140 replies to this topic

[CHASLX200]

With my Towa Jason 313 60mm refractor:

Today, while testing how well I could see the Moon during daylight, I decided also to test the idea of stacking Barlow lenses. I'd never heard of that until a few days ago on this forum! Hard to know the exact power when stacking Barlows that vary in power depending where they are in the optical train. Two 2x Barlows and one 17mm Plossl in a 60mm refractor of 910mm focal length for about 200x. But, as expected, resolution maxed out at about half of that.

The value here was in using an available, small telescope to test how much power would be needed at a star party focused on the Moon. More aperture would, of course, be needed to see details well.

One reason i would never go back to 60mm.

[Bomber Bob]

One reason i would never go back to 60mm.

Ever used a Goto 60 F20?   Mine was a doublet (visual) APO.  Yeah, it's a LONG tube.  TS-65P / 500 almost gets there, and is sharp at up to 120x / inch, too.

Edited by Bomber Bob, 20 February 2024 - 05:27 PM.

[Joe Cepleur]

Every used a Goto 60 F20? Mine was a doublet (visual) APO. Yeah, it's a LONG tube. TS-65P / 500 almost gets there, and is sharp at up to 120x / inch, too.

That's amazing! There must be more to good quality optics than I know. Are you saving that, for example, if you increased the power from 100x/inch to 120x/inch, the image would not only enlarge, but also show increased detail?

[starman876]

That's amazing! There must be more to good quality optics than I know. Are you saving that, for example, if you increased the power from 100x/inch to 120x/inch, the image would not only enlarge, but also show increased detail?

That  would be very interesting with  65mm scope.  Considering I have one of these TS65 scopes I will have to try it and see what happens.   Must be one hell of a mount to hold that scope steady while focusing at 120X per inch.

Edited by starman876, 20 February 2024 - 03:00 PM.

[Joe Cepleur]

One reason i would never go back to 60mm.

Depends upon one's kicks. 60mm is quick and easy to carry and set up, the equatorial mounts are fun to play with, and it's fun to see how good a view can be coaxed into the eyepiece. The view is typically beautiful in a good long focus classic and fairly immune to poor seeing, rounding out the details seen in larger scopes. They have their place.

[Joe Cepleur]

That would be very interesting with 65mm scope.

...which is why I'm asking. I'd expect instead for the image to be of no greater resolution when enlarged, but to become increasing easier to see up to a certain point, which may be 120x/inch for that scope.

[bobhen]

Magnification is object dependent. High contrast objects like globular clusters and small, bright planetary nebulas and double stars can take much more power than Jupiter, what with Jupiter's low contrast disk details.

 

Having said that, in very rare nights of excellent seeing, my old Astro-Physics 152mm F9 triplet could do 100x per-inch and probably more on the moon and remain sharp. 

 

Bob

[starman876]

Magnification is object dependent. High contrast objects like globular clusters and small, bright planetary nebulas and double stars can take much more power than Jupiter, what with Jupiter's low contrast disk details.

 

Having said that, in very rare nights of excellent seeing, my old Astro-Physics 152mm F9 triplet could do 100x per-inch and probably more on the moon and remain sharp. 

 

Bob

The 6" AP I had was fantastic on the moon.  However, that is like looking at a search light at high magnification.  I am sure that higher powers can be used, but a 60mm at 120X? Having had a lot of 60mm scopes, like Tak and others I was never happy when I tried ultra high powers.  The light gathering ability just was not there,

[Garyth64]

And why do we 2 threads on the same topic?

[deSitter]

The 6" AP I had was fantastic on the moon.  However, that is like looking at a search light at high magnification.  I am sure that higher powers can be used, but a 60mm at 120X? Having had a lot of 60mm scopes, like Tak and others I was never happy when I tried ultra high powers.  The light gathering ability just was not there,

Well 120x in a 60mm is 50x per inch I had mine up to 180x which is 75x per inch and the view was OK, but no better than 150x.

 

Any two scopes with the same sized exit pupil will present an Airy disk of the same surface brightness, other things like coatings and baffling ignored. So extended objects will appear at the same surface brightness regardless of the actual magnification. Since the largest usable exit pupil is 7mm, no telescope can ever produce an image with higher surface brightness than the naked eye produces!

 

-drl

[Terra Nova]

I'm thinking exo planets here.

Crank it up Gary.  My barlow stack is much longer than my telescope.

Edited by Terra Nova, 20 February 2024 - 04:24 PM.

[triplemon]

I wonder why folks stack barlows. All it takes is an extension tube ...

Actually - my dob is pretty stable with 7 truss poles, still, so there is an totaly natural and aberation free way to fully utilize my scope to its fullest.

[Bomber Bob]

That's amazing! There must be more to good quality optics than I know. Are you saving that, for example, if you increased the power from 100x/inch to 120x/inch, the image would not only enlarge, but also show increased detail?

No.  What I look for is at what magnification I can no longer focus a planet's limb to a sharp edge.  That could be 40x / inch, or 140x / inch.  How do I know that I've gotten there?  I start "chasing focus" without nailing it.  

 

Now, on a near-perfect night, and with a high-quality scope, going that extra little bit of magnification may be useful for some features.  For Jupiter, the GRS will fade at 312x with the TS-65S, but the Gap is easier to see:  distinct interruption in the cloud belts, and that thin white arc between it & the GRS itself.  Or, the thin "tails" that trail off & away from some festoons.  IOW: Limited-purpose, but worth it to confirm / enhance something seen at a lower power.  Tight constraints; which is another benefit to using a low to no visible CA scope.

[starman876]

No.  What I look for is at what magnification I can no longer focus a planet's limb to a sharp edge.  That could be 40x / inch, or 140x / inch.  How do I know that I've gotten there?  I start "chasing focus" without nailing it.  

 

Now, on a near-perfect night, and with a high-quality scope, going that extra little bit of magnification may be useful for some features.  For Jupiter, the GRS will fade at 312x with the TS-65S, but the Gap is easier to see:  distinct interruption in the cloud belts, and that thin white arc between it & the GRS itself.  Or, the thin "tails" that trail off & away from some festoons.  IOW: Limited-purpose, but worth it to confirm / enhance something seen at a lower power.  Tight constraints; which is another benefit to using a low to no visible CA scope.

you need to talk to Terra. She is using her Questar at powers you only have dreamed about.  She has reported powers I will not even try.    I would be scared to try that high a power.  If I would accidently swing past the moon at 3500 power or more my Questar would blow up. 

[Bomber Bob]

I hope she paid the $5 extra per month for Questar's Explosive Session insurance...

[Bomber Bob]

That  would be very interesting with  65mm scope.  Considering I have one of these TS65 scopes I will have to try it and see what happens.   Must be one hell of a mount to hold that scope steady while focusing at 120X per inch.

You'll fail to focus - you don't have steady Pilot Hands.  Yep, Ol' BB... and the Waco Kid...

 

https://www.youtube....h?v=Mzcgyk62cHU

[Bomber Bob]

I try to avoid Math, but to repeat myself...

 

Your View at the Eyepiece = Object + SEEING + Telescope SYSTEM + You!

[starman876]

I try to avoid Math, but to repeat myself...

 

Your View at the Eyepiece = Object + SEEING + Telescope SYSTEM + You!

i think it needs correction

 

Your View at the Eyepiece = Object + SEEING + Telescope SYSTEM + Your Imagination

[oldmanastro]

I learned about the futility of ultrahigh magnification when, as a kid, I tried 600x on my 76mm f/16 Sears (RAO) telescope. It was fun anyway. Since then I behaved myself with 50-60x per inch max depending on seeing conditions and, of course, optical quality.

[Bomber Bob]

That's amazing! There must be more to good quality optics than I know. Are you saving that, for example, if you increased the power from 100x/inch to 120x/inch, the image would not only enlarge, but also show increased detail?

Astro Optical & Yamamoto cranked-out hundreds (?) of high-quality 76mm F15 refractors, sold at - of all places! - Sears.

 

I routinely used my Model 6336 (RAO) refractor at 200x, and zoomed-in to 250x, to sketch Mars back in the day.  I look at those sketches now, and... kinda miss that Classic.

 

Anyhoo, they're not hard to find; and, they don't cost much $$$.  I felt guilty paying just $115 (total, including shipping) for my TS-65S, but I've overpaid for other Old Scopes, so I guess it evens-out over the years...

[Bomber Bob]

i think it needs correction

 

Your View at the Eyepiece = Object + SEEING + Telescope SYSTEM + Your Imagination

You're using the Percival Lowell version...

 

NOT Imagination:

 

 

Dept Store Monolux 4380 60mm F15 operating at about 170x / inch (408x) on an 8+ / 10 seeing night.  On a high-quality monitor, the original RAW image can be enlarged to about 600x without breaking down.  

 

Yeah, yeah, stacking 1000s of AVI frames removes lots of intervening errors; and, it also takes YOU out of the equation.  My fatigue, hay fever, tipsy-ness, etc. don't affect the camera.

Edited by Bomber Bob, 20 February 2024 - 06:06 PM.

[starman876]

You're using the Percival Lowell version...

 

NOT Imagination:

 

M4380-Mars-20140426EP06A01CP20.jpg

 

Dept Store Monolux 4380 60mm F15 operating at about 170x / inch on an 8+ / 10 seeing night.

I normally see the moons of Mars at that magnification.

[Mirzam]

5000x is only 50x per inch..

 

https://www.mtwilson...cope-observing/

 

JimC

[Bomber Bob]

Terra, No Math, please!  Otherwise, I gotta call Eric Weinstein, and it gets into a whole bunch of other topics, and I forget my original question...

[CHASLX200]

Slap in a 2.5mm and 2x barlow like i do in all my scopes. I would have no probs jacking that Q up to 450x on Venus the moon or a star.  Forget Jup as after 200x you are done. But Mars when close and big should do 350x in that scope.  Venus can really soak up the pow wow if not too low.  Nothing like a big 15% sunlit Venus at 600x.