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Hi Stellaris, If you use a barlow you should not be using the camera lens. Your camera can probably come to focus without either camera lens or barlow - attached directly to the telescope focuser (if it has an M42 thread). Cheers

Hi Olly, What about chaos theory? Does this fall into "being consitent"? Cheers

... so FR on camera side

Hi Michael8554, you mean it should be on the camera side (of the focuser) - for the reason you stated?

Hi SteveBz, Maybe you can try on the NASA/IPAC Extragalactic Database. There are fit images you can download. Cheers.

So the problem seems to be fixed. It may have been that the camera was not on manual mode. I remember seeing a warning in Ekos but had disregarded it since everything seemed to be working. Anyway I did not think it would lead to errratic exposure time - maybe the warning should be more strongly worded Best

Hi almcl, So both High ISO and Long Exposure noise reduction features were off. I found the "CCD Temp" value in the FITS header, as can be seen by the KStars image viewer and all subs were at 16 degrees. Best

I will check if I have not disabled the noise reduction in the camera, I don't have the raw files - just the FITS.

Hi All, I noticed a few times while imaging with my Canon 700D (KStars/Ekos) that one of a series of subs will have much less background noise than those immediately before and after. At first I just though it was the way the FITS viewer displayed the images but when I check later there was a huge difference. I attached a screenshot (to reduce size) with successive images side by side opened in AIJ. I captured the sequence automatically and did nothing between subs. The subs are 60s and maybe max 30sec between the subs while the image downloads over WiFi. Any ideas? Best

Maybe you have to post a series of bloopers to be appreciated again - before posting the big one 🙂. I would like to know which of your scopes/lenses did you use?

Very nice and interesting. I checked the specs of your scope and it seems to be corrected to APS-C size with no additional accessories - and at f5.3. Just wondering why this kind of scope is not more popular for astrophotography. I searched SGL for your image of And XXX but could not find it. I would appreciate it if you could link it. Best

Well, the FWHM will be smaller for a larger aperture regardless of magnification . But for the theoretical PSF intensity profile, there seem to be intensities (like at the level of the red line) where the airy disk is narrower for the smaller aperture. What i would like to know is how that translates to what we see at the eyepiece. Cheers.

Hi Viaiv, I understand that our vision is extremely complex. But surely we can speak of broad thresholds, like the 6th magnitude naked eye limit or that specified for their instruments by the likes of Celestron. In my plot the red line could be like the limiting magnitude for the Green scope. But let me ask a related question. If we had two APO scopes (perfect optics) differing only in aperture and ignoring other factors like seeing, sky brightness etc. Would we see the airy disk of the same star to be the same size in each scope - or will it be "bloated" in the scope of larger aperture? I think the latter 🙂. Best

Our vision will have an intensity threshold for some particular situation, though of course will vary from time to time and from person to person - for example if dark adapted etc. What I was attempting to illustrate was that if the threshhold for a particular observer at the time of observation (no suggestion that it is linear) is at the level of the red line then it is possible that the size of the disk seen for a certain star might be bigger for a scope of larger aperture vs one with a smaller aperture - which we might interpret as bloat. Hi CraigT82, actually the size of the airy disk depends only on the aperture and not the focal length for a point source like a star.

Hi All, I have heard of that SCT views are "soft" or "mushy" several times on the forums. I was curious about this because I could not really imagine the views through my SCT being any crisper. On globulars and open clusters, if the faint stars were any more pin point then I wouldn't see them (and I don't use glasses). So I tried to simulate the Point Spread Functions (PSF) for different apertures of scopes shown in the image below, and this is my take on it... The curve for the lowest aperture is the flatest Purple curve, the next flattest Green curve has double the aperture, and the tallest Blue curve has three times the aperture of that of the Purple. If the threshold intensity that our eye can see is at the Red horizontal line, we can see that the width of the PSF is larger for the Blue curve than that of the smaller aperture Green - meaning it will appear more "bloated". We can also have a similar situation between the Purple and Green a little lower down. Thus for certain stars the image would appear more pinpoint in a scope of smaller diameter than that for a larger one. Together with the larger image scale of SCTs, and the fact that larger apertures are more susceptible to seeing conditions, this could explain why we might perceive SCT images as soft, bloated or mushy. Best