DSLR Modification for Astrophotography

[imhotep]

This topic recently came up in one of my threads and several members have asked me to elaborate on what it means to modify a DSLR for astrophotography. This topic comes up a lot within the Cloudy Nights community and no doubt has surfaced among the Canon forums before. My original thread is getting fairly cluttered (not in a bad way) so for the sake of keeping these topics easy to look up in the future I’m devoting a new thread to the questions I’ve received.

There are several excellent references that are most likely written better than my explanations below. Please refer to these as well.
http://www.hapg.org/camera%20mods.htm
http://www.lifepixel.com/shop/cart.php?m=product_list&c=1
http://www.pbase.com/samirkharusi/image/48558817


Q: What is DSLR modification for astrophotography?
A: Simply put, it is the removal of the stock IR/UV filter that comes factory-installed in your DSLR. Several options exist for what to replace it with, and whether or not to replace it at all.

Q: Do I have to modify my DSLR if I want to take astrophotos?
A: No, but you will be operating with a severe handicap (explained below).

Q: What advantage does a modified DSLR have over a stock DSLR in terms of performance for astrophotography?
A: There is a very important wavelength at about 650µm called the Hydrogen-Alpha emission line. Many nebulae rich in ionized hydrogen gas emit light at this wavelength. Unfortunately the stock IR/UV filter prohibits the vast majority of this light from reaching the sensor chip. Its spectral sensitivity really tanks as it approaches the Ha emission line. There are several replacement filters available which still filter out IR and UV wavelengths but permit about 95% of Ha energy. Performing this replacement will allow you to image MANY object that are virtually invisible to a stock DSLR even assuming long-exposures under typical observing conditions. There are also several objects that, while visible in significant detail to a stock DSLR, will take on a new level of detail and brilliance when imaged with a modified DSLR.

Q:How is this modification done and where can I buy the replacement filter?

A:

Baader and LifePixel manufacture replacement filters. The Baader filters are sold in the US by Alpine Astronomical.
http://www.lifepixel.com/shop/cart.php?m=product_list&c=1
http://www.alpineastro.com/filters/filters.htm#DSLR%20Filters

There are a couple of people online who are very experienced performing the necessary surgery on a DSLR. Costs are usually around $250 to mail you DSLR to a technician and have the camera modified.

http://www.hapg.org/camera%20mods.htm

Another option is to perform the modification yourself. WARNING – do not attempt this unless you feel VERY comfortable with tiny ribbon cables and using a soldering iron. I modified my own 350D successfully but it definitely involves taking some risk. Here are several tutorials that will guide you through the process:

Various makes and models - http://www.lifepixel.com/IR.htm
Canon 350D - http://astro.ai-software.com/articles/mod_350D/mod_350D.html
Canon 40D - http://strgazr27.zenfolio.com/p71444939/ (this the website of a POTN and CN member. I’ve learned a great deal from him).

I hope this info is helpful to anyone interested in equipping themselves for DSLR astrphotogrpahy.

[canonloader]

The conversion to "normal" IR is not the same as converting for astrophotography? I have seen bodies for sale that have been converted for IR. Just wondered. Great info here.

[imhotep]

Originally Posted by canonloader

The conversion to "normal" IR is not the same as converting for astrophotography? I have seen bodies for sale that have been converted for IR. Just wondered. Great info here.

I'll hazard a guess without knowing exactly what 'normal IR' refers to, although I think this is a pretty good guess. Infrared photography makes use of IR wavelengths to expose an image. The Ha emission line is technically a part of the visible spectrum and is not IR energy.

This is where it gets a little complicated. There are three general options when modifying a DSLR:

1. Remove the stock filter and replace it with nothing.

2. Remove the stock filter and replace it with clear glass.

3. Remove the stock filter and replace it with a 3rd party IR/UV filter that permits the Ha line.

Overall #3 is going to be the best choice for MOST people who want to image the night sky. The first two options can be problematic for refractive optics because, while the best apochromatic glass will focus the visible spectrum to a point within a very good margin of error, those same optics are not necessarily corrected for IR and UV. So if you permit IR and UV with refractive optics you may be asking for trouble in the form of bloated stars and fringing effects. However, none of this applies to reflective optics. That being said, option #3 is the standard choice for people who image with refractive optics.

Options 1 and 2 are also not necessarily a good choice even with reflective optics depending on what you want to do. My understanding is that even though reflectors can focus visible + IR + UV to the same point, inclusion of IR and UV can diminish image contrast to an extent. For me personally the IR and UV wavelengths just aren't wanted for most of my imaging of dim diffuse objects such as nebulae and galaxies. However there are some very specific applications where narrow-band imaging with either IR or UV wavelengths is the weapon of choice. Shooting Venus in purely UV is one of them.

Probably way more information than anyone cares to know. If you're planning on shooting SWA portions of the sky with a DSLR and camera lenses, I'd stick with option #3. Same applies for the vast majority of DSLR imaging that amateurs choose to spend their time on, regardless of the telescope or camera lens being used. Other mays disagree and that's fine. I view hundreds of amateur astrophotos every year, many of which are shot with modified DSLRs as per option #3.

[imhotep]

I forgot to mention....

Another big whopping problem with option #1 is that you will lose the AF functionality of your DSLR. If you choose #2 (for some reason) you can retain AF but IF AND ONLY IF you get a piece of clear glass that has the same refractive index as that of the stock IR/UV filter. If you haven't already guessed, the replacement IR/UV filters that permit Ha energy do in fact match this refractive index so AF is retained.

By the way, some folks may say "forget it! I've only got one DSLR and I'm not going to sacrifice it for the occassional astrophoto!" Definitely a valid concern. Here are two suggestions:

1. You can purchase an IR/UV filter that does the exact same job as the stock filter but screws onto the front of your lens. This will cause a modified DSLR to perform as though it were stock in terms of spectral sensitivity. Personally I think this is kind of a hassle.

2. IMHO a better thing to do is to just buy a second DSLR and modify that one. I say this because the bodies are getting rediculously cheap compared to when I bought my first 350D. A brand new 350D body is less than $400 on B&H and even less than that used. Going with a more recent version is of course also much cheaper these days. One advantage to the 350D is that there's a huge knowledge base for modifying it and using it for astrophotography. If you are serious about getting into this with a DSLR and can spare a few hundred dollars to get a dedicated body to be modified, this is by far the best way to go.

[canonloader]

I had already planned on getting another body, although I do have a D30 sitting in the closet. Low shutter count and nobody wants it. It's a sneaky little body though, it takes fantastic images if you know how to edit them. If the Northern Lights aren't enough for me, I can have that one converted.

[imhotep]

You may be able to find some instructions for that model. Seems like I saw the D30 listed on the LifePixel website. I'm not trying to get you into to trouble, but it really isn't that bad if you feel reasonably confident in your ability to work with tiny things.

I modified my 350D in my garage about six months ago. There are several very good tutorials already in existence so I didn't go crazy trying to photo-document the effort, but I did snap some shots at key steps in the process. They're in my Flikr account with captions:

http://www.flickr.com/photos/2091093...7603814702374/

[canonloader]

HAHA, nope, not me. Last year I tried changing the focus screen on my 30D. That was a fiasco and shouldn't have been that hard to do.