Adam J

The esprit range are better scopes all round, the AVX will Handel it well.

Getting separation on the double star in the neck of the trunk is a mark of good optics. Adam

You are not going to get into sub 1"/pix territory reliably with a HEQ5 pro and a heavier load irrespective of what you put onto it. The best I have ever managed is 0.6"/pix for a short period the normal RMS is about 0.8 - 1.1"/pix though. What I would do is get something like a 200mm F5 Newtonian and an IMX290 mono based guide camera and use the short exposure technique. That way the guiding wont matter, use <8 second exposures and 1000's of them at high gain, will give very good results. With your current camera you are a little stuck with longer exposures and so I would keep the focal length less than 800mm, something like a SW 150PDS might get you something ~1.2"/pix but nothing close to the detail you can get with the short exposure technique. I think its good to reflect on the fact that the best amature image of M82 I have ever seen was taken with a QHY5III 290m guide camera: https://www.cloudynights.com/topic/568316-m82-full-power-with-short-exposure-t300-qhy5iii-290-m-qhy5iii-178-c/ Larger scope of course but the technique will still work with a 8 inch Newtonian just less detail. Adam

In effect it means that the sensor is not at 90 degrees to the optical axis and so you get poor star shape and focus at the edge of the sensor. The bigger the sensor the more prominent the effect because the change in distance is greater across the sensor surface. It can also cause poor correction of coma / spherical aberration as the optics of the correct can also be tilted to the optical axis. Its not something that is ever really going to effect you with your smaller sensor or even something the size of a 460EX or ASI183mm pro, its more an issue with 4/3rd sensors and larger. Hence you don't need to worry about it right now. I am going to take a look at your data BTW I just have not had the chance yet its all go here. Adam

It's the correct test and your interpretation is also correct.

Its more than 100 pounds, easy to get confused between the focus cube and the motor controller.

As above, they might be but its unlikely your scope is so I would not worry too much about it.

For dedicated imaging of small galaxies with a 200PDS then either a QHY178m or a QHY290m. Wider view vs higher sensitivity, as the 178 can fit things like m81 in the FOV i might sway towards that and I would be using short exposures <10s for detail. https://www.modernastronomy.com/shop/cameras/cooled-ccd/qhy-cooled-ccd-cameras/qhy290-coldmos-uk/ https://www.modernastronomy.com/shop/cameras/cooled-ccd/qhy-cooled-ccd-cameras/qhy178m-cool/ If you want to work on large nebula though the scope will have to go, I would look at selling it and switching to a 130PDS and a second hand mono camera. Or you could go even shorter and grab a 70-80mm refactor at a little more cost. But for small galaxies keep your scope get a small sensor mono CMOS and try the short exposure technique. Adam

Try and choose something that will still allow you to have a threaded connection to the x0.85 reducer or you run the risk of solving one problem and introducing another different problem. Adam

Last one, the TS. The Starwave 80 edt-r is no longer made / avaliable, I have attempted to purchase it from RVO before. Yet for some reason they still persist in saying its "generally in stock" I think that you would also do well to consider a WO GT71 Adam

If they want to sell it they will reply, if they don't want to sell it then just move on.

I would not use dark frames with a DSLR as you just cant control the temperature sufficiently. Dithering is the way forward.

No I would not do that, its crumbly and cracks very easily while drying, horrble stuff really.

The latest modification to my 130pds. The addition on a Pegausus Astro focus cube V2 and a new clamping system I designed to eliminate tilt cause by the eye piece holder (although not focus tube droop). The clamp works to pull the coma corrector tight up against the flat of the eye piece holder by placing two rings, one scope side and one camera side of the eye piece holder and then using three thumb screws to draw the coma corrector tighly against the flat. This method of longitudinally clamping the gear to the focuser is much better than any lateral clamping via thumb screws or a compression ring as it does not rely on the coma corrector being fully flush during tightening. Note: you need to mount the focus motor upside down and add a spacer or it will not clear the thumb screw that tightens the spider vein in place. Adam

If only it was not locked down to ZWO products.

Yes already noted that there are other factors and that its just a starting point earlier in the thread.

I am an analyst by profession and a physicist by degree. I did not try to fit to the entire curveas looking at the data it appears that the last few points are tending towards linear anyway, the last point in the series (800mm) was an outlier for the model which otherwise had very low residuals so I removed it.

Probably said it before but a image of a bright ish star with all three ultra narrow band filters would be great.

There are different mechanics for filter reflections, the above are reflection internal to the filter. I would expect those would be unaffected by reversing the filter. The other type are reflections between the filter and the camera surface or the filter and another optical element, the spacing is larger so the size of the reflections is bigger and more diffuse, its that type of reflection that has a dependency on filter direction.

I feel you missed my sarcasm

This is in your price range, color or mono, the mono is more expensive but worth every extra penny / cent. https://www.altairastro.com/Altair-Hypercam-183C-PRO-Colour-Camera-Fan-cooled-4GB.html Or you could just go with a DSLR as above but make sure you get a IR modified one if you do that. Adam

Voices only you can hear whispering paranoid thoughts to you. Maybe you should see a doctor about that?

OIII is the hardest narrow band filter to produce due to the shorter wavelength requiring more precise coating thicknesses. Hence you will see cheaper filters creating more reflections and often having lower peek transmission in OIII than in Ha or SII. Thats not to say that the cheaper filters will not give you good results, just don't expect perfection. 12nm is really quite wide for OIII as its also where you have the worse light polution. I would say that if your going to spend money on a filter then OIII is not the one to skimp on.

On Alnitak nothing but a premium filter will result in no reflections. So its within what I would expect for filters in their price category. Depending on if its the V1 or V2 ZWO filters it will be better or worse. As you have only two reflections visible I would say these are the updated ones, if it had been V1 then you would have had 6 or more rings. None concentric reflections of this type are normally a sign that the filter is slightly tilted, its not too bad though.

I plotted the TS optics data on spacing vs focal length into excel and derived an equation to fit the last three values to the line: y = -0.0103x + 63.699 Spacing = -0.0103 * 1050 + 63.699 = 52.9mm Of course there are other factors beyond just focal length of the scope that effect spherical aberration so that can only ever be a starting point. Adam.