14 replies to this topic

[BlueMoon]

Howdy folks, just another "I'm curious" question.

 

Is there any reason why a filter can't be placed between the diagonal and the eye piece instead of between the diagonal and the telescope? I'm thinking about adapting a filter tray and replacing the filter wheel I currently have. The tray will significantly reduce the light path over the wheel, give me more in/out adjustment for focusing and reduce some weight. I use 1.25" format UHC, OIII and a ND 1.3 for a moon filter.

 

I can't see any optical reason why repositioning the filter would have any negative effect but I thought I'd toss the question out as I've been known to miss the obvious "don't do that" aspects.

 

Clear skies.

Edited by BlueMoon, 08 March 2021 - 08:06 PM.

[Couder]

Well, the filters screw onto the bottom of the eyepieces, so I can't see where it would matter. (So that would place them between the diagonal and the eyepiece.)

[Supernova74]

Well there is only two ways I know of unless you have a diagonal which can actually slot in filters,or an imaging arrangement of some discription,so either the end of the diagonal barrel which useally has thread or on the eyepiece itself 

[BlueMoon]

Now that I reread my question, it seems a bit silly of me. As you point out, the filters can be installed into the EP itself so it's basically the same thing optically. I think what strikes me as unusual is the tray will be oriented horizontally instead of vertical. Just seemed strange to me ... 

 

Thanks for the input. Be well.

Edited by BlueMoon, 08 March 2021 - 12:21 PM.

[Starman1]

Now that I reread my question, it seems a bit silly of me. As you point out, the filters can be installed into the EP itself so it's basically the same thing optically. I think what strikes me as unusual is the tray will be oriented horizontally instead of vertical. Just seemed strange to me ... 

 

Thanks for the input. Be well.

Lumicon sold a filter slide for many years that mounted under the eyepiece and above the star diagonal, though it could also be mounted between the diagonal and scope:

https://farpointastr...ilter-selector/

They weren't usable in newtonians because they require a LOT of in travel of the focuser.

They were more practical in SCTs and MCTs.

The main disadvantage was it left the filters exposed to dew.

Such a slide makes a quick comparison of filters easy.

[Supernova74]

Lumicon sold a filter slide for many years that mounted under the eyepiece and above the star diagonal, though it could also be mounted between the diagonal and scope:

https://farpointastr...ilter-selector/

They weren't usable in newtonians because they require a LOT of in travel of the focuser.

They were more practical in SCTs and MCTs.

The main disadvantage was it left the filters exposed to dew.

Such a slide makes a quick comparison of filters easy.

There is a diagonal don,t know much about (alpha Lyrae,nPAE Theia Star diagonal with filter changer )

[Starman1]

That's like the Baader system--the filter is in a cassette, and the cassettes are dropped in.

Faster than changing filters on the bottom of the eyepiece, but slower than a filter slide.

[BlueMoon]

 

The main disadvantage was it left the filters exposed to dew.

I looked at that awhile back but as you point out it leaves the filters exposed.  I couldn't reconcile myself to it but it prompted me to consider a wheel.

 

There is a diagonal don,t know much about (alpha Lyrae,nPAE Theia Star diagonal with filter changer )

Interesting. Thanks for the tip, I haven't run across this one before. https://www.npae.net...-star-diagonal/

 

The issue for me is all my filters are 1.25" format. I'd have to find threaded adapters I imagine.

Edited by BlueMoon, 08 March 2021 - 05:09 PM.

[Supernova74]

I looked at that awhile back but as you point out it leaves the filters exposed.  I couldn't reconcile myself to it but it prompted me to consider a wheel.

 

Interesting. Thanks for the tip, I haven't run across this one before. https://www.npae.net...-star-diagonal/

 

The issue for me is all my filters are 1.25" format. I'd have to find threaded adapters I imagine.

Well all due respect I know really nothing about the product!? It just rang a bell with me that I’ve seen it somewhere,well far as I’m aware it’s only available in 1.25” format anyway. Admittedly for someone who likes useing filters I can see the appeal however quality is often more important than functionality in my opinion.its true performance yet again i still don,t know,I think the important decision one have to make is how much hardship and time does it take to change filters anyway during the duration of an observing session,perhaps a few minutes tops.as an alternative you could always puchase two diagonals to save a bit of time mind you seems a tad over the top to me.

Edited by Supernova74, 08 March 2021 - 05:41 PM.

[BlueMoon]

 

is how much hardship and time does it take to change filters anyway during the duration of an observing session

Frankly, I don't mind the time, but there is another aspect for me in this. I've recently upgraded to a Moonlite CF2 focuser on my 100ED. The Moonlite tips the scales at 3 lb. 8oz which is almost 2 lbs heavier than the GSO linear bearing focuser I  had. It's causing some irksome issues with balance when my filter wheel is attached so I'm sort of investigating a filter tray as a lighter weight alternative.

Edited by BlueMoon, 08 March 2021 - 05:47 PM.

[Supernova74]

Frankly, I don't mind the time, but there is another aspect for me in this. I've recently upgraded to a Moonlite CF2 focuser on my 100ED. The Moonlite tips the scales at 3 lb. 8oz which is almost 2 lbs heavier than the GSO linear bearing focuser I  had. It's causing some irksome issues with balance when my filter wheel is attached so I'm sort of investigating a filter tray as a lighter weight alternative.

Oh I got ur yes the moonlite is a bit of a lump built like a Sherman tank tho.(what do you mean by balance are you imaging or visual)

[BlueMoon]

Oh I got ur yes the moonlite is a bit of a lump built like a Sherman tank tho.(what do you mean by balance are you imaging or visual)

Just visual right now. I use a TeleOptik Giro GR2 DX alt/az which has no slo-mo controls. I had it all in perfect balance with my Astromania 5 filter manual wheel and optics train. I could change eye pieces without locking it down or adjusting the drag and the scope would stay put. The weight of the Moonlite changed that. So, if I can find a lighter filter tray solution, I think I can get it back where I'd like it.

[Supernova74]

Just visual right now. I use a TeleOptik Giro GR2 DX alt/az which has no slo-mo controls. I had it all in perfect balance with my Astromania 5 filter manual wheel and optics train. I could change eye pieces without locking it down or adjusting the drag and the scope would stay put. The weight of the Moonlite changed that. So, if I can find a lighter filter tray solution, I think I can get it back where I'd like it.

Ok I got ur now so back end heavy then focuser!? Yes the moonlite was a bit heavy handed regarding weight with my Meade 12”ACF um!? Couldn’t you perhaps put an OTA ring or two at the objective lens end to help balance a little better 

or if that’s to much some small lead weights of some discription!? Just an idea maybe

[rexowner]

That's like the Baader system--the filter is in a cassette, and the cassettes are dropped in.

Faster than changing filters on the bottom of the eyepiece, but slower than a filter slide.

I have the Baader system - UFC.  One nice thing about the UFC (Universal Filter Changer)

is it doesn't add as much backfocus as other systems.  There are adapters for many

common interfaces on either side.  In my case it goes:

2" Nosepiece -> UFC -> Diagonal 

 

The UFC itself is 13mm, the adapter to the nosepiece is 3mm, and the adapter to the diagonal is 1mm,

so the whole thing only adds 13+3+1 = 17mm of backfocus requirement, which isn't too bad  to add a filter vs.

other systems.  Also lets me use filters up to 50.4 (vs. 48mm "2") or 50mm square, so less vignetting. 

For those reasons, I really like this system, as it works with most of my setups.

[BlueMoon]

Couldn’t you perhaps put an OTA ring or two at the objective lens end to help balance a little better or if that’s to much some small lead weights of some discription!?

Entirely possible. If I can't find a lighter weight solution using a tray system, I may indeed have to go down that path.