Homemade H-Alpha scope?

[Merlin66]

Good question!

I don't honestly know....all the mods I've done so far have used refractors... there's no technical reason I can think of as to why an f10 reflector would NOT work.

The size of the PST etalon and the negative lens built into the front of the assembly is designed to sit 200mm inside the prime focus of an f10 beam. So if you can still meet this criteria with a reflector....why not???

(Edit) I should have added that this is a prime focus f10 not one involving secondary barlows etc - the etalon doesn't seem to like, for instance a f5 beam coupled with a x2 barlow......

Ken

[brianb]

does it have to be a refractor

Yes. The concentrated heat will likely crack the secondary of a reflector or catadioptric scope. And the refractor had better be one without lenses at the eye end of the tube i.e. no Petzvals, no field flatteners etc. (A plain achro is fine since chromatic aberration is totally removed by Ha filtering anyway.)

[Tim]

Thats how I understood it Ken, that the etalon works with an f10 light cone.

I just happen to have a C9.25 sitting around not used much...........dread to think what a D-ERF would cost for it though!

[Tim]

There's something in the back of my mind about a Swedish 6" SCT. Nick will know what (probably wrong) tree im barking up?

[Merlin66]

Brian,

The amount of heat behind a proper ERF ( ie Baader D-ERF) I find is minimum. It effectively blocks everything ( UV/ NIR etc) other than a "band" above 600nm to 750nm (?) ( I haven't had one under the spectroscope for a while....)

So I'd think it should be OK???????

Ken

[Merlin66]

TJ, you could always put a spectroscope on the 9.25 and do some REALLY interesting solar imaging.

There's a freeware program which allows you to scan the surface of the sun ( with a webcam or DMK etc) and builds up a high resolution image ( better than 0.5A - depending on the spectroscope!) in ANY bandwidth of your choice! - Ha, Hb, Cak, Mg, Na etc the list is endless....

Ken

[brianb]

The amount of heat behind a proper ERF ( ie Baader D-ERF) I find is minimum.

I'd want to be very careful ... there is quite a lot of solar radiation in the 600-750 nm range and it does have a heating effect. Even if the secondary doesn't crack, there is a serious risk of heating affecting the secondary support mechanism, maybe causing distortion of the optical component or melting glue which may be used to hold the secondary in place. Any heating of the secondary will also have dire effects in terms of tube currents. All in all I think it's safer to use a 'frac ... you don't need a triplet objective for Ha work as there is no possibility of chromatic aberration!

Specialised solar reflectors do exist but usually have an uncoated primary mirror and an open rear cell allowing ~95% of the incoming radiation to pass straight out of the back of the tube.

[NickH]

Some tests on an ETX style scope have been done by TH...it didn't work out very well :-)

F10 refractors are £100 for a good second hand one...not worth the hassle doing it any other way

[RichieJarvis]

So whats the on-top cost of the Ha conversion then, excluding the Vixen

I've got the first bit, just need to get a saving target in my head....

[Merlin66]

400gbp for a PST, 260gbp for a D-ERF gets you started....Oh add a few pounds for adaptors...that's about it; Until you want to go for a Stage II mod and then you need to find a good BF10.....

[NickH]

Under £1000 all in Richie....should be doable, gives you something which on a good day will compete with pretty much anything up to an SF70