jetstream

Dark skies are everything with respect to DSO IMHO. After a while this stuff gets very predictable...seasoned members can help out and cut the learning curve down greatly and with the effect of more money left in the wallet.

https://focusscientific.com/

100% Agree Stu- when we get right down to it exit pupil is a huge factor. An example is my 24" f4.1- it gives big magnification at nice bright exit pupils. The ability to observe with the parameters mentioned gives views that are a sight to behold on brighter galaxies and DSO and with this big fast scope I dont usually "up the mag for contrast" as the 2500mm fl gives the big image scale and the f4.1 gives great eye illumination. IMHO the real goal is to observe targets with as much eye illumination as possible and with a scope that provides the needed mag. Since eye illumination is provided by the exit pupil it is a major factor . There is contrast then there is "perceived contrast" which @John is referring to.

An object that is not a point source is an extended object- they dim equally (extended object and sky) with magnification unlike stars. I'm not the best to answer all this eventhough I do understand it. From Clark, Blackwell Bartels Carlson etc " A long held concept in amateur astronomy observing is to increase the magnification of a telescope to "increase the contrast of the object being viewed." While the effect is real, the explanation is incorrect. As one changes magnification, all objects change size (e.g. object and sky background), so the contrast stays constant. But the eye's sensitivity to contrast changes as the object size changes, with lower contrast objects easier to detect when they appear larger, meaning at higher power. " " its surface brightness (e.g. apparent magnitude per square arc-second)" " A low-contrast object is more easily detected if it is larger. For an extended object such as a galaxy viewed in a telescope, magnification does not change the contrast with the background, because both the sky's and the object's surface brightnesses are affected equally. Some visual observers have stated that a dim object's contrast with the sky background increases with higher magnification, but this is clearly wrong. The contrast merely looks greater because of the increased detection capabilities of the eye. Clark (1990) coined a name for the maximum magnification that will help detection: the "optimum magnified visual angle" (OMVA). This angle is shown in Figure 2.6 and also Figure 2.7b." https://www.bbastrodesigns.com/visual.html https://www.bbastrodesigns.com/blackwel.html

Contrast is fixed and is the difference between sky brightness and the surface brightness of the object.

@gorann excellent just excellent. and thank you.

@Ships and StarsWhich HCG's? Congrats!

For whatever reasons refractors offer superiors views with lower Strehls. The beauty of these top refractors is that the Strehls are so high anyway that differences between them are not important IMHO- except for bragging rights possibly. I could care less about the TSA120's Strehl- Ger's mark 1 eyeballs say that it is right up there with the best of them. From what I gather differences between the top refractors might be down to how they present the target, tone wise etc. I wanted to try an AP and called them- I just didn't want to wait so long for one. They were great to talk to btw. ps- I do care about the Strehl etc for reflectors...

I just learned something here- the Kruepax- phenolic impregnated paper that makes superior tubes. Always wondered what the stuff is- it sounds top notch for scope tubes. https://www.krueger-und-sohn.de/en/tubes-made-of-kruepax/round-tubes/

Awesome awesome scope!!

Theres more- you will easily see Barnards Loop with a quality Hb in your scope- its absolutely perfect for this, start near M78 and once found and observed numerous times try no filter. You scope will show it no filter. While in the area observe the huge Meissa nebula, your scope will outperform my TSA120 on this one, use a top OIII or UHC. The whole Veil neb will be a piece of cake in this scope too. Exit pupil matters for this stuff as you likely know and lightweight 2" eyepieces are a goto. theres more...

Exactly. NELM of 8? There must be a bunch of people with better eyes than me in Bortle 1. I get around 7.

I also have an issue with the Bortle scale- how many here can see M33 naked eye in Bortle 4? yeah right.

You are unleashing the power of your Tak Mewlon 180 as well as processing abilities in some of these images-excellent! Keep up the good work Fedele

Great report! Your scope will show M42's "lower loop" easily under dark skies and the North American nebula will be stunning as well, among many others. My limited experience with Takahashi telescopes has shown me they can offer superb contrast and transmission on DSO while offering near unlimited magnification on the moon and planets. And yes, I see no scatter in mine as well- as the velvety blackness description nicely relates which is a Tak characteristic.

Btw, whats just as important as the secondary specs is what is holding it in place...

My 24" has an Antares secondary and is excellent.

It does, see the detached blue little triangle patch off the tip in top of its image? follow this left on the image and there is a very faint really thin thread there, sharp in nature- this is the feature I'm talking about. Btw that triangle detached patch is easy. I dont see the wider more diffuse stretch that the thin thread sits in however. Ill have to check that MW image, thanks Vlaiv

I do in one place in particular, around the Double Double and Vega, I can confirm seeing these truly faint shade edges in both the SW120ED, TSA120 and the 200mm F3.8. I dont however see the things exactly the same as Bartels. Who knows what it really is. If you have an image of the Eastern Veil I can show you another feature to discuss, I dont have an example image anymore. Edit: forgot to say I also see the Pleiades Bubble every time conditions allow, this is the easiest one IMHO.

Ah yes perceived contrast - a favourite term of mine! Another 100% agree! Can you please explain how I can see some features of IFN? another filtered example is a very thin line off the end, side of the Eastern Veil that does not show in some images. Ive reported on it in the past- do you have an image of the Eastern Veil to identify what I mean Vlaiv? 100% true and I've taken years to find the "sweet spots " In my experience minor differences in exit pupil can make differences on many objects, mostly very faint object features. Mind you it could also involve the eyepieces used to achieve the minor differences so probably a combination.

Yes, except contrast of an extended object is fixed between the surface brightness of the object and the sky brightness. I know exactly what you mean Vlaiv 👍 but for the OP I thought I'd mention that we can't make the object brighter IMHO.

Stu is absolutely correct. Larger exit pupils increase eye illumination. If your interested in the short answer as to what works use an exit pupil of 4mm-5mm with an OIII or UHC for diffuse nebula such as the Veil, North American nebula etc. The parameter "exit pupil" is a universal one applicable to any scope- using this number and disregarding magnification simplifies things, at least for me. If you run the numbers using different scopes you'll see what I mean. Btw, planetary nebula can use much lower exit pupils than stated above.

I go against the grain and use more dish soap that many say, not by much just a couple of good squirts. I use RO water ie a couple of Aquafinas. Spray the soap water mix on and keep spraying until all lose junk is off, then its nice and lubed. Spray de greased hands and use finger tips then repeat soap rinse, Final rinse is pure water, no fingers involved. The soap is a lube so no scratches.

I too use the fingertip method. I degrease my hands and then use a sprayer water mix to soak the mirror, hands sprayed too- the soap is a lubricant. Works for me.

The 18mm BCO is vg, the 10mm superb but the 6mm bloats the stars and is not used anymore by me-not sure why it does this.