SolarChat!

Hi,

My name is Bob, I live in West Yorkshire, UK and I’m new to the Solar Chat forum. I have a particular interest in the science and observation of our nearest star, our Sun, hence the reason I wished to join Solar Chat.

I’ve taken an interest in understanding the construction and use of the spectrohelioscope and I’ve found fascinating the wealth of information available on this forum. I’m particularly interested in Philippe Rousselle’s SHG adapted from a 115/900 mm Newtonian and after reading the details on his website on astrosurf.com some questions have come to mind which I would hope those who are more knowledgeable than me could answer.

At the moment I’m trying to understand Philippe’s use of the divergent meniscus lens to increase focal length of the telescope. I appreciate the reason for this is to increase the F/D ratio so that the telescope has a greater focal ratio than the collimator. From my understanding a divergent lens produces a virtual image on the same side of the lens as the object image, so the virtual image does not form a visible projection. In this case how can the image of the Sun be seen on the slit to ensure that the image is in focus?

I’ve got other questions, but rather than have lengthy posts I’ll take it a step at a time.

Many thanks, Bob

Hi Bob, welcome to the forum. I don't know the answer to this but there are lots of knowledgeable people here when it comes to SHG, so i'm sure before too long you'll get an answer

Bob

As philippe mentioned, he's using this negative lens as a barlow in order to increase the scope focal from native 900mm to 1170mm. He probably made this in order to achieve the max image size of the sun on the 62x62mm gratting...

Philippe's SHG was designed to accommodate his optics.
With his support I have included an English description of his instrument (and results) in the forthcoming book "Imaging Sunlight"
If I can assist you further, just drop me a PM or email.
Ken

Thank you for the replies everybody.

Ken, I've sent you a PM.

Bob

Hi Bob

welcome to that wonderful site. Have fun in the sun

I should also mention that at least eight other dedicated digital SHG users have contributed information on their equipment to the book. This will then provide a wide range of SHG solutions to the novice.
Fred Veio has also given permission to upload his book (and related material) to the astronomical spectroscopy website.

Hi Bob.

My two cents' worth: If you are interested in details about Phil's SHG, don't hesitate to contact him. I've found him to be very responsive and helpful.

Cheers.
Peter.

Good point Peter. I've found Philippe's email address on his homepage on astrosurf.

Thanks everybody for your help.

Cheers, Bob