Any visual filters worth using for single stack H-a?

[Luke]

I do quite a bit of solar observing with my single stack SolarMax 60 hydrogen alpha scope. It's great for proms, and I can see a lot of disc detail but I find a lot of the disc detail to be bright and low in contrast. I wondered if you have any suggestions for visual filters that may help with the disc details? I've tried a red filter, which seemed to help a small amount, unless I was just kidding myself. I don't mind if it kills the proms a bit, as I can of course take the filter off when I want to see the proms.

Thanks for any help!

Luke

[michael.h.f.wilkinson]

I think the only solution is to double stack. For disk detail, I often simply go to higher magnification, which lowers the surface brightness

[RikM]

I would have thought the extremely narrow pass band of the Ha would render most EP filters useless. If you think the view is too bright and that is 'washing out' the contrast, then a ND or variable polariser might help. This could be the effect the red filter is having...dropping the brightness a little bit.

The other option is to save for a double-stack unit

[moriniboy]

On some occasions I find a polarising filter helps, not a massive difference though.

[michael.h.f.wilkinson]

I always find the best way is to take time and let my eyes adjust to the brightness. The detail then suddenly pops out (not always possible with our weather). Fiddling with the tuner and getting the sun in the sweet spot is another way of getting more detail

[Luke]

Thanks all for the tips Can't wait to try them out.

I think it is the brightness that is the killer for me, more so than the contrast. I joke with my other half that I have CCD eyes (good on faint galaxies) and she has webcam eyes (awesome on planets). "Did you see the polar ice cap?" "Err, no..."

I did bring a polariser with me today to try for white light during solar lunch as I am finding white light with a Herschel wedge a bit bright too even with the Solar Continuum and an 80mm scope (and of course the visual ND filter). As far as I know, it is polarised light through the wedge, but I had no idea whether it would work for H-a too? If it does a bit, that would be ideal as maybe I can use a simple polariser and rotate the eyepiece for full brightness and proms, or rotate to kill the brightness a bit. That would seem very practical for a quick session, and also if my other half, Sarah, wants to view at full brightness  - as is usually the case with the moon and planets!

Great tips as usual, thanks, all!

[michael.h.f.wilkinson]

Thanks all for the tips Can't wait to try them out.

I think it is the brightness that is the killer for me, more so than the contrast. I joke with my other half that I have CCD eyes (good on faint galaxies) and she has webcam eyes (awesome on planets). "Did you see the polar ice cap?" "Err, no..."

....

Apparently I have multi-mode eyes. Galaxy-hunting skills came in quite useful with the large but very faint prom I spotted yesterday, planetary camera eyes were needed for the disk, as usual.

[Pig]

Luke, before you spend cash on a ND filter

I have tried the ND polarising filter I bought with my Herschel wedge, it does not help with increasing the surface contrast with Ha.

Sorry !!!

[allcart]

Adding a second ERF to the system will lower the brightness levels if you have one kicking around. (not likely unless your a modding fan)

Next best thing is probably a 35nm ha filter.

Don't rush out and buy one yet. I'll test mine over the weekend and post the results.

[Luke]

Thanks, Shaun and Allan.

So are you all saying there is no cheap way to get almost double-stacked? :grin:  We have a double stack that we use at home but I take the single stack to work for solar lunch, partly because I prefer to image single stack on my non-tracking mount (to keep things simpler, and it seems to me that there's a wider sweet spot single stacked, though I have not imaged with the double stack a lot).

I hope to try the polariser properly today for starters. I got a very tiny test of it yesterday, but it was through thin cloud, so that may have had an effect. The polariser certainly seemed to be dimming the disc and it also looked like it reduced glow around the Sun, which seemed to help the disc stand out more. So I'm keen to give it a good whirl today if the clouds play game!

Allan, that would be very kind of you if you're able to give the 35nm H-a a spin, that would be interesting. I've thought about trying my 7nm H-a filter but I've assumed it will make the view far too dim. Funny enough, I have been thinking about a 35nm H-a filter. I think I would sometimes find it useful for lunar imaging. I sometimes use my 7nm H-a on the Moon, but when I use a Barlow, the view gets so dim (or the frame rate so slow when I increase the exposure length to compensate), so I wondered if a 35nm H-a would help me out there.

EDIT: Perhaps I haven't tried the 7nm H-a because it's 2 inch!! I was forgetting it won't fit, it needs to be 1.25 inch, but I imagine it would dim things too much anyway?

[allcart]

Hi Luke, I'm just waiting to get my mount back and then I can use the scope again. I have noticed that when double stacking the image is dimmer, but I have also removed the DS erf to make the image marginally brighter again to increase frame rate. I found the ERF dimming greatest when I used my LS60/120 XLT mod. That uses a double ERF system, but when I add the DS filter I then have 3 ERFs in the system and the image is greatly dimmed.

It was discovered in testing (on another solar forum) that the 35nm Ha filter could be used as a replacement ERF for a degraded one in a PST with good results, so I would assume it has similar light attenuating properties.

 I will test mine asap for you and let you know the my opinion.

[Pig]

I think we should all meet up somewhere the next sunny spell we get so we can try to establish a standard set up that gives the best results   

We surely have enough kit between us all.

[Luke]

Well I managed a bit more of a go today with the polariser, the cloud was thinner, but there still a bit of it about. So I can't be 100% sure, but it looks like the polariser will be a good help for me unless its effect falls off radically when it is properly clear It dimmed the disc today for me from uncomfortably bright for my CCD eyes to just right, with room to make it duller still if I'd wanted. I could make out the detail a little more easily, and just as importantly for me, it made the viewing feel more comfy. Again it reduced the glow around the Sun, which I liked.

This may just be me, but I really don't like bright views! Even if I give time for my eye to adjust, I just don't see the same amount of detail as Sarah on bright planet views. My shutter speed is too slow.   Must get myself a pair of those multi-mode eyes

[allcart]

Well after an extensive 5 minute test, I can say that the 35nm Ha filter made no discernable difference to my eyes. The sun only seemed to get a bit more red saturated and barely any dimmer. In fact due to the extra saturation I would say that I actually lost detail. So for solar Ha viewing I would say don't bother with this filter. If you are getting the required result with the polariser, then stay with it.

On the other hand, the 35nm Ha filter is better suited to white light viewing. Instaed of the strange green sun that the continuum filter produces, you can have a lovely red sun with no loss of contrast.

[Luke]

Thanks, Allan, that was very kind of you and is very interesting, sorry it took me ages to see your reply. I was away at SGL9 with the World's slowest Internet connection!

I have at last had a chance to test the polariser under decent conditions. and, bingo! It does the trick for me. It does not make a massive difference to the brightness, but it does just enough to tame it for my budget CCD eyes that can't cope with the bright ojects It mainly helps me with H-a, but I also like it for white light with my Lunt 1.25 wedge, where again I find the view a bit on the bright side with the mag that I tend to use.

With the H-a, it did indeed seem to kill off a bit of the glow kicking around the Sun, darkening the area around the disc. The big prom today (evolved from the twin towers of yesterday, I think?) was still pretty bright and almost seemed sharper/better defined - perhaps because of slightly better contrast against the sky??

So I would say a polariser might be worth a try if anyone like me finds white light or single stack H-a views a touch bright for their taste. Though the one I used did not make a massive difference, I think I was using it close to the max darkening, so it might be best to try before you buy, if possible!