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 Post subject: The Moon
PostPosted: Tue, 30-01-18, 11:14 GMT 
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There was a very bright (almost full) moon tonight, so I took a couple of shots.

It was so bright, it was necessary to reduce the exposure quite a bit in order to avoid all the detail being washed out by glare. In reality it was much much brighter than you see in the shot below.

It was also a very hot day here so even at 11pm there was still a lot of heat coming off the land which probably didn't help at all with the sharpness. Anyway, here's the best I could do under the circumstances...
Attachment:
_DSC0355_200%.jpg
_DSC0355_200%.jpg [ 103.69 KiB | Viewed 1303 times ]


This has been cropped and resized by a factor of 2, with a little un-sharp applied (~5%), and then a bit of a boost in brightness to restore some of the original naked eye brightness.

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 Post subject: Re: The Moon
PostPosted: Tue, 30-01-18, 12:15 GMT 
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No bad Chuft. Could you describe more accurately your photo equipment? Do you have a chasing mount? What ISO do you had set? Indeed the "sawtooth" rim could be ought to bad seeing.

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 Post subject: Re: The Moon
PostPosted: Tue, 30-01-18, 21:37 GMT 
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Hi Fenerit,

The moon is bright enough that no special equipment is necessary because exposure time can be quite short. So no tracking mount required. That's usually only needed for dimmer objects like galaxies which require long exposures.
(I did however use a monopod, though probably not really necessary at the shutter speed used.)

On this occasion it was, to coin a favorite street photographer's saying, a case of "f8 and be there".
ISO would have been 200, and I think shutter speed was 1/400th.

Camera: Nikon D300 @ 200mm focal length.

CORRECTION: I checked the EXIF data and the image above was in fact:
ISO200, F/10, 1/1250th @ 135mm

Unfortunately, there's total cloud cover here now, so I'm unlikely to get any shots of the Super - Blue - Lunar Eclipse tonight.

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 Post subject: Re: The Moon
PostPosted: Wed, 31-01-18, 9:08 GMT 
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Thanks. You must try to stack several images together, although a common tripod in this case should be preferable for stability and pointing either. here a freeware stacker and align program.

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 Post subject: Re: The Moon
PostPosted: Mon, 05-02-18, 12:40 GMT 
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Yes, stacking several images really improves the result and reduces a lot of noise.
This is an example of a moon image I took with a Nikon D7200 on a very basic Newtonian telescope (152/750mm, i.e. 750mm focal length). I don't remember the exact ISO (probably 200) and exposure time settings, though.


Attachments:
File comment: Moon, stacked in Registax, with some wavelets sharpening and post-processing in Darktable
Mond-2017-08-06-Registax-wavelets2_dt.jpg
Mond-2017-08-06-Registax-wavelets2_dt.jpg [ 554.3 KiB | Viewed 1208 times ]
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 Post subject: Re: The Moon
PostPosted: Tue, 06-02-18, 11:54 GMT 
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That's awesome. Do you have imaged some DSOs also?

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 Post subject: Re: The Moon
PostPosted: Tue, 06-02-18, 12:23 GMT 
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Yes, I have :DD


Attachments:
File comment: M31 - Andromeda Galaxy
Stack of 93 images, ISO400, 45sec exposure time each

M31-Andromeda_2017-10-16_(93x45s-ISO400)_dt.jpg
M31-Andromeda_2017-10-16_(93x45s-ISO400)_dt.jpg [ 1.36 MiB | Viewed 1187 times ]
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 Post subject: Re: The Moon
PostPosted: Tue, 06-02-18, 12:56 GMT 
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schreiberste,

Thanks for this great shot! But M31 was not taken with your "very basic" 6" telescope, right? The star imaging in the image periphery does not look like from a simple parabolic mirror ;-), but (because of your perfectly round star images) rather from a wide angle Schmidt camera...

Actually, since many years I own a motorized 8" Celestron (Schmidt Cassegrain) telescope. Of course, with this size one sees more details on the Moon, too (provided the optics is 1st class...). Since the latter is somewhat complex in my case, aberations (and frustration) are not uncommon...

Before the Celestron I only had one of these cheap Japanese 4" Newtonians with a wooden tripod. But then I had that mirror refigured by a "famous" Swiss mirror maker for < 100 SFR. The result (i.e. resolution) turned out simply breathtaking, despite the mirror's relatively small size.

For the Moon and the planets, the sensation of imaging quality is superior to the 8"!
For DSOs the 8" is clearly superior.

Cheers,
Fridger

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 Post subject: Re: The Moon
PostPosted: Tue, 06-02-18, 13:21 GMT 
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t00fri wrote:
Thanks for this great shot! But M31 was not taken with your "very basic" 6" telescope, right? The star imaging in the image periphery does not look like from a simple parabolic mirror ;-), but (because of your perfectly round star images) rather from a wide angle Schmidt camera...


Yes, it was. The used instrument was this one:
https://www.astroshop.de/omegon-teleskop-advanced-n-152-750-eq-300/p,43622
(I hope the shop link is OK, please just edit this, if not...)
In addition, I added a simple motor for tracking (RA axis only, unfortunately), no auto-guiding.
The mount is so bad and has such a strong periodic error, that the 45 seconds exposure time are really the maximum, and there is still a huge rejection rate - i can mostly just get one somewhat sharp picture from about 10 captured images.
There was a coma corrector in place to help with the stars in the image periphery.

Grüße,
Steffen


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 Post subject: Re: The Moon
PostPosted: Tue, 06-02-18, 17:48 GMT 
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Beautiful!
t00fri wrote:
schreiberste,

Thanks for this great shot! But M31 was not taken with your "very basic" 6" telescope, right? The star imaging in the image periphery does not look like from a simple parabolic mirror ;-), but (because of your perfectly round star images) rather from a wide angle Schmidt camera...

Fridger

I see spikes on the most huge field stars, this is a feature of the Newtonian reflectors having the secondary mirror's spider. I think shouldn't possible to frame out the whole M31 within the C8... The visual back of C8 is 31.75mm (1.25inch). At this field stop you can achieve: (57.3x31.75)/2032 = 0.89deg. M31 is well above 3 degrees.

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 Post subject: Re: The Moon
PostPosted: Tue, 06-02-18, 20:41 GMT 
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schreiberste wrote:
Yes, it was. The used instrument was this one:
https://www.astroshop.de/omegon-teleskop-advanced-n-152-750-eq-300/p,43622
(I hope the shop link is OK, please just edit this, if not...)


Thanks for your further info about the used telescope. The link worked fine.
While the imaging is --no doubt-- pretty good, I had previously overlooked the expected fan-shaped comatic aberrations of parabolic mirrors in the periphery of the image. Here is a 4 times magnified portion:

Attachment:
M31-Omegon_telescope.png
M31-Omegon_telescope.png [ 193.83 KiB | Viewed 1166 times ]


But anyway without such excessive magnification, hardly any aberrations become visible despite your instrument's relatively short focal length and wide angular view...
Apart from such unavoidable distortions of parabolic mirrors, you were lucky with buying this particular exemplar ;-)

Anyway, your main point seems rather to demonstrate the gain in quality by superimposing a number of identical photos. This is impressive, indeed.

Cheers,
Fridger

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 Post subject: Re: The Moon
PostPosted: Tue, 06-02-18, 21:00 GMT 
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fenerit wrote:
Beautiful!
t00fri wrote:
schreiberste,


Thanks for this great shot! But M31 was not taken with your "very basic" 6" telescope, right? The star imaging in the image periphery does not look like from a simple parabolic mirror ;-), but (because of your perfectly round star images) rather from a wide angle Schmidt camera...

Fridger

I see spikes on the most huge field stars, this is a feature of the Newtonian reflectors having the secondary mirror's spider. I think shouldn't possible to frame out the whole M31 within the C8... The visual back of C8 is 31.75mm (1.25inch). At this field stop you can achieve: (57.3x31.75)/2032 = 0.89deg. M31 is well above 3 degrees.


Yes, Fenerit, that's true of course. 1 degree (~ two full moons) is about the undistorted non-shadowed limit for 1.25" diameter output. As you sure know, there are special devices that enlarge the max. C8 field somewhat: like 2inch super wide-angle eyepieces, a focal reduction lens, along with a custom enlarged visual back for example. But then again, since the C8 is a Schmidt-Cassegrain design rather than a coma-free pure Schmidt camera, comatic aberrations hit again unavoidably for larger visual backs and/or focal reduction...

Hence with a C8 field we should better stay below a full-size M31. Yet in the sky above us, it is easy to find many smaller sized objects ;-)

Cheers,
Fridger

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 Post subject: Re: The Moon
PostPosted: Tue, 06-02-18, 22:13 GMT 
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IMHO, that image magnification crop shows what a good coma corrector inside the focuser can do with reflectors. Without it the stars would have waaay a lot of comatic shapes that no stacking/deblooming program could correcting. Moreover there is not field distortion, so I ask schreiberste whether the M31 image has been cropped at margins or a field flattener has been used. That scope has 2inch focuser: if the camera adapter is of the same size, the field stop is about 46mm and the true FOV should be about 3.5 deg.

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 Post subject: Re: The Moon
PostPosted: Wed, 07-02-18, 8:06 GMT 
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fenerit wrote:
Moreover there is not field distortion, so I ask schreiberste whether the M31 image has been cropped at margins or a field flattener has been used. That scope has 2inch focuser: if the camera adapter is of the same size, the field stop is about 46mm and the true FOV should be about 3.5 deg.

Well, as I told you, my mount is quite bad. It is shaking so much, that I get offsets between captured images of sometimes more than 500 pixels (!!!) on the 24MP sensor.
So in the end, I get a lot of images that are - in a way - shaking around the center.
This has the effect of potentially increasing the FOV, as after aligning the images I can create a kind of panorama or mosaic. On the other hand, only areas that really got a lot of images and therefore exposure time are usable, so I have to crop noisy borders after stacking.

No field flattener was used. The camera is adapted using the coma corrector and a T2 adapter, which reduces the 2inch a bit.


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 Post subject: Re: The Moon
PostPosted: Wed, 07-02-18, 8:15 GMT 
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For comparison, this is an older image taken without coma corrector and with a Nikon D90.
151 exposures of 30 seconds each.

by the way - @chuft-captain: sorry for hijacking this thread :°
Maybe we need a new one for astro photography?

Steffen


Attachments:
File comment: M33 - Triangulum Galaxy
M33_Dreieck-2017-01-19_(151x30s_dss).jpg
M33_Dreieck-2017-01-19_(151x30s_dss).jpg [ 2.57 MiB | Viewed 1155 times ]
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