Adam J

Yes that is my entire point, what your paying the money in your FSQ is a scope that has the same pixel scale and the same FOV as a Z61 but is multiple times faster due to having a larger aperture. Which is exactly the same thing as saying its got a faster F-ratio at the same focal length. You paying about 4k more for a scope that is equivalent to a ZS61 but is four times faster. Comparing it to a longer focal length scope makes no sense. Anyway I am exiting this chat now as the CAPS are coming out. Its just that you clearly think about imaging in a very different way to me. I would chose my focal length to mach the size of object I want to image then get the largest aperture I can afford at that focal length. So if I wanted to image at about 300mm and had no cash it would be a ZS61 if I wanted to image at 300mm and had the cash it would be the FSQ 106, but a 130mm at F7.7 would not factor in that thinking at all. Bye for now. Adam

Yes and with a smaller aperture and identical focal length its a slower F-ratio. So one way or the other F-ratio matters at your chosen focal length. Which will image faster a FSQ or the ZS61? In the end thats what your paying for. Forget longer focal lengths they are for a different job mate.

I do understand the way you feel mate. But put it this way if you wanted to image objects at 300mm focal length you could be using a ZS61 at F6 and that is going to be much slower. It really doesn't work when you compare the scope to a scope of a different focal length. Its Better to think of it as paying for a 100mm lens that operates at 300mm focal length than thinking in terms of f-ratio. your competitor is not a 130mm f7.7 its a 60mm F6......

Sorry but its not, put a ASI1600mm pro on the liverpool telescope and you will need to expose for a very long time to reach the same SNR.

yes but there is fainter nebulocity in one image than the other due to the fov. While the center so bright its not SNR limited and focal length plays a bigger part in image quality. The real test would be on a dim object like the squid.

Sorry cant agree with that Rodd they are not directly comparable because they are not images of the same thing. One is only a small part of a larger object the other is the entire object. Not to mention the fact that if you only take a image of the bright center area of course it looks better without the dimmer outer stuff If i had a penny for every time that example is used, that telescope has a liquid nitrogen cooled sensor with 90%QE and pixels the size of dinner plates. It performs exactly how you would expect according to the maths, nothing magical about it. Less read noise than a 8300 and about 100 times the pixel area or more. I can dig the spec out and show you that a 30second exposure is about equivalent to half an hour with a amateur camera on the same scope. I calculated that for Olly once in a different thread.

Yes but your not resolving detail at the pixel level with the TOA at F7.7 hence you can use more noise reduction in processing without losing detail if your critically sampled with the FSQ your certainly over sampled with the TOA, in effect your lacking efficiency because although both images are good quality how many pannels do you need with the TOA?

The difference is most likely coming in the sampling and hence the scale of the noise presented in the final image. That is not normally a factor because at a given scale the noise scale will remain fixed, the problem comes when you try to present an image from a longer focal length at the same size as a shorter focal length image. The over sampled image will always look better even if both images have identical SNR. As an example if you take two images of M42 and you present them at full screen one long focal length the other short focal length cropped then the noise can be mathematically identical, however the more course structure of the noise in the critically sampled image will appear more noisy to the eye even if the resolved detail is identical, this would in turn prompt you to go for a longer integration. Hence why you should always image at a FOV that is appropriate to the target, essentially cropping is a bad for perceived SNR independent of image scale. For this reason seeking a fast scope over and above a scope of an appropriate focal length is counter productive. So you should only have purchased the FSQ if you wanted to image wide field targets with it and present them uncropped and at the original image scale. Adam

430mm for the 130 so F3.3. 500 for the 180mm at F2.8. So several factors may be at play here. Thats a significant difference in focal length between the Epsilons and the FSQ. What camera are you using? Is it the same on both? Adam

what scope is this?

Btw whats the focal length of both those scopes?

I understand but there is a difference between pure optical speed and perceived image quality. Sometimes longer focal length alone will result in an increase in perceived image quality as SNR is only one factor, once you reach a certain level of SNR in an image then its no longer the deciding factor. Perhaps posting some example images would help demonstrate your point. Adam

I don't have that kind of money.

Over a year. My impression was that they never changed the LRGB.

Yes it is... but that's clearly not what I said. Read above, what I said was that a focal reducer of 0.8x will only provide a 1.56x increase in optical speed, 2.8x was with referance to the delta between F3 and F5. Hence in my book 1.56x is very different from 2-3x. Well F-stop is a non linear scale used on camera lens. So to be clear moving from F5 to F3 doesn't equal 2 f-stops at all. The scale is as follows: f1.4, f2, f2.8, f4, f5.6, f8, f11, f16 Hence: (2/1.4)^2 = 2 = one f-stop (16/11)^2 = 2 = one f-stop (2.8/1,4)^2 = 4 = Two f-stops (8/4)^2 =4 = Two f-stops Sorry but I cant agree with that, its just not the case. If your using the same camera between those two scopes optical speed is determined by f-ratio. Ok here is the thing...what if I told you that I would not necessarily expect you to be able to tell the difference in SNR between those two images by visual inspection alone? Lets say that you take a 20hour image without a reducer and a 20 hour image with a reducer. We have shown above that the expected difference in optical speed is about a factor of 1.56x So for those two images to be of identical SNR your would expect to need 13 hours of exposure with the reducer and 20 hours without it. However the thing is that the way you perceive noise is non-linear and so its a well known rule of thumb that to make a significant impact on image quality you need to double the total exposure time. Hence to make your reduced image significantly better than your non reduced image you will need to expose for 26 hours not 20 hours. Looking at that the other way around if you want your non-reduced 20 hour image to be significantly better than the reduced 20 hour image then you will need to exposure for 40 hours. So 6 hours more vs 20 hours more integration with a reducer vs without before your see significant differences. But if both are 20 hours you are at the edge of being able to perceive the difference via simple visual inspection. Simple changes in imaging conditions and variable processing could easily obscure the SNR improvement. All things being equal the visual difference will be slight but probably better measured by software. So as I said above, everything is as expected and the main issue is that you have over inflated expectations of what the reducer will give you leading to disappointment. I think I am going to leave it here Rodd as if that has not convinced you nothing will. Best wishes, Adam

I would say that is the case, and note to you that those coatings are more important for narrowband than LRGB. Personally I would not pay good money for the older type narrow band filters. you can argue that they miss sold them to you if they did not stat that they are not the current version. just send them back under distance selling regulations. Adam

Well for a start its not 4x or 6x if you calculate it then you get (5/3)^2 = 2.8x faster, so your expectations are not inline with the mathematics. The second thing is that F-ratio = (Focal length / Apperture) so its litterally physically impossible to change only one of those variables since as soon as you change one you have by definition changed the other. Looking at reducers if you start out at a more typical F7 and reduce that via a 0.8x reducer to F5.6 that will give you (7/5.6)^2 = 1.56x faster not 2-3x faster as you seem to be expecting. Like I said above I think that your expectations for speed increase are not inline with what the mathematics predicts and hence you are naturally going to be disappointed. Adam

Its more than just that they changed the coatings also and added more effective anti-reflection coatings in addition to adding the edge blackening. In essence you will experience reflection artefacts with the older ZWO filters. Adam

A reducer should increase your per pixel photon collection rate though, that can be mathematically demonstrated. The problem comes when you use a reducer but change camera maintaining the image scale through using smaller pixels...that won't make anything faster.

Don't forget you will need spacing to make the corrector to sensor total 55mm you will want to order it with the corrector! Also I had a cc the I don't use now could have sold you it lol. To work out the spacing you will need 55mm - sensor dackfocus - filter wheel thickness - and other converters. Ask FLO for advice.

In theory you will not have to calibrate each night so long as the ASI air has the ability to remember the previous calibration between sessions.. My next purchase would certainly be a field flattener then as you can see distortion in your stars despite the small sensor. Adam

No reason why you cant do OIII, but I would get a good feel for how your system is performing in Ha first, I know there is always a rush to get a colour image when you start out, but I would focus effort on getting a high quality Ha image first. Small and bright objects like the Bubble nebula are actually an ideal target for your camera / scope combination and should have a strong OIII signal. Are you using a coma corrector currently? Adam

Got ya, lest see the stacked image then

I am very confused by this statement Rodd, am not sure what your driving at.

moved off? are you dithering between subs? or is it flexture? as it should not move off unless it loses the guide star.