Venus (and Moon) through a Herschel Wedge

[Stu]

I currently have the somewhat ludicrous luxury of owning two Baader CoolWedges, so decided to try out the Mark I version with no filters fitted on Venus as I had heard this can help to cut the glare and improve the views.

Removing the filters was an easy job, and despite the hazy cloud I popped the scope out and picked Venus and the Moon up at around 20.44.

I can safely say that it was a successful experiment. Venus was sharper and dimmer, and as a result it actually showed some variation in surface brightness. This was largely a dimming towards the terminator but there was also some subtle difference in brightness running across this too. It’s the most convincing view of some sort of cloud visibility I’ve had, so I’ll keep on trying this approach.

Whilst I had the Wedge fitted, I tried an experiment which was doing a Facebook  Live broadcast. It is often very hard to control exposure on these, and the Wedge really helped this. I was able to run a live broadcast which maintained correct exposure even without zooming in, and I had none of the usual nonsense of the image flashing off and on when I got to higher zoom settings. It worked very well and I did a couple of broadcasts to different groups which worked well, including Venus as well.

So, I can recommend this as something to try, but PLEASE be careful to refit the filters before viewing the Sun again as it would be catastrophic to view without them. I would do it immediately after finishing so there is no chance of forgetting.

[saac]

I caught a glimpse of them last night just before I went to bed, they look absolutely stunning at the moment. That is a lovely image Stu, quite a neat solution as well. 

Jim 

[Mr Spock]

Interesting solution. I observe Venus with a variable polarising filter and a 80A blue filter. Variations in surface brightness are there once you get Venus down to the right 'dimness'.

[Littleguy80]

Really interesting, Stu. I've never heard of this approach. The TS Optics wedge I have makes this quite easy to do so will have to give this a go. Good shout on replacing filters immeadiately afterwards. Too easy to forget otherwise.

[Stu]

1 hour ago, Mr Spock said:

Interesting solution. I observe Venus with a variable polarising filter and a 80A blue filter. Variations in surface brightness are there once you get Venus down to the right 'dimness'.

I think it would be worth me trying a few coloured filters as well, to see if that helps bring out the detail better. Think I’ve got some squirrelled away somewhere.

[Paz]

That is interesting thanks for posting. I've had some success on Venus recently with an nd1.8 filter and also by stacking colour filters with a nd0.9 filter. A herschel wedge would do a lot of the dimming work but with fewer surfaces and fewer bits of glass in the light path. I'll give it a try.

[Stu]

I knew I had seen it mentioned on here before. My old friend @Moonshane used to use his wedge in a similar way. Hope alls well with you Shane if you see this 👍

 

[Louis D]

Short of using a perfectly cleaved crystal surface or a vacuum sputtered crystal surface, a Herschel wedge's uncoated first surface mirror should yield just about the smoothest, lowest scatter diagonal surface possible.  And, unlike a prism diagonal which has a similarly smooth surface, there is no possibility of introducing chromatic aberrations into the image.  Thus, it probably would yield the highest contrast possible for ultra-bright objects short of straight through viewing.  Of course, with straighter through viewing, you'd probably have to introduce some sort of dimming filtration, and that could add scatter itself.

For those not familiar with the internals of a Herschel wedge, I've attached a Wikipedia diagram below:

[Paz]

I've got my C8 set up with a wedge for tonight on Venus. The moon looks pretty good, it will be interesting to see how it goes when the scope is cooled and the sky dims a bit.

[Alan White]

Interesting idea and good on you for trying this out @Stu.

I observe Venus as per Michaels method, but with a fixed nd rather than a variable one.

[Mr Spock]

Yesterday I ordered a darker blue and a violet filter. I'll see if they make a difference.

[Louis D]

On 27/05/2023 at 04:45, Mr Spock said:

Yesterday I ordered a darker blue and a violet filter. I'll see if they make a difference.

I would think a pure blue filter like that used for RGB color separation coupled with a variable ND filter would be ideal for experimentation.

[Littleguy80]

I gave this a try tonight. Worked really well with Venus. I also felt that cloud detail along the terminator was perhaps easier to see. Venus perhaps wasn’t as sharp though this may well be due to seeing.

I was less keen when using it with the moon. It just felt too dark though maybe it would work better with larger scopes. I like the bright views and don’t use a polarising filter with a normal diagonal and my 100mm scope. 
 

[Stu]

48 minutes ago, Littleguy80 said:

I gave this a try tonight. Worked really well with Venus. I also felt that cloud detail along the terminator was perhaps easier to see. Venus perhaps wasn’t as sharp though this may well be due to seeing.

I was less keen when using it with the moon. It just felt too dark though maybe it would work better with larger scopes. I like the bright views and don’t use a polarising filter with a normal diagonal and my 100mm scope. 
 

Glad you found it useful on Jupiter Neil. I tend to agree on the Moon, though certain brighter features may benefit as it helps reduce the glare.

[Littleguy80]

10 minutes ago, Stu said:

Glad you found it useful on Jupiter Neil. I tend to agree on the Moon, though certain brighter features may benefit as it helps reduce the glare.

Really worthwhile experiment and something I would never have thought to try without this post so thank you! Will definitely use this approach with Venus again. Not so sure on the Moon but, as you say, there may be some features where it helps. 

[knobby]

I've used my imaging set up to capture the Moon during the day using the Ha filter, quite surreal to see it looking like midnight during the day. Might be worth a bash if anyone has an Ha filter ?

[Louis D]

On 28/05/2023 at 17:47, Littleguy80 said:

Really worthwhile experiment and something I would never have thought to try without this post so thank you! Will definitely use this approach with Venus again. Not so sure on the Moon but, as you say, there may be some features where it helps. 

Try it on the full moon to see if features are easier to discern thanks to the dimming effect.  I find binoviewing really helps with observing the full moon thanks to putting two eyes on the target instead on one on the target and one eye closed seeing blackness.

[Louis D]

On 29/05/2023 at 04:04, knobby said:

I've used my imaging set up to capture the Moon during the day using the Ha filter, quite surreal to see it looking like midnight during the day. Might be worth a bash if anyone has an Ha filter ?

I could see where that works because most of the scattered light of a blue sky is blue to teal blue to shades of bright green while the Ha (C line below) has much less scattered light:

[Stu]

3 hours ago, Louis D said:

Try it on the full moon to see if features are easier to discern thanks to the dimming effect.  I find binoviewing really helps with observing the full moon thanks to putting two eyes on the target instead on one on the target and one eye closed seeing blackness.

Just tried this with the FC100, MaxBright IIs and a de-filtered CoolWedge. I must say, I liked the view. There was very good contrast on the features still, unlike the usual fairly bland views. I think this will become a regular method for me.

[knobby]

Blimey, doesn't time fly ! just found the Moon pic I took through an imaging Ha filter ... 

 

3 years ago 🙂

 

 

[Louis D]

1 hour ago, knobby said:

Blimey, doesn't time fly ! just found the Moon pic I took through an imaging Ha filter ... 

 

3 years ago 🙂

 

 

That's very cool.  I wonder if an IR-pass filter would work well?  It doesn't seem like there's much scattered light in IR in a daytime sky.

[knobby]

Some of the Cloudy nights lot have used IR pass on the Moon, needs longer exposures but good results.

[John]

I tried this approach this evening with my ED120 refractor and the 1.25 inch Lunt Hershel Wedge, de-filtered.

The resulting views of Venus were very crisp and glare-free. It made for relaxed observing and was an all-round pleasant experience.

I'm not sure that I saw any more detail than using a mirror diagonal and a moon filter, tonight at any rate, but I think the overall view of the planet was "cleaner" if that makes any sense.

Thanks for passing on this tip @Stu - I will use it often when observing Venus in future I reckon 🙂

I did take your advice and replaced the filters in the wedge as soon as I took it off the scope. With all this solar activity no point in risking an accident ! 😮

 

Edited June 5, 2023 by John

[John]

51 minutes ago, John said:

I tried this approach this evening with my ED120 refractor and the 1.25 inch Lunt Hershel Wedge, de-filtered.....

 

 

Just a quick point in case anyone else would like to try the Lunt 1.25 inch HW in this mode. I found the ND3.0 filter installed in the eyepiece holder of the wedge impossible to remove. The filter is screwed into the bottom section of the stock eyepiece holder. Luckily I had an ordinary 1.25 inch mirror diagonal available and the eyepiece holder from that screwed straight onto the Lunt HW body. So I was able to observe Venus just using the prism within the wedge to reduce the light throughput.

It might be possible to unscrew the installed ND filter from the stock eyepiece holder but it would need more force than I was willing to apply. It may also be worth using the HW with the ND filter in place on Venus - it is a bright target.

And I did put the original Lunt eyepiece holder and filter straight back onto the wedge once I had finished observing Venus - safety first !🙂

 

Edited June 5, 2023 by John

[Stu]

1 hour ago, John said:

I tried this approach this evening with my ED120 refractor and the 1.25 inch Lunt Hershel Wedge, de-filtered.

The resulting views of Venus were very crisp and glare-free. It made for relaxed observing and was an all-round pleasant experience.

I'm not sure that I saw any more detail than using a mirror diagonal and a moon filter, tonight at any rate, but I think the overall view of the planet was "cleaner" if that makes any sense.

Thanks for passing on this tip @Stu - I will use it often when observing Venus in future I reckon 🙂

I did take your advice and replaced the filters in the wedge as soon as I took it off the scope. With all this solar activity no point in risking an accident ! 😮

 

I’m glad you found it worthwhile John. I agree it gives a nice clean image, pleasant to view. It’s not a magic bullet though, those elusive clouds are still just that with me. I think I see something, but really cannot convince myself that it’s real.

Perhaps give the Wedge a try on the full Moon too next time, it does seem to give very nice contrast to the normally washed out surface features.

Thanks also for the repeated reminder to refit filters, let’s keep doing that even if it feels unnecessary to avoid any accidents.

I’m using two wedges currently, one with filters for the Sun and the other with them removed for Venus and the Moon. If the wedge doesn’t sell I’ll have to label it up as a ‘Venus and Moon only’!