Problem With SS 83mm Jaegers Objective
Posted 02 February 2013 - 01:53 PM
The halos look very much like an optic element is fogged. The halo around bright Jupiter is about 3 times the size of the planet. I can see no detail on Jupiter. Sirius focused down to a bright dot, but was surrounded by twinkling spikes jutting way out from the star. I get a nice round out of focus image on a star, but no diffraction rings can be seen.
I checked the entire optical train and nothing is fogged. I tried a different diagonal and a couple of different eyepieces with no luck.
BTW, the scope was cooled down, had been outside for a couple of hours.
I also have an 80mm Towa lens and when mounted in the cell and same OTA I get beautiful images. One difference, the Jaegers has a slightly longer focal length and I have to rack the focuser way out, several inches further out than with the Towa objective (for which the OTA was originally designed). The focuser is just an inexpensive Synta R&P focuser with a long drawtube.
Could there have been some really weird seeing conditions for me last night? If so, I've never seen anything like it in months of observing. Last night I didn't think to try a different scope.
Any suggestions before I call Surplus Shed?
Posted 02 February 2013 - 02:42 PM
I got one of those but coated a while back togather with an aluminum cell and tested out beautifully on autocollimation (at least to my eye). But I had to tweak it a bit (rotate the lens one against the other), also the spacing wasn't really spot on. The markings on the edge weren't very clear to me. I'm not sure if the markings were made by jaegers or SS.
I'm also not sure how careful are the guys from SS on testing these lenses before shiping so anything is possible. I guess this is the real price for being surplus.
Posted 02 February 2013 - 03:15 PM
So I guess who knows for sure? Guess my next step would be to rotate the crown element a few degrees at a time and see if I can hit a sweet spot. I do have an artificial star I can aim at across the yard.
Posted 02 February 2013 - 03:19 PM
Well inside focus, most of the light will lie withinin a ring, with a dimmer center.
Getting close to focus, the image will be a more or less uniformly bright disk.
At sharpest focus, there will be a tiny, bright central point, surrounded by a small halo.
Continuing to rack outside focus, the intensity of the central point will diminish as more light is put into the halo.
If overcorrected (not so commonly found), the sequence will be reversed.
What is the objective's focal length or f/ratio?
Posted 02 February 2013 - 03:22 PM
If you had a bad lens, you wouldn't see halos anyways, so we know it's the orientation, not the quality.
Posted 02 February 2013 - 03:26 PM
SS makes claims, that sometimes I really wonder how they got the numbers, except by guessing; however, they are totally golden on returns.
I would have a hard time going anywhere else; they are that good for 99.9% of what they sell.
Posted 02 February 2013 - 03:35 PM
"The crown with the slight curve faces the sky, then the spacer ring, then the flint with the negative side goes on top of the spacer" So going in the direction away from the scope, towards the sky it should be "crown - spacer - flint? Sorry, I'm confused.
Posted 02 February 2013 - 03:59 PM
You have a concave element and a convex element. the curves are different on both sides of both elements. One concave side and one convex side match, those face each other. The other concave side is almost flat and is the back of the objective. The last convex surface is the front of the objective and points towards the sky.
These curves are not as obvious as most would have you think. Also, some cells load from the front and some for the back. There are so many variations among manufacturers I no longer berate myself when I assemble my objectives incorrectly. I now consider it part of the process. I mean, If I don't know what the images look like wrong, how will I know what they look like right?!?! Right? Anyways, that's what I tell myself. Yeah, that's it, I assemble them incorrectly on purpose, that's my story...
Posted 02 February 2013 - 04:16 PM
Every two element acromat I've dealt with has had the flint concave side mating with the crown convex side. BUT, every acromat I've dealt with has had the crown on the outside, facing the sky and the flint on the telescope side.
I do seem to remember reading in a thread somewhere about an objective that required the flint to be on the sky side. I can't seem to find it now with a search.
Posted 02 February 2013 - 04:50 PM
As Glenn stated your seeing a large amount of spherical aberration. Either one or more of the surfaces is not spherical, the radius is off, or the two elements are not for the same design. They might have mixed up elementsfrom two different focal lengths. Rotating elements against each other isn't going to fix the problem.
I've had good luck with Surplus Shed over the years but they do make mistakes. A number of years ago I purchased some long focus 60mm achromats were the elements were air spaced and came unmounted. Two of the pairs were correct for each other but the third pair had an element that was very wrong. I sent it back and they refunded the price without any problems.
Posted 02 February 2013 - 05:09 PM
Well, the real test will be when the sun goes down. If the star images are still crud, the Jaegers will go back to SS...
Thanks guys for all your input and advice..
Posted 03 February 2013 - 02:14 AM
But oh my, CA is the worst I've seen in any telescope. The CA on Jupiter is horrible. I put on my minus violet filter plus my #8 yellow filter and the CA was still bad. CA isn't as bad on my 6" f/5 750mm refractor!
Any ideas on what I'm doing wrong now? Or does this puppy need to go back to the Shed?
I put my 80mm f/15 Towa lens back in the scope. Beautiful tight stars again. Looked at the trapezium for a bit, over to Jupiter where I saw at least 3 cloud belts and some hints of detail. Just barely a hint of purple halo. M81 and M82 were easy to see. And I'm sitting here right now waiting for M51 to clear my neighbor's house. Again, thanks all for the help today.
Posted 03 February 2013 - 07:26 AM