Why are DSLRs "not suited" for narrowband

[Ags]

I have always been confused by the apparent perception that DSLRs can be used to take RGB images of nebulae but are less suited to making narrowband images of the same nebulae. The usual argument is that DSLRs are not 'sensitive enough' for narrowband.

The reason for my confusion is that the nebula is narrowband itself - by using a narrowband filter you are not excluding any light from the nebula in the wavelength of your choice... A modded camera is going to get just as much red Ha light regardless of whether a Ha filter is in the train. And the red signal of the nebula is almost entirely composed of Ha light.

So you should be able to get just as much depth with narrowband filters as without when using a DSLR - more depth in fact as you are excluding so much light pollution.

[badgerchap]

I share your confusion

[RikM]

I think it is more to do with you imaging an effectively mono target, with a colour sensor, so it could seem like you don't get the full resolution. I expect by taking enough subs of a suitable exposure time and employing dither guiding, you will build up a good enough signal.

[badgerchap]

Sounds logical!

[GlassWalker]

The argument is more that a DSLR is a less optimal choice compared to a mono CCD. A mono CCD, with no colour filter in the way, will be fully effective with whatever filter you use. A DSLR with colour filter will only be significantly sensitive where the narrowband and colour filters overlap e.g. only "red" pixel will be sensitive to Ha and SII. OIII sits between blue and green so you get a bit more out of that. So a DSLR is arguably more effective if you use it to do colour imaging of broad spectrum objects, for example, of galaxies.

[Ags]

Mmmmm... But with my UHC filter I would be using all three colors of my sensor, with the drawback that Hb and OIII are combined.

[Dave Smith]

A DSLR basically has a mono chip and over that chip is an array of red, green and blue filters in an RGGB arrangement. So for example the Ha may well get through the R filter but is blocked by the G and B filters. So for starters only a quarter of the Ha gets to the chip. It is probably worse than that because of spacing/matrix between the colours.

Dave

[Ags]

To play the devil's advocate... The DSLR may be three times less sensitive to any given light, but perhaps it makes up for that by having a light gathering area three times larger than the typical CCD :-)

Obviously a CCD is going to be better than a DSLR, but my point is that, theoretically at least, a DSLR should be as able to image an emission nebula in narrowband as in RGB.

[Merlin66]

Depending on the plate scale of the image - bang per buck ( light/ pixel) - forgetting the sensitivity (QE) issues there's less photons collected by the DSLR red pixels say than you'd get with a mono CCD where ALL the pixels, not just 1 in 4 collect the data.

[Gina]

You can do NB with a modded DSLR - I have, and have the images to prove it. But DSLRs are far less efficient at the process than mono CCD cameras. Now I have both I can see the comparison for myself.

[Ags]

I can't see myself ever affording a CCD :-(

[badgerchap]

I can't see myself ever affording a CCD :-(

There's always larceny

[laser_jock99]

You can image narrowband on a DSLR but the point people are making is the Bayer Matrix filter present on the sensor surface

effectively reduces the number of recording pixels by up to three quarters. So using a DSLR gives you larger FOV but less detail within it. The ideal solution is a large format CCD- but these are the price of small car!

Here's one of my typical narrowband DSLR shots. Large FOV but lacks fine detail and is noisy due to being a non cooled camera.

Now if you fancy modding you DSLR............

http://stargazerslounge.com/topic/166334-debayering-a-dslrs-bayer-matrix/

polish off the Bayer Matrix!!

[badgerchap]

You can image narrowband on a DSLR but the point people are making is the Bayer Matrix filter present on the sensor surface

effectively reduces the number of recording pixels by up to three quarters. So using a DSLR gives you larger FOV but less detail within it. The ideal solution is a large format CCD- but these are the price of small car!

Here's one of my typical narrowband DSLR shots. Large FOV but lacks fine detail and is noisy due to being a non cooled camera.

Now if you fancy modding you DSLR............

http://stargazerslou...s-bayer-matrix/

polish off the Bayer Matrix!!

Blooming luvverly shot though mate