Lack of infocus with Baader Herschel wedge and Tak 76DS ?

[Clifff]

Been a while since we've had decent conditions here in Sydney,nice to see the Sun again.

Over 6months after ordering  I received my Baader herschel wedge impressive .

With either the original Tak accessories or my Clicklock holder on the scope I can just reach focus with the focuser all the way in but can't adjust through the focus point, Thought a barlow on the eyepiece might improve things no change. Yet to try a camera probably my 174mm. 

Tried with a 40mm Plossil and my Baader Zoom eyepieces.

Can I put a 2X extender before the wedge to fix backfocus/infocus.  I use a 2x or 4x with my combo quark .

Appreciate any ideas 

Cliff

[Highburymark]

You can’t put any barlow or extender before the wedge itself - it would likely shatter very quickly. Essential that any additional filters or lenses are only added after the wedge.  
A barlow or GPC should help you reach focus more easily. I use a binoviewer with Baader GPCs. It’s also possible to save a few mms (if you’re binoviewing) by removing the 2” clicklock and attaching the binoviewer directly to the wedge - you’ll need a couple of extra Baader T2 adapters for this. SGL member Stu has shown this in another thread recently.

[vineyard]

Im guessing if its a Baader cool wedge its 2"?  Those have longer lightpath.  For a 76mm aperture, a 1.25" Herschel prism would be sufficient & would have shorter lightpath I suspect so that might give you the infocus you're looking for?  That's what I found between the Lunt 2" & 1.25".

Although since you waited 6m for your cool wedge that's probably not what you want to hear!

[Stu]

2 minutes ago, vineyard said:

Im guessing if its a Baader cool wedge its 2"?  Those have longer lightpath.  For a 76mm aperture, a 1.25" Herschel prism would be sufficient & would have shorter lightpath I suspect so that might give you the infocus you're looking for?  That's what I found between the Lunt 2" & 1.25".

Although since you waited 6m for your cool wedge that's probably not what you want to hear!

I’ve not tried vs the 2” Lunt Wedge, but vs the 1.25” the CoolWedge certainly has an advantage in detail/sharpness at high power.

@Clifff, this thread shows how I shortened the light path. Not sure it would work unless connecting directly via T2 but it may be of interest.

 

[Paz]

5 hours ago, Stu said:

I’ve not tried vs the 2” Lunt Wedge, but vs the 1.25” the CoolWedge certainly has an advantage in detail/sharpness at high power.

@Clifff

That is interesting, is there a systematic reason why a 2" wedge would show more detail than a 1.25" or do you think it's just the way it happened to be with the particular wedges you were comparing?

[Stu]

1 hour ago, Paz said:

7 hours ago, Stu said:

I’ve not tried vs the 2” Lunt Wedge, but vs the 1.25” the CoolWedge certainly has an advantage in detail/sharpness at high power.

@Clifff

That is interesting, is there a systematic reason why a 2" wedge would show more detail than a 1.25" or do you think it's just the way it happened to be with the particular wedges you were comparing?

I don’t think it is related to the size, my assumption is that the prism in the CoolWedge is better/more accurately ground, although there aren’t any specs around that prove that as far as I’m aware.

[Clifff]

Thanks for all the comments ,

and no a 2X Focal extender will not get damaged if in the light path as i use it or a 4X powermate in front of my Combo Quark all the time. Whats the difference if i put the Hershel Wedge where the Quark is ?

Maybe I should have got a 1.25" now looking back but I thought a 2" is future proof . I did order the parts mentioned in the Baader manual  a t2 adapter and a 1.25" t2 Clicklock which will reduce the infocus needed won't have them for a couple weeks.

One of the guys on cloudy nights actually uses the same ES 2X Focal extender with his 2" APM Herschel wedge. 

Just a comment I don't see how glass could build up heat unless it was reflected in-between elements, the Front Objective is Glass doublet in my case, My 4X Powermate and ES2X are also 2" Glass no sign of damage anywhere after extended Ha imaging. . Maybe if Plastic parts where used in the focusser ?

I will update when I try a few things

Cliff

 

 

 

 

[PeterW]

Wedges give much better views than the other options but need careful use and filtration to use safely. I have an old cheap 1.25” INTES model and it works fine. The backfocus issue with 2” models is a little known one, as you’re working at quite high power on the sun there is no need for 2”, but manufacturers don’t seem to care. The ND filter will probably warm Up slightly (never tested), but it wouldn’t pose a problem. Always check things before you use them though.

 

Peter

[Highburymark]

15 hours ago, Clifff said:

Thanks for all the comments ,

and no a 2X Focal extender will not get damaged if in the light path as i use it or a 4X powermate in front of my Combo Quark all the time. Whats the difference if i put the Hershel Wedge where the Quark is ?

Maybe I should have got a 1.25" now looking back but I thought a 2" is future proof . I did order the parts mentioned in the Baader manual  a t2 adapter and a 1.25" t2 Clicklock which will reduce the infocus needed won't have them for a couple weeks.

One of the guys on cloudy nights actually uses the same ES 2X Focal extender with his 2" APM Herschel wedge. 

Just a comment I don't see how glass could build up heat unless it was reflected in-between elements, the Front Objective is Glass doublet in my case, My 4X Powermate and ES2X are also 2" Glass no sign of damage anywhere after extended Ha imaging. . Maybe if Plastic parts where used in the focusser ?

I will update when I try a few things

Cliff

 

 

 

 

I’d missed that you were using a 76mm scope tbh. Most of my WL observing has been with 100mm and 120mm fracs, and I wouldn’t risk an expensive Powermate or barlow with those ahead of the wedge. But interesting to hear you haven’t had any problems with a smaller frac.
There’s a lot of conflicting advice out there about using barlows for solar. Including among manufacturers. Altair, for example, advise no barlows or extenders before the wedge on any scope. Agena too. I’ve just been corresponding with Baader about using an extender to slow down the system with a Solar Spectrum Ha filter - and they said I shouldn’t use the extender ahead of the etalon - even after a full D-ERF over the objective….. because even a D-ERF passes a significant amount of heat.  They are probably being ultra cautious. But I’m cautious as a result.

Edited May 4, 2022 by Highburymark

[Stu]

1 hour ago, Highburymark said:

I’d missed that you were using a 76mm scope tbh. Most of my WL observing has been with 100mm and 120mm fracs, and I wouldn’t risk an expensive Powermate or barlow with those ahead of the wedge. But interesting to hear you haven’t had any problems with a smaller frac.
There’s a lot of conflicting advice out there about using barlows for solar. Including among manufacturers. Altair, for example, advise no barlows or extenders before the wedge on any scope. Agena too. I’ve just been corresponding with Baader about using an extender to slow down the system with a Solar Spectrum Ha filter - and they said I shouldn’t use the extender ahead of the etalon - even after a full D-ERF over the objective….. because even a D-ERF passes a significant amount of heat.  They are probably being ultra cautious. But I’m cautious as a result.

It’s sometimes hard to know what is ok and what is not. It has often been said that you shouldn’t use petzval scopes with Herschel Wedges, but @Merlin66 has confirmed with Televue and I think some other manufacturers that it’s actually ok. I still haven’t braved my Genesis though!

I specifically haven’t used my FC76DCU in Q mode with a wedge ie with the extender module fitted, in case there is any heat build up in the tube or the extender lens.

[Highburymark]

10 hours ago, Stu said:

It’s sometimes hard to know what is ok and what is not. It has often been said that you shouldn’t use petzval scopes with Herschel Wedges, but @Merlin66 has confirmed with Televue and I think some other manufacturers that it’s actually ok. I still haven’t braved my Genesis though!

I specifically haven’t used my FC76DCU in Q mode with a wedge ie with the extender module fitted, in case there is any heat build up in the tube or the extender lens.

Baader said one of the problems was the cement used in many barlows is sensitive to heat and breaks down if used before the solar filter. Always worth posting these warnings so newcomers to solar are aware. Interestingly, the AP Barcon we use Stu doesn’t have any cement keeping the lenses in place. So I presume the Barcon (and probably AP Baradv) are safer. Anyway, looks like it’s not a problem for the OP. Don’t want to divert from the main issue of reaching focus.

[Clifff]

A followup after using the Baader Wedge with my ES 2X and a 2" ext tube in front of the wedge I reached focus on my 76DS no problem , no longer get a full disk but works fine.

Nice sharp images both visually and with my 174mm. Seeing was just ok.

Zero heating even after several hours . 

 

small sample.I guess you would call first light!

Stacked but not processed in Autostakkert

Edited May 7, 2022 by Clifff
update