Quote: Quote: Using a violet or blue violet filter on many a star would dim it substantially but the diffraction pattern never changes size. That is actually wrong. They DO change size with wavelength. The spurious disk ALSO change size with changing brightness. Clear skies!Thomas, Denmark
Quote: Using a violet or blue violet filter on many a star would dim it substantially but the diffraction pattern never changes size.
Used acronyms: NEML=Naked Eye Magnitude Limit, SQM=Sky Quality Meter, TML=Telescope Magnitude Limit, CO=Central Obstruction, delta_m=difference in magnitudes between double star components, RoT=Rule of Thumb, pD_mm=proposed D_mm for resolving a binary (ident with earlier used pA=proposed Aperture), D_mm=Diameter (of scope) in mm, UCAC4=USNO CCD Astrograph Catalog 4th edition
Quote:...Where I'll support Thomas is in his (briefly) pointing out there are two matters regarding how we see a diffraction pattern - first, the size does change with wavelength - see the standard equation which includes lambda (wavelength) in determining the angle subtended by the image. The other factor is perception - a fainter image will have an apparently smaller spot size (Airy disc) than a brighter star, because the eye sees less of the full diameter of the disc. Here, of course, the spacing of the rings is unchanged, though they become dimmer too.
Quote:...I will make an Excel spreadsheet with this RoT proposal with a link for downloading ...
Norme 150mm MCT f/13, 31% CO Yellow Zone "People say I'm in denial. I disagree."
Quote:I do not consider light pollution as serious influence - as stated elsewhere I even have the experience that the seeing her is most of the times better than in darker places with a stronger drop in temperature in the evening.
Quote:I assume this could be valid down to about half of this separation.
Anyway it is quite a feat to resolve a +13.05mag star with a 140mm refractor in "fairly bright moonlight"...This would also support the claim in the article "Some notes on Visual Urban Astronomy" from Tom Bryant that you can resolve stars up to the TML even under severe light pollution.
Quote:Wilfried, I'm a little puzzled about STF 450 in the Pleiades - I'll have to re-observe it with my 140mm refractor...