jetstream

Your TV barlow will be perfect. To my eyes the 6mm bloats stars a bit and while it offers excellent contrast its sharpness is not what the 10mm gives. But I guess I'm kind of fussy on certain things.

My 10 BCO competes (very well) with some eyepieces costing 8x more... it barlows extremely well and with the VIP will take super high mag. I'm not really fond of the 6mm BCO, just me.

We will be hard pressed to find a better galaxy/Pn eyepiece than the 10 BCO IMHO. I also painted the inside of the barrel flat black- does it make a difference? depends on the dob its used in. Refractors, no difference. If the dob has stray light very well controlled, no difference. If it doesn't- difference. Of course this is to my eyes.

Learning about the effect's of telescope parameters is interesting- like what I quoted from you now. It might be possible that this increased spread of light due to magnification will engage more of the eye, and when done with larger exit pupils and could be object size dependent- the result might be a brighter image in the brain.I think this and other factors contribute to getting brighter images. Years ago I observed and calculated object size in in EP (arc min) for different exit pupils using many objects. What I kind of figured is that each object size needs a certain scope to provide best views ie illumination at the entrance pupil of the observer and enough aperture and speed to make it happen. Then there is the fact that many of the enlarged objects now show detail...which needs more again... I would love to observe through a 40" f2.5, with CC.

You and I have similar skies Olly and I have a problem with the Bortle scale... I find it misleading. M33 in bortle 4??!! It takes my very best skies for me to see M33 naked eye- rain washed or snow washed. My SQM varies from 21.5-21.9 with an avg on excellent nights of 21.8. To others in this thread- M33 NAKED EYE IS EXTREMELY DIFFICULT! These days I simply use the look of the Milky Way- if its shows sharp structure galaxies will be good- if it reflects off my car windshield and looks very jagged, with constellations being difficult to see for stars- galaxies will be excellent, superb. Under these good skies mentioned M33 is a bright puff ball in the H130- its better to make this galaxy smaller than bigger if all you want to do is see it (no structure). Of course these are just my opinions.

Exit pupil is one factor that is absolutely important IMHO. I like bright objects in my 24" such as M81/M82 because I can use a large exit pupil while still having a large image scale- the results under a dark sky are very impressive. The large exit pupil also might contribute to the hocus pocus phenomena above(HET). For reference I can see pink under the wings of M42 in the 200mm f3.8, good for a 200mm-the 15" f4.8 and the 24" f4.1. The 24" f4.1 also shows blue... Regarding another thread- my brain does not "fill in" blue in the other scopes after repeated observations. One thing that puzzles me is the PCII- it allows more contrast in the 24 f4.1 on the Veil (test target) eventhough it pushes he effective f ratio to f4.7, must be Suiters wobbly stack thing.

Yes, thats why I asked actually. I think we should draw from @John experience to find a cost effective 32mm-34mm eyepiece. Suggestions John? hows the Panaview 32mm at f8 for filtered/ widefield use? I think going straight for a 2" Astronomik or new Televue OIII is the way to go, spend the money here and find a nice cost effective eyepiece. Btw queenie you have an excellent telescope, nicknamed "APO killers" for a reason.

Just curious- what eyepiece are you going to use with the filter?

Well its about time! glad you guys got out and are reporting again Calvin, excellent report

In practise the HET is used primarily on very large very faint objects, but it also works well on large not so faint ones like Meissa,etc. Note that I can see some IFN near the Double Double and also up by Vega using my SW120ED/TSA120/42mm LVW @2.9deg. My SV90mm falls short on this stuff despite the larger TFOV ie the scope has to be capable of showing these objects- they all don't.

I'm not sure but I think that between the needed"L" dimension , the speed of the scope and possibly the illumination he wants dictates the larger size. I'll run it through his calc.

@Ships and Stars Important, from link " If there is any advantage above the mentioned binocular summation factor of 1.4, this is attributed to this mechanism, which is called binocular facilitation or neural summation" Its possible to get more than 1.4x IMHO...

Just remember Robert, that we will all respond differently to the binoscope- some might see more than calculated, some less and some might see different objects differently, gain wise. The math is hard and fast, the brain is not. Your response to binoculars is a very good sign.

For sure! Read Arie Otte's PDF I link a bit back.... and this too"http://arieotte-binoscopes.nl/Why a Binoscope.htm

You just might Robert!! You don't know until you try. Good idea about sourcing the mirrors and also the structures, possibly on the latter.

Make me one too! your gonna need a big binoscope to really out do your 20"... From Mel "I see dimmer stars. The difference is clear: go outside on a dark night and compare one eye to both eyes. Can the difference be quantified? The surface area of a binoscope's two mirrors equals a single mirror 41% larger. With binoscopes I see a magnitude gain of about 20% for stars, more than a single scope but less than naively combining the apertures. In other words, based on my observing experiences with binoscopes, I anticipate that a 30 inch binoscope will have the magnitude grasp of a 36 inch telescope. "

http://arieotte-binoscopes.nl/Binocular Summation Factor revised 2019.pdf Read this...

From what I see the binoscope guys share information and technology across the globe- some much needed prisms etc being made in Europe. I too want a binoscope, a very fast binoscope but the cost ..... https://www.bbastrodesigns.com/30/30 inch binoscope.html

Thinking conventionally I agree, however I think, but don't know that some other factors come into play. It might be possible that under the right stimulation that the brain can "fill" in information correctly, after repeated observation. What triggers this interests me.

However, what do you guys think of this: "what is a HET (High Etendue Telescope)? Imagine a water pipe. Etendue is the total amount of water flowing through the pipe. How can we get more water? Well, we can enlarge the pipe allowing more water to flow through and we can turn the valve on more to increase the flow of water. Enlarging the pipe is equivalent to increasing the apparent field of view while turning on the value more is equivalent to increasing aperture. Etendue is the amount of light flowing through the field of view into the eye. To calculate etendue, use this simple formula: etendue = aperture squared * real field squared. For example, a 12 inch f4 with a 21mm Ethos eyepiece has an etendue close to 1700 cm^2deg^2 where as a 12 inch f3 with the same eyepiece and coma corrector has a greater etendue close to 2200 cm^2deg^2. The increased etendue allows me to see lower contrast objects. In dark skies with my High Etendue Telescopes I can get down to ~3% contrast (ratio of object+sky to sky). I have an object contrast calculator here. And if the real field is held constant, then greater etendue allows me to see fainter stars. Looking at the equation again, we see two factors that drive etendue: aperture and real field. Compared to a conventional RFT, a HET (High Etendue Telescope) has either increased aperture for the same field or increased field for the same aperture." https://www.bbastrodesigns.com/HET.html

I want to say that what has come out of this thread is how I was taught and how I believe ie making the object larger at a proper exit pupil, making objects easier to see. My 24" f4.1 is a good example. I have read Crumeys (Acey) paper as well as these in the links: https://clarkvision.com/visastro/omva1/ http://www.bbastrodesigns.com/visual.html From Bartels: "So why then is aperture the dominant factor? If exit pupil or sky background brightness is kept constant then as aperture increases so must the magnification."

He used a very fast 6" reflector for the sketch. I also see this- not quite the same as him- in our Heritage 130 and 200mm f3.8, among others. Observing IFN is a hobby of mine, as elusive as it is. The Pleiades is a very favorite of mine and your image is the absolute best I've seen Goran. Many kudos!

If all else is the same will a faster f ratio increase the number of photons that hit the eye per time unit? Btw, theres a reason I only use 100 deg EP's on large nebula- actually I only use 2 now, the 21E, 20APM lunt. A wider TFOV makes a difference at least to my eyes. There is something to Al Naglers "Majesty factor" IMHO.

His sketch. He is an advanced visual astronomer.

This fine image shows what Bartels is talking about ie the Pleiades Bubble.