jetstream

"The human eye's MTF, which is limited at high angular frequencies by the eye's optical system and cone density, does not tell the whole story of the eye's response. " @vlaiv what I'd like to know is exactly what an individual aperture can show without the human eye looking through it and for this case planetary detail. Thoughts?

I agree that we are governed by the laws of physics and as such each aperture is bound by a spacial frequency maximum. Now the question is- does Dawes apply to planetary detail or is it described better by MTF and spacial frequency? and also each individuals contrast sensitivity function? "Contrast sensitivity function (CSF) Contrast sensitivity function The human eye’s contrast sensitivity function (CSF) is limited by the eye’s optical system and cone density at high spatial frequencies and by signal processing in the retina (neuronal interactions; lateral inhibition) at low frequencies. Various studies place the peak response at bright light levels (typical of print viewing conditions) between 6 and 8 cycles per degree (around 4 for the CSF equation used for acutance). We have chosen a formula, described below, that peaks just below 8 cycles/degree. You may learn something about your own eye’s CSF by viewing the image below at various distances and observing where the pattern appears to vanish. Contrast is proportional to (y/h)2, for image height h. Although the image appears to decrease in contrast linearly from top to bottom, the middle of the chart has 1/4 the contrast as the top."

Great scope! I tried to get one but my messages were not replied to so I went for the Tak. I still want the TEC however.

It really changes things when its enlarged, I'd giver a try.

Mike, did you click on it to make it larger like Vlaiv said? At what distance do you see the 17?

Yes thanks for pointing this out Vlaiv. When doing this I can see it from about 16 inches.

The above goes a long way to explain how a truly good optic can go 90x/inch or more and pull out more detail than Dawes or others can explain. A truly good optic preserves MTF. IMHO.

Peachs take on the ability of a telescope to use very high mag on the planets/moon is interesting. I find this to be the case. http://www.damianpeach.com/simulation.htm "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."

This is interesting... try seeing the "17" https://www.imatest.com/docs/sqf/#csf

Somewhere I have an article discussing exit pupil and the eye regarding "resolution" . After reading it I went on a mission to find what works for me using the text as a guideline- I found that around an .8mm exit pupil is a sweet spot for me,eventhough I can use lower. When designing my 15" I had this in mind and it gives 457x at this eye illumination. This is a very useable mag here which gives mind blowing views of Jupiter, Saturn and the moon. Mind you this scope has used double this mag on occasion on the moon (barlowed Vixen HR).

If you have good optics and seeing then the HR's will strut their stuff. By good optics I mean at least a true 1/4 wave (or .8 strehl) or better. @John I totally agree with your assessment regarding the tiers of the mentioned eyepieces.

These eyepieces can be excellent, my 4.9mm version is a nice performer.

My 12.5mm Tak LE offers a soft view of the planets/moon and sub par contrast on nebs. In addition the transmission is average at best, at least to my eyes. It was one of my most disappointing EP purchases. My Tak orthos are good but no better than my other Fuji orthos- but- the eyecup is a big plus. For these reasons I'm hesitant to buy the TOE's.

I must hurry and get the 2mm for my TSA120- thanks for the heads up Mike.

If you mean Vixens 2.4mm HR it belongs to the best series of planetary eyepieces I've used.

Fantastic set! I must say that the Docter 12.5mm UWA is a nice addition to any set.

Excellent Stu! I must get one.

Naked eye split- yes no issues here. My TSA 120 goes a squeak lower mag.

Re :scatter -have you checked your eyes for scatter on a street lamp at night? If I remember I looked through eyepieces from the bottom, our eye scatter is shocking showing under certain conditions. The dark spot would imply a mismatch between your eye and exit pupil of the scope/eyepiece I think?

Maybe the effect is related to how a barlow works?

10mm Delos.

Vixen 2.4mm HR, superb at 765x in the 15" and 375x in the TSA 120. The TSA 120 can take piles more mag- I barlowed the 2.4mm but not sure of the true mag- 1.5x barlow for 1.6mm fl I think for 560ish x. I need a complete set of HRs for this scope. Noted mags were on the moon under vg seeing.

And rightly so- I never know whether to comment on what one is considering or offer an opinion on what I think might be a better option.

f6 is a nice place to be IMHO.

Not sure if others have the same experience- I find that the differences between eyepieces show up under the best of seeing- at a minimum of Pickering 7. Obviously some of the differences show up at other times ie edge aberrations and distortions but the difference in on axis sharpness reveals itself ^^. I have had views of Saturn that rival some of the best images (most details) using the sorted out eyepieces.