Derf or IR filter for pst stage two mod and 80mm f6 apo

[Moonshane]

Hi all

I have a tal based stage 2 pst mod with derf but this is a bit large for travel. I use an 80mm f6 apo as my travel scope for night and white light. I wonder if I could use it for ha too.

There may be issues with focal point (I won't be cutting the tube) and I realise that I will lose some aperture to vignetting but would I need an IR filter or a derf to use it like this?

Any help appreciated

Cheers

Shane

[michael.h.f.wilkinson]

I would say an ERF would certainly be the safe option. The PST mod is not a Quark, after all. Better safe than sorry, I would say

[Moonshane]

True Michael

I wonder if they are available in a 2" filter cell?

[Merlin66]

Shane,

The Baader Ha 35nm filter, available in 2" sizes has exactly the same filter coating as the DERF.

The only significant difference is the thickness of the substrate.

[Moonshane]

Cheers Ken

Sounds like a possibility. I was hoping to get a filter that I can add to the front of my pst mod by simply screwing it on when in use. That said I can currently use my original pst tube for travel maybe as this requires nothing else.

[Stu]

Shane,

The Baader Ha 35nm filter, available in 2" sizes has exactly the same filter coating as the DERF.

The only significant difference is the thickness of the substrate.

Ken, is that likely to be an option for Quark users? Any benefits over a simple UV/IR filter?

[michael.h.f.wilkinson]

A 50mm filter would constitute a half-size ERF, which should work if you can get it into the tube at the right place. The PST mod needs to work at F/10, I assume, so placing a 2" filter in front of the objective, you automatically get a 46mm or so diameter, or about F/10. An unmounted 2" diameter filter could get you the 48mm which hits F/10 exactly with your 80mm F/6.

[michael.h.f.wilkinson]

Ken, is that likely to be an option for Quark users? Any benefits over a simple UV/IR filter?

Lower heat load on the system, I would guess

[Moonshane]

I was going to screw it onto the focuser end in front of the etalon. As it sits behind the drawtube end it will be larger than the light cone. I suspect even a 1.25 would be enough.

[michael.h.f.wilkinson]

If the aperture is stopped down to 48mm to reach F/10, a 31.7mm filter diameter should do the trick. In any case the filter should be some 240mm or more in front of the primary image plane, or else the heat may be too great.

[Peter Drew]

Whilst I agree with the the above opinions, I wonder whether the increase of 8mm over the standard 40mm PST if using a vignetted 80mm f6 is worth the expense/effort?

[Zakalwe]

Ken, is that likely to be an option for Quark users? Any benefits over a simple UV/IR filter?

There's an interesting thread on this topic over on Solarchat:

http://solarchat.natca.net/viewtopic.php?f=10&t=16698#p163351

[Moonshane]

This is exactly one of the considerations in my mind Peter. I fear the focal point may seal it as I won't be chopping my apo even though it was only £200 :0)

In some respects I am just trying to cut down on one box in the camper which will make my wife a bit happier!

[Davey-T]

 I am just trying to cut down on one box in the camper which will make my wife a bit happier!

I'm off to Hersty soon and have decided to leave my wife at home and have more room in the camper for boxes 

Dave

[michael.h.f.wilkinson]

Whilst I agree with the the above opinions, I wonder whether the increase of 8mm over the standard 40mm PST if using a vignetted 80mm f6 is worth the expense/effort?

I was wondering that as well