Lunt LS60F question

[Allcart]

I am going to get a LS60F ds unit for my LS60T. I notice on the Lunt site that it can be bought with many optional BF configurations or bought on its own.

Q. if purchased with a blocking filter, can the LS60F be mounted on the front of any suitable refractor. There is no mention of the LS60F needing an additional ERF. Does it have one built in? and if so, why.

[marktownley]

Stephen made a post recently about how the LS60F filters are tuned slightly in the red compared to normal etalons so that they double stack effectively when used with the LS60T. If you use the LS60F in isolation on a different OTA you may find that you have to tilt it excessively to get it on band which may well result in a 'sweetband' of detail.

[Allcart]

Cheers Mark. Do you know if the LS60F has its own ERF. I got the impression it may have. If it does, would this effect imaging or be not noticable as the Ds would now have 2 ERfs.

Where is Stephens post?

[brianb11213]

The "in band" transmission of an ERF is pretty high & you would certainly get away with stacking them from the transmission point of view. The real issue here is that multiple ERFs mean extra surfaces which might (probably will) reduce contrast by creating ghost images.

Not sure if the Lunt "double stacking" units have a (redundant) ERF but if they have it's probably a safety feature: so you simply can't stick a "bare" etalon and a blocking filter onto a scope, have no ERF in the system and compromise your eyeball.

[Allcart]

The "in band" transmission of an ERF is pretty high & you would certainly get away with stacking them from the transmission point of view. The real issue here is that multiple ERFs mean extra surfaces which might (probably will) reduce contrast by creating ghost images.

Not sure if the Lunt "double stacking" units have a (redundant) ERF but if they have it's probably a safety feature: so you simply can't stick a "bare" etalon and a blocking filter onto a scope, have no ERF in the system and compromise your eyeball.

From reading the available info on the Lunt website it seems that it can be used in isolation with a blocking filter, so it must have its own ERF. Doesn't sound like a major issue when double stacking, but I will find out when I get it.

Thanks

[Merlin66]

Allan,
I use a pair of SM60 front etalons (with their ERF's)on an ED80/BF10 set-up.
No major issues (other than the fiddle of getting them tuned!!)
The overall throughput is much less due to the reduced bandwidth, but the views are fantastic.