very first image - HelloWorld

[FrenchyArnaud]

I suppose the Moon is the HelloWorld of sky imaging. So here is my first image of the moon. I definitely do not post it to brag (open the pic and you'll understand why), but because it's my first step on a steep learning curve and this simple image raises a lot of questions.

The gear : 150*750 unguided + Sony Alpha 300. The sky was far from perfect, quite some high alt. mist.

First of, impossible to focus ! The focuser just does not far enough. I found out in here that it sometimes takes a barlow to be able to focus. That's because the barlow doubles the focal length rather than magnifying. And sure enough, I was able to get focus with the extra lens. 

 - Question 1 : is there any way to avoid the extra glass ?

But now here is the deal : 750mm*barlow*APS-C = 2250mm. At this focal length, the moon just does not fit in the FOV ! Its diameter just, just fits in the length of the frame, definitely not in the width. So I had to actually take 2 pictures in portrait framing, right and left halves, then stitch them by hand in gimp, ending up with a "square panoramic" if there is such a thing. 

- Question 2 : is there a trick to get part of the FOV back ? Apart from buying a full-frame camera ? 

I was willing to use the aperture mask to reduce diffraction and increase contrast. But with the mask, the shutter speed falls below 2s. Due to atmospheric disturbances, this means a single shot cannot be crisp - in other words, to get contrast and details you need to consider stacking. I tried with the moon filter, but it does not seem to improve things a lot - contrast is slightly better but barlow + filter = even softer image. And the soft but contrasted image does not look natural. So I ended up with no aperture mask, no filter, and a shutter speed of 1/25 to 1/50. Which is too slow in my opinion, because getting enough light is not the problem with the moon.

- Question 3 : is it possible at all to get crisp planetary images (the moon to begin with) in a single shot or is stacking the only realistic way ? 

I did, the same night, shoot the moon directly with the beercan lens at 210mm, f8-1/200. The resulting image is clearly, clearly sharper. However the moon is also about 1/12 of the total width of the image. There I am puzzled, unable to decide if the beercan is simply optically better, if the much higher shutter speed makes the difference, or if the size difference tricks my perception of sharpness.

Attached is a reduced version of the shot - the original is 3500*3500 (basically, the length of my APS-C squared). You will notice that the contrast is not great, and the image is really, really soft.  When reduced to 800*800, then it begins to look good - any closer to original size and it is like looking through an old dusty greasy window. There are plenty of identifiable features due to shear magnification but not a lot of details.

Any input will be welcome. 

 

 

 

[D4N]

1). Which scope is it?  A 150P?  Newtonian are notoriously stingy on back focus, you can change or modify the focuser or you can move the primary mirror up the tube.  This brings the focal plane further out but may mean you need extension tubes to focus with eyepieces.

The other thing you can do us use a planetary camera or web camera that can have its sensor closer to the focuser but this would have a smaller fov.

 

2). Pretty much as in 1 except the different camera bit.

 

3). Very difficult, stacking allows you to take the lucky best bits where atmospheric distortions have provided a perfect image and collect them all together to form one really good image.  It is possible to get great single shots but it requires very good seeing conditions or lots of luck.

 

Filters are normally only used for lunar imaging in the day when you can use a red or IR pass filter to filter out the sky.  At night you normally just reduce the exposure time to reduce the brightness.  The shorter the exposure time the better chances of getting a sharp image during moments of good seeing.

 

That is a good first image though and you did a good job of stitching the two together.

[cjdawson]

I think D4N has given all the advice that I could.  Except for one thing....

 

Bragging rights are allowed and in fact should be encouraged.  Firstly, it's a good effort at imaging, you've already understood the issues that have been presented by the attempt.  This would put a lot of people off, but instead you are rising to the challenge.   Kudos for that, and keep going