I did another Roddier test, this time of my son's Orion XT4.5 Dob. This is a 114mm f/7.9 dob with a spherical primary mirror. Star testing visually I rated it...
Zoiks! I just processed a NexImage webcam run on the TEC APO180FL using polychromatic data. I took the image with the NexImage attached to an AP MaxBright...
Hi Philip, It is encouraging that the webcam is in the same range as the CCD camera! This "polychromatic" value is, I think, different from what a lens...
Using ray-tracing in ZEMAX, I get something like 1/16 wave RMS error (550nm green light) for a spherical mirror with these specs -- pretty good agreement with ...
You raise some very good points about the "polychromatic" test, which definitely should be put in quotation marks. I think the best that can be said is that...
hi to all,i want test my optics whit webcam,i do insert a barlow and defocus a star in intra and extra focal,or i don't insert a barlow and defocus a star?...
It is better to not use the Barlow if possible. You need to take images a few mm inside and outside best focus, using same distance on each side of focus. If...
You may want to try looking at the "cookbook" that John so helpfully put together. It's in the "Files" section of this group and shows exactly the steps...
Hello, I have a question re; the size of images used with this program. I stacked two green waveband images from an avi taken with a Neximage at prime focus,...
Based on the JPG images posted of the original intra & extra focal images - I believe that a Strehl of .95 is likely a little to high. Keep in mind that this...
I do not know if it's small enough to effect the accuracy of the test. The software author recommends 100 to 150 pixel image with with 9um pixels (the google...
Hello Mardi, Some nice results with interesting questions! I will try to answer below. ... at ... achromat. ... skewed ... to ... About the image size....
Hi Mike, Lots of interesting questions.... ... I agree 0.95 may be a little high for the astigmatism, but I have not used his scope so I do not know of course....
Hi Philip, ... test. ... micrometers ... 100 ... I think "misters" must be "millimeters." From what I have seen the image size does not effect the results very...
Hi John, Thanks so much for the "step-by-step" instructions, etc. :) I applied the 3x reduction you suggested for better estimatation of the astigmatism to...
Hi Mardi, Very nice web page you have there! Comparing the Roddier image with the Zerike values, I would say it seems consistent. It looks to me like the...
Hi, My name is Jerry. I have a couple of 114mm mirrors I need to get checked out. Specifically I need to check for parabloid vs spherical shape. Also I would...
Hi Jerry, If these scopes have only mirrors (no lenses) then you can probably skip the IR filter. I mention it since there are some short 114mm scopes with a...
Hi John, thanks again for the thoughtful response. :) and yes feel free to link to the test page. I have not noticed any astigmatic images visually, no. The...
Hi Mardi, Some quick answers.... ... so ... it. ... the ... I ... of ... Yes, reflector has bright first Airy ring due to central obstruction. And indeed, a...
I did a test of my daughters Hardin DSH 6" f/8 Dob. The images were taken with a NexImage webcam ( I can't get the SBIG ST-5C to focus in my small Dobs)....
Looking back at the images I took, I realized that the ST-5C images are not good images. They are far too close to the full well capacity of the CCD device...
Hi Philip, ... capacity ... second ... Yes, I was wondering about that. ... closer ... for ... the ... I'll ... Will be very interesting to compare Roddier and...
Interesting. I have sometimes seen that the odd run will give a strange (usually low) result for Strehl. Not sure if it is S/N, moments of bad seeing, etc. ...
So I took some shots of Capella through the Traveler tonight. The results in green light of a NexImage webcam are 1/61.8 RMS, 1/11.0 PTV and a strehl of 0.99....
Hi Philip, ... I think this is excellent agreement. I would not worry about the last 0.007. Curious -- who did the interferogram? ... Yes, I'd be interested...
When I got my Traveler back in 1997, I was concerned about it's performance because I read on SAA (sci.amateur.astro) about all these "perfect" star tests....
I have been informed that when one does not use a filter, an apo appears undercorrected in a star test. When you use a green-yellow filter, does the ...
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