CCD filter queries again...

[Andrew*]

Could you please answer these questions for me. I'm getting mighty confused.

1. There are huge differences in the prices of LRGB filters. Why? You could pay £25 for Opticstar or ~£55 for Baader or £125 for True Techology (at the bottom) and then right up to £160 for Astronomik (bottom). Can I get away with Opticstar using an additional IR block, or is it worth to double the price for Baader, or even quadruple for TT? Has anyone demonstrated the quality of filters and what differences were noticed in the actual outcome of the image?

2. What actually IS a luminance filter? In the description of the Baader filter set, it says it includes "red / light blue / light green as well as the Baader IR cut filter", suggesting, at least to me, that the L filter is simply an IR cut filter

Thanks a lot

Andrew

[GazOC]

There isn't an 'L' filter as such, you take the L channel from whatever wavelength(s) you think is best for a particular object. The L channel can be Ha, Sodium or no filter at all....

[MartinB]

This is an excellent question and difficult to get a satisfactory response. To clear up the luminence 1st - as Gaz says, when LRGB imaging you can use all sorts to provide your luminence component however in LRGB filter sets the L is normally a simple IR cut filter. For RGB there are basically 2 types of filter absorbtive filters which as the name suggests just absorb unwanted wavelengths and let the desired colour through and reflective or dichoic which reflect away unwanted wavelenghts. Dichoic filters are supposed to transmit more of the desired wavelengths than absorptive filters. The better ones also purport to have very accurate transmission curves for getting ideal RGB matching. All the filters in a set should be precisely parfocal.

I do suspect you get what you pay for but whether that equates to value for money is another matter. I have been impressed by my Astronomik filters - they are genuinely parfocal and the coatings are very tough. Baader do a significantly cheaper set of absorptive filters and I know Steve (FLO) is planning to use these so it will be interesting to see how he gets on.

It would be interesting to see some side by side comparisons.

[barkis]

I was about to post on the subject of filters yesterday Andrew. I too am so flummoxed by the variations in filters, both in types and prices.

It's an absolute minefield, which could only possibly be negotiated by the seasoned astronomical imagers.

I took one type of filter, and explored the various makers/ suppliers of it, and the difference in the prices were astounding./

Now I know there are bound to be claims of differences in quality, that argument could be applied to a whole range of goods.

I bought my filters On AB&S on the basis they were classed as suitable for CCD imaging. Fortunately, through communication with the seller, I was absolutely in no doubt that the seller and the filters were genuine. I think now I have all I need, apart from the Oxygen one, which I will buy later.

I am sure a great many members would appreciate a table of sorts, that would list each filter that is required, or required but not essential, for imaging. It would not be fair to include any recommended dealer, but allow the potential buyer to make their own decision on that.

I hope this does not sound too silly, but I the gist of what I am trying to get across is evident.

A lot of guys are going to have aspirations towards imaging, when they see what is coming through on this forum. The population of SGL is growing fast, and the more that can be done to accommodate their needs, the better. Grant, I know your workload is quite sufficient, so I am not directing this appeal towards you personally. I think maybe some of the experienced imagers could get together to provide the information necessary to put into a table of sorts.

This is a request more than a demand, if I am out of order then please slap me down, I won't take any offence.

Also, if there already is something of this nature already available on the forum, then please ignore everything I have said.

Ron.

[trevboyd]

I agree wholeheartedly Ron - a simple table summarising the different types and their uses would be invaluable to those of us considering these things. Even just a new thread the more experienced imagers could contribute to would be very helpful

Trev

[Andrew*]

hear hear!

I think I'll save a few pounds and go for the opticstar ones. I don't think I can go far wrong at £30.

I'll use a CLS for general LP cut, and when I get there, an Ha and OIII will complete the set.

Now to find a filter wheel :insects1:

Cheers

Andrew

[GazOC]

Now to find a filter wheel :insects1:

I think theres one in the 'For Sale' section...

[barkis]

Yeah, I saw that one, But it was the Observers one, now sold. There is a three hole one available.

What differentiates an observers one from a one imagers would use?

[MartinB]

Ron, I posed a question about the benefits of dichoic vs absorbtive filters on Ron Wodaski's NewCCD astroimaging Yahoo forum. This is a very rarified place and much of the discussion is very high powered and esoteric. It has some of the best astroimagers in the world on there. The first time I posted I got no response. I got a single response to a second posting - from Ron himself, but it wasn't really that enlightening - better transmission with dichoic filters and more precise cut off points to the transmission curves, but it was much vaguer than Rons usual responses.

I could happily write something up on narrow band filters for deep sky imaging and a bit on LRGB although, as I say, there is a great deal of uncertainty.

We would need a planetary imager to discuss the use of IR pass filters and a visual observer to explain the different filters used in this situation.

It sounds like a good idea to me.

As for filter wheels, I can thoroughly recommend the Scopeteknix model as sold by FLO. Quality construction, very low profile and well priced. It is probably the lowest profile wheel on the market.

[Andrew*]

I only see one, but it doesn't take 1.25" filters, apparently.

Mike B had an AE observer's one, but ...

I'll keep an eye out for the Scopeteknix 2nd hand

Andrew

[centroid]

I think the answer to the price difference is in the quality of the glass used and the filter itself.

I might be wrong but it may be that the cheaper ones are nothing more than coloured glass, whereas the better quality ones are true Dichroic (or a word simillar to that ) filters.

I'm positive that the Astronomik ones fit into the latter type, and as such, command a higher price tag.

Its fairly safe to say, that with optics, its generally a case of 'you get what you pay for'.

When I was doing LRGB, I went straight for the Astronomik filters, and when I sold them, they were 'snapped up' very quickly.

Dave

[barkis]

I am sure anything you contribute would be highly appreciated Martin. You are held in very high esteem on SGL and much wider afield without doubt.

I wonder in the field of planetary imaging, would our friend Pete Lawrence care to contribute some words of wisdom pertaining to filters and the use of on the planets.

He may read this, and volunteer, on the other hand, he may need to be coaxed.

Maybe someone on SGL is close to him?

Ron.

[barkis]

I have been looking around the net, and came across Lumicon's website. I don't know how useful this may be, but I post the link anyway.

Ron.

http://www.lumicon.com/filterspec.php

[cygnusx1]

I have been looking around the net, and came across Lumicon's website. I don't know how useful this may be, but I post the link anyway.

Ron.

http://www.lumicon.com/filterspec.php

many thanks barkis, exactly what i've been looking for, a succint summary of filter characteristics :thumbup:

does anyone know if the following filter is for visual or photo

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&rd=1&item=170091687196&ssPageName=STRK:MEWN:IT&ih=007

it doesn't seem to have Ha filtering included?

[Kaptain Klevtsov]

I've got one of those Kevin, and its on the list of stuff to try out. I particularly want to see how it gets on with the DSLR and the Horsehead. I might even have a look through it.

Kaptain Klevtsov