Spot diagramsPosted By Roland Christen |
For those who mised the posted semi-apo, here it is.
RC
RC
Posts Made By: Roland Christen
October 12, 2004 04:21 PM
Forum:
Chinese Optics Imports
October 14, 2004 11:46 PM
Forum:
Chinese Optics Imports
Re: A review of the semi-apo prototype?Posted By Roland Christen |
I'm willing to bet he got himself a $555 achromat same as any other, maybe a sharp well made one, but no ED glass in it.
In fact, I'll be willing to measure the color error on this lens if someone wants to send it here and report honestly what it is, or you can send it to Yuri at TEC and I know he will measure and report honestly.
Roland Christen
In fact, I'll be willing to measure the color error on this lens if someone wants to send it here and report honestly what it is, or you can send it to Yuri at TEC and I know he will measure and report honestly.
Roland Christen
October 14, 2004 11:57 PM
Forum:
Equipment Talk
Why Bother With Super Planetary EP's ??Posted By Roland Christen |
You can judge the coatings and internal scatter of almost any eyepiece quite easily yourself. Most coatings are not ideal when applied to multiple elements, and although when properly applied, they may indeed produce good results, all too often coatings in production fall far short of their peak performance. Here is a way to see what you have in any particular eyepiece. I call it the sidewalk test: http://voltaire.csun.edu/roland/coating.html
The test is simple, and instantly shows how much light is scattered internally in an eypiece. Light from the sky is allowed to flood the optics and proceed through to the black cover. Any light that bounces around the optics and comes back to your eye is not only lost to the image, but also contributes to lowering the overall contrast. A "Super Planetary eyepiece" will have few scattering elements and few air-glass surfaces to scatter, reflect and absorb light. Therefore the image will have more contrast inherently.
Roland Christen
The test is simple, and instantly shows how much light is scattered internally in an eypiece. Light from the sky is allowed to flood the optics and proceed through to the black cover. Any light that bounces around the optics and comes back to your eye is not only lost to the image, but also contributes to lowering the overall contrast. A "Super Planetary eyepiece" will have few scattering elements and few air-glass surfaces to scatter, reflect and absorb light. Therefore the image will have more contrast inherently.
Roland Christen
October 15, 2004 09:54 PM
Forum:
Equipment Talk
Re: Sidewalk TestPosted By Roland Christen |
Now, I have tried to duplicate the test as you performed it Roland. The camera was held 3' above the EPs and a bit of telephoto was used to bring them in close so that they could be easily seen.
3 feet is a bit close. Ideally you want to be far away so as not to shade the eye lenses from the light above with your body, and also to provide an almost straight up shot, not from an angle. Still, you can see major differences between the Parks and the Pentax. Now remember, you MUST have the black caps on the other end to absorb the light that does go through - I am assuming that you did do that, correct? You cannot just set them on the white concrete without the end cap because the light from the concrete will then reflect back up and totally spoil the test.
Roland Christen
3 feet is a bit close. Ideally you want to be far away so as not to shade the eye lenses from the light above with your body, and also to provide an almost straight up shot, not from an angle. Still, you can see major differences between the Parks and the Pentax. Now remember, you MUST have the black caps on the other end to absorb the light that does go through - I am assuming that you did do that, correct? You cannot just set them on the white concrete without the end cap because the light from the concrete will then reflect back up and totally spoil the test.
Roland Christen
October 15, 2004 10:52 PM
Forum:
Equipment Talk
Re: Sidewalk TestPosted By Roland Christen |
Now you're cooking with gas. The Pentax and Radian are a mile ahead. The UAW shows typical Meade piss-poor coatings. Maybe their new line will be better.
Even though the UO Ortho says Multi-coated, I doubt seriously that all surfaces are. Probably only one, the eye lens top is multi-coated.
The red coating on the Pentax means that they are off a bit from ideal. Normally when lenses are coated in a chamber, hundreds are placed on a large fixture. The evaporant is down below about 3 - 4 feet away. The distance from the evaporant to the glass is not quite equal for all the different elements, so the layers are not all exactly the same thickness for every lens. The outermost lenses on a fixture normally get slightly less exposure to the evaporant, hence their layers are a bit thinner. Thinner coatings will have a warmer color, thicker a colder blue color. The eye is very sensitive to slight differences, but in this case it amounts to less than a hill of beans.
Roland Christen
Even though the UO Ortho says Multi-coated, I doubt seriously that all surfaces are. Probably only one, the eye lens top is multi-coated.
The red coating on the Pentax means that they are off a bit from ideal. Normally when lenses are coated in a chamber, hundreds are placed on a large fixture. The evaporant is down below about 3 - 4 feet away. The distance from the evaporant to the glass is not quite equal for all the different elements, so the layers are not all exactly the same thickness for every lens. The outermost lenses on a fixture normally get slightly less exposure to the evaporant, hence their layers are a bit thinner. Thinner coatings will have a warmer color, thicker a colder blue color. The eye is very sensitive to slight differences, but in this case it amounts to less than a hill of beans.
Roland Christen
October 15, 2004 10:59 PM
Forum:
Equipment Talk
Cleaning my Nextstar's Corrector Lens ??Posted By Roland Christen |
Interesting. First time I've seen the front of one of these legendary scopes. Measuring the ratio between clear aperture and central obstruction in that picture, I come up with 37%. Is it really that high?
Roland Christen
Roland Christen
October 16, 2004 05:47 PM
Forum:
Equipment Talk
Question for Roland - Was Sidewalk TestPosted By Roland Christen |
I don't use any lens cleaners on eyepieces. I use only common denatured alcohol. I wipe the surface gently with a cotton swab and follow it afterwards with one gentle wipe using a lintless tissue called Opto-Wipe and one or two drops of alcohol. Opto-Wipe is made in Rochester N.Y. by Opto-Alignment Technology.
Roland Christen
Roland Christen
October 16, 2004 09:33 PM
Forum:
Equipment Talk
Sidewalk test continuedPosted By Roland Christen |
Very good! You will see that simpler optical elements show lower reflections due to less air-glass surfaces and the fact that most of them use low index materials like BK7. These will generally have the lowest reflections because multi-coating technology gets more and more difficult to apply in high index glasses like Lanthanum and dense flints. These high index glasses are used to provide large aberration free fields, but they require the utmost care in the coating design and manufacture.
This is generally where the manufacturers cut corners to either save money or to speed up the process (to save money). As long as you, the purchsing public does not know this, they will take every advantage they can get because this is a super competitive field.
Roland Christen
This is generally where the manufacturers cut corners to either save money or to speed up the process (to save money). As long as you, the purchsing public does not know this, they will take every advantage they can get because this is a super competitive field.
Roland Christen
October 19, 2004 02:16 AM
Forum:
Equipment Talk
"ENOUGH" EYEPIECES?Posted By Roland Christen |
You only have 12??? I have at least 50 eyepieces if I count the one I got out of the scrap heap at B&L back in 1968.
Roland Christen
Roland Christen
October 25, 2004 06:51 PM
Forum:
Equipment Talk
Coronado Newsflash!Posted By Roland Christen |
I believe that Daystar has offerec Calcium filters in the past. Not a hot seller.
Rolando
Rolando
Funding Member
