Increased detail with a 2” Herschel Wedge?

[Alan White]

I presently have and enjoy using a 1.25” Lunt Herschel Wedge on a 4” Refractor in WL use,
but I struggle for detail on most days beyond super Sunspot detail.

Is this atmospheric or should I seriously consider a 2” wedge?
And if the answer is a bigger wedge, does any one model rule?

Many thanks, Alan

[Dr Paul Leyland]

According to Sidgwick, the resolution of a properly collimated 4″ refractor should be around 1.2-1.4 arcsec though, to be fair, those values are for resolving double stars rather than extended objects. That does, of course, assume that the ocular is illuminated by the whole objective. Back in Sidgwick’s day I suspect that 2″ eyepieces were extremely unlikely to be fitted to a 4″ refractor.

I have no idea what typical seeing is like at your location but guess that it is likely to be around 2-3 arcsec. That is a typical figure at Tacande Observatory though occasionally the seeing can be as good as 1-1.5 arcsec.

Neither do I have any idea about the acuity of your vision.

Based on this analysis, I suspect you are seeing limited. The phrase “most days” also leads me to this opinion.

[Jeremy Shears]

I don’t think a larger prism will help, Alan. As you suspect, it’s probably due to unstable seeing.

As an aside, I reckon I see as much detail using Baader solar film as using a Lunt Herschel wedge. I do find a solar continuum filter helps (in addition to the solar filter of course), tho the Sun turns green! It also helps to dim the image a bit, which also helps with a prism (could use a polarising filter to a similar effect- if your image is too bright it might make it harder to see detail)

• This reply was modified 1 year, 5 months ago by Jeremy Shears.
• This reply was modified 1 year, 5 months ago by Jeremy Shears.

[Alan White]

Thanks gents for the responses.

I use a Baader Single Polariser and a Baader Continuum filter as my default.

I think the seeing is probably my limitation, my eyes are good and I visually observe on a very regular basis.

My train of thought was if a larger wedge or differing model might bring out any more detail,
but the 4” scope may just be what it can show on most days.

[David Arditti]

I would not rule out the possibility that your 1.25″ Lunt solar wedge is sub-par. I don’t have experience with this unit, but I do have experience with the Lunt 1.25″ diagonal blocking filter units for H alpha telescopes. I tried two, the B600 6mm one and the B1200 12mm one. On the same telescope, the 12mm one was clearly better. However, and this is where I get to my point, I tried a home-brew experiment (that I do not recommend to anyone who does not know what they are doing) where I pulled the 12mm blocking filter out of the 1.25″ diagonal (it was glued in) and made (on a lathe) a straight tube unit of 2″ outer diameter to house it, and a 1.25″ eyepiece tube. I was then able to use my H alpha system with a 2″ diagonal. The result was clearly better. There was therefore definitely a quality difference between the 2″ diagonal I had substituted and both Lunt 1.25″ diagonals, that was perceptible even in typical poor daytime seeing conditions. The Lunt diagonals did not seem good when one pulled them apart – well-finished outside, weighty, but just crudely glued together inside, unlikely to be precise. One experience.

[Alan White]

I should add the 1.25 was purchased by me new in 2017 when I moved on from Baader Film,
the quality is not my issue ( I think), more a curiosity of would a larger unit make a change?

It’s most interesting to read of the quality inside from your post David.
That concerns me as my Lunt 40mm Ha scope has a b600 diagonal and filter unit, however that scope performs superbly and I have compared that to other kit of similar size.
Often the kit looks good on the outside, but behind scenes it’s not the same, something I call Hotel or Shop Front engineering.
Looks good up front, but ….

Are the Baader Cool wedges any better than the Lunt wedges for instance?

Or am I expecting just too much visually in WL with a 4” scope?

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