DSLR and Narrowband filters

[Tommy B]

Howdy folks,

The weather seems unrelenting lately where I am so im gonna use the time to clear up some queries I have about this and that.

Lately I've been looking at the wonderful pictures people have been taking with narrowband filters and would like to move in that direction in the future. I know people use mono astrocams and filters but my question is, will these filters work well with an unmodded dslr camera? or do they specifically need a mono camera?

Thanks

Tommy.

[swag72]

You can use a Ha narrowband filter with your DSLR, but it is I believe almost crucial to have it modded, otherwise you just are not going to catch the data. You will need to be prepared for long exposures though, I was generally looking at 15-20 minutes for my DSLR, but then noise was causing me some major issues at these sub lengths. I got a couple of Ha narrowband images with the DSLR and 12nm Ha filter combo.

[Tommy B]

Thanks for that. What about if I were using a "colour" ccd astrocam, would the fact that its not mono cause problems?

[swag72]

If you are wanting to be doing narrowband imaging, including OIII and SII, then you really do need a mono camera I think. You can do Ha with a OSC (one shot color) CCD camera quite successfully though.

.

[TonySparsis]

Not quite sure where this question would fit in. I have an Canon EOS 550D. Do I need to moddy the camera to use for DSO ?

[Merlin66]

The problem with DSLR's or OSC cameras is the Bayer matrix. This means for the red response there's only one pixel in four doing it's job and in the case of the DSLR the response curve falls off towards the red.

They can obviously be used for DSO etc, but modding the camera can give an increase (from 20% to >40% ie 100% improvement) in the Halpha response which allows many more photons to be collected.

HTH

[Tommy B]

The problem with DSLR's or OSC cameras is the Bayer matrix. This means for the red response there's only one pixel in four doing it's job and in the case of the DSLR the response curve falls off towards the red.

They can obviously be used for DSO etc, but modding the camera can give an increase (from 20% to >40% ie 100% improvement) in the Halpha response which allows many more photons to be collected.

HTH

Ahh yes this makes sense. Thanks

[Flea77]

They can obviously be used for DSO etc, but modding the camera can give an increase (from 20% to >40% ie 100% improvement) in the Halpha response which allows many more photons to be collected.

HTH

So if I read what you wrote correctly, if I am using 5 minute subs with a modded DSLR I could do the same thing without modding using 10 minute subs, correct?

Allan

[MikeWilson]

I'd say it's more like 20% to 60%, at least when I experimented on M42 it seemed that way.

But then with the longer subs you get less Ha contrast (since you let in other wavelengths of light disproportionately more) which may or may not be important to you depending on what you want to image.

You'll also get more noise and you're more likely to have a ruined frame with longer exposures.

Mike

Sent from my mobile using TapaTalk (so please excuse bad grammar & spelling!) :-)

[Flea77]

You'll also get more noise and you're more likely to have a ruined frame with longer exposures.

Mike

I would think that noise would be removed with the application of dark frames. Although reduced contrast and more chance of a ruined frame is true, that would be the case any time you do long exposures.

So basically if you already have a DSLR that you use for daytime use as well as AP, you can either buy another body+mod it, or deal with longer subs and lower contrast.

For that amount of money I would say it is worth it to try without modding. Worst case is it does not work that well and you end up modding or getting a dedicated CCD. Best case is you save a bundle of cash. Either way you haven't wasted anything but a little imaging time and who here doesn't do that anyway :-)

Allan

[MikeWilson]

I would think that noise would be removed with the application of dark frames. Although reduced contrast and more chance of a ruined frame is true, that would be the case any time you do long exposures.

So basically if you already have a DSLR that you use for daytime use as well as AP, you can either buy another body+mod it, or deal with longer subs and lower contrast.

For that amount of money I would say it is worth it to try without modding. Worst case is it does not work that well and you end up modding or getting a dedicated CCD. Best case is you save a bundle of cash. Either way you haven't wasted anything but a little imaging time and who here doesn't do that anyway :-)

Allan

Pretty much :-)

Pound for pound though, it's hard to beat the grasp of a modded 1000D/450D.

All the best,

Mike

[Flea77]

Mike,

Just thought I would chime back in to say I did indeed grab a filter and try a test, and the results are not at all what I expected....

Here is a complete stacked, stretched image of the Rosette. This consists of 11 480sec exposures at ISO800 from my unmodded D7000 with only a LPF.

Here is a stretched single frame with the same setup of the same target, except the LPF has been replaced with a Baader Ha filter, same 480sec at ISO800 then converted to B&W to use as a layer in CS5:

Impressive amount of detail for a single unstacked frame I would say. What is really interesting here is that I did not increase the exposure at all.

Allan