How to do Solar Imaging

[Gina]

I would like to have a go at solar imaging again.  Last time I did it was several years ago and I can't remember what I did.  In any case I have different scopes and cameras.

I have a new sheet of Baader AstroSolar Safety Film in A4 size ready to make up filter(s) for white solar imaging.  That is no problem

What I would like advice on is which of my several scopes (or camera lenses) would be most suitable and what would be the best camera.

Telescopes and lenses :-

MN190

Evostar 80 ED with or without field flattener.

Esprit 80 ED

Camera lenses ranging from 300mm FL down to 35mm.

In view of the FOV I can't imagine lenses being appropriate but the scopes range from 400mm to 1000mm FL.

Cameras include Atik 460EX and 314L+ which I assume would not be suitable due to their long download times - but am I right?  I also have guide cameras which are faster viz. Lodestars and QHY5.  Then there are various webcams including Microsoft HD Cinema and Studio, Philips CCD and various cheapo webcams.  Or would I do better to buy a camera for this purpose.

Later on when the Lunt LS50THa H-alpha Solar Telescope becomes available from FOL I'm hoping to get one, so I would like a camera to cover this as well.

Suggestions would be most welcome - thank you

[Alien 13]

I would have thought the std ED8O would be the best option i use my 71mm with ok results.

Remember its the same apparent size as the moon so if you are happy with that scale all will be ok.

Alan

[JamesF]

Were you thinking about full disc images Gina, or concentrating more on sunspots?

I'm sure the MN190 would do a nice job, but you would need a large sensor (not entirely sure if the 460EX would be large enough off the top of my head).  Or you could use a DSLR.  Might be tight getting the solar film to fit it though, unless you took the aperture down a bit.  You could probably quite happily reduce it to around 120mm and with a 1000mm focal length get an image about 10mm across.

The other issue with the astro cams is whether they'll give short enough exposures.  With a DSLR it's not uncommon to be using exposures of less than 1/1000th.

James

[Gina]

I would have thought the std ED8O would be the best option i use my 71mm with ok results.

Remember its the same apparent size as the moon so if you are happy with that scale all will be ok.

Alan

Ah yes - thank you Alan   I remember now, I used the ED80 with solar film fitted in the reduced aperture exposed by taking the cap off the scope cap - if you see what I mean.  It's beginning to come back to me   Yes, I know the sun and moon have the same apparent size.

A bit later...  Just popped out to the obsy and looked at the Evostar ED80 cap and yes, the solar film is still there.  Aperture is 52mm.  I could have this set up on my no.2 pier (SW pillar mount) with NEQ6 mount on it.

[Gina]

Were you thinking about full disc images Gina, or concentrating more on sunspots?

I'm sure the MN190 would do a nice job, but you would need a large sensor (not entirely sure if the 460EX would be large enough off the top of my head).  Or you could use a DSLR.  Might be tight getting the solar film to fit it though, unless you took the aperture down a bit.  You could probably quite happily reduce it to around 120mm and with a 1000mm focal length get an image about 10mm across.

The other issue with the astro cams is whether they'll give short enough exposures.  With a DSLR it's not uncommon to be using exposures of less than 1/1000th.

James

Both full disc and zooming in on sunspots I think James

The MN190 produces an image of the moon that just fits nicely into the frame of the 460EX.  Using a DSLR is certainly an option with minimum exposure of 1/4000s compared with 1/1000s for the 460EX.  Not sure how fast a DSLR could be persuaded to take subs though, without risking damaging the shutter.  I think I'll check up on the video mode - that might be an option.  Haven't tried that believe it or not   I think video works at a reduced resolution though.  I would be happier not using a mechanical shutter to determine the exposure.

As for making a solar filter, yes, I would certainly use a reduced aperture, probably to one side of the secondary mirror obstruction.  A large disc of cardboard (or foamboard perhaps) with an offset hole for the solar film.  I made a cardboard solar filter for my first scope - a Celestron AstroMaster 130.  The MN190 is bigger but the principle is similar (instructions c/o Baader).

[Merlin66]

Gina,

The optimum aperture for the normal seeing conditions is around 100 - 120mm.

I'd go with a full aperture filter on the ED80.

[Gina]

Thank you Merlin

[JamesF]

I don't think you need to take the frames that rapidly.  I don't know what Steve (Ward) does, but in my case I'm not firing the shutter as fast as possible -- there's a few seconds delay between each frame.

If the Moon fits nicely on the 460EX then so should the Sun.  They are, after all, pretty much the same apparent size.

I'd not worry too much about the central obstruction in the MN190 to be honest.  You want the aperture to give the best resolution (though as I said, I think 120mm is considered "optimal" for white light) and it shouldn't affect that.  Having the central obstruction in the aperture may reduce contrast slightly, but you're hardly short of light in this situation.  I think it might be better to wholly include the central obstruction within the aperture rather than have it cutting into one edge where it may cause additional odd diffraction effects.

James

[Gina]

Thank you James  

I'll check the size of the central obstruction - I think it's something like 50-60mm.  I'll do as you suggest and cut a 120mm hole in the centre for the solar filter.  I'll try the 460EX as it's all set up ready to go.  I can simply remove the dew shield and replace it with the solar filter when I want to do solar imaging.  The finder scope isn't on ATM but I'll make a solar filter for that as well for when I put it back.

Since the scope already has the FW on it, I can use the 5mn Ha filter to further reduce the light (or even the 3nm OIII filter).  I use the Ha filter for setting up in daylight, then I can get away with 1ms exposures on the 460EX.  The reduction in transmittance for white light compared with full visible spectrum is very substantial (as you know, of course ).

A 12Mpx DSLR (or better) would give slightly better resolution in view of the pixel size using RAW and not decoding the colours (or with a debayered sensor).  The larger sensor would mean tracking could be relied on for a lot longer to keep the image in the frame though I think a well polar aligned EQ8 should do fine - time will tell, and it will be interesting to see.  Not that my PA is that good yet   As it is, the tracking allows about a minute exposure without star misshaping with the 460EX unbinned.  I think I can improve on that.  Trouble is, I'm reluctant to spend the time doing PA when I can be using it for imaging

[JamesF]

I think Steve uses an O3 filter with his white light images, so that might well be a sensible thing to try.

James

[JB80]

I image full disk white light with a dslr and 150mm f/8 newt with a full aperture filter, it works out quite OK most of the time but there are limitations based on seeing and I think even more critical are air currents in the OTA due to heat. Admittedly heat will be more of a factor for me in Spain but at times I really do struggle.

http://www.astrobin.com/users/JB80/

All of my white light shots for the year are here, my best results were back in March/April.

I use an astronomic clip in OIII filter with my set up, another thread mentioned if your dslr is not modified then it will have it's UV/IR filter intact so that may save on a new filter at least.

I have only just got an ASI120mm but early tests lead me to believe that under good seeing it will eat up close ups of spots on my newt at about f/24 but it will be very hit and miss given changing conditions.

I can't say for sure about your MN but I think you will be fine with it in the cooler environment of the UK, it wasn't really until it started getting towards 27° that I started having issues. Still it might be wise to start imaging straight away and not let the black tube heat up too much.

  I don't know what Steve (Ward) does

Witchcraft

He truly get the best out of his setup, all his pics are quite impressive.

edit: re shutter times I just have the remote on continuous and as it is processing the pics in camera there is a 3-5 second delay between pics which seems to be fine as long as you have a reasonable polar align.

I was taking images at 1/500th sec ISO100 but recently I have boosted the ISO and shoot at 1/2000th and it has made a marked improvement of the number of usable subs I am getting but again that is due mainly to the heat.

edit:2 Personally I think I have pushed my set up as far as I can, there may be more to learn in processing that I can improve on but I think if I want to step up again I will need a frac and wedge.

[Gina]

Thank you James and Jarrod   Very interesting

MN190 central obstruction is 52mm so that's not too bad   Now I'm looking around for something big enough and stiff enough to use for the solar filter frame.

[Gina]

Found a big enough cardboard box with thick and stiff walls and cut out a 12" diameter disc with a craft knife.  Then cut a 120mm hole in the centre, a 150mm disc of Baader solar film and glued this on using Pritt Stick.  Next I will cut a cardboard ring to sandwich the solar film and a ring for the outer edge to fit the scope and arrange a method of holding it securely onto the scope.

[Gina]

Added a ring of cardboard 200mm OD and 120mm ID on top of the Baader film and overlapping onto the thick cardboard.  Glued with Bostik All Purpose clear glue.  That should fix it   The Pritt Stick didn't stick very well to the solar film.

[JB80]

I did much the same thing for mine, in the end I used some of the kids old cardboard toy boxes. I'm still using it now but it's a bit tatty these days.

[Gina]

Very pretty

[Gina]

I've cut a ring for the outside from an unused piece of foam floor tile left over from my obsy.  I have it on the scope ATM and it's very firm.  Filter glued on and now just waiting for the glue to set.

[Gina]

Solar filter complete and firmally attached to scope.  Scope lined up on sun and now solar imaging   The focus needed changing a bit from the nighttime setting and varied considerably from frame to frame.  Exposure is 0.05s using OIII 3nm filter.  It's a lot dimmer than the moon (without solar filter, of course).

[Gina]

Some photos.

[Gina]

Here is the first saved image of the sun full frame resized and cropped around the top left set of sun spots.

[Gina]

I did a run of 100 subs but the clouds came in towards the end giving me 90 good subs which I'm now stacking in DSS.  But is this the best software for stacking solar subs?  I could probably do with something to choose the best focussed frames rather than stacking [removed word]-nilly.  DSS is designed for deep sky oblects not the bright sun where noise is not a problem.

[Alien 13]

PIPP then registax is the best method for me with lunar and planets the good thing with solar is you only need a 10min gap.

Alan

[JB80]

Great stuff Gina!

DSS really isn't the best for solar, lunar or planets. I agree with Alan, Registax is the perfect starting point and I would even use PIPP to convert the raws to TIFs and centre the images first as Registax like them more than raws.

Roger has also made an excellent tutorial which is hard to go past.

http://stargazerslounge.com/topic/153712-simple-white-light-solar-imaging/?hl=%2Bsolar+%2Bfull+%2Bdisc+%2Bimaging

[Gina]

Thank you both   Have downloaded and installed PIPP and Registax 6 and have the latest R6 update ready to install.  Now reading Roger's tutorial   I have used Registax in the past but it was a long time ago

[Alien 13]

Nice 1st image you have there Gina.

Alan