Should I be getting halo's?

[swag72]

On an imaging run the night before last on NGC6960 I noticed that I was getting a bad halo on the bright star. I put it down to not checking the focus and user error.

Last night, I imaged the same and checked the focus again and again - Yet I still have a halo.

I am using a Canon 1000D, modded and an Astronomik UHC clip in filter. The filter is fitted properly and the focus was checked after the filter had been fitted and adjusted accordingly. I was taking 8 min subs. I have not noticed halo's with my other clip in filters (CLS and Ha) - Is this something perhaps that I have to live with and accept with this particular filter?

[ollypenrice]

Although it's only Mag 4.2 and a K0 class star, 52 Cygni seems to defeat most people! It certainly did me. http://ollypenrice.smugmug.com/Photography/Widefield-images-including/VeilFinalDec09/753146766_7Q5WN-X2.jpg

I shouldn't worry about it. To reduce it in Ps you can put a feathered lasso around the halo, open curves, pin the background sky on the curve and then drag the curve down just above that.

You see few if any images with a clean 52 Cygni.

Olly

[johnh]

The UHC filters do not have IR block so if your original mod has an IR block glass placed over the sensor this will be fine. Bright stars will always carry some halo.

John.

[swag72]

I've not got an IR block placed over the sensor - The filter was removed and there was no replacement.

[johnh]

Then you need an IR block over the nosepiece of the DSLR and the halo will reduce or disappear if the UHC clip filter does not have an IR block layer built in. UHC filters are excellent for DSLR's to show nebula, you will not get as good a contrast if IR is not blocked so it would be worth considering for that as well.

John.

[swag72]

What size filter would I need - A T2 thread?

I am currently using a T thread connected to the SW 0.85 reducer, then screwed into that I have an adaptor from FLO that allows me to fit it all into my moonlite focuser.

[johnh]

Sounds like you will need a 2" UV/IR filter if the adapter has filter thread?

John.

[swag72]

Here's my imaging setup from my DSLR and the inside of the adaptor - It says on the FLO website that it's threaded to accept 2" filters - SO maybe another expense is needed!!

[johnh]

Looks like 2" filter will fit, but as Olly says halos can be lessened greatly using Marquee tool and feathering in PS, using curves to reduce brightness will moderate the halos significantly but if they are all over the place its a pain to do.

John.

[ollypenrice]

Would a 1.25 nosepiece and cheaper filter vignette? Probably, but I don't know.

You don't need an expensive filter, I don't think. I use a real old cheapo in front of one of my cameras. Doesn't seem to matter.

Olly

[Psychobilly]

Would a 1.25 nosepiece and cheaper filter vignette?

Olly

Oh yes...

[ollypenrice]

Oh yes...

Yup, I feared so but I get away with 1.25 on my 15mm square chips so wasn't sure. You guys have so many pixels!

Olly

[Psychobilly]

About the only place you can put it is in the same place as the Clip-in... thats what Hutech do with their "MFA" - it uses 1.25" filters but with lower profile threads.. I use one with an IDAS P2...

IIRC Steve (Steppenwolf) put a 1.25" filter holder in a short extension tube...

Peter...