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Wide Angle Night Vision on meteors and such

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#26 john hraba

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Posted 24 July 2020 - 03:21 PM

I think that this is not entirely true. 75 and 50mm stand-alone f/1.8

 

What users write in the review, you must match the position in the lens adjustment at infinity (or close) and a sharp image on the tube. Otherwise, the picture becomes softer around the edge. Although it may have something to do with my next comment.

 

Likewise. The closer the lens (glass) is to the tube (more precisely to the out hole), the less vignetting. In my case, there are additional option. I can cut the right side of the threaded bronze c-mount adapter to a minimum. Photo. In order to further reduce vignetting. Whether this makes sense, we'll see later.

 

This is not the case for 75 mm. I don't see vignetting using 2" filters.

In any case, I am moving in the direction of decreasing the focal length of the lens and my next step will be CF25 mm (package on the way).

 

Should not be concerned about the shine of the internal thread of the adapter. In any case, Televue doesn't care.

My comments are true and correct as written.



#27 john hraba

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Posted 24 July 2020 - 03:22 PM

Forgot to give location-(Fireball-Photo)-March 2002 Astronomy Magazine, Pg 103. Article by me too.

A link, if available, would be appreciated.



#28 a__l

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Posted 24 July 2020 - 05:11 PM

My comments are true and correct as written.

Specify, with your washer (1 mm), the lens position at infinity corresponds to focusing on the tube (sensor)? For 1.4 Actually for me the most important nuance until my CF25 arrived.

As for the CF75, I have a different opinion on both vignetting and softness of the image.


Edited by a__l, 24 July 2020 - 05:32 PM.


#29 john hraba

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Posted 25 July 2020 - 02:03 PM

Specify, with your washer (1 mm), the lens position at infinity corresponds to focusing on the tube (sensor)? For 1.4 Actually for me the most important nuance until my CF25 arrived.

As for the CF75, I have a different opinion on both vignetting and softness of the image.

I will try to answer your question.  With the 1mm shim in place the lens produces an in focus image of stars (infinity focus) with the lens at what I will call the infinity focus position.  Since the lens does not have a distance scale, this infinity focus position is near the extreme in, what the lens indicates is, the far focus direction. If I increase the shim pack thickness to 1.2 mm the lens will no longer reach infinity focus.  

 

Please do not assume that the lens' flange focal distance is incorrect because of this need for a shim.  The MOD3-C when equipped with an Envis lens would normally have a 1mm thick o-ring in place between the back flange of the Envis lens and the c-mount mounting flange.  The 1mm thick shim I am using makes up for that o-ring not being present.

 

With regard to your opinions on vignetting and softness which I believe to be true for your CF75HA-1;  I understand and expect each of the focal lengths in the series to have some differences.  This is why in my original post I said "I believe most of what I learned would apply to the other focal lengths in the CF-HA series".   I did not say that what I learned would apply to all focal lengths in the CF-HA series.


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#30 a__l

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Posted 25 July 2020 - 05:45 PM

Ok. Thanks.



#31 PEterW

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Posted 26 July 2020 - 02:29 AM

I picked up a low cost 16mm, stars seem pretty good across the field, but it’ll need a thin shim to move infinity focus away from right at the end of the focal range. Now need a way to hold a filter on the end.

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#32 a__l

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Posted 26 July 2020 - 05:09 AM

It looks like the filter problem for CF16 has no solution. Wide light cone at the lens input. There is no way to install a filter between the lens and NV.


Edited by a__l, 26 July 2020 - 05:11 AM.


#33 nimitz69

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Posted 26 July 2020 - 11:13 AM

Never say never when it comes to needing a solution for something connected to NV astronomy ....smile.gif

#34 GrahamDFyffe

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Posted 26 July 2020 - 12:04 PM

Will lenses designed fir APS-C fully illuminate the sensor on a Mod . There seem to be many of these available in the 16mm range. Some seem to be Nikon F Mount that I can fit filters in.



#35 cnoct

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Posted 26 July 2020 - 12:22 PM

Yes, yes it will.



#36 a__l

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Posted 26 July 2020 - 06:17 PM

Never say never when it comes to needing a solution for something connected to NV astronomy ....smile.gif

I'm talking about a specific lens and specific NV body and standard filter sizes of 1.25 or 2". Buy a larger filter and fix the problem. But it will be expensive. In this case, it is cheaper to switch to another lens standard.


Edited by a__l, 26 July 2020 - 06:20 PM.


#37 a__l

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Posted 27 July 2020 - 06:36 PM

The filter can be used with CF25 without any problem. The stars are pretty good all over the field. Slight vignetting around the edge. I recommend.

Attached Thumbnails

  • CF25_.jpg

Edited by a__l, 27 July 2020 - 06:42 PM.


#38 GrahamDFyffe

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Posted 30 July 2020 - 12:55 PM

I bought a Bower 16mm wide cine lens. It's only F2.2 but it does seem to fully illuminate the Mod3 sensor and I can simply attach 1.25 filters also with no significant vignetting

 

 

16mm lens setup

 

This shows how I attach the 16mm F2.2 Bower lens to the Mod 3c.

Left Bower 16mm lens, Nikon F type attachment
Right Mod 3c
Center Top to Bottom
Pixco Nikon F type to M42 adapter
10mm T2 extension
ScopeStuff T2 1.25 filter adapter
1.25 filter
ScopeStuff C2TT adapter


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#39 hoof

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Posted Yesterday, 01:33 PM

The Samyang 16mm F/2 (which the Bower 16mm is based on) is a nice lens, if you can find a good copy.  I had one for a few years.  Replaced it with the Tokina 14-20mm F/2, as it was optically just as good, but zoomed.

 

A few nights ago I tried a few of my wide-angle lenses for meteor hunting.  Didn't see any meteors, unfortunately.  However, I did get to try both my Tokina 14-20mm F/2 and my Samyang 8mm F/3.5 Fisheye.  

 

The 14-20mm was brighter.  The zoom helped as 14mm's distortion is really uncomfortable to me when sweeping and walking around, so zooming out to 20mm helps with the queasiness as I moved around my property in the dark.  I actually found the 8mm much better for that, as it's a stereographic projection, and for some reason that's more comfortable when sweeping.  

 

I can see much of the sky with the 8mm.  It's only flaw is it's slow.  The 14mm F/2 setting on the other lens worked better for brightness and also works well, if you avoid sweeping.




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