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Help with Filters on an F/5 refractor under Bortle 8 skies

Filters Beginner Observing
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#1 WRD

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Posted 07 December 2022 - 05:07 PM

Hello all, this is my very first post.
I am just returning to astronomy after a 20-year hiatus. My first telescopes all those years ago were an original ES Astroscan, a Meade ETX-90mm and a William Optics 66mm ZenithStar SD APO. I enjoyed them all at the time. I still have the ZenithStar which I put on a tabletop Dobsonian mount. Assume that I know a little more than nothing but not much more.

I recently bought two used scopes on Ebay, both ETX-80mm refractors and I gave one of them to my 12-year-old granddaughter. We intend to have our own star parties over facetime on our ipads.

I have a specific question which I have not found the answer to on Cloudy Nights so far. The question relates to filters for viewing NOT for astrophotography (I am going to walk before I run). The ETX-80 mm is an F/5 achromatic refractor as you all know. I live in the Windsor-Detroit area and generally the skies would be classified as an 8 on the Bortle scale. My question is:  What would be the best single or stacked 1.25-inch filters for my F/5 scope in my Bortle 8 backyard (for general viewing)? I intend to mount the filter(s) on my diagonal.
Your help is much appreciated.
WRD


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#2 vtornado

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Posted 07 December 2022 - 05:37 PM

Hello WRD and welcome to the forum.

 

If you mean by planetary filters.  The only one that I have found useful is the 82A

(light blue) this can make the GRS and banding on Jupiter a bit more pronounced*

 

I have heard the same thing about Mars, but I have not seen this.

 

Some Lunar observers say that crater rays stand out more during

the full moon and a filter.

 

I have a moon and sky glow and this is best filter I have found for enhancing

Jupiters bands.

 

A yellow #8 is a cheap way to filter out some of the chromatic abberation from

a fast achro refractor.

 

For emission nebulas (dumbell, orion ...) a narrow band nebula filter will help*

I have the orion ultra block.

 

*you will not have to hold onto your socks lol.gif

 

Also note, that filters take away light.  Dark planetary filters like many in standard planetary kits,  remove too much light, especially in a small scope. The result is not enough light to see clearly and a color pallette that completly swamps the intended target.   Additinally  taking away light, means some other feature is diminished so that another feature is more easily seen.


Edited by vtornado, 07 December 2022 - 05:39 PM.


#3 WRD

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Posted 07 December 2022 - 05:57 PM

Hello vtornado,

Thank you for the timely and very useful information. I have a #8 LY filter and a moon&skyglow filter now. Can they be stacked? Also could I stack a #8 and #82A if I buy one?

Thanks,

WRD


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#4 vtornado

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Posted 07 December 2022 - 06:31 PM

I have a blended set of filters from Meade, Celestron, Orion and Vite (chinese knock off)  

They all screw into one another.  So I can stack whatever I want.  Whether that is effective ??? 

 

 I keep my dark planetaries in a tower all

screwed together and store it  in a repurposed eyepiece bolt case.  That takes

up less space than a stack of filter boxes.

 

The dark ones I don't use very often.  I use the green for testing achromatic refractors, and I have heard that dark red may work for imaging glaxies (untested).

 

That being said everyone's brain and peepers are different.  perhaps your

visual system responds differently to color than mine.


Edited by vtornado, 07 December 2022 - 06:34 PM.


#5 WRD

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Posted 07 December 2022 - 07:03 PM

I just ordered the Meade #82A filter as you suggested. I will also do some experimenting with stacking.

The main issue I remain unclear about is whether any of these options can mitigate the Bortle 8 skies in my area?

WRD


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#6 aeajr

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Posted 07 December 2022 - 07:19 PM

Hello all, this is my very first post.
I am just returning to astronomy after a 20-year hiatus. My first telescopes all those years ago were an original ES Astroscan, a Meade ETX-90mm and a William Optics 66mm ZenithStar SD APO. I enjoyed them all at the time. I still have the ZenithStar which I put on a tabletop Dobsonian mount. Assume that I know a little more than nothing but not much more.

I recently bought two used scopes on Ebay, both ETX-80mm refractors and I gave one of them to my 12-year-old granddaughter. We intend to have our own star parties over facetime on our ipads.

I have a specific question which I have not found the answer to on Cloudy Nights so far. The question relates to filters for viewing NOT for astrophotography (I am going to walk before I run). The ETX-80 mm is an F/5 achromatic refractor as you all know. I live in the Windsor-Detroit area and generally the skies would be classified as an 8 on the Bortle scale. My question is:  What would be the best single or stacked 1.25-inch filters for my F/5 scope in my Bortle 8 backyard (for general viewing)? I intend to mount the filter(s) on my diagonal.
Your help is much appreciated.
WRD

I have an ETX-80.  My first scope 7 years ago.  I have 4 others but I will keep it for ourtreach events.

 

If most of the street lights have been switched over to white LEDs, then light pollution filters will be fairly ineffective.

 

You don't need any filters for that scope for general use.  If you find the Moon too bright then perhaps a 25% Moon filter.  I have one from Orion that I like very much.  I use it on the ETX 80 and all of my other scopes. Also useful on Venus.

 

A nebula filter will come in handy for observing certain bright nebula, but not all.  The DGM NPB is the one I use BUT not on the ETX 80.  Using an 80 mm aperture it is only likely to be useful on very bright nebula, like the Orion Nebula.  I have used it on my 125, 203 and 305 mm scopes.  I don't think I ever used it on my ETX 80. It works better on scopes with larger apertures.

http://www.npbfilters.com/

 

Orioin UltraBlock also has a good reputation but still, I am not sure how well it will serve you on an 80 mm.  

https://www.telescop...d=nebula filter

 

I have played with colored filters with the ETX 80 but have not felt they were very useful. They were more effective on my 8" and 12".  The 82a is worth a try. I occasionally use it with my 102 and larger but not on the 80. 

 

My suggestion is to use the ETX 80 without filters, again, except perhaps a Moon filter.

 

The key to success with that scope, especially under Bortel 8 sky (same as mine) is to properly pick your targets

 

Galaxies and most nebula will not be good targets unless you can get to a very dark location, Bortel 4 or better would be my suggestion.

 

Moon, planets, stars, open star clusters, brighter globular star clusters, easier double stars would be your best targets.  Plan to stay under 120X.  If the seeing is really good you might be able to push 150X on the Moon, Jupiter and Saturn.  That gives you thousands of targets to go after.

 

You can also put a solar filter across the aperture and observe the Sun.

 

The GoTo works well for me.


Edited by aeajr, 07 December 2022 - 08:02 PM.

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#7 WRD

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Posted 07 December 2022 - 07:57 PM

Hello aeajr,

Thank you for your ETX-80 specific recommendations. I would be interested to know if the no filter recommendation takes into account the Bortle 8 sky in my neighborhood.

Thanks,

WRD


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#8 aeajr

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Posted 07 December 2022 - 08:21 PM

It takes into account the Bortel 8 sky in my neighborhood.  I can't say anything about yours but I would expect it to be similar.

 

 I often use this website tool to help me plan my targets.  Naturally you have to set it to you location. Keep your targets above 30 degrees, at least in the begining.

https://tonightssky.com/MainPage.php

 

Stick with naked eye and Binocular targets at first. (click both boxes)  See how that goes.  Then add small scope targets next (click all three). 

 

The andromeda galaxy from my location is just a slightly brigher spot in the sky.  Nothing to look at.  I had it in my field of view a dozen times and swore that it could not be seen.  When I realized it was there I was very disappointed, but that is what it looks like in an 80 mm in Bortle 8 location.

 

Enjoy the Orion nebula, Ring nebula and other bright nebula, but most nebula will be disappointing even with a 100 mm scope from your location. 


Edited by aeajr, 07 December 2022 - 08:40 PM.


#9 aeajr

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Posted 07 December 2022 - 08:49 PM

Trying a light pollution filter in your location will not likely do any harm, it just may not help much if at all. 

 

 

Light Pollution
https://telescopicwa...ight-pollution/

 

 

Understanding Filters
https://telescopicwa...escope-filters/


Edited by aeajr, 07 December 2022 - 08:51 PM.

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#10 WRD

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Posted 07 December 2022 - 08:53 PM

Hello aeajr,

Thank you for the very helpful guidance.

WRD


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#11 aeajr

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Posted 07 December 2022 - 09:02 PM

TIPS

 

 

Top right of the screen you will see your screen name with a little down arrow.
Go to My Settings.  This is where you can make a number of changes.

 

You can set whether you want to receive private messages from people and how
you want to be notified about posts.

 

 

COUNTRY/REGION/STATE:  A good thing to do, if you have not, is to go into
your profile and enter your country and/or your city so people who are
trying to help you will know approximately where you are in the world.

 

 

 

SIGNATURE:   Also, I recommend you create a signature (my settings)
where you can list your telescope your eyepieces or whatever you wish.  My
signature is at the bottom of this post.  A signature helps people help you
because they know what you have.  We get a lot of requests from people
saying, "I am new, what eyepieces should I get?"   Now we play 20 questions
to find out what telescope they have, what eyepieces they already own, etc..

 

 

 

BUDGET: When asking about things to buy it is good to provide a budget.   An
eyepiece can be $30 or it can be $300.  If we don't know your budget we
won't know how to advise you.

Terms like "budget-priced" or "low cost" have absolutely no meaning.  What
is low cost to me may be expensive to you.  We need numbers. In fact, consider
rephrasing to something like this, “I have the following telescope and
eyepieces and this much to spend.   What would you suggest?"   Give it a try.

 

 

LINKS: If you are asking a question about a specific product I suggest you
provide a link to that product so we know exactly what you are talking
about.  For example, Orion sells the Starseeker IV 150.   Well, it turns out
there are two different telescopes that could be described by that name.
One is a 150 mm Newtonian reflector and the other is a 150 mm
Maksutov-Cassegrain.   Which are you asking about?

 

Or someone says they just got a 5” Celestron scope and wants to know what eyepieces to get.  

Well, Celestron makes a number of 5” scopes.   If there is no link then people will answer
based on the one they think you are asking about rather than the one you
want to know about.

 

 

If you are not in the USA, a link is even more important.   Offer a link to
a website in your country that sells telescope equipment so we can try to
understand what things cost and what equipment is available in your country.

 

 

Part of what makes Cloudy Nights so great is that people are very happy to
help one another.  These tips just make it easier for us to help each other
or to understand what is being discussed in the thread.  I hope you find
these tips helpful.

 

Glad you decided to join us in the sky.   :)


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#12 Tony Flanders

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Posted 07 December 2022 - 09:18 PM

I would forget about filters for now.

Unless you're a hard-core planetary observer trying to eke out the last iota of detail, most people find the planets much more attractive in their natural colors than tinted weirdly with various filters.

As for deep-sky objects, the only ones that are significantly helped by filters are emission nebulae like M42, the Orion Nebula, or planetary nebula like M57, the Ring Nebula. Actually, both of those are super-bright, so I prefer the unfiltered views of them as well. And most of the fainter nebulae aren't going to look like much in Bortle-8 skies even with a nebula filter.

Star clusters and galaxies are definitely best observed without filters in 99% of all cases, regardless of how bright or dark your skies are.

 

Filters advertised as "light pollution filters" tend to be useless or counterproductive on most targets. No filter will make light pollution go away, or even reduce it significantly. And if it does reduce the light pollution, it will do so at great cost to the objects you're viewing.


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#13 dnayakan

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Posted 07 December 2022 - 09:46 PM

Filters, for the most part (at least in my experience), are subtle. And they require a sort of trained eye to see the effects. None of them really can counter aspects of the sky massively. 

 

The thing to keep in mind is that all filters reduce the amount of light. This is of help to some people who find very bright objects like the moon and planets difficult to look at when they are overly bright. Neutral density filters or a pair of polarizers can cut the brightness a bit. 

 

Colored filters are used to alter contrast - very commonly used in B&W photography, especially since the emulsions have (had) their own spectral responses. Colored filters are usually designed to pass a specific set of wavelengths while curtailing others. In astronomy, I would argue they are of limited use. Remember they are subtractive - they block some wavelengths. So, unless the object is bright and colorful to begin with, you are unlikely to see much effect. Given the fact that we are using scotopic vision most of the time, there are relatively few objects that colored filters are useful for - mostly just for planets. The effects here again I think are subtle. Some people are very bothered by the fact that they color the entire image - it takes some training to ignore that and focus on contrast. I will reiterate again - given that the colors of the object are not vibrant, pure wavelength colors to start with, the contrast effects are modest and require a great deal of discipline to notice.  

 

Then you have filters which are designed to pass relatively narrow bands of wavelength. Often called narrowband filters - these are usually designed to capture emissions from nebulei. When radiation hits certain areas, they can ionize particles in the medium - these particles then emit a specific wavelength as they fall back to their stable state. Examples are things like O-III filters (designed to pass the specific wavelength of doubly ioninzed oxygen), H-alpha and H-Beta filters, S-II etc. There are also some filters designed to pass some combination of things. Often called nebula filters, most often they are designed to pass the O-III and H-Beta lines. All these filters can be recognized from the fact that they look like mirrors - they pass a certain wavelength and reject the rest which reflects back, therefore looking like a mirror. These filters can be useful for some objects - the O-III filter is famously useful in being able to see the Veil nebula. However, and this should be obvious given they look like a mirror, they make the image very dim. In contrast to colored filters, they do have a marked effect on the contrast of the objects they are designed for, though. 

 

Cheers, DJ



#14 drd715

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Posted 08 December 2022 - 03:44 AM

Most likely filters will not help you much on a small scope for visual use. You may find a uv/ir filter could trim some of your out of focus spectrum off of the high and low ends or a minus violet filter to reduce  the blue/ violet blooming on bright stars. Your best choice is to drive to a darker viewing site. Maybe think about a XT8 or xt6 solid tube dob if one might come up for sale near your location. Find a local astronomy club and you will be able to get hands on help in using your scope.


Edited by drd715, 08 December 2022 - 03:47 AM.


#15 WRD

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Posted 08 December 2022 - 09:00 AM

Many thanks to vtornado, aeajr, Tony Flanders, dnayakan and drd715 for the important information and thoughtful recommendations regarding my question about filters for visual astronomy. It will take some time for me to assimilate all the information and explore the links provided. 

In the meantime I will take the recommended "no filter" approach and conduct some experiments with the three filters I have. I have thought about finding a dark sky location but the closest one is several hours away. I also will be joining the local chapter of the RASC (Royal Astronomical Society of Canada) in January 2022.

All the best,

WRD


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#16 vtornado

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Posted 08 December 2022 - 09:12 AM

I would wager someone in the club will loan you some filters.

I have loaned equipment to other members in the past.


Edited by vtornado, 08 December 2022 - 09:12 AM.



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