Adam J

So I have spent over 2 years saving for and agonizing over a scope to replace my 130PDS with and tonight I ordered an Esprit 100 + ES reed test + flattener from @FLO ......and some how after all that managed to let Chrome auto populate my e-mail address with one I have not had access to in years without noticing (well it appears)...so now I have to wait till tomorrow for FLO to answer my e-mail and hopefully be able to re-associate the order with my current e-mail address / account. 😰 Hopefully I wont be sweating it for too long. Anyway a little about why I made this choice. I wanted a worthy replacement for what is an extremely capable imaging scope in the form of the 130PDS and a 80mm scope which I might have been able to move to with less of a wait was just not cutting it for me. I wanted something as close to the F-ratio and focal length of the 130PDS as possible and 550mm @ F5.5 is not too distant from 650mm @ F5. In terms of image scale 550mm will give me 1.45" / pix and that is good resolution with my ASI1600mm pro for imaging smaller objects (with my sky and mount) while not being so narrow as to prevent imaging of larger emission nebula. While I know its not the best idea to try and have a jack of all trades imaging scope I am simply not going to be able to own two scopes any time soon. Why not stick with the 130PDS? Well a number of reasons, the focuser is poor and I would need to upgrade to a moonlight to prevent the tilt that i see (although I have high expectations in this matter and many would not be bothered by it). I am now a father and was not when I started imaging and so my time to tinker has been reduced to almost zero and for now while I will miss the 130PDS I need something that just works every time and that also ties into the kind of projects I am undertaking. I am a fan of larger mosaics I like to take my time over them and dont like to trade detail for a wider view so collecting as much data per panel as I would for a single panel image. That can mean multiple seasons on a single project with two or three on the go at different times of the year. The goal of that is to produce images of sufficient resolution and quality to allow for large prints. As a result I noted that while an Esprit 80 did give a larger FOV it did not give a sufficiently larger FOV such that I would reduce the total number of panels within the majority of my planned projects i.e 2x2 with the Esprit 80 was for the most part still 2x2 with the Esprit 100 with only a couple of exceptions and in those two examples I had a preference for the framing of 3x1 vs 2x1 anyway in order to produce a panoramic aspect ratio print of 2:1 (I match my images to the readily available aspect ratio of prints). A larger sensor that a ASI1600mm pro is not going to happen for me any time soon either. Finally as per this recent thread aperture is not entirely irrelevant to imaging as I can software re-sample individual panels to an acceptable 2.5"/pix and gain significant SNR in narrow band shots, that option is not nearly as effective in the case of the Esprit 80 which has less overhead for SNR gains through re-sampling. 3 years back when I started to build my observatory it was designed with the ESPRIT 100 in mind so wile I have wavered a little over the years about what scope to go for and had weak moments when I came very close to purchasing a smaller or cheaper scope its always come back to this scope in the end. Its a obsy for imaging only and so it is very small and the Esprit 100 is the largest scope that will fit under the roof when closed while still allowing a full range of motion. I also have no intention of letting my spending go any further and dont want to move away from the HEQ5 for this reason, FLO have reassured me that the HEQ5 pro will not have issues guiding the Esprit 100 and I dont want to move to larger mounts. Why a Esprit and and not a WO or the various clones or for that matter something more premium like a TAK. That basically comes down to time looking through astrobin and reading threads on here and cloudy nights and the Esprit range has very few complaints in terms of their optics and focuser also I note that FLO offer the ES reed test as an option with the Esprit but a default with the WO triplets, I can see only one reason why that would be. As for a TAK, lets get real I have been saving for the ESPRIT 100 for almost three years so that is just not happening. I will do a review when it arrives but it will be a long wait FLO dont expect it back in stock until mid December. Adam

No its just variation dependent on how the objective lens is mounted by the manufacturer. The lens within the cell is probably of identical size in a 70mm / 71mm etc, all that changes is how they stop the lens down to block lens spacers and similar from entering the light path. Some manufacturers (WO) tend to push it too far and it can result in incomplete star halos due to exposed lens clips. Apart from all that though some manufacturers produce lenses in inches but need to sell them in mm due to EU regulations and so that does not translate to whole numbers. My guess is that these will be triplets but not using FPL53 and having improved mechanics. I would be disappointed if its just a doublet with better mechanics. Not that I care I am most likely buying a Esprit 100 this week Measuring the length / diameter of the tube from the pictures it looks like an F6 design. I would say that is quite fast for a doublet design at 82mm aperture there is a good reason why most go with F7 or higher for a 80mm doublet. Adam

My preferance would be for the Z73 I dont think that you really need more than a FPL53 doublet to get good results with a 73mm aperture at F6 and so being even slower the quad is a little redundant in my opinion. You do know what your getting with William optics, as above there is not much point in a quad with a 71mm aperture and even slower than the Z73 while costing more and more to go wrong optically due to the complicated design than with a F6 doublet. The 86mm scope is much more attractive in that range but even then you have to go winder is it worth it over a Esprit 80. Makes no sense to me. Adam

Only just seen this. It's not the number of frames it's something wrong with the exposure and or your calibration process.

I get about 0.8 on a regular basis if its higher then its down to poor seeing / wind. On the very best nights it can hit 0.6 for periods.

At the risk of sounding arrogant, this is conceptually a very difficult subject for most to grasp as we are proving here, not least because most people are not willing to spend the amount of time considering these matters that we do. Just have a think about number of concepts you need to grasp in order to answer the seemingly simple question "should I use a reducer". So I go back to my original point, there is no myth only people who understand optics and those who do not understand optics. If you are sufficiently interested to consider and research the issue then eventually you will not need a rule of thumb or caveats you will just understand it. If you don't fall into that category then I would simplify things into a number of questions that anyone should ask themselves to determine if they should use a reducer or not. For example: Should I use a reducer: 1) Is my F-ratio F6 or lower? 2) Is my Pixel scale greater than 1" / Pix? 3) Does my target fit into my FOV. 4) Am I able to consistently guide to an RMS error of less than my Pixel scale (ideally 50% of my pixel scale). 5) Is the Dawes limit of my telescope significantly larger than my Pixel scale? If you answer No to any of the questions above you will probably benefit from using a reducer so long as doing so does not result in your image scale moving to exceed 2" / pix when galaxy imaging or 3" / pix when imaging diffuse nebula, if you answer yes to all of the above then there is no pressing need to use a reducer but you may still benefit from doing so in some situations. Will that cover everything? - no, Will it help someone understand why they should or should not use a reducer? - no Will it help someone who wants to image without having to become an expert in optics and sensor performance decide if a reducer is appropriate for their setup or not? - Maybe Threads like this are useful to help the minority like Rodd who want to understand the science / detail and fully optimize their imaging, but when they come to truly understand the factors involved they wont need the rule of thumb or the caveats they can just work it out for themselves. But the majority who don't want to dive that deeply into this and just want to know they are in the right ball park are best off forgoing the diagram and asking themselves the above questions. Bottom line: I know many people who seem to manage perfectly well taking great images without understanding anything more than "aim for between 1"/pix and 2" / pix while also choosing a scope and sensor combination to provide a FOV suited to your target size", so the only thing to add is that if a focal reducer helps you achieve that then crack on and use a focal reducer. Don't use one just to get a lower F-ratio at the expense of all other considerations in the misguided belief that it will lead you down the path towards some kind of imaging utopia or you will probably be disappointed. Just my opinion. Adam

Well apparently that has been deleted lol

You get micro lensing on M13!?!?!

I dont have massive issues with my asi1600mm pro considering the cost is 25% of the QHY600. But in honesty if you really want speed go with a duel rig mate.

so is starnet ++ now a part of pix insight?

yes because the QHY600 is coming out and that will bin in hardware up to the size of the 11000 pixels and have higher QE and lower read noise.

There is a slight benefit over software re-sampling but only if your under sampled at the native focal length. In that case a focal reducer is marginally better in terms of increasing SNR than software re-sampling, but it is probably too marginal for you to see the difference.

You kinda looking at it the wrong way around. Lets say I have a 102mm F7 and I want to image medium galaxies ~M101. I can do one of two things. I can image at native focal length with an ASI 1600mm pro and get around 1.1" / pix. Or I can use a reducer and get F5.6 and 1.4" / pix The objects fits in the FOV in both cases. I would most likely chose to reduce the scope with a 0.8x reducer and go with 1.42 / pix. I would do that because I dont believe that with my skys and mount I can acheive 1.1" / pix. In this situation I would use the reducer because I wont loose real world detail in my image but I will gain some SNR. But here is the thing. I can most likely software re-sample the 1.1"/ pix image down to 1.4"/pix or even less in software and get a similar SNR improvement. Hence the reducer is not really adding much in this case. Its marginally better than software re-sampling. On the other hand. If with my camera sensor size I needed a 550mm focal length to fit my target into the FOV and I had a 80mm F7.5 then I would need to use my 0.85x reducer to fit the object into the frame. Hence software re-sampling is not going to help me and I must use the reducer. My other options would be to use a 100mm F5.5 scope. If I use the 100mm F5.5 scope then I will also fit my target in, but it will be at a faster f-ratio than the reduced 80mm F7.5 and so I will image in a shorter time. Or I could use a 70mm scope at F8. Thats probably not the best option but all of these give allow me to fit my target perfectly into my FOV. Lots of this come down to affordability. Its more affordable to own a 80mm F7.5 and reduce it than it is to own a 100mm F5.5 and operate it at native focal length. By a factor of about 3x the cost. That help? Adam

You chose your scope according to what you want to image though and according to the camera you intend to purchase. You dont just buy a scope based on its F-ratio like say a Samsung 135 F2 slap a Atik 4000 on it and expect it to image the crescent nebula, clearly a 130mm F7.7 would do a better job. At the same time if i want to image the Heart nebula I would not choose a 130mm F7.7 and a Atik 414EX. You dont buy a scope to shoot every new target but you buy it having some idea of what size targets you want image and the appropriate image scale. Adam

Yes so that would go in with my theory at least, That is quite different from my scope at F5 and 650mm. But same aperture 130mm.

I would say that is as bad as I have ever seen it to be honest.....I dont get it that bad. You have clear separation of the pattern and two different sizes of reflection in the pattern indicating two surfaces in play. Which scope was this and what f-ratio?

If my SNR is already acceptable though would that not result in reduced detail as you cant get detail back by up samping? My current heart project is four frames with the 130PDS and ASI1600mm pro. I find that I need very little noise reduction after re-sampling so am recording true details at the pixel level, hence over four frames I end up with an image that will print to a 60cm x 60cm size on Alu very nicely. Would I be better off getting a 70mm F5 and getting it in one frame but four times the integration in that single frame....not sure but if you only have a hammer every problem is a nail. Adam

Well different methods aside I know if I software re-sample my 130PDS from 1.24" / pix to 2" / pix (my scale for presenting nabula) there is a significant increase in image quality / perceived image smoothness and gives me a nice balance between detail captured and smoothness when viewed at full scale while keeping integration times managable. Thats just using the re-size function in Photoshop nothing fancy.

Yes, but if you then took the up reduced image and software re-sampled it to the same image scale as the 0.8x reduced image you would be back to almost parity So Craig stark is correct, but you can almost achieve the same thing in software without the need to use a reducer. I say almost because there are some mathematical advantages to a reducer over software re-sampling, however in the end after you software re-sample the none reduced image you would have a hard time seeing the difference in SNR visually.

Did he re-sample both images to the same image scale?

In software you don't have to re-sample by a factor of 2 you can do it by any amount you like and the algorithm will still work to increase SNR (if thats even the best way to describe it). So you could re-sample to 2"/pix or 1.2"/pix with the corresponding level of improvement in image quality. You can then combine both focal reducer and software to get the desired samping while also getting the benefit of a wider field from the reducer.

Its all tide together in the same argument. All a reducer is is a tool to expand the FOV while reducing resolution and gaining SNR. In software you can reduce resolution and gain SNR too, but you cant increase the FOV like a reducer can.

The target matters if the target wont fit into your FOV. Hence so long as your target fits in your FOV larger optics re-sampled and or reduced are always better.

A focal reducer will only allow you to redice by fixed factor, you can re-sample to any scale you want to in software or by using a combination of the two. See my esprit example that I added above.

What you want it the lowest F-ratio possible for imaging at your chosen focal length / image scale. That also translates to the largest aperture possible for you chose focal length. This all comes back to the comparison I previously made between your FSQ106 and a WO ZS61, both similar foacl lengths so a good comparison in terms of relative F-ratio. If you can use a reducer and achieve your desired focal length while having a larger aperture then you win. But what you should not do is compare scopes of different focal length in terms of f-ratio alone. If you are over sampled then a focal reducer is always a good idea. There is no f-ratio myth, just people who don't understand optics. Here is a good example of re-sampling. If I take a ASI1600mm pro and put it on a ESPRIT 80 @F5 and a ESPRIT 100 @F5.5 and re sample the Esprit 100 image in software to match the Esprit 80 at 1.91 arcseconds per pixel then the 100 image will have a lower SD then the 80 image at a smaller FOV, now if my target fits within the FOV of the 100 then why would I want to use the 80 despite it being a lower F-ratio. So in that case what matters is a larger aperture for my desired fixed image scale as oppose to the F-ratio of the optics themselves. Adam