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With x5 barlow you are very likely to be over sampling. What do you want to image? What is refractor F/ratio and what is pixel size of your DSLR?

Why would you need x5 barlow? You can use x5 telecentric from ES or x5 Powermate from TeleVue together with 1.25"/T2 nose piece if you really need x5 amplification.

https://www.astroshop.eu/other-adapters/omegon-sct-adapter-ultrashort-t2-male-2-/p,33228 You now have 50mm - OAG - 10 mm, why not simply change it for 30mm - OAG -30 mm combination (or something similar)

Select a piece of background without much "stuff" in it (few stars is ok, but try not to have nebulosity or galaxies or such) in one of your subs and measure median ADU value (median is used because of any odd star that ends up in selection - it will "ignore" it). Multiply that value with e/ADU for your gain - in case you are using unity gain - then it is easy - value is 1e/ADU and you don't have to multiply anything - just use median ADU. Take square root of that number - that is your LP noise. You can get read noise value from published data - for ASI533MC Pro it is: about 1.5e for unity gain. You can go the other way around - starting with read noise. You have 1.5e of read noise. This means that you need 7.5e (x5) of LP noise or square that to get signal - 56.25e for signal. Compare this number to actual number you measure from background with median and that will give you idea by how much you need to extend or if you can shorten your subs. Just be careful that you need to properly calibrate your sub. Use one of the channels for measurement - green is probably the best as it carries the most of luminance information (humans are most sensitive to noise in luminance data).

I was not aware of the bundle, so yes, it is most likely the case that it is IR/UV cut filter. In either case - your advice is very sound. One should look at respective QE graphs of transmission and multiply them if attempting to stack filters. Sometimes it can be beneficial but in most cases - it simply lowers efficiency of the setup - or even, like you pointed out, causes complete blockage of light.

People often use couple of thousand of subs. It is more important to keep individual subs short - less than 5ms to freeze the seeing. You will have trouble capturing full lunar disk with that camera - camera sensor is very small and at 750mm focal length - it won't cover whole lunar disk. FOV will look something like this: You will need at least 6 to 8 panels to do whole disk. Another issue with that camera is that it is USB 2.0 camera that uses compression. That introduces artifacts in the image and if you follow usual tutorial for planetary lucky imaging (capture video, stack, wavelet sharpen) - it is likely that you will have issues with compression artifacts. Having said all of that - you need at least one hundred of stacked subs and often people only use few percent of total capture. Good thing is that you are not time limited when shooting the moon (unlike other planets) - and you can shoot say 5000 subs even at 30fps (that will take 5000/30 = 166.7s or about 3 minutes) and keep 2% best subs - that will give you 100 subs to stack (maybe you will get to keep even 5-10% of best subs - depending on seeing during the session).

Yes, that is true, however, from OP - it is not clear if it is IR pass or UV/IR cut filter that is mentioned. IR pass filter can be stacked with CH4 - although it won't bring in any benefit to do so - but rather somewhat reduced total transmission.

You can use filters alone or stack them. If you are unsure - then use them alone as individual filters. If you have the need to stack them - then you will now both how and why.

It is always worth adding simple wratten #8 filter to these comparisons as it is by far the cheapest option for dealing with blue fringing in achromat scopes.

Where did you get info that it is Supernova remnant? It is usually described as emission nebula / star forming region.

Naming is also a funny thing: https://en.wikipedia.org/wiki/Leo_A Leo A (also known as Leo III) (Same result in Simbad) But yes, you are right - wiki lists result from NASA/IPAC Extragalactic Database - where entry is from 1991 - SIMBAD gives value from 2014 Spitzer data

Since you are used to full frame sensor - it will be very difficult to get dedicated astro camera to replace that. You probably want to choose between full frame sensor astro camera, and APS-C sized astro camera. Depending on your budget, well - there are two predominant versions (I'll link versions from one vendor - but there are others out there that produce cameras based on these chips). Full frame version: https://www.firstlightoptics.com/zwo-cameras/zwo-asi-6200mc-pro-full-frame-usb-30-cooled-colour-camera.html APS-C: https://www.firstlightoptics.com/zwo-cameras/zwo-asi-2600mc-pro-usb-30-cooled-colour-camera.html Those are currently the best sensors based on various parameters like quantum efficiency, read noise, cleanness of dark frames and so on ... ASI071 is not bad camera compared to DSLR - you will certainly feel effects of cooling and proper calibration, but compared to ASI2600 above - it is much less sensitive. It has QE of 50% while ASI2600 has peak QE of 80% so that is quite an improvement. Other parameters are about the same and ASI071 has larger pixels (which I personally see as a bonus). If ASI071 had larger QE - it would be excellent value.

Radius of coma free field is F^3/90 in mm If you have F/4.4 telescope - then coma free field is ~0.9465mm (radius or about 1.893mm diameter). That scope is rather fast and you really want to use barlow lens with it. Critical sampling will be at about F/ratio = pixel_size * 4 (that is for 500nm wavelength - good value to use for full spectrum sampling). You want to be at ~F/15 so you'll need at least x3 barlow if you want to go for critical sampling. In any case - diameter of coma free field will be enlarged by barlow factor. x2 barlow will make it ~3.8mm. That is ~700x700 ROI with 3.8um pixel camera. With x3 barlow - you'll be able to do ~1024x1024 ROI.

I usually eyeball it - but it is very simple procedure to do - not really eyeballing in common sense of the word. Follow certain pattern - like left to right until you reach the end then "step down" and reverse direction for next row (do it row by row like that - each time stepping down and doing a row). - Make sure your FOV is aligned in RA/DEC direction - When moving single FOV - think about which direction you are moving in and then simply look at a feature in live view and position that feature on opposite side of FOV - simple as that. For example - moving to the right would be like this: Note feature that I outlined at the right side of FOV - slew so that it is positioned on left side of the FOV: Always use feature that is roughly the same size - this will be your overlap zone for easy joining of the panels. When moving up/down - choose feature on appropriate edge (for moving down - use bottom edge and place one of features that is there - on top of subsequent FOV).

This is actually not an easy question to answer as there are a lot of things in play. Best option (but not always) is Peltier cooled dedicated camera with set point temperature. Being at low temperature is not that beneficial in some cases (in some it is) - but being at set point temperature is very important. It allows you to properly calibrate your data. I'm going to list pros and cons of dedicated non cooled / air fan cooled vs DSLR Neither is capable of achieving set point temperature (not even air fan cooled as it depends on ambient air) which means that neither is capable of proper calibration. DSLR pros: - very large sensor for the money (often APS-C). This is important bit as it can mean significant increase in SNR if used properly - has internal dark calibration (most modern DSLRs do). This is both pro and a con - depending on how you look at it. Pro is that you can get good dark calibration if sensor has uniform dark current noise (no amp glow) - and in most cases this is true. Con is that it is not proper calibration and that it makes subs noisier than they need to be (using just few pixel values for dark current reduction as opposed to stack of dark subs). DSLR cons: - Not as easy to work with as dedicated astronomy camera attached to laptop (this is subjective) - Has very restrictive IR/UV cut filter installed and if you want good sensitivity across all visible range - you need to remove / replace that filter (not easy or cheap operation) - Can't achieve higher FPS or be used for planetary imaging Dedicated astro camera without TEC (air cooled or regular) Pros: - Full spectrum sensitivity - Fast readout - Usually higher QE than DSLR Cons: - Very complicated dark calibration that depends on algorithms and is not 100% correct ( again - no proper calibration) - Expensive - small area sensors available in price range of DSLR Bottom line - I'm not sure which one I would choose - and even maybe am leaning towards DSLR. You really need to crunch the numbers to see which one is better. Both have awkward dark calibration (DSLR is actually easier in this regard). Probably only issue with DSLR that is really important is that nasty UV/IR cut filter that needs replacing / modding. Lower QE is offset by the size of sensor. Place larger sensor to the larger telescope (to get the same FOV) and match resolution - you have faster system with DSLR as aperture is larger and collects more light. That offset lower QE.

Perfect length for subs depends on magnitude of read noise compared to other noise sources (LP noise, thermal noise or target shot noise - depends which one is the strongest) and how much of it will you tolerate impacting your final image. It also depends on quality of your guiding, how often do you have ruined frames and your storage and processing capacities. Here are some rules: - you want your read noise to be at least x5 lower than highest noise component in your subs (usually LP noise when shooting faint targets with cooled camera) - processing algorithms favor more data, so shorter subs - storage and processing capacity likes working with less data so longer subs - unforeseen circumstances mean more lost data with long subs (you loose 10 minutes of data for one ruined 10 minute sub, and only 1 minute of data for one ruined 1 minute sub).

Which of "theirs" interpretations do you think is correct? One that says that sampling should be half of seeing FWHM or one that says its better to go for 1/3 of seeing FWHM, and how do you explain the fact that 80mm telescope simply can't resolve down to either one of these two values in 1" FWHM seeing? Fact that we are using pixels has certain impact that we did not discuss here, but I've shown before what extent it has - and it is to slightly lower resolution by adding so called pixel blur. Theorem is very clear about what it says - neither of two sources explain how are their recommendation related to maximum frequency of band limited signal nor why is it band limited in the first place.

Well, that is another example of misinterpretation of Nyquist theorem. Why don't you have look at actual theorem and what is says in 1D or Multidimensional case: https://en.wikipedia.org/wiki/Nyquist–Shannon_sampling_theorem I asked above question because 80mm scope has critical sampling at about 0.64"/px and smaller scopes - even coarser sampling than that. Many people image with smaller scopes - and to say that under 1" FWHM seeing you should use 0.5"/px - even if your scope can't resolve that much even under perfect conditions - is clearly nonsense. (not to mention whole planetary high SNR and massive amount of sharpening vs DSO / low SNR and barely any sharpening at all thing).

@Magnum According to http://astronomy.tools/calculators/ccd_suitability You can even go down to 0.33"/px - in good seeing: Does this mean that I can take my 80mm scope and image at 0.5"/px if I have very good seeing around 1" FWHM? Does this hold true even for people that use 60mm scopes or Red Cat with 51mm of aperture?

So this is not about the device - it's about you needing an excuse for a new telescope

I'm not sure you fully understand how filters work and why there is a shift. There is no design for converging beam - only for collimated beam. Nothing changes in etalon itself because light hits it at a different angle. Every etalon design suffers from this as sun is not point source. There is always some light that hits etalon at an angle - even with front mounted etalons that don't get any sort of instrument angles. In order to get very narrow FWHM needed Solar Ha - two parallel surfaces are used as source of interference - like single layer of dielectric coating on regular night time Ha filter. Unlike night time Ha filters where you have designed wavelength that is center and that you can adjust for faster light beam - wavelength of F-P etalon depends on distance between parallel surfaces. This is controlled by tilting of etalon (tilt tuning), or by pressure between plates (pressure tuned) or by temperature expanding mica crystal (mica is used as it can be split on atom boundary and creates perfectly flat surface - this is how quark is tuned). CWL shift and FWHM widening happen just because some of the rays are not perpendicular to etalon. You can never have all rays be perpendicular to etalon. Imagine front mounted etalon pointed at the center of sun. Light ray coming from the center of the Sun will be perfectly perpendicular to etalon - but light rays coming from the edge of the disk will be at an angle of 0.25 degrees (sun is about half a degree in diameter, so 0.25 degrees radius). As soon as light wave is not perpendicular - it no longer presents correct wavelength to filter. Light is still correct wavelength but since it is at an angle - filter sees longer wavelength of light. (above orange is actual wavelength, but as soon as we tilt wave with respect to vertical - wavelength "seen" by filter becomes - red one which is longer) Now important thing happens. I'll write larger numbers (around 656nm) as it is simpler - but this actually works on fraction of angstrom when we talk about Solar Ha filter. If light is perpendicular than any small change in wavelength results in lowering of transmission. Say filter transmits 90% for 656nm and only 70% for 655nm and 657nm But if we have wavefront that we tilt a bit - this is what happens: 656nm will present to the filter as 657nm and will start transmitting at 70% 655nm will present to the filter as 656nm and will start transmitting at 90% 657nm will present to the filter as 658nm and will start transmitting at even lower - say only 40% We have shift in CWL! This happens to front mounted etalon. Although we did nothing to the etalon - as you move from center of the sun to the edge - CWL slowly changes as angle increases. With converging beam something else happens as well. Not all light that is for same point at focal plane is coming the same angle - here even for central point angle is changing! Now you can't simply say - transmission is 90%. It is for that central ray - but as soon as you observe other rays - they change wavelength that they present to etalon and their transmission falls. Total transmission is sum of all these transmissions. Wider the beam (faster F/ratio) - more total transmission is lowered. This is why there is dip in above diagram: Not because transmission at particular wavelength changed - but because wider beam contains more rays that are at an angle (and wider angles) so average transmission goes down. This is also the reason why there is broadening of curve (when you consider other light that is initially not of needed wavelength - but gets shifted to correct wavelength by being at an angle). You can't design this away. You can choose one of the three setups: 1. front mounted etalon - that only suffers from CWL shift 2. internal etalon with collimated beam (like Lunt 50 has for example) - it has completely parallel beam as it employs a pair of lenses - one diverging before etalon that will create collimated beam and then one converging that will then bring collimated beam to focus. This configuration has advantage that etalon can be made smaller (easier to manufacture and less expensive), but has disadvantage that angles associated with sun disk get amplified and are no longer from -0.25 to +0.25 degrees but larger - which again impacts CWL shift more 3. Converging beam - this is what "eyepiece" filters do. They suffer from both CWL shift and FWHM broadening / peak transmission reduction, but can be made the smallest as they are closest to focal plane. They are in essence the same as point 2 - if you apply pair of negative / positive lenses (before and after the filter) - like barlow and reducer carefully placed. Although, it is best to have lens specially designed for that purpose and optimized for 656nm. In any case - closer the beam to collimated - less of that broadening will happen. CWL shift will still happen due to the fact that sun has dimension and different parts of the sun will send light at different angles.

Problem with this approach is that focus position alters primary to secondary distance and that in turn alters actual focal length of instrument (it is no longer 2032mm) - so we can't really be sure of those figures.

There is simple T2-1.25" filter adapter that just screws in the camera nose piece (even if you have that 11mm removable T2 extension). After you put it in - you still have plenty of T2 thread to attach camera to rest of the system. It saves you using filter drawer and optical path.

It is better to guide on unfiltered light so OAG should come before filter. Having said that - why are you using filter drawer with ASI294MC? It is OSC sensor and I'm guessing you'll be using either LPS filter or some sort of UHC/Duo band filter. In any case - such filter won't need swapping mid session and it is sensible to just put it in T2 adapter right in front of the sensor rather than use filter drawer that facilitates easy filter change.

It would certainly work. There are few things that you should be careful with: 1. Maks have moving primary mirror - and guide scope is not the best way to guide them (much like SCTs) - OAG is better option. It might work for you as scope is small but you could easily get differential flexure - just something to keep in mind. 2. You'll probably get vignetting with APS-C sized sensor on Mak102 (and even Mak127), so flats are a must 3. You will need long subs - like 4-5 minute subs because of long focal length - light is spread over many pixels (which will be binned in software later) and it takes longer to swamp the read noise.