Posts Made By: Bruce Bayleran

I have several questions concerning star tests and spacing of lens elements.
1. Am I correct in assuming that, in an under-corrected lens, the diffraction rings appear more obvious and clearer inside of focus and less so outside of focus? If so, then the opposite is true for an over-corrected lens?
2. Is it the spacing of the lenses that determines the degree/type of spherical aberration? So, under/over correction would be corrected by adjusting the amount of space between elements?
3. When viewing a lens that is out of collimation through a Cheshire eyepiece, I understand that the point in collimating is to get a single black dot image in the centre of the larger white circle. Now, before this has been achieved (via collimation screws), what does it mean when the still "stray" black dot appears to be two very tiny black dots either very close or touching each other (in other words, not a single black dot)?
Bruce

I hope I'm in the right forum area for mount qusestions. In any case, if you are able to balance a scope with a smaller weight further down weight shaft, and you can also balance scope with heavier weight further up shaft, which is preferable? I mean, which situation, if either, will give less stress to mount gears and motors?
Also, similar tripod question. I have a GP mount with a half pillar. I'm not too tall so, with the AL 150 Vixen aluminium tripod (lighter weight version but also the longest/tallest they sell) I'm able to use scope/mount without having to extend tripod legs at all. Now, in an attempt to make things a bit sturdier, I was thinking of getting HAL 110 heavy tripod. However, that tripod is shorter and to get same height I'd a have to extend legs. Anyone have any idea how sturdy is HAL 110 tripod? Is it worth it?
Thanks,
Bruce

I recently purchased a 60mm f/11.7 achromat. While I consider a "small" refractor to be anything between and including 60mm to 90mm, there seems to be a great difference between the abilities of these instruments. I have refractors of 80mm and 90mm and I'm reasonably adept at this point viewing through both of them. I know what to expect when I look through these scopes and they do provide some excellent views.
I did have a 60mm(?) scope quite some years ago. However, I can't very well remember the experience using it. I'd like to know from some of you who might be experienced with 60mm scopes just what should be expected of an instrument of this size. When I first looked through it earlier, I couldn't believe how bad things looked, very dim. I can't tell if the scope is bad or I'm just expecting too much. I know this is just probably my own lack of experience. Presently, I have use of only one 6mm ortho. This gives a power of 117x, close to the limit of the aperture. What powers should be best used with such a scope? Diffraction rings in this scope, at this power, are really large! Is there a place to talk to folks about the smallest of the small? I'd like to know more about the subject before purchasing more eyepieces, etc., for this little scope.
Thanks,
Bruce

I recently purchased an old 60mm achromat. It has very narrow, 0.965" drawtube. It also came with a faulty 0.965" diagonal, apparently the prism is out of whack. So I need to get a new, good diagonal anyway for use with this scope. At first I assumed I'd just look for all 0.965" optics since they normally fit this little scope. Recently I became aware of 0.965"-1.25" adapters and hybrid diagonals, which would allow the use of my existing 1.25" eps. I will stick to 0.965" optics w/ new (to me) scope, however, if there is something special about that kind of vewing of which I'm unaware. Is the veiwing experience "better", or in some way different? If so, how? If there is no advantage to 0.965" optics then maybe I should stick with 1.25" optics and just get a good quality hybrid diagonal.

Also, another reason for this question is that, my old 90mm achromat apparently originally came with a 36.4mm - 0.965" threaded drawtube adapter so that scope could be used with 0.965" optics as well as 1.25". So, for me, investing in these tiny optics might be worth it IF there is something worth it about them.
Thanks,
Bruce

Generally, I've always heard that a given amount of overcorrection in a refractor lens is considered to be worse than having ~the same amount of undercorrection. Is this true? Why? Can overcorrection be "corrected" in some practical way?

Hi Folks,

I'm wondering what kind sticky adhesive material is used on foil lens spacers. Foil spacers need something tacky so the lens elements will stay basically in place. Foil spacers usually always have this. I assume that whatever is used, it should be acid free. I'm working on a lens and the sticky stuff has pretty much been cleaned off. Is there some sort of special adhesive material that's good to use for this purpose?

Thanks,

Bruce

I just received a new set of manufacturer's foil spacers for a refractor lens. While the backs of the spacers are sticky, there seems to be nothing on the exposed top surfaces. It seems to me that there they need some tacky substance applied to hold lenses in place. Does anyone know what is used for this purpose? I suppose I could just hold lens elements together via pressure from the retaining ring alone. However, I'd rather not rely on retaining ring alone.

Thanks

Does anyone have experience with the 5 inch ad 6 inch refractors sold by AstroZap? There's really no other info on their website than photos and basic specs. I assume they are Chinese made? However, they don't really look like Meade or Antares.

Does anyone have experience with the Williams Optics 83mm ED spotting scope? I'm wondering how it compares to the Nikon 82mm ED fieldscope.

Brian,

When you say that there is dust in between the lens elements, how much? How bad? How large are the pieces of debris? Reason why I ask is that, in the case of any doublet, when you take it apart it is not easy to remove dust without getting more or "new" dust settling before you mate the two elements again. Blowing with a bulb atomizer will often not be sufficient to dislodge certain junk. In such cases a clean, dry red sable, reasonably large watercolor brush can work very well for a few contact swipes. I have done this with very good success, however, be prepared to take the top element off several times,,,trial and error, until you see no dust. Also, check the lenses against DARK background in order to see clearly that there is no dust, or, at least, that you have done a satisfacotory job, before securing lens in cell again. Now, I don't know how curved is the fluorite element in your scope, but I can tell you that the ED elements are extremely curved. This makes perfect mating extremely difficult. Achromatic doublets, especially longer focus ones, on the other hand, are actually rather easy to mate accurately. So, beware of the possible pitfalls, especially with an old Vixen 4" fluorite!