Solar imaging with NO SUNFILTERS....

Frankenscope? Let's see it!***be advised that NOTHING in this forum has been safety tested and you are reading and using these posts at your own peril. blah, blah, blah... dont mess around with your eyesight when it comes to solar astronomy. Use appropriate filtration at all times...
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Cschur
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Solar imaging with NO SUNFILTERS....

Post by Cschur »

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


Chris Schur

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Birch Mesa Observatory, Payson Arizona

Clear Creek Canyon Observatory, Happy Jack, Arizona
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swisswalter
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Re: Solar imaging with NO SUNFILTERS....

Post by swisswalter »

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.


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brianb11213

Re: Solar imaging with NO SUNFILTERS....

Post by brianb11213 »

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.


BelOptik_Oliver

Re: Solar imaging with NO SUNFILTERS....

Post by BelOptik_Oliver »

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...


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Re: Solar imaging with NO SUNFILTERS....

Post by Merlin66 »

Hmmmm
Not too many images taken at a focal ratio of 160 nowadays.....


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Re: Solar imaging with NO SUNFILTERS....

Post by colinsk »

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.


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