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2x objectives

 
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johan



Joined: 06 Sep 2011
Posts: 1004

PostPosted: Mon Jan 09, 2012 5:23 am    Post subject: 2x objectives Reply with quote

Hello,

Does anyone have successful experience using a cheap or noname finite 2x objective and using a long bellows to stretch this to 3,4,5x to get decent quality? I can find plenty of 2x objectives around but they seem to be either ultracheap or ultraexpensive with relatively little in the middle.

Many thanks
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Charles Krebs



Joined: 01 Aug 2006
Posts: 5805
Location: Issaquah, WA USA

PostPosted: Mon Jan 09, 2012 8:53 am    Post subject: Reply with quote

johan,

Ironically you really need to watch out for the working distance with 2X objectives. I have a 2 Nikon finite 2X objectives... a Pan Apo and an Plan Achromat. The working distances are 5.3 and 5.8 respectively. This is about half what you can get with some 10X achromats, and about 1//3 what a 4X (Apo or Achromat) can provide.

A 2X finite objective has a focal length in the 75- 80mm range. A Plan Apo may have an aperture "equivalent" to about f/4.1, but the typical achromat will have an aperture "equivalent" to about f/6.7. As a result you are generally better off using a good 80mm enlarging lens. You will have much greater working distance and not be giving up much, if anything, in the way of maximum usable aperture.

10x is generally the point at which it is very hard to beat a microscope objective for image quality (the larger useful aperture= greater resolution). At 4X and 5X there are other options that will provide results comparable to objectives. (But a good 4X or 5X is nice to use on a bellows, and can have adequate working distance).
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johan



Joined: 06 Sep 2011
Posts: 1004

PostPosted: Mon Jan 09, 2012 9:10 am    Post subject: Reply with quote

Charles,

Thank you very much for the warning regarding this. I have been using my son's 10x objective to try out objectives and the 9?mm wd is, let's say, not without considerable challenges. I wouldn't like to try even less, yet. Working with that 10x was well worth doing but on my apsc it only shows one fly eye (see flickr link in sig) so I was after something with less magnification, hence the question.

Thanks again.
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