2" or 1-1/4" narrowband filters?

[obscura]

Narrow band filters beckon and 2" at that. Or can 1-1/4" be OK in the interests of economy.

Camera = Canon 550D. The mirror is in and around an inch so I guess the sensor is similar. It is possible I may go for a mono 314L+ or its like eventually - hence my query here.

If vignetting - how serious? Could it be doctored out with flats and/or in PS/CS?

I have a sneaking fealing that I might get away with it - would I?

[GlassWalker]

Canon sensor is roughly 23x16mm. I think you can get away with it, but I haven't tried on a ~120mm refractor (yet). I have used a 1.25" eyepiece adapter and assorted crop sensor DSLRs to image on a 4 inch Mak, random daytime example follows:

There does seem to be slight corner darkening on the right side here but I suspect my scope mirror isn't well aligned so is a bit asymmetric.

I can have a go with my new ST120 and same camera and see how the corners compare on that...

Another option could be Astronomik EOS clip but you will be limited to using them only with Canon crop sensor bodies.

[obscura]

Hi.That is very interesting. It does seem that 1-1/4" will work. The right shadowing on the pic must be as you say as filter vignette would appear evenly over the frame. Clip filters wouldn't work for me as I would want to go down a filter wheel route.

I appreciate your help and time in this.

Thank you.

[obscura]

I managed to cobble my WO80 with the 550D and a 1-1/4" green filter and shoot a grey gloomy summer's sky. This needed to be cobbled as all my kit is geared to 2".

The vignetting needs no description thus its back to 2" filters sometime at a later date I think. Would you agree?

[swag72]

While there is vignette in one image, why don't you try getting rid of it with a flat? Most people in imaging use them to sort out precisely this issue. Cheaper than 2" filters as well!

[GlassWalker]

With hindsight maybe my earlier example wasn't the best, as that was processed which may have masked any vignetting. Also my mak is rather slow at f/13, so would likely show less of an effect than fast(er) optics would. That reminds me, I still haven't tried it on the 120mm yet...

[obscura]

Following on from the 1-1/4" green filter shot above I needed to directly compare with my normal 2" setup. This shot is through a 2" Baader UHC-S filter and what a difference!!!

Hi Sara.

I have used flats extensively with my 2" filter set up mainly to dump dust bunnies and any potential vignette. My original post here asked that very question. Would flats, PS, sort vignette out? I cannot help but feel that with the 1-1/4" filter set up data would be lost.

The price difference for 3x filters Ha, OIII, SII would be about £150 incl. filter wheel. That would not concern me in itself but if I did go Atik 314/420 etc then I'd need 1-1/4" filters which would concern me. But then, as I write this, can I fit 2" filters to Atik 314 e.g.????

[obscura]

Of course, size of filter is irrelevant to a CCD camera like 314L I now reason if using a filter wheel. A 2" wheel can take 2" filters.

So I think my answer to this thread of mine is use 2" filters for the Canon (large sensor) and with a 2" filter wheel for CCD. (In fact the filters would sit permanently within the wheel.)

If there is anything wrong with my assumptions please let me know. Its a devil when you've never seen the appropriate hardware.

[Avo]

A 2" set would future proof your choice.

I think I'm going to standardise on 2" filters and get the full set when I have the dosh.

I have a 314L but who knows what in the future. New cameras and sensors are coming out all the time just to confuse and tempt you.

There's always the trade the 1.25" set in option, but being a bit of a gear freak, I know I would probably keep the old set anyway, just in case.....

The manufacturers have us firmly hooked on the upgrade path.

I used to be into Hifi and that was the same, reading reviews of that elusive / expensive bit of kit that was going to revolutionise ones listening experience. In the end I sold the amp and bought a drum kit, best decision I made.

(Now I'm deaf as a post, Hifi is pointless anyway !! )

[obscura]

The 2" filters is a decision but maybe one at a time as and when.

I am constantly amazed at the inflationary prices of astronomical equipment in these times of cutbacks. Its cannot be exchange rates, its not oil, its not strikes, its not supply and demand. The end result is the clever stuff is and will always be outta reach.

But then so is an Aston Martin for me.

[MeyGray3833]

I decided to go the 36mm filter route with a SX 7 position filter wheel so I can run L R G B Ha SII OII in one wheel and please my self what I image. Even using 2" filters you should always flat field your images for possible vingetting and of course the obligatory fluffy bunnies. I am using a Kodak 8300 sensor camera which is a few mm smaller than a DSLR APS-C chip, however, it should still be suitable. I must admit, it was expensive to set up, however will cover me for a few years and several chip sizes.

[obscura]

I looked at 36mm, and the other unmounted versions, but came back to 2" mainly because of the better availability of filter wheels. Whichever way, it don't come cheap. With most CCDs the question for me is mono or osc. My gut feel is mono but three or four exposures per frame is asking a lot with few clear consecutive nights but they are more versatile.

I normally take flats regardless with my home made flat box. They are quick and easy to do as are bias frames.