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H-alpha Zeiss APQ 130

Posted: Tue Sep 26, 2017 3:25 am
by Christopher
Way back in 2007 while attending NEAF, I had the pleasure of looking through a Zeus APQ 130 that was set-up with a Coronado 90mm etalon. The view was unforgettable. At the time I owned a Solarmax 40 so I had some perspective on the h-alpha solar observing experience. Additionally, there were other comparable scopes there (large APs and the like). The Zeiss was simply the standout. I subsequently was both determined and fortunate enough to acquire an APQ 130 of my own. That scope rekindled my enthusiasm for visual astronomy and I've never looked back. I've often thought about setting it up for h-alpha solar viewing. Needless to say, much has changed since 2007 in the world of h-alpha solar. My question is what sort of set-up would you recommend in conjunction with this scope (low end $ to high end $$$)? Is there a disadvantage to using a fluorite lens to view light in h-alpha?

Thanks for your interest in my questions.


Re: H-alpha Zeiss APQ 130

Posted: Tue Sep 26, 2017 12:28 pm
by Montana
Hello Christopher, if your telescope is anything like my TEC140 then I recommend a Solarscope front mounted etalon for the best quality (expensive though). I tried a rear mounted Quark and the difference was night and day. Probably a Solar Spectrum rear mounted would be a lot better than the Quark, but for visual I would have the Solarscope any day. There are plenty of choices though, the Lunt are good, even a PST modification could work for you. The decision is yours really.

Re: H-alpha Zeiss APQ 130

Posted: Wed Sep 27, 2017 5:11 pm
by Christopher
Hi Alexandra,
Thank you for the reply and advice. I vaguely recall Solarscope (hailing from the Isle of Man) as being at the apex of consumer etalons, a spot they appear to still occupy. Unfortunately, it is an investment I'm not yet ready to make. I'm thinking I may opt for a rear mounted option at this point in order to get a foot back in the door of h-alpha solar that enables me to use the quality and aperture of the APQ. It might be nice to have something flexible enough to work with both the APQ and my MiniBorg (45ED) thus having a grab and go option as well.

Anyone have any thoughts on configurations providing this level of flexibility?

On a separate note, congratulations on your APOTY awards - fantastic work! Also admire your eclipse corona photos as well. The prominences are well incorporated. I've worked on similar compositions for the 2006 Egypt elcipse. For this one I mainly focused on the experience and the science (shadow bands and temperature monitoring). I was in TN for totality.


Re: H-alpha Zeiss APQ 130

Posted: Wed Sep 27, 2017 8:15 pm
by Montana
Thanks Christopher, the solar eclipse was an experience of a life time I think :)

If you want rear mounted I would go for good quality, I would buy a Solar Spectrum, I think there is a thread on here (this section) explaining all the combinations by the maker viewtopic.php?f=10&t=23035


Re: H-alpha Zeiss APQ 130

Posted: Thu Sep 28, 2017 5:01 am
by marktownley
You will need a full aperture DERF filter if you are going to use a rear mounted etalon Christopher.

Re: H-alpha Zeiss APQ 130

Posted: Thu Sep 28, 2017 6:31 am
by Carbon60
A warm welcome, Christopher.

I'm confident you'll find on this forum all the answers you're looking for.


Re: H-alpha Zeiss APQ 130

Posted: Thu Sep 28, 2017 3:23 pm
by Christopher
Thanks Stu. I'm very happy to have discovered it several days ago and have been pouring over it late in the evenings ever since :) . Wonderful resource!

Hi Mark,
Yes, I had come to that sobering realization whilst perusing Daystar's website and the fact that I am probably looking at another $800 to $1,000 for that component. I"m assuming the most common approach with refractors fitted with dew shields is to size the DERF ring to mount on the outside of the dew shield - as opposed to some sort of direct contact with the objective assembly itself (APQ objectives are not inside threaded). True? Looks like Baader and Daystar both offer similar configuration options and prices. Are there others?


Re: H-alpha Zeiss APQ 130

Posted: Fri Sep 29, 2017 9:32 am
by marktownley
The Baader DERF would be my choice over the Daystar equivalent...

It may be worth your while contacting Rupert at Astrograph, he deals with high spec solutions for quality equipment ... Categories

Solar Grab Bag

Posted: Sun Nov 05, 2017 2:08 am
by Christopher
This week I had the good fortune of running into a solar grab bag of sorts. While still focused on equipping the APQ for high quality H-alpha I ran into a very interesting pre-owned bundle of gear containing at least one of the components needed - the full aperture (130mm) mounted ERF. But there was more - much more. A 100mm f/30 custom built Daystar scope, .6A T-scanner, and a Baader Herschel Wedge. There’s also a telecentric Barlow made by Astro-physics for their Starfire 130 EDT (might work with the APQ). All at a bundle price I could not refuse. Of course, the sun is nowhere to be found in the forecast :lol: but I hope to try things out in the next week or so. The Daystar scope came with handwritten notes presumably taken at the time of order which state it’s the first custom H-alpha scope built by Del Woods for a customer (circa 1989). The gear was in storage for at least 20 years. I still intend to acquire a Solar Spectrum 0.5A filter but this adds an interesting twist while moving things along a bit don’t you think? :P
Daystar 100mm f/30 with 0.6A T-scanner
A8FB224E-0A2E-4FF3-9040-46292F42CE64.jpeg (1.82 MiB) Viewed 1679 times
Baader Hershel Wedge on Zeiss APQ130
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130mm ERF on Zeiss APQ130
227D0193-E611-4C1A-81BD-0DE7F379E21E.jpeg (1.98 MiB) Viewed 1679 times
Double barrel solar power
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FC1D4625-6602-4E81-A40E-040BBC73948D.jpeg (1.32 MiB) Viewed 1679 times
Daystar T-scanner
20B5B9AE-92E9-409E-94E3-CCFE51FD698D.jpeg (1.15 MiB) Viewed 1679 times

Re: H-alpha Zeiss APQ 130

Posted: Sun Nov 05, 2017 11:01 am
by marktownley
A cool setup there Christopher!

Re: H-alpha Zeiss APQ 130

Posted: Sun Nov 05, 2017 7:33 pm
by Christopher
Thanks Mark. I’m anxious to get out and work out all the plumbing.

Re: H-alpha Zeiss APQ 130

Posted: Sun Nov 05, 2017 9:21 pm
by Bob Yoesle
Hi Christopher,

There is no advantage to using a fluorite refractor for H alpha, and if were me, I NEVER would. While this can be a "heated" topic, fluorite has a very high coefficient of thermal expansion. Any IR will almost certainly deform the lens at least, and may present a cracking issue at worst. This is compounded by the ERF. The 130 mm ERF (and the 100 mm f15 objective) is a relatively simple "red glass" RG630 UV filter, and has no IR blocking whatsoever. So I wouldn't risk such a delicate and expensive objective to the RG630 ERF. Obviously this also would apply to use for WL use with a Herschel wedge. Of course you could take your chances, but I'd be sure to have a policy rider on your home insurance for a "just in case" scenario.

This IR can also lead to early failure of the T-scanner blockers themselves at that aperture. Replace the ERF with a Baader, BelOptik, or Lunt ERF, all of which will block IR in addition to UV. Or you could add the BelOptick UV/IR on KG3 filter to the T-scanner, or another high-quality IR/UV blocking filter from Baader, Astronomik, etc.

The AsroPhysics "telecentirc" barlow is just the same as the TeleVue Pwermate barlows - neither are true telecentric lens systems. Here the Baader or BelOptiK telecentrics will be a better solution. I could never get either my Astrophysics of TeleVue "telecentric" systems to give me very good contrast uniformity with my DayStar filter. It might be OK with the 100 mm f15, but likely will be unsatisfactory with a shorter FL/FR scope.

See Christian Viladrich's excellent treatises on mica etalons and telecentircs: ... lar/FP.htm

The T-scanner is likely the only really useful component, IF it works in your range of temperatures. These are designed for a specific range of ambient temperatures. The etalon is made to be a bit above the H alpha line, and tilting it blue-shifts it on band. However, if it is too high at your ambient temps, it will need too much tilting and could develop banding. Since the filter doesn't state the tmep. ranage, you may not be able to use it at times.

There is a reason the 90 mm front etalon impressed you - front mounted etalons offer the best overall performance for a given aperture, as there are no increased field angles or instrument angles presented to the etalon. The internal and rear mounted filter systems have a harder time due to these impediments. However, for apertures above 100 mm, there are no other reasonable choices. You are then left to optimize the internal or rear filter system as much as possible.

If you are interested in a front mounted filter system, I would recommend filters that incorporate spacers in the aperture. My experience with the 100 mm SolarScope filters is that while they are exquisitely made, they are not as thermally stable as filters with a central spacer(s) such as the Lunt 100 mm or the Coronado's. See:

See here for a detailed description of etalon basics: ... on-basics/

Re: H-alpha Zeiss APQ 130

Posted: Mon Nov 06, 2017 3:41 pm
by krakatoa1883
I used several fluorite refractors for observing the Sun in H-alpha with rear-mounted etalons and in WL through Herschel wedges and never had any problem... It is just my experience, however, I would not translate it into a general law.... are there any recommendations from fluorite apo manufacturers in this respect ?

I am not so sure that fluorite - and more generally apochromatic - refractors are of no advantage for observing the Sun with narrowband filters. I would say instead that this advantage exists but is not immediately apparent for several reasons. Theoretically, Fraunhofer achromats are not corrected outside the e-line, in fact they can be aberrated up to one wavelength or more depending on design and focal length. Their Strehl falls below 0.8 well before 600nm and in the near UV close to Ca-II lines things are even worse (see this page for a discussion).

However solar imaging is not as demanding in terms of resolving power as lunar or planetary imaging, the daytime seeing makes differences in aperture and design less evident than what would be under ideal conditions, and finally filter characteristics can actually be more important than the chromatic correction: an achromat provided with a good narrowband and high-contrast filter is certainly superior to an apochromat equipped with a poor one.

Most achromats are therefore usable for narrowband imaging notwithstanding their poor correction outside the yellow-green, but I think that for best results from Ca-K to H-alpha an apochromat is always preferable.

Re: H-alpha Zeiss APQ 130

Posted: Wed Nov 08, 2017 4:54 pm
by Bob Yoesle
Hello Raf:

No doubt the Zeiss fluorite APO is an excellent performer - I have never had the privilege or opportunity to view through one. I do have a relatively nice oil-spaced AP130EDT that I wont use for solar without adequate IR/UV blocking prior to the objective. Just a bit OCD about this telescope (center):
DSC01395.JPG (593.32 KiB) Viewed 1552 times
I would have to say the very best instrument I have used my Coronado SM90 filters on was a relatively pedestrian Synta 4 inch f15 refractor (abandoned due to length of the OTA). And I would say this even compared to my current Synta ED 100 f9 doublet (f10 with the 90 mm filters). This could be due to any number of optical reasons, including that most eyepieces generally will do better with longer f ratio objectives.

However, perhaps more than daytime seeing conditions, I would rate the thermal stability of the optical materials of significant importance with solar applications. I have very direct experience with this, as I had purchased - based largely on reputation - a pair of quite well regarded and exquisitely made SolarScope DSF 100 mm front etalons. In every instance, the much less expensive Coronado's provided superior contrast and more impressive views:


Part, if not most, of this was due I'm sure to thermal stability issues, wherein the SolarScope filters lack of a central spacer allowed the etaon plates (fused silica) to deform from a uniform gap spacing, whereas the Coronado's did not. Only by adding a Baader DERF with better IR blocking to the RG630 ERF of the SolarScope filters did they become close to being able to match the SM90's level of contrast performance. This seems to confirm the importance of thermal stability and the reduction of IR downstream in optimizing performance.

Therefore, and this was confirmed by Mike Jones, a frequent contributor to the Cloudy Nights ATM, Optics and DIY Forum, and a Lockheed optical engineer for NASA in Houston, TX, fluorite may not be an ideal material for solar applications due to its extremely high coefficient of thermal expansion (CTE):

Fluorite: 18.9 x 10^-6/K
FPL53: 14.5 x 10^-6/K
Crown (NBK-7): 7.1 x x 10^-6/K
Flint (F2): 8.2 x x 10^-6/K

Also note that the CTE of fluorite is roughly 2.5 times that of plate glass - which few people would use these days for a telescope mirror due to its lack of thermal stability. One could conclude that fluorite would undergo significant changes in shape as it tries to acclimate to thermal changes encountered in daytime solar observing, thereby not achieving its theoretical advantages found under ideal (constant) temperature conditions. Adding a IR blocking ERF would be a good remedy for perhaps some of this (e.g. continuum viewing with a Herschel wedge), and perhaps better protect an essentially irreplaceable objective. If used with a front etalon which incorporates said IR blocking on the ERF, you're likely to be much better off. A DERF135 would be ideal for both continuum and H alpha, but won't work for CaK.

One other thing that occurred to me is that with narrow band solar imaging, we are not trying to achieve simultaneous focusing of multiple spectral lines, and therefore traditional chromatic aberration is not relevant. For the two commonly used wavelengths, it becomes a question of how well that particular wavelength can be viewed or imaged by the particular optical prescriptions used for the objective. While I'm no expert with optical designs or interpretations of chromatic aberration diagrams, I will note the following from the citation you referenced:
Spherochromatism in lens objective (sic), sometimes called tertiary spectrum, can be more serious problem with apochromats. It becomes the dominant form of chromatic aberration, increasing exponentially with the relative aperture. Emphasis added.
Figure 144 is an interesting exploration. It therefore seems that a long focus achromat with more thermally stable optical materials might perform as well, if not better, than the modern short-focus APO using less thermally stable optical materials - IF the dyatime seeing allows one to distinguish between the two... just food for thought.

Best wishes,


Re: H-alpha Zeiss APQ 130

Posted: Wed Nov 08, 2017 9:33 pm
by Christopher
Hi Bob and Raf,
Thanks for weighing in on the fluorite question. I'm curious about the force/process that would result in the catastrophically high thermal expansion of the fluorite. I'm hoping Bob is willing to weigh in further still. :? It would seem it is only subject to ambient temperatures since it is pure pass through and nowhere near the point of focus. I'm unable to find anyone else who will lend support to the concerns raised. I reached out to the folks over at Astro-physics who originally sold the ERF for use with their 130EDT as well as Markus Ludes at APM who originally sold me the Zeiss and all had much the opposite perspective in that they encourage using this particular scope in both the ERF/H-alpha and WL Hershel Wedge configurations. BTW, AP was also able to tell me that they acquired the ERF glass from Baader. Baader, on the other hand, has no information on the specs for the glass from that era. There certainly do not appear to be any coatings applied as Bob surmised. I like the idea of adding an "affordable" UV-IR blocker filter directly in front of the rear etalon to prolong its life. This seems prudent if the reality is that the real risk of degradation is from concentrated IR energy near the point of focus. Sounds like, in conjunction with the older ERF, it would theoretically provide the same protection to the etalon as the newer D-ERF designs.

As a risk management professional I'm drawn to that discipline to deal with the question of thermal expansion inflicted damage. 1. Is the risk real? I'm still assessing. 2. How does the risk score on probability of occurrence and severity? Probability - waiting on 1. Severity potential is extremely high. 3. Manage the risk - Transfer, accept, mitigate, or avoid. Transfer - Bob mentioned the policy rider on homeowner's insurance. This is likely not an effective strategy since if the risk is real then the loss is probably excluded under inherent vice or peril limitations for fragile articles. Accept - unlikely if the risk is real. Mitigate - Newer technology full aperture D-ERF or front mounted etalon (stopped down) are the two options on the table for protecting the objective. Both seem to be viable alternatives worthy of further consideration. Avoid - don't use the APQ for solar observing. Well there is that Daystar 100mm f/15...

On Bob's point regarding the effect of daytime solar observing temperature fluctuations am I to understand that these fluctuations are, as a rule, more extreme than those experienced during night time observing? Perhaps I'm being naive but I guess I've assumed that for a given 24 hour period that a proportional distribution of temperature change exists between daylight and darkness (e.g. during winter more change occurs during darkness and the opposite occurs in summer). If that's truly the case, when does one experience the theoretical advantages of fluorite? Thus far, I can only speak to my darkness experiences and I've not seen any abnormal effects of thermal instability compared to other instruments. I'll definitely dig into this further.

Bob, that's one fine looking rig you've got there. Thanks for sharing the picture. I can't tell from the picture what sort of solar configuration you're using on the AP scope. Would you elaborate?

I was aware of the climate considerations for using the T-scanner and frankly, I have low expectations. My thinking on the grab bag hardware benefits in priority order was:
130 ERF mounted and ready to go
Baader Hershel Wedge - high quality WL observing
Telecentric optics - willing to give em a try as part of a bundle
100mm f/15 - Another OTA option (who doesn't love that?) :lol: for rear etalon usage
T-scanner (if it hasn't degraded significantly) no power requirements/high portability

...Buyer assumes all liability. Actual results may vary... :lol: The telecentric optics may be a complete bust. Seems it's a two piece system and I've only got 1 piece. Seller is investigating.

Finally, I just want to say how much I'm enjoying this forum. I'm happy I joined and really appreciate all the deep knowledge sharing. I'm drinking from the firehose! (where's that emoticon?!)

Re: H-alpha Zeiss APQ 130

Posted: Thu Nov 09, 2017 3:48 am
by Bob Yoesle
Hi Christopher,

I think it all comes down to how much of a risk taker one is. The risk of a large comet or asteroid hitting the Earth in my lifetime is pretty remote, but I think it’s a good idea to invest in a mitigation strategy to avoid it if possible because as improbable as it is, the consequences are likely catastrophic. I’m a paramedic and I see every day at work how improbable but very bad things can happen, from which I have learned to do mitigation as much as possible. As a result I’m Mr. overkill, yet I have found usually that small incremental improvements can have large cumulative benefits. If I had listened to all the manufactures who stated you can’t and shouldn’t try to do this or that, I’d have not discovered that, for example, double stacking CaK filters is of great benefit, despite the width of the CA absorption line, or that you can indeed double stack a mica based near the focal plane filter, enclose a Herschel wedge to make it safer for public outreach, etc., etc.

Structural failure for a fluorite objective is in the very low probability and very high (catastrophic) cost position of the risk management matrix. Maybe I’m crazy, but given the cost of replacing the APQ130 ($15,000 + if you can find one) I’d consider $1000 for the Baader DERF135 to be cheap insurance despite the very low probability of lens failure. I have tremendous respect for Mike Jones, and as he advised “I ain’t doing it, ever…” with my AP130 ED, which would cost far less to replace ( ... -fluorite/ ). As opposed to the others you have spoken to, he's an actual optical engineer who has worked for many years in the aerospace industry. You may want to PM him on Cloudy Nights.

With my ED100’s on the other hand, I’m happy to risk them for Herschel wedge use, as the remoteness of the failure possibility and the cost of replacement (pre-owned) is relatively cheap compared to the DERF cost which could be used to protect them. And being APO’s the wedge can perform as intended across the visible spectrum. However, for my AP130EDT, it’s Baader film or my Zeiss SFO – only, or at least until I get a DERF135.

The optical deformity issue, on the other hand, is more likely, and as I pointed out, is something I am more familiar with when it comes to etalon performance, where even if the material is fused silica with a CTE of 0.55 x 10^-6/K, it can suffer from thermal equilibrium issues with ambient solar throughput. And as far as temperature fluctuations, ask Alexandra Hart about the stability of her etalons when a passing cloud temporarily interrupts the flux of IR through her filters… I’m not sure if this would happen to affect the optical figure of a fluorite objective, but it seems more reasonable to assume it would than it wouldn’t, given the much larger CTE. Whether or not it is significant enough to observe as focus shift or something else, I don’t know. I just know I would feel better knowing I may have eliminated or mitigated the possibility as much as I can.

Your grab-bag component priorities are good, but I have higher hopes for your T-scanner and less hopes for your ERF, as to the best of my knowledge no one was doing IR coating of RG630 20 years ago – and you’d be lucky if it was AR coated on one side. It most likely will only block UV and not IR, which in my book makes additional IR blocking to protect the etalon mandatory.

With regard to the AP telecentric system, mine was also a two-piece affair:
HaComponents Arrowed.jpg
HaComponents Arrowed.jpg (1.17 MiB) Viewed 1525 times
This thread has reminded me that I might have to get back to those 100/1500 achro objectives, and get the remote motorizing T-Max stuff out again ;-)
CoronadoSetup.jpg (472.78 KiB) Viewed 1525 times
All the best,


Re: H-alpha Zeiss APQ 130

Posted: Thu Nov 09, 2017 8:30 am
by mdwmark
HI Christopher,
Well, the T-Scanner was ship in 3/1990. The temperature for on band, would depend where we would had sent it. If it was going where Del thought it would be be cold then, it would probably be 6564-5A at 25C. In Southern California then it would had been 6563A at 25C. But most where +1 to 1.5Ang in the red at 25C.
The scope would had been a RG610 singlet, no Ar's. He also used surplus red filter glass. But they would had been checked to be at least 1/4 wave in transmission.
For solar scopes, we didn't make very many. We had a small batch of lens in stock. They ranged from F/15 to F/30, 3" to 5". I made some 3"/F15 that had a -300mm lens for a 2X barlow. They worked OK for broad filters (.7-.9). But only a few. I am still using one , but have changed it to a telecentric instead of a barlow.
If you want to know where the bandpass is, let me know and I will measure it for you. The HW would be what it is before tilting.
About the fluorite , I'm kinda with Bob on that. I have used Tak 78 and Sky90 but they both had a Baader C-ERF on the front.
I have always preferred a standard air spaced doublet. People have this thing about being afraid of stopping down the scope. But a little lost of aperture can greatly in prove the performance of a scope.
Mark W.

Re: H-alpha Zeiss APQ 130

Posted: Thu Nov 09, 2017 9:11 am
by mdwmark
OK , I forgot to say.
The AP telecentric was designed for his old 6" F/12. It was an 2X telecentric. So the idea was to stop the 6" scope to 4" to get to F/36 where it work well. It will work on a 100mm scope, but it won't really be a telecentric.
All solar filters will move off band from the extra energy the sun is putting on them. That is why they tilt or increase the air pressure on the air spaced etalons. For an solid etalon, the only way to hold the wavelength is to use a TEC controlled oven for the etalon. It needs enough power to balance the extra energy from the sun to hold the wavelength at its set point.
With an narrow Hw filter . There is a real difference from being in the center of the absorption line compared to being on the wings of the line.
Mark W.

Re: H-alpha Zeiss APQ 130

Posted: Thu Nov 09, 2017 12:29 pm
by krakatoa1883
Interesting discussion, indeed, thanks Bob for your informative contribution.

Spherochromatism is of utmost importance in apochromats because foci are close each other and shall be all corrected from spherical aberration, as far as possibile, depending on lens design and glasses. In achromats, spherochromatism is less important as long as they are used in WL, i.e. close to the (only) color for which they are corrected, usually the yellow-green. But if you isolate the foci for which achromats have not been corrected - as when a narrowband filter is used, spherical aberration becomes, or should become, evident (see top fig. 143 of the page I linked). However it is a matter of fact that achromats can be very satisfying solar scopes :D

I can't exclude to have been lucky so far in using my apochromats for solar observing without a front ERF, however when I bring my apos from indoor to outdoor in winter they are certainly subject to some thermal stresses (say from 22°C inside home to something around 0°C, even below 0° in some instances outside) although I always take precautions to avoid abrupt exposure of the lens to the external temperature by leaving the dewcap covered for some time. I never experienced any failure, so I wonder if daytime observing of the Sun can really lead to even higher stresses up to the point where glass may crack. I know that Baader Planetarium warns FFC users that overheating the fluorite element shall be avoided, but this device is a rear mounted one, for example close to the Herschel wedge.

That said, prevention is better than cure - a broken fluorite element can't actually be cured in any way :lol: - so the above is only my personal experience, I'm not encouraging anyone to do the same.

Re: H-alpha Zeiss APQ 130

Posted: Thu Nov 09, 2017 8:28 pm
by Bob Yoesle
Hi Mark and Raf ;-)

Raf, I'm curious about figure 143 as you referenced, as the non-e line diffraction spot patterns appear to be what they would be if observed at the e line focus (e.g. they are out of focus - longitudinal chromatic aberration) as shown in figure 144 top middle. Again I'm not an expert in interpreting the diagrams, but if I'm correct, could/would the diffraction spot patterns be better to much better if the focus was shifted to the longitudinal position of the particular line in question... as would be done in narrow band solar imaging?

Just thought I'd add this link for the discussion on thermal effects by Mike Jones: ... sign-r2948

BTW, Mike also prepared an number of optical designs which are optimized for narrow band use at 394 nm and 656 nm (CaK and H alpha) which might be of interest to some: ... ke-filter/

Re: H-alpha Zeiss APQ 130

Posted: Fri Nov 10, 2017 5:10 pm
by krakatoa1883
Bob Yoesle wrote:
Thu Nov 09, 2017 8:28 pm
Raf, I'm curious about figure 143 as you referenced, as the non-e line diffraction spot patterns appear to be what they would be if observed at the e line focus (e.g. they are out of focus - longitudinal chromatic aberration) as shown in figure 144 top middle.
based on the caption it would seem that each image corresponds to focusing each color through a monochromatic filter, but it could also be as per your understanding if one looks to lambda values above, it is not clear. I asked the author to clarify how the figure shall be interpreted.

Re: H-alpha Zeiss APQ 130

Posted: Sat Nov 11, 2017 5:22 am
by marktownley
Interesting thread chaps!

Re: H-alpha Zeiss APQ 130

Posted: Sun Nov 12, 2017 6:02 pm
by Christopher
Here's the documentation I received from Astro-physics with the handy schematic at the bottom showing how to plumb with their telecentric system.
Daystar filter attachement.pdf
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Turns out the Daystar 100 f/15 has a 2X Barlow lens built into the focuser bringing it to the required f/30.
IMG_5066.JPG (993.92 KiB) Viewed 1387 times
Still no sun in southwestern Ohio. :cry:

Re: H-alpha Zeiss APQ 130

Posted: Thu Jan 25, 2018 9:05 pm
by Christopher
"This IR can also lead to early failure of the T-scanner blockers themselves at that aperture. Replace the ERF with a Baader, BelOptik, or Lunt ERF, all of which will block IR in addition to UV. Or you could add the BelOptick UV/IR on KG3 filter to the T-scanner, or another high-quality IR/UV blocking filter from Baader, Astronomik, etc."
Can a narrow-band CCD H-alpha filter such as the Astronomik H-alpha 12nm Filter serve the same purpose?

Re: H-alpha Zeiss APQ 130

Posted: Fri Jan 26, 2018 9:29 pm
by Bob Yoesle
Yes, I believe the 12 nm will block IR out to about 1200 nm or so, making it similar to the other nighttime H alpha filters, and the UV/IR filters and ERF's. Only the BelOptick filter or their ITF replacement filter will block out to ~ 4000 nm or more, as it is specifically uses KG3 filter glass for this, making is similar to an ITF filter in this regard.