Combo Quark with 4X powermate problem ?

[Clifff]

After a lot of reading and a Combo Quark came up used so I took the plunge and got it along with a Aperture filter for a 8"SCT

Only tried it on a Tak 76mm F7.5 and a ES80ED F6 refractor but seems a ES X2 works fine but can't find focus on the Sun with the 4X Powermate

The Powermate works fine looking at a tree and appears to only have about 13mm extra out focus compared to the 2X but on the Sun no go.

Could this be just the seeing or something else.?

I was impressed by the detail I get with a 2X focal extender but the 4X should be way better. Only had a Coronado PST previously.

Appreciate any ideas , yet to try it on a reflector style scope.

Cliff

 

 

[vlaiv]

13 minutes ago, Clifff said:

, yet to try it on a reflector style scope.

Not sure that is good idea - at least not without full ERF at the front of the scope.

What eyepiece have you used with x4 telecentric lens? If you think that you have "too much magnification" - use longer FL eyepiece, like 20mm or 25mm plossl? Maybe it just won't reach focus properly because of focus shift?

If you want to check effect of F/ratio on the view and you don't have x4 telecentric lens (you can't get x4 powermate to work for any reason) - use x2 ES focal extender and aperture mask.

You have 80mm F/6 frac. With 40mm aperture mask, you'll turn that into F/12 instrument and then with x2 ES focal extender into F/24. That should be good for combo and still allow you to see full disk (focal length will be only 960mm).

Aperture mask size in combination with x2 ES will create range of F/ratios - so you can choose which one you find the best - F/15, F/18, F/20 or F/24 for example.

[Clifff]

Thanks for the ideas, yes maybe F7.5 with a 4X Powermate is pushing it ?  The eyepieces I tried are my Meade 26,32,40mm Plossils.

I have one of those Daystar offset filters for the front of a  8" SCT should work with my Vixen VMC200L F9 it fits.

Good idea using an Aperture Mask  .  Though I thought larger aperture more details?

Only had the Combo Quark a couple of days so lots to try.

 

[Clifff]

The image is using a ZWO 174MM , a Tak F7.5 scope and a ES X2 .

[vlaiv]

9 hours ago, Clifff said:

Thanks for the ideas, yes maybe F7.5 with a 4X Powermate is pushing it ?  The eyepieces I tried are my Meade 26,32,40mm Plossils.

No, you should be fine with those eyepieces.

76mm f/7.5 has 570mm of focal length. With x4 powermate that will be 2280mm of effective FL. With 26mm EP you'll get ~ x87.7. That is well within range of 76mm scope.

You need to check few things, in order to see what might be going on with x4 powermate:

1. Order of elements

You need to place telecentric lens before your quark, so order should be: Scope, some sort of IR/UV filter (you don't need that if you use front ERF) - it can be simple UV/IR cut filter or maybe ~30mm Ha filter for night use. Next is telecentric lens and then quark and eyepiece.

2. Optimum working distance for x4 powermate. Although telecentric lens should not vary magnification with distance - they sometimes do. Since you can have significant optical distance between powermate and eyepiece - magnification factor can change.

According to this chart, x4 powermate does not change significantly (up to x4.5 at 100mm separation where best position is around 25-30mm).

3. Focus position of your telescope.

Barlow elements shift focus further out, but powermate does not. This means that you could be running out of backfocus with all those elements in optical train.

If you are using diagonal - try loosing that and seeing if you can reach focus that way. Also, where is best focus position that you can achieve? Is it at point where your focuser is fully racked in? If so - you might need a bit more "in travel" than you have with that scope.

9 hours ago, Clifff said:

Good idea using an Aperture Mask  .  Though I thought larger aperture more details?

Yes, aperture mask will reduce visible detail, however, it works fine if you want to observe at low magnifications - like full disk viewing. If 40mm or 50mm dedicated solar scopes show nice image of full disk - same will be true for 40 or 50mm aperture mask and quark combo.

9 hours ago, Clifff said:

The image is using a ZWO 174MM , a Tak F7.5 scope and a ES X2 .

Critical sampling optimum F/ratio depends on wavelength and pixel size. In regular planetary imaging you have a choice since you are imaging whole range of wavelengths (between 400 and 700nm) - and you can aim for particular part of spectrum (I usually advise to go for 500nm in that case) - but here there is single wavelength - 656nm and you should aim for that.

Optimum F/ratio is F/17.9, that means you want F/6 scope and x3 telecentric lens for optimal working conditions with ASI174mm camera. F/15 that you used is not far from that, and for the time being - use that. Using x4 telecentric lens will give too high sampling rate and you'll be oversampling. Not sure if you want to do that (SNR loss due to oversampling).

[Rodd]

8 hours ago, vlaiv said:

No, you should be fine with those eyepieces.

Not to intrude--but this caught my eye as I am considering a Quark.  It must be remembered that the Quark already has a 3x barlow (or something like that) as part of its design.  So if you stack the two types of quarks (are there 3 types now?)  and add a 4x powermate, I would think it would be well above what a smll scope, or seeing for that matter, could handle comfortably.    

[vlaiv]

2 minutes ago, Rodd said:

Not to intrude--but this caught my eye as I am considering a Quark.  It must be remembered that the Quark already has a 3x barlow (or something like that) as part of its design.  So if you stack the two types of quarks (are there 3 types now?)  and add a 4x powermate, I would think it would be well above what a smll scope, or seeing for that matter, could handle comfortably.    

Here we are discussing Combo quark - version without integrated telecentric lens - hence the talk about using additional telecentric lens.

Thing with Ha etalons is that ideally require collimated light beam - or at least very small incidence angles. Most work well with F/20-F/30 beams. That is why original quark has x4.3 telecentric lens and is recommended for F/7 scopes as 7 * 4.3 = 30.1 or ~ F/30.

Combo quark is made for F/15-F/20 scopes, but one can experiment with different speeds to see what results they get. One of ways you can change F/ratio of the scope is by adding telecentric (barlow like) element - that changes focal length. Another way to do it is by adding aperture stop and changing F/ratio of the telescope.

As far as imaging goes - we are not concerned about seeing as lucky imaging approach is utilized - it uses very short exposures - just few milliseconds and that freezes the seeing, then poor frames are discarded and best kept and stacked. With this type of imaging you want to optimize F/ratio with respect to pixel size used and wavelength imaged - in this case it is 656nm of Ha light.

Mind you - telecentric lens needs to be placed in front of etalon and not behind (if etalon is in converging beam - for front mounted etalons, no telecentric element is needed as light already arrives collimated).

[Rodd]

12 minutes ago, vlaiv said:

Here we are discussing Combo quark - version without integrated telecentric lens -

I was not aware they had this--thank you.  But with respect to seeing--if seeing is bad, it doesn't matter how short the exposures are--they will be bad.  That is why on poor nights, planetary imaging is impossible (good planetary imaging) - because seeing is just plain bad--there are no fluctuations to take advantage of.  

[vlaiv]

Just now, Rodd said:

I was not aware they had this--thank you.  But with respect to seeing--if seeing is bad, it doesn't matter how short the exposures are--they will be bad.  That is why on poor nights, planetary imaging is impossible (good planetary imaging) - because seeing is just plain bad--there are no fluctuations to take advantage of.  

It does not work quite like that.

When we say that seeing is bad - that means that integrated seeing is bad. One that is sum of individual distortions over period of time - usually 2 seconds if we talk about FWHM - or 30ms if we talk about visual seeing.

With lucky imaging, we use exposures that freeze that seeing, and meaning of "bad seeing" is a bit different than in regular imaging or visual. It is related to percent of subs we can keep. Good seeing means that we can keep say 20% or even 50% of frames from our recording. Average seeing means that we get to keep maybe 5% or 10%. In very poor seeing - we get to keep maybe 1-2%.

That does not mean that we can't take image, and that image will be much sharper than seeing suggests (like in general with lucky imaging - where we produce stunning results even in average seeing) - it just means that we won't be able to sharpen the image as much as we like because SNR will not be good enough when stacking 1-2% of subs.

 

[Rodd]

6 minutes ago, vlaiv said:

That does not mean that we can't take image, and that image will be much sharper than seeing suggests (like in general with lucky imaging - where we produce stunning results even in average seeing) - it just means that we won't be able to sharpen the image as much as we like because SNR will not be good enough when stacking 1-2% of subs.

I had done planetary and lunar imaging quite a bit.  there are nights that do not produce good (what I call good) images because seeing is bad--no matter how long a vid you take and what percentage you use.  I have shot 10 minute videos of the Moon, generating 20-30,000 subs and still--the results were poor.  It does work like that.  Seeing fluctuates over a very short time scale--when one uses lucky imaging, one is able to take a sub during that brief period of good seeing.  If you take enough of them and throw out the others--you have a good sharp image.  the problem arises when seeing is bad and there are no periods of really good seeing.  Can you still image, sure, but the results will be nowhere as good as on a night of very good seeing.

[vlaiv]

17 minutes ago, Rodd said:

  I have shot 10 minute videos of the Moon, generating 20-30,000 subs and still--the results were poor.

What was duration of your exposure?

10 minutes is 600s and for 30000 subs out of 600s - that is 50fps or 20ms duration of single sub.

You should really be talking about at last x4 as much subs (150-200fps) and 2-3ms exposure length on the moon

[Rodd]

3 minutes ago, vlaiv said:

What was duration of your exposure?

10 minutes is 600s and for 30000 subs out of 600s - that is 50fps or 20ms duration of single sub.

You should really be talking about at last x4 as much subs (150-200fps) and 2-3ms exposure length on the moon

I don't really know--the point was I took a 20 minute vid shooting at the fastest frame rate I could--30-40/sec...maybe 60/sec.   It was a long time ago.  My point is, there is an upper limit to what lucky imaging can provide--otherwise, everyone would take shots like Damien Peach takes.   He happens to image where seeing is exceptional.  If seeing wasn't important--he would not be famous.  Will lucky imaging AT ALL TIMES produce an image better than one could achieve with normal imaging....yes, most definitely.  But there is wide variation of results from night to night, because the best lucky imaging can do is still controlled by seeing.  

[Clifff]

17 hours ago, vlaiv said:

No, you should be fine with those eyepieces.

76mm f/7.5 has 570mm of focal length. With x4 powermate that will be 2280mm of effective FL. With 26mm EP you'll get ~ x87.7. That is well within range of 76mm scope.

* I thought that would not be a problem,  I did try my Baader IV Zoom and it seemed ok also with the ES2X 

17 hours ago, vlaiv said:

You need to check few things, in order to see what might be going on with x4 powermate:

1. Order of elements

You need to place telecentric lens before your quark, so order should be: Scope, some sort of IR/UV filter (you don't need that if you use front ERF) - it can be simple UV/IR cut filter or maybe ~30mm Ha filter for night use. Next is telecentric lens and then quark and eyepiece.

*Yes I have the correct sequence , tried both before and after the diagonal with the 4X. Have a UV/IR filter as the first element ERF

2. Optimum working distance for x4 powermate. Although telecentric lens should not vary magnification with distance - they sometimes do. Since you can have significant optical distance between powermate and eyepiece - magnification factor can change.

According to this chart, x4 powermate does not change significantly (up to x4.5 at 100mm separation where best position is around 25-30mm).

* Seems the Powermate is not so critical in placement as a Barlow. 

17 hours ago, vlaiv said:

3. Focus position of your telescope.

Barlow elements shift focus further out, but powermate does not. This means that you could be running out of backfocus with all those elements in optical train.

If you are using diagonal - try loosing that and seeing if you can reach focus that way. Also, where is best focus position that you can achieve? Is it at point where your focuser is fully racked in? If so - you might need a bit more "in travel" than you have with that scope.

* When I get some sunny skies raining here again. I'll try with out the diagonal. 

* With the 2X it is only about 10mm from being fully in for sharp focus. . I did a trial on a tree and it showed the 4X needed about 14mm extra out focus  though I didn't see a sharp focus when putting the focus 14mm back from where I had sharp focus with the 2X when replacing it with the 4X.

Yes, aperture mask will reduce visible detail, however, it works fine if you want to observe at low magnifications - like full disk viewing. If 40mm or 50mm dedicated solar scopes show nice image of full disk - same will be true for 40 or 50mm aperture mask and quark combo.

* May be reducing the aperture will reduce the intensity as at least with the 2X I can see little surface detail visually good sharp Proms though. Using the 174MM camera not a problem as I can control exposure easily.

17 hours ago, vlaiv said:

Critical sampling optimum F/ratio depends on wavelength and pixel size. In regular planetary imaging you have a choice since you are imaging whole range of wavelengths (between 400 and 700nm) - and you can aim for particular part of spectrum (I usually advise to go for 500nm in that case) - but here there is single wavelength - 656nm and you should aim for that.

Optimum F/ratio is F/17.9, that means you want F/6 scope and x3 telecentric lens for optimal working conditions with ASI174mm camera. F/15 that you used is not far from that, and for the time being - use that. Using x4 telecentric lens will give too high sampling rate and you'll be oversampling. Not sure if you want to do that (SNR loss due to oversampling).

* How did you calculate optimum F/ratio?. Sound like you are right with my current imaging it might be as good as I can get .

I have a FSQ106ED F5 scope but it has very limited focus travel and is a Petzval type , nervous about using that on Solar. Some say its ok others say you need a ERF which is really expensive. 

It would give around F20 with the 4X.

Really appreciate your suggestions. I can use the ES80ED F6 but the focuser assembly isn't the strongest. A lot of weight with the extenders etc.

[vlaiv]

5 hours ago, Clifff said:

* How did you calculate optimum F/ratio?.

It is derived from two things:

https://en.wikipedia.org/wiki/Spatial_cutoff_frequency

and

https://en.wikipedia.org/wiki/Nyquist–Shannon_sampling_theorem

In a nut shell - optical system acts as a low pass filter (blurs the image) and has a cutoff frequency, and sampling theorem states that you can perfectly reconstruct band limited signal if you sample it at twice highest frequency component.

 

[Clifff]

2 hours ago, vlaiv said:

It is derived from two things:

https://en.wikipedia.org/wiki/Spatial_cutoff_frequency

and

https://en.wikipedia.org/wiki/Nyquist–Shannon_sampling_theorem

In a nut shell - optical system acts as a low pass filter (blurs the image) and has a cutoff frequency, and sampling theorem states that you can perfectly reconstruct band limited signal if you sample it at twice highest frequency component.

 

Ok thanks, makes sense. 

I guess the next thing is to calculate or by trial an error the back focus with the 4X Powermate.

I have the ES 2" Diagonal (or without the diagonal) , Powermate 4X or ES2X , Combo Quark - eyepiece/camera.

 

[vlaiv]

9 minutes ago, Clifff said:

Ok thanks, makes sense. 

I guess the next thing is to calculate or by trial an error the back focus with the 4X Powermate.

I have the ES 2" Diagonal (or without the diagonal) , Powermate 4X or ES2X , Combo Quark - eyepiece/camera.

 

That is a lot of elements and I think that you don't have enough inward focuser travel for all of that.

Loose diagonal as a first step and see if you can focus properly with x4 Powermate.

[michael.h.f.wilkinson]

I briefly had a 4x Powermate for my Solar Spectrum filter. I needed to have a seriously long extension tube in the focuser of my 80 mm F/6 to reach focus, i.e. the focus travel outwards was not nearly enough. This is probably the reason you cannot reach focus. The Baader TZ-4 I have now have requires less. A 4x powermat eon an F/7.5 scope delivers an F/30 light cone, which is perfect for most etalons. I now use a Baader TZ-3 with my F/10 Tri-Band SCT. My ASI174MM is quite happy at that magnification (although it can take faster optics, like F/25).  The Baader TZ tele-centrics have an optimal rated back focus, which allows you to set the correct distance between rear element of the tele-centric, and image plane of the camera. Keeping that fixed, you then simply tweak the focuser until you reach focus. The same could be done with the powermate, but I do not know the optimal back focus distance.

[vlaiv]

5 minutes ago, michael.h.f.wilkinson said:

I briefly had a 4x Powermate for my Solar Spectrum filter. I needed to have a seriously long extension tube in the focuser of my 80 mm F/6 to reach focus, i.e. the focus travel outwards was not nearly enough. This is probably the reason you cannot reach focus. The Baader TZ-4 I have now have requires less. A 4x powermat eon an F/7.5 scope delivers an F/30 light cone, which is perfect for most etalons. I now use a Baader TZ-3 with my F/10 Tri-Band SCT. My ASI174MM is quite happy at that magnification (although it can take faster optics, like F/25).  The Baader TZ tele-centrics have an optimal rated back focus, which allows you to set the correct distance between rear element of the tele-centric, and image plane of the camera. Keeping that fixed, you then simply tweak the focuser until you reach focus. The same could be done with the powermate, but I do not know the optimal back focus distance.

From what I understand, Powermates should not extend focus point the way barlows do?

Even TV on their page on Powermates say:

Quote

The 2" Powermate™ fits all the way into 2" Star Diagonals, requiring minimal refocus compared to a 2" Barlow.

 

[michael.h.f.wilkinson]

13 minutes ago, vlaiv said:

From what I understand, Powermates should not extend focus point the way barlows do?

Even TV on their page on Powermates say:

 

Indeed, with a star diagonal you are fine, but without you need a huge extension tube. Star diagonals have a long optical path, after all (Amici prisms are worse). If you place the diagonal in the powermate, rather than the reverse, you are in trouble. The 2x teleXtender (I have the Meade version) doesn't really have an issue like this.

[Clifff]

On 24/08/2021 at 22:53, michael.h.f.wilkinson said:

Indeed, with a star diagonal you are fine, but without you need a huge extension tube. Star diagonals have a long optical path, after all (Amici prisms are worse). If you place the diagonal in the powermate, rather than the reverse, you are in trouble. The 2x teleXtender (I have the Meade version) doesn't really have an issue like this.

Interesting the Explore Scientific 2X Extender I have seems to work similar to your Meade. 

Looks like i might need another extension tube to use the 4X Powermate. 

[Clifff]

On 24/08/2021 at 21:32, vlaiv said:

That is a lot of elements and I think that you don't have enough inward focuser travel for all of that.

Loose diagonal as a first step and see if you can focus properly with x4 Powermate.

This is my setup : Still waiting for a clear day - typical except for one or two days its rained since I got the Combo Quark.

 

• Takahashi FC76DS 173mm Back Focus
• 63mm Focus Travel
• Baader Clicklock 31mm

 

• Combo Quark needs 67mm  rearward  or 99mm with SCT wedge.
•  
• ES Diagonal 50mm roughly added
•  
• ES 2X Extender ?
•  
• 4X Powermate ?

[vlaiv]

I'm slightly confused - you say ES diagonal? Is that 1.25" or 2" version?

I can't seem to find 1.25" version, and 2" version will not add 50mm. Shortest 2" diagonals add about 100-110mm of optical path.

173 - 31 = 142mm - that is longest optical path that will come to focus (racking out focuser just shortens that).

Let's say that

a) ES diagonal is 2" and has minimum optical path of 100mm

b) Powermate and ES Extender need 0mm optical path (they move focus point out the same amount as they are long so they don't change anything)

c) Combo Quark needs 67mm

100mm + 0mm + 67mm = 167mm, but you only have 142mm available (racking out focuser just shortens what you have available).

On the other hand:

Loosing diagonal would make this:

67mm + 63mm of focuser travel = 130mm still less than 142mm - you would not be able to reach focus in that configuration and would need some sort of extension as @michael.h.f.wilkinson pointed out.

Maybe best course of action would be to loose diagonal (at least for imaging) and use 30mm 2" extension tube in this configuration:

focuser -> click lock -> 2" 30mm extension -> Telecentric lens -> quark combo -> camera

For visual - get 1.25" diagonal instead and maybe ditch the click lock adapter and go with stock one. Most 1.25" have 70-80mm of optical path and then you'll have: 80mm + 67mm = 147mm.

[Clifff]

12 hours ago, vlaiv said:

I'm slightly confused - you say ES diagonal? Is that 1.25" or 2" version?

I can't seem to find 1.25" version, and 2" version will not add 50mm. Shortest 2" diagonals add about 100-110mm of optical path.

173 - 31 = 142mm - that is longest optical path that will come to focus (racking out focuser just shortens that).

Let's say that

a) ES diagonal is 2" and has minimum optical path of 100mm

b) Powermate and ES Extender need 0mm optical path (they move focus point out the same amount as they are long so they don't change anything)

c) Combo Quark needs 67mm

100mm + 0mm + 67mm = 167mm, but you only have 142mm available (racking out focuser just shortens what you have available).

On the other hand:

Loosing diagonal would make this:

67mm + 63mm of focuser travel = 130mm still less than 142mm - you would not be able to reach focus in that configuration and would need some sort of extension as @michael.h.f.wilkinson pointed out.

Maybe best course of action would be to loose diagonal (at least for imaging) and use 30mm 2" extension tube in this configuration:

focuser -> click lock -> 2" 30mm extension -> Telecentric lens -> quark combo -> camera

For visual - get 1.25" diagonal instead and maybe ditch the click lock adapter and go with stock one. Most 1.25" have 70-80mm of optical path and then you'll have: 80mm + 67mm = 147mm.

Yes you are right it is the ES 2" diagonal so at least a 100mm not 50mm 

I have no trouble reaching focus though the focuser is nearly all the way in with the ES2X.

I would rather image without the diagonal so a 2" ext makes sense. (I have a 35mm and a 70mm 2" extension here)

The only really good 1.25" diagonal I have is the Tak but thats a prism not mirror not sure that is ok with solar ? I would guess not.

I have an old Meade 1.25" but not really that solid with the extra weight. 

Going with the 1.25" diagonal would mean I can't use the Powermate or ES 2X as they are both 2" unless I put it before the diagonal.

Thanks again for all the suggestions/ideas

Cliff

 

[Clifff]

I think I have had a 'Eureka' moment I was putting the Powermate or ES2X as the first item after the focuser and without a diagonal couldn't find any focus.

Now i have the Extension tubes both 35mm and 70mm first then the Powermate 4X and currently a 40mm Plosil.

No trouble focusing on my tree now with either 2X or 4X . So i probably need another 2" extension to use the Quark . A long system !

Getting closer I think.

[Clifff]

Ok I have a question now i have the Powermate at the end of the system , if I add a diagonal either a Tak 1.25" prism or the ES 2" there is only about 3mm difference in focus position and 6mm respectively compared to straight through ?

I know its only optics but usually a diagonal adds 100mm or so as noted in above message from vlaiv