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Quality Filters and the secondhand market.


alan potts

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Now I have to start by saying that filters never really caught my eye until on the advice of a member I picked up a 2 inch Olll filter by Astronomik's, fairly rare S/H. this works wonders on some subjects like the Veil, though my first attempt was a let down as this target hates the Moon and hides until it is out of the way.

Careful checking on regular basis turned me up a DeepSky 2 inch Lumicon which I can't say has had the same impact but I must give it a better chance on selective targets. It is a filter that is sort of sold as a LP filter but I have read many things to say this is the case but it works even better from a dark site on different subjects.

So I have the H Beta filter now coming ( from the Moon I think by the time it has taken) and I see now it will be for later in the year. This will also be an Astronomik and I went for the smaller size knowing it's main target of the Horses Head which is setting now earlier every night.

So then up comes a 2 inch UHC filter by Astronomik, I have been waiting for a secondhand one for over two years, at 100 pounds I jumped and got in there before anyone else. I tried it on a few targets with the LX and it's massive 3m focal length and it is very nice as it does show a little more of M42 than naked so to speak, an impressive sight. However on most of my other scopes with many targets I think I pressed the "I want button" before I put the brain in gear. Most of the targets require shorter eyepieces all with 1.25 inch filters threads, before I thought no matter I will just screw it into the diagonal. Now here is where you see how new and green I am, Dobsonians don't use diagonals, do they. Now I am looking for a 1.25 inch UHC as well, spending never ends even when you have almost all the eyepieces you could ever want.

However the 2 inch work well in the Meade as it is mainly 2 inch eyepieces that i use in that and it also is used with diagonal. The other thing that slipped my mind was though the Ethos range have 2 inch fittings below 17mm there is a 1.25 inch sleeve getting in the way, can't believe I over looked that small detail.

I think that will be an end to the filters though as I do feel these enhance some targets but nothing like the Olll does on the Veil, I can't wait for it to come around again though I will only be able to look at parts with the 18 inch. It took me over 2 years to find all these top end filters on the secondhand market, they really are pricy now brand new.

Alan.

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Hi Alan, half of my Lumicon filters were bought on US Ebay.com which had quite a few on my wants list, but s/h Lumicon began to get scarce, so I ended up buying new from AgenaAstro, so I now have all the filters I need.

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I have both the OIII and UHC, not the H-beta. 

As far as I can say with my limited experience, exit pupil is my guide when it is about filters (although it is also for eyepiece selection).

A few people commented that you need a very low power eyepiece (~5.0mm exit pupil) to see the horse nebula (plus dark sky). Therefore a 1.25" h-beta filter might not be the right choice if you don't have a low power 1.25" eyepiece. Maybe others can comment on this too.

In general, it seems to me that your dilemma is more about having mix 2" and 1.25" eyepieces and 2" filters. I thought filters could be attached to the 2-1.25" adapter on dobson telescopes. Is this not true?

Curious to read further comments by other members  

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Mark,

I didn't think of that of course there will be a 2 inch thread on the Moonlite. On the M/N 190mm there is no such thread because it is very cheap and rather nasty but I can use one of the others i have. I think it was when I was using the M/N that I had the thought, looked at the reducer and of course knew there was no thread. ( best I can come up with for not knowing)

Can you believe I have just found a Lumicon 1.25 inch on Astro B&S and written to the seller, 50 quid, I guess as Robin said they are rather difficult to get now and with what seems to be a sizable interest in all filters a test between Lumicon and Astonomik's would be nice, I have run out of eyepieces to test.

Alan

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Piero,

I thought an exit of  4mm was optimum was going to try my 24mm Panoptic which would be used with or without Paracorr at F/L 1980mm. the scope is 458mm.

Looking at that I would get an Exit Pupil of 4.77 with the Paracorr.

Alan

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I've been aiming for an exit pupil of between 5mm and 3mm to use with my Lumicon 1.25" H-Beta filter and my Tele Vue 25mm and 20mm plossls seem to be about right with my F/5.3 12" dob. Not that I've managed to see the darned horsey yet !  :rolleyes2: 

My other filters are now a Lumicon O-III and an Omega DGM NBP both in the 2" fitting. I sometimes use them on the eyepiece adapter but often on the end of the barrel of the eyepiece as well.

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I think thanks are in order to Mark and Piero who helped point me in the right direction with regards to the use of the 2 inch filter with the Sumerian and M/N 190mm. As it happens I have cancelled the purchase of the Lumicon 1.25 inch and saved myself 50 quid.

Alan.

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Thanks Alan, although I feel I said little! 

Anyway, I think filters are a bit a personal thing depending on targets of interest, type of desired detail and location transparency.

I am currently testing my filters (oiii and uhc) on a list of nebulae that John suggested me. I don't want to anticipate my results as these are not ready yet, but so far it seems to me that both have they pros and cons.

uhc pros: it filters less so you can use more high power eyepieces (decreasing the exit pupil).

uhc cons: you gain contrast w.r.t. no filter at all, but not as much as oiii

oiii pros: nice contrast 

oiii pros: you cannot magnify as much as the with uhc.

Of course, due to the size of my scope, this is a bit biased because I cannot magnify too much keeping a decent exit pupil for certain objects. For this reason, so far, I can say that I do not have a specific preference between them.

True, there are objects that are reported to be only visible with an oiii filter. I hoped to try to catch the Owl nebula, but currently have a problem with my diagonal and prefer not to point the telescope too high and risking to drop the eyepiece. (Beside this, the Owl can be very challenging with my scope as it is at the limit of my visible apparent magnitude).

I think that for general use an uhc or oiii are fine tbh. If your main interest is planetary nebulae and you have a sufficiently large telescope, I suspect the oiii is all what you need. For these targets, if the telescope has small-ish aperture, it seems to me (so far) that the choice is based on whether you like to magnify more or not (basically playing on the exit pupil of the background sky - which is filtered). I would be tempted to say the same for extended nebulae, although I need to view a few other targets before comment on this.

Personally, I wouldn't buy a h-beta filter because of its limited use, and because as far as I know the targets requiring it are very faint. In my opinion, for these targets, a real dark sky can make the difference rather than the filter itself. Under a dark sky, a decent uhc filter passes the h-beta bands too and therefore, I think it could be used for these targets. .. but this is just a thought as I have not ever tried it, and in this hobby having a plan is good, practice in the field is better   :smiley:

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