08-01-2017 11:17 PM
Ok, It's August. 20 days to go until the eclipse.
I've got my telescopes solar filter on it's way. I've never tried to take pictures of the sun so any tips, settings etc. to get the best shots would be greatly apprciated.
08-02-2017 08:06 AM
Yes, check out Fred Espenak's page (aka "Mr. Eclipse"). Fred is a retired NASA physcicist who does all their eclipse predictions and a top expert on eclipse photography.
Assuming you will be in the path of totality...
Also, it's best to have the camera under computer control so that you can enjoy the eclipse instead of having to pay attention to your camera.
If you have a Mac, then you may want to download "Solar Eclipse Maestro".
If you have Windows, then you may want to download "Eclipse Orchestrator" or "SETnC".
I'm familiar with Eclipse Orchestrator and Solar Ecipse Maestro, but not SETnC.
Solar Eclipse Maestro and Eclipse Orchestrator both allow you to script the eclipse capture but the timings are based on the eclipse path prediction data and your precise location (either via GPS or manually entered).
The shots before and after totality are shot with the solar filter on.
Double check frame & focus a minute or two before totality (with filter still on camera).
At 20 seconds prior to totality (and no sooner than 50 seconds prior to totality) you can remove the filter but DO NOT LOOK THROUGH THE CAMERA once the filter is off (that's why I mentioned doing the final frame & focus before removing the filter).
At about 9 seconds prior to totality you may see the "Diamond Ring" effect.
At about 1.5 seconds before you may see the "Baily's Beads" effect.
The software script can be set to announce warnings (e.g. 5 minutes to totality, 2 minutes to totality, when to remove filters, etc.) so you know when to do each step.
Once totality begins, it is safe to look directly at the sun. You'll see the solar corona. It has tremendous dynamic range and requires about 10-12 stops of bracketed exposures to capture the entire corona (you can merge the shots with HDR processing).
Once totality ends you'll likely get another Baily's Beads, followed by another Diamond Ring. After you capture that, it's time to put the filters back on the camera (which should happen about 20 seconds after totality ends.)
Solar Eclipse Maestro is free for non-commercial use (he charges if it's meant for commercial use). He does appreciate donations.
Eclpse Orchestrator has a free mode which limits it's functionality, but it's a paid license to unlock all features.
Both Eclipse Orchestrator and Solar Eclipse Maestro use the same scripting language.
I have not used SETnC. What I've learned about it is that it (a) runs on Windows, (b) only controls Canon cameras (no support for any other brand), and (c) it's free.
Clear skies & good luck!
08-02-2017 04:41 PM
Awesome info as usual Tim - Thanks.
Unfortunatly I will be between 80 and 90% total. I could drive down to my Moms place in Emerald Isle, NC and get closer to 95% but I'd have to take a few days off from work and convinve the wife it's a once in a lifetime event. If in NC we could drive a few hours to get in the totality band. That may be the plan.
08-06-2017 05:07 PM
Received my filter material from Thousand Oaks Optical and made my solar filter for my telescope, spotting scope and made some glasses for my kids. The film works great.
The only problem I can see is when I'm using my camera with my scope the FOV is small and I can't get the entire sun in the frame. Would a focal reducer allow for full frame shots of the sun?
08-06-2017 05:16 PM
For any camera, the goal is to get a focal length that allows the Sun to occupy about 1/4 to 1/2 (with 1/3rd being nominal) of the height of the sensor (in the short direction).
The Sun is about 1/2º from edge to edge. So that means you want a field of view between 1 and 2º in the narrow direction (which would be about 1.5 to 3º in the wide direction).
For a Canon APS-C sensor camera, that translates to a focal length in the range of 391mm (you could call it 400mm) to 782mm (but 800mm would be fine) with 521mm being nominal.
For a full-frame camera, it works out to 634mm to 1268mm with 846mm being nominal (round to nearest available values).
You CAN use a focal reducer but there are a few things to know.
Focal reducers are commonly available with a .62x or .63x reduction. Meaning, if you had a 1000mm focal length, it would reduce it to about 620 (with a .62x) or 630mm (with a .63x). If you had an 8" f/10 SCT (that would have approx a 2000mm focal length) then a .62x reducer would drop it to 1440mm -- which is still a bit much.
The other caveat is that the amount of reduction depends on you getting the back-focus distance correct. Most focal reducers expect about 105mm of backfocus (meaning the distance from the last element in the focal reducer to the sensor inside your camera should be 105mm away... they are optimized for that distance and while they may work if the distance is shorter or farther the reducer to both focal length as well as focal ratio will not be accurate.
What brand/model scope do you have and also which camera model do you have?
08-07-2017 07:56 AM - edited 08-07-2017 07:57 AM
It's a Meade 2080 f/10 F=2000mm as posted on page one of this topic. Camera = Canon T6i APS-C
Thanks for the tip about backfocus. I'll keep that in mind. Since I can only hope to acheive ~1440 I'll have to live with it. I can always make a filter for my T6i since I have some left over and put it on the tripod for full frame shots.
Found this on Meade's web-site. Appears I can get my f10 to f6.3 with this.
I may pick one up:
Meade f 6.3 Focal Reducer/Field Flattener #07545. For Meade Schmidt-Cassegrain models. Improves edge-of-field correction and reduces exposure times by close to 50%. Threads into rear cell of any Meade SCT. Threads into rear cell of any Meade SCT. May be used to increade field of view and reduce magnification for visual applications.
An important advancement in high-resolution focal reduction systems, the Meade 4-element, multi-coated f/6.3 Focal Reducer/Field Flattener threads on to the rear cell of any LX90, LX200 or other Schmidt-Cassegrain or Advanced Coma-Free model and is typically used with an Off-Axis Guider or T-Adapter. Reduces the telescope's focal ratio by a factor of 0.63: f/10 telescopes are converted to f/6.3. Simultaneously, the 41mm-diameter lens system helps flatten the field of Schmidt-Cassegrain models, significantly improving edge-of-field corrections.
This handy accessory enables a reduction of photographic exposure times by about 50%, while producing an actual field diameter of 1.5" at the film plane.
08-07-2017 10:34 AM
The Meade f/6.3 on a 2080mm scope will bring your effective focal length to 1310mm.
See if you can get accurate info on the back-focus distance (if you buy it from someone like Oceanside Photo & Telescope (OPTcorp) they're probably the largest telescope & astronomy equipment dealer isn't the country and they have pretty good technical support, they can probably find that info. Meade tech support used to be fairly bad but they've been bought out by a new company and I'm told things are better. But you might be able to get the info direct from Meade.
Anyway, the original reducer had a 105mm back-focus dsistance. Then they redesigned the the product and I'm told that "briefly" their website listed the back-focus distance at 45mm (which is really surprising), but then redid their website and no longer list the back-focus distance. I have, however, seen the "Q&A" section list that it's 105mm even though others claim it's 45mm. I don't own the current model so I don't know the real story.
Canon EOS cameras have 44mm of space from the lens mounting flange on the front of the body to the imaging plane inside. So if it really is 45mm you'd basically want to find a T-Ring that can adapt Canon EOS mount to the Meade SCT size thread (and most T-rings adapt from EOS mount to "T-thread" which is not the same diameter as SCT thread. So I'm somewhat skeptical of the 45mm back-focus claim. Part of me wonders if someone didn't measure the distance of the extension tube at 45mm (and by the time you add in the 44mm in the camera you're at about 90mm ... and add in the T-Ring which usually adds another 5mm and now you're basically at a 95mm back-focus distance (and there are reducers on the market with 95mm back-focus distance).
The distance doesn't have to be bang-on accurate. If the back-focus distance is supposed to be 105mm... you'd still be ok if you were anywhere in the 100-110mm range. Technically it'll fractionally change your focal length and focal ratio ... but not by enough to have any meaningful impact on the exposure.
BTW, Meade used to make an f/3.3 focal reducer but you don't want that. The flat field that it can generate is very small (about the size of your pinky fingernail) and it's designed to work well for small-chip cameras (e.g. Web-Cam size chips) that are often used in planetary video capture. But on a DSLR camera you'll find only the very center of the field can be focused and the rest will be strongly blurred (and this is normal - it's not designed to produce a large enough flat field for a DSLR camera.)