Dan_Paris

Which ones ? The latest from today ?

Well, here a comparison with the bin2 image enlarged with Lanczos : To my eyes the difference in resolution between bin1 and bin2 is still obvious.

So here are some comparisons, using a set of 120 luminance frames (2" seeing, Bortle 7). For the left panel, the subs were binned down 2x before registration (to 1.32"/pix) while for the right panel the subs were kept in bin1 (0.66"/pix). I did exactly the same basic processing on both : BlurX, GHS, a bit of HDR, no noise reduction. The bin1 image is obviously more detailed, as one may have anticipated, while the difference in SNR is not obvious. To quantify the noise levels, the relevant comparison is between the stack of bin2 subs (left) and the stack of bin1 subs which is subsequently scaled down 2x (right), in linear state, with no processing at all: According to measurements (StdDev on the background) the right image has 7% more noise than left image (but is smoother in particular regarding star shapes). So indeed binning before stacking give a bit lower noise leveI on unprocessed image, I must concede that! An interesting question is whether the denoise algorithms work better with the bin1 images or the bin2 images (which have, in a sense, being already filtered for small-scale noise). Here is a completely unscientific comparison, with bin2 on the left and bin1 on the right, with no processing except NoiseX: The difference in detectivity of faint structure is rather small to my eyes. In any case, for me the significant resolution increase of the bin1 image is much more important than its possible 7% noise penalty (that could be compensated easily by shooting more subs).

Don't trust everything that you read and try for yourself 😉 I don't make an unsubstantiated claim as you seem to suggest but share my experience of several years of galaxy imaging. The resolution increase when I swap a camera with 1"/pix to 0.66"/pix was just plain obvious. And none of the serious imagers that I know personally shares your point of view. Btw I don't think that the link to a grossly overprocessed image is relevant for the debate 😉

My 200/800 Newtonian at dawn, after a night of imaging, in Drôme Provencale (not so far from @ollypenrice's place)

There's nothing wrong with oversampling (within reason), as long the level of read noise from the sensor is well below the photon noise from the sky background. There is no benefit in binning with CMOS cameras except that it demands less computer resources (storage and CPU) but they are cheap these days. If you want to adapt to seeing conditions rescaling the final processed image gives always better results. Regarding the ideal sampling you should first evaluate your seeing conditions, or more accurately what the combination of your seeing conditions and tracking accuracy allows you. My current setup (200/750 newt with ASI183mm) gives me 0.67"/pix which is a perfect match for my seeing condtions. Indeed the average of the FWHM values that I got on my luminance stacks this year (24 imaging sessions) is 2", i.e. three times the sampling (ranging from 1.46" to 2.6"). On those nights with good seeing my best subs are around 1.3" so I could sometimes benefit from a tighter sampling like 0.55". My previous camera was an ASI1600mm which gave me 1"/pix. It gave me clearly inferior results, resolution-wise. Instead of an 8" EdgeHD, you could consider a 200/1000 Newtonian with a Paracorr (effective focal length 1150mm), which gives an ideal sampling for 2" seeing. In those conditions it would give a larger FOV than the EdgeHD, without sacrificing resolution.

AstroPC Pro from Astro-gadget to replace my buggy ASIAIR Took ten days to arrive from Kharkiv in Ukraine, pretty remarkable given the circumstances.

Quite well actually, significantly better than Starnet v2 which leaves behind some faint spike remnants. An example with StarX : Btw refractors are not free from diffraction artefacts, I've seen many FSQ106 images with diffraction patterns from lenses spacers around bright stars...

Indeed. For visual you "just" need to ensure that the optical axis of the primary (reflected by the secondary) and the mechanical axis of the focuser intersect at the focal plane, in order to minimize coma in the center of the field. This can be ensured, for instance, by collimating on a star once rough alignment has been done. However for deep-sky imaging this is not sufficient. You need, on top of this, to have the optical axis orthogonal to the focal plane, otherwise tilt occurs. This cannot be assessed with a star test on-axis.

A heavily modded 200/800 newt, more details here Out of curiosity, you never had the same problem with this filter and the corrector of one of your refractor? It may be a faulty design of your coma corrector then. If you don't like spikes I agree that a newt is not a good option ! The mak-newt is an interesting proposition. A theoretical analysis of the SW 190 MN design can be found there : https://www.telescope-optics.net/commercial_telescopes.htm#most It seems well-corrected for moderate sized sensors (and spike-free !)

It is the Newton fault, but rather the filter fault, or a a shared responsibility between the filter and the corrector. According to the size of the reflection, it occurred approximately 50mm away from the focal plane. No mirror there. Here's a deep exposure with my newt including mag. 2.4 Phecda in the field, there's only a faint reflection in the upper-left corner :

It really depends on the type of imaging. For broadband imaging with a relatively fast telescope, especially with high levels of light pollution, you typically stack a large number of short exposures (for me, typically 300x60 sec for the luminance). In those conditions even a 12bit camera will give you far more than 16 bits of dynamic range at the end. For narrowband imaging, the number of frames is usually much less so the bit depth of the camera is more important.

I started imaging with a 200/800 Newtonian, in my experience collimation is not really a challenge. After three years of experience it won't be an issue. This is especially true is you use the right tools. I found that the Catseye tools are the best (but a bit expensive). It really just takes two minutes and can be done comfortably indoors just before taking the setup outside. What's nice with Newtonians is that everything can be upgraded easily to improve the performance: stronger springs for steadied collimation, flocking as you mentioned, new focuser, etc. At the end you can turn a modest mass-produced instrument into a truly premium astrograph. In my opinion Newtonians are the most suitable telescopes for general imaging with the current small pixel cameras. Their focal length in the 800/1200mm range are the perfect balance between FOV and resolution (you are seeing limited under most conditions while keeping a large field) and their speed allow to achieve a good SNR in a rather short time. But if you are really not into tinkering this may not be the right type of telescope for you (for me it is part of the fun). Or buy an already upgraded OTA like an ONTC from Teleskop Service or a Lacerta Fotonewton from Teleskop Austria. A RASA 8 is not suitable for monochrome cameras and I doubt it can achieve the same resolution than a 8" newt. Mine gives 1.3" stars across the field when the seeing cooperates.

Thanks Olly. That's a dream region for deep sky lovers indeed.

Thanks a lot @peter shah, @mackiedlm and @ollypenrice ! Yes, 20km precisely. Near Marseille ? I guess the Peltier of your cameras have a harsh time these days...

Thanks Colm ! clear skies, Dan

beautiful version with a spooky feeling that I like !

I did not know this object, wonderful image Peter

great image Adrian!

Hi, sorry for not being original but this is one of the showpieces of the season! This is actually a project that started last year. My plan was to do a two-panel mosaic of NGC7331 and the Quintet but unfortunately seeing was very bad for NGC7331 in 2022. Last night the seeing conditions were rather good over Paris so I shot new luminance data. Quality of both panels is now roughly the same: 1.9" vs. 1.75" in terms of FWHM and m=21.1 vs. m=20.9 in terms of limiting magnitude. For each panel there is about 5 hours of luminance and 30 min for each color filter, shot from my Bortle 7 backyard near Paris. The setup consists of a 200/800 Newtonian astrograph on an AP900 mount with an ASI183mm mono camera. Here's first a crop on NGC7331 and friends A crop on the Quintet And finally the mosaic (right click for the full-resolution, which worth a visit): clear skies, Dan

I have LRGB filters from ZWO (31mm size) I don't see reasons to complain. No haloes, and parafocal enough that I don't need to refocus even at f/4 with a tight sampling (0.66"/pix). I don't have a full SHO set but I had a Baader 7nm H-alpha which produced big haloes. I replaced it with an Antlia Edge 4.5mm which is much better.

Hi, based on my experience (under Bortle 7/8 skies) Light pollution filters are useful for emission nebulæ (some others will advise you better about which filter model to choose for this application) but not really useful (I would even say counterproductive) for galaxies, globular clusters or reflection nebulæ. In those cases the proper way to fight against light pollution is to shoot rather short subs without any light pollution filter (in my case, 60sec at f/4) and to stack many of them (in my case, at least 200, often 300 or more). Light pollution implies a big penalty in terms of signal/noise ratio. To fight against it you'd like to accumulate as much signal as possible, a goal that you could accomplish in much less time with a mono camera than with a color camera. Color cameras work well under very dark skies, under light-polluted ones not so much.

Hello everyone, The galaxy NGC7013 is not far from the Veil Nebula in Cygnus. It is a rather unusual lenticular galaxy, with some characteristics of a spiral, about 40 millions l.y. from us. The field is interesting as it contains also some nebulosity that looks a bit like the Witch Head Nebula. This is a rather challenging object from my suburban Bortle 7 backyard. I imaged it last night with my usual setup (right-click for full resolution) : Thanks for looking and 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 ASI183mm (0.66"/pix) TS 2.5" Riccardi-Wynne corrector ZWO LRGB filters Guiding : ZWO OAG + ASI120mm mini + AsiairV1 Luminance : 240 *60sec Chrominance : 20*60sec for each R,G and B. Conditions : Bortle 7 skies in Paris' suburbs, hazy skies and decent seeing (2.06" median FWHM on the luminance stack) Stacking with Siril, processing with Pixinsight

Wonderful image! This nebula is high on my target list but I doubt my suburban skies would permit...

Hi, the face-on intermediate spiral galaxy NGC 6946, known as the Fireworks galaxy, is one of the few large targets in summer for galaxy addicts like me. It constitutes also a beautiful optical pair with the open cluster NGC 6939. The seeing was excellent at the beginning of the night (1.3") and worsened progressively. The median FWHM on the luminance stack is 1.8", allowing to extract interesting details from the galaxy. Due to the poor transparency and the light pollution (Paris' suburbs) the IFNs are challenging to bring out. Here's first the full field of view (right click for full res, it's worth it!) And a crop on the galaxy: Thanks for looking and 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 ASI183mm (0.66"/pix) TS 2.5" Riccardi-Wynne corrector ZWO LRGB filters Guiding : ZWO OAG + ASI120mm mini + AsiairV1 Luminance : 260 *60sec Chrominance : 20*60sec for each R,G and B. Conditions : Bortle 7/8 skies in Paris' suburbs, hazy skies and variable seeing (1.8" median FWHM on the luminance stack) Stacking with Siril, processing with Pixinsight