robertm

Hi all, I’m looking around for a pair of ultra narrow band filters to use with my 2600 camera. I already have an NBZ to use with my fast scopes but need something a bit more tailored to the light polluted UK skies (Bortle 6-7). I have had good success with the NBZ even with the Squid nebula but the contrast has been poor in my local skies. Presently I’ve been looking at the AA DualBand Ultra filters. I’ve had good feedback from someone but I really need to look at some more images before deciding - they are pretty expensive and my loathing of haloes is extreme! I’ve seen no images of known problem stars (for example Sadr, 52Cyg) so it’s a bit of a difficult investment decision. On the plus side these filters do specify out of band blocking (OD 4-5) ‘over the majority of unwanted visual wavelengths’ although cameras do have sensitivity outside the visual wavelengths. Has anyone experience if these particular filters or any others that are 4nm and have some guarantee of halo free design? I’m not interested in wider bandwidth or those that are known to produce haloes (l-ultimate and the like). Some images with problem stars would be great. Many thanks in advance. Robert

That's interesting what you say about the Esprit. I had a 150 and it seemed, at least to me, optically excellent but I haven't had anything similar to compare it against. Was this image in the binned 4.6um or 2.3um pixel mode?

Not too shabby for 30 minute panes, the filter seems to be working well at that focal ratio so thats great news. I'm not familiar with the 294 - presumably the horizontal pattern noise will calibrate out easily with a bit more data? Have been interested in moving to the 106 myself but my wallet keeps rebelling. PS. I know what you mean about never getting dark in London. BB targets are a real pain and getting worse by the year! <rant>I wish something would improve in this country - the French seem to have worked out that turning streetlight off at night saves money, all we do is try to make daytime last 24 hours!</rant> Robert

Thank you for the kind comments.

I've seen this recently and thought I'd have a go when on holiday in Herefordshire last week. One from Lynds' Bright and Lynds' Dark catalogues side by side. I've reoriented the image so it shows, what looks like, two dragons facing up to each other - took me a little while to recognise them so I wouldn't blame anyone for not. There are also a couple of blue reflection nebulae and an orange reflection nebula (RNO 129 with a young stellar object at it's core). I just wish I'd managed to get more time on it but that's life in the UK! Capture Details: Location: Lower Harpton Herefordshire (Bortle 4 supposedly) Telescope: FSQ85 with Reducer QE 0.73 Mount: ZWO AM5 Camera: ASI2600MC Pro Guiding: ASI462 and SV165 guide scope Captured using an ASIAIR Plus Filter: None Exposures: 45 x 300s (3hr 45min total integration time over two nights) Calibrated (Bias+Flats),Stacked and processed in Pixinsight Any critique gratefully received.

Thanks all. I have the ASI2600MC so know how good the sensor is. I find the sensor in the ASI needs the tilt plate for correct alignment. QHY quote that their sensor is well adjusted - can anyone quantify that for fast optics i.e. the tilt plate is unnecessary ? Edit: By fast I mean f/2 or f/3

Am also interested in the 268m and was wondering how good the cooling is - can it do a -40C delta from ambient ? Thanks Robert

It good that yours is working well, I’m finding mine a bit challenging at the moment... one for another thread.

What a superb image, great capture ! Am trying to dial in my RASA 8 and 2600 combo now so can appreciate what you’ve been through to get this right. Thanks for sharing Robert

I think this is where experience comes in. A lot of lenses look superb for terrestrial but as soon as you look at the bright pinpricks that are stars then that's where you see astigmatism, coma and chromatic aberration rear themselves. The last thing you want is a compromised image before processing even starts (that's my personal opinion).

The main reason for stopping down is to avoid use of the glass around the edge where lens design is most compromised. I'm afraid the trade off is to make the lens a bit slower but that depends what the use is. The 200L II is definitely good for f/3.2 narrowband but for broadband (I.e. luminance) then I suspect the f/4 that has already been mentioned is where the sweet spot is. One thing to note is that at f/4 you are only using 200/4 = 50mm of aperture and that's within a knat's of a 48mm threaded filter. Also if you use a threaded filter then, as well as the f/4 stop, you won't be troubled with awful diffraction spikes. I've not used the 70-200 so can't comment. One new lens of mine is that Samyang 35mm f/1.4, live view with the A7s is absolutely astonishing. It does need to be stopped down a tad to around f/2 for that sensor size but an APS camera might be able to use it opened up a bit more. I've had a few bad samples (sent back to Amazon) so you need to take a critical look to make sure the aberrations are symmetrical. Robert

An interesting topic, this is exactly what I went through a few years ago. My images were taken with Baader 7nm filters and I feel they worked well at f/2.8. I think the shift in band pass was still well within the filter profile. You may also want to consider filter size and how large the sensor is as well as filter to sensor spacing. As others have mentioned getting a filter wheel into the equation may be a challenge but I gave up with adding an oag. The light path is so narrow that any prism will affect the image even if you could fit it in. An alternative is to go with larger format lenses but demand by people who think they need them has pushed up prices massively over the years.... sigh ! If you're worried about over sampling then consider dithering and drizzle stacking as that might help. Something else I've done is doubling the image size before stacking, that can work quite well. Robert

If you want to even consider using it wide open then it has to be well collimated (check for centred vignetting). If it's out, then because it's a professional lens, you can send it back to Canon (UK branch is Enfield I think) free in the first year for adjustment. It's very good at f/2.8 with an 8300 sensor equipped camera but I found that f/3.2 produced outstanding images (in narrow band) if you can get it focussed accurately enough; the edge stars will be squiffy if you don't ! https://www.flickr.com/photos/29673723@N04/5007278823/in/album-72157624216353110/ The next is full size unbinned showing how good it is at the edges: https://www.flickr.com/photos/29673723@N04/4238477498/sizes/o/ There are other examples there but it really is a top lens ! Hope that helps Robert