Solar Scope. What would you buy ?

[Elp]

I've found larger aperture usually gets affected by seeing more too. You can see slightly more detail with a larger aperture but I don't think it's that significant. What is significant is looking at what you're seeing and concentrating on it for at least a minute or two without breaking contact with the eyepiece, your brain "dissolves" the initial bright red glare and starts to see details. An image will always be better contrast and sharper as they're altered to be presented as such.

[Stu]

12 minutes ago, Elp said:

I've found larger aperture usually gets affected by seeing more too. You can see slightly more detail with a larger aperture but I don't think it's that significant. What is significant is looking at what you're seeing and concentrating on it for at least a minute or two without breaking contact with the eyepiece, your brain "dissolves" the initial bright red glare and starts to see details. An image will always be better contrast and sharper as they're altered to be presented as such.

I completely agree that larger apertures are more affected by seeing, but do think that the detail you see through them can be dramatically better when conditions are good. I’ve used a PST40, Quark with scopes from 60mm to 106mm, and currently have 102mm and  150mm PST mods. Often even the 102mm is affected by seeing, and I’ve yet to see the best in the 150mm but even so, what I’ve seen so far knocks my socks off at times! Watching arcs of plasma moving in real time is fascinating and really shows the dynamism of the Sun. I do want to try to make my FS-60Q function as a mod too, as that seems to be an excellent aperture for cutting through seeing whilst showed very good detail still.

This is a handheld phone shot through the 150mm which gives an idea of the image scale, but doesn’t do the scope justice in terms of the fine detail which can be seen. I do get tempted to learn how to image properly through this thing as the results could be pretty cool.

[michael.h.f.wilkinson]

I certainly feel my 80 mm consistently outperforms my 60 mm. I have also use an 8" Tri-Band SCT (a modified C8 with coating on the corrector plate acting as a tri-band ERF), and there the effects of seeing are visible, but under good conditions, it shows a great deal more detail, both in white light and H-alpha. In Ca-K seeing is much more of a problem than in H-alpha, I should add. Both images below were taken with the tri-band SCT

[Elp]

I've tried my SF102 briefly with a quark, I found it a bit blurry but maybe the seeing was bad at the time, and I know it can also support higher magnification. My Z61 on the other hand I could sit at for ages taking in more of the view, a lot of the viewing comfort comes from being able to sit still comfortably whilst in the sun, a towel over the head and eyepiece end is absolutely essential, you also want to try to stop your body from moving as any movement away from the eyepiece will blast your eyes with bright light from the environment, and you really want your eyes adapted to the solar view, much like dark eye adaptation at night.

Edited March 7 by Elp

[michael.h.f.wilkinson]

I should add that using an ERF, which isn't required for a quark or Ca-K module, cuts down tube currents a lot. Imaging in Ca-K without an ERF in place causes considerable reduction in sharpness, I find. With my tri-band ERF (which transmits Ca-K, H-alpha, and the solar continuum band) gives much better results. It may be that the larger aperture scopes suffer from similar issues more than a 60 mm would when using a quark.

[Elp]

My understanding is if you're using 100mm+ it needs a derf to reduce the energy (thus heat) entering the front objective as the derf will reflect a lot of the light. This also protects the quark somewhat. When I tested the SF102 I used one of my photographic HA filters in front of the diagonal, but kept the scope pointed at the sun for only a few seconds as it's not recommended to do this. Some people have been using wide bandpass ha filters to the same end prior to the quark but anyone whom does this is likely doing it at some risk, a 2 inch filter isn't as thick as a derf I'd presume and no filter manufacturer will recommend such use, only a derf will be recommended.

Edited March 7 by Elp

[michael.h.f.wilkinson]

9 hours ago, Elp said:

My understanding is if you're using 100mm+ it needs a derf to reduce the energy (thus heat) entering the front objective as the derf will reflect a lot of the light. This also protects the quark somewhat. When I tested the SF102 I used one of my photographic HA filters in front of the diagonal, but kept the scope pointed at the sun for only a few seconds as it's not recommended to do this. Some people have been using wide bandpass ha filters to the same end prior to the quark but anyone whom does this is likely doing it at some risk, a 2 inch filter isn't as thick as a derf I'd presume and no filter manufacturer will recommend such use, only a derf will be recommended.

Most likely, the view would be a lot better with an ERF of some kind. Apart from being safer, the thermal currents in the tube caused by the heat will be massively reduced. BTW, the thickness of the filter isn't really an issue in a D-ERF. In this case, the coatings do the filtering, the glass is merely there to hold the coatings in place. A smaller aperture requires thinner glass to do the job.

[josefk]

Hey guys. Do these comments re a D-ERF and it’s benefit in reducing tube currents apply to white light too. I don’t have to use a D-ERF with white light but I do if I go down a rear mounted Etalon route. It being potentially being useful in both cases is something to think about. 

Edited March 8 by josefk

[michael.h.f.wilkinson]

1 hour ago, josefk said:

Hey guys. Do these comments re a D-ERF and it’s benefit in reducing tube currents apply to white light too. I don’t have to use a D-ERF with white light but I do if I go down a rear mounted Etalon route. It being potentially being useful in both cases is something to think about. 

A regular D-ERF combined with a solar continuum filter would not work, as the D-ERF doesn't transmit green light. A tri-band ERF does transmit the solar continuum band, so it does help. The tri-band SCT passes O-III rather than solar continuum, so you should use a green or O-III filter instead.

[Stu]

11 hours ago, Elp said:

My understanding is if you're using 100mm+ it needs a derf to reduce the energy (thus heat) entering the front objective as the derf will reflect a lot of the light. This also protects the quark somewhat. When I tested the SF102 I used one of my photographic HA filters in front of the diagonal, but kept the scope pointed at the sun for only a few seconds as it's not recommended to do this. Some people have been using wide bandpass ha filters to the same end prior to the quark but anyone whom does this is likely doing it at some risk, a 2 inch filter isn't as thick as a derf I'd presume and no filter manufacturer will recommend such use, only a derf will be recommended.

I believe the Baader 20nm (or the older 35nm) Ha filter are safe to use in lieu of a D-ERF in scopes up to 152mm, as evidenced by the statement at the bottom of this link on the Astrograph website.

https://astrograph.net/epages/www_astrograph_net.mobile/en_GB/?ObjectPath=/Shops/www_astrograph_net/Products/AGBPHA35-2

In my scopes I have internally mounted D-ERFs, 75mm in the 102 and 110mm in the 150. I have no way of knowing whether the performance would be better if I was able to use full aperture D-ERF but I can’t afford that and am quite happy with the performance. My observing conditions are normally not that hot so I don’t see it as a problem. If I were observing in 30 degree plus heat with the Sun overhead I may think differently.

As soon as I can get hold of one, I plan to use a 20nm Baader Ha in my FS-60Q to see if I can get a small aperture Ha travel scope up and running.

Astrograph statement below:

[Elp]

2 hours ago, Stu said:

Baader 20nm (or the older 35nm)

This is the one I was looking at originally as DERFs are hideous in price (but you can't put a price on your safety), but I tend to image more than do visual so it wouldn't really matter so much to my usage scenario if I decide to use a small diagonal mounted filter. I used my ccd ha filter as it's a much smaller transmission bandpass than the above and the front side has a reflective coating on it, I think this would be a suitable alternative.

You don't need to use one below 100mm aperture with a quark, but if I'm doing visual for my own piece of mind I use a 1.25 inch UV/IR cut filter on the front of the quark.

Saying the above Baader don't recommend using an internally mounted filter, to paraphrase them when I asked:

"A derf is designed different to a night use filter as it is built on much thicker glass. This therefore can take much more heat. A derf is in front of the aperture, not inside where you're concentrating the light to a more fine focal point and higher concentration of energy."

Note, if anyone is reading this do not take it as gospel recommendation, it has been discussed on many solar forums. Never skimp on safety, always inspect your equipment prior to use. Diverting away from manufacturer recommendations you do so at your own risk, and never put your own safety at risk (biological risk and also risk of sun heat damage if youre not taking care in what your doing).

Edited March 8 by Elp

[michael.h.f.wilkinson]

2 hours ago, Elp said:

This is the one I was looking at originally as DERFs are hideous in price (but you can't put a price on your safety), but I tend to image more than do visual so it wouldn't really matter so much to my usage scenario if I decide to use a small diagonal mounted filter. I used my ccd ha filter as it's a much smaller transmission bandpass than the above and the front side has a reflective coating on it, I think this would be a suitable alternative.

You don't need to use one below 100mm aperture with a quark, but if I'm doing visual for my own piece of mind I use a 1.25 inch UV/IR cut filter on the front of the quark.

Saying the above Baader don't recommend using an internally mounted filter, to paraphrase them when I asked:

"A derf is designed different to a night use filter as it is built on much thicker glass. This therefore can take much more heat. A derf is in front of the aperture, not inside where you're concentrating the light to a more fine focal point and higher concentration of energy."

Note, if anyone is reading this do not take it as gospel recommendation, it has been discussed on many solar forums. Never skimp on safety, always inspect your equipment prior to use. Diverting away from manufacturer recommendations you do so at your own risk, and never put your own safety at risk (biological risk and also risk of sun heat damage if youre not taking care in what your doing).

Note that a front-mounted ERF (D-ERF or otherwise) just sits in ordinary daylight. It should not get hotter than any other surface exposed to dirtect sunlight. A D-ERF will actually reflect most of the heat, rather than absorbing much, so will stay comparatively cool. A thicker filter is needed at larger apertures not because it is expected to get hotter, but because it might otherwise deform. A half-aperture ERF, i.e. one halfway down the OTA (which is usually recommended as the smallest one you should consider), receives a 4x larger concentration of light, which is manageable for all sorts of optical glass, especially if it reflects the light and heat, rather than absorbing it.

[Stu]

3 hours ago, Elp said:

This is the one I was looking at originally as DERFs are hideous in price (but you can't put a price on your safety), but I tend to image more than do visual so it wouldn't really matter so much to my usage scenario if I decide to use a small diagonal mounted filter. I used my ccd ha filter as it's a much smaller transmission bandpass than the above and the front side has a reflective coating on it, I think this would be a suitable alternative.

You don't need to use one below 100mm aperture with a quark, but if I'm doing visual for my own piece of mind I use a 1.25 inch UV/IR cut filter on the front of the quark.

Saying the above Baader don't recommend using an internally mounted filter, to paraphrase them when I asked:

"A derf is designed different to a night use filter as it is built on much thicker glass. This therefore can take much more heat. A derf is in front of the aperture, not inside where you're concentrating the light to a more fine focal point and higher concentration of energy."

Note, if anyone is reading this do not take it as gospel recommendation, it has been discussed on many solar forums. Never skimp on safety, always inspect your equipment prior to use. Diverting away from manufacturer recommendations you do so at your own risk, and never put your own safety at risk (biological risk and also risk of sun heat damage if youre not taking care in what your doing).

Yes, plenty of discussion around them. The idea is to get them ahead of the focus point as far as possible without vignetting to reduce the concentration of heat. They are reflection based filters so the thickness of glass is less relevant ie they don’t heat up as much as absorption ones. Ultimately they are there to take the strain off the etalon and other blocking filters and the bandpass on these filters is actually tighter than on the ERFs so I don’t believe they offer less protection. As you say though, everyone is responsible for their own safety and should make sure they are happy with their setup. I know of a number of people who use these in this way so am personally happy they are safe.

I will use one (if I can get hold of one!) in my 60mm and see if I can reach focus with it. Personally I wouldn’t go up to 150mm with one, but would be ok with one in a 100mm I think.