Posts Made By: dan coyle

In Rutten and van Venrooij's Telescope Optics, in the chapter on eyepieces, the second paragraph begins:

"A most important aspect of the eyepiece (self evident, but not always recognised by telescope users) is that the focal ratio of the light cone entering the eyepiece, fe/de, is the same as the focal ratio of the objective system,fo/do, when there are no other optical elements between the objective and the eyepiece. This equality of focal ratio has important cosequences, particularly in the off-axis perfmance of eyepieces."

I haven't seen anyone discuss this on the web. I wonder if anyone here is paying attention to this. Wadda ya know?

Thanks,Dan

I am trying to select a site on my land for planetary observation, and am trying to balance sight lines vrs tree cutting.
I would like to know how many degrees above or below the plane of the ecliptic the moon goes in it's entire 19 year cycle, if someone has that info in mind. Thanks.
Dan

This question is based on seeing an ad for an eyepiece that has 60 mm eye relief.
Am I correct in abstracting my experience with my eyepieces with 20 mm er and saying that I will get kidney beans or black out if my eye is nearer or farther away than the specified distance?
Is this eyepiece really for visual use?
Is there a term that describes the tolerance of how deep the range of distances are before loss of field? Where can I find a discussion or explication of this? It seems different ep types have this effect to different degrees. Comments?
Thanks,
Dan

Rather than having to call up each one individually?
A newbie question, but I haven't noticed a way to do it yet.
Thanks,
Dan

I bought one of these, but it has been cloudy or raining at my house for weeks, which is good in N.M., but...

I was curious if anyone here has any experiences, if it has been covered in this forum in some way that can be recoverd(I looked at the last 90 days), or in any other venue.

My impression of it in daytime is positive, but I'm a novice. It seems to resolve as well as my 32mm 52 deg "fully multicoated" Celestron ep.

I have to say that, while I bought it to have the widest field available from my f8 6" refractor, I looked foward to the 80deg field after seeing all the discussion of "Porthole". So far it hasn't knocked me out, to my suprise, and, I guess, economic relief.

Thanks,

Dan

Is there anyone here who can use a 6 mm ortho without putting lash oil on the lens?
If I blink without pulling my eye back from the ep, I deposit.
It seems to spread out fairly wide and low, because the interference effect color is uniform within the discoloration, which leads to my second question:
Has anyone quantified the performance of an eyelashed ep with great coatings, like the UO 6mm HD Ortho (which is the particular EP that prompts my questions), compared to a clean one, or compared to an EP with more eye relief, but two more clean surfaces, like a barlowed one?
What goes through my brain is I may be better off with extra surfaces and some eye relief rather than a great minimalist ep that is dirty.
Any comments or measurements?
Thanks,
Dan

I ask because there was a post about adding a 20 and a 10 together.
Are there rules of thumb, like a value of no more than 30 for an 8", etc?
(trying the question again)
Also, can someone refer me to a website where the numbering system is explained?
Thanks,
Dan

Mike Hosea said:

"...the 24mm will vignette a bit at the edges with an f/4.3 light cone...".

I wonder if someone could explain how that calculation is made?

Thanks,

Dan

I understand the Nagler and panoptic EP's are better at handling low f/ reflectors, and that they have a lot of curvature of field as a result of their strong saggitta varying where the image ends up for equal length light paths for rays across the mirror.
I also see in Rutten and vanV ( I forget how to spell the man's name) that the first Naglers had significant curvature of field, as quantified by how many diopters of eye accomidation it took to use them.
I've learned one reason the nagler types work well on wide light cones is the negative lens in the first group lessens the steepness of the light cone the following lens need to deal with.
Question: is there anything, besides the barlowing effect, about current naglers, with regard to ability to handle curvature of field, like reverse curvature in the EP balancing out the primary, etc, that explaines their success with low f ratios?
Also, can some one share the equation that describes the negative effect on the image due to curvature of field in low f/'s?
Thanks,
Dan

I spent the weekend making a and silicone collimatable platform for my Chinese helical focuser on my 8" aluminum tube Dob.
Last night I put my new Scope Stuff laser in the holder and let it shine down on the opposite tube wall to set the angle of the focuser. When I rotated the focuser, the laser dot moved about a 6mm dia circle. When I held the focuser still and rotated the laser in the 1 1/4" holder (with the screw snug but not tight,) the dot rotates about a circle that is 4mm dia.
This brings a whole 'nudder set of epistemological questions (how do we know what we think is true, is true?).
Re. the laser:
Is this true: if the laser is off center in it's holder, I may get its rear end adjusted to not rotate at 12" amay, but unless it is paraxial, it will be off at some further distance, nes pa?
How can I tell if it is paraxial?
Should I get it to be a nonrotating at the distance of twice my focal length and be happy?
Is that close enough to then use my new auto collimator?

Re. the focuser:
If it's out, I'm basically cooked, right? Is this a common problem with threaded helical focusers? I love the fineness of the adjustment, but I wonder why I'm going to allthe trouble of collimating when the eyepiece holder is wandering so for about in each revolution.