vlaiv

Don't use bias in regular workflow - you don't need them and they can cause issues (maybe even issues that you are seeing). Since you did not take flat darks (or dark flats - whichever way you prefer) - use bias that you captured instead of those. Btw offset of only 15 looks suspiciously low. Since you have bias subs - you can check if offset 15 is indeed adequate. Could you do following: Make a stack of bias subs only but use simple minimum stacking method, then run stats on it (min,max, average, stddev and such) and histogram and post those?

I don't know any company that does such a thing, but why not enlist help of fellow SGL members? Many people enjoy processing data, and all you should do is create a post with a link to your data and ask people to process it - I'm sure you'll get many different renditions of your target and you can select one to your liking.

Yes, and it works well. I've done it on short & fast ST102 F/5. I made couple of aperture masks, and did some testing. Even managed to take a decent deep sky photo without any blue bloat around stars - by using 66mm aperture mask and yellow #8 filter. Just be aware that putting aperture mask on will reduce maximal attainable magnification - good rule as always is aperture in mm x2. 80mm scope will be good for up to x160. Of course image will be dimmer. Btw, I've now got Evostar 102 F/10 and Baader contrast booster filter removes almost all CA while keeping things almost natural looking (there is small color shift). If you go for something like 70-75mm aperture mask, you will in principle eliminate chromatic aberration pretty much completely (CA index >5). Btw, here is "a study" for photographic purposes I did at a time with ST102: Rows contain same image, but stretched to different level (first one the most obviously as hot pixels / noise start to show). From top to bottom - no mask, no mask+#8, 80mm, 80mm+#8, 66mm, 66mm+#8, 50mm, 50mm+#8. Exposure times were scaled appropriately.

Just to throw in a wrench or two ... Since OP almost decided to go for Mak180, I'm wondering if this could be something worth considering: https://www.teleskop-express.de/shop/product_info.php/info/p10753_TS-Optics-8--f-12-Cassegrain-telescope-203-2436-mm-OTA.html As far as I know, Australia has a dealer of GSO equipment as well, so worth checking there for availability as it would certainly be more affordable then shipping it half way across the globe. Quick comparison: 200mm vs 180mm - more resolution and sharper image at lower magnifications (given same optical quality). Price about the same - slight edge for 8" Cass in TS pricing. Slight weight advantage for 8" Cass (7.5 vs 7.8kg). Much less of a dew magnet since no front corrector plate. Cool down time is consequently less in 8" Cass Probably better focuser as it has 10:1 reduction and does not cause mirror shift when focusing. CO size - Mak180 probably wins - I've seen figures around 30% quoted online - 33% for 8" Cass F/ratio and focal length - again +Mak180 as it is F/15 vs F/12 and 300mm additional FL - easier on EPs, easier to reach high magnifications. 8" Cass - diffraction spikes - might detract some people, better baffling of the tube - probably very small boost in contrast because of this.

Don't get AZ3 - I had that exact combo and later switched to AZ4 on steel legs. Very big improvement. AZ3 has couple issues that annoyed me quite a bit. Stiff to move telescope by hand (although there are adjusters - it is not very smooth mount). Slow motion controls needed rewinding after a bit of use - they are not 360 degrees but rather section of the circle so you when you reach the end - you need to move scope manually and "unwind" slow motion control back to middle (if you plan to pan around slowly) or all the way if it is only for tracking single object. Looking at zenith was next to impossible on that mount. If you want slow motion controls then AZ5 is better option than AZ4. With AZ4 it is pretty much only feature that is missing (and I believe AZ5 is slightly lighter).

Not very long I'm afraid. Two major things that you will be facing is periodic error and polar alignment error. Out of the two, I think that periodic error is going to give you more issues than polar alignment error. Let's run some numbers so you can get the idea of what sort of exposures will be attainable. You are imaging at ~ 1.6"/px, so let's set upper limit to 2px, or about 3" as maximum drift per exposure that will produce acceptable stars (a bit elongated, but still round enough). With regular polar alignment, you are looking at something order of 5 minutes of arc or PA error. In worst case scenario this translates to drift of about 1.3"/minute. Stock HEQ5 can have as much as 30-40" P2P periodic error. Since you've done belt mod, this tends to drop quite a bit, but it is still in range of let's say 12-14" P2P. Period of HEQ5 mount is 638s. If we assume perfect sine wave then max RA drift rate due to PE will be 4.13"/minute - in reality PE is never sine wave and you can expect it to have a bit higher drift rate at some point, but let's go with 4"/minute because P2P might be even less like 7-8". This shows that PE will be limiting factor, rather than PA error (unless you did a very poor job of polar alignment and error is something like 16 minutes of arc - which is quarter of a degree, so yes very large indeed). With drift rate of about 4"/minute you are looking at about 45s exposures. This is worst estimate, so not all frames will be distorted (it depends where on period of mount you are at the moment, what is the DEC of the target, etc ...). I think that you can use 1 minute exposures and expect to throw away something like 10% of frames if your target is close to equator. Higher up in DEC you can maybe do 90 seconds and still keep most of your subs.

Well spotted - I did not see it is in fact different mount. I guess freedom find is indeed handy - you can point the scope by hand and it will know where it is pointing and continue tracking. It sort of defeats the point in getting this package - resale value won't be as good as full Gti version.

Well, I was thinking about mentioning that scope, but decided not to because you mentioned previously that: As far as AZ-EQ avant goes, I have no idea how good it is. I like the idea of such mount, and I think that it is probably one of better light weight grab & go beginner mounts. It looks versatile, and only down side that I can see is fairly small capacity of only 3kg. Then again, one can't expect grab and go small mount to handle 10kg of load Here is fairly nice review video of this mount: https://www.youtube.com/watch?v=wkVergOxt_E&t=706s I already fast forwarded the video to important part (102mm Mak and AZ-EQ avant section as video overviews whole avant range, but you have "jump list" in description to go to particular segment of review). Here is quick list of differences between Mak102 and small refractor that you need to be aware of before deciding: - Mak will have significantly higher magnification and smaller FOV with same eyepiece because it has about twice focal length of refractors (more than twice compared to 705 and just a bit less than 707). It can give you about 1.2-1.3 degrees field of view with 32mm eyepiece - still wide enough for general observing, but it simply can't provide you with wide field of view - like 2-3 degrees that is possible with short focal length refractor (or reflector). You can use tool that I linked previously to see field of view with different eyepieces. - It is better suited for viewing Moon, planets and double stars than those small refractors - It won't have any chromatic aberration and will give sharper image - there will be a bit of "cool down" time when you want to use it at higher magnifications - about 10-20 minutes or so for image to stabilize. There is front glass element and main mirror in this scope design - larger pieces of glass need more time to come to ambient temperature. This is more pronounced in winter if you keep your scope at room temperature (like in house / apartment) and take them out to observe. - you can still use it for terrestrial observations - with 90 degrees astronomical diagonal it will have left/right reversed so you need amici prism to get proper image orientation. However it will give you quite a bit magnification - about x4 or more over standard binoculars (depending on eyepieces used) - there is a very small chance that you will have to collimate it. It is very slim chance, as these scopes hold collimation very well and are sold already collimated, but unlike small refractors (that can also get out of collimation, although similarly unlikely) there is a way to collimate it yourself. Small cheap refractors usually have lens cell that won't allow for collimation - lens are fixed in place at factory. With Mak you can adjust primary mirror, but it is hardly unlikely that you will have to do it - it will come in good collimation and stay that way for years. In fact - there is a section in user manual that describes this: https://smallscopefocus.files.wordpress.com/2016/06/makcasscollim1.pdf and to quote it: This is from Orion's manual - but those are same scopes under different brand.

Old saying goes: "Best scope is the one you use most often", so you are right in saying that you don't want something that is going to end up collecting dust because it is too complicated/heavy to use regularly, or does not provide enough enjoyment. There will be no difference in 705 vs 707 with regards of what they can show you on deep sky objects. 707 will have slightly narrower field of view when using same eyepieces, but 700mm focal length is not very large focal length, in fact as far as visual goes it is shorter focal length. I use visual scopes that have 1 meter of more of focal length and never felt "boxed in" with "small" field of view. There are just a few objects out there that can't fit in such FOV - Andromeda galaxy and couple of large nebulae (North American nebula for example) which are couple of degrees in diameter. If you want to compare the two scopes on FOV that you will have with 25mm stock eyepiece - visit this page: https://astronomy.tools/calculators/field_of_view/ For example, here is comparison of two scopes on Orion Nebula (something that you will definitively enjoy observing - although probably won't be able to see as much of it with 70mm aperture, unless you have very dark skies). A side note, I've seen Mercury 705 come with AZ3 mount. I had that mount and was not particularly happy with it - sold it. It was stable enough, but my primary objections were - It has to be rewound every so often to be able to use slow motion controls. It's not very smooth - at least mine was not, and it is very hard to observe near zenith - and that is the place you most often want to observe deep sky objects as there is least of atmosphere and light pollution is often of the least intensity. I've found a very interesting package that you might want to have a look at: https://www.firstlightoptics.com/sky-watcher-az-gti-wifi/sky-watcher-mercury-707-az-gte.html Some people prefer manual scopes to start with, some like go-to ability. For planets and double stars it would be good to have tracking. But this is not main reason I'm telling you to take a look at that package. In the case you decide that observing is not quite your thing, I'm fairly certain that you will sell more easily AzGti mount than any of the starter mounts. Unfortunately az-eq avant mount is not sold with Mercury line of scopes, neither as stand alone mount, although I feel it would be probably best starter mount for such scope - it can work in both EQ and AZ mode, and can be easily fitted with tracking motor (and rather affordable one - it's like 50 euros or so).

What is your budget btw? Maybe check out this little guy instead? https://www.firstlightoptics.com/evostar/sky-watcher-mercury-707-az-telescope.html It is F/10 version of 70mm SW scope

I have to say that this is beyond me ... I have no clue what might be causing this - it is possible that flats are to blame. You said that you used old flats? If you remove camera from the scope or change focus or anything - old flats are not going to work. Also need to do proper calibration - which includes darks or at least bias. I tried fixing things, and there is simply no way to fix the above. Concentric rings look like some sort of issue with vignetting - possibly due to use of old flats and wrong calibration. Interestingly enough green channel does not have this issue - only red (I did not check the blue one).

Ah, I need to correct myself first - that is the second silly thing I've written on SGL today, it is indeed time for a holiday .... 80mm F/5 will provide a bit wider fields than 70mm F/7.1 - simply because it has 400mm focal length and not 500mm like I written in my first post - 80x5 =400 and not 500 like I written for some unknown reason Everything else is ok in my first post apart from that. As for filtering, there are number of filters that you can use, some cheap and some more expensive. In cheap range, simple yellow wratten #8 (light yellow) will give good results on reducing blue/purple halo that is most noticeable in CA. It does impact a slight yellow cast on the image. On expensive side, there are different "semi apo" and "fringe killer" filters. I've got Baader Contrast Booster filter and it removes much of purple halo on my 4" F/10 scope. There is another thing that you can do to reduce chromatic aberration of your achromat refractor - you can actually "slow" it down. If you for example have 80mm F/5 scope, you can easily turn it into 50mm F/8 scope that will have color index about 4 in above table and have minimal levels of CA. You do this by use of something called aperture mask - it is simple mask that you can do yourself out of cardboard or piece of plastic - with a central hole of wanted diameter (smaller than diameter of the lens). This will make image a bit more dim and reduce maximum usable magnification (again it will be x2 the aperture, so for 50mm aperture mask it will be x100) but it will clean up CA nicely. Have a look here for example: https://10minuteastronomy.wordpress.com/2017/02/11/why-and-how-to-make-a-sub-aperture-mask-for-a-refractor/ On the other hand if you purchase something like ED80 above - you won't need to bother with any filters and aperture masks. ED80 will have much lower levels of CA (you will be hard pressed to see it even on highest magnifications) than you can get with either filters or aperture masks. Do take into account that it will be quite more expensive route than mentioned ST80 or 70mm Mercury even if diagonal and EPs are included, although it is offered at very low price for such scope, as you will have to purchase an astronomical mount for it as well.

Hi, and welcome to SGL. Actual FOV depends on couple of factors and is in principle related to F/ratio. Maybe easiest way to think about it is via magnification and apparent FOV of eyepiece. Eyepieces have apparent FOV (AFOV) and most likely you will get eyepieces supplied with your scope that give you about 52 degrees of AFOV. Eyepieces have focal length which is used to determine the magnification that they give with any particular scope. To obtain magnification - divide focal length of scope with focal length of eyepiece. To get true field of view - divide AFOV with magnification. Let's do an example - let's compare 25mm 52 degree eyepiece in two scopes that you mentioned 70mm F/7.1 scope (500mm FL) and 80mm F/5 scope, again 500mm FL. 25mm EP will give same magnification in both scopes - because their focal length is the same and it will be 500mm / 25mm = x20. You have 52 degrees of AFOV, and divided with magnification that gives - 2.6 degrees of true field visible in both scopes. Although scopes are of different "speed" (f/ratio) they will give same field of view with the same eyepiece because their focal length is the same and hence obtained magnification. This goes to show that F/ratio alone can't be used to determine true field of view. F/ratio can tell you something though - slower the scope - more likely it is to have longer focal length, and longer focal length means higher magnification with given eyepiece - which in turn means smaller field of view. However this all also depends on aperture (there are two things that go into F/ratio - aperture and focal length). For this reason, while in principle F/ratio is related to true FOV, you need to know what you are comparing (like same aperture scopes with different F/ratio, or different F/ratio but same focal length, or in general case - everything is different - so you need to use above calculation to determine TFOV). Here is another good thing to know - in general, maximum useful magnification of a telescope is about twice that of aperture in mm. So 70mm scope will have max magnification about x140. 80mm will have max magnification of x160. This rule applies for "perfect" scopes. If scope has some issues - like chromatic aberration or less then perfect figure - you will not benefit from such magnification. On the other hand magnification is also limited by stability of atmosphere. In general average seeing conditions (seeing means how "wobbly/blurred" image is due to atmosphere) you will be limited to x100-150. In better seeing conditions you can go to max x200. Only in excellent seeing conditions it's worth going over x200. Magnification is not everything. It is useful for planets and the Moon and some types of observing like splitting close double stars. Aperture is more important in the scope. If your preferences are sharp views of the planets - get your self first scope 70mm F/7.1. If your preferences are deep sky observing - get the scope with 80mm aperture - second one. In answer to your question relating to levels of chromatic aberration in refractor - there is nice little chart that sums it all, let me see if I can find that for you: According to this chart, 80mm F/5 scope is in "yellow zone" - CA (short for chromatic aberration) will be visible and obvious, and in principle you can reduce it with appropriate filter. 70mm F/7.1 will also show it, but it will not be as obvious (only on higher magnifications) and you will be able to filter it pretty well with appropriate filter. I have 102mm F/10, which according to this chart will show about the same level of CA as 70mm F/7.1. In that scope - CA is there, you can see it on high magnifications, on very high magnifications it is obvious, while on medium you need to search for it. This is of course provided that target you are looking at is bright enough - like the Moon, or planets, or very bright stars. Using appropriate filter almost completely removes it. I used to have 102mm F/5 scope. That is a bit worse than 80mm F/5 scope and it was all but usable to view planets on anything than low power views. Such telescope is wide field deep sky scope - good for fainter stars / star clusters / wide nebulae and galaxies all viewed on low to medium power.

Yep, just realized that I started with two reasons, but listed only 8bit .... it's time to go on a vacation and give ol' brain a rest ...

Like others said - it is great start. You probably have more data in there that could be pulled out with proper processing, but like imaging, processing also has a learning curve - and with practice you will get better at that as well. 15 minutes of total imaging time is short, and you should not expect great results out of it - so for next target - do a bit more - results will be much better if you go for an hour or two, or even four hours total (that is about as much as one can get on single target per night) Now to address your questions, and some general tips. This can only be corrected with flat calibration. You need to take flats for your setup to correct any vignetting / dust shadows that appear on the image. Look it up on internet. Best way to do flats is to have flat panel, but in absence of one people use T-shirt and do flats when it is still some light out (either in the evening at setup time, or early in the morning after night session). You can also use laptop/tablet screen with some white image displayed full screen. Aiming scope at uniformly lit white wall can be used as well. You need to take your flats while everything is still set up, because flats need same focus, same camera orientation and all the dust to be in the same place, so there is probably no chance to do it now to correct this image. You can try to correct it in post processing though - select with circular selection just that part of the image and adjust brightness a bit to make it the same as surrounding. It is easy fix in this case since there is not much of anything in that part of the image. This is produced by hot pixel. Simple way to deal with this is to use sigma clip stacking method. For it to work the best you need a lot of frames - it is statistical method that estimates if some values are too large or too small and does not include them in result. One more reason to get more frames and have longer total imaging time. With 20 frames it will still work, so give it a go. This is a big NO-NO. Only time to use jpeg in astro photography is when you have finished image and you want a small file to put on web (post here or elsewhere). Jpeg has two features that make it's use highly problematic in astro processing. First is that it is only 8bit per color format - you loose much of precision in 8bit formats. Ideally you want to use 32bit (tiff or fits) as your intermediate save format between processing steps. Sometimes you can get away with using only 16bits but I strongly recommend against this as well. It's best to use 32bit format. I personally use Gimp 2.10 for much of my processing. Others use Photoshop, and very often dedicated astro processing software like Pixinsight (which is probably too complex for you at this stage, get a bit more practice in both imaging and processing before you consider purchasing it - it has way too many options that will just confuse you at this stage). Have a look at recent thread for simple processing steps in Gimp: This is somewhat advanced topic - proper color in astro images. For the time being you should just try to do color balancing your self with color mixer / curves to get the feel for it, and leave color calibration for later. You can increase saturation in processing if you want a bit stronger colors, but don't over do it - it gives unnatural feel to the image if you push it too much. This is generally done via histogram manipulation - curves and/or levels. However, your background is fairly dark and in general you don't want your background to be completely black - it creates artificial feel in the image and you run a risk of clipping your signal. Most natural looking astro image has black color (or rather very dark gray) having value of about 4-5%. If you like, you can post your unprocessed stack (try to save it as 32bit format, and if you can't - at least 16 bit) and I'm sure people will do some processing on it so you can see exactly how much data there is in your image and what sort of result you should be striving for (maybe even get some processing tips for your image that you can try yourself for practice).

Not sure if the issue is with flats. Inspect your subs - you might have couple of them with high altitude clouds creating uneven background.

I pretty sure that you don't have to give a special price based on that - It can't be seen on the image, and I'm pretty sure that it will not impact the performance of the scope. Maybe just a full disclosure about it and what you think would be fair price for second hand item given it's overall condition?

Ah forgot - I did bin x2 in ImageJ as well - prior to background removal and color calibration.

ImageJ / custom plugin written by me was used to remove background gradient. It looks for faintest pixels in the image and tries to do linear fit on those pixels only. I do multiple rounds of this fitting / removal (until residual gradient is small enough compared to signal in the image) Next was color calibration - I again used ImageJ to measure star value and do pixel math to multiply each channel with proper value for white balance (I used Stellarium to find suitable star, however it looks like Stellarium has wrong/outdated information in stellar color indices due to catalogue used, and this sometimes fails - in this case there were excessive red cast after this calibration). Result of these two operations is linear Tiff that I provided link to. After that, it was all Gimp 2.10 - levels/curves to do the stretch and do slight color corrections (toned down red, boosted green in bright areas to get nice yellowish color in galaxy core, and boosted low values of blue to give outer star lanes a bit of a "pop"). Horizontal / vertical flip is self explanatory. In the end I did a bit of selective noise reduction. This is done by creating another layer of the image. On this layer you perform noise reduction - I used G'mic-qt under filters, then selected "repair" and somewhere down the list there is wavelet denoise. I ran default settings. This tends to blur details somewhat, so we need to selectively mix this layer into base layer. We do this by adding a layer mask to denoised layer - value only and inverted. This will blend denoised version in dark areas only (mostly background) - you can adjust level of this effect by selecting opacity of this denoised layer lower than 100% (I think I set it somewhere around 70-80% - was not paying attention to actual number and was looking more at the image to find most pleasing mix).

Here we go again (it's 28MB so it should not be an issue, but in previous post it failed twice for some reason): Ok, it failed again ... I'll upload it to my server and post a link for download here ... http://serve.trimacka.net/astro/Forum/2019-09-01/post_01/andromeda.tif In the meantime, here is a bit more tweaked version (need to stop now, as I'll just get into that "which version is better" mental loop ... ) - horizontal flip - slight tweak on green curve to make galaxy core yellowish rather than reddish - slight tweak on blue curve to make blue low range a bit more "sparkly" - selective wavelet denoising ...

Ok, so here is 32bit tiff with some things done to it: 1. I binned x2 to recover some of the SNR 2. I wiped the background of any gradients 3. I tried color balance on one star that Stellarium classifies as color index 0.32 (which should be white star). Results are not the best - too much red color, but it can be fixed with curves - like I did with my processing. 4. Vertical flip to put andromeda in more familiar orientation (maybe should have done horizontal flip as well ). I did not do any noise reduction - just levels / curves (levels as shown above and a bit of curve adjustment to kill off excessive red) stretch and I got this result: For some reason, I can't upload linear tiff - it fails. Let me try in another post ...

It's looking better and better ...

Ok, this is only in Gimp with 32bit data - fiddling with levels and curves: But there is gradient in the image, so I'm going to see it removed now and look if results improve things (and of course they should).

Ok, yes, I see what you mean and I probably jumped the gun on gradient removal. I'm not sure if I can do it in Gimp - will need to check if any plugin is capable of doing it properly. I do it in ImageJ with plugin that I wrote. I can remove the background and then post you results so you can give it a go at processing with clean background. There are couple of paid software out there that can do it, but I did not try any of them. I've heard of gradient exterminator (plugin for PS). Pixinsight has dynamic background extraction (often abbreviated as DBE). Iris which is free software can also do it: http://www.astrosurf.com/buil/iris/tutorial4/doc14_us.htm But it is a bit involved. Color balancing is rather easy once you have your background removed. Simplest form is to find white star in the image (using Stellarium or similar - look for F2 class star) and measure R, G and B levels. Then multiply needed channels to get white color - or same values of R, G and B (for example if you measure R to be 0.4, G=0.6 and B=0.2 then you need to multiply R with 2.5, G with 1.66666 and B with 5 - which are inverse of measured values). More advanced version of color calibration would be to measure bunch of stars and determine transform matrix that give you proper RGB triplets depending on stellar class (or rather temperature). I'll have a go at a bit more serious processing and I'll post results as well as cleaned image (and maybe color calibrated) for you to also have a go at processing it further.

In DSS, after stacking, just save as 32bit - either Tiff or Fits For item marked as 2 select 32bit float point For item marked as 3, depending on type, select some level of compression to get smaller file (TIFF supports compression, but Fits does not) In options choose not to apply adjustments to the image (either embed it or just ignore it, but don't apply it)