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3x NV afocal

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#1 GOLGO13

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Posted 21 January 2020 - 10:57 AM

Don't have a 3x capability yet. What would be needed to get that up and running. I have a Mod 3C with an Envis.

 

What's the best one out there that's reasonably priced?

 

Thanks.



#2 Eddgie

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Posted 21 January 2020 - 11:52 AM

There are two different models of 3x on the surplus market.  

The first model has hard steps on the lens housing, while the second model has more of a conical or bell curve profile with one small sharp step.

 

My experience is that the conical/bell curve model vignettes far less than the model with hard steps. This is the profile:

 

NVD with 3x afocal lens.jpg

 

To use this with a filter between the 3x lens and the ENVIS, PVS-14, or PVS-7 objective, one can remove the snap on connector on the 3x lens assembly:

 

Afocal lens - Copy.jpg

 

With the snap on connector removed, the RAF PVS-14 to 3x adapter is screwed on to the 3x lens in place of the snap on connector.  This adapter is long enough that it will slip over a filter mounted to the objective using the RAF filter adapter ring.    I designed it to be long enough to work with even stupidly long filter housings so no worries about that.  There are two screws at different depth.  The screw closest to the device is used when there is a filter mounted, and the screw closest to the 3x is used when no filter is mounted.

 

Now I do not really tighten these screws because it can chew up your Objective.  I just snug them so that the head is between the lands and solidly in a groove so that it will focus when turned. This means that when you point the lens at the ground, it can fall off.  Now you can tighten it if you want to, but for terrestrial use, I recommend going back to the snap on connector.  The only time I use these is when I am running filters.

 

Here you see the RAF adapters installed on a pair of 3x lenses.  These are inexpensive.

 

Mod 3 3x.jpg

 

One day I plan on re-designing it, but an O ring solution probably would not work because filters all seem to have different size housings.  For now, this is as good as I could do.  Maybe someone will come up with a better design. This works well enough and won't mark up the lens housing if mild pressure is used, but again, it come off if the device is pointed down. Best to grip it with your fingertips when not pointing up.  This is what I designed when I started though, and for now, it works acceptable to me and RAF makes the price quite reasonable (Shout out to Rafael for making these things so affordable!)


Edited by Eddgie, 21 January 2020 - 11:53 AM.


#3 Eddgie

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Posted 21 January 2020 - 11:59 AM

This is the stepped lens.  At the center of the field they are about the same, but this design vignettes in all modes and vignettes more severely when using filters than the above type. 

 

s-l1600.jpg

 

Sadly, the one in the previous post (conical profile) are hard to come by, but there was one on auction a couple of weeks ago.. When I see them, I usually either post on CN or alert people  know that are looking for one..


Edited by Eddgie, 21 January 2020 - 11:59 AM.


#4 GOLGO13

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Posted 21 January 2020 - 12:52 PM

So another option maybe using a camera lens that gives me something similar? I have not adjusted my c-mount to Nikon lens adapter to take filters. But I figure that wouldn't be too hard to do. 



#5 Mazerski

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Posted 21 January 2020 - 02:02 PM

I had 2 of those 3x bell shaped lens... sold both due to how the view was not sharp to the edge and for my area, they let too much light in.

 

The Nikon Nikkor non-Ai lens that zooms from 1.5x to just over 3x provides a much nicer view.

The 135mm f2.8 (5x) is a great lens. 



#6 Eddgie

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Posted 21 January 2020 - 02:04 PM

Yes, the SLR lens is an absolutely great alternative!  

The 3x working with objective on the NV device gives something like f/1.8 so if you can find a nice, fast 70mm or 80mm SLR lens, it works quite well. Now depending on the lens, stars my not be quite as sharp as the 3x (which was designed to focus red best) but worst case, an IR pass filter will tame any CA from most lenses.

 

And of course with the SLR setup, it is easy to get higher powers and at f/2, there is only a little vignetting.  A jump from 3x to 6x does not seem like that much, but it would be the same scale increase as going from 100x to 200x in a telescope.  

 

Now on my PVS-14 objective binocular I am kind of limited to 3x, but on my monocular, I use my 180mm and 70:210 zoom all the time!

 

Most people running the Mod 3 are running SLR lenses for a lot of viewing I am betting 


Edited by Eddgie, 21 January 2020 - 02:06 PM.


#7 chemisted

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Posted 21 January 2020 - 02:19 PM

Just this morning I was considering a Nikkor 85 mm f/1.8 lens for just this purpose.  These date from the late sixties with the "C" mount, good multi-coatings (NIC) and optics that have received very high ratings throughout all the intervening years.  KEH has one listed at this time.  I probably won't go this route as I plan to use my 50 mm with the TC-14A teleconverter that I recently dug out of storage but if you can find the 85 at a price you like it would certainly serve the purpose well.



#8 Jeff Morgan

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Posted 21 January 2020 - 04:19 PM

Another vote for the SLR option. Common, affordable, easy to filter.

 

An 85mm lens is on my hit list (as is the 200mm).

 

Already have 50mm, 135mm, and 300mm. All work exceptionally well. In fact, between the 300mm and the Lockwood 16" f/2.8 I have coming, my Epsilon e180 may be out of a job.

 

Divide the lens focal length by 27 (the NVD eyepiece focal length) to obtain magnification.

 

85/27 = 3.1x

 

Divide 40 (the NVD apparent field of view) by the magnification to get the true field of view.

 

40/3.1 = 12.9 degrees True.



#9 Dale Eason

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Posted 21 January 2020 - 11:17 PM

I have the Nikkor 85 bought used on ebay for only $100.  It claimed to have spider webs inside it so the price was reduce by $80. I did not see how spiders could get inside so decided to take a chance. Turns out that was mold.  It can be an issue with very old Nikkor lenses.  I found how to take the lens apart and clean the mold off.  Now I use it and it is my main hand held lens with the Mod3 C.  After more research I discovered my lens is from the 50's.  Without mold they are still considered very good lenses.

 

Dale


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#10 slavicek

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Posted 21 January 2020 - 11:18 PM

nv0.JPG

 

Going for camera lens is probably the best approach. But, Just FYI, I've got myself Kowa 75mm f/1.8 C mount lens. Excelent optics, I believe around $650 each. Front mounted 2" filters. 3x is the way to go for hand held.


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#11 GeezerGazer

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Posted 22 January 2020 - 12:46 AM

I had the 3x (stepped version) afocal lens and used it with the slide on adapter, the snap on adapter and screwed directly to the Envis lens.  I did not favor it.  I purchased a Nikon 105 at 4x and liked it much better... no vignetting and seemingly better correction to the edge of field.  I created a Nikon adapter that allows for 1.25" filters inside the adapter; see the second method detailed in this link:

 

Each method of getting to 3x or 4x has advantages and disadvantages.  I originally purchased a 105 Nikon f:2.5, that was older and I found, had a black speck of interior paint trapped between lens elements.  I can't get it out.  Bought a nice 50mm Nikon f:1.4; I then spent a lot more money on a 105 Nikon f:1.8   It is a little better with NV than the 2.5 version, and has no issues.  I had and sold a Nikon 180, then just recently bought another one.  My most used camera lens is a 300mm Nikon f:2.8.. which seems perfect for a large number of nebulae.  I use all of these lenses for NV phonetography.  The point is that if you consider a camera lens, look at the focal lengths available within a series of lenses so you purchase ONE C-mount adapter that is used with them all.  There are a lot of old lenses around at reasonable prices.  

Good luck.  



#12 Mazerski

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Posted 22 January 2020 - 09:29 AM

I agree that the (in my case) Nikon F to C adapters work very well for hand-held. My attempt to simplify and reduce handling of filters. I have the 6nm Ha in adapter (not shown).

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  • FFFCAdapters.JPG

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#13 Eddgie

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Posted 22 January 2020 - 10:05 AM

I have the Nikkor 85 bought used on ebay for only $100.  It claimed to have spider webs inside it so the price was reduce by $80. I did not see how spiders could get inside so decided to take a chance. Turns out that was mold.  It can be an issue with very old Nikkor lenses.  I found how to take the lens apart and clean the mold off.  Now I use it and it is my main hand held lens with the Mod3 C.  After more research I discovered my lens is from the 50's.  Without mold they are still considered very good lenses.

 

Dale

Nice!  Yeah, some of these older fixed focus lenses are much easier to work on than the later lenses with microscopic screws.  85mm is a nice size.  Lots of big nebula should be really good at 85mm. 



#14 Eddgie

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Posted 22 January 2020 - 10:10 AM

I agree that the (in my case) Nikon F to C adapters work very well for hand-held. My attempt to simplify and reduce handling of filters. I have the 6nm Ha in adapter (not shown).

Looks like you have made a serious commitment to SLR lens observing!

 

Depending on the lens, I have made mounts for filters that actaully attach to the back of the lens rather than in the housing. The most annoying thing is that the way I prefer to do it is to use an empty filter cell and mount it to the rear of the lens, then screw the front of the filter on to the empty cell, but a lot of these H-a fitlers don't have any thread on the front, or not enough to get a grip.

 

If I can find a way to attach it, I now 3D print a stretchy filter holder where the filter just press fits into the holder.  Not all lenses make this easy though.

 

thumbnail_20191219_124633.jpg

 

A 3d printer helps.  

 

Now this lens was a Tamron Adaptall and it had this tube that stuck out so easy to concoct this setup.


Edited by Eddgie, 22 January 2020 - 10:11 AM.


#15 Mazerski

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Posted 22 January 2020 - 11:02 AM

I was out Monday night for 6 hours with a new scope... it was 20 degrees or so + no wind. There are lots of occasions throughout year where for whatever reason, I do hand-held and the last thing I want or need is to be constantly handling filters. We all know how easy and fast it is to change a lens or attach a different Nikon adapter. 
 

3D printer sounds like a great idea and it appears that you can come up with all sorts of solutions for easier observing.


Edited by Mazerski, 22 January 2020 - 11:03 AM.


#16 Peregrinatum

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Posted 23 January 2020 - 12:26 PM

As mentioned you could get a used 85mm LSR lens off ebay, possibly Canon FD compatible.

 

You would need the C/FD adapter.

 

To attach filters you would need a few adapters, I finally worked this out.  Assuming the lens has 55mm threads for filters (the front ring of the lens will show the thread size) , you would need:

 

55mm/48mm step down adapter  (ebay)

48mm/1.25" step down adapter  like this:  https://agenaastro.c...apter-m-01.html

 

I tried this last night and it worked fine with the small filter in front of the larger lens.


Edited by Peregrinatum, 23 January 2020 - 12:33 PM.



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