Best Focal Length for Totality Photo ??

[Craney]

Hello everybody,

I have gone all 'astro' for my holiday this year and am venturing out to the States to watch the eclipse.

In preparation, I have been trying to find the optimal focal length for the small rig I will be taking ( Celestron 90Mak F.L=1250mm with solar Filter on AZ3 mount, Canon 600D). 

I want to experience the eclipse all hippy style, and so the camera will be on continuous image taking  (Magic Lantern), I do not want to be continually fiddling with controls or having to adjust / change anything and miss the ambience.

The issue is, I would like the full frame detail of what 1250mm would bring  ( detail on the limb,,,, Bailleys Beads etc...proms  etc).......BUT....

using a 0.5X reducer gets me the corona....and I will not have to worry about manual positioning of the image.......and I can crop to get the full size effect later.... but it is a Solar minimum corona and it might not be that impressive or extensive........  oh dear !!.

 

Any eclipse veterans out there suggest which is best.... or any helpful advice.   I have more or less convinced myself that 625mm is best.  (or is it ??....)

 

Cheers,

 

Sean.

[Alien 13]

If it was me I would probably stick to a 400 mm fl camera lens or similar (200 mm with a x2 TC in my case) the corona can be quite large.

Alan

[Craney]

Thanks Alien,

 I have used all my money on the holiday and I am trying to optimise the kit I already have ( well the travel friendly stuff)....  and the longest camera lens I have is 80mm  !!!!...

[tooth_dr]

Subscribed to this thread. Starting to panic now !

[ronin]

I would expect the corona to be at least the size of the sun on either side and sure I have seen images where it is more extensive, as in twice the diameter on each side. So the 1250 will I suspect lose the outer portion of it. So the effect of the reach and extent of the corona and it fading into space is lost.

Why a Mak as I would have thought it adding to the difficulty? Although with a reducer you are down to more easy to use focal lengths.

I would say that until you get the images and analyse them it is guesswork. Someone may have a wide field and small sun but whatever about it clicks, another may get the obscured disk and close in and not the full reaches of the corona and again that may work What comes out at the end is going to be a bit of chance. I know that from trying to photograph something and I found that about 1 in 5 were worth keeping (the other 4 didn't even get the subjectmost of the time), and really just 1 in 2 of those were actually a case of "Have a look at this" so 1 in 10. Someone on the same trip as me found exactly the same - we sat comparing results on the rear screens. At least with a DSLR there is a delete button.

Really your choice: Would you rather try for the in close and possible detail, or, the wider and full corona with a reduction in the possible detail.

[Craney]

Hi Ronin,

Yes a Mak is not optimal, but it is really dinky, robust and compact, should travel well and gives me a choice of two useful focal lengths with the addition of a small screw-in reducer.

This trip is a one holdall and one one rucksack type of venture. I'm even stripping out the extension legs of the tripod to save weight.

I think you are right....  2 scopes = total coverage...... 1 scope = compromise.  As you say, it is down to a choice.

I think the 625mm option is the more favoured as it it allows me to re-frame later.  

Cheers.

[fireballxl5]

An overexposured view from 2006 uisng a 640mm fl scope with a cropped DSLR shows how extensive the corona can be...I'd go with 625mm - In fact I'll be using a 610mm scope on the 21st

[Craney]

Thanks Fireball........  that's exactly what I wanted to hear.

[Mick J]

You seem to be sorted Craney, but as a btb - The Amazing Sky website may yield some help, Alan Dyer has some tips and more, and may be worth looking at some of his past pictures.

All the best for your trip, and anyone else going, fantastic - already looking forward to the results.

The US post stamp issue looks more than cool.