Narrowband filters for DSLR, and using 2" filters with 1,25" camera

[Jannis]

I'm planning on getting some narrowband filters, but still haven't decided on which ones.

I use the explorer 200 PDS with it's stock 2" focuser, combined with the Baader MPCC MK3.

I'm mainly using my unmodded 550D for imaging, so 1,25" would be too small.

The Astronomik clip-in filters was my first thought, but this would leave me stranded with no usable filters at all should i one day afford to get a CCD camera, or any other camera for that matter.

So then i was thinking about going for a set of 2" NB filters from Baader, as they have a nice price and i've heard nothing but good about them (the NB filters, that is).

These would, from what i know, attach directly to the MPCC and i can use any camera that would otherwise attach to the MPCC, correct?

But then the issue.. What if i were to get a 1,25" camera later on, or if i want to give my QHY5L-IIM a try for? Would it still be possible to use my 2" filters by using a basic 1,25" to 2" adapter for example?

[MarsG76]

I use a modded Canon 40D (same size sensor as 550D) for my NB imaging and use Baader 1.25" Ha, SII, OIII and Hb filters on a filter wheel. I find that there is very little vignetting, those size filters work fine. One thing you need to think about is narrowband imaging on a unmodded DSLR where is will not be very sensitive to HAlpha and not at all to SII. you would be limited to OIII and Hbeta and VERY long Halpha exposures. 

Most of the time I expose my NB subs at 20, 30 or 40 minutes per sub (object and filter dependent). So if a modded DSLR is 5 times as sensitive to Halpha, how long would your subs need to be?? 

[Jannis]

Thanks for the reply. I'm surpriced you're able to use the 1.25" filters with the APSc sensor, i was sure it would cause serious vignetting, from what other people have said.

I'm awere the Ha sensitivity is limited, but i'm willing to pay the price in significantly longer exposures.

As for SII, i thought i would still be able to capture it, just that it needed even longer exposured then Ha, but you're saying the IR cut-off filter cuts off SII completly?

If so it might be better to take the Ha and SII data with the QHY5L-IIM, but..

The main reason i want to go NB imaging is because i have light pollution where i live, and the sky is rarly clear with the moon gone.

The CLS CCD filter was in mind first, but this wont help much against moonlight.

You gave me something to think about, i don't want to be spending 5-600£ on filters i might not even be able to use...

[MarsG76]

Vignetting is minimal, I do have the filter wheel attached just before the DSLR so the filters are relatively close to the sensor. Still I don't know why other would tell you that you get vignetting since if you compare the size of the 1.25" filter to the back of a EF-S lens, the 1.25" filter is actually bigger. The way that vignetting would be caused is if the filter is too far away from the sensor, but if its the next item in line than there is no vignetting problem, at least no more than with a normal lens which would be caused more by the light fall off on the sensor than obstruction.

With SII, I use a modded Canon and SII is still faint on most objects, even with longer than 40 minute subs exposures, so, in an unmodded DSLR I'm thinking that exposing longer might not be a option for SII... might not be enough time in the night.

HAlpha  can be captured with a stock DSLR, but think of it this way, the amount of Halpha you'd capture on a modded DSLR in 10 minutes would take almost a hour on a stock DSLR.. and I usually capture 20-30 minute subs.. I use ISO400-800 so I guess ISO 3200 or 6400 would also be needed, and with many subs, stacking will cancel out the noise, so Halpha is more possible than SII.

You can get some great images with using just Ha and OIII, so I advise to stick to bi color.

[Jannis]

Thanks.

I think i'll follow your advice and go for the OIII and Ha for now, at least until i get more used to narrowband, and/or get my hands on a dslr i can mod.