jetstream

I need an explanation Vlaiv as I don't understand this. The red line seems to add information that must be limited by aperture, optics etc etc? Am I thinking correctly?

Well, the graph shows a slight increase in contrast at high frequencies for obstructed telescopes- the (one of) reason(s) that many top lunar/planetary images dont worry about obstruction IMHO. What defines resolution? is it needed to use 2 similar objects or features to define? I can see shade differences in there like Enke- does this define resolution?

Thanks for confirming this Andrew, I have thought this for a while actually.

I would like to start a thread that I will contribute to very little. Maybe a question here and there- I hope to learn a bit about something that continues to puzzle me. How much information (units of light) does it take to form a complete representation or image that we can photograph or see visually? ie does one packet of light or one photon contain all the information about an object? Any thoughts are much appreciated, Gerry

It is complicated for sure and maybe I could start a thread in the physics section on it? The QED has been enlightening but just a synopsis of thoughts from members such as yourself would be fantastic. One thing is for sure- I never realized before just how complicated the actual workings of seeing an image in a telescope actually are. For me it adds to the respect and admiration for my simple telescopes that allows the exploration of the sky.

"Understanding Resolution and Contrast Two points it is important to understand is the resolution a telescope can provide, and how the contrast of the objects we are imaging affects is related to what can be recorded. Its often seen quoted in the Dawes or Rayleigh criterion for a given aperture. Dawes criterion refers to the separation of double stars of equal brightness in unobstructed apertures. The value can given given by the following simple formula: 115/Aperture (mm.) For example, a 254mm aperture telescope has a dawes limit of 0.45" arc seconds. The dawes limit is really of little use the Planetary observer, as it applies to stellar images. Planetary detail behaves quite differently, and the resolution that can be achieved is directly related to the contrast of the objects we are looking at. A great example that can be used from modern images is Saturn's very fine Encke division in ring A. The narrow gap has an actual width of just 325km - which converts to an apparent angular width at the ring ansae of just 0.05" arc seconds - well below the Dawes criterion of even at 50cm telescope. In `fact, the division can be recorded in a 20cm telescope under excellent seeing, exceeding the Dawes limit by a factor of 11 times!. How is this possible?. As mentioned above, contrast of the features we are looking at is critical to how fine the detail is that we can record. The Planets are extended objects, and the Dawes or Rayleigh criterion does not apply here as these limits refers to point sources of equal brightness on a black background. In fact it is possible for the limit to be exceeded anywhere up to around ten times on the Moon and Planets depending on the contrast of the detail being observed/imaged." From Peach. Whats your thoughts about telescope resolution in this context?

This has always puzzled me Andrew- thanks for clearing things up. From my completely unscientific observations I can say that stars can be made to disappear with too high a mag, whether because of seeing or other things. There seems to be a sweet spot mag wise for them. Can I ask one more question Andrew, slightly off topic? How much object information is in one unit of light- packet, photon or whatever? When I place my hand over part of my scope the image is still there as itself but suffers more diffraction- I think lol!

https://www.cloudynights.com/topic/471216-exit-pupil/ If you limit effective aperture with the eye what resolution is available? the aperture of the scope or the stopped down aperture with the eye? does this affect the f ratio of the system including the eye? @andrew s?

Yeah but my 130mm newt won't show the Horse Head- we need one of those magic Taks for this lol!😂

Me neither even in my 24, mind you I dont study this underwhelming challenge, it just an occasional pass through observation now. I like the Flame much better and do spend time on it but even a little bit of "untransparency" (new word) makes it hide IMHO. For me the value of the HH was the worthwhile pursuit and eventual observation.

I think its dense dust that might have ice or something else in there that blocks most light. Some are very striking in appearance. Speaking of Orion have you seen the dust lane that cuts M43 ?

Excellent! You've tried almost as many times as me before I saw it lol! The dark nebs are a favourite here. Its easy really, use no filter, observe under dark transparent skies and look for patches of sky with no (or very little) stars. Many to choose from- around the stunning M24 ( a must see) there are a couple and more in the area. Buried in the North American nebula there are a couple of dark ones and much more around it- 2 easy ones just off it. I mentioned the Aquila/Tarazed ones because they are easy to find- go to Tarezed and move a squeak over and your in one. No searching etc. Use your 26mm Nagler for these bigger dark neb and practise finding the edges. These things are all over the place. The 26 Nagler can work on the HH but controlling Alnitak is a huge asset espc at first. I have never been able to see the HH with a 3mm exit pupil or less...

This one is more realistic IMHO

🤣 Well I can get a whiff of the lensing galaxy and I hold no delusion of seeing every lensed quasar image- one or 2 with a very faint possibility on a third. This will take the unusual gathering of fantastic seeing, fantastic transparency, my darkest skies, complete dark adaptation, the right magnification with orthos and piles of luck lol! Question Steve- have you seen other dark nebula before? For practise trying to find them and in their particular edges would be good. Aquila offers excellent and easy, large dark nebula. Head to Tarazed to hunt some excellent dark nebula. A very wide field helps here ie the 26mm Nagler.

To each their own I say, whats not worth the effort for one might be a great challenge and reward for another. My current one is Einsteins Cross- many times on it no luck but maybe in a few years of trying. If I don't ever see the lensed quasar so be it, but the pursuit has been an eye opener.

oops forgot- completely dark adapted- check!

Perfect! I use one myself with great success. Have you tried the California neb? or the edge of Barnards Loop? All do able under dark skies 21 mag plus will do it and transparent. In response to @estwing FOV experience, he is right that large dobs make the HH bigger-image scale. However his TFOV with the 21E is 1.2 deg with the 18" f3.9 and I personally dont like upping mag such as with the 13E at f4 ish, too dark for me espc with a filter. To stack things in your favour Steve, use a high quality Hb-check low scatter eyepiece @ 5.3mm exit pupil -25mm NPL-check looking for a small thumbprint at 1200mm fl- check seeing the edge of IC 434 where the thumbprint resides check - IC 434 will either appear as a "line" or funnel dark, transparent skies?.... This challenge object is well worth the effort and will increase ability to see other faint objects.

It might look Long Perngish to me, this could be a good thing.

Nope. This does matter IMHO, as does using a low scatter eyepiece. Larger dobs can get away with scatter rich 20/21mm 100 deg eyepieces as the long FL narrows the view and the HH is bigger in the EP.My 24" shows the HH no filter with the 20 APM and 21E at .82 deg TFOV. You are right about the 1 deg TFOV IMHO and even a bit less is better. You have a 25mm Vixen plossl- perfect! My 25mm Super plossl shows it as does the 25mm TV plossl. Question Steve- what filter do you have? Kudos for your planning btw- you will see it no question and yes seeing the Flame, no filter is a pre requisite.

yes

Me too, with the exception of the 42mm LVW for large nebula observing- the TSA120 is a super, super nebula telescope which will show IFN easily.Inserting a Delos into the focuser gives as close to a zero scatter combination I think is possible, using the prism diag. Actually I must say the Vixen HR's are the least scatter EP's I've seen.Getting down to splitting hairs here. I wish Televue would make a 25mm Delos.

If I was going to get a 22mm eyepiece I would drop 1mm and get the 21mm Ethos. The other one that might tick the boxes is the 26mm T5 Nagler. They are heavy eyepieces however. The TSA120 can make almost any eyepiece look good IMHO Mine seems to like the Baader/Zeiss 2" prism diagonal- what a low scatter combination.

To have the "cleanest" and possibly highest "contrast" views a Paracorr II could benefit you. They bring out the best in Televue eyepieces (and others) at the f ratios you list. My 10mm Delos is close to my 10mm BCO, but in terms of transmission the Baader is a little bit better, only noticeable on the darkest and clearest nights. An example of this can be found on the central star in M57, which likes high transmission eyepieces and good seeing. My Zeiss zoom, while excellent falls behind the Delos/10BCO and Docter UWA on this object. My cheap Circle T orthos do well on it. Another sensitive object is Hickson 55 which loves the 10mm BCO/Baader VIP and also the Docter, Delos and other orthos. The absolute best view of the trapezium in M42 is with the 17.3mm Delos, very high transmission and super clean stars. Discounting the ZAOII, the best in terms of transmission and contrast are the Delos in the widefields according to many. It takes a good ortho to beat them. I hear good things about Morpheus and when I can get one I'll test it against some of the mentioned eyepieces. For serious DSO work I humbly suggest avoiding 100 deg EPs as well as 82 deg EPs. The 10mm Baader Classic ortho is the cheapest best way to get a super high transmission/contrast eyepiece. Note that the design is Zeiss, but not a true Abbe- it has a larger field and with a bit more distortion than Abbes. It has better transmission than my 12.5mm Tak ortho.

After another fine session with this scope I checked the mirror and it needs a clean. Before diving in blind I would like some advice before I proceed. How does the mirror come out? that outside back ring?

Last night the Heritage 130 performed very well on the Leo triplet. They were first found in the VG 24mm ES 68 and then fine tuned in a Circle T 12.5mm ortho. 2 very bright and the third an easy catch in direct vision. I sure like this ortho that cost me 50 bucks. This same set up caught a dozen or so galaxies in Virgo during a brief panning session. @Nick Sargeant your 200mm dob is a super instrument and will show a boggling amount of DSO under dark skies.