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A 'naked sensor' is not really naked. A common misconception.

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#1 asanmax

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Posted 03 December 2021 - 05:04 PM

So I get a lot of questions about the full spectrum modification and if it's better than an H-alpha mod.

I totally understand the confusion about the modification types that are available and which one is the best for astrophotography.

Honestly, there is no right answer to this question and everyone's situation is different. But I'm not going to get into the details of the mod types since this topic has been discussed a 1K times.

 

Instead, let's talk about what's known as a Naked Sensor Mod.

It seems there is some confusion about the naked sensor (aka bare sensor) modification.

I think that people get scared by the words 'naked' and 'bare' and come to a conclusion that the sensor is left open to the outer world totally unprotected.

And it's quite understandable, from a regular digital camera user's point of view it does sound like the sensor is left 'naked' after the modification.

 

I'd like to provide some details about this type of mod and why it might be better that a regular full spectrum mod with the use of an additional clear glass filter.

First off, with all the filters removed, the sensor it left with a protective glass on top of it. 

Yes, that's right, there is still a layer of glass above the sensor itself and that glass protects the fragile sensor from the outside environment.

It may either be a quartz or a fused silica piece of glass that is absolutely transparent to all light waves, including IR and UV.

And that glass can be cleaned using the same methods that are used to clean the 'normal' sensor with all the stock filters in place.

There are special fast drying solutions available and a little drop of pure 99% alcohol can also be used on the tip of a sensor cleaning swab.

 

Naked sensor 01.jpg

 

Naked sensor 02.jpg

 

Now, I get asked a lot about the difference between a naked sensor full spectrum mod and a full spectrum mod where a third party clear glass filter is installed in place of the stock filters.

I always suggest to go with a naked sensor simply because adding another layer of glass doesn't improve the image quality. That additional filter may actually cause a well known issue with halos around bright stars.

This of course depends on the optical train and may or may not appear in the images. I don't really find this as a major problem though.

 

Let's talk about when a third party filter should be added.

When the stock filters are removed from the sensor assembly, the sensor needs to be moved forward just a tiny bit to compensate for the missing layer(s) of stock filter glass.

This is usually done by either re-shimming the sensor or by adjusting the spring-loaded sensor mount position. This operation is called sensor calibration.

With the re-shimming, the original sensor shims (washers) are either removed or replaced by the new ones so that the sensor can be precisely moved towards the lens mount flange.

In the digital cameras that have a 'floating' sensor mount, the calibration is done by tightening the sensor mounting screws to achieve the best position when the lenses will still focus at infinity and the internal autofocus gets in sync with the on-sensor autofocus aka 'live view focusing'.

This operation can get very complex because the sensor needs to be kept absolutely parallel to the lens mount flange.

 

Now what do you do if the sensor mount has not enough room to be calibrated? 

You add a third party clear glass. That clear glass filter replaces the stock filters and a technician can proceed with sensor calibration.

 

Based on my optical engineering background and experience, I think that a naked sensor is the best solution. Some may disagree.

I hope some folks find this quick explanatory article helpful.

 

Max


Edited by asanmax, 03 December 2021 - 09:32 PM.

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#2 TOMDEY

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Posted 03 December 2021 - 05:40 PM

Hi, Max - Interesting!

 

Closely-related >>> For some ~Scientific~ cameras, there actually is a truly naked sensor option if you go all the way to the chip manufacturer and specifically request it. What they do is to only tape the glass over the chip, and then you take it from there and integrate it into your camera, remove that "dust cover" and use the truly naked array. It is also possible to remove a stock glued-on slip by cutting it (four straight cuts like around a picture frame) using a diamond saw. I witnessed this process and wouldn't have believed it if just brought up in casual conversation. Once inside like that, a RGB color sensor can be rendered monochrome by chemically removing the microscopic filter matrix. I believe that FLI offers cameras with upgrade options, including quartz window and precision/hardened placement of the array to the body structure in all six degrees of freedom (x y z roll pitch yaw). We got those upgrades for use in our labs at work... but usually kept the fused silica slip, unless our application specifically required buck naked. I worked at Kodak, at the time... were able to get "special request" select chips right from their production plant in Rochester, NY.     Tom



#3 asanmax

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Posted 03 December 2021 - 06:17 PM

Hi Tom. 

Quite interesting details. We have actually been debating at Night Sky Camera whether to start doing mono mods or not. 

The camera manufacturers use different 'glue' types on that protective glass. Some are easily removed by applying some heat. Some are glued to the frame with another compound that needs to be dissolved.

The mono mod is just one of the ongoing projects and we're in the process of acquiring the chemicals that are supposed to dissolve the bayer matrix.


Edited by asanmax, 03 December 2021 - 09:36 PM.


#4 TOMDEY

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Posted 03 December 2021 - 06:31 PM

Yeah, I watched George doing this at home, of all places! He was very methodical and had the chemistry there inside a bell jar by the kitchen sink with manipulators, as I recall. I got the impression that there was a significant partial vacuum, but wasn't paying too much attention or inclined to distract his work. Yet he seemed completely relaxed proceeding with that. Nearly all of my friends are engineers, scientists, techs, faculty, etc. One of my favorite thoughts is, "I wonder what would happen if I...?" that drove my parents nuts, but eventually proudly so!    Tom



#5 asanmax

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Posted 03 December 2021 - 06:35 PM

"I wonder what would happen if I...?"

Haha, exactly what I was doing back in my university years. Also the last words of a nuclear physicist grin.gif



#6 TOMDEY

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Posted 03 December 2021 - 07:56 PM

Haha, exactly what I was doing back in my university years. Also the last words of a nuclear physicist grin.gif

Heh! Just don't turn off the levitating containment switch on an innocent-looking vacuum bottle of antimatter.    Tom



#7 galacticinsomnia

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Posted 03 December 2021 - 10:17 PM

Do you know which sensors have glass, and which ones do not ? 

Good info..  Still lovin my full spectrum mods lol

Clear Skies !!


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#8 sharkmelley

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Posted 04 December 2021 - 01:18 AM

Thanks for this thread!  Next time someone is worried about the risk of a "naked sensor" I can point them here smile.gif

 

Mark


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#9 asanmax

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Posted 04 December 2021 - 01:36 AM

Do you know which sensors have glass, and which ones do not ? 
 

I have not seen one so far.



#10 T~Stew

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Posted 05 December 2021 - 09:15 AM

Good info asanmax. It might be down to semantics though. I know there is glass built into the sensor itself, but by saying "bare sensor" mod we are talking about removing the additional UV/IR and color correcting layers added onto it. Its kind of like saying you're not naked when undressed... you still have skin on. However it is nice to bring this up since some don't realize the extra layer on most sensors and think it is extremely more fragile because of it.

 

I'm not sure that people add the glass as means of protection, though it certainly does add a more easily removable layer should it get scratched or damaged. I think its normally there to maintain factory focus with the usual lenses, or mitigate the difference in focus somewhat without adjusting the sensor. I think adjusting the sensor is not very hard in most cases, but you have done a lot more of this than I. My 100D had very little adjustment, those screws were within 1 turn of being bottomed out stock. So when I went to mod my next camera I got the clear glass to avoid having too much issue with maintaining calibration. It was only $65 so no real biggie. I think it had much more range and may not have been needed though.


Edited by T~Stew, 05 December 2021 - 09:32 AM.


#11 whwang

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Posted 05 December 2021 - 08:15 PM

I believe it's always good to keep the number of glass minimal.  There is absolutely no sense to add another layer of glass just to protect the sensor.  The sensor is always protected.

 

On the other hand, I almost never recommend people to do a real full spectrum mod.  You will need a UV/IR-cutting filter to maintain the image quality, especially on systems with several refractive elements, like camera lenses and refractors other than the best APOs.  


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#12 asanmax

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Posted 05 December 2021 - 10:31 PM

I believe it's always good to keep the number of glass minimal.  There is absolutely no sense to add another layer of glass just to protect the sensor.  The sensor is always protected.

 

On the other hand, I almost never recommend people to do a real full spectrum mod.  You will need a UV/IR-cutting filter to maintain the image quality, especially on systems with several refractive elements, like camera lenses and refractors other than the best APOs.  

I agree with you, keeping the refractive surfaces to an absolute minimum is the best. Most of those folks who request a full spectrum mod typically use their cameras for IR photography as well.



#13 galacticinsomnia

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Posted 06 December 2021 - 05:12 PM

I believe it's always good to keep the number of glass minimal.  There is absolutely no sense to add another layer of glass just to protect the sensor.  The sensor is always protected.

 

On the other hand, I almost never recommend people to do a real full spectrum mod.  You will need a UV/IR-cutting filter to maintain the image quality, especially on systems with several refractive elements, like camera lenses and refractors other than the best APOs.  

Everyone has a personal preference for sure, but as a photographer first, I always opt for full spectrum as it helps in imaging other areas.  Adding an L-2 or L-3 in the image train is pretty much a don't care for me, and having the option to take UV and full IR photo's has it's benefits.  Planetary, Solar, and earth objects. 
Also the resale value of a full spectrum camera is higher, as well as it is much easier to sell. 

It is personal preference, but if I am going to have a mod done to my camera, I'm going to make sure I have access to the full spectrum a sensor can deliver. 

Clear Skies !! 



#14 Serial

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Posted 28 December 2021 - 04:29 PM

 You will need a UV/IR-cutting filter to maintain the image quality, especially on systems with several refractive elements, like camera lenses and refractors other than the best APOs.  

 

I'm modding my Nikon D5300.  I'd like to use it with camera lenses and refractors.  Will it work to replace the internal hot mirror with a rectangle cut from a cheap UV filter?  

 

Why would I want to block more IR?  I thought that was the point of the mod.  Is IR outside or H-alpha bad for astrophotography? 



#15 Mike in Rancho

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Posted 28 December 2021 - 04:50 PM

Approximately 400-700nm is pretty much what you want for astro.  The shorter and longer wavelengths can act funnier through the lens elements I think, and also the response of some of the Bayer filters can start acting up when you get outside their comfort zones.  Thus, not only might you get focus issues, but proper color balancing of your astro images will be difficult or more likely impossible.

 

I use external filters on my lenses or the adapters to the telescope.  ICE makes reasonably-priced ones for daytime photography to fit lenses, and I use SVBony or Optolong 2-inchers otherwise for telescopes.  UV-IR cuts, or L-eNhance, etc.

 

If you ever want to play with your naked sensor D5300 in the UV or IR, there are special filters for that too, with varying cutoffs.



#16 T~Stew

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Posted 02 January 2022 - 06:13 PM

I'm modding my Nikon D5300.  I'd like to use it with camera lenses and refractors.  Will it work to replace the internal hot mirror with a rectangle cut from a cheap UV filter?  

 

Why would I want to block more IR?  I thought that was the point of the mod.  Is IR outside or H-alpha bad for astrophotography? 

H-alpha sensitivity is what we want. IR is not, unless you are specifically wanting to do infrared photography (sometimes useful for planets). IR usually requires the use of an IR-pass filter since you don't want to image IR along with normal RGB, as it will not all be in focus and make a poor picture. This is why there are several different methods to modify your camera, like H-alpha mod and Full Spectrum mod, IR-mod etc. Full spectrum is the most versatile, but then you need to add UV-IR cut filter back in there somehow (usually not a big deal). All most really need though is the extra H-alpha sensitivity and usually you can do that by simply removing the hot mirror filter and retaining the sensors other filter.


Edited by T~Stew, 02 January 2022 - 06:15 PM.


#17 galacticinsomnia

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Posted 02 January 2022 - 07:17 PM

I'm modding my Nikon D5300.  I'd like to use it with camera lenses and refractors.  Will it work to replace the internal hot mirror with a rectangle cut from a cheap UV filter?  

 

Why would I want to block more IR?  I thought that was the point of the mod.  Is IR outside or H-alpha bad for astrophotography? 

UV and IR are a bane to DSO photography, if you do not filter them out.  Bloated stars, etc etc. 
400 to 700 is a reliable generally good advice.  However, maybe you want to capture some solar or lunar in the IR range, now you are looking at another mod, or another camera.

Getting the full spectrum mod IMO allows for visual music in greater than 7 octaves.  How many cameras do you want to own ?

Clear Skies !!



#18 sharkmelley

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Posted 03 January 2022 - 02:05 AM

I'm modding my Nikon D5300.  I'd like to use it with camera lenses and refractors.  Will it work to replace the internal hot mirror with a rectangle cut from a cheap UV filter?  

No, because you need to block the IR beyond the H-alpha and SII wavelengths. However, it will work to replace the internal hot mirror with a rectangle cut from a IR/UV blocking filter designed for astrophotography.



#19 asanmax

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Posted 03 January 2022 - 04:30 PM

I'm modding my Nikon D5300.  I'd like to use it with camera lenses and refractors.  Will it work to replace the internal hot mirror with a rectangle cut from a cheap UV filter?  

 

Why would I want to block more IR?  I thought that was the point of the mod.  Is IR outside or H-alpha bad for astrophotography? 

Be very careful with those cheap filters. They might not meet the quality level required for long exposure astrophotography.

Besides the proper transmission (400nm-700nm) the filter should have excellent anti-reflective coatings. I personally spent a lot of time working with an optical lab and testing many filters until we came up with a perfect UV/IR cut filter for the D5300. 




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