180 replies to this topic

[mmalik]

Thought I'll outline major DSLR modification types for easy understanding, and knowing what choices one has available when modifying a DSLR.

 

 

IMPORTANT: First and foremost, DSLR filters are referred to with many names, and all mean different things to different people. Here is a compilation of names these filters may be referred to. BUT I would advise that you use standard naming convention like LPF-1 or LPF-2 instead...

 

 

LPF-1

• Front Filter
• Dust removal filter
• Piezo element filter
• IR/UV block filter
• H-alpha pass filter
• Larger filter
• Pinkish looking filter
• Anti-alias filter (1)

 

LPF-2

• Rear Filter
• Color limiting filter
• White Balance filter
• IR/UV block filter
• H-alpha block filter
• Smaller filter
• Bluish looking filter
• Anti-alias filter (2)

 

 

Mod Choices:

 

 

1. LPF-2 removed and replaced with a modified filter [stock LPF-1 AS-IS]

 

2. LPF-2 removed and NOT replaced [stock LPF-1 AS-IS] (My recommendation...)

 

3. LPF-2 removed and replaced with clear glass [stock LPF-1 AS-IS]

 

4. Both, LPF-2 and LPF-1 removed (full spectrum) [external UV/IR block required]

 

5. LPF-2 removed and replaced with a modified filter & stock LPF-1 removed

 

 

 

Note: All options, except #4, 'may not' require external UV/IR block; additional UV/IR block can be added for refractive optics (to prevent star bloating). Light pollution suppression is something that can be used with any mod type

 

 

Note: Narrowband (NB) filter can be used with any mod type; 'NO' #4 external UV/IR block required if using a NB filter

 

 

 

To conclude, remember this...

 

"Essene of any astro mod is to get rid of stock LPF-2"

 

 

 

Edited by mmalik, 03 December 2014 - 06:01 AM.

[GJJim]

I've seen the term "anti-alias filter" used in discussions on modding cameras.  In the category lists above, where would the A-A filter place?

[mmalik]

 Anti-aliasing, otherwise referred to as 'blurring effect', is a combined function of both, LPF-1 and LPF-2. A diagrammatic representation below:

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Edited by mmalik, 01 December 2014 - 03:29 AM.

[Ranger Tim]

A sticky for sure! Countless requests have been made to explain these filters and what does what for which mod. Thanks Malik! I chose the LPF-2 removal and have been well pleased. My Canon won't autofocus accurately now and also has problems with some Nikkors with the Fotodiox adapter, but it was worth it. A dedicated astro camera doesn't need auto focus anyway. I like the fact there is still some UV/IR filtering which reduces the need for extra filtration and helps control blooming. There is still a filter in place to prevent sensor contamination too. I have friends that swear by the full mod/ complete removal of both filters and they achieve great results as well. What's in your camera? ; )

[mmalik]

Thanks Tim; I am using #2 mod (above...); an image sample of the same:
 

• 25x5min [125min], ISO 1600, Multiple LENR...
• 254mm TMB APO/elCapitan
• Minor crop

 
High resolution...

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Edited by mmalik, 04 December 2014 - 02:45 PM.

[mmalik]

While most Canon LPF-2 is single-layered (as shown above...), Sony a7S, for example, is double-layered LPF-2. Following is a graphical representation of major a7S mod types...


Note: Although LPF-2 on a7S is double-layered, exact nature and function of those layers (other than anti-aliasing) is not known at the time of this writing; manufacturer/technical references are welcome...

Source: Own rendering

 

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[AnakChan]

What would be the result of a full spectrum be for astrophotography? No external filters, etc. Subjects would be DSO's, no planetary.

Is it advisable or are filters of some sort at least are required?

[mmalik]

Generally speaking, I would 'not' advise full spectrum for long exposure DSO imaging; the reason best I could describe from my own experience is here...

 

 

What I would advise is 'Removed LPF-2' mod while stock LPF-1 is still in place (middle one in the pic below...). Of course additional decent light pollution fileting is mostly needed.

 

 

With my setup, what I mostly use for DSOs?

LPF-2 removed and NOT replaced [stock LPF-1 AS-IS] + external filtering with IDAS HEUIBII filter...

 

 

Hope this helps; feel free to ask more. Regards

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Edited by mmalik, 21 January 2015 - 09:42 PM.

[AnakChan]

Malik, cheers for that. I've read your post. I understand now why you're not recommending full spectrum. With regards to your mod choices of #2 vs #3 in your initial post, would the clear glass in #3 assist in maintaining the same focus point? I came across the Astrodon AD40Clear which claims to have the same refractive index thus maintaining focus point (or more precisely without having to worry about calibration).

[17.5Dob]

So is it just Canon cameras that are so crippled with lack of red sensitivity ?

I ask, because I've only been shooting AP for 4-5 months, and my Nikon seems to be doing fine without any modding.

This is my very first attempt at the Horsehead for example. No filters other than a broadband Orion SkyGlow filter to be able to image from my Red Zone backyard.

 

Edited by 17.5Dob, 22 January 2015 - 12:44 AM.

[mmalik]

...would the clear glass in #3 assist in maintaining the same focus point? I came across the Astrodon AD40Clear which claims to have the same refractive index thus maintaining focus point (or more precisely without having to worry about calibration).

 

Clear glass is for day-time, auto-focus calibration, something NOT needed in an astro dedicated DSLR. Regards

Edited by mmalik, 22 January 2015 - 01:45 AM.

[mmalik]

So is it just Canon cameras...

 

Not really; all stock DSLRs will block 'some' H-alpha; your image looks good for a stock but is still muffling H-alpha, just a fact. Here is a refresher for all, hope you don't mind.

 

 

Consider these three wavelengths:

 

• Ultraviolet (UV).....................10 nanometers (nm) - 400 nm [wide bandwidth] "Invisible"
• Infrared (IR).........................700 nm - 1 millimeter (mm) [wide bandwidth] "Invisible"
• Hydrogen-alpha (H-alpha).....656.3 nm [narrow bandwidth] Visible

 

 

Idea is to “block” first two (UV/IR) [to prevent star bloat] and to “pass” H-alpha [to capture the brightest wavelength of visible light in stellar astronomy].

 

 

H-alpha (Hydrogen-alpha) is a specific red visible spectral line created by hydrogen with a wavelength of 656.3 nm, which occurs when a hydrogen electron falls from its third to second lowest energy level.

 

 

Source: Wikimedia

 

 

 

 

Typical stock camera configuration:
1. Stock LPF-1 (IR/UV Block) does NOT block H-alpha
2. Stock LPF-2 (WB & IR/UV Block) “blocks/restricts” H-alpha

 

 

Typical modified camera configuration:
1. Stock LPF-1 (IR/UV Block) does NOT block H-alpha
2. "Removed LPF-2" (preferred...) OR Modified LPF-2 (WB & IR/UV Block) “passes” H-alpha

Edited by mmalik, 22 January 2015 - 02:27 AM.

[pedxing]

I've heard that in normal photography, Nikons tend to saturate reds, so I'm not suprised that this is also the case for AP...

[skycamper]

So is it just Canon cameras that are so crippled with lack of red sensitivity ?

I ask, because I've only been shooting AP for 4-5 months, and my Nikon seems to be doing fine without any modding.

This is my very first attempt at the Horsehead for example. No filters other than a broadband Orion SkyGlow filter to be able to image from my Red Zone backyard.

 

My first attempt with a unmodified T1i was nowhere near this.   Plus my CLS LP filter turns everything blue and totally restricts red. Combined with an unmodified camera is no fun.  I may have to try the orion filter.  What is the stats on you photo?

Thanks

Abraham

[SKYGZR]

Seems the only "benefit" between 2 & 3 is the ability of the cam to still auto focus w/auto focus lens's. Same performance/results with -or- without the glass for astro?

[mmalik]

Same performance/results with -or- without the glass for astro?

 

Even clear glass is a layer/medium that light has to traverse; my recommendation is 'no' clear glass if camera is dedicated for astro. I look at clear glass as old/traditional way of doing the mod; most modern mods are done without clear glass.

 

 

LPF-2 thickness varies from camera to camera, see here... and here...; chances of finding same thickness and same refractive index third party glass (if not quality) might be slim to none.

 

 

Last but not least, latest sensor designs, e.g., a7S... are even more complex, making clear glass fittings almost impossible, if not futile. Hope this helps. Regards

 

 

On a side note, clear glass related discussion here...

Edited by mmalik, 23 January 2015 - 02:24 PM.

[m1618]

This is an excellent resource. The few that I did modify and sell...gees they ask that question each time. I've always recommended LPF2 removal only as well. It's also that extra protection in front of a naked chip.  Correct me if wrong but most folks use light pollution filters on their nosepiece anyway or image with newtonians (on a budget or more aperture) and would not have to worry about IR anyway UNLESS they want to do some artistic daytime photography and require autofocus through the viewfinder.

[mmalik]

A mod never exposes the CMOS sensor; there is pretty decent strength cover glass in front of the CMOS that never gets removed, not even in full-spectrum mod. Regards

Edited by mmalik, 23 January 2015 - 06:56 AM.

[Whuppy]

I have a canon 550d that I bought used, specifically for DSO photography. Judging by the comments above and your recommendation it's best to NOT do the full spectrum mod and just remove the LPF2 filter, leaving the LPF1 filter in place. With this arrangement would it still be possible to use the auto focus after adjusting the remaining clear filters position in respect to the CCD? I only ask because it would still nice to retain that function after modding, just in case I wanted to use the camera during the daytime with the proper filters and white balance adjustments. Not that I plan on doing that but you never know. Also piggy backing the camera with a lens for wide field shots, but then manual focus could always be a last resort?

[mmalik]

If you replaced LPF-2 with clear glass you should be able to retain auto-focus without doing any other calibrations. Regards

 

 

FYI: Gary explains other calibrations here...

[pablotwa]

Hi Mike. I' new at this and I'm thinking of modifying my "B" camera an old Canon 7D. (Not touching the 5D Mark III!). I'm thinking of full spectrum so I can use it for several uses

 

1) I will be doing grating spectroscopy (http://www.rspec-ast...m/dslr-adapter/) will the full spectrum mod affect the spectroscopic results?

 

2) Does your price list INCLUDE the external filters necessary for full spectrum?

 

Thank you

 

Pablo Lewin

[mmalik]

Pablo, may be someone who has done spectroscopy can answer your first question better than I can; mod, especially full-spectrum, definitely will open up your camera to entire spectrum and I am quite sure it will affect your spectroscopic results if I were to go by the frequencies referenced in your link. External filters are NOT included in a mod by most folks. PM or email me if you need more information. Regards
 

Here are the frequencies that astrophotographers mostly concern themselves with:


•Ultraviolet (UV)........................10 nm - 400 nm (nanometers) "Invisible"
•Hydrogen-beta (H-beta)............486.1 nm
•Oxygen-III (OIII)......................500.7 nm
•Hydrogen-alpha (H-alpha).........656.3 nm
•Nitrogen-II................................658.4 nm
•Sulfur-II....................................672.4 nm
•Infrared (IR).............................700 nm - 1 mm "Invisible"

[mmalik]

There is a class of cameras like a7R and others (5Ds R, D810) which do NOT have low-pass filters (LPFs) by default; what that means is that they only have an IR/UV block filter instead.

 

 

Note: In this instance (a7R for example), only mod choice one has is 'Full-Spectrum'; 'Removed LPF-2' mod choice is NOT there given the base architecture!

 

 

Source: Own rendering

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Edited by mmalik, 04 February 2015 - 04:09 PM.

[msalganik]

errr, so you're saying the A7r can only be moded as an astro-only camera? Can the default UV/IR be replaced with one that has expanded Ha transmission? 

[mmalik]

Things are getting bit more complicated (paradoxically, may be simpler...); let me preface with the following, read more here... and here...

 

 

LPF (low-pass filter) terminology is getting antiquated with new breed of DSLRs without LPFs (a7R, D810, D810a, etc.) I suggest we call LPF-1, 'Filter-1' and LPF-2 'Filter-2' and refer to their replacements as such; following diagram will clear the concept in terms of a7R vs. standard configuration (a7S for example).

 

 

Note: What this all means is that LPF-2 becomes a component of 'Filter-2' complex when present; when NOT, the remaining components make up 'Filter-2', as in a7R.

 

 

There still is a "glass filter" that does the IR/UV filtering in a7R, just no anti-aliasing.

 

 

ONLY mod choice one has with a7R is 'Full-Spectrum'; 'Removed LPF-2' mod choice is NOT there per se for a7R given the architecture.

 

 

Regards

 

Source: Own rendering

 

Edited by mmalik, 27 March 2015 - 07:22 PM.