10 replies to this topic

[PaulEK]

I recently got a 100mm f/8 achromat in a nice metal cell, and want to build a scope around it for use with a DayStar Quark. I also have a decent 2-inch, 2-speed Crayford focuser. I don't yet have a Quark, and have never used one. I'd be grateful for advice. I plan to use the scope only for solar, but would like to use it for both viewing and imaging, if possible.

 

I built a 'telescope on a stick' today, so I can figure the length of tube I need for this scope (and three others I'm building). What should I know for planning the Quark's use in the train of the scope? Can I imagine it like, say, an eyepiece with a given focal length, and use a comparable eyepiece to plan the length of the tube? If so, what would the focal length of that eyepiece be? Or am I thinking of this incorrectly?

 

By the way, if it makes any difference, I have a 0.8x focal reducer, and already have a Baader IR/UV cut filter.

 

I don't have a camera yet, so any suggestions for one would be appreciated, too. I have lots of other refractors -- 80mm f/11 and f/15; 90mm f/10; 100mm f/4.5, f/6.3 (apo) and f/10; 115mm, f/4.5; and 150mm f/10 -- so a lot of choices. This 100mm f/8 will be the only one dedicated exclusively to solar, but a camera to use for both solar and other astro imaging, both wide and narrow-field, would be best. I've been away from camera development for a few years. Oh, and our observatory has a 10-inch SCT and 14-inch f/4.5 reflector.

 

I'll be using this scope and camera for myself, but it will also be used by other club members, and for public outreach.  

[msl615]

Of the refractors listed, only the 100mm f4.5 will be wide enough to fit in the entire disk of the sun with a Quark.  You have to have a focal length of less than about 460mm to get in an entire disk.  Quark recommends, and I concur, that TV plossls at 40,32 and 25mm are just about the entire set you would need.  There are superb solar fans on this site, and they can weigh in with tons of great ideas, solutions and ideas, far better than I can.  But, I thought I would at least get the conversation started. 

 

Mike

[FlankerOneTwo]

The Quark requires f/30 at the etalon to function properly - the stock Quark is designed to work with an f/7 scope and has a 4.2x Barlow built into it. If you are using a 4/3" format camera such as an ASI1600, this will not fit the full disk. You can add a 0.5x reducer after the Quark, this will fit the disk on the ASI1600, barely.

 

This is not the ideal camera for solar imaging however, because the frame rates at full frame are quite slow. Solar imaging is similar to planetary in that the technique consists of very high frame rate acquisition in order to freeze the seeing (100fps or so is not uncommon). IMX174 based cameras are very commonly used, the frame size is quite a bit smaller than the ASI1600. Even with the 0.5x reducer you will get not quite 1/2 a full disk.

[donniesoprano]

The Quark requires f/30 at the etalon to function properly....

 

I think you meant ‘optimally,’ as the Quark still works just fine at other f ratios above and below f/30.  For example, mine operates at f/25.2 quite well.

 

I’m not trying to nitpick, but I do feel it’s important that the information is accurate for the OP and anyone else who gets info from this thread.

 

ds

[FlankerOneTwo]

Thanks for the clarification. "Properly" as in FWHM bandpass within spec - which admittedly for the Quark is not specifically stated, but appear to range anywhere from 0.3A to 0.7A or so from what I've heard, depending on specific example. Daystar state f/4 to f/7 will work for the standard Quark design spec (thus f/16.8 - f/29.4 after the barlow), however they recommend at least f/30 at the etalon for their products where the FWHM is specifically guaranteed such as the Quantum. The Quark is of the same construction (mica spaced Fabry-Perot etalon). Lower f ratios will work and will have a brighter image, but less contrast. Higher f ratios will have better contrast, but a dimmer view. So what one uses depends on ones expectations and requirements.

[MalVeauX]

Heya,

 

There's nothing special to building your ATM refractor with respect to solar, and especially with the Quark in mind.

 

Note, there are two Quarks to consider (out of 3; ignore the prominence model). The standard Quark (with an internal 4.2x telecentric amplifier which controls the focal-ratio delivered to the etalon and effects total effective focal length0 and the Quark combo (this model lacks the internal amplifier, so you would have to provide one to control the focal-ratio delivered to the etalon). The combo unit is interesting because you get a little more control with it, but it will ultimately cost more because you still need to use a telecentric amplifier in front of it (such as a true telecentric from Baader, costly, or a non-true telecentric such as a powermate). Anyhow just be aware of the two. The standard Quark is simple and works out of the box and will cost less. Most use it. Just keep in mind the 4.2x telecentric amplifier in it, this makes it a lot more challenging to view/image full discs with larger telescopes.

 

If doing visual, you will get a full disc FOV out of a standard Quark with a 400mm focal length telescope. 

 

If doing imaging, you will not get a full disc FOV out of any standard telescope frankly. Consider the Quark to be a high magnification, narrow field of view device when it comes to imaging. The goal being high resolution, large aperture visual/imaging. If you want more full disc FOV imaging/visual, consider a different option (like a PST or Lunt 50mm or SolarMax 60).

 

Your ATM refractor will not need any special consideration for focus and distance, you can build your refractor as a standard refractor.

 

A truss body may be ideal or open body design could be ideal for your tube, to allow tube currents to be low or non-existant, and to allow for easier thermal blocking. A Quark will work with just a 2" UV/IR filter on the focuser's tube with apertures like 100mm that you are considering. So you don't need any additional ERF in this design. But if you ever did you have more options with an open tube to avoid needing a full aperture front mounted ERF (greater than 100mm total), which are expensive, but are also more ideal. Anyhow, worth exploring.

 

A 100mm F8 is an excellent configuration for high resolution Quark use.

 

Camera wise, you'll want big fat pixels and a focal reducer. It's very common with this setup to use the ASI174MM or similar camera with that sensor (big 5.86um pixels) and then a 0.5x focal reducer to control scale delivered to the camera for good imaging.

 

Very best,

[BYoesle]

Anyone contemplating purchase of a Quark or any other near-the-focus etalon system from DayStar or Solar Spectrum should first familiarize themselves with how these filters work and are affected by the focal ratio ("instrument angles") presented to the etalon.

 

Christian Viladrich has done an excellent analysis:

 

Lessons learned from these simulations on mica-spaced Fabry-Perot etalons:

 

In order to benefit from the full performance of mica-spaced F-P etalons, the following requirements are to be met:

 

a) Use of a true telecentric lens system (such as Baader TZ or Beloptik). So called "telecentric Barlow lenses" are not telecentric and will give results of lower quality. The good news is that true telecentric lens systems give good performance, even when used at a focal length different to their designed focal length (within some limits ...)

 

b) Check out the the squareness of the F-P etalons to the optical axis. In other words, there should be no compromise on the mechanical set-up. As a rule of thumb the maximum allowance for the tilt is 0.1°.

It is a very easy to check out the squareness of the F-P etalon by auto-collimation:

 

- Place yourself at a few meters from the objective of your refractor.

- You should see : the circle of the objective, the cercle of the etalon, and ... the reflection of your eye on the etalon.

- The reflection of your eye should be centered on the image of the etalon and on the objective.

 

Otherwise you should arrange the mechanical set-up.

 

c) The longer the focal ratio the better the performances are. F/D 30 seems to be a good starting point.

[PaulEK]

Thanks for the helpful responses! I knew some of these points, but several are new to me.

 

I'm a bit confused about some things.

 

1) So the Quark does not interfere with the focal train of the scope? I mean, by placing it between the objective and eyepiece, I do not need to take its physical length into consideration? I plan to mount the objective at one end of my 'telescope on a stick' and place the focuser on the other end. Then I'll aim at something far away, and use a variety of eyepieces of varying focal lengths, as well as cameras and diagonals to figure out how long to make the tube. I thought I'd need to consider the Quark's length as part of that train.

 

2) About telecentrics: does the TV Powermate come close enough? I already have a 5x 1.25-inch Powermate. If it is acceptable, would a Combo Quark make sense? (And if it is missing something the 'regular' Quark has, why is it called the 'Combo'?)

 

I just got my March, 2019, Sky & Telescope, and it has a write-up about the DayStar Scout 60C. It only costs $100 more than the Quark on its own. Would it make sense to get this? According to the article, and this page at DayStar's site, says it includes a Quark that can be used in other scopes. I'm not sure I see an advantage, since I have plenty of scopes already, other than that it is a small, complete unit that might be good for outreach use. The 60mm f/3.75 (225mm focal length) scope is smaller than my Lumicon 80mm f/3.75 (300mm FL) finder.

[FlankerOneTwo]

Not sure what you mean by "interfere with the focal train". The Quark is designed to be used between the eyepiece and the diagonal of a normally functioning scope. As long as you have adequate length and focuser travel for the scope to function and focus with a range of eyepieces in the absence of the Quark you shouldn't have an issue. If you image straight through you may need an extension to make up the path length of the diagonal, no big deal.

Re: PowerMates, it's a matter of degree. The more parallel the beam, the better performance you will get from the Quark. Barlow OK, PowerMate better, Baader TZ best. I've switched to the TZ-3 for my f/10 SCT and the TZ-4 for my refractor.

 

It's called the Combo Quark because the different nosepieces allow it to be used either on axis (refractor, full aperture SCT / Mak with appropriate ERF), or 2 deg off axis with a subaperture ERF on an SCT or Mak. The standard Quark only has a straight through nosepiece and cannot be used in an angled off axis application.

[MalVeauX]

Thanks for the helpful responses! I knew some of these points, but several are new to me.

 

I'm a bit confused about some things.

 

1) So the Quark does not interfere with the focal train of the scope? I mean, by placing it between the objective and eyepiece, I do not need to take its physical length into consideration? I plan to mount the objective at one end of my 'telescope on a stick' and place the focuser on the other end. Then I'll aim at something far away, and use a variety of eyepieces of varying focal lengths, as well as cameras and diagonals to figure out how long to make the tube. I thought I'd need to consider the Quark's length as part of that train.

 

2) About telecentrics: does the TV Powermate come close enough? I already have a 5x 1.25-inch Powermate. If it is acceptable, would a Combo Quark make sense? (And if it is missing something the 'regular' Quark has, why is it called the 'Combo'?)

 

I just got my March, 2019, Sky & Telescope, and it has a write-up about the DayStar Scout 60C. It only costs $100 more than the Quark on its own. Would it make sense to get this? According to the article, and this page at DayStar's site, says it includes a Quark that can be used in other scopes. I'm not sure I see an advantage, since I have plenty of scopes already, other than that it is a small, complete unit that might be good for outreach use. The 60mm f/3.75 (225mm focal length) scope is smaller than my Lumicon 80mm f/3.75 (300mm FL) finder.

Heya,

 

1) The Quark goes into the train just like anything else does. Think of it like a big 4.2x telecentric amplifier that happens to filter things down to 6562.8A and handles thermal load from the sun while it's at it. So you put a 2" UV/IR block filter on the nose of your diagonal. Put the Quark in with it's 2" skirt. Put your eyepiece in the Quark. Find focus just like you were doing visually before. Same thing if you replace the eyepiece with a camera nose. It doesn't require any changes to your scope.

 

2) The TV Powermate isn't a true telecentric. Baader has a true telecentric. They're costly. The combo Quark exists so that you can control the focal-ratio more specifically and has a larger blocking filter if I recall (?), which makes it useful for other telescope designs like SCT/Mak, etc, with long focal ratios. They can totally be used on refractors the same way. Lots of people use 2x, 2.5x powermates, etc, on them with long focal ratio scope designs. Most of those scopes also need full aperture ERFs. The Quarks can only handle refractor designs up to 150mm aperture without a full aperture ERF. The design of the SCT/Mak/Reflector doesn't work this way and you must use a full aperture ERF (or sub-aperture, but masked over the entire aperture of the scope). Those designs would build heat unlike a refractor. You really don't need the combo. It's just another way of doing things, which costs more, but has more potential versatility. For simplicity the standard Quark is the way to go.

 

I wouldn't pay extra money for their tiny achromatic refractor with a Quark jammed in it. I wouldn't get any of the Daystar telescopes at all. The whole point is being able to use it on any scope you want.

 

Also, note, you can always mask aperture on  your scopes to control the focal-ratio to get to whatever you want it to be at the end.

 

Very best,

[PaulEK]

Thanks again! I think I have enough to go on, and I just sold another of the things I had on eBay to raise the funds needed for buying the Quark. If the temperature for the next few days was not well below 0 F (weather with or without the windchill from the 30 mph gusts), I'd get out there and measure the tube length I need.