Herschel wedge recommendations

[StuartT]

11 minutes ago, TerryMcK said:

My Altair Astro 2" solar wedge is ok up to 7" (175mm) apertures according to the manufacturers specs. They also go to state "The Altair Solar Wedge has been fully tested with the sun remaining in the centre of the field of view for 5 hours of continual exposure with a 6" (152mm) aperture refractor in mid-summer in the UK. At no point did the outer prism housing become too hot to touch, a problem common with other wedges. Whilst we cannot recommend use with telescopes of larger than 6 (152mm) aperture for longer or shorter duration, if your telescope is larger, then we suggest trying the wedge for a short time initially, to assess the heat build-up and make your own informed decision."

I use mine on my WO ZS73 and have left it pointing at the sun for hours and the wedge never gets too hot to touch. The OTA has never got hot either.

Right. So it is the wedge itself that's the potential concern, rather than the OTA. That's good. I think I can live with the wedge heating up. I'm about to upgrade from a 90mm to a 150mm frac so I don't really want to have to buy the 2" wedge when I already have the 1.25" one.. unless it absolutely necessary.

[Stu]

1 hour ago, StuartT said:

Thanks for sharing this thread Stu. So just to be clear, even a 150mm refractor would potentially be ok with a 1.25" wedge? i.e. without any objective filter on it? Are objective filters ever necessary on refractors? I guess I am just worried about heating up the tube with so much aperture, but maybe I'm worrying unnecessarily

With a wedge you don’t need a front filter. It’s wise to choose an OTA with no plastic parts, as the heat does get concentrated towards the focuser.

As I said, I think I would probably be cautious using a 1.25” on a 150mm if I happened to live in California! But in the U.K. there is less to worry about. The reports from Markus Ludes imply that the 1.25” can be used on larger scopes, all I can say is that I would be quite happy using one in a 120mm. There is no safety risk as such, worst case you might crack the wedge but it wouldn’t cause any risk to your eyes.

It would be great to have clear manufacturer guidance on it.

[John]

1 hour ago, StuartT said:

Right. So it is the wedge itself that's the potential concern, rather than the OTA. That's good. I think I can live with the wedge heating up. I'm about to upgrade from a 90mm to a 150mm frac so I don't really want to have to buy the 2" wedge when I already have the 1.25" one.. unless it absolutely necessary.

My 1.25 inch Lunt wedge works fine with my ED120 refractor. I've often used it at outreach events with this scope as well. The heat sink on the back of the wedge body gets quite warm but that's what it is supposed to do. It does not get too hot to touch or anything like that.

I've not used my wedge with a larger aperture than the 120mm though.

 

Edited May 29, 2021 by John

[johninderby]

While the 1.25” wedge should survive being used on a 150mm frac I would be a lot more comfortable using a 2” wedge. I did use a Baader Coolwedge on a TS 152mm  f5.9 frac and the back of the wedge did get very hot. Wouldn’t have wanted to touch it with a finger.

Edited May 29, 2021 by johninderby

[nfotis]

Supposedly the Lacerta wedges are quite good, but I haven't tested any as I don't own a refractor yet.

In hot climates like in Greece, I think that investing on a 2" wedge would be prudent, but it seems that it eats too much backfocus... This might be a problem with binoviewers too.

N.F.

 

[johninderby]

Infocus travel is a problem with many refractors and a wedge. When I used a Lacerta 2” wedge with an Orion 120 frac fitted with a SW crayford had to shorten the tube a bit to reach focus. 

With my Tecnosky 125APO not a problem even without removing the focuser extension piece. 

[Louis D]

2 hours ago, TerryMcK said:

The Altair Solar Wedge has been fully tested with the sun remaining in the centre of the field of view for 5 hours of continual exposure with a 6" (152mm) aperture refractor in mid-summer in the UK. At no point did the outer prism housing become too hot to touch, a problem common with other wedges.

I wonder about late-spring in Texas.  I just picked up a Hercules 1.25" for my 90mm APO, and there doesn't appear to be any heating of the rear ceramic even around noon.  Of course, 90mm is a lot less than 152mm.

I was breaking into a full on sweat, though, making it miserable to observe.  And it's not even summer yet!

[StuartT]

14 hours ago, Louis D said:

I wonder about late-spring in Texas.  I just picked up a Hercules 1.25" for my 90mm APO, and there doesn't appear to be any heating of the rear ceramic even around noon.  Of course, 90mm is a lot less than 152mm.

I was breaking into a full on sweat, though, making it miserable to observe.  And it's not even summer yet!

that sounds fine to me Louis.

Totally take the point about sweating tho! I wear a hat and use a cloth around my head for viewing

[Louis D]

2 hours ago, StuartT said:

that sounds fine to me Louis.

Totally take the point about sweating tho! I wear a hat and use a cloth around my head for viewing

I may bring out my box fan that I use at night to blow away biting bugs.  I set it up to blow perpendicular to the scope's axis and across my body, so I don't disturb the column of air I'm observing through.

[MortonH]

Can anyone advise if the TS wedge has a safety stop to prevent the eyepiece hitting the filter?