140 replies to this topic

[starman876]

Well i don't need to get down to that much nitty gritty kitty. I only use what eyepieces i got. They are all loaded with glass.  My eyes are past the point to even try.

[CHASLX200]

Reason i need a big Jupiter to see detail more easy.

[starman876]

Reason i need a big Jupiter to see detail more easy.

Chas, you are not the only that likes to have a big image to see more detail.  Nothing unique about  you wanting a bigger image. We all want that.  To be able to get there requires some interesting details to make it possible. You are lucky your seeing conditions allow bigger images. Most of us have to stay within the normal limits of physics due to seeing conditions and the quality of our optics and our  eyes.    It is very hard for seeing conditions, the quality of the optics and our eyes to come together at the right time to see those wonderful images we all dream about seeing with amazing detail. 

[CHASLX200]

Chas, you are not the only that likes to have a big image to see more detail.  Nothing unique about  you wanting a bigger image. We all want that.  To be able to get there requires some interesting details to make it possible. You are lucky your seeing conditions allow bigger images. Most of us have to stay within the normal limits of physics due to seeing conditions and the quality of our optics and our  eyes.    It is very hard for seeing conditions, the quality of the optics and our eyes to come together at the right time to see those wonderful images we all dream about seeing with amazing detail. 

I have had my share of bad seeing this winter.

[starman876]

I have had my share of bad seeing this winter.

Oh Yeah    Some of us have bad seeing 12 months of the year.  I was lucky i had shoes when I walked to school in the snow. 

[Terra Nova]

I'll try it! What should I expect? Just a few days ago, I tried 200 power on the Moon while experimenting with stacked Barlows; how will the view change with the next 50 power?

As resolution goes, a 60mm (2.4 inch) telescope is capable of 120x at 50x/inch. If you buy that 60x/inch works, then 145x may be possible. If you believe (as I have found to be true under my wobbly skies) that 30/inch is about most possible under local conditions, then 70x is more typical.

At 200x in my 60mm, I saw craters on the Moon dimmed and enlarged, not as clear or pleasing a view as at lower powers. But, Venus is a different object. Even in larger telescopes, I have only ever seen it as a bright disk or crescent. How will that change if I crank the power to 250x? What change—any improvement?—should I expect to see in the eyepiece?

I found over the years that my Mayflower model 814 (60mm, 700mm f.l.) gave consistently good results with a 5mm eyepiece (140X ~60X/inch) on planets and tight double stars like ε₁& ε₂ Lyra, (Trapezium too) when seeing was good. With so so seeing, it did quite well with a 6mm (117X ~50X/inch). However, I never found that going to a 4mm (175X) was a visible improvement, and when I used barlows to go above 200X, I found the results to be quite unsatisfactory, even on the moon. Yes, there was an image but it wasn’t sharp, it was blurry and dark.

[Terra Nova]

Oh Yeah    Some of us have bad seeing 12 months of the year.  I was lucky i had shoes when I walked to school in the snow. 

LOL, I rode a horse but it had shoes too!

[Joe Cepleur]

You cannot judge optics with additional complicated items in the train. Use a 4mm eyepiece with a f/15 refractor to get extreme power, 6mm for very high power, 9mm for high power. Barlows add aberrations of their own, no matter how well made. You want something as simple as possible. If you have Huygens eyepieces around, use those. As little extra glass as possible.

-drl

Thank you for the reminder. I know that, but have not thought about it in years. Seems obvious: I want to test the objective, not a mix consisting of objective-Barlow-Barlow-eyepiece.

I have a 4mm Plossl. I also have a Royal Astro 5mm Huygens (or, at least, a 5mm Huygens made by whoever supplied them to Royal Astro; did they make their own,?), but to use that on some scopes, I'd need a 1.25"-to-0.966" adapter.

[Joe Cepleur]

I guess it will vary by person. I have used 250x in a 60mm for the moon and Venus. Yes the view gets dimmer but image is bigger and sometimes it is just fun to blow things up.

Yes; that is exactly what I expected. I had been unclear about what you thought you were seeing, regarding "over-magnification" and resolution. Venus could be a good object to enlarge beyond what resolution would allow, since it will not be possible to see any detail anyway. Just a disc or crescent! Personally, I prefer a smaller image with sharper edge.

I have a simple approach to eyepieces. No complicated calculations. I start with the lowest power, widest field. If I want to increase the power, I step up a bit at a time, seeking the optimal view. If the image becomes too dim or otherwise breaks down, I revert to a lower power.

I have long been skeptical of the high powers many claim to have used, but I have really only observed objects with extent. I can see now, for example, how high powers for examining the Airy discs of double stars are valid, although outside of my experience — but something I should try!

[Bomber Bob]

You cannot judge optics with additional complicated items in the train.

 

DPAC Rig.  Simple.  Objective [pun intended].  Reliable 99.9% of the time.

[Joe Cepleur]

You cannot judge optics with additional complicated items in the train.

DPAC Rig. Simple. Objective [pun intended]. Reliable 99.9% of the time.

I think deSitter meant that, sure, one could put a million items in the train to test the system, but if there were problems, that would not identify which elements in the system caused them. Thus, his reminder to me to star test my objective using only a single, simple eyepiece.

[deSitter]

I think deSitter meant that, sure, one could put a million items in the train to test the system, but if there were problems, that would not identify which elements in the system caused them. Thus, his reminder to me to star test my objective using only a single, simple eyepiece.

You are evaluating the objective by star testing. It's not the Webb. It's a good time to learn Airy patterns. Get this book.

 

https://www.amazon.c...n/dp/0943396905

 

It's actually helpful to back off the eyepiece so you just see the Airy pattern at high magnification. You don't need a wide field. You don't need anything but the very central part. It's more important to be relaxed. So get the polar alignment accurate, get it tracking and back off after centering until you are comfortable.

 

Don't use the brightest star. Usually a 3rd or 4th magnitude star is best for small apertures (4" or less). One of the handle stars in the Little Dipper. Delta or epsilon UMi for a 4", Gamma Cep for a 3". Polaris itself for a 2.4".

 

-drl

Edited by deSitter, 24 February 2024 - 03:45 PM.

[deSitter]

You cannot judge optics with additional complicated items in the train.

 

DPAC Rig.  Simple.  Objective [pun intended].  Reliable 99.9% of the time.

Not to start a war, but DPAC is overrated unless you are making optics. it becomes an end it itself instead of a means to an end. It's not magic either.  It has its own interpretation issues. The star test is always available and contains IMO far more useful information about what to expect on the sky.

 

-drl

[Bomber Bob]

No War, just facts:  No star tests on cloudy nights.  Or, in monsoon rains.  Test environment is much more uniform inside than outside; and with fewer other factors, like tracking a star while testing at high power.

 

DPAC doesn't lie.  Patterns are easy to read, and replicate - so long as your procedures are consistent.  This redneck doofus from rural Alabama built a Rig, and learned how to use it.  How hard can it be?  [Thanks Again to Dave G. for all the inputs!]

 

And, so far, every objective with a good DPAC Pattern in green has been an excellent to outstanding visual optic.  I can test in red, blue, & white as well - added that in my DeeeLux Version 3.

[CHASLX200]

No War, just facts:  No star tests on cloudy nights.  Or, in monsoon rains.  Test environment is much more uniform inside than outside; and with fewer other factors, like tracking a star while testing at high power.

 

DPAC doesn't lie.  Patterns are easy to read, and replicate - so long as your procedures are consistent.  This redneck doofus from rural Alabama built a Rig, and learned how to use it.  How hard can it be?  [Thanks Again to Dave G. for all the inputs!]

 

And, so far, every objective with a good DPAC Pattern in green has been an excellent to outstanding visual optic.  I can test in red, blue, & white as well - added that in my DeeeLux Version 3.

DPAC that 826.

[Joe Cepleur]

You are evaluating the objective by star testing. It's not the Webb. It's a good time to learn Airy patterns. Get this book.

https://www.amazon.c...n/dp/0943396905

It's actually helpful to back off the eyepiece so you just see the Airy pattern at high magnification. You don't need a wide field. You don't need anything but the very central part. It's more important to be relaxed. So get the polar alignment accurate, get it tracking and back off after centering until you are comfortable.

Don't use the brightest star. Usually a 3rd or 4th magnitude star is best for small apertures (4" or less). One of the handle stars in the Little Dipper. Delta or epsilon UMi for a 4", Gamma Cep for a 3". Polaris itself for a 2.4".

-drl

I know that book, thanks! Good advice. My club has a copy, but I had no idea it had become so expensive. I skinned through it once, but decided that it was more than I wanted to learn at the time. I ought to revisit it.

A friend in my club can star test an objective and understand its flaws, although be uses bench tests, too, when refiguring optics. I get the point that if the Airy disk is asymmetrical, something is wrong!