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Infinity objective tube lens - use zoom or Raynox
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rjlittlefield
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Joined: 01 Aug 2006
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Location: Richland, Washington State, USA

PostPosted: Thu Dec 06, 2018 11:54 am    Post subject: Re: I think I have the distance and magnificaiton bit down n Reply with quote

kpassaur wrote:
You mentioned changing the distance from the tube lens to the objective would not change magnification. Would it change the size of the image on the sensor. Currently I am losing a little in the corners on a FF, would changing this distance correct this or is it just how it goes?

I assume that "size of the image" means the size of the high quality image circle, with no change of magnification.

That's hard to predict. If you have darkening of the corners, then reducing the distance between objective and tube lens can help. If your corners are not darker but are losing quality due to aberrations, then changing the distance may help but you have to test both less and more.

Quote:
I could correct it by shortening the distance from the tube lens to the sensor but that would be a trade off as mentioned above.

Shortening? I would expect improvement by lengthening the distance from tube lens to sensor, thus making the image larger (both circle and magnification). Is "shortening" a typo, or have I missed something?

--Rik
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kpassaur



Joined: 24 Mar 2015
Posts: 21

PostPosted: Thu Dec 06, 2018 11:59 am    Post subject: Typo Reply with quote

Yes, you are correct I think shortening the distance may correct the corners. It only loses a little when using a Raynox 150. I will see what I get with the 250.
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santiago



Joined: 25 Sep 2018
Posts: 86
Location: Nijmegen, The Netherlands

PostPosted: Thu Dec 06, 2018 12:42 pm    Post subject: Re: Converting Um's Reply with quote

rjlittlefield wrote:
That range is wide for small NA objectives, and progressively narrower for larger NA.


Definitely, with my Nikon 10x/0.25 I can expand or contract the accordion as much as my bellows allows it without degrading the image quality dramatically. I was actually shocked to discover this!

For larger NA I believe this range of acceptable change becomes exponentially narrower... actually I need to test deviating from the design point with the Mitutoyo 20x/0.42 and see what happens!

Very interesting graph btw. For some reason I cannot open/download the PDF of the original article (I tried with 3 browsers). Or is this article not for public access?
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Santiago
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kpassaur



Joined: 24 Mar 2015
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PostPosted: Thu Dec 06, 2018 12:58 pm    Post subject: Bellows Lenght Reply with quote

I am seeing the same thing. If I focus at infinity with the Nikon 10x Plan .25 I am right at 10x (3 lines exactly on my ruler). If I expand the bellows a little more it seems to start to go down a little in quality. I'm not sure how much and it could be me my bellows does not go much beyond it anyway. However, shorter the bellows and the image quality seems to be very good down to between 5x and 6x. So this looks like just what I wanted.
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rjlittlefield
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Joined: 01 Aug 2006
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Location: Richland, Washington State, USA

PostPosted: Thu Dec 06, 2018 1:02 pm    Post subject: Re: Converting Um's Reply with quote

santiago wrote:
For some reason I cannot open/download the PDF of the original article (I tried with 3 browsers). Or is this article not for public access?

You have to pay money. For me, clicking the PDF link refreshes the page with a different right-side panel that asks me to login or "Purchase instant access". A couple of years ago I did pay the required $38 to get a PDF that I can now refer to whenever I want. But of course the licensing terms don't allow me to redistribute it. $6 will get you "rent for 48 hours".

Quote:
For larger NA I believe this range of acceptable change becomes exponentially narrower

It's a power relationship, NA^4 for dry objectives. In the graph, the power is designated v.

--Rik
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santiago



Joined: 25 Sep 2018
Posts: 86
Location: Nijmegen, The Netherlands

PostPosted: Thu Dec 06, 2018 1:08 pm    Post subject: Re: Bellows Lenght Reply with quote

kpassaur wrote:
I am seeing the same thing. If I focus at infinity with the Nikon 10x Plan .25 I am right at 10x (3 lines exactly on my ruler). If I expand the bellows a little more it seems to start to go down a little in quality. I'm not sure how much and it could be me my bellows does not go much beyond it anyway. However, shorter the bellows and the image quality seems to be very good down to between 5x and 6x. So this looks like just what I wanted.


Yes, it's not that bad indeed Smile

Quote:
Yes, you are correct I think shortening the distance may correct the corners.


I think what Rik is saying is that lengthening the distance from tube lens to sensor will improve the quality, not shortening it. If you lengthen the distance, the projected image will get larger and the problematic corners will be "excluded" from the sensor.
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Santiago
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santiago



Joined: 25 Sep 2018
Posts: 86
Location: Nijmegen, The Netherlands

PostPosted: Thu Dec 06, 2018 1:21 pm    Post subject: Re: Converting Um's Reply with quote

rjlittlefield wrote:
For me, clicking the PDF link refreshes the page with that asks me to login or "Purchase instant access". A couple of years ago I did pay the required $38 to get a PDF that I can now refer to whenever I want. But of course the licensing terms don't allow me to redistribute it. $6 will get you "rent for 48 hours".


Yes, I missed that panel Embarassed

Quote:
It's a power relationship, NA^4 for dry objectives. In the graph, the power is designated v.


That is a huge reduction... and for immersion even worse: 6.33!
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