using external dualband filter

satch984

Hello
Is it possible to use narrowband filter with seestar? In this case is better to turn off the internal filter or not?
I want to buy new filter because the internal one gives problems with reflection of the brighter stars (the filter seems not perfect aligned in my model)
Thanks
Thanks

starnet59

satch984 You should of course not use two narrow band filters at the same time. Unless the narrow passbands happen to overlap they will simply block each other.

support

satch984 You can use your own external filter wheel that fits over the front of the telescope.
When the light damage filter is not on the default ircut filter is used.

curtismacc

Yes, you can get an external filter holder for the Seestar and attach your filter on the outside of the optics. But, there would be no point using both the external and internal filters.

Regards,
Curtis

satch984

starnet59
I saw a video of Cuiv the lazy geek on YouTube
He said that is better to use both filter when imaging
He used a 4nm narrowband dualband filter

https://youtu.be/qsdorWyasT0?si=Q4hBEcmziibXGcSm

starnet59

satch984 You will not gain anything, the narrower filter will always win, that is if the passbands of the two filters overlap completely. If the overlap is partial or not at all then you get almost nothing. The other drawback of stacking filters is that there is always some passband attenuation, no filter is fully transparent. When you stack filters, those attenuations multiply.

It is true that the attenuations in the stopbands also multiply and that could help with light pollution, but the price you pay with such filters is longer (and in the case of stacked filters much longer) exposure times. As we know, the S50 does not excel in this area, anything over 1 hour is very problematic. This is not to pan down the S50, the hardware is exceptional, but the SeeStar app seems designed to discourage anything but casual "point and shoot" astrophotography.

satch984

support

Is better use ircut or lp filter with narrowband front of the lens?

curtismacc

I watched his video and he said he used the internal Dual Band filter in addition to his external Dual Band filter because he had reason to suspect that the internal UV-IR filter cut off some of the Halpha signal. First, since his external filter has band widths of 4nm and the internal Dual Band filter has bandwidths of 30 and 20nm the internal filter isn't adding any additional filtering since the bandwidths are much wider than his filter. In other words, all of the light passed by his external filter will pass through the internal filter, aside from some light lost due to reflections from the additional glass surfaces of the internal filter. Second, looking at ZWO's external IR cut filter band pass graph which you can buy from ZWO or any astronomy retailer, it clearly does not impinge on the Halpha signal, not even close. Now, the internal UV-IR filter may have a different IR cut-off wavelength than their external filter but I would be very surprised if it came anywhere close to the Halpha wavelength. So I don't see any basis for Cuiv's comment/concern. Either way, I believe it is best not to use any internal filter with the external Dual Band filter since it also cuts off the IR and we always want to avoid any unnecessary glass in the optical path. Ultimately, I don't think you would be able to detect much difference one way of another.

Regards,
Curtis