I didnt want this to be on the main solar chat forum, its a bit off the wall. I was reading an old 1967 sky and telescope, and there was on the inside cover a Questar add showing an extreme close up of a spot group in white light, that showed a bit of granulation and one hell of an image scale. But my jaw dropped when I read HOW he took the image. Using eyepiece projection, he obtained a equivalent focal length of 50 feet. I grabbed a calculator - holy cow thats just over 15,000 mm! And it gets better. He was using "Microfile film" with an asa of like 25. Since the image was so insanely dim, to get his exposure time up to the required 1/1000 second to freeze the seeing he would center the subject then during the exposure - PULL OFF THE SUN FILTER COMPLETELY. Now I do realize that 3.5 inches of aperture is not too much but this is the first time I have ever heard of this method. Is this nuts or what? Was a nice photo though!
Anybody ever dared try anything like this?
Chris
Solar imaging with NO SUNFILTERS....
Solar imaging with NO SUNFILTERS....
Chris Schur
----------------------------------
Birch Mesa Observatory, Payson Arizona
Clear Creek Canyon Observatory, Happy Jack, Arizona
----------------------------------
Birch Mesa Observatory, Payson Arizona
Clear Creek Canyon Observatory, Happy Jack, Arizona
- swisswalter
- Way More Fun to Share It!!
- Posts: 17948
- Joined: Thu Feb 06, 2014 4:28 am
- Location: Switzerland
- Been thanked: 1 time
- Contact:
Re: Solar imaging with NO SUNFILTERS....
Hi Chris
15 m FL is a huge number. I would be scared to work without any filter on my scopes. So never tried anything like it.
15 m FL is a huge number. I would be scared to work without any filter on my scopes. So never tried anything like it.
Only stardust in the wind, some fine and some less fine scopes, filters and adapters as well. Switzerland 47 N, 9 E, in the heart of EUROPE
from 7 am - 7 pm http://www.nanosys.ch
from 7.01 pm - 6.59 am http://www.wastronomiko.com some times vice versa
from 7 am - 7 pm http://www.nanosys.ch
from 7.01 pm - 6.59 am http://www.wastronomiko.com some times vice versa
Re: Solar imaging with NO SUNFILTERS....
Maybe this method was justified for very large scale images when ultra slow film was available. But if you look at the results obtained using mild filtration & slow film, granulation was rarely imaged at all - with modern digital equipment & heavy filtration recording of granulation is routine. There simply isn't any need to go light on filtration any more.
However using filtration which is lighter than is acceptable for visual use - e.g. ND 3.8 "photo" film instead of ND 5 "visual" film, or ND 1.8 in a wedge instead of ND 3.0 - can work well with modern digital sensors, especially when used with coloured filters - may well be worth trying if you have trouble with seeing.
You don't need such a long focal length with digital cameras, either - the raw resolution of the filter tends to be higher than was the case even with ultra slow fine grain film emulsions.
However using filtration which is lighter than is acceptable for visual use - e.g. ND 3.8 "photo" film instead of ND 5 "visual" film, or ND 1.8 in a wedge instead of ND 3.0 - can work well with modern digital sensors, especially when used with coloured filters - may well be worth trying if you have trouble with seeing.
You don't need such a long focal length with digital cameras, either - the raw resolution of the filter tends to be higher than was the case even with ultra slow fine grain film emulsions.
Re: Solar imaging with NO SUNFILTERS....
Hi guys,
Yes, that's works...
3.5" aperture and f=15000mm is aperture ratio F/168 -> The sun diameter in focal plane is around 140mm ~50mm bigger than entrance pupil.
That's not realy a burning glass...
Yes, that's works...
3.5" aperture and f=15000mm is aperture ratio F/168 -> The sun diameter in focal plane is around 140mm ~50mm bigger than entrance pupil.
That's not realy a burning glass...
- Merlin66
- Librarian
- Posts: 3970
- Joined: Tue Dec 13, 2011 1:23 pm
- Location: Junortoun, Australia
- Has thanked: 173 times
- Been thanked: 615 times
- Contact:
Re: Solar imaging with NO SUNFILTERS....
Hmmmm
Not too many images taken at a focal ratio of 160 nowadays.....
Not too many images taken at a focal ratio of 160 nowadays.....
"Astronomical Spectroscopy - The Final Frontier" - to boldly go where few amateurs have gone before
https://groups.io/g/astronomicalspectroscopy
http://astronomicalspectroscopy.com
"Astronomical Spectroscopy for Amateurs" and
"Imaging Sunlight - using a digital spectroheliograph" - Springer
https://groups.io/g/astronomicalspectroscopy
http://astronomicalspectroscopy.com
"Astronomical Spectroscopy for Amateurs" and
"Imaging Sunlight - using a digital spectroheliograph" - Springer
Re: Solar imaging with NO SUNFILTERS....
Slavich still sells rolls (1 x 30 meters) of very slow film. I would guestimate the PFG-01 is ASA .001 or slower! I can get better than 2000 lines per millimeter of resolution.