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oil spacing in fracs

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56 replies to this topic

#51 bobhen

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Posted 11 January 2020 - 01:00 PM

Seems that serious lens centering issues with "TOAs" and its "first run" was:

 

"There is some misunderstanding about the earlier model of TOA-130. At the first stage of our introduction of TOA-130, we have received many claims for almost all TOA-130 OTA from our USA dealer that there was astigmatism on TOA-130, and according to their expectation, the astigmatism was caused by the lens cell.
After receiving this claim from USA, our technicians have checked and investigated in details spending a lot of time and finally found that the USA dealer has used inaccurate collimation tools and they have visited Japan, and have acknowledged their misjudgment. This is the real story and we confirm that there was no problem at all on the lens cell of TOA-130 from the beginning. If you heard such claim from somebody, it is a definitely rumor, and we have never changed nor modified the lens cell of TOA-130 since our first introduction till now." (Takahashi Japan)

 

https://www.cloudyni...40-tak-toa-130/

Okay I can believe that.

 

The same, however, cannot be said for the first run of Sky 90s, which were revised to the Sky 90 II. The point is that lens cells are a lot more critical with air-spaced designs.

 

Bob


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#52 edif300

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Posted 11 January 2020 - 04:45 PM

I think there is no prone to being critical by just using an air gap, oil gap or cemented lens.

Direct pointly made pressure over the lens could produce aberration and oil sealing by tape could leaking.

A good design is the answer to avoiding issues.

#53 Jeff B

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Posted 11 January 2020 - 05:44 PM

I think there is no prone to being critical by just using an air gap, oil gap or cemented lens.

Direct pointly made pressure over the lens could produce aberration and oil sealing by tape could leaking.

A good design is the answer to avoiding issues.

Yes but it needs to be well made too as a well made poor design will give you the same result as a poorly made good design.  

 

You really need both in the same sample.... a well made, good design.


Edited by Jeff B, 11 January 2020 - 05:44 PM.


#54 Mike Spooner

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Posted 13 January 2020 - 09:36 PM

Use synthetic and you can go 10,000miles between changes. lol.gif

I oiled my nine inch doublet when I made it 25 years ago and it's been light years without a change.wink.gif

 

Seriously though, I used a couple drops of medical grade mineral oil and haven't had any problems. 

 

Mike Spooner


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#55 Jared

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Posted 13 January 2020 - 10:17 PM

Good grief, one would think from the discussion here that a lens that needs to be re-oiled or re-aligned is a disaster. Sure, it’s an annoyance and will involve some cost to repair, but the lens can be made good as new. Truly. Good as new. That’s true for re-oiling. It’s also true for air spaced lenses that get de-centered.

These aren’t common events or routine maintenance items, though. Refractors, in general, are the most maintenance free telescopes out there. No mirrors to re-aluminize. No routine collimating. Both oiled and air spaced designs can last a lifetime without issues. Would you avoid fluorite because it’s prone to shatter if you drop it? I saw this happen once. It’s not a myth. Lenses can shatter. Should we avoid just avoid telescopes altogether because they might break or malfunction in less than fifty years of use?
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#56 donadani

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Posted 14 January 2020 - 10:53 AM

Fluorit is very sensitive to temperature - I heared if one puts an fluorit lens out in winter nights it could break shocked.gif - imagine what this means to an oil spaced apo... shocked.gif  shocked.gif  shocked.gif



#57 bobhen

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Posted 14 January 2020 - 11:08 AM

Fluorit is very sensitive to temperature - I heared if one puts an fluorit lens out in winter nights it could break shocked.gif - imagine what this means to an oil spaced apo... shocked.gif  shocked.gif  shocked.gif

Do you really think manufacturers would use Fluorite if that were the case? Come on now.

 

Oil-spaced objectives actually have advantages in cold weather, as they cool relatively quickly. 

 

Fluorite is and has been used successfully in both air and oil-spaced objectives for almost 50 years, not to mention camera lenses.

 

People; just buy the refractor that meets your needs. Chances are it will outlast you and with much less maintenance.

 

Bob


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