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Subject: Is 5" too small?? By: Anonymous (xxx.xxx.178.2) Date: 11/10/2002 06:38:42 am PST Is 5" a too small aperture for a O-III filter? Subject: Re: Is 5" too small?? By: Anonymous (xxx.xxx.175.63) In Reply to: Anonymous (xxx.xxx.178.2) (Original Message) Date: 02/05/2003 07:57:06 am PST >Is 5" a too small aperture for a O-III filter? The answer depends on the telescope type and F ratio. I have tried using an O-III filter on a 5 inch catadioptric, and I can say that because of the high F-ratio, it makes the objects I have observed too dark. With a lower F-ratio refractor or reflector, under low magnitification this type of extremely narrow filter may provide noticeable benefit for the intended class of nebula, but I would recommend using a less selective narrowband filter such as the Lumicon UHC or Orion Ultrablock. The O-III filter makes sense when starting out with a large amount of light collection, say a 10 inch aperture, and the target is one known to emit strongly at the narrow spectral range passed by the most selective filter type. Subject: Re: Is 5" too small?? By: Anonymous (xxx.xxx.23.10) In Reply to: Anonymous (xxx.xxx.175.63) (Original Message) Date: 06/26/2003 02:34:18 pm PST >>Is 5" a too small aperture for a O-III filter? > I use a 2" OIII on my TMB-105/650 with wonderful results. I have picked up the Veil easily from the suburbs on a 1/4 moon night.. and that's only a 4" scope! Now... by "easily" I mean I can see it... it's clearly there. It's not like the same image with detail and convolutions and folding, as seen through a 12.5" Portaball or (the Orion Neb through a ) 25" Zeiss SCT! Be aware that every Lumicon filter has different transmission numbers.. mine are in the mid-90's. You may have different results if the filter has rates in the 80's. Subject: o-III filters By: Anonymous (xxx.xxx.44.119) Date: 08/19/2005 02:45:09 pm PST I agree that an O-III filter is a MUST for almost all planetary nebulae. Some require a UHC filter. Without the O-III, the Dumbell nebula looks like a hazy, fuzzy patch of light. With the O-III filter , you can even see the outer extentions in this nebula The O-III is a highly recommended filter for ANY deep sky obsever. Page 1 of 1 | ||||||||
