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3x afocal lens versus 75mm fujinon c mount lens

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#1 Gavster

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Posted 08 June 2021 - 02:14 AM

I had a few minutes last night so decided to compare my two ultra grab and go setups, looking at Cygnus and Sagittarius which are both now in decent positions (but with little sky darkness of course given time of year!)

One of the things I really like about my gen 3 thin filmed tubes is that they give very sharp stars and therefore, with the gain adjusted down a bit, show exceptional natural views, just like a normal setup, but of course able to see much more. The North America, Gamma Cygni, Swan and Eagle were all very nice even at just 3x and in a 17ish sqm sky.

 

Despite the vignetting caused by the positioning of the filter, I much preferred the views with the 3x afocal setup, pin sharp stars and very nice nebulosity. In comparison, the 75mm fujinon (which gives very close to 3x as well) showed bloated stars and even with no vignetting I just didn't like the views - they weren't natural.

 

The 3x afocal setup generally gets little love on here, but for me its definitely my preferred ultra grab and go setup. Last night's experience has really confirmed this. 
 

Photo below shows the fujinon setup on the top with the afocal 3x below.

Attached Thumbnails

  • CAFABB60-3EDA-4582-9AC9-6847163A1E5E.jpeg

Edited by Gavster, 08 June 2021 - 02:23 AM.

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#2 AllStarez

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Posted 08 June 2021 - 03:47 AM

Interesting  

any picture of both results on sky ? grin.gif



#3 Gavster

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Posted 08 June 2021 - 03:57 AM

Interesting  

any picture of both results on sky ? grin.gif

Not yet. Will try sometime. I think the difference will show quite easily.


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#4 ArsMachina

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Posted 08 June 2021 - 03:59 AM

Very interesting indeed.

 

What is the outside diameter of the 3x lens, I wonder if it is also usable binocular with an IPD of 62mm?

And what is the weight of one of these?

 

Thank you Jochen



#5 a__l

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Posted 08 June 2021 - 04:37 AM

 In comparison, the 75mm fujinon (which gives very close to 3x as well) showed bloated stars and even with no vignetting I just didn't like the views - they weren't natural.

 

There are no bloated stars in this Fujinon.
You have some problem. Does the lens correspond to infinity (or close) when you look at the stars? Is it in focus? Is the lens fogged up?
 


Edited by a__l, 08 June 2021 - 04:51 AM.


#6 Gavster

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Posted 08 June 2021 - 04:43 AM

There are no bloated stars in this Fujinon.
You have some problem. Does the lens correspond to infinity (or close) when you look at the stars? Is it in focus?
At one time, Gavster looked into this Fujinon and noted its advantage over the standard 3x.
I don't see any problem with this lens, everything is fine.

Yes it’s in focus, and I don’t have a problem with the setup. Over time I’ve changed my mind on the fujinon, the stars were always less sharp. My personal preference now is for very sharp stars and accept some vignetting.



#7 a__l

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Posted 08 June 2021 - 04:59 AM

Strange, earlier you wrote something completely different. When the comparison was made with standard 3x.
My opinion has not changed.



#8 Gavster

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Posted 08 June 2021 - 05:55 AM

Strange, earlier you wrote something completely different. When the comparison was made with standard 3x.
My opinion has not changed.

Yes my opinion has changed with further use of these setups.


Edited by Gavster, 08 June 2021 - 06:30 AM.


#9 Gavster

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Posted 08 June 2021 - 06:48 AM

Very interesting indeed.

 

What is the outside diameter of the 3x lens, I wonder if it is also usable binocular with an IPD of 62mm?

And what is the weight of one of these?

 

Thank you Jochen

Jochen

This thread may be useful for you - see Eddgie’s solution using 3D printing.

https://www.cloudyni...-the-way/page-2

The diameter is 66mm at the end, but you can take the end caps off to reduce this further. Not sure on weight but they are light.
 


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#10 ArsMachina

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Posted 08 June 2021 - 07:10 AM

The diameter is 66mm at the end, but you can take the end caps off to reduce this further. Not sure on weight but they are light.

 

Thanks, also for the 3D printing link, Gavin.

My limit is 62mm, can this be reached by taking the end caps off?

 

Thanks Jochen



#11 a__l

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Posted 08 June 2021 - 08:00 PM

The bloating of stars in NV depends on the brightness of the star and on the properties of the tube. If the lens does not show obvious others aberrations, a technique is needed to detect the contribution to the bloating of one or another lens. I hope you have it.
Fujinon-CF75HA this megapixel high resolution (machine vision) lens.
Vignetting 62 mm (3x standard) and 49 mm (Fujinon) for filter 2" (~48 mm) is clearly visible and can be immediately attributed to the properties of the lens.



#12 Gavster

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Posted 08 June 2021 - 11:30 PM

The bloating of stars in NV depends on the brightness of the star and on the properties of the tube. If the lens does not show obvious others aberrations, a technique is needed to detect the contribution to the bloating of one or another lens. I hope you have it.
Fujinon-CF75HA this megapixel high resolution (machine vision) lens.
Vignetting 62 mm (3x standard) and 49 mm (Fujinon) for filter 2" (~48 mm) is clearly visible and can be immediately attributed to the properties of the lens.

Indeed I do. The 3x afocal lens is specifically designed for use with the nv monocular whereas the c mount isn’t - it makes a difference. See this thread which covers some of the issues that standard c mount lens have when used with nv monoculars. For 1x viewing I use either the envis lens or with my pvs14, milspec Carson lens (much superior to European pvs14 front glass) which both give very sharp stars.

https://www.cloudyni...n-device/page-2
I use a 1.25 filter put ahead of the afocal lens not a 2 inch filter mounted to the 62mm ish front lens.


Edited by Gavster, 08 June 2021 - 11:58 PM.


#13 a__l

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Posted 09 June 2021 - 12:33 AM

It does not follow from your last post and links that the stars in Fujinon are more bloated than in the standard 3x.
Use in a converging fast cone requires filters which are absent (for fast 1.2 ... 1.4)

About vignetting in the discussed Fujinon there is your post earlier (about six months).  It is insignificant.


Edited by a__l, 09 June 2021 - 12:48 AM.


#14 Gavster

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Posted 09 June 2021 - 01:06 AM

It does not follow from your last post and links that the stars in Fujinon are more bloated than in the standard 3x.
Use in a converging fast cone requires filters which are absent (for fast 1.2 ... 1.4)

About vignetting in the discussed Fujinon there is your post earlier (about six months).  It is insignificant.

I’m reporting what I actually see when directly comparing the two setups. The stars are more bloated with the fujinon.



#15 GeezerGazer

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Posted 09 June 2021 - 08:53 AM

This issue, concerning vignetting vs. star bloat, may come down to personal preference.  I personally would rather see a little star bloat rather than moderate vignetting, but I have never compared the two systems (prime vs. afocal) for star bloat.  I did compare them for vignetting, which is very annoying to me personally.  But alas, I no longer have an afocal lens to conduct a comparison, so I rely on Gavster's perceptions.  However, I do have several prime lenses that I can compare specifically for star bloat, including the Fujinon 75mm.  But this will have to wait until I am next at home, as Ohio skies are pretty dreary at the moment.  

 

This issue may also be affected by filter placement... a first surface (front mounted) filter presents much different issues than a filter mounted behind the objective optics.  I tentatively attribute the differences to the change in the structure of the light cone after passing through the optical system, to a rear mounted filter.  For sure, band shift/vignetting is much more pronounced with first surface filters.  More to follow about this in a separate thread... soon.  

Ray


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#16 a__l

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Posted 09 June 2021 - 07:10 PM

I’m reporting what I actually see when directly comparing the two setups. The stars are more bloated with the fujinon.

Details appear, which is good.
It is correct to check not on two different NVs, but on one.
Another point, the f/1.2 lens has problems on the edge. Added to this is an f/1.4 Galilean afocal lens. Fujinon was originally designed as a single f/1.8 unit. I don't have PVS-14, so I can't compare. Therefore, we will wait for the photo.



#17 a__l

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Posted 09 June 2021 - 07:40 PM

Despite the vignetting caused by the positioning of the filter, I much preferred the views with the 3x afocal setup, pin sharp stars and very nice nebulosity. In comparison, the 75mm fujinon (which gives very close to 3x as well) showed bloated stars and even with no vignetting I just didn't like the views - they weren't natural.

 

The 3x afocal setup generally gets little love on here, but for me its definitely my preferred ultra grab and go setup. Last night's experience has really confirmed this. 
 

Photo below shows the fujinon setup on the top with the afocal 3x below.

Did someone disassemble your Fujinon and assemble it incorrectly? Is it used or new? The narrowband filter further reduces star bloating. Curious this is how bad the lens, has to show nebulae with stars "weren't natural" in Fujinon and "natural" in 3x.

 

Ps. I will probably have to take my wife's iPhone and study photography on it smile.gif My camera is heavy and I already fear for my FT focuser, it turns out to be a heavy and long console and already now my device is working at its limit (in my opinion). For hands-on use with Fujinon+NV, this is also a problem.

I don't use iPhon in my everyday life due to size, weight and electricity consumption.


Edited by a__l, 09 June 2021 - 10:44 PM.


#18 Gavster

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Posted 10 June 2021 - 01:10 AM

I have a brand new fujinon lens which has not been disassembled!
I have checked this with the same nv unit since I have an envis lens that can be used easily with the 3x afocal lens. Both my envis lens and milspec Carson pvs14 lens are very good across the full fov including the edge - I understand you use different f1.2 lens which may have different results. Indeed the envis lens on its own operating at 1x shows very sharp stars across the fov compared with the fujinon.

 

Of course, due to the edge vignetting of the 3x afocal lens the extreme edge performance of the envis/pvs14 lens isn’t relevant in any case.


Edited by Gavster, 10 June 2021 - 01:17 AM.


#19 a__l

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Posted 10 June 2021 - 01:14 AM

Ok.
It will be interesting to see a comparative photo. If possible.



#20 GeezerGazer

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Posted 12 June 2021 - 11:19 AM

Please see post 11 in this thread:  

https://www.cloudyni.../#entry11157498

The photo results that are of interest in this post were limited to rear-mounted, 3.5nm filters on an f:1.4 lens. 

 

This might be wrong headed, but the star bloat I have seen in the past has been pretty much limited to my 120mm f:5 achromatic refractor, where different light colors are not focused at the same point.  With that optical system, using a 7nm H-a filter actually reduces star bloat by eliminating much of the visible spectrum!  I wonder if the star bloat described in post #1 in this thread by Gavster has anything to do with chromatic distortions... because of the combination of fast optical speed (f:1.4) combined with the very narrow band 3nm filter? 

 

Neither my 50mm Nikon lens, nor my Fujinon 75mm lens are apochromatic.  I have always assumed that the use of an H-a filter reduces so much of the visible spectrum that only a small slice near the H-a band is presented in the NVD ocular.  But I don't know what actually happens to the light that is passed through the filter and the lens optics, especially with rear mounted filters.  I now have questions about star bloat; the tests I suggest in the other thread may reveal some answers.

 

In dealing with different optics, I have found that optical focal length AND aperture size seem to have a bearing on H-a performance.  And I know that it is more difficult to see star bloat when using a 26mm, 1x lens with 40° FoV... compared to a 75mm, 3x lens with ~13° FoV.  My gut tells me that all tests for star bloat should be conducted on each lens, using 2-4 lenses as the basis for the test.  

Ray


Edited by GeezerGazer, 12 June 2021 - 11:38 AM.

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#21 a__l

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Posted 17 June 2021 - 06:32 PM

Gavin, there are many topics on this forum on how to distinguish PVS-14 fake lenses from real ones.

Here is a link to one of the topics.

 

https://www.ar15.com...rmal/18-510682/




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