Does aperture matter for solar observing?

[bobmoss]

OK, this is probably a dumb question, but here goes...

For solar observing, does aperture size make any difference to what you can see? Normally in astronomy the bigger the aperture the better, but with the sun being so bright, does it change things?

I've got a 10" LX200 and will soon have an 80mm refractor. I want to have a go at solar observing and so if size doesn't matter I'll get a solar filter for the smaller scope (which should be cheaper).

Thanks.

[michael.h.f.wilkinson]

Size does matter up to a point. In H-alpha, my little 35mm LS35 sees much less detail than a bigger scope, but seeing problems caused by the sun's heating of the atmosphere often limits the effect of aperture to 4-6" in many cases. The quality of the optics is also important. My Celestron C8 with solar filter does not seem to produce more detail than my APM 80mm triplet apo with a Herschel wedge. If you use Baader solar film in your refractor, it might be inferior to the 10" SCT with the same foil at full aperture (with an 80mm sub-aperture mask, which I think should fit on a 10" SCT the results should be roughly equal). With a Herschel wedge (ONLY FOR REFRACTOR USE!!), the 80mm might equal or even just beat the 10" SCT.

[Moonshane]

I use my 6" f11 scope (newtonian) for solar mainly and there's little perceptible difference in the detail I can see when I use an off axis aperture mask of 60mm.  in your shoes, I'd buy the filter for the 80mm but make an off axis one (which I think but am not sure will work like it would with a newtonian) that will cost less and still allow you to use both scopes for solar. personally, I make solar filters for all my smaller scopes. 

[Peter Drew]

As mentioned, you can make a full aperture filter for the 80mm or an off axis 80mm filter for your 10" SCT from one sheet of solar film. Interesting to try the comparison but the 80mm refractor will be more manageable. 80mm is usually enough aperture for good solar results. Let us know how you get on.    

[bobmoss]

Size does matter up to a point. In H-alpha, my little 35mm LS35 sees much less detail than a bigger scope, but seeing problems caused by the sun's heating of the atmosphere often limits the effect of aperture to 4-6" in many cases. The quality of the optics is also important. My Celestron C8 with solar filter does not seem to produce more detail than my APM 80mm triplet apo with a Herschel wedge. If you use Baader solar film in your refractor, it might be inferior to the 10" SCT with the same foil at full aperture (with an 80mm sub-aperture mask, which I think should fit on a 10" SCT the results should be roughly equal). With a Herschel wedge (ONLY FOR REFRACTOR USE!!), the 80mm might equal or even just beat the 10" SCT.

Excellent, some good info there - thanks. Am I correct in thinking that with a Herschel wedge you don't use a solar filter?

[bobmoss]

I use my 6" f11 scope (newtonian) for solar mainly and there's little perceptible difference in the detail I can see when I use an off axis aperture mask of 60mm.  in your shoes, I'd buy the filter for the 80mm but make an off axis one (which I think but am not sure will work like it would with a newtonian) that will cost less and still allow you to use both scopes for solar. personally, I make solar filters for all my smaller scopes. 

Thanks. I'm guessing an "off axis" filter is basically a lens cap with an 80mm hole cut out of it to one side (to miss the central obstruction) and the solar filter just covering the hole?

[bobmoss]

As mentioned, you can make a full aperture filter for the 80mm or an off axis 80mm filter for your 10" SCT from one sheet of solar film. Interesting to try the comparison but the 80mm refractor will be more manageable. 80mm is usually enough aperture for good solar results. Let us know how you get on.  

Thanks, I think I may try both. Like you say, it would be an interesting comparison, especially if I can get an image from them at roughly the same time to compare.

[michael.h.f.wilkinson]

Excellent, some good info there - thanks. Am I correct in thinking that with a Herschel wedge you don't use a solar filter?

No filter at the objective side is needed. One or more filters at the EP side must be used, however. These can usually be bought as a set with a Herschel wedge

[Umbraldot]

Excellent, some good info there - thanks. Am I correct in thinking that with a Herschel wedge you don't use a solar filter?

That's right, you use the HW as the filter in effect.  Its construction dumps the solar heat elsewhere leaving only a safe image of the Sun to your eye.  People swear by them but the whole idea fills with me with terror for some reason!  I like the full aperture Type II glass solar filter personally.

[Umbraldot]

No filter at the objective side is needed. One or more filters at the EP side must be used, however. These can usually be bought as a set with a Herschel wedge

Ah right, never used one.

[Merlin66]

Current experience shows a 100-125mm aperture ( which has your choice of SAFE filters) is about the optimum aperture of solar observing.

[Mark at Beaufort]

I use my Astro Tech 102mm APO frac with a Herschel Wedge and to be honest its the best view of the Sun that I have ever experienced. At the recent SGL9 star party RikM used my Herschel Wedge on his Televue Pronto (70mm) and the view was very sharp. I have used an Orion glass, Thousand Oaks Glass and Baader film in the past and all provide very good views of the Sun.

Of course the HW is not cheap so in your position I would buy a full aperture filter for your 80mm frac - you won't be disappointed.

[Solar_observer]

Using a lunt herschel wedge....what would be a decent and light frac to use and not Ann expensive one either? Also what else would I need? I have a lunt zoom eyepiece, so I'm ok on that front. I have an horizon tripod, could I mount a small frac on this?

I've used baader solar film before, would a small frac and wedge, better the view? Thanks

[Pig]

Nice looking cake  

[RikM]

Using a lunt herschel wedge....what would be a decent and light frac to use and not Ann expensive one either? Also what else would I need? I have a lunt zoom eyepiece, so I'm ok on that front. I have an horizon tripod, could I mount a small frac on this?

I've used baader solar film before, would a small frac and wedge, better the view? Thanks

As Mark says above, we tried his Herschel wedge in my Pronto. I normally use a full aperture Baader film mask for visual observing. The wedge seems to give a more stable/consistent view but it wasn't vastly better than the Baader film. It was a brighter view and that washed out the contrast a bit compared to what I am used to. I suspect a ND filter would have helped, we did use a Baader continuum filter, but I am sure that a stronger filter would have really highlighted the extra detail visible with the wedge. The Herschel wedge is better than the Baader film but I have plenty of other astro toys to buy before I get around to ordering a wedge.

Before the Pronto, I used an ST80 with Baader film and this is really very good for the money. I have not used a wedge with it, but there is no reason why it wouldn't work well.

[Bizibilder]

Just to clarify one point - a Herschel wedge can ONLY be used with a refractor.  Never use one with any other type of scope.

[RikM]

As if by magic, to emphasise the need for safety while solar observing...

Prompted by this thread I just popped out for a bit of solar observing and discovered that my Baader film filter has developed a cluster of pinholes. That doesn't happen with a Herschel wedge! It's not terminal as I can safely cover them with a bit of gaffa tape but it will soon be time to order another sheet of film. This one has lasted at least two, maybe three, years. Not bad value for £20

Always, always check, and never, never risk it!