OIII Imaging

[samir_ansari]

Hi there, I picked up a second hand 2" Lumicon OIII filter a while back and have only had a chance to test it twice. Both times I ended up with a very flat image no matter how much I tugged on the curves.

Last night I tried it on the Rosette nebula at F6.3 for 10mins (bin 2x2) and was left with a rubbish and light grey image with no nebulosity at all. The moon was only just about on the horizon so the sky was still relatively dark. Is this normal or is my filter not very good?

Thanks very much,

Samir

[lukebl]

I depends on the subject matter. As I understand it, the Rosette is very rich in Hydrogen-alpha emissions but low in O-III so won't show so much through an O-III filter, but will show a lot more with H-a. Some planetary nebulae have a lot of O-III so respond to that filter much better, such as NGC1514 which I had a go at last night. The H-a filter showed very little, whereas the O-iii revealed a lot more detail. I found the same to be true with the Jones-I planetary neb, and a few others. Basically, any nebulae which appear generally red in images are probably good for H-a, whereas those which are more blue have more O-III (probably a gross oversimplification, but that seems to be what I have found)

[Stephen]

As Luke says, you got to pick your targets with OIII. Veil for example is magnificent, but obviously not suitable at present.

Also, is the Lumicon not a visual filter? Could that not make a difference from an imaging filter ...

Finally, I was reading a post somewhere previously but Olly suggested he never binned his Ha (I assume this applies to other NB such as OIII as well) due to bad results.

No idea if any of this is useful, I hope you get something from it

[samir_ansari]

Thanks for the replies guys. From what I've seen people have managed to get a really nice and bright blue core to the Rosette when their subs are of equal length to the Ha and that's why I was expecting to see at least something?

[samir_ansari]

ok so im typing this on my phone right now from the battlefield (my roof) and i can happily report that so far it seems like it IS the binning that keeps ruining my pictures!

I think its because the gain/offset values i have for bin 1 are just far too much for bin 2 so i was getting clipping even in the midtones. Ill try and post some before and after pictures tomorrow in the hope it may help someone who is having the same problem.

[ollypenrice]

At my regular FLs of up to a metre I don't bin NB. There are many reasons but blocky stars is the main one. I am binning NB in Yves' 14 inch with an FL of 2.4 metres but that's another situation entirely.

Thor's Helmet is an O111 classic and, as Luke says, planetaries are often good. O111 is no good in the moonlight. And yes, it does need to be the CCD filter not the visual, or you'll get no contrast.

Olly

[samir_ansari]

Thanks Olly, I bought this filter second hand and am fairly sure it is IR blocking but just to be on the safe side I might just double stack my CLS filter onto it.