Jump to content

Stargazers Lounge Uses Cookies

Like most websites, SGL uses cookies in order to deliver a secure, personalised service, to provide social media functions and to analyse our traffic. Continued use of SGL indicates your acceptance of our cookie policy.

sgl_imaging_challenge_banner_terminator_challenge_winners.thumb.jpg.6becf44442bc7105be59da91b2bee295.jpg

parallaxerr

Which WL Frac?

Recommended Posts

Not seen any fading at all. Don't forget that the scope is in the shadow if pointed at the sun. I think quality of coating is better on the Equinox than e.g. the Lunt wedge as this did fade to greenish as mention. I have use a 1.25" wedge for a long time on 120mm scopes with no averse effect. It does get hot but that's its job. The scope should not get hot as if it does there's something wrong in the chain. I once tried a IR/UV blocker and whilst this reduced the heat on the wedge it seemed to create tube currents as the view was better without. I changed to a Baader 2" wedge purely as I wanted to use binoviewers and the T2 connectivity is great for reducing light path.

  • Like 1
  • Thanks 1

Share this post


Link to post
Share on other sites

ps. I was once told by the designer of the 1.25" Lunt wedge that he uses one all the time on a 10" Apo. I suspect you'd be able to fry an egg on the red disk with that scope though!

  • Like 3

Share this post


Link to post
Share on other sites

For a given aperture, a short focal length gives a more concentrated focal point solar image than a long focal length.

  • Like 1

Share this post


Link to post
Share on other sites
2 minutes ago, Peter Drew said:

For a given aperture, a short focal length gives a more concentrated focal point solar image than a long focal length.

That's interesting Peter, can you expand a little more on the benefits of this? Are you saying that faster optics are better for solar, provided the figure is good?

Share this post


Link to post
Share on other sites

I am being thick Peter

Does that mean the image is more detailed with a faster scope or that the focal point gets hotter or both / neither?

Share this post


Link to post
Share on other sites
23 minutes ago, Moonshane said:

ps. I was once told by the designer of the 1.25" Lunt wedge that he uses one all the time on a 10" Apo. I suspect you'd be able to fry an egg on the red disk with that scope though!

Yep, found your post on this Shame, I remembered you saying it :)

Share this post


Link to post
Share on other sites

The focal point gets hotter as all the heat is concentrated into a smaller area. Taken to the extreme, a flat lens would produce no more heat than the ambient temperature. My camera obscura 8" objective is F25 and produces a solar disc at focus just over 2" diameter and is nowhere near hot.

  • Thanks 1

Share this post


Link to post
Share on other sites
7 minutes ago, Moonshane said:

I am being thick Peter

Does that mean the image is more detailed with a faster scope or that the focal point gets hotter or both / neither?

I'm with you Shane, not sure if that's a good or bad thing! I would still bet on slower scope being better, or more specifically better figured....

Share this post


Link to post
Share on other sites
11 minutes ago, Peter Drew said:

The focal point gets hotter as all the heat is concentrated into a smaller area. Taken to the extreme, a flat lens would produce no more heat than the ambient temperature. My camera obscura 8" objective is F25 and produces a solar disc at focus just over 2" diameter and is nowhere near hot.

I see where you're going now Peter. Fast scope = hotter wedge. So, slower the better with the 1.25" wedge.

  • Like 1

Share this post


Link to post
Share on other sites

cheers Peter, I see now that it make sense. A 100mm f5 has a solar image at focus of about 5mm and a 100mm f10 has a 10mm image so the heat is spread over a wider area with the latter.

  • Like 2

Share this post


Link to post
Share on other sites

Interesting stuff :smiley:

Share this post


Link to post
Share on other sites

I've been using the Lunt 1.25" HW with my ED120 today ........ and nothing has caught fire or fried I'm pleased to say.

Lovely views of the 2 current active regions  :smiley:

  • Haha 3

Share this post


Link to post
Share on other sites
7 minutes ago, John said:

I've been using the Lunt 1.25" HW with my ED120 today ........ and nothing has caught fire or fried I'm pleased to say.

Lovely views of the 2 current active regions  :smiley:

That's a relief John.

I confess I was a little worried when I looked up 'lunt' and found this definition:

'a match; the flame used to light a fire.'

http://www.dictionary.com/browse/lunt

Eeeeek! ;)

  • Haha 2

Share this post


Link to post
Share on other sites

Well I managed a brief half hour first light with the Lunt 1.25" wedge over the weekend and I'm not sure what to make of it.

The HEQ5 was setup in the garden from last weeks night time observing, so already polar aligned. I put the Equinox on along with the wedge and ES82°11mm fitted with solar continuum and polarising filters stacked together. I used the shadow method of aligning with the sun and got it in the FoV fairly easily and set the mount to track solar rate.

Initially the view was very sharp and I could make out some granulation and AR2715, I tried a few different EPs as it was a strange feeling at first viewing something that filled the FoV so much. It was only after 4-5mins though that I tested the heat of the disc on the wedge and it was very hot! Too hot to hold my finger on for more than a brief moment, which worried me slightly, though this may be perfectly normal. It is the wedges job to dissipate 95% of the energy of course.

I had to pop inside the house for 5 minutes so I slewed the scope away from the sun, noting that the wedge cools quite rapidly when off-target. However, the next problem was that when I came back out, the OTA, being black, had got more than warm to the touch and now the view of the sun had turned to mush and was impossible to focus. I could see heat currents, which I assume were now inside the OTA.

I felt a little uncomfortable at this point with both OTA and wedge being hot and the views poor, so I wrapped it up. I just don't feel comfotable using the Equinox for this, it is my only scope and my pride and joy so I have a decision to make...Buy another frac with smaller objective and a white tube, or return the wedge and filters. My heart says another frac (obviously) but my head says return the wedge etc.

  • Like 1

Share this post


Link to post
Share on other sites

The back heat sink of the wedge will get hot especially with the ED120, but the body of the wedge should not.

I wonder if using both the solar continum filter AND the polarising filter at the same time is too much filtering ?

With my Lunt wedge, even with the ED120 (mine is the gold tube version of that scope) I use a single polarising filter (not the double polarising type) on the end of the eyepiece and of course the ND filter fitted in the bottom of the wedge eyepiece tube. Seems to work very well with my scopes from the 70mm Ranger to the ED120 including for outtreach.

But if you are not comfortable then I can understand if you decided not to pursue this.

  • Like 1

Share this post


Link to post
Share on other sites

Agreed. Do what you are happy doing. An option is to simply turn off the tracking or leave the tracking on and just offset the scope a little which should then avoid the tube heating. You could even buy a white sheet to reflect the heat and cover the scope when not in use? 

  • Like 1

Share this post


Link to post
Share on other sites
7 minutes ago, John said:

I wonder if using both the solar continum filter AND the polarising filter at the same time is too much filtering ?

Actually I found this the only way to get a comfortable view John. With just the polarising filter, I found the image too bright. I also noted that the brightness wasn't as adjustable as I'd imagined it might be, there was a definite dimming as I rotated the eyepiece, but not quite enough, the SC helped tone it down a touch further and only then could I see granulation.

I am of course completely new to WL observation, so what I am seeing may be perfectly normal.

Share this post


Link to post
Share on other sites

That's a shame, but don't rush any decisions, you have some time before you would need to return the Wedge.

I think slewing the scope away from the sun is a mistake as then the whole length gets heated up. As Shane said in a previous post, when the scope is pointing at the sun it is pretty much out of the sun. I normally just put the end cap on and leave the scope tracking.

Seeing conditions do also change quite rapidly and can go from good to poor in a short space of time, so give it some time. Last point is that often early morning and sometimes later in the evening is better as it is cooler. Certainly the mornings are generally good as the land and buildings have not had a chance to heat up so the seeing is better.

  • Like 1

Share this post


Link to post
Share on other sites
12 minutes ago, John said:

The back heat sink of the wedge will get hot especially with the ED120, but the body of the wedge should not

Yes, this was the case. To clarify the heat sink got hot, not the body. It just got a lot hotter than I'd expected!

Share this post


Link to post
Share on other sites
Just now, Stu said:

I normally just put the end cap on and leave the scope tracking.

Good shout Stu, probably a better option.

Just now, Stu said:

Last point is that often early morning and sometimes later in the evening is better as it is cooler. Certainly the mornings are generally good as the land and buildings have not had a chance to heat up so the seeing is better.

Agreed, I think mornings would definitely be better. I was out at around 2pm and it was blazing hot, I was sweating at the EP which didn't help!

Share this post


Link to post
Share on other sites
10 hours ago, parallaxerr said:

Actually I found this the only way to get a comfortable view John. With just the polarising filter, I found the image too bright. I also noted that the brightness wasn't as adjustable as I'd imagined it might be, there was a definite dimming as I rotated the eyepiece, but not quite enough, the SC helped tone it down a touch further and only then could I see granulation.

I am of course completely new to WL observation, so what I am seeing may be perfectly normal.

I guess brightness is something that we have different tolerances and preferences on. I find the single polariser gives enough control for me to get a detailed but comfortable image :dontknow:

 

 

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


  • Recently Browsing   0 members

    No registered users viewing this page.

×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.