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[GeezerGazer]

NV Photography… a Beginner’s Introduction

 

By GeezerGazer… Ray Taylor
Edited by CN Members:jdb_astro, Moshen, Gavster, RVA_Chris and Eddgie

 

Night Vision (NV) technology amplifies light 1000’s of times which makes it a great tool for low light photography.  This narrative will explain how you can capture images through a NV device (NVD).  Let’s start by looking at two examples of images taken through an NVD.   

 

Some years ago, CN member jdb_astro, started posting photos that he had taken through his NVDs.  He is a NV Photography pioneer and you can see many of his NV photos here on his Cloudy Nights Gallery: 

 

https://www.cloudyni...30311-jdbastro/

 

This image of the Rosette is an example from his gallery of photos.  A Takahashi TSA 120 telescope was used with a Sony A7S full-frame mirrorless camera looking into an unfilmed NVD via a specialized relay lens; imaging was 1/30 second exposure, taken at ISO 250, and using a 12nm H-alpha filter. 

 

 

While some of his photos were taken through telescopes, some were taken using very fast (low focal ratio) prime lenses attached to his NVD.  His images are high resolution, taken with mirrorless interchangeable lens cameras (MILC’s) and semi-custom NV relay lenses.  And while this type of photography seems limited to a few who have this specialized equipment, it is no longer a limited domain.

 

For example, the next photo was taken by CN member RVA_Chris, and it is also of the Rosette Nebula, but at a different scale and resolution.  To take this image, he used a Skywatcher 130mm Newtonian with an Antares .7x reducer, his Mod 3C NVD with an Omni 7S tube.  The scope was carried on a Celestron Nexstar SE mount, and he used his Samsung Galaxy S8 phone for a single 10 second exposure at ISO 350.  Comparing this image with the view through the NV eyepiece, Chris said, “I’d say all of the detail was there at the eyepiece but some of the dark lanes and wispier bits required careful study and averted vision.  The photo makes it all readily apparent.”

 

 

To take a good, low-light photo of a nebula or galaxy through a telescope has traditionally required the efforts of photographers who used specially built cameras, sensitive to particular bands of light or specialized filters, really good optics and a perfect tracking mount for very long exposures, sometimes with hours of exposure to capture the wisps of light that are their targets.  But with NV, the length of exposure is dramatically reduced, to seconds, rather than minutes or hours.  How is this accomplished?

 

There are websites that explain how a NV tube accomplishes light intensification, and a web search of “How Night Vision works” will provide many learning opportunities.  But most NVD’s available for retail purchase, whether they are binocular or monocular, have a similar design… objective lens at the front, intensifier tube in the middle, ocular at the back.  The ocular or eyepiece at the rear, has a 27mm focal length designed to focus on the intensifier tube’s 18mm diameter small, phosphor, output screen.  For the astronomer, peering into an NVD, the visual experience is like looking into a traditional eyepiece.  Some NVDs have a “gain” control to adjust the brightness of the image at the phosphor screen. This control lightens or darkens the image and influences the brightness of the background sky.  The ability to brighten the image of a celestial object makes it easier to capture a photograph because the exposure can be shorter and the ISO setting can be lower, resulting in less visual noise and/or graininess in the photo.  Think of the gain control as turning up the lights in a dark room to take a photo.

 

There are terms here that need a short explanation, because most of them began with film camera photography.  Shutter speed was set depending on the brightness of the object being photographed; brighter targets required shorter shutter speeds.  Film speed, referenced as ASA (American Standards Association) or ISO (International Standards Organization), was the sensitivity of film used in the camera; the higher the number, the more sensitive the film (and the more grainy the image appeared).  In digital cameras, the ISO setting still references sensitivity, but instead of film, it is the variable adjustment of the sensor sensitivity (and, like with film, the higher the number, the more grainy an image appears).  When using digital cameras, instead of “shutter speed,” many use the term “exposure.”  For both ISO and exposure, there is a mathematical formula that doubles the brightness with each change of both ISO and exposure.  Changes in either ISO or exposure are evenly incremental.  A web search of “camera ISO” will provide learning options. 

 

With NV, a camera must be able to focus on the phosphor screen inside the NVD, so a camera lens is necessary.  For a digital SLR camera or MILC, a lens on the camera is held close to the NVD ocular and the exposure taken, click.  To hold the camera perfectly still, an adapter is usually employed, allowing for a hard connection between the camera lens and the ocular/eyepiece of the NVD.  You might think that the camera lens would require close (macro) focus capability for this connection, but since the camera lens is looking into the NVD ocular which provides an infinity view (parallel light rays), the reality is that the camera lens will be focused at infinity too. The combination of the camera lens and NVD ocular forms a relay lens.

 

Now it gets slightly complicated, because with a telescope, there are two ways to use an NVD… “prime” and “afocal.”   A "Prime Lens" refers to a fixed focal length objective.  It can be ANY objective... a telescope, a camera lens, an objective made for an NV device.  A prime lens gathers light and focuses this light into an image.  An eyepiece is used to magnify this image and present it to the eye at infinity focus (for relaxed viewing).  The focal length of the eyepiece determines the magnification.  In the case of a NV device, if the front objective (prime lens) is removable, then the NVD can be used as the telescope's eyepiece; in this configuration, the telescope is the prime objective in the optical system.  For an NVD to produce unity (1x) magnification, it is usually supplied with a 27mm objective (prime lens) and a rear eyepiece of similar focal length; like with a telescope, magnification is determined by dividing the focal length of the eyepiece into the focal length of the prime objective.  But a telescope can only become the prime lens in the optical system when the NVD’s front 1x lens can be removed from the NV device, thereby exposing the NVD’s front photocathode sensor to the telescope’s focused image.  Not all NVD’s have a removable front objective lens.
 
Afocal systems use two or more complete sets of objectives and eyepieces.  Think of afocal as one optical system with its own objective and eyepiece, like the NVD with 1x objective, looking into the eyepiece of another optical system, like a telescope with its own glass eyepiece.  Adding a camera with its objective lens for a photograph is adding ANOTHER afocal system.  Adding a camera in this manner is called afocal photography or afocal projection photography.  
 
So if you have a camera WITHOUT a lens, and you attach the camera body directly to your telescope’s focuser, you are using the telescope as a prime lens for the camera... this is called prime photography.  If your camera has a camera lens attached, and you take a photo through the glass eyepiece that is in your telescope’s focuser, this is called afocal photography. 

 

With this basic information, you should understand the two systems that are used by astro photographers.  But as I explained earlier, NV amplifies the light that falls on its sensor, so photos are easier and much less time consuming.  And, like with cameras, the faster the optical system (focal ratio), the brighter the image will be.  Whether the NVD is used in prime or afocal configuration, the image will always be brighter than a traditional glass eyepiece. 

 

There is a second benefit of NV photography that is closely related to the size of the exit pupil of an eyepiece.  In an optical system, the exit pupil is the diameter of the light cone as it exits an eyepiece.  The average, dark-adapted human eye can take in about a 6mm-7mm exit pupil.  A typical NVD 1X objective (e.g. 27mm at f:1.2) has a 22.5mm aperture, so it can accept a light cone up to this diameter… more than 3 times the diameter useable by the human eye. That means that the starting image received at the NVD sensor, can be brighter than can be seen visually, with the naked eye.  Even in prime configuration (with the 1x objective removed), most NVD’s require a light cone diameter of up 18mm, to fully illuminate the sensor.

 

The NV image is so bright that it can be captured photographically with a regular digital camera… almost any camera… including a smartphone camera.  Images are so easy to take, that you can hold your phone to the NV eyepiece and click on the brightest deep sky objects, even from a non-tracking mount.  But to take better images, there are a few things that will definitely help.  You need a mount or bracket to hold your phone steady on the NV eyepiece; if you want longer exposures up to 10 seconds or stacked photos for up to 15 or 20 seconds, you’ll need a mount that tracks automatically; and then, there is the phone camera used to take the images.  Current information to explain Phonetography of DSO’s (as of May 2018) is in an article written by three of us who use smartphones to take NV astro photos, located here:

 

https://www.cloudyni...otography-r3149

 

Phone camera technology continues to advance at a rapid rate, so if you read this information, even a month in the future, you should search CN for the latest posts with an NV tag to make sure you have the most current information. 

 

Why is NV Phone Photography, now known as NV Phonetography, so appealing?  Because nearly anyone with an NVD, a telescope and a smartphone can do it.  Anyone with these three items has the means to photograph the DSO’s we commonly see… and many that can not be seen with traditional glass eyepieces.  NV enhances light through the visible spectrum, but it peaks in near infrared, and this serves as an advantage.  The IR and H-alpha filters we use block most of the visible light spectrum but still allow plenty of light through at longer wavelengths for the NVD to amplify, and the camera to photograph.  Nebulae have never looked brighter!  This is also why NV is a good choice for amateur astronomers who commonly observe from a light polluted site.  And you don’t even need a telescope!  Here’s a great image of a very wide swath of sky that includes the North American Nebula, Pelican Nebula and the huge nebula near Gamma Cygni (Sadr).  This photo was taken by CN member Gavster in the Isle of Wight in the UK and was taken with his Galaxy S9 through a PVS-14 with a Photonis 4G tube, with a 6nm H-alpha filter.  This very compact optical system (about 8” long) was mounted on a Skywatcher AZ GTI, which is a very small tracking mount designed for cameras.  Settings for this photo were ISO 50 with a single 10 second exposure.  In the lower right, you can see the roof line of his house.

 

 

NV photography can be a dedicated effort to produce photos like CN member jbdastro; or, it can be fairly simple snapshots using a digital camera or smartphone, that does not intrude on a more visual experience.  Once a target is in the eyepiece, it only takes a minute or two to attach a camera or phone to the NVD, set the camera and take a photo of the object.  On a non-tracking mount, you are limited to using higher ISO and exposures of 1-3 seconds, to prevent star trails; but photos are still possible of brighter objects.  A tracking mount allows the camera or camera application within the smartphone to exceed normal automatic settings for exposures from 1/2 up to 10 seconds.  And a camera application (available for IOS devices) can automatically stack shorter photos of 1/2 second or less, for 10-20 seconds as necessary to smooth out a grainy appearance.  And the stacking is done automatically within the application as the photo is in progress.  It is very fast, and is a great record of what you saw visually during your observing session.

[GeezerGazer]

To show a little more scale, CN member Moshen used a Borg 90FL refractor reduced .65x, with a L3 White Phosphor Mod 3C and NO filters.  This scope was mounted to a non-tracking Stellarvue M1V Alt-Az mount on a carbon tripod, ISO 100, exposure 1/3s, stacked for 3.5 seconds.  Of this image, Moshen wrote:  “In the field of view, you can see Lagoon, Triffid, M21, Globular NGC 6544, Open Cluster NGC 6546 and Milky Way dark lanes.”  This is still a very wide angle image of the night sky.

 

 

You might ask, why the green or blue color?  The color is a function of two factors.  First, many second and third generation NVDs use tubes that meet military contract specifications, like the Omni VII tube.  The tube itself reveals the image in green phosphor.  Second, most cameras including phone cameras, automatically adjust white balance when taking an image.  In photography or videography, color balance is adjusted to alter primary colors (red, green & blue) to render neutral colors correctly.  Color balance or white balance, as it is also called, is used in digital cameras to automatically make color corrections before the image is taken. 

 

Many digital cameras and phones offer the ability to alter the white balance before the image is taken; not adjusting the white balance means that it is left in “auto” mode which is based on special algorithms within the camera. In this case, if the camera sees a green image it will probably leave it green. 

 

At the eyepiece, the background sky is usually darker, almost black.  The lighter background sky in a photo is the result of the camera taking in more light in 10 seconds than our human eye sees and our brain computes in a very small fraction of a second… cameras do not have the dynamic range of our eyes, but they have the advantage of being able to capture light for a longer period of time, so they can produce a brighter image than our eyes can see at the eyepiece.

 

A good example is this excellent photo of the Horsehead Nebula, which RVA_Chris took with an Orion XT 10G, using his Galaxy S8, 10 second exposure at ISO 600 with a 6nm H-a filter.  This photo is very bright green, because with a large aperture and high ISO, the camera was seeing a much brighter image than his eyes could see.  Here’s how Chris compared the image in the photo with the image at the eyepiece:  “The view at the eyepiece does not reveal the same extent of nebulosity but the background sky is also much darker.  The head figure is there to see easily with direct vision, but the overall image (at the eyepiece) is maybe not quite as smooth.”

 

 

Chris observes and captures his NV phone images from a light pollution red zone (Bortle 8).  When such heavy light pollution exists, it will reflect off of atmospheric moisture and airborne particulate pollution.  Under those circumstances, the NVD can pick up that veil of light to brighten the sky background in the NV image.  To cut through light pollution, IR or H-a filters can be used with NV to reveal stars and nebulae and darken the background sky… allowing the user to observe from the light polluted city.  All of RVA_Chris’ images demonstrate what NV with filtration can do for a city dweller who wants to observe and/or take photos… even from down town!

 

I referenced White Balance (WB) as a separate tool to alter the way photos appear.  So here is a demonstration that illustrates the effect of changes in the WB settings.

 

 

There are 4 photos that each represent a change in the Kelvin scale.  As astronomers, we usually think of light and color in terms of light waves and would represent measurements of those waves in nanometers.  But color and light, especially in photography, is measured in degrees on the Kelvin temperature scale.  These images were taken with my iPhone 6+ using a Mod 3C with white phosphor tube in prime configuration with a TV-60 refractor.  Dark blue starts at about 2500 degrees K, light blue 3500, light green 4500, and dark green is at 8300… there IS a setting that falls between light blue & light green, that pretty much looks like a gray scale.  To find it I would take another range of images between 3500 and 4500 degrees.  Then I would probably use that  setting if I wanted my NV phone images to appear without, or almost without, a tint.  This is a really simple test that takes about 2 minutes to complete.  Although this WB setting could be effected by changes in filtration from IR to H-a or by changing NVDs with a different tube, the setting you find for use with one NVD could be used for nearly all H-a or IR filtered photographs.

[GeezerGazer]

To demonstrate the effect of a white balance adjustment, the photo below (no post processing) shows very little green tint, even though I saw a slight green tint visually when looking into my NVD at the Bubble Nebula.  This photo was taken through an Orion 120mm  f:5 achromat, mounted on an iOptron AZ Pro tracking mount, using my iPhone 6+ and my Mod 3C NVD with a white phosphor tube, a 7nm H-a filter, ISO 1250, exposure 1/2s, stacked for 15 seconds.  There is very little green tint in the image.  Of course remaining tint could be removed by simply changing the color balance in post processing on the phone, or by changing the image to black and white. Those adjustments only take a few seconds and can correct or alter almost any photo in a very dramatic way.

 

 

I was recently with 16 other observers who had never looked through a NVD before and some of them were surprised that my NVD showed such a slight green tint.  But at least one of them saw the tint as blue and some saw no tint at all.  Those different descriptions exist because we all see colors the way our brain interprets the electrical impulse from the receptors in our eye. 

 

The retina in your eye contains about 120 million rods and about 6.5 million cones.  Although the rods are more numerous and more sensitive than cones, they are not sensitive to color.  The cones are very sensitive to color and they are much more concentrated near the macula (the central yellow spot on the retina).  These millions of receptors may work really well when we are young, but age has a way of causing issues with our vision.  Conditions such as age-related macular degeneration, cataracts, diabetic retinopathy, dry eye or glaucoma can all deal a blow to our vision.  Even floaters can cause issues for high magnification observing. 

 

So here again, NV and NV photography may offer a potential solution for aging eyes to keep observing for a few more years.  The phosphor screen inside the NVD offers a much brighter image of DSOs than can be seen with a glass eyepiece through any telescope.  So using the NVD for observing should be of significant benefit to aging eyes.  And, it has already been demonstrated that the image in a NV photo can provide more detail than the human eye is capable of seeing visually through a NVD.  So if an observer is having trouble seeing an object in the NVD eyepiece, a quick photo might be of considerable advantage.  It would be like a super quick and easy way of doing EAA.  Take a photo using your digital camera, phone or electronic pad, open it and expand it to see what you might have missed visually at the eyepiece.  Or, take several photos, take them home, load them on your computer and look at them on the “big screen.”   There are possibilities here for NV photos that did not exist just a few years ago. 

 

If you have not seen NV Phonetography images, below are four links containing several images each.  These links are worth visiting to see what can currently be done with NV and a smartphone.  But Phonetography results might improve next month, so again, it is best to do a current search of NV tagged posts with Photos, NV Photos, NV Photography, or NV Phonetography to learn more about a procedure or to see current results.

 

The first link is for the gallery photos of CN member RVA_Chris.  You will see a difference between photos he took in 2017 compared to those in 2018 because he upgraded from a Galaxy Note 5 to a Galaxy S8 smartphone.  The Note 5 limited ISO to about 800 and exposure to 1/16 second.  The Galaxy S8 provided the opportunity to take a single exposure of 10 seconds along with upgraded manual controls for settings with a much higher ISO!  The difference in his photos is astounding! 

 

https://www.cloudyni...7824-rva-chris/

 

The next three links include several phone photos with different refractors, an SCT or a Dob.  All three links demonstrate photos taken from dark sites, which offer a distinct advantage over images taken from a site suffering from heavy light pollution.  But it is clear that NV photography, even under a severe light dome of pollution, offers the amateur astronomer new avenues with much greater reach to see and capture deep sky objects. 

 

https://www.cloudyni...h-night-vision/

 

https://stargazerslo...-isle-of-wight/

 

https://www.cloudyni...o-with-friends/

 

Since there are two ways to use the NVD for observing and photography, afocal and prime, there are differences in how parts fit together and there are a few advantages and disadvantages to each system.  Afocal uses a glass eyepiece in the focuser or diagonal between the prime prime objective and the NVD with its own objective lens; to change magnification, you change the glass eyepiece.  When compounding optical systems, you will sometimes find that reflections will occur between the many glass surfaces, especially from very bright point sources of light such as mag 1 or 2 stars.  Afocal also imposes a greater strain on the focuser and mount because of greater weight from the needed assembly of eyepiece, NVD and camera.   And the stack extending from a diagonal can present balance issues when moving from a view of the horizon to one at zenith.  BUT, with afocal, if a traditional eyepiece comes to focus in your telescope, then the NVD will absolutely work with your scope. 

 

With Prime, you need no glass eyepiece, and the small prime lens on the NVD must be removed and replaced with a simple 1.25” or 2” barrel to fit your diagonal or focuser, so you eliminate the glass eyepiece and the small NVD objective required for afocal use.  There is a small risk that some telescopes might not come to focus in prime because a NVD requires about 15mm of extra in-travel (extra back-focus); if your scope comes to focus with a 31 Nagler, you are on safe ground.  The NVD has a focal length of 27mm, so calculating magnification for your scope simply requires that you divide the scope’s focal length in millimeters by 27mm.  To change magnification you can add a barlow or a reducer… but adding reducers to compress the image for a larger field of view (and resulting faster focal ratio & brighter image) requires additional back focus that your telescope may not be able to provide.  And many reducers compress the image so much that full field illumination of the NVD sensor is compromised.  There are always tradeoffs with astronomy equipment and NV is not exempt.  However, if the 1x prime lens of the NVD is removable, then the NVD is capable of performing either in afocal or prime giving greater flexibility.  If the small front lens of the NVD is not removable, then the NVD is limited to afocal usage. 

 

The mechanics of actually attaching a camera or phone to an NVD or an NVD to an eyepiece for afocal projection, is very simple with screw-on or clamp-on adapters.  To attach a 35mm camera to the NVD eyepiece, requires a split ring adapter, such as this one:

 

https://tnvc.com/sho...ter-for-pvs-14/

 

It screws into the front of a camera lens (like a filter) and clamps onto the NVD eyepiece for afocal projection photography. 

 

To attach the NVD to a traditional eyepiece for afocal projection, requires an adapter such as this:

http://www.televue.c..._page.asp?id=73

 

or this:    https://tnvc.com/sho...ronomy-adapter/

 

These are proprietary adapters made to clamp onto TeleVue eyepieces equipped with the groove under the rubber eye guard designed to accept the TeleVue Dioptrix lenses.  TeleVue’s website lists all of their eyepieces that are so equipped, and there is a nice explanation of afocal projection as used with a NVD and telescopes found here:

 

http://www.televue.c...rn=Advice&id=85

 

There are some eyepieces, like my old Scopetronics Maxview 40mm Plossl or the Baader Hyperions, that have T2 threads at the top of the eyepiece. An adapter made with female T2 threads on one side which screw onto the top of the eyepiece and male 1.2” x 32 tpi threads to screw into the 1x lens at the front of my NVD also makes a very rigid connection, as seen below for afocal projection.

 

 

Using a telescope as a prime lens focuses light directly into the NVD without using a glass eyepiece.  This provides a shorter optical system, reducing the possibility of reflections arising between the many glass surfaces of afocal projection.  And some scopes used afocally, tend to display field curvature which shows up in photos as elongated stars close to the perimeter of the field of view.  Using a prime optical system, minimizes the risk of reflections and curvature, and is a less cumbersome way of achieving satisfactory photographic results.   Here are two photos of a NVD in prime configuration for comparison to the above afocal system:

 

 

To take a prime focus image, there are three NVD monoculars in current production that have a removable C-mount lens (the C stands for Cine or Cinema, as was used for small movie cameras many years ago) and all three are made by AB Night Vision:  the Pitbull, the Micro and the Mod 3C.  The Micro is a little smaller/compact; the Pitbull is slightly larger, and the Mod 3C is slightly larger than the Pitbull, but is the only one having gain control which allows brightness adjustment of the phosphor screen… this allows greater control of light when taking photos.  There are a few out-of-production NVDs that have a C-mount lens, but none of them had gain control.  The Mod 3C was also made with a removable battery housing so that it can be used with a proprietary bridge and a second Mod 3 as NV binoculars.  To use these monoculars in prime mode with a telescope, the small 1x lens is unscrewed and a C-mount to 1.25” or 2” nose is screwed in; the left photo above shows the 1x objective unscrewed with the 1.25” and 2” nose adapters.  This takes about as long as it does to change a filter on an eyepiece barrel and these nose adapters are readily available at most telescope stores, camera stores and on Ebay.  They are easy to find and they are inexpensive at about $10 to $40, depending on how fancy they are. 

 

Once the 1.25” or 2” nose is applied, the NVD is used just like any other eyepiece… put it in the diagonal and focus with the telescope’s focuser.  An adapter to connect the camera to the NVD eyepiece or hold a phone in place over the NVD eyepiece to do afocal projection photography is still necessary, but in this configuration, the telescope is being used as a prime lens for the NVD. 

 

If the NVD lens IS removable, then C-mount adapters can also be used to allow a regular camera lens to be the NVD prime objective.  C-mount adapters are made for all majors camera lenses including Nikon, Cannon, Pentax, Zeiss, Fuji and others.  I purchased an old Nikkor 50mm lens and a C-mount adapter to serve as my 2x lens when attached to my Mod 3C for very wide field views and images.  Using a 105mm lens would provide 4x and a 135mm, 5x.  If you have some old camera lenses in your closet, you could put them back to good use.  The trick here is to use lenses that are not reliant on an electrical connection to a camera for automatic focus or aperture settings.  The camera lens must allow manual control of both focus and aperture.  The aperture will be left wide open for the fastest focal ratio and the focus will be used at infinity.  Adding an H-a filter to the front of the objective provides the opportunity to take some very wide field images of the largest hydrogen alpha objects, like the rich field near Sagittarius or the Cygnus complex including the North American, Pelican and the nebulosity near Gamma Cygni (Sadr).  Here’s a photo of a 2x NVD optical system using a camera lens belonging to CN member Jeff Morgan; he used a Cannon 50mm lens with a Cannon to C-Mount adapter to attach it to his Mod 3C NVD:

 

Edited by GeezerGazer, 25 June 2018 - 03:36 PM.

[GeezerGazer]

And, if you have deep pockets, there are very fast focal ratio prime lenses, specifically made for NVDs, that have been modified to provide a C-mount connection.  These lenses were designed with optics and coatings for optimal transmission at near-infrared wave lengths… because NV sensitivity peaks in the near infrared.  These C-mount prime lenses are available in 3x, 4x and 6x.  This is a 6x prime objective made by Litton for the military, but modified for C-mount, used by CN member jdbastro; this one is attached to a Litton M944 monocular.

 

 

If an NVD’s objective is removable such as with the Micro or Mod 3C NVDs, greater possibilities exist for using other lenses for prime focus.  Often, a telescope’s focal length precludes using it for very wide field photography.  Using these shorter focal length lenses allows more visual and photographic flexibility at very low magnification… which is needed for some of the largest celestial objects. But for the optical and photographic systems to work properly, there are parameters that must be met. The following link provides a learning opportunity to understand sensor and lens formats so that you can choose wisely if seeking a C-mount lens (scroll down to see all 6 parts of the “instructable”):

 

http://www.instructa...o-43-and-APS-C/

 

Camera CCD and CMOS sensor and lens formats are usually defined as 1/3", 1/2", 2/3", 1", or 4/3" (plus many others including 35mm)... these are rectangular formats and each format has a diagonal measurement that represents the size of the fully illuminated image. The 2/3" format has an 11mm diagonal measurement; the 1" has a 16mm diagonal measurement, and the 4/3" format has a 23mm diagonal measurement. The sensor on the Mod 3C has a diagonal measurement of 18mm. So we are faced with choosing either a 1" C-mount lens that will vignette, causing the dark edge at the perimeter of our image... or, a 4/3" lens that will crop, but provide a fully illuminated image on our 18mm sensor.

 

Camera lenses in C-mount that are commonly available, are matched to camera sensor formats. Using a camera lens with a 1/3" format on a camera with a 1" format sensor will result in severe vignetting. If I reverse that example, and use a 4/3" lens on a 1/3" sensor, the light cone/image from the lens would mostly wash around the sensor... the sensor would only capture a small portion of the image from the lens. That result is cropping. Although the magnification provided by the lens is maintained, the resulting field of view is smaller because the smaller sensor is only capturing the center portion of the image. This change/smaller FoV is represented as if a longer FL lens was being used... although cropping has no influence on the magnification the way a longer FL lens would produce. A 4/3" lens would fully illuminate our sensor and it is a smaller format lens than 35mm camera lenses. But old, manual camera lenses perform quite well, and can be found at reasonable prices. A C-mount 4/3 lens might be smaller and lighter weight, so if that is critical to your use, then the higher price of the C-mount might be justified.

 

The following link to the Thorlabs website includes a learning opportunity regarding camera lenses and sensor formats and includes a short explanation of vignetting and cropping and includes tables that show which of their lenses work best with specific size sensors:

 

https://www.thorlabs...tgroup_id=10418
 

For C-mount lenses that do not fully illuminate the sensor in your NVD, the amount of vignetting that you are willing to accept will determine your satisfaction level. The 1" lens might be completely acceptable to your requirements for visual use with only mild vignetting. But images taken with a lens that vignettes are usually unsatisfactory. This is where personal preference and budgetary constraints play a part in decision making.

 

Some C-mount lenses are rated to 1.5mp (megapixels) while others are rated to 10 megapixels. Lenses that have been designated as 10mp have passed a test called an MTF Curve, which is a test of resolution on line pairs, with very small measurements between the lines. CCD or CMOS sensors are capable of differing resolution depending on their pixel count. As manufacturers are able to cram more pixels onto sensors of a specific size, the MTF Curve test indicates that these lenses are capable of diffraction limited resolution on a sensor with a particular number of pixels. Remember that the pixels on a 1/2" format sensor containing 10mp are smaller than those found on a 1" format sensor containing 10mp. The MTF test and rating of 10mp gives assurance that the 1/2" format lens will provide diffraction limited resolution on a 1/2" sensor containing 10mp. Lens designs that do not meet the MTF Curve test are not diffraction limited. You might see a softer image, but you might not, depending on its resolution. 10mp lenses might be used for research where the highest level of resolution is needed.

 

If you would like to learn more about C-mount lenses and how they might be used, the following link should be very helpful:

http://www.instructa...&sensor formats
 

Whether you use a specialized full-frame 35mm camera, a point and shoot digital, or a smart phone, a manual alt-az, GEM or platform tracking mount, a 60mm refractor or a 20” Dobsonian, keep at it.  Don’t give up, don’t hesitate to ask questions within the NV forum, and above all, have fun.  Before you know it, you'll be taking amazing photos of the objects we all love to observe... like these photos of the Lagoon Nebula or Omega Centuri, both taken through an ST 120 achromat mounted to an iOptron AZ Pro, using a Mod 3C and an iPhone 6+ with Night Cap Camera application for manual control.

 

 

 

Or, this one if the Eagle Nebula with the Pillars of Creation, also taken using the Mod 3C with the iPhone 6+, but through a fast 20" Dob:

 

[GeezerGazer]

This Beginner's Guide to NV Photography was written last July to supplement an effort to create a NV pinned thread to help those wanting to know more about NV.  But many months have passed and we have yet to develop an organized pinned thread.  Since the information in this post is already becoming dated in terms of capability and performance, it was decided to publish this thread now.  Within a few days, I'll try to post an update here to discuss improvements in adapters, smartphones and camera sensor capability, showing a few improved results.  

Ray

[star drop]

Folks this thread is a tutorial thread by member GeezerGazer. Please do not post in it. If you do your post(s) will be removed.

[GeezerGazer]

NV Photography... a Beginner's Guide    Update:  March 2019  

Ray Taylor

 

Since this tutorial thread was written in July 2018, there have been some technology advancements and techniques that have improved performance for certain areas of NV Photography. 

 

First, the major camera manufacturers have all introduced new Mirrorless Interchangeable Lens Cameras (MILCs) that offer lighter weight, better low light sensitivity, and better resolution through improved sensor technology and mechanics.  These cameras serve as very good options for those who practice astrophotography.  But they are also excellent for NV photography.  If you have not looked at new cameras lately, you will be pleasantly surprised.  Using a split ring adapter to attach a camera lens to the NV ocular will produce some spectacular results (see original guide, above for details and link to the adapter).  Some of the 4/3 format cameras have upped the pixel count of their sensors to 24,000 while full frame cameras have 50,000 and more pixels and allow ISO settings far in excess of 100,000 for very low light performance.  Please visit the gallery photos of cnoct and jdbastro for current NV photos and links to videos that push the boundaries of this sophisticated technology.

 

https://www.cloudyni...r/139776-cnoct/

 

https://www.cloudyni...30311-jdbastro/

 

The other big change affecting NV photography has been the improvement in smartphone capability.  Android smartphone maker Samsung, introduced the S9 over a year ago, which permitted manual control of the camera and allowed up to a 10 second single exposures using a 12 megapixel sensor.  Then Huawei introduced the P20 Pro, which also allowed manual control and up to a 32 second exposure; but the P20 Pro also included THREE camera lenses with separate sensors, having 8mp, 20mp and 40 megapixels!  The 20mp sensor is monotone, so it takes very large file images in black and white.  Just like with a full frame digital camera, you can watch the image build in long exposure mode on these smartphones.

 

Apple increased their maximum exposure from 1/3 second in the iPhone X, to 1 full second in the XS/XR.  These are short exposures, but the iOS application, NightCap Camera, continues to provide manual camera control and the benefit of photo averaging.  Although NightCap cannot currently access the new 1 second exposure setting, iOS version 12.2 will soon solve that problem… another advancement for iOS users.  

 

Both Android and iOS provide for in-phone photo editing tools to crop, rotate, and make various adjustments to light, contrast, color and tint and they have some digital filters that can enhance a photo automatically with just one click.  (Please keep in mind, images posted in the EAA forum may NOT be post-processed except for cropping and compressing to meet CN guidelines; post-processed images can be posted in the gallery or in the astrophotography forum.) 

 

The advances in both standard cameras and smartphone cameras have provided improved results for NV photos taken during the past six months… that’s how fast this segment of NV changes.  The advances are not likely to slow down anytime soon as camera and phone manufacturers compete to build better products.

 

There have also been some changes in the optical systems that are used for NV imaging.  Gavster in the UK, uses his C-11 with an Astro Physics .75x reducer and a 55mm Plossl afocally to reduce his telescope’s focal ratio from f:10 to f:3.75.  Attaching his P20 Pro, he has been pushing the limits of phonetography, illustrated with these two 8 second exposures:

 

 

 

And having moved to a tracking iOptron AZ Pro, I have been able to use an iPhone XR to full advantage.  An f:4 Explore Scientific 8” Newtonian used with an ASA reducer yields an f:2.8 focal ratio for very quick snapshots.  This 1/4 second image of the Rosette was taken with a 7nm H-a filter at ISO 4000 and was averaged for 10 seconds as the image developed on the phone:  

 

 

This image of the Flame and Horsehead was taken with the exact same equipment at the same settings as the Rosette image above:

You can use full frame, video, APSC, Micro 4/3, or smartphones… it doesn’t really matter.  If you want to record what your see, NV with just about any camera is going to let you preserve images in an uncomplicated way.  For best results a tracking mount is necessary, but the availability of modern, compact and light weight tracking mounts makes it fun to go shopping.  Then, you’ll have something to look at on those Cloudy Nights.

Clear Skies