407 replies to this topic

[bsavoie]

Gemini nice view of M45 Pleiades. Nasa did this, but it looks like it has 90 degree spikes, and halos around stars. I think NASA released that photo in 2004. Here is another, notice the lack of halos.

 

It would seem to me that the optical properties of the scope, the obstructions, or the 90 degree star effects, could be erased with software. It doesn't look like NASA did that in 2004. I think we need more math, in our use of telescopes. Math would allow us to get closer to the truth of reality, without the automatic distortions of our equipment. 

 

If that is the case, then it wouldn't make much difference which type of scope we used, Newton, or Refactor. We would just process our pictures with a different piece of software. Of course if we only use our eyes, then we must use math differently, we must apply it to the equipment to minimize these type of scope differences.

 

Bill

[Joe C]

There have been several posts that ventured well off topic. Please keep the discussions within the realm of the threads topic.

 

Regards

Joe C

[ed_turco]

I always like a lively discussion but I didn't write my article and build my telescope so others could go so off-topic.  I went through some difficulty to do this and I find the offhand remarks to be most discouraging. 

 

Please?

 

 

 

ed

[ed_turco]

Oh brother, did I miss the boat!!  I've just finished my first round of reading the Amateur Astronomer magazine, winter edition and the outstanding article, "Contrast in Eyepieces."   The highest compliment I can give an author is "Gee, I wish I'd written that."  It is a fine discussion that neatly fits in with my article that started this whole thread off.

 

I just stopped writing a little too soon!  Surely, as the article demonstrates, an eyepiece is an integral part of any telescope and this new article deserves close reading.

 

I am still of the opinion that a well-made Plossl eyepiece gives the best bang for the buck and gives even a beginner a leg up on some fine viewing.

 

 

 

ed

[AtmosFearIC]

T'was a long read to get through all 17 pages! Refractors are better than reflectors in some instances, and visa versa. I would not expect my 5" APO to even come close to the viewing capacity of my Orion 12" Dob at my dark site. I'd prefer to buy a house than buying a 12" APO when a 12" dob costs spare change in comparison. After the dob cools down and starts pulling another mag or two deeper than the 5" APO, the refractor gets packed away for the rest of the evening.

 

When doing wide field imaging, I would also never expect to be able to buy a 130mm F/5 newtonian with a 55mm corrected (flat and illuminated) imaging circle. I would never expect to get excellent views from a 130mm F/5 newtonian with a Nagler 31mm and near 4º FOV. Running my 130mm F/5 APO at 15x magnification with just shy of 4º FOV at my dark site during winter is breathtaking, especially when surfing around the centre of the Milky Way!

 

A refractor excels at short focal lengths with potentially HUGE imaging circles and still usable as a visual instrument. I mean, how many <10" newts out there are you put a KAF-16803 sensor or AND use for visual work? 50% obstruction would be needed. I also doubt I would ever buy a refractor larger than the 5.1" mark either, that is why I have a 12" dob

 

Can a 5" newt do as good as a 5" APO? They can both perform to the extent that I wouldn't be able to tell the difference at the EP when looking at a planet. I would however not be able to put a 55mm plossl on the newt and still not notice the difference

I personally believe that anyone just getting into astronomy, their first telescope should be something along the lines of a 100ED F/9 refractor. Someone just beginning to dabble in astronomy, they want a system that they don't have to work for, one that will cool down in 15 minutes and give fantastic views. For the same price you can buy a 10" dob but with that comes its own complications. It may be able to out resolve a 4" ED but the refractor works straight out of the box and performs.

[gdd]

T'was a long read to get through all 17 pages! Refractors are better than reflectors in some instances, and visa versa. I would not expect my 5" APO to even come close to the viewing capacity of my Orion 12" Dob at my dark site. I'd prefer to buy a house than buying a 12" APO when a 12" dob costs spare change in comparison. After the dob cools down and starts pulling another mag or two deeper than the 5" APO, the refractor gets packed away for the rest of the evening.

 

When doing wide field imaging, I would also never expect to be able to buy a 130mm F/5 newtonian with a 55mm corrected (flat and illuminated) imaging circle. I would never expect to get excellent views from a 130mm F/5 newtonian with a Nagler 31mm and near 4º FOV. Running my 130mm F/5 APO at 15x magnification with just shy of 4º FOV at my dark site during winter is breathtaking, especially when surfing around the centre of the Milky Way!

 

A refractor excels at short focal lengths with potentially HUGE imaging circles and still usable as a visual instrument. I mean, how many <10" newts out there are you put a KAF-16803 sensor or AND use for visual work? 50% obstruction would be needed. I also doubt I would ever buy a refractor larger than the 5.1" mark either, that is why I have a 12" dob

 

Can a 5" newt do as good as a 5" APO? They can both perform to the extent that I wouldn't be able to tell the difference at the EP when looking at a planet. I would however not be able to put a 55mm plossl on the newt and still not notice the difference

I personally believe that anyone just getting into astronomy, their first telescope should be something along the lines of a 100ED F/9 refractor. Someone just beginning to dabble in astronomy, they want a system that they don't have to work for, one that will cool down in 15 minutes and give fantastic views. For the same price you can buy a 10" dob but with that comes its own complications. It may be able to out resolve a 4" ED but the refractor works straight out of the box and performs.

A 130mm f/5 Newtonian has the same field curvature as a 130mm f/15 refractor. That combined with a coma corrector should provide a well corrected field for a large imaging circle. Am I wrong?

 

Gale

[ed_turco]

T'was a long read to get through all 17 pages! Refractors are better than reflectors in some instances, and visa versa. I would not expect my 5" APO to even come close to the viewing capacity of my Orion 12" Dob at my dark site. I'd prefer to buy a house than buying a 12" APO when a 12" dob costs spare change in comparison. After the dob cools down and starts pulling another mag or two deeper than the 5" APO, the refractor gets packed away for the rest of the evening.

 

When doing wide field imaging, I would also never expect to be able to buy a 130mm F/5 newtonian with a 55mm corrected (flat and illuminated) imaging circle. I would never expect to get excellent views from a 130mm F/5 newtonian with a Nagler 31mm and near 4º FOV. Running my 130mm F/5 APO at 15x magnification with just shy of 4º FOV at my dark site during winter is breathtaking, especially when surfing around the centre of the Milky Way!

 

A refractor excels at short focal lengths with potentially HUGE imaging circles and still usable as a visual instrument. I mean, how many <10" newts out there are you put a KAF-16803 sensor or AND use for visual work? 50% obstruction would be needed. I also doubt I would ever buy a refractor larger than the 5.1" mark either, that is why I have a 12" dob

 

Can a 5" newt do as good as a 5" APO? They can both perform to the extent that I wouldn't be able to tell the difference at the EP when looking at a planet. I would however not be able to put a 55mm plossl on the newt and still not notice the difference

I personally believe that anyone just getting into astronomy, their first telescope should be something along the lines of a 100ED F/9 refractor. Someone just beginning to dabble in astronomy, they want a system that they don't have to work for, one that will cool down in 15 minutes and give fantastic views. For the same price you can buy a 10" dob but with that comes its own complications. It may be able to out resolve a 4" ED but the refractor works straight out of the box and performs.

Gale,

 

You mixed up some points and have beclouded the discussion..  The point of my piece is that a Newtonian Reflector can be built in an easy way to make it the equal of an apo in the formation of the Airy Disk, to the point that even an above average observer cannot tell the difference.  Others who make related claims about the wide field of an apo negate my first premise by placing emphasis away from the center of the field, negating the basic premise of an average amateur who moves an object of interest to the center of any field in any telescope.  Any time in my discussion a reader gets away from the basis of my reading, I become suspicious; after all, I did make a scientific challenge stated thus:  Any reader of my article is welcome to write one himself to prove me wrong and for the enlightenment for the general ATM community, but only citing new sources in the way I did.  After roughly nine months, I haven't seen or heard a thing from enlightened apo owners or otherwise. 

 

I am sorely tempted to call a halt to this discussion;  perhaps I will when a greatly expanded version of my work makes its promised appearance in Amateur Astronomy Magazine.

 

 

ed

Edited by ed_turco, 03 February 2016 - 09:48 PM.

[gdd]

What am I beclouding? The issue of wide field was already brought up. I supported your position by pointing out that even a short fast Newtonian has a wide flat field and should be able to compete with an APO in that regard. I did not consider illumination (also brought up in the post I commented on) or the airy disk (your main point).

Gale