Dan_Paris

Good capture well done ! I like this FOV with the two galaxies (Bear's claw and Needle) so different form each other

clear skies,

Dan

Thanks Geof !

clear skies,

Dan

If you want something reliable and fuss-free, for about 2000£ you can get a second-hand Takahashi EM200 Temma (at least in France, presumably also in UK).

You should maybe tell us first which kind of DSO you want to image. A small APO is fine but restricted to large nebulæ and clusters, and a few galaxies. If those are on the top of your list this is a good choice, otherwise you should look for something else. And as the previous posters said, it is a poor choice for planetary imaging.

1 hour ago, ONIKKINEN said:

Very nice, although cant help but notice that your stars on the left side of the image are teal/green?

Thanks for noticing it, I actually did a stupid mistake : I forgot the red channel for the stars layer 😅  OP is corrected.

Hi,

after M81 imaged earlier this month  I had three clear nights this week for M82, despite the nearly full moon. The first two nights were devoted to H-alpha (18 hours in total), with rather bad seeing. The t I did the LRGB (6 hours of L and 3*40 of RGB) with much better seeing (2" FWHM after stacking).

Here is first the mosaic with M81 (right-click for full resolution):

A crop on M82:

and on M81 (image already posted)

Thanks for looking and clear skies,

Dan

Edit : stupid processing error corrected (thanks @ONIKKINEN !)

Equipment

200/800 custom Newtonian astrograph with Romano Zen optics and carbon fiber tube
AP900 CP4 mount on Losmandy HD tripod
TS 2.5" Riccardi-Wynne corrector
ZWO LRGB filters
Guiding : ZWO OAG + ASI120mm mini + AsiairV1

Bortle 7/8 backyard in Paris' suburbs

Very detailed view of a photogenic galaxy, nicely done!

Nice view of this beautiful part of the sky with good colors! I think that your sky background was leveled a bit too much during the processing. This area is full of dust, so the background should not be as uniform.

Thanks !

On 08/02/2023 at 00:24, ONIKKINEN said:

. If only good seeing weren't so rare!

and unpredictable!  More than once, I set up everything in the garden for nothing...

excellent, the structure of the nebula is well displayed!

Really excellent level of detail given the equipment used, congratulations !

Nice framing and processing Göran. Did you have an AF motor on your Samyang?

Thanks a lot Maximidius!

15 minutes ago, Maximidius said:

Your newt looks to be extremely well collimated. 

It was actually the first image I took after having dismantled completely the telescope for cleaning the mirrors. Thankfully, the Catseye tools are precise enough to get the collimation spot on without further tweaking.

Hi,

last week I had a  night of rather good seeing  over Paris for the first time since mid-September  (median FWHM 2.04" after stacking), with low transparency and invasive moonlight however.

I acquired 4 hours of luminance on M81 with an ASI183mm and my 200/800 Newtonian astrograph. The RGB data is from last year with an ASI1600mm.  The resolution is much better than in last year luminance, thanks to the tighter sampling of the ASI183 compared to the ASI1600 (0.65"/pix vs. 1"/pix)

Here's the result (right click for full resolution):

Clear skies,

Dan

Technical details

200/800 custom Newtonian astrograph with Romano Zen optics and carbon fiber tube
AP900 CP4 mount on Losmandy HD tripod
TS 2.5" Riccardi-Wynne corrector
ZWO LRGB filters
Guiding : ZWO OAG + ASI120mm mini + AsiairV1
Luminance : 240 *60sec with the ASI183mm
Chrominance : 40*60sec for each R, V and B filter with the ASI1600mm
Conditions : Bortle 7/8 skies in Paris' suburbs (20km from the Eiffel tower), decent seeing (2.04" FWHM), gibbous moon, lot of humidity
Processing with Pixinsight

Thanks @alpal ! I'm now thinking about making a bigger one 😉

1 minute ago, vlaiv said:

this is enlarged with use of nearest neighbor interpolation - stars are not "pixelated" even when undersampled - that is artifact of interpolation algorithm.

Yes it was enlarged in the viewer if this is what you mean. Otherwise I barely see anything on my small-pixels screen !

2 minutes ago, vlaiv said:

What do you use for FWHM measurement? Different software will give you different results.

I use the FWHMEccentricity script of Pixinsight. I believe it is rather robust, and measurements are done over the whole image, not a single star.

3 minutes ago, vlaiv said:

I can't say because you used nearest neighbor interpolation.

This was with Lanczos.

3 minutes ago, vlaiv said:

This does not look like undersampled star. It has at least 5-4px in both width and height. I don't know how much data is stretched and where is FWHM - but you only need ~1.6 px per FWHM to properly sample the star.

FWHM measurement on this rescaled image gives 1.07 pix.

I just did a simple experiment with the linear stacked image of the quintet.

The original image has a median FWHM of 1.75".

If I resample at 50% and then back to 100% (using Lanczos algorithm) the FWHM raises to 1.97".

16 minutes ago, vlaiv said:

but not as simply as "half that value".

If I take 1.8" as an ideal sampling rate, as you suggest,  stars look rather undersampled ?

1 hour ago, vlaiv said:

Ok, I know something might look one way or another, but that is why we have science.

The median FWHM on this image is 1.75".

According to Shannon's theorem, you should sample at least at half than that, i.e. 0.875". But since it is two-dimensional data and that the pixel are square, to get adequate resolution along the diagonal you should aim for 1.75/(2*sqrt(2))=0.62". This is also science.

1 hour ago, vlaiv said:

How can we tell that it contains all the data in the image above? We can simply enlarge that reduced version and we will get the same image as base line above - without any loss of detail:

How did you enlarge ? Most rescaling algorithms introduce some sharpening.

And for an accurate comparison  one should rescale  the raw files before aligning and stacking them (for the same reason that drizzle integration allows to resolve sub-pixel  details).

What I know experimentally is when I changed my camera from the ASI1600 (1.04"/pix) to the ASI183 (0.66"/pix), there was an obvious improvement in resolution (without changing the telescope). I have taken tens of images with both so I am pretty confident that this is not due to the atmospheric conditions.

10 hours ago, vlaiv said:

Both of the scopes will require binning. I'd say that RC8" will require x3 most of the time on ASI294 (native / not unlocked) - with 4.63um pixel size. Natively it will give ~0.59"/px and that is oversampling. Even if you bin x2 - for 1.2"/px, that will also be over sampling 95% of the time. 1.8"/px will be good sampling rate most of the time.

I tend to disagree with that. To image galaxies and small stuff, a sampling around 0.6" / pix should actually be the goal to achieve (with a mono sensor, I have no experience with OSC cameras). For a given camera, the ideal focal length is the one that gives such sampling in bin1 (shooting in bin2 with CMOS sensors is, in my opinion, a big waste of FOV and money).

Under light-polluted and rather mediocre European skies (average seeing 1.8" to 2.5"), a sampling of 0.66"/pix gives me this with a 200/800 Newtonian:

And that:

which look adequately sampled.

If your average local seeing is really bad  (above 2.5") and  not compatible with such a sampling , in my opinion galaxy imaging would be a rather frustrating experience.

Regarding the scope choice, Newtonians are much easier to collimate than RCs as there is only one optically active reflecting surface, and can be done indoors with the right tools. There are also easier to tweak and improve if needed (a mass-produced newt can be turned into a premium astrograph with the right upgrades). A 200/800 is rather compact and light, but you would need a smaller pixel cameras to reach the adequate sampling (an IMX183-based model)

Thanks  Mike and Adrian !

23 hours ago, CCD Imager said:

Great image! wait till you add Russ Cromans Blur XTerminator!!

I tried it, I found it more efficient on  small objects than big ones (but I have yet to try on M33),

clear skies,

Dan

I did not find the NP but I really like your image.

Lacerta is a very interesting part of the sky, with lots of nebulosity, dust and galaxies at the same time.

Really beautiful and colorful David!

On 12/10/2022 at 20:14, Ouroboros said:

I’m thinking of moving on up from my SW Evostar 80ED. I have in my sights something with more aperture (100mm, 130mm).  It will be used for imaging, almost certainly an astrograph, but must also be useful for visual.

According to your signature, you have a Skywatcher 200mm Newtonian. Why not upgrading it for imaging  (solid focuser and good coma corrector) ?

And also, which kind of objects do you want to image ? Large nebulæ or galaxies ?