Shortening or lengthing the tube

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JCTyler
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Shortening or lengthing the tube

#1 Post by JCTyler » Tue Feb 14, 2023 7:01 pm

Would an adapter (RMS to M26 thread) that adds 5mm to the front the revolving nosepiece be considered as adding to the tube length? From what Ive seen tube length is measured from bottom of revloving nosepiece. On a similar point, what affect does lengthening or shortening the tube have?

apochronaut
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Re: Shortening or lengthing the tube

#2 Post by apochronaut » Tue Feb 14, 2023 7:31 pm

It depends whether the system is infinity or finite ?

BramHuntingNematodes
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Re: Shortening or lengthing the tube

#3 Post by BramHuntingNematodes » Tue Feb 14, 2023 9:02 pm

Either way that would le.gthen the tube. Infact it's simpler for finite as it's very obvious that you are change the position of the objective with respect to the eyepiece. In infinite systems there is a reference length but it's my understanding that objective performance will not suffer from changing the tube length
1942 Bausch and Lomb Series T Dynoptic, Custom Illumination

apochronaut
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Re: Shortening or lengthing the tube

#4 Post by apochronaut » Wed Feb 15, 2023 2:12 am

BramHuntingNematodes wrote:
Tue Feb 14, 2023 9:02 pm
Either way that would le.gthen the tube. Infact it's simpler for finite as it's very obvious that you are change the position of the objective with respect to the eyepiece. In infinite systems there is a reference length but it's my understanding that objective performance will not suffer from changing the tube length
The reference length is between the telan lens and eyepiece. Adding a small amount of length in the infinity space does not affect the reference length.

JCTyler
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Re: Shortening or lengthing the tube

#5 Post by JCTyler » Wed Feb 15, 2023 2:40 am

Its a finite distance objective lens. Its a Nikon BD plan

apochronaut
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Re: Shortening or lengthing the tube

#6 Post by apochronaut » Wed Feb 15, 2023 3:39 am

There is more effect upon long focal length objectives, mainly the working distance and parfocality. Above about 16mm , not so much.

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blekenbleu
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Re: Shortening or lengthing the tube

#7 Post by blekenbleu » Wed Feb 15, 2023 9:56 am

JCTyler wrote:
Wed Feb 15, 2023 2:40 am
Its a finite distance objective lens. Its a Nikon BD plan
Nikon sold adapters for that purpose, e.g. to use M Plan objectives in a BD turret.
Those objectives are 210 tube length; a few mm has about 1/4 less impact than for 160 tube length objectives.
Metaphot, Optiphot 1, 66; AO 10, 120, EPIStar, Cycloptic

JCTyler
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Re: Shortening or lengthing the tube

#8 Post by JCTyler » Wed Feb 15, 2023 9:59 pm

So what would putting an adapter tube shorter that 45mm do? What about constructing an adapter with 5 mm increments marked thats two tubes that can slide one inside other thats at least 60 mm long to see what quality of image I get, from 40,45 and 50 mm?

Is there any way to improve the deptth of field without changing the lens?

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blekenbleu
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Re: Shortening or lengthing the tube

#9 Post by blekenbleu » Thu Feb 16, 2023 10:18 am

JCTyler wrote:
Wed Feb 15, 2023 9:59 pm
So what would putting an adapter tube shorter that 45mm do?
Much depends on objective optical design specifics.
https://blekenbleu.github.io/microscope/basics/#TL
Metaphot, Optiphot 1, 66; AO 10, 120, EPIStar, Cycloptic

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