Filters for a 4"

[Sunshine]

Just wondering if filters of any kind are commonly used for such a small scope as a 4", I am aware of how helpful filters are for AP and for visual when using dobs but I am not so sure they're used for small refractors.

In my case I guess I would benefit from an LP filter and maybe a filter which enhances nebulae, if it would help with such small aperture. Since I am not using a camera, I would guess the filters would be screw on which

fit on the diagonal.

Edited December 28, 2021 by Sunshine

[ScouseSpaceCadet]

Tbh I find using filters a pain, however I own two & occasionally use them...

A Moon & Skyglow filter is used as a moon filter if I'm having a longer lunar session. It just takes the edge off the brightness without unnatural colouring.

The second is a UHC filter that does enhance detail in bright nebula.

[John]

I use UHC and O-III filters with my 4 inch refractors and find them effective on a variety of nebulae. For some targets the O-III filter is the only way to get anything much visible in the eyepiece. Using an effective exit pupil is important to the impact that these filters make. I find that 4mm-6mm exit pupils help an O-III filter the most while with a UHC filter I think you can push that to the 2mm - 5mm range. Not hard and fast rules though.

I don't use an LP filter myself but many folks find the Baader Neodymium filter good for this role.

 

 

 

 

[Sunshine]

Thanks for the replies, in other words, Meh on the filters.

[John]

1 hour ago, Sunshine said:

... Meh on the filters.

Not for me, I really think they are worthwhile (well, the UHC and O-III anyway)

(apologies if I have misunderstood "Meh" !)

[scarp15]

If situated within a dark sky environment, a H-beta filter is also valid. Had used this filter with a 76mm refractor and since 85mm, to gain, amongst other objects the California.

[Sunshine]

Hard to describe “meh” but you got it right, just means like oh well not worth it.

[Stu]

2 hours ago, Sunshine said:

Thanks for the replies, in other words, Meh on the filters.

Certainly not. A good OIII and UHC are very worthwhile in a 4” scope, and even smaller. Dark adaptation helps, so if you have LP/glare then an observing hood will help, plus keeping the exit pupil up too to maintain image brightness. Don’t forget these filters don’t make the image brighter, in fact they make it dimmer, but they do increase the contrast between the target and background.

[mikeDnight]

I find the OIII blocks star light in smaller aperture scopes, which when I'm sketching, can make positioning the sketch difficult. I called my OIII filter my Veil filter, because its a superb filter for the Veil nebula. I find my UHC filter to be more general across the board, and it doesn't block out star light. It's a great filter for smaller apertures. I use a H-beta filter for the Flame nebula, though I can see the Flame without a filter with patience and with Alnitak out of the field. For the planet's I sometimes use Wrattan 21 orange for enhancing the darker markings on Mars, and Wrattan 80A blue for enhancing the white polar caps and mists in the impact craters Hellas, Argyre and around Olympus Mons. W 11 is supposed to enhance Venus, but I rarely use it as I seem to see detail without much difficulty.

Edited December 28, 2021 by mikeDnight

[Sunshine]

Great to hear, thanks for the info!

[RT65CB-SWL]

The filters I use are...

• Baader Planetarium Neodymium - my 'Swiss-army knife' filter.
• a BST variable polarising filter set - [images below] - when using a star diagonal, I screw one into the nosepiece and the other one into the nosepiece of the eyepiece or supplied eyepiece holder or accessory. Then rotate until I get the desired brightness/contrast, when viewing the Moon and/or discerning the phases Venus. 

    

• #47 - violet - recommended for discerning the phases of Venus too. 
• Explore Scientific UHC. 
• Explore Scientific Olll. 
• a set of colour filters - for visual observing of the planets only. 
• Baader solar continuum - used with a single polarising filter and solar wedge. 
• Baader Planetarium contrast booster. 
• Explore Scientific CLS. 
• IR - infrared on a webcam. 

Edited December 30, 2021 by Philip R
all my filters and supplementary notes added.

[ollypenrice]

I've had huge success with filters at 4 inches and below - from dark sites. I can't comment on how they work under light pollution.  Initially I used a UHC but its coatings failed so I tried a visual OIII the second time. 

They allowed me, finally, to see the full Rosette nebula clearly and the entire Cygnus Loop, both in a TeleVue Genesis. Basically they subdue the background sufficiently to bring faint, extended target into view. I wouldn't be without mine.

Olly

[michael.h.f.wilkinson]

I use both UHC and O-III filters in my 80mm F/6. Both can really bring out more detail.

[PeterC65]

I've been impressed with the Astronomik UHC filter, used with a 5" Mak to observe nebulae. It noticeably improves contrast. I have various filters and the UHC is the most impressive, followed by the Baader Neodymium which is a good all rounder for slightly improving contrast on any target.

I've been tempted by an OIII filter but I'm concerned that I just don't have enough aperture with my current scopes.

 

[TakMan]

Found filters useful in the TSA102 and the bigger TEC.

Agree with everything said in terms of making subject dimmer but improved contrast allowing the object to stand out. OIII is superb (almost vital), on the Veil, the UHC more general purpose as a ‘benchmark’ before swapping to the OIII to compare… Dumbbell and Orion region prime examples!

Utter pain to be unscrewing on and off eyepieces… I use an old TruTech 2” x 5 slot manual wheel to quickly go between filtered and unfiltered - far easier to compare views and far less risk of damaging anything! Also very easy to open and swap filters around (more for colour filters depending on subject or preference - plan observing and do before heading out, not in darkness!)

If needs must, just buy a second carousel and fill one with colour filters for lunar and planetary and the other for deep sky. 

So 2” Lumicon UHC and OIII, a ‘moon filter’ (ND filter), and either a colour wratten filter as described above or a single polarising filter (with the other ‘half’ screwed into the eyepiece bottom - undo the tension on the diagonal eyepiece holder and rotate chosen eyepiece to vary polarisation..) Obviously one carousel aperture kept free for unfiltered use!

2” filters, despite the initial added cost allow the use of any sized eyepiece in the collection - buy once and get it sorted!

The FW is easy to swap between any scope with a 2” compression holder…

Damian

Edited December 30, 2021 by TakMan