Fast vs Slow for solar observing

[spaceboy]

Hi All

I am considering investing in a 6" refractor for solar white light and got to thinking does it really matter if you have a long or short focal length when looking at something as big as the sun ?

The only thing I can think is in an f/8 a 12.5mm eyepiece is going to offer x96 with an exit pupil of 1.56 and the same scope in f/5 is going to require an 8mm eyepiece giving x93.75 and a more favourable 1.6mm exit.

8mm eyepieces aren't the most uncomfortable and it still allows some room for magnification before you get in to squinting through an eye lens. The obvious advantage of the longer focal length is the edge in the FOV should be slightly sharper and CA better controlled although not an essential requirement for solar observing.

I would not consider an f/5 length 6" frak as being much more manageable than a f/8 as both would require substantial mounts so is there anything else I might be missing or not considering. The pricing is similar and they do come up used from time to time. I know it should be pretty straight forward given there is only one object I'm intending to use it on but thought it best to put it to the vote so to speak.

[nightfisher]

I would say the short one, the f8 really is a big old beast, the f5 will work on an EQ5 or some thing like that

[spaceboy]

Thanks mate. I have seen both in person but I also know that things magically appear smaller in shops till you try getting them in your car 

[Peter Drew]

I would go for a 4" F10 Tal refractor instead, ample aperture for solar, lighter, cheaper, better quality and if you get hooked on solar observation (as you will) it eventually makes a great PST Ha modification.  

[Steve Ward]

+1 for the Tal 100RS ... 

[Moonshane]

+2 but I love my 120 f5 and wedge as a cheap dedicated white light scope.

[ollypenrice]

I'd say that, if investing a semi-modest sum, saving on the scope and going for a Herschel Wedge rather than a front filter would give the best return.

I don't know what kind of solar filtration you had in mind though.

Olly

[spaceboy]

Well a 6" f/8 Evo came up so I decided to give it a go. I have seen one previously so knew what I would be taking on regards its size and weight. I have the ST102 for a quick grab and go for between clouds but figure for those lovely sunny days setting up the EVO150 next to a couple cold ones will not be any kind of a chore.

I will be extremely cautious when trying this for the first time with my 1.25" wedge and only to see if pursuing a 2" wedge is economical. I had originally considered a Baader cool ceramic wedge if it is a success as I have come across reviews to suggest this offers the best views in white light but was surprised to see that these are only recommended for apertures up to 120mm so a larger Lunt HW may be on the cards ??? 

[Merlin66]

Spacebody,

I don't know where you saw that limitation on the Baader Herschel wedge.

The 2" version, I know, has been used safely on apertures >200mm.

There's effectively no real limitation.

I use the Baader wedge on the TS102 f11 (similar to the Lyra) as well as a quick change over to the PST mod.

A great, easy and enjoyable arrangement.

[nightfisher]

Nick, did you get the 6" f8 blue tube with mount and ep`s that was on the bay of thieves last week, it went for a song

[spaceboy]

Spacebody,

I don't know where you saw that limitation on the Baader Herschel wedge.

The 2" version, I know, has been used safely on apertures >200mm.

There's effectively no real limitation.

I use the Baader wedge on the TS102 f11 (similar to the Lyra) as well as a quick change over to the PST mod.

A great, easy and enjoyable arrangement.

I'll be honest with you Merlin that I am beginning to think that manufacturers don't know themselves what their kit is capable of ????? My info was sourced from FLO regarding max aperture but no doubt this info is handed to them from their suppliers???

IMPORTANT:

1. The Baader Herschel Wedge must only be used with Refractor telescopes with metal and glass construction, not plastic. Telescopes with apertures 70-120mm work particularly well. Larger apertures can cause the rear heat trap to become uncomfortably hot.

2. Not suitable for use with Petzval or other telescope designs with a rear lens element positioned close to the focuser drawtube.

3. Due to production standards, the 2“ nosepiece in front of the Baader Safety Herschel-Prism features a 2“ (M48) filter thread. However - never mount a 2"“ filter in front of the Baader Herschel Wedge! Any filter mounted into the full beam of Solar energy so near to the focus point will become extremely hot and damaged within seconds (see safety advice, page 3 in manual). Filters must only be mounted above the exiting side of the prism.

4. Solar observing is dangerous and can be hazardous to eyesight. Safety is everyone’s responsibility, please use the correct equipment and read the safety notes supplied with the products carefully.

It may well be the case of a "sue happy society" putting pressure on to manufactures/ suppliers to cover their own backs by leaving no room for error when using their equipment ??? 

I have recently questioned the capability of Lunt HW as they say the 1.25" works best in 4" aperture and the 2" in 6" aperture yet a fellow member has shown that the 1.25" are capable of working in greater apertures (with obvious caution). I will be trying my 1.25" Lunt HW in the 6" but think I will add a Baader UV/IR filter to the front of the wedge for peace of mind when doing so.

[spaceboy]

OK so I got a very brief moment out under the sun and the stars with the EVO150 and I have to say I am impressed greatly with this scope.

While the scope was purchased with the intent for solar only, this time of the year the sun only just gets above the roof tops in the day and the only really good views are in the evening which are so short lived before the tree line blocks sunlight so the scope also had a run out the other night on the moon, Jupiter and a couple other DSO's just to get a feel for the scope.

I can't really comment in depth on the performance of the scope for solar observing other than I again found that similar to my AR127 the increase in aperture seems to wash out the surface detail as regards granulation. The seeing wasn't the best and it was only just above a roof top so I will guess this had a lot to do with it. What I did like about the EVO150 is there is a stopper in the dust cap that reduces the aperture down to the 'recommended 4" aperture for best performance' in the 1.25" Lunt wedge. At f/12 this also offers more magnification over my 4" f/4.9 with any given eyepiece so there is no need to use a barlow or squint through a small eye lens in a short fl eyepiece.

Despite the temperature being below 10° and the sun being very low the heat sink got rather warm when used at the full 150mm aperture. Not hot enough to burn yourself on but warm enough that you would not want to leave the scope unattended for even the shortest of times. I was though surprised that despite getting warm / hot it cooled quickly when exposure to the sun was halted. I'm sure there was also some cooling when stopping down to the 4" but  this may just be the fact my fingers were getting quite numb from the cold. There were very fleeting moments when the potential of the increased aperture revealed a more defined facula extending some way in to the solar disc but this may have been just a good patch of clear seeing on an otherwise poor day so I will have to update on this when the sun sits more favourably.

As for the EVO150 under the night sky....well this really was a different story. I have for a long time pondered on getting an EVO150 after having had some good sessions with my old EVO120 but advice was that the 150 really does show an awful lot of CA due to the larger objective and relatively short focal length. All I can say is either I got myself a lost gem of Evostar glass or some people really don't like purple fringing. I was totally blown away by Jupiter for only 6" of aperture. Although I will take a quick peak at Jupiter in most of my scopes I often reserve a serious planetary observing session to my 250PX but on this occasion I was sucked in by the contrast offered up by the EVO. OK the detail doesn't come anywhere near that of the 10" newt but what was there seemed to stand out better. It was more black and white over greyscale. There was a light misting of purple fringing around the gas giant but no where near as distracting as I had built my expectations up for. The moon was just under half illuminated and again the surface reminded me of the same feeling I get when I swap from a plossl to an ortho. Everything just seems more defined. Subtler details just seem to grab your attention more effortlessly. Again there was fringing on highly contrasted lunar peaks but I would say I had to look for it. This is not the case for all my refractors so to say I am shocked at the quality of the glass in the EVO150 is an understatement.

I admit to being accustomed to CA now that I have a handful of refractors but given all the comments that have suggested 6" fraks are awash with purple I can't help but think I must have had a result with this particular scope. I wanted the older blue tube EVO as I wanted one with a collimateable cell as I thought getting the collimation spot on would help with purple fringing and any other aberrations that could be introduced with a scope that was slightly of collimation so whether this has made a difference I don't know?

The EVO150 is a stunner on DSO also with the trapezium in the Orion nebula splitting up in to pleasant airy discs. I like my newts but I personally think you just can't beat how stars look in refractors. They just look so much cleaner and more settled. There was an abundance of colour in the double cluster and M45 could be tightly framed with near pinpoint stars right to the very edge.

All in all I couldn't be happier with the purchase of the Evostar 150. It does though have it's shortcomings. The obvious one being this is a scope that's some way over 1.2mtr in length with a couple big old lumps of glass right at one end. Even adhering a couple small slab of lead in the focuser end this scope is still going to have me on my hands and knees at some point during an observation session. And for those who may be considering one, a mount of capable payload would have to be budgeted for. I know Sky watcher has been know to under-mount scope packages but this example is a fine example of why you should always do your research even when buying what seems to be a match made in synta heaven. I had the good fortune to have recently upgraded my AZ mount from a GIRO III to a GIRO Ercole. This was more due to an OCD affliction than to do with any intension of getting a big frak but although I think the GIRO III would have been up to the task I don't think it would have coped so effortlessly as the Ercole does. There is no need to counterweight AZ movement although I'm sure this would only go to improve smoothness is I did and the ALT as with all AZ mounts, just needs consideration when swapping out eyepieces. As for an equatorial mount I think the bare minimum is going to be the HEQ5 and the EQ6 probably offering more suitable stability. What ever mounting option an extension is an absolute must for the EVO150 IMHO unless your a munchkin. The biggest shortcoming of the EVO by far is it's focuser but the good thing is that this can be replaced with ease and "relatively cheaply".

I agree with others that the EVO120 is a large refractor that may be more than some would care to handle but I would also say it isn't as bad as some make out. Having a AR127L I would not say there is a great deal in it between the 2 yet there are a many members who happily use the Bresser or Meade AR127 with rare comment to it's weight. The EVO offers up another 1" of aperture and is roughly the same length. I dare say on a set of scales there has to be something in it but in the hand I can't tell much in it.

A couple pics while waiting for my first sun light with the EVO.