D-ERF Question

[Stu]

I've put this here as it will hopefully get to the solar experts more quickly.

I'm installing an internal D-ERF in my 150mm f5. Simple question, are they directional at all or can I install it either way around?

Cheers

Stu

[Peter Drew]

Hello Stu.

Yes, a D-ERF is directional, the correct way round is indicated on its edge. 

[Stu]

Thank you Peter!!

[Stu]

So, my next dumb question.... Does the arrow point towards or away from the sun????

[Stu]

Ahh, read the blinking manual [emoji6]

[Moonshane]

I am sure mine is right but what are the implications of putting it in the wrong way round?

[Stu]

I am sure mine is right but what are the implications of putting it in the wrong way round?

We will have to wait for those that know Shane, I'm teetering on the brink of ignorance again [emoji6]

[Merlin66]

The highly reflective coated surface is on the Sun side...this prevents any heat build up in the body of the D-ERF as 99.9% of the energy is reflected out before the rest pass through the filter.

[allcart]

That's an interesting question, and one I have never really thought about. My ERF is in a threaded holder that used to screw onto the front of an ED80 so I automatically face it the right way as if I was using it on the ED80.

So at the risk of showing my ignorance as well, I'll assume the ERF has an energy rejecting coating and that the coating is only on one side. So I would naturally assume that the coated side should face the sun and be first point of contact and deflect the energy before it goes any further.

Still assuming the ERF is only coated one side, if it was faced the wrong way round, the full force of the suns energy would be absorbed by the filter glass before being rejected by the coating. This may cause heat to build up in the glass filter and possible destroy it.

I could be totally wrong, but it sounds plausible.

You beat me to it Ken.

[Moonshane]

Cheers Ken

I suppose then the impact of back to front installation is more heat and more internal reflections?

[Merlin66]

""This may cause heat to build up in the glass filter and possible destroy it.""

There will be unnecessary heat build up but the filter would definitely not be destroyed.

[Stu]

Thanks Ken. To the rescue again [emoji3]