[Gina]

This may sound an odd question but which types of filter might I want to use with a DSLR for DSO imaging? I imagine LRGB sets would only be of benefit with a mono camera but what about narrow band?

Thanks

[Ags]

I'm also interested - I believe that NB filters can work with DSLRs. I tried my visual UHC filter on the NaN nebula, and given that my 'orrible mount can only manage 30 second subs, I was quite surprised to see I picked up (just) a little bit of signal. With insane stretching, the shape of the NaN was visible in the picture.

[AndyUK]

NB filters can indeed be used with DSLR's (Astronomik even sell Canon clip-in filters), but due to their narrow bandwidth, the amount of light they admit is obviously significantly less... which makes focusing / framing somewhat trickier than "normal" RGB imaging, especially if only using the display / liveview on the back of the camera.

In additon, in order to capture a good signal, you really need to "up" the exposure too - Even with mono images I've found that some subjects need 10 mins... others 20 mins, and others even more (I haven't been any higher yet, but I've certainly felt the need to do so!), so with a DSLR you'd really need to go longer still to get a similar signal. At this time of the year it may not be quite such an issue, but when the weather gets warmer you may find digital noise becoming an issue with such long exposures.

If not done already, the logical progression would really be to have the camera modded first (either filter removal or filter replacement, dependent on the camera), and use it with an LP filter (again, I found an EOS clip filter pretty much removes most of the LP in my area). You'll be amazed what a 10 min exposure can pick up on an emission nebulae such as Rosette, Horsshead/Flame, Cone, NAN etc etc etc... But back to using NB filters on a DSLR, IMO I think it's a case of something that CAN be done, but requires a fair amount of patience and certainly good guiding...

[Gina]

Originally Posted by AndyUK

NB filters can indeed be used with DSLR's (Astronomik even sell Canon clip-in filters), but due to their narrow bandwidth, the amount of light they admit is obviously significantly less... which makes focusing / framing somewhat trickier than "normal" RGB imaging, especially if only using the display / liveview on the back of the camera.

Thank you for your reply I use live view on a 17" monitor in the warm room and a remote controlled electric focuser. I realise that focussing is more difficult in red light as well as lower intensity though the software increases the luminance on the display.

In additon, in order to capture a good signal, you really need to "up" the exposure too - Even with mono images I've found that some subjects need 10 mins... others 20 mins, and others even more (I haven't been any higher yet, but I've certainly felt the need to do so!), so with a DSLR you'd really need to go longer still to get a similar signal. At this time of the year it may not be quite such an issue, but when the weather gets warmer you may find digital noise becoming an issue with such long exposures.

Yes, I realise the exposure will need increasing and the problem with noise at higher temperatures. I plan to provide Peltier cooling later on and have read threads on that with interest. Two methods :-
1. Easiest is to make a box big enough to take the whole camera and cool that. This is probably what I'll try first. At least it can make the ambient temperature that the camera is in nice and low but there is still thermal resistance between the heat emitting components in the camera and the outside. So the sensor warms up as the exposure progresses and time will be needed for it to cool down before the next exposure.
2. Much more difficult but more efficient is to use a tab of copper or aluminium from the back of the sensor and out through a slot in the side of the camera body and attach a Peltier cooler to that. This provides the cooling just where it's wanted.

If not done already, the logical progression would really be to have the camera modded first (either filter removal or filter replacement, dependent on the camera), and use it with an LP filter (again, I found an EOS clip filter pretty much removes most of the LP in my area). You'll be amazed what a 10 min exposure can pick up on an emission nebulae such as Rosette, Horsshead/Flame, Cone, NAN etc etc etc...

Yes, I'm certainly planning to remove the IR filter before going on to NB. LP is pretty low here.

But back to using NB filters on a DSLR, IMO I think it's a case of something that CAN be done, but requires a fair amount of patience and certainly good guiding...

Yes, that's much what I thought - thank you

[Stephen]

Pretty much to concur with the above, mod the camera if not already done (it's really easy honest!) and then consider Astronomik CLS and Ha.

I "think" the 1100 uses the double filter system as well, so you don't need an IR cut if you leave the front filter in place (and as such don't need the CLS-CCD version)

[AndyUK]

Hi Gina - You sound as if you've done all your research... Peltier fingers are indeed supposed to be FAR better - As you say, they apply cooling directly to the back of the chip, so it can be maintained at MUCH lower temps... but my, that's some SERIOUS surgery!

The peltier cooled box is indeed another route - Carastro (Carole) has one of these (you might want to PM her to get the low-down on it - I believe she uses APT as well), but if you're good with your hands they can also be made... I tried an experiment with Swag72 (Sara) as sort of a half way house - A sandwich cooler bag from Wilkinsons and 4 ice gel bags (about £15). It did bring the chip temp down, but not really sufficiently far (and for me it was a bit of a faff setting up as I have a low profile nosepiece on the camera and it was a real struggle to get it to fit flush with the focuser..

I envy you not having much LP... and I take my hat off to all those who mod their camera's themselves (my DIY skills are totally non-existant though!), but if you can do it yourself it'll save you £150-£200!

[Sp@ce_d]

I use a 2" baader 7nm ha filter with my self modded 1000D. Focusing is fine on a bright star using a bahtinov and 20 - 25 secs @ ISO800. It really needs a minimum of 5mins on the target, I've not gone past 10 though with the noise build up concerns.

[Ags]

Modding the camera will increase sensitivity to Ha and SII, but OIII and Hb are unnafected by the mod. From what I've read, it seems SII is too slow to be feasible with a DSLR anyway.

[Gina]

Thanks for your replies Very interesting and useful