Herschel wedge 1.25 in - safe refractor size limitations

[Alan64]

"...and the 100mm limitation you set yourself is over cautious."

I've observed the "Aten" with my 4" f/8, and with a Thousand Oaks RG-film filter, and it's more than bright enough for my eyes; of course, there's always variable polarisers to employ, therefore I understand your point of view.  Incidentally, I have a sheet of Baader film that I'm going to try out, as I understand it's superior to said filter, but the view may very well be brighter still through that.

The two aspects that concern me most regarding a Herschel wedge is that refractors with any accessory inserted into the visual-back are then totally closed tubes; and that wedges only passively exhaust the excess heat, not actively as it would were it equipped with a fan.  I've read others stating that the lens itself doesn't get hot.  Whether it does or not, I'm primarily concerned with heat building up within the tube.

Quite right; the view through your Takahashi is indeed the best.

I am somewhat in earnest in wanting to try out a wedge, but with an inexpensive 80mm or 90mm longer-focus achromat.  I would then think nothing of drilling a small hole through the side of the optical-tube, about midway, and inserting a temperature probe whilst observing.

[Stu]

12 minutes ago, Alan64 said:

"...and the 100mm limitation you set yourself is over cautious."

I've observed the "Aten" with my 4" f/8, and with a Thousand Oaks RG-film filter, and it's more than bright enough for my eyes; of course, there's always variable polarisers to employ, therefore I understand your point of view.  Incidentally, I have a sheet of Baader film that I'm going to try out, as I understand it's superior to said filter, but the view may very well be brighter still through that.

The two aspects that concern me most regarding a Herschel wedge is that refractors with any accessory inserted into the visual-back are then totally closed tubes; and that wedges only passively exhaust the excess heat, not actively as it would were it equipped with a fan.  I've read others stating that the lens itself doesn't get hot.  Whether it does or not, I'm primarily concerned with heat building up within the tube.

Quite right; the view through your Takahashi is indeed the best.

I am somewhat in earnest in wanting to try out a wedge, but with an inexpensive 80mm or 90mm longer-focus achromat.  I would then think nothing of drilling a small hole through the side of the optical-tube, about midway, and inserting a temperature probe whilst observing.

Yes, my understanding is that the Baader film is better than other options, including the glass filters but I've only looked through the Baader film (which was good, but not up with a Wedge) so can't compare.

Obviously it depends to an extent how hot and high your sun is, the U.K. Is not often hot, but it can be in mid summer and I've had no problem with tube heating.

I can only encourage you to take the step and try a Wedge out, you won't regret it so long as the scope you use is of sufficient quality. If the inexpensive option is just to convince yourself about tube temperatures before going on to a better scope then that sounds a perfectly sensible route for you to take if it allays your concerns.

[Alan64]

32 minutes ago, Stu said:

Yes, my understanding is that the Baader film is better than other options, including the glass filters but I've only looked through the Baader film (which was good, but not up with a Wedge) so can't compare.

Obviously it depends to an extent how hot and high your sun is, the U.K. Is not often hot, but it can be in mid summer and I've had no problem with tube heating.

I can only encourage you to take the step and try a Wedge out, you won't regret it so long as the scope you use is of sufficient quality. If the inexpensive option is just to convince yourself about tube temperatures before going on to a better scope then that sounds a perfectly sensible route for you to take if it allays your concerns.

 

I live at about the same latitude here in the U.S. as...Casablanca in Morocco.

But here, we usually have some snow in winter...

...that, late-February of 2015.  But yes, the summers in Mississippi are quite legendary, especially the current one...

If said inexpensive achromat star-tests well, then that will be the only one with which to use a wedge.

[Merlin66]

Stu, et al,

Once again I must correct the misconception that Petzval design refactors are somehow at risk when using a Herschel Wedge....

Al Nagler has gone on record (check out S&T) that the TV Petzval design is 100% safe to use.

Please, please take note and ensure future correctness.

 

[Stu]

1 minute ago, Merlin66 said:

Stu, et al,

Once again I must correct the misconception that Petzval design refactors are somehow at risk when using a Herschel Wedge....

Al Nagler has gone on record (check out S&T) that the TV Petzval design is 100% safe to use.

Please, please take note and ensure future correctness.

 

Thanks Ken, appreciated. I was just being cautious and there are obviously other four and five lens designs out there which have not been clarified by manufacturers so thought it best to be safe.

Do you know if, for instance the Tak FSQ and WO71 (think that's the 5 element one?) are also safe?

Stu

[Merlin66]

Good question!

I believe all the other Petzval designs, like the TV should be safe to use, but as you say this should be confirmed by the manufacturer.

Do we have direct contact details for them??

 

[John]

Vixen do Petzvals and Bresser do at least one. The TAL Apolar 125 has lens groups right down the tube too.

 

[Stu]

19 minutes ago, Merlin66 said:

Good question!

I believe all the other Petzval designs, like the TV should be safe to use, but as you say this should be confirmed by the manufacturer.

Do we have direct contact details for them??

 

FLO certainly have Vixen contacts, Pete Gamby I believe. We would have to go via Ian King or Nick Hudson to understand Tak I guess. I know Nick so will drop him a line. Then there are all the WO71 clones...... Not sure how many would be used for solar anyway as they are more deep sky scopes.

I did use my Genesis with a wedge once and it suffered no ill effects, as Al Nagler states.

[John]

I guess a lot hinges on where the petzval element is actually placed in the optical train. If it's well up the train (as in the Tele Vue 101 etc) then presumably the converging light cone is not too hot at that point. Further down the tube and there must be a point where the heat would pose an issue ?

 

[Alien 13]

The one issue I have that stopped me buying a wedge was the thought that the focusser assembly and hence any grease would get warm and melt dont know if anyone has found this a problem in practice.

Alan

[John]

33 minutes ago, Alien 13 said:

The one issue I have that stopped me buying a wedge was the thought that the focusser assembly and hence any grease would get warm and melt dont know if anyone has found this a problem in practice.

Alan

As long as your scope is in collimation and the focuser axis is aligned with the objective lens (it would need to be quite a way off) I don't seen how the light cone would come into contact with any of the focuser internals

I've not noticed any warming of anything other than the wedge heat sink.

[xtreemchaos]

hi Alan ,i havent noticed my focusers getting warm, the heat is focused on the wedges  surface and the heat gos straight through to the heatsink, i guess if a focuser was out of alinement it might happen.charl.  sorry john ive just said the same

[Merlin66]

I've emailed Takahashi and William Optics re Herschel Wedge.

let's hope they reply.

 

[Alien 13]

4 hours ago, John said:

As long as your scope is in collimation and the focuser axis is aligned with the objective lens (it would need to be quite a way off) I don't seen how the light cone would come into contact with any of the focuser internals

I've not noticed any warming of anything other than the wedge heat sink.

I had in mind the situation where you had been observing and had nipped inside for a cuppa and the sun had moved off axis putting the semi focused image of the Sun against the tube.

Alan

[Merlin66]

Alan,

You should NEVER leave a telescope pointed towards the Sun unattended.....never!

The dangers to anyone in the vicinity is obvious......don't do it!!

 

[Merlin66]

I've just received emails from Takahashi and Williams Optics confirming that their refractors are safe to use with the Herschel wedge.

 

[Moonshane]

Cheers Ken - you obviously have influence! 

[jam1e1]

going to buy a 1.25" wedge to use with apm152 - ive done solar with the SWED80 and baader film, seeing as a lot of people report improved quality with wedge looks like a good investment

Ive emailed APM distributor they say the 152 is fine with 1.25" and no need for 2" wedge (astrograph.net)

 

[Merlin66]

Any confirmation from Vixen and others?

sounds like all/ any refractors are good to go with the Herschel Wedge.....