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My first DSLR arrives this week! Questions, questions, questions.


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20 minutes ago, Swithin StCleeve said:

This thread's been great, thanks everyone. I'm hoping there'll be a window of clear sky later (sun's out now), so I'll start with some simple moon shots. I'll put the camera on auto exposure and see what I get.

Hi

You want to set the camera to manual exposure. Low iso for the moon. Getting focus right is important :)

Louise

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Thanks, will do.

So when I set the low ISO, what does that make the camera do?

Shutter speed I understand, and aperture speaks for itself, but ISO, back when I had the darkroom, meant the speed of the film. The higher ISO the film had, the more receptive it was to faint light, as I remember. But with a DSLR, there's no film, so why the ISO?

I bet that's a really daft question.

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2 hours ago, Swithin StCleeve said:

Thanks, will do.

So when I set the low ISO, what does that make the camera do?

Shutter speed I understand, and aperture speaks for itself, but ISO, back when I had the darkroom, meant the speed of the film. The higher ISO the film had, the more receptive it was to faint light, as I remember. But with a DSLR, there's no film, so why the ISO?

I bet that's a really daft question.

 

In brief, with a dslr you have the electrical output of the sensor which is subject to in-camera electronic processing including amplification. Increasing iso increases signal amplification. That would be great but increasing the signal is accompanied by increasing the ever-present noise. There is an iso value which is the best value to use and which has unity gain. That varies by camera model but is usually around iso 800. In the case of the Moon, it's obviously a very bright object so only needs a short exposure - maybe only 1/250s or even shorter, which is an exposure you might use in normal daytime photography. In this case the read noise is less of a problem but with dsos which need long exposures, noise is an important consideration as you will need to do histogram stretches. I'd recommend reading a good text on astrophotography such as 'Making every photon count' - available from our sponsors :) 

Louise

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The Moon can be way bright it doesn't need light receptive boosting particularily in prime imaging.

Film in a DSLR is the sensor.

Astro imaging is pushing the camera in manual. The more you try/practice the more you'll get it right (I look at it this way) and there is no waste as the image is digital so no waste of film badly exposed.

The only waste is a clear sky.

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I set the scope up tonight and gave the camera its first try-out. I couldn't get it focused at all to start with, until I put the barlow in. Then I could focus, does that sound normal?
I'm useless, I couldn't figure out how to change the ISO (sorry Louise), so I just ended up shooting loads with different shutter speeds. This is about the best.
Comments anyone?

moon.jpg

I couldn't resist taking some pictures of Saturn, but they were pretty rubbish. You could see the rings, but I shouldn't have bothered really. I'll stick with the moon for a while, and read my camera manual to sort this ISO malarkey out.

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Thats not to bad for a first go.

To change the ISO there is a button on the top plate marked ISO.
Normally you should be able to hit the Q button to the right of the screen and cycle to the ISO as well.

If you using a Newt? some do not come to focus with a dslr, there is not enough inward focus travel.
You soived it with the Barlow method. :icon_biggrin:

The very best planetary images are done by shooting videos and stacking the frames, it's called lucky imaging.

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In one of your comments I read that you did not realize the importance of balancing. It is the most important part of the whole set up process! Especially for AP
So important that your camera should be  at the side of the counterweight bar, in order to get radial balance as well.

So, in fact you have three balancing directions:

1 Radial (the easy way to do this is to move the guiderscope or RDF opposite the focuser and have the focuser with camera pointing downwards, in the samne direction as the CW bar)
2 DEC
3 RA

Succes!
Waldemar

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