Fair price for Unitron 75mm f/16 Objective.
Posted 07 April 2013 - 07:15 PM
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Posted 11 April 2013 - 09:59 AM
Posted 11 April 2013 - 10:09 AM
Posted 11 April 2013 - 10:59 AM
Posted 11 April 2013 - 11:26 AM
Posted 11 April 2013 - 12:14 PM
While that maybe true, I don't believe they understand how to test these lenses. When you do a double pass autocollimation test you need to adjust the position of Ronchi screen so your viewing 5 bands or less. If your viewing more bands the sensitity is not very great and lines will look straight.
I sent Surplus Shed an e-mail asking for a matched set, and they said they Ronchi test each lens set before shipping.
I've purchased a number of Jaegers objective from them over the last 2 years. Attached is picture of 4" f/15 on my test setup using double pass autcollimation. As one can see the lines are bowing and from the amount I judge this objective to have about 1/4 wave or worse of overcorrection. This is typical of the objectives I have purchased.
Posted 11 April 2013 - 02:53 PM
Posted 11 April 2013 - 02:57 PM
Posted 11 April 2013 - 04:26 PM
I used the spacer provided with the lens and also varied the spacing. It didn't help. I have the Baker design in OLSO files so I can see what happens when the air space is varied. When you vary the air spacing you also change were the red and blue wavelengths come to focus. So you need to test that has well, if not the performance can look better in the green but the color correction can then be much worse.
Did you use the 0.100 to 0.120" spacer in that test? I did notice with my 4" F15 that the correction was best with the spacer as it is a supposed to be a Baker design. 2-3mm may not give enough under correction. to fix the over correction.
The best way to fix one of these objectives is to refigure a surface or surfaces. That is why I have purchasing the uncoated ones since I can starting refiguring them without having to polish off the anti-reflective coating.
Posted 11 April 2013 - 04:42 PM
Posted 11 April 2013 - 05:26 PM