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Best way to zoom in - Afocal?

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#1 vicuna

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Posted 02 May 2024 - 07:04 AM

I have been reading on here for weeks but it's still not quite syncing in my brain. so appreciate any help.

 

I have a PVS-14 used in afocal mode and the TV-67 eyepiece. using a 92mm refractor.

 

what is the best way to zoom in? (without modifying my NV device or changing telescope?)

 

I am understanding that if I use shorter focal length eyepieces the views get dimmer...but is there a point where it's worth it to lose a little brightness to zoom in a bit?

 

was looking at Gavster's galaxy photos from last month and blown away. I know a 16 inch dob is a different world than a 3.5" scope. 

 

for me I was looking at a few galaxies last night...they look like bigger fuzzier stars. I don't see any details at all.

 

or is that just normal / expected with a 92mm refractor? would a shorter focal length eyepiece help? or a reducer of some kind?

 

(don't get me wrong. I was blown away knowing I was looking at galaxies from bortle 5 on my front porch...not disappointed at all - just hungry for more)

 

thank you!!


Edited by vicuna, 02 May 2024 - 07:04 AM.


#2 Thierry Legault

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Posted 02 May 2024 - 07:28 AM

what is the best way to zoom in? (without modifying my NV device or changing telescope?)

You can already:

- remove the additional lens on top of the TV67, to use it at 55 mm and change the reduction factor approx from 0.4x to 0.6x (the TV55/67 already behaves as focal reducer)

- use the NV at prime focus

- put a Barlow lens in front of the NVD (you can find Barlow lenses between 1.4x and 5x or more)


Edited by Thierry Legault, 02 May 2024 - 07:30 AM.

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#3 Thierry Legault

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Posted 02 May 2024 - 07:36 AM

was looking at Gavster's galaxy photos from last month and blown away. I know a 16 inch dob is a different world than a 3.5" scope. 

...and photo is not visual (the sensor integrates light in time, no the eye). Most galaxies are small compared to many nebulas and need more power, but your telescope gathers 20 times less light than the 16"!

 

A good option could be a 8" or 10" F/4 Newtonian, it's quite light and cheap and it would already give a better view of the galaxies. I used a Skywatcher 10" before buying my ES400.


Edited by Thierry Legault, 02 May 2024 - 07:39 AM.

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#4 ytserrof

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Posted 02 May 2024 - 07:45 AM

In my experience you should not worry about zooming in in case of galaxies. I even use my setup with a 3x barlow with very good results, so if you can use your NV in afocal prime mode, barlow is the way to go.

My native focal lentht is 1200 mm and a 2 or 3x barlow gives me very decent views.

 

If afocal is the only option then a shorter focal lenght eyepiece is your only option...

 

Don't forget to apply IR filter for more details.

 

 


Edited by ytserrof, 03 May 2024 - 03:08 AM.

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#5 eyeoftexas

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Posted 02 May 2024 - 09:55 PM

The other way to increase magnification is to use shorter focal length eyepieces. I often switch between my 67/55 and Panoptics 35 and 27.  Of course this option is more expensive than using Barlows. The plus side is that you can use the various eyepieces with your scope without the NVD.  


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#6 vicuna

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Posted 03 May 2024 - 02:33 AM

In my experience you should not worry about zooming in in case of galaxies. I even use my setup with a 3x barlow with very good results, so if you can use your NV in afocal mode (as you mentioned above), barlow is the way to go.

My native focal lentht is 1200 mm and a 2 or 3x barlow gives me very decent views.

 

Don't forget to apply IR filter for more details.

Why Barlow over a different eyepiece?



#7 Joko

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Posted 03 May 2024 - 02:53 AM

Why Barlow over a different eyepiece?

 

Afocal with TV 67mm + 3x barlow is very far in terms of magnification compared to the OVNI-M 26mm (used by ysterrof) in prime + 3x barlow. In prime there is no issue to observe at very high magnification like 500x or more which is not possible in afocal (more than 100x is already dim in afocal).

 

Afocal limits the observation to few dozen of objects (the main Messier / NGC objects + wide nebulae from other catalogues) while prime gives you access to thousands of deep sky targets.

 

Many people using terrestrial NV devices think that NV is not good at high magnification on telescopes, which is a wrong statement if you use a NV eyepiece built for astronomy.


Edited by Joko, 03 May 2024 - 02:55 AM.

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#8 Joko

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Posted 03 May 2024 - 02:59 AM

You can already:

- remove the additional lens on top of the TV67, to use it at 55 mm and change the reduction factor approx from 0.4x to 0.6x (the TV55/67 already behaves as focal reducer)

- use the NV at prime focus

- put a Barlow lens in front of the NVD (you can find Barlow lenses between 1.4x and 5x or more)

PVS-14 are limited to afocal and doesn't work in prime. So he can't use it at prime focus nor add barlows directly in front of his NVD.

Although he can't switch the lens for handheld use to get different magnifications.


Edited by Joko, 03 May 2024 - 03:00 AM.

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#9 ytserrof

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Posted 03 May 2024 - 03:11 AM

Why Barlow over a different eyepiece?

Sorry it was a typo on my end. If afocal is the only option, then barlow is not the ideal solution, rather a shorter focal leght eyepiece.


Edited by ytserrof, 03 May 2024 - 03:11 AM.

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#10 The Ardent

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Posted 03 May 2024 - 03:42 AM

300x with 6mm Delos, afocal NV . 
 

First is IC 4997 in Delphinus 

http://stars.astro.i...sow/ic4997.html

It is noisier probably taken with the PVS7 without manual gain. 

 

These were handheld cellphone, and look better in b+W instead of green. 
The manual gain can reduce the noise significantly. 

Attached Thumbnails

  • IMG_3224.jpeg
  • IMG_3233.jpeg

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#11 PEterW

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Posted 03 May 2024 - 03:51 AM

Pvs14 can do prime with a rafcamera adapter, so you can choose what you want to do.
https://www.mjkzz.de...4-mount-adapter
Someone else can advise if the thickness enables it to work with old m42 camera lens backfocus or not.

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#12 Joko

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Posted 03 May 2024 - 04:54 AM

Pvs14 can do prime with a rafcamera adapter, so you can choose what you want to do.
https://www.mjkzz.de...4-mount-adapter
Someone else can advise if the thickness enables it to work with old m42 camera lens backfocus or not.

Peter

It would be a good idea to explain the full story to get prime with a PVS-14. In addition to buy the rafcamera adapter, you'll also have to buy additional tools and adapters, take risks in making modifications on the NVD and the mod will void the warranty. What's more, it requires an additional 5cm backfocus so it won't work on many telescopes. When I spend 5,000 USD or more, I don't like to think I must do extra DIY.


Edited by Joko, 03 May 2024 - 05:58 AM.


#13 cnoct

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Posted 03 May 2024 - 08:18 AM

Someone else can advise if the thickness enables it to work with old m42 camera lens backfocus or not.


Prime configured PVS-14 works a treat with M42 camera lenses.

PVS-14 Prime M42 Lens 1.jpg

PVS-14 Prime M42 Lens 2.jpg
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#14 vicuna

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Posted 03 May 2024 - 08:37 AM

It would be a good idea to explain the full story to get prime with a PVS-14. In addition to buy the rafcamera adapter, you'll also have to buy additional tools and adapters, take risks in making modifications on the NVD and the mod will void the warranty. What's more, it requires an additional 5cm backfocus so it won't work on many telescopes. When I spend 5,000 USD or more, I don't like to think I must do extra DIY.

 

yeah I am thinking along these lines so sticking with afocal for now.

 

it's not even the DIY part of it (which I'm not handy with) but I'm legit afraid to break something.

 

I might just put a Prime NVD on the xmas list...or when I feel I've maximized afocal - still feel like I have a long way to go there though.



#15 vicuna

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Posted 03 May 2024 - 08:48 AM

so if I'm staying afocal for now...what should be my next 2-3 eyepieces?

 

I've read others recommend 41 panoptic and 27 panoptic and high power delos from threads a few years ago (and ardent just now). wondering if there's been any update there? which 2-3 would be my workhorses?

 

I also don't quite understand what would be the benefit of a 41 panoptic over a 40 plossl if i'm only using the middle 40 degrees?

 

tyty



#16 ytserrof

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Posted 03 May 2024 - 09:26 AM

 

 

I also don't quite understand what would be the benefit of a 41 panoptic over a 40 plossl if i'm only using the middle 40 degrees?

 

tyty

 

The more you spend the higher the satisfaction is. :D I'm using the TV 40 plossl and it is completely fine. I am not really sensitive to aberrations though...

 

If you plan to use it without NVD (and why not?) the advantage of the 41 over the 40 is more obvious to me.


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#17 mccarthymark

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Posted 03 May 2024 - 10:08 AM

Afocal with TV 67mm + 3x barlow is very far in terms of magnification compared to the OVNI-M 26mm (used by ysterrof) in prime + 3x barlow. In prime there is no issue to observe at very high magnification like 500x or more which is not possible in afocal (more than 100x is already dim in afocal).

 

Afocal limits the observation to few dozen of objects (the main Messier / NGC objects + wide nebulae from other catalogues) while prime gives you access to thousands of deep sky targets.

 

Many people using terrestrial NV devices think that NV is not good at high magnification on telescopes, which is a wrong statement if you use a NV eyepiece built for astronomy.

This might be getting too off topic, but I don't quite understand how afocal vs. prime would have a difference in the ability to magnify.

 

As I understand it, in afocal, one wants the largest exit pupil to feed the 22mm entrance pupil on the PVS-14.  Thus the TV 67mm plossl which most people use.  Exit pupil is a function of the telescope aperture and focal length, and the eyepiece focal length -- shorter focal length eyepieces have smaller exit pupils which can "light starve" the PVS-14.

 

How is this different in prime?  Does a barlow also shrink the exit pupil entering the night vision device?  Or does it magnify while retaining a relatively large exit pupil?

 

With afocal the best way I "zoom in" is by using larger apertures with the 67mm plossl.  I've tried shorter focal length eyepieces but the views are typically too dim or too noisy.


Edited by mccarthymark, 03 May 2024 - 10:08 AM.

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#18 sixela

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Posted 03 May 2024 - 12:14 PM

The entrance pupil of the NVD is not the NVD objective (since you no longer use it), but the entrance pupil of the telescope (which functions as a replacement of the f/1.2 27mm objective usually on the NVD). The surface brigthness, though, still depends on the f/D ratio of the telescope (or telescope plus coma corrector plus barlow or reducer).

If you want to compare it to an afocal stack, then you may consider the eyepiece plus NVD objective as a focal reducer or extender for the telescope with a multiplication factor that is the NVD objective focal length (26mm for FOV calculations, 27mm for the paraxial surface brightness) divided by the eyepiece focal length.

So an afocal stack with a 27mm eyepiece is identical to an NVD in prime mode (with more light loss and more aberrations), an afocal stack with a 13mm eyepiece is identical to an NVD in prime with a 2x barlow, and an afocal stack with a 35mm eyepiece is equal to an NVD in prime with a 0.75x reducer.

If you can use prime mode, then the only real use for afocal stacks with eyepieces shorter than 26mm are when you use zoom eyepieces (can't easily "zoom" with a barlow, although you could in fact use variable length extensions between the barlow and NVD to "zoom", but it would be far from parfocal in the fairly narrow range).

Edited by sixela, 03 May 2024 - 12:21 PM.


#19 PEterW

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Posted 04 May 2024 - 02:27 AM

Prime configured PVS-14 works a treat with M42 camera lenses.

PVS-14 Prime M42 Lens 1.jpg

PVS-14 Prime M42 Lens 2.jpg


Which adapter are you using to do this? Is it the Rafcamera one?

Peter

#20 vicuna

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Posted 04 May 2024 - 09:03 AM

so last night I took out a few of my normal visual eyepieces that had bigger eye relief and looked at a few galaxies, open clusters, and M3

 

transparency and seeing were below average...bortle 4/5 (92mm F6 refractor).

 

I just held the device right up to the eyepiece instead of messing with the adapters since I knew I'd be changing them around. as an aside handholding them was fairly comfortable and really not that inconvenient. for some of my wider field eyepieces I tilted the PVS-14 and paned around the field (slight distortion obviously but it was nice to move around a little bit to put the objects in context).

 

I was able to use my Leica Zoom (18-9mm) all the way down to 9mm...there was a little scintillation that low but didn't take away from the view. I would say down to ~12-15 mm there was almost zero scintillation.

 

M3 even with my 31 Nagler transformed from a cotton ball to individual stars...and down to 9mm I could see individual stars all the way to the middle.

 

I tried to throw a barlow on the Leica extender but below 9mm it got pretty dim.

 

not sure why I made it this complicated


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#21 vicuna

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Posted 04 May 2024 - 09:14 AM

So an afocal stack with a 27mm eyepiece is identical to an NVD in prime mode (with more light loss and more aberrations), an afocal stack with a 13mm eyepiece is identical to an NVD in prime with a 2x barlow, and an afocal stack with a 35mm eyepiece is equal to an NVD in prime with a 0.75x reducer.

If you can use prime mode, then the only real use for afocal stacks with eyepieces shorter than 26mm are when you use zoom eyepieces (can't easily "zoom" with a barlow, although you could in fact use variable length extensions between the barlow and NVD to "zoom", but it would be far from parfocal in the fairly narrow range).

 

so last night I *really* enjoyed my time with eyepieces under 20mm. so I am for sure more compelled to try prime mode. (I got a ten year warranty so I'm a little bit chicken). is there a way to quantify how much light loss / aberrations we're talking about in prime vs afocal say at:

 

prime vs 27mm panoptic

and

prime plus barlow and 12mm delos?

 

tyty



#22 chemisted

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Posted 04 May 2024 - 09:28 AM

Judge by your latest experience. I have posted this before but I'll say it again. If you use top quality eyepieces (which you have) there is no reason to go to prime.  I have done both prime and afocal (same magnification) with the same telescope on the same night and views are completely comparable.


Edited by chemisted, 04 May 2024 - 09:31 AM.

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#23 eyeoftexas

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Posted 04 May 2024 - 10:32 AM

so last night I took out a few of my normal visual eyepieces that had bigger eye relief and looked at a few galaxies, open clusters, and M3

 

transparency and seeing were below average...bortle 4/5 (92mm F6 refractor).

 

I just held the device right up to the eyepiece instead of messing with the adapters since I knew I'd be changing them around. as an aside handholding them was fairly comfortable and really not that inconvenient. for some of my wider field eyepieces I tilted the PVS-14 and paned around the field (slight distortion obviously but it was nice to move around a little bit to put the objects in context).

 

I was able to use my Leica Zoom (18-9mm) all the way down to 9mm...there was a little scintillation that low but didn't take away from the view. I would say down to ~12-15 mm there was almost zero scintillation.

 

M3 even with my 31 Nagler transformed from a cotton ball to individual stars...and down to 9mm I could see individual stars all the way to the middle.

 

I tried to throw a barlow on the Leica extender but below 9mm it got pretty dim.

 

not sure why I made it this complicated

Good report.  Was this all using your 92mm refractor?  What f/ stop is it?



#24 vicuna

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Posted 04 May 2024 - 10:56 AM

 I have posted this before but I'll say it again.

welcome to my wife's life. she has to tell me things 40 times before there is a chance it settles in to me.


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#25 vicuna

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Posted 04 May 2024 - 10:59 AM

Good report.  Was this all using your 92mm refractor?  What f/ stop is it?

 

yes all at 92mm at f6 - so ~550 mm focal length. it's a very good APO triplet. baader bbhs diagonal.


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