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.
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?
Baader and LifePixel manufacture replacement filters. The Baader filters are sold in the US by Alpine Astronomical.
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.
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.