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Well, there is obvious difference between the two - one without filter has much higher average signal level in the sub: I assume that these are taken successively and that conditions are pretty much the same? Do you have calibration frames for them? At least darks? That way we can actually estimate SNR difference in some part of the image. In the mean time I can estimate gradient (not very precise as there is vignetting) in each image and compare them These are gradients "normalized" one against another - this shows that one without filter is much larger and in comparison, one with filter is almost no gradient at all - it just looks like gray background (but in reality, there is a bit of gradient as there as well) So first iteration of gradient estimation for filtered version gives about 61ADU of difference between brightest and darkest part of gradient. While no filter version has 137ADU gradient. Btw - these are gradients of binned version of the image - that means R, G and B data combined / added together. If you like, I can do comparison of each channel for you, but I'd rather do that on calibrated subs as it makes more sense.

Barlow will have two distinct effects on eyepiece - regardless of positioning. 1. Will increase magnification - and hence reduce exit pupil as exit pupil is aperture divided by magnification 2. Will increase eye relief of eyepiece. Difference of using barlow before and after diagonal is in barlow magnification. Barlow magnification depends on its focal length and distance between barlow element and focal plane. Larger this distance - more magnification barlow gives. If you place barlow before diagonal - you are adding another ~80mm of optical path between barlow and eyepiece - that means significant increase in magnification. I highly doubt that it will only make x2 barlow act as x3 barlow. I think it will be closer to x4 We can do calculation on a example barlow to see what sort magnification change will diagonal make. Say we have barlow like this: Based on this image, I estimate barlow element to eyepiece distance to be around 50mm. Barlow formula is: Magnification = 1 + distance / focal length This is x2 barlow this means that it has focal length of about: focal length = distance / (2 - 1) = 50mm Here are optical paths of some diagonals: We can safely say that using barlow in front of diagonal mirror will result in distance increase of about 80mm, so it will be 130mm (80+50) instead of 50mm. Magnification = 1 + 130 / 50 = x3.6 As shown, magnification is probably closer to x4 then it is to x3 in that configuration. That is one reason you are seeing more floaters. Second is extended eye relief. With 5mm eyepiece - you have 0.5mm exit pupil - but it is concentrated in a single spot: In above diagram - exit pupil is 0.5mm and as such it only covers small part of your pupil. However, if exit pupil is significantly shifted - like when eye relief is pushed back, you'll get into this situation with normal eye positioning: You still won't experience blackouts because exit pupil is still 0.5mm and even if you have 6 of them lined up (or rather not still merged into single) - it will be 3mm wide - so you'll be able to see without blackouts - but much larger area of your pupil will be illuminated. This simply changes how light hits floaters inside your eye and can make them more visible. People reported seeing floaters more with barlow lens and less in wider AFOV eyepieces.

Not sure what the problem with your DSS version was - but here is what came out of mine (after a bit of stretching in DSS): Version that I was using: 4.2.5 Settings: I changed to no background calibration since you seem to be using subs of different temperature (is your camera cooled?) - at least according to their names. In any case, here is 32bit float point fits for you to try out: stack.fits

Don't be so disheartened. You don't have many lights, right? How about uploading those (you can either zip them or maybe use google drive or something) - and I'll try stacking those in DSS to see if I can figure out where the problem is?

That again is normal - ASI533 is the most sensitive in green and you need to color correct the image. Again, Siril will do that for you - it won't do full color correction - but will scale R, G and B according to stars in the image. That will be sufficient to provide you with nice color and neutral cast.

If you think about DSO imaging - well, good guiding / poor guiding - that will over sample. Simple truth is - seeing won't allow for such resolution. Planetary & lunar type / lucky imaging works differently - it beats the seeing by using very short exposures around 5ms or less. It effectively freezes the seeing and while view is distorted - it is not "motion blurred" additionally. Barlow is good option for those, but for DSO imaging - you are already up there without barlow.

This is highly strange. No, subs are fine - at least, they appear fine. Here is single sub that you posted and I just made it mono and stretched it: There is simply no effect visible - sub looks really nice (except for focusing issue - do pay attention to fix your focus). It is stacking that is lacking (rime?). Try Siril for stacking. I got recommendation to try it out and it really looks ok (still haven't downloaded the latest version).

Just saw your screen shot again - you are using 4.2.2 version I have 4.2.5 version. Maybe try to update to latest version as well - 4.2.6? In the mean time, if you want to keep 4.2.2 version - maybe try one more option if above does not work - check this checkbox as well: I don't have that option in 4.2.5 so it has been removed - maybe that is culprit?

What version of DSS are you using, and can you try to use these settings: I'm guessing that you are not using any calibration files, right? In that case, dark flat and bias settings should not be important, but if you using them - just set everything to average as well.

Ok, something is seriously wrong with DSS and the way it stacked the data. Single sub is just what I would expect. Here is histogram of it: There are like three normal peaks - red, green and blue peak as this image is not debayered so contains all three color pixels. But stacked image is sooo strange. Background is perfect, here is green channel: It is nice and uniform noise - looking just beautiful If I do histogram of just that "part" of the image - it looks wonderful: Just as it should. But if I examine actual nebulosity - everything falls apart. Everything except background is highly posterized: Not only that - histogram looks very weird as well: So it is not perfectly posterized - with single spikes every so often - it has some very strange repetitive patterns. I'll try now looking at DSS file you included - although that is "encoded" so I will take me some time to figure out what each number means as option.

What DSS settings are you using and can you post 32bit floating stack for inspection - to see what might be the problem?

Did you by any chance shoot it in 8bit format? In Nina, you should be able to choose what sort of format camera produces. There are two different formats in which images are stored - 8bit and 16bit. Posterization will arise from shooting in 8bit format.

Try saving as 32bit floating point instead of 32bit integer?

Now stack your image and save it as 32bit TIF or Fits after stacking. Open in gimp and do simple 3 point level stretch to start with. Step 1 - do a round of levels - move top slider until you start saturating the target (don't saturate it - back off a bit). Apply levels. Step 2 - do another round of levels - this time move middle slider left - to bring out faint stuff. Don't worry if background becomes bright. Don't over do it - you don't want the noise to show too much. Again apply. Step 3 - move left slider to the base of histogram. This sets black point / restores background as dark.

That is sort of normal. When you capture data it is linear. You can preview it debayered and stretched - like Nina is showing you - but data is still linear and not debayered - as DSS is showing you. Make sure you have debayering turned on in DSS to produce final color stack and process stack in image processing app like gimp once you are done stacking - and it will look again like one in Nina - but with more detail and less noise.

Those are too long exposures. Cut them down to say 5-6ms instead of 18-22ms You can image for up to 5 minutes without having to worry about derotation and stuff. If you use AS!3 it will handle a bit of planetary rotation in that time frame. Ideal sampling rate for 2.9µm pixel size is F/12 - so you don't really need barlow with ASI462. Use extender to place camera about 10cm from the back of the scope. Focal length and correction of cassegrain scopes depends on distance between mirrors - scope is usually optimized to be used with prism and that adds about 10cm of optical path.

DSS has feature called groups - where you can group your files. As soon as you add files to one group - next "tab" appears so you can add another group of files. Add all files from first night into Main group and add all files from second night into Group 1 Files in group should be processed with calibration files in the same group - files from all groups should then be stacked together (I never used this feature myself - but I think that is how it will work).

Indeed, as @Ags mentioned - if you are interested in planetary and lunar there are a few things to consider. 1. For planetary, there is something called critical sampling rate / critical resolution. This means that you should not "zoom in" further than this as it makes no point to do so - you won't be able to record any additional detail as simply - telescope will not resolve it. There is limit to how much telescope will resolve and that depends on aperture. ASI533 has 3.75µm pixel size and critical sampling rate is achieved at about F/15 (it depends on wavelength of light used, and we usually use green light around 500nm to get this value). This means that you should not use stronger than x3 barlow lens on your 150 F/5 newtonian 2. You are using fast newtonian and such scopes have rather small diffraction limited field. As soon as you move away from optical axis - coma will start to increase. You need to use coma corrector for larger sensor if you do DSO imaging - but for planetary imaging coma corrector is not good - as it introduces spherical aberration on axis. For planetary imaging you want best sharpness possible. This means that you won't be able to use whole ASI533 sensor to image the Moon and planets - you'll need to use only central portion of it by using ROI - region of interest. Coma free field in newtonian is given by this expression: from: https://www.telescope-optics.net/newtonian_off_axis_aberrations.htm In F/5 scope that would mean - ~1.39mm or about 2.8mm diameter. If you add x3 barlow - that gets magnified to 8.34mm - or about 1/2 of 16mm diagonal of ASI533. For lunar - use only half of the sensor if you use x3 barlow. For planetary - use just part of sensor that fits and keeps the planet in FOV - like 640x480px, as that impacts achieved FPS 3. You can use barlow element (not telecentric lens - you can't do this with telecentric) - to dial in magnification. Move sensor away from barlow element - get higher magnification, move closer to sensor - get lower mag. You can dial in how much magnification you want (just be careful that coma free field is always 2.8mm diameter to start with - use x2 barlow and you can only image 5.6mm diameter without coma) 4. Baader VIP is the best barlow to use for imaging. APM has x2.7 coma correcting barlow - which is good option for lunar as it will extend usable field. But you can use simple GSO x2 barlow element as well, it won't make great difference on image quality (much more depends on other factors like collimation of the scope, seeing, way you capture and process and so on) in the end, don't use barlow for DSO imaging. Although it may seem that you'll get better framing and get closer in when using barlow - and that you can offset that with longer exposure, with DSO imaging similar thing holds as with planetary - there is limit to how much "magnification" you can use. In DSO imaging it is expressed in arc seconds / pixel - or pixel scale, and you want to stay above 1.2-1.4"/px with your setup. You are already at 1.03"/px with ASI533 and 750mm FL scope - you are already slightly over that sky imposed limit. Using higher sampling rate / resolution will simply result in "zoomed" in - but blurry image devoid of detail when you look at it at 100% zoom level.

Yes - stack all subs together No, don't mix calibration subs. Calibrate each set of subs with their respective calibration files.

Do simple three step stretch of your data 1. Step 1 - use right level slider and bring it down until you start to saturate parts of your target - then back it off a bit. You want to move it down as much as you can without saturating core of your target. Apply change 2. Second step - use middle slider in levels and bring it left / down again until you are happy with how your target is exposed. In this step don't worry if background gets too bright. Just don't push your data too hard for noise to be obvious. Again apply change 3. Third step - move left slider / black point again to the foot of histogram. This time histogram will be broader and this will be easy to do.

That will mess up a bit things in DSS. You have option to tell your Canon what to save. It is somewhere in menus, on my Canon, I have three different options: - Jpeg only - Jpeg+Raw - Raw only It can be either like this: Or like this: Where you select quality / size and if you want to shoot it for each raw and jpeg

It looks like you have some passing high altitude clouds in one or several of your subs. You should inspect them. Another possibility is that DSS messed up calibration somehow (it sometimes does that - and that it clipped your red channel - leaving patches of red light around the frame - this happened to me several times). You should also try stretching your data to see what is really there. When you stack - you are creating high dynamic range data unlike single sub - and you should stretch it to show all the details. As far as using longer exposure on your EQ6R Pro - that depends on the mount. Not all mounts behave the same although they are built to same specs - manufacturing errors create variance between specimens. Maybe your mount is good enough that it can handle 30s exposures with only minimal frame rejection - maybe it can do only 15s. You won't know until you try. Just be aware - longer you go - you'll need to discard larger percentage of frames - but image in given time (total time of subs you kept) will be better.

DSS has background calibration feature and depending on what you select for it - it will produce different background. In any case, having purple background is no issue if you set black point properly for your image. You can do that by selecting each of R, G and B channels respectively and setting left levels slider just at the base of histogram on left side, like this:

It is very hard and next to impossible to digitally solve such issue on whole image. Although it is easily seen on stars - this sort of blur affects whole image. You can always stop down your lens a bit - that tends to solve some of such issues. Another option is to get better lens - one that is sharper / has less aberrations. Third option - one that is most involved is to use longer FL better quality lens - or even better - small scope that is properly corrected and diffraction limited - and make mosaics to get really wide field shots of the sky. This option is really involved as it requires you to take numerous shots - and then process them in particular way - like mosaic stitching that is by no means easy on wide field as there are geometric distortions in the image (Microsoft ICE does good job of this but it is no longer available for download from Microsoft download site). For example, in order to create equivalent image to 28mm lens with scope like this: https://www.firstlightoptics.com/william-optics/william-optics-redcat-51-v1-5-apo-f49.html Would require about 81 exposures / panels and 9x9 mosaic. Another good lens that you can use would be this one: https://www.samyanglens.com/en/product/product-view.php?seq=311 With that - you would need only 9 panels and 3x3 mosaic. Bonus would be shooting at F/2.8 (F/1.4 and F/2.0 are a bit soft for astronomical use).

I find my 8" F/6 dobsonian really comfortable to use in seated position. I'm also about 6'1" - but that does not make a difference when seated if you get observing chair that is adjustable. 10" F/4.7 has same focal length and same tube length (give or take) as 8" F/6 - so using it would be the same. Even using 12" (1500mm FL) is doable in seated position if you have height adjustable chair.