatically, and with these cameras, you don't have to change the dial manually.  There is only one way to find out... try it and see if your camera works without touching the camera.

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On 12/10/2023 at 6:11 PM, astroman133 said:

If you try to capture an image with the shooting mode set to M and the Shutter value in BYE set to AV-Flat, BYE will complain that the shooting mode must be set to Av.

In Av mode, the aperture is fixed and the camera's exposure is determined by its internal exposure measurements. If you are shooting sky flats or t-shirt flats when the sun is setting or rising this can help to provide some consistency in brightness for a series of exposures taken over time.

When I was actively imaging I used an artificial light source so the brightness was fixed. I initially used AV-Flat to get an the camera's idea of what my exposure should be and then switched to Manual and adjusted that exposure to shift the histogram to where I wanted it to be. Then I used that exposure for my flat frames going forward.

I hoped this helps.

Good idea, it's true that in AV Flat mode you get the histogram in the centre, but how do you know if it's better a bit brighter or a bit darker, I've never understood.

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23 hours ago, admin said:

On most camera models, you have to turn the dial to M or Av for AvFlat.

On the higher end camera models, BYE can set the dial mode programmatically, and with these cameras, you don't have to change the dial manually.  There is only one way to find out... try it and see if your camera works without touching the camera.

Now that you mention it, I think that one night, I heard the "whine" of the camera. hehe, but you're right, there's no better way to find out than to try it out in situ. 😁

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14 hours ago, s3igell said:

Remember, for Flats you need to keep the same Aperture as you shot the Lights.  Otherwise, the change in Aperture will effect the Vignetting - voiding one of the main purposes for the Flats.

I know, if you connect the DSLR to a telescope, you can hardly change the focal length, it's a different matter if you change the focal length of a lens, but on a telescope you can't change it easily unless you manually change the diaphragm with a smaller cap. I think the most important thing is not to move the orientation of the camera, nor touch the focus at all, everything must be the same as in the captures.

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