Solar mods and duty cycle ??

[spaceboy]

So we have had a few scorchers and set for several more so it got me thinking just how long can your solar kit be used to observe the sun for when the days are super hot, clear and the sun is high in the sky?? My reason for asking pertains to solar mods more so than dedicated scopes but I guess there is also a recommended duty cycle on those as well?

Are all solar mods 100% safe for long tracked and interval free sessions is I guess what I'm asking. I appreciate that all the parts in a mod are safe for solar observing but how safe are they on days when they are tested to their max? Are the ones where internal rejection filters have been employed over external ones as safe for long durations or is it wise to take 5 for everything to cool onepce in a while?

On another note. I recently had to change my rusty ITF on a PST. It is my understanding that this does the same sort of job as an ERF. So is it true that an ERF on PST mods can also become rusty / fail after time? If so do the filters remain safe if they do fail?

[Davey-T]

Given that folks use these scopes in much hotter climates than ours I doubt the UK weather will trouble them.

Dave

[spaceboy]

I agree but when you consider that mods are done beyond the purpose of the parts involved it makes me wonder has anyone ever done a bench mark test to see if PST mods ever fail ?

[Ibbo!]

if sunny tomoorow I will put a thermocouple behind the ERF on my mod

 

cannot see it being a problem too be honest as Dave says they are used in much warmer places than here US and Austrailia for example

[Merlin66]

Spaceboy,

I'm not sure where you are coming from.....

The ITF (mini ERF) will eventually fail whether it's in the original PST, a Coronado/ Lunt diagonal ITF . When it "fails" the contrast is compromised - not the safety.

We regularly use the solar scopes for extended periods here in Oz, with no problems.

 

[spaceboy]

@Merlin66 Forgive the confusion. I meant if ITF can fail can so to a D-ERF and ERF ?? They are all basically the same thing aren't they?

[Peter Drew]

First things first. You need to know what you are doing before modifying a PST and using one. There are several elements to a Ha telscope, it's highly unlikely that each would fail at the same time, even if they did it would still be safe as it wouldn't work. Bespoke commercial Ha telescopes are mainly American made or soursed. We are all aware of their compensation culture!. Observing in Ha is probably as safe as it can get.

The standard PST comprises a 40mm F10 achromatic doublet, 20mm diameter etalon, a pentaprism, a 15mm ITF and finally a 5mm blocking filter. The earliest PST's had a coating deposited between the components to attenuate some of the heat and light that reached the etalon, this acted as a ERF. It is well known that this coating eventually failed giving the "rusted" appearance, at no time did this compromise the safety of the instrument, just a gradual drop off in contrast.

Latest PST's do not have any form of objective ERF, this now resides as a stand alone 15mm diameter filter situated between the pentaprism and the blocking filter. This filter too, unfortunately also deteriorates with time, gradually becoming opaque but again safely. Etalons and blocking filters seem to have a much loger life expectancy.

When considering a PST mod it's almost universally to increase the aperture leading to higher resolution for both visual and photographic purposes. The increased aperture also introduces increased heat and the small ITF at the "hot" end , on its own, is inadequate. In this instance a larger ERF is placed forward of the etalon, as near to the objective as the new ERF's diameter will allow before vignetting the aperture. With a good reflective ERF such as those offered by Baader it isn't stricktly necessary to have a secondary ITF between the pentaprism and the blocking filter unless the image brightless is too high for your taste.

I've no evidence that lengthy exposure to the Sun accellerates component failure but it does seem sensible to cap the objective when not actually observing. Having said tha, I often forget and leave a 6" mod running for extended periods. I am purely visual and have been experimenting with and using Ha telescopes and modded PST's for decades. As far as I can tell, my eyesight is still as good as my age permits.    

[Merlin66]

The Baader D-ERF is a different design and construction from the Coronado/ Lunt ITF.

Does the same job better and doesn't seem to suffer deterioration like the ITF.

 

[Ibbo!]

I have tested the temp at the front end of the lunt with doouble stack on the front The ERF was about 3 degs higher than ambient ie 32 as to 29 where the etalon and internaL ERF the temp was 27°C and where the beam actually focus (about 100mm further out than the internal ERF and etalon sit it was 52°C.

 

Even if the front ERF was to fail the focus is not at the point where the etalon and filters sit so it is not a problem.

[spaceboy]

On ‎25‎/‎05‎/‎2017 at 23:26, Peter Drew said:

First things first. You need to know what you are doing before modifying a PST and using one.

We are all aware of their compensation culture!.

I have one of your mods Mr Drew so I'm pretty sure it's all good there  as for using on I put the ep in and spend the rest of the time catching my breath at the views.:D

With how hot it has been the past few days I just couldn't help but wonder how durable they are given they are modified beyond their intended uses is all. Spending longer than ever at the ep I just wanted to put my mind at rest. I'm sure Coronado, daystar and lunt test their scopes to destruction, because as you say they are a compensation hungry folk over the pond. Although tbh I did still wonder if even these have a duty cycle of some sort. I'm guessing no such rigorous tests have ever been performed on Ha mods so wanted peoples thoughts on it.

I appreciate that mods have been used in hotter climates than ours in the UK but we do seem to get a different kind of heat in the UK. I have spent all day out in the July sun while on holiday in Rhodes and not burnt but an hour under our sun at it's peak has me screaming in pain once I get in the shower. I'm not the first to notice we seem to get a harsher sun in the UK so it cant just be my skin type.

[Merlin66]

I think the extended and extensive testing of the PST mod in various countries and harsh sunlight over the past ten years certainly show that the mod, done correctly is as safe (if not safer - due to the additional ERF) as  the original instrument.

 

[Peter Drew]

Always sensible to be cautious about all things solar. The only differences between PST and a PST mod are the addition of a larger objective and an extra safety level ERF to the latter, all other tried and tested items are the same.

[spaceboy]

Thanks guys my mind has been put to rest 

On another note has anyone experienced any adverse effects from using an internal ERF? Thermal currents, ota expanding due to heat, objective getting hot, visual deterioration, paint bubbling, reflectiins etc, etc, etc

[Peter Drew]

No. 

[spaceboy]

Actually if memory serves I think it may have been @Stu had troubles with too much tilt on an ERF when doing a mod with his quark ? Hopefully he will be along to put me right if I remembered wrong.

[spaceboy]

6 minutes ago, Peter Drew said:

No. 

What about one that's been flocked? Would this insulate the scope trapping heat?

[FLO]

On 25/05/2017 at 17:39, Merlin66 said:

Spaceboy,

I'm not sure where you are coming from.....

Spaceboy contacted us recently saying a crack has formed in his telescope's paint, along the OTA's weld seam. I don't think he mentioned what the telescope is or how it was modified, only that he purchased it secondhand a few months ago and the previous owner had used it for two years.

He is concerned the fabric solar observing hood (recently purchased from us) might have caused it, we think that unlikely. He emailed this evening saying he had started this thread in an attempt to understand how it happened. 

HTH, 

Steve 

[Merlin66]

Thanks.

I like many others regularly use the telescope exposed to the sunlight for extended periods. My TS102 and SW ED80 after some ten years use show no signs of deterioration or damage.