Viewing the sun

[KenG]

With the amount of expertise floating around here, perhaps someone could advise me about solar observing. Would it be possible to equip my 200mm reflector in such a way as to safely do this, or should I stick to nights? I haven't researched this in any way, so a few "pointers" would be very welcome.

Cheers!

[Merlin66]

The easiest and safest way to observe (and image) the Sun in white light is to make a solar filter which will fit over the open end of the telescope tube. It doesn't have to be the full 200mm - an 80mm hole in a stiff card cover would work very well.

Use the Baader Solar film to make the small filter. It's 100% safe.

ALWAYS make sure the solar filter/ cover is securely fixed to the end of the scope, and remember to cover the finder! (or fit a small piece of Baader film on it)

[KenG]

Thanks for the information. I thought that might have been the way to go, but given the risks involved it seemed too simple to be true. I'll give a bit of thought to the materials and construction of the filter holder and buy a sheet of solar film when I've got that done.

[E621Keith]

200mm Newtonian is very common, so it worth a look to see whether there are any commercial front filter such as these

Orion Solar Filters - SCS Astro

Orion website states the 8" dob and skyview pro needed filter 07722. I don't know if your f4 takes the same filter, but worth asking.

btw, reflector is NOT compatible with solar wedges so don't try it.

[KenG]

That's great. Now I've got two alternatives to consider. I hadn't given any thought to solar observing until the other day, and where I live there are no astronomy shops or societies, so no-one to ask(plenty of dark sky and no light pollution though). Now that I know I can safely add a filter to my scope, I'll do a bit of research into the options.

Thanks guys.

[Altair40]

I had my first look using Baader film last weekend. I just followed the instructions that came with the film and made a filter to fit my tiny 8 by 50 monocular.

Did observe the Sun but couldn't really hold the mono still enough to look for sunspots. I'll have to make a larger version for my newt.

Quick question: does a smaller apeture than the scope apeture improve resolution or contrast as it says (I think) in the instructions?

[E621Keith]

Reducing scope aperture will improve the image quality at the expense of resolution. It works by only using the best part of you optics which is the centre of your lens or mirror. Most aberration affect off axis image and are caused by light rays following different path, converging at different angle to different point. Reducing the aperture effectively reduce the off axis and only use the parallel rays in the middle, hence the improve image. However, resolving power depends on the separation of the widest part of the lens and light gathering depends on area, so resolution will suffer from stopping down. Also, you paid a lot of money for the extra glass (aperture), so by covering that up you are effectively wasting your money.

[PeterW]

Why not a wedge with a reflector. The prism will chuck 96% of whatever you throw at it, bigger scope... stronger final ND filter. It doesn't absorb, so it won't heat up, the only issue I can see is that the eyepiece is at a funny angle and you would need to be careful where you pointed the 'exhaust' port.

Cheers

PEterW

[jgs001]

Peter, I've not used a reflector, but as I understand it, the focused light from the primary to the secondary will cause all sorts of problems with the secondary itself, and possible other components of the scope. A filter on the front is a much much safer option.

[Merlin66]

An aperture around 80 to 100mm is more than adequate for most seeing conditions.

Re the herschel wedge on a reflector:

It was used but with the primary mirror UNCOATED!!

If you use a standard reflector you stand a great risk of cooking the secondary mirror (and its supporting glue) - not recommended.

[brianb]

Re the herschel wedge on a reflector:

It was used but with the primary mirror UNCOATED!!

Yeah, uncoated primary plus wedge secondary (instead of the usual diagonal mirror) is a good combination requiring only a light ND filter in the eyepiece ... but use of a commercial Herschel solar wedge with a reflecting scope of any type is a recipe for destroying the secondary mirror and/or its mount. In fact the wedge should not be used with a Petzval type refractor, or a refractor with a field flattener / focal reducer / Barlow / tele-extender fitted in front of the wedge, as again the heat buildup in the concentrated beam just in front of the wedge can be dangerous to the lenses.

[E621Keith]

The reason for not using a wedge on reflector or Cats, as others have already mentioned, is the heat can melt part of the the secondary. Some say Gregory Maks might be able to handle the heat because the corrector is thick and the secondary is coated directly onto the corrector, but I don't think I will try it myself.

[Altair40]

Thanks for that - I think I'll try a slightly less than full apeture area for my 'window' with the Baader film.

I'm still vacillitating between using cardboard and duck tape. Or moulding my own filter housing.

Something tells me the cardboard will be better and more secure, if I can keep it in a box to protect the film.

thankyou!

[KenG]

I've looked into a DIY job on this. Since it's my eyesight I'm playing with, I'm wary of anything to do with glue or sticky-tape, so I won't go down that road. I've found several suppliers who sell plastic drainage pipes and jointing pieces in a wide variety of sizes, so this is an obvious starting point for an end cap. The film I would intend to sandwich between two pieces of 1/8" MDF, and use model engineering screw-bolts to both join these and secure the film. I think I'd be able to modify a jointing piece to hold the MDF ring securely in place...............research is on-going.

[Altair40]

Nice one, the plumbing idea sounds good...

I have read the two DIY contributions here and both seem more than safe to me.

My mono may not be so good because I already have a wrinkle in it. I followed the instructions and made two cardboard collars with the film sandwiched inside. But the film is not held flat. Good enough for a first try but I need to do better!

The thing I like about Baader's own instructions is how to attach the film to cardboard without any wrinkles or stress - the 'many bits of double sided tape' on the card board, then you just offer the cardboard to the film while it's sitting on a single layer of tissue.

That would work with MDF, also. Tape and bolts might be good. The weak spot for me is how to fix the film holder to the collar, whatever they are made of. Any ideas apart from more Duck tape? If the glue etc fails and the film falls off, that's it - blinded.

I do trust authentic US Duck tape for making the collar. I've seen that stuff holding the side of an aeroplane together after someone's reserve parachute went off inside the aircraft!

Duck tape is very sticky indeed. I use it in my lab to make a handle for lapping small specimens on a grinding wheel. Works a treat...

There are some other manufacturers of tape similar to Duck tape but the adhesive is only about 1/10th the strength.

[Altair40]

Maybe the answer for me at least is to cut some angle iron and drill two holes for bolts but thick enough to cut a thread so I can clamp to the telescope body at one end and also put a bolt and nut through some MDF as per your idea. Four of those...

And Duck tape it down past the collar onto the scope body. Ugly, but going nowhere!

I'm lucky in that I have a workshop...

[KenG]

The problem with adhesives is that they deteriorate through time without any degree of consistency, which is why I'm so wary of relying on them. I think I'll be able to create a glueless/tapeless filter holder using tried and tested commercially available plumbing components. Keep you informed.......................

[LukeSkywatcher]

The problem with adhesives is that they deteriorate through time without any degree of consistency, which is why I'm so wary of relying on them. I think I'll be able to create a glueless/tapeless filter holder using tried and tested commercially available plumbing components. Keep you informed.......................

Ive thought of this myself because i am useless with scissors etc. The trick is to find a plumbing tube to fit over your scopes aperture and then another slightly smaller to fit inside on which to place the solar filter.

P.S.~~~i'm done spending money on sheets of solar film. I have a 70mm Celestron Travelscope that i would like to buy a ready made solar filter for. Can ANYONE tell me the OD of this scope?

If i buy a standard 70mm filter will this work?...........................i dont want to buy an 80mm one because this will be too big?

[brianb]

I have a 70mm Celestron Travelscope that i would like to buy a ready made solar filter for. Can ANYONE tell me the OD of this scope?

Do you have a ruler?

A few mm oversize is fine as there is adjustment in the fixing screws.

Incidentally the adhesive in genuine Duck Tape is very strong indeed and will not deteriorate significantly over a period of only a few years, even when exposed to high levels of UV from strong sunlight.

[Merlin66]

Re Duck tape....

I've used a strip of Duck tape to form the hinge on my "solar observatory" 60 liter grey container. The tub sits on its side and the lid is hung back to allow me to have the laptop in the shade.

It's been left out in the weather now for over four years..the tape may be "cosmetically challenged', but still does its job 100%

[david's dob]

I have made a DIY one myself.

Using 2x Toilet Roll

With SW 200P you get the top lid with 2 Holes, with caps. took about an hour to make. all i need know is the Sun.

[kev]

the astro film filter that I made and use - and have done for some time is made thus...

Cylindrical extendion to Dewcap... about 2 inch long so it slides on and over nice and tightly and cant blow off (!), then that its taped and glued onto a square cardboard sheet about an inch bigger than the tube. On top of that is another sheet of cardboard which on one side it taped to the over, as a hinge. This then traps a nice square sheet of astrosolar film between the two sheets, without crumpling or bending the film. the other 3 sides are then taped down.

This means, that if (when) the sheet gets dirty, or minute hole appear in it (check regularly - I note I end up changing mine about twice a year or if its rained on it!) then all I have to do its untape 3 of the sides of the double cardboard, slide out the old film, put the new into it and retape it up. Presto!

Pic of resultant setup attached!

[KenG]

Great minds think alike! My solution in light of this discussion is virtually the same - viz. Plastic drainage pipe, two pieces of 1/8'' MDF - round or square, but 2'' or so wider than the pipe, hinged on one side and clamped on the other - attached to the pipe with "L" brackets. I've got various ideas for keeping the film securely in place, but none of them involve glue or tape.

Thanks for all the advice. I'm going to have a solar filter for the cost of the film.

[shepsboss]

I recently attended a starter course at the Norman Lockyer Observatory. Peter, lecturing on the Sun and Moon said "you can only observe the sun twice with a telescope, once with the right eye and once with the left eye!" He went on to say, ALWAYS, even with the correct filters, put your hand in front of the eye piece before you put your eye there. Rather a burn hand! I will never forget that advice, but then I don't think I would ever take the risk.

[John]

.....He went on to say, ALWAYS, even with the correct filters, put your hand in front of the eye piece before you put your eye there. Rather a burn hand!....

Thats good advice I think

Having been bought up on 30 years of "don't ever view the sun directly with any optical device" I was even nervous the first time I used a Personal Solar Telescope, despite knowing that they are safe. It seemed almost counter-intuative to put my eye to the eyepiece !.

I'm glad I did though - the views were amazing