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Going IMX455 on a TOA-130 at a B1 site, which filters?

Takahashi TOA-130 Filters Acquisition Narrowband Deep Sky
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John Stone avatar
John Stone avatar
I need to find some filters for the new camera.

I was thinking Antlia Dark + Antlia Ultra 2.5 nm (both made on a quartz substrate) but Antlia doesn’t offer the SHO in 50mm round, but instead only 2”

Also, there’s been some posts about the 2.5 nm being too narrow for the SII double and another post about choosing a 5 nm Ha in order to compensate for high red-shift targets (which I think would also apply to SII and to OIII too.)

as an amateur I’ve always believed that narrower is better which is absolutely true in my B7 backyard, but I’m putting my new TOA-130 out at the new StarFront which is B1.

So what are the best filter choices for B1.  Most choose Chroma but that’s out of reach for me. 

I can go with 2” Antlia Dark + Ultra SHO describe above

I could go with Antlia V-Pro 50mm round which seems really popular but it doesn’t have the highest transmission specs.

I could go with Antlia V-Pro + Edge 4.5 nm 50mm round to deal with red-shift.

Optolong is out due to too many reports of Haloing.

I could go with Astronomical Dark Sky + SHO 6.5 nm in 50 mm round but that’s getting a bit too wide for moonlight nights? (And I’ve ready one post where there was a defect that wasn’t addressed properly)

I've also recently learned of the Altair 2” filters that have a good buzz around them.

Personally if I had to choose I'd rather miss out on a little red-shifted targets than deal with halos.

So experienced B1 imagers, how do you balance all the trade offs?  What did you choose?
Kyle Goodwin avatar
Kyle Goodwin avatar
I agree that there's a bit of a difficulty when you want really good filters, but not super narrow, but not as expensive as Chroma.  The wider Antlia filters have poorer peak transmission and halo issues, so they're not really an option.  Astronomik 6nm would be one option, but their filters put the Ha peak at the red end of the bandpass so far as I can tell and thus redshift will be an issue when trying to get Ha for galaxies just like it is on 3nm filters.  There's not an awesome option except maybe used 5nm Chroma perhaps if you can find anyone selling them.
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John Stone avatar
John Stone avatar
Kyle,

thanks for your reply. 

buying a single chroma 5nm Ha filter won’t work for me because it’s 3mm thick while my other filters would be 2mm.

This would cause my OAG to be out of focus when using this filter.

The Deep Sky Geek faced a similar problem which led him to develop his own OAG auto focuser and a special pass-through filter wheel driver that watched which filter you were using and applied a focuser offset to the OAG to compensate for.

pretty cool idea but he only made a small single batch of them and he observes from his backyard so little glitches that might happen can be fixed easily.

for me I don’t think that’s the right answer for a remote setup.

In addition to red shift stretching the light out of the filters bandpass isn’t another advantage of a 5nm Ha filter the capture of Nii?

I guess if you had an 8 position filter wheel and a 2.5 nm Ha and a 5 nm Ha you could isolate Nii by continuum subtraction?  Which would be pretty cool.

its too bad that the only 8 position wheels I know about are 1.25”
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Kyle Goodwin avatar
Kyle Goodwin avatar
I desperately want a larger 36mm filter wheel so I can do as you say for Nii, but also because I want a "dark" filter to take remote darks (I don't have a Moravian camera with a real shutter).