Unprotected sunlight?

[Robindonne]

While scrolling through some ads on our marketplace i came across a small newtonian.  It wasnt the telescope itself that caught my attention but the “faulty” eyepiece picture.   Is this the result of a scope aimed at the sun without a filter?

[Cornelius Varley]

43 minutes ago, Robindonne said:

Is this the result of a scope aimed at the sun without a filter?

I would suspect so.

ps the "eyepiece" used to be a barlow.

[Robindonne]

Ha yes is saw it on the picture.   It was described as a broken lens.   So the light centers on that lens, what gets immense hot, and melts the housing?

[Physopto]

Ouch !!

Accidents can happen but in truth I suspect many a time it is user error or lack of knowledge about the subject. Done some daft things myself in the past. It only needs a moments distraction sometimes.

[John]

1 hour ago, Robindonne said:

....  So the light centers on that lens, what gets immense hot, and melts the housing?

Or the collimation is off to the extent that the light cone hits the plastic surround ?

[Don Pensack]

As for the sun, one poster described leaving his big dob on the porch when he went to bed.  The morning sunlight reflected off the mirror on the eave of his house and set the house on fire.

Fortunately, very little damage was done.  But if you ask if sunlight can melt a Barlow or eyepiece?  Yes, it can.

[Robindonne]

Thats why all the warnings constant.  Never seen the results of damaged instruments before.  

[DaveL59]

34 minutes ago, Don Pensack said:

As for the sun, one poster described leaving his big dob on the porch when he went to bed.  The morning sunlight reflected off the mirror on the eave of his house and set the house on fire.

Fortunately, very little damage was done.  But if you ask if sunlight can melt a Barlow or eyepiece?  Yes, it can.

yikes! I store my gear in the conservatory but am careful that the OTA's are pointing away from the sun's path, just in case a cover comes off unnoticed. I cap the finders too as well as remove the EP's and cap the focuser. No sense courting disaster knowing what you can do with the sun and a small magnifying glass let alone a 4-inch frac or large mirror. Folks have set places alight by just hanging a crystal in the window after all...

[Louis D]

2 hours ago, Don Pensack said:

As for the sun, one poster described leaving his big dob on the porch when he went to bed.  The morning sunlight reflected off the mirror on the eave of his house and set the house on fire.

Fortunately, very little damage was done.  But if you ask if sunlight can melt a Barlow or eyepiece?  Yes, it can.

I read about another person allowing the Dob's mirror to dry in the sun after washing and rinsing.  The angle was such that the sun was focused on the eaves and started to scorch it.

As for the OP, this seems to point to using a Newt to project a solar image which is not a good idea.

[John]

13 hours ago, Robindonne said:

Thats why all the warnings constant.  Never seen the results of damaged instruments before.  

 

[Peter Drew]

We had a small fire indoors when the magnifying side of my sister's makeup mirror on the window sill set fire to the curtains.       😱

[Physopto]

We have Flemish Glass in some of our windows. There were more when we bought the house 38 years ago but as time and finances permit, they are being removed. There were quite a few warnings some years ago about this type of glass and the possibility of fires. It was about the time that warnings went out about the Bulls Eye glass fitted in doors etc. Never had any problems but why take the chance if you don't need to. There are plenty of houses in the UK with this glass type and so far never actually heard of any fires  caused by it. Still a bit old fashioned for my tastes.

Derek

Edited June 17, 2020 by Physopto

[Don Pensack]

17 hours ago, Louis D said:

I read about another person allowing the Dob's mirror to dry in the sun after washing and rinsing.  The angle was such that the sun was focused on the eaves and started to scorch it.

As for the OP, this seems to point to using a Newt to project a solar image which is not a good idea.

Using a newtonian for projection of the solar disc works OK with simple eyepieces like Ramsdens or Huygens as long as they are glass and the housings metal.

Good luck finding such an eyepiece.  They were common in the '60s when I got started, but the ones out there now are usually plastic.

[Louis D]

2 hours ago, Don Pensack said:

Using a newtonian for projection of the solar disc works OK with simple eyepieces like Ramsdens or Huygens as long as they are glass and the housings metal.

Good luck finding such an eyepiece.  They were common in the '60s when I got started, but the ones out there now are usually plastic.

I just wouldn't want that amount of concentrated sunlight on my secondary mirror.  I've got to think it would get mighty hot which can't be good for the coatings or the holder.  The actual glass of the mirror would probably be okay.

[Don Pensack]

It's been done for over a century.  However, rarely on a scope > 6" in size.

[Louis D]

17 hours ago, Don Pensack said:

It's been done for over a century.  However, rarely on a scope > 6" in size.

I remember the Keck scopes covering their apertures with solar filter film when a solar eclipse passed over Hawaii some years back.  Can you imagine one of those beasts doing solar projection? 😱

[Star101]

On 16/06/2020 at 10:17, Peter Drew said:

We had a small fire indoors when the magnifying side of my sister's makeup mirror on the window sill set fire to the curtains.       😱

We had a similar thing. The convex mirror side was tilted down and the sun scorched the dressing table ...A real mess the size of a tea plate. Fortunately, no fire. Just a horrid smell in the room for a few days.