Best DSLR settings for work with Baader Solar Film

[RobF]

Ok, so I've left my run a bit late to be practicing for the transit, but I did finally get my film mounted last week and managed a few practice shots through and between clouds this afternoon. I have about a 7" aperture of film on my 8" newt, with T-ring/MPCC on the Canon 450D. I've seen people using ISO 100 and 1/100 and faster. 1/500 seemed a good compromise this afternoon.

I guess my real question though is should I shoot for a dim image expecting to have to stretch it later, or shoot for final expected "brightness" (or a tad less) on the Quick Preview window as I go?

Any recommendations appreciated.


P.S. I've also got a Toucam - should I be collecting video and stacking in preference to the DSLR?:question:

[rat156]

I'm not sure about the 450d, but my Nikon does auto bracketing, I can set it to do 3, 5, or 7 shots at 1/3 EV intervals. That's what I'll be using when the time comes. At present I have to tap the remote between each shot, but there may be a way around that as well.

I just had a quick look on Google, seems that the 450d does AEB so look it up, it saves all the hassle.

Cheers
Stuart

[RobF]

Thanks Stuart - haven't used AEB much, but that's a very sensible thing to use on the big day.

[Dennis]

Hi Rob

Here is what I found using my Tak Mewlon 180 F12, fitted with the Baader Astro Photo Film with OD=3.8.

Details:

Full aperture Baader Astro Photo Film
Mewlon 180mm operating at F12 prime focus
Canon 40D
ISO 100
1/3200 sec

The histogram is as shown in the attached screen print, as is the FOV.

Remember, I was using the OD=3.8 Photo Film and not the denser OD=5 Visual Film.

This was around 10:42am on 31 July 2011 so the settings may be different with the Sun much lower towards the horizon.

Cheers

Dennis

[Steffen]

Use the histogram on your camera screen. Expose to push the bright peak to about 80-90% to the right.

Cheers
Steffen.

[RobF]

Thanks Dennis and Steffen. I'm pretty sure I'll just get into strife if I try to sort out Toucam settings on the day (the sun will have only just cleared my neighbour's roof when the eclipse starts I expect).

My rough efforts were close but not as sharp as the Mewlon (as you'd expect), so think I better stick with the 450D. One thing about such short exposures, it doesn't cost anything to keep shooting and tweaking settings.

[Nico13]

Hi Rob,
I have very similar results to Dennis and I was using my ED80 and Pentax K5.
ISO 80 or 100 were similar but I found 1/3200th a good shutter speed to work with the raw images after but as noted it'll be a bit different with the early morning sun so be prepared to try a few different shots.

This shot has been reprocessed with false colour.

[RobF]

Amazing field Ken. Did you have to crop in much? So much detail.

[Nico13]

Yeh its almost at 100% crop there but I've just finished a Baader filter for the SCT8" will give me a full frame shot with a 6.3 field reducer or even a bit closer clipping top and bottom of the suns image without the reducer.
Looking foward to trying out.
Hope I get it right on the day but will be running both scopes side by side and two cameras fortunately so should get something, it's just the weather now. :D

[Dennis]

I noticed on a couple of my photos taken at 1/2000 that the Blue channel had saturated (255) with the Red and Green remaining just short of saturation, around 245 – 252.

This appeared to affect the detail in the “hotter” (photographically) central region and led to a loss of contrast compared to the limb regions. I have significant vignetting in my system and this leads to a central hot spot with darker edges.

For my set up, I have noticed that the contrast of solar granulation and sun spots improves if I slightly under expose, to deliberately prevent the central region of the FOV from getting too close to the 255 values in the histogram.

Cheers

Dennis

[RobF]

Appreciate this extra info Dennis. I guess this was one of my chief concerns with a light guzzling Newt - that I might end up over-exposing. I would imaging under-exposure is no great problem after a little stretch if you have headroom, but over-exposing could be like digitial-clipping audio (i.e. BAD!)